Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title: Multi-Phase Contacting Process Using Microchannel Technology
This invention was made with Government support under Contract DE-FC36-
04G014271 awarded by the United States Department of Energy. The Government
has certain rights in this invention.
This application claims the benefit under 35 U.S.C. 120 to U.S. Application
Serial No. 11/177,941, filed July 8, 2005. This application claims the benefit
under
35 U.S.C. 119(e) to U.S. Provisional Application Serial No. 60/727,126, filed
October 13, 2005, U.S. Provisional Application Serial No. 60/731,596, filed
October
io 27, 2005, and U.S. Provisional Application Serial No. 60/785,732, filed
March 23,
2006. These applications are incorporated herein by reference in their
entireties.
Technical Field
The disclosed technology relates to a multi-phase contacting process
conducted in a microchannel. The process may comprise any multi-phase
contacting process wherein mass transfer between a liquid phase and a second
fluid
phase occurs. The second fluid phase may comprise a liquid, gas, or mixture
thereof. The process may be a distillation process, absorption process,
stripping
process, or rectification process, or a combination of two or more thereof.
Background
Mass transfer may involve the transfer of one or more components from one
discrete phase (e.g., a gas phase) to another discrete phase (e.g., a liquid
phase).
Processes involving the use of mass transfer may include distillation,
absorption,
extraction, and the like. A problem with many of these mass transfer processes
is
that they employ relatively large pieces of equipment that are highly
inefficient with
respect to energy consumption. For example, distillation accounts for about a
quadrillion BTUs of energy consumption per year in the United States.
Conventional
distillation systems may reduce lost work and increase plant energy efficiency
by
incorporating capital-intensive reboilers at multiple sections. However, the
capital
cost of adding multiple reboilers to conventional distillation columns is
typically
prohibitive. The trade-off between energy and capital often results in
favoring the
lower cost solution. The efficiency of mass transfer stages in distillation
columns
may be set by the effectiveness of trays or packing, which have not changed
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significantly in many years. For the separation of components with similar
boiling
points, such as ethane from ethylene, commercial distillation columns may be
hundreds of feet high, due to the need to use many mass transfer stages.
Another
problem relates to the fact that the equipment (e.g., distillation columns,
reboilers,
condensers, etc.) used in many distillation processes requires relatively
large
internal volumes for processing the materials being treated. These large
internal
volumes may render the equipment slow to respond to changes in operating
conditions (e.g., temperature, etc.). This may make the processes using this
equipment slow to start up and subject to imprecise control.
Summary
The disclosed technology, in at least one embodiment, may provide a solution
to one or more of these problems by using microchannel technology. With the
present invention, in one embodiment, process intensification may be achieved
through the use of stacked layers of thin sheets of material with stamped,
etched or
piece-wise assembled channels, that is, microchannels, providing narrow flow
paths
with short diffusion distances for mass transfer. The use of these
microchannels
may provide for reductions in the required flow length of process sections
dominated
by mass transfer, resulting in relatively short processing units. Heat inputs
and
outputs may be closely integrated with the flow of the liquid and gas in the
process
microchannel..
The disclosed technology relates to a process for contacting a liquid phase
and a second fluid phase, comprising: flowing the liquid phase and/or second
fluid
phase in a process microchannel in contact with surface features in the
process
microchannel, the contacting of the surface features with the liquid phase
and/or the
second fluid phase imparting a disruptive flow to the liquid phase and/or
second fluid
phase; contacting the liquid phase with the second fluid phase in the process
microchannel; and transferring mass from the liquid phase to the second fluid
phase
and/or from the second fluid phase to the liquid phase.
In one embodiment, the liquid phase is in the form of a contiguous liquid
phase over at least part of the length of the process microchannel, the second
fluid
phase is in the form of a contiguous fluid phase over at least part of the
length of the
process microchannel, the contacting between the liquid phase and the second
fluid
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phase occurring at an interface between the liquid phase and the second fluid
phase.
In one embodiment, the process microchannel comprises a first interior wall, a
second opposite interior wall, and a gap positioned between the first interior
wall and
the second interior wall, the surface features being positioned on and/or in
the first
interior wall, the liquid phase being in the form of a contiguous liquid phase
over at
least part of the length of the process microchannel, the second fluid phase
being in
the form of a contiguous fluid phase over at least part of the length of the
process
microchannel, the second fluid phase contacting the liquid phase at an
interface, the
1o bulk flow of the liquid phase being in the gap between the surface features
and the
interface, the contacting of the surface features by the liquid phase causing
at least
part of the liquid phase to flow towards the interface.
In one embodiment, the process microchannel comprises a first interior wall, a
second opposite interior wall, and a gap positioned between the first
interiorwall and
the second interior wall, the surface features being positioned on and/or in
the
second interior wall, the liquid phase being in the form of a contiguous
liquid phase
over at least part of the length of the process microchannel, the second fluid
phase
being in the form of a contiguous fluid phase over at least part of the length
of the
process microchannel, the second fluid phase contacting the liquid phase at an
interface, the bulk flow of the second fluid phase being in the gap between
the
surface features and the interface, the contacting of the surface features by
the
second fluid phase causing at least part of the second fluid phase to flow
towards
the interface.
In one embodiment, the process microchannel comprises a first interior wall, a
second opposite interiorwall, and a gap positioned between the first interior
wall and
the second interior wall, the surface features being positioned on and/or in
the first
interior wall and the second interior wall, the liquid phase being in the form
of a
contiguous liquid phase over at least part of the length of the process
microchannel,
the second fluid phase being in the form of a contiguous fluid phase over at
least
part of the length of the process microchannel, the second fluid phase
contacting the
liquid phase at an interface, the bulk flow of the liquid phase being in the
gap and
being between the first interior wall and the interface, the bulk flow of the
second
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fluid phase being in the gap and being between, the second interior wall and
the
interface, the liquid phase contacting the surface features on and/or in the
first
interior wall, the contacting of the surface features on and/or in the first
interior wall
by the liquid phase causing at least part of the liquid phase to flow towards
the
interface, the second fluid phase contacting the surface features on and/or in
the
second interior wall, the contacting of the surface features on and/or in the
second
interior wall by the second fluid phase causing at least part of the second
fluid phase
to flow towards the interface.
In one embodiment, the liquid phase is in the form of a contiguous liquid
1o phase over at least part of the length of the process microchannel, the
second fluid
phase is in the form of a contiguous fluid phase over at least part of the
length of the
process microchannel, a contactor is positioned between the liquid phase and
the
second fluid phase.
In one embodiment, the contactor has a first surface facing the liquid phase
and a second surface facing the second fluid phase, the first and/or second
surface
of the contactor containing surface features in the form of depressions in
and/or
projections from the first surface and/or second surface.
In one embodiment, the first surface of the contactor contains surface
features in the form of depressions in and/or projections from the first
surface.
In one embodiment, the second surface of the contactor contains surface
features in the form of depressions in and/or projections from the second
surface.
In one embodiment, the liquid phase and the second fluid phase are mixed
with each other in the process microchannel.
In one embodiment, the process may be conducted in a microchannel
processing unit, the microchannel processing unit comprising a plurality of
the
process microchannels, at least one header, and at least one footer. In one
embodiment, the header and/or footer may have only one phase in it.
In one embodiment, the process may be conducted in a distillation unit, the
distillation unit comprising a plurality of the process microchannels. The
distillation
unit may be used with at least one condenser, and/or at least one reboiler.
The
condenser and/or reboiler may be contained within the microchannel
distillation unit,
or either or both may be added as separate discrete hardware.
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In one embodiment, a mixture of the liquid and the second fluid flow into the
process microchannel, and separate phases flow out of the process
microchannel,
one of the separate phases comprising the liquid and one of the separate
phases
comprising the second fluid.
5 In one embodiment, a mixture of the liquid and the second fluid flow into
the
process microchannel, and separate outlet streams flow out of the process
microchannel, one of the outlet streams comprising the liquid and one of the
outlet
streams comprising the second fluid.
The liquid phase may comprise any liquid. The second fluid phase may
1o comprise any gas, liquid or mixture thereof. The liquid of the liquid phase
and the
liquid of the second fluid phase may be partly miscible or immiscible with
each other.
The liquid phase and/or second fluid phase may comprise a phase transfer
catalyst.
In one embodiment, a chemical reaction may be conducted in the process
microchannel.
In one embodiment, the disclosed technology relates to a process for
contacting a liquid phase and a second fluid phase, comprising: flowing the
liquid
phase and/or second fluid phase in a process microchannel in contact with
surface
features in the process microchannel, the superficial velocity of the liquid
phase
being at least about 0.1 m/s, the contacting of the surface features with the
liquid
phase and/or the second fluid phase imparting a disruptive flow to the-liquid-
phase
and/or second fluid phase; contacting the liquid phase with the second fluid
phase in
the process microchannel; and transferring mass from the liquid phase to the
second
fluid phase and/or from the second fluid phase to the liquid phase.
In one embodiment, the disclosed technology relates to a process for
contacting a liquid and a second fluid, comprising: flowing a mixture of the
liquid and
the second fluid in a process microchannel in contact with surface features in
the
process microchannel, the contacting of the surface features with the liquid
and the
second fluid imparting a disruptive flow to the liquid and the second fluid;
and
transferring mass from the liquid to the second fluid phase and/or from the
second
phase to the liquid.
In one embodiment, the disclosed technology relates to a process for
contacting a liquid and a second fluid, comprising: flowing a mixture of the
liquid
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the second fluid in a process microchannel in contact with surface features in
the
process microchannel, the contacting of the surface features with the liquid
and the
second fluid imparting a disruptive flow to the liquid and second fluid;
transferring
mass from the liquid to the second fluid and from the second fluid to the
liquid; and
removing separate streams from the process microchannel, one of the separate
streams comprising the liquid, and one of the separate streams comprising the
second fluid.
Brief Description of the Drawings
In the annexed drawings, like parts and features have like designations. A
lo number of the drawings provided herein are schematic illustrations which
may not be
drawn to scale or proportioned accurately.
Fig.1 is a schematic illustration of a process microchannel that may be used
with the disclosed process.
Figs. 2A-2D are schematic illustrations of microchannet processing units that
may be used in accordance with the disclosed process. The microchannel
processing units illustrated in Figs. 2A, 2B and 2C comprise a microchannel
processing unit core, at least one header, and at least one footer. The
microchannel
processing unit illustrated in Fig. 2D is a microchannel distillation assembly
which
comprises a microchannel distillation unit which may include a condenser
and/or
2o reboiler.
Fig. 3 is a schematic illustration of a process microchannel that may be used
in accordance with the disclosed process.
Fig. 4 is a schematic illustration of an alternate embodiment of a process
microchannel that may be used in accordance with the disclosed process.
Figs. 5-23 are schematic illustrations of surface features that may be
employed in the process microchannel used with the disclosed process.
Figs. 24-27 are schematic illustrations of microchannel repeating units that
may be used in the microchannel processing units illustrated in Figs. 2A-2D.
Fig. 28 is a schematic illustration of a wall of a process microchannel that
may
3o employ dual depth surface features that promote capillary retention and
mixing.
Figs. 29-35 are schematic illustrations of surface features that may be
employed in the process microchannel used with the disclosed process.
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Figs. 36-39 are schematic illustrations of shims that may be used to form a
microchannel processing unit core for use with the disclosed process.
Fig. 40 is a schematic illustration of a shim stacking orientation that may be
used with the shims illustrated in Figs. 36-39.
Fig. 41 is a schematic illustration of an alternate embodiment of the shim
illustrated in Fig. 38.
Figs. 42-45 are schematic illustrations of shims that may be stacked to form a
process microchannel for use with the disclosed process.
Fig. 46 is a schematic illustration of the shims illustrated in Figs. 42-45
1 o stacked to form part of a process microchannel which may be used with the
disclosed process.
Figs. 47-48 are schematic illustrations of shims that may be stacked to form a
process microchannel for use with the disclosed process.
Fig. 49 is a schematic illustration of a microchannel processing unit formed
using the shims illustrated in Figs. 47 and 48.
Fig. 50 is a schematic illustration of an exploded view of the microchannel
processing unit disclosed in Example 1.
Fig. 51 is a schematic illustration of the flow distribution feature section
for the
microchannel processing unit disclosed in Example 1. In this figure all
dimensions
are in inches.
Figs. 52-53 are schematic illustrations of surface feature patterns used in
the
microchannel processing unit disclosed in Example 1. In these figures, all
dimensions are in inches.
Fig. 54 is a schematic illustration of a first channel configuration which is
disclosed in Example 1.
Fig. 55 is a schematic illustration of a second channel configuration which is
disclosed in Example 1.
Fig. 56 is a top surface view of the channel configuration illustrated in Fig.
55.
Figs. 57-60 are plots that show the relative residence time of tracer
particles
in the surface features for test runs disclosed in Example 1.
Figs. 61-74 are representative profiles for the test runs 1-14, respectively,
disclosed in Table 1 for Example 2. The results are shown in terms of path
lines
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released from the vertical and horizontal inlet center lines, a and c and b
and d,
respectively. Figs a and b show the path lines viewed from the channel side.
Figs. c
and d show the path lines viewed from the exit plane of the channel. All views
are
orthographic. The channel inlet is shown for reference.
Figs. 75 and 76 are plots showing concentration measurements indicating the
degree of conversion of material A in response to contact with the upper
channel
wall for the test runs disclosed in Table 1 of Example 2. Measurements begin
after
the initial 2.54 mm featureless section, which is taken as the 0 point of the
normalized channel length. The channel length is normalized upon division by
25.4
1o mm which is the channel length. The legend numbers correspond to mole
fraction of
A numbers in Table 1 of Example 2.
Fig. 77 is a plan view of the geometry of the surface features simulated by
Computational Fluid Dynamics (CFD) in Example 3.
Fig. 78 is an isometric view of the microchannel with surface features
simulated by CFD in Example 3.
Fig. 79 shows the path lines of flow beginning along the horizontal center
line
of the inlet plane looking down the access of flow from the inlet plane for
the process
disclosed in Example 3.
Fig. 80 discloses path lines of flow beginning along the horizontal center
line
of the inlet plane as viewed from-the side for-the process disclosed in
Example 3.
Fig. 81 discloses path lines of flow beginning along the vertical center line
of
the inlet plane looking down the access of flow from the inlet plane for the
process
disclosed in Example 3. Flow rotates (spirals) along the channel length.
Fig. 82 is an isometric view of the process microchannel, which contains
surface features, that is simulated in Example 4.
Fig. 83 shows path lines of flow beginning along the horizontal center line of
the inlet plane for the process disclosed in Example 4.
Fig. 84 discloses path lines of flow along the horizontal center line of the
inlet
plane looking down the access of flow from the inlet plane for the process
disclosed
in Example 4.
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Fig. 85 discloses path lines of flow beginning along the vertical center line
of
the inlet plane looking down the access of flow from the inlet plane for the
process
disclosed in Example 4.
Fig. 86 discloses one-sided (Fig. 86a) and two-sided (Fig. 86b) surface
feature configurations for the test runs disclosed in Example 5.
Fig. 87 discloses representative rib orientations for the test runs disclosed
in
Example 5. The rib orientations are trans (Fig. 87a), cis A (Fig. 87b), and
cis B (Fig.
87c).
Figs. 88-96 show representative profiles for the test runs disclosed in
1o Example 5. Results are shown in terms of path lines released from the
vertical and
horizontal inlet center-lines, a and b and c and d, respectively. Figs. a and
c of each
of Figs. 88-96 show the path lines viewed from the exit plane of the channel.
Figs. b
and d show the path lines viewed from the channel side. All views are
orthographic.
The channel inlet is shown for reference.
Fig. 97 discloses channel geometry, which includes chevron shaped surface
features (Fig. 97a) and path line profiles (Figs. 97b and 97c) for the test
runs
disclosed in Example 6. Figs. 97b and 97c show the formation of vortices
spanning
the chevron legs of the surface features. Fig. 97b shows the path lines
released at
the center line of the inlet plane gap viewed from an angle. Fig. 97c shows
the same
path lines viewed from the exit plane.
Fig. 98 discloses channel geometry, which includes chevron shaped surface
features (Fig. 98a) and path line profiles (Figs. 98b and 98c) which show the
formation of vortices centered about the chevron apex in each surface feature.
Fig.
98b shows path lines released at the center line of the inlet plane gap viewed
from
an angle. Fig. 98c shows the same path lines viewed from the exit plane.
Figs. 99a-99g show various continuous chevron surface feature designs that
may be used in the disclosed process microchannel. All of these figures,
except for
Fig. 99b, have a 90 subtending angle. Fig. 99b has a subtending angle of 60 .
Detailed Description
The term "microchannel" may refer to a channel having at least one internal
dimension of height or width of up to about 50 millimeters (mm), and in one
embodiment up to about 10 mm, and in one embodiment up to about 5 mm, and in
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one embodiment up to about 2 mm, and in one embodiment up to about 1 mm. In
one embodiment, the height or width is in the range of about 0.01 to about 10
mm,
and in one embodiment about 0.05 to about 5 mm, and in one embodiment about
0.05 to about 2 mm, and in one embodiment about 0.05 to about 1.5 mm, and in
one
5 embodiment about 0.05 to about 1 mm, and in one embodiment about 0.05 to
about
0.75 mm, and in one embodiment about 0.05 to about 0.5 mm. Both height and
width are perpendicular to the bulk flow direction of flow through the
microchannel.
The microchannel may comprise at least one inlet and at least one outlet
wherein
the at least one inlet is distinct from the at least one outlet. The
microchannel may
10 not be merely an orifice. The microchannel may not be merely a channel
through a
zeolite or a mesoporous material.
The term "process microchannel" may refer to a microchannel wherein a
process is conducted. The process may be any process wherein a gas contacts a
liquid. Examples of these processes may include distillation, absorption,
extraction,
and the like.
The term "adjacent" when referring to the position of one channel relative to
the position of another channel may mean directly adjacent such that a wall or
walls
separate the two channels. In one embodiment, the two channels may have a
common wall. The common wall may vary in thickness. However, "adjacent"
channels may not be separated by an intervening channel that may interfere
with
heat transfer between the channels. One channel may be adjacent to another
channel over only part of the dimension of the another channel. For example, a
process microchannel may be longer than and extend beyond one or more adjacent
heat exchange channels.
The term "thermal contact" may refer to two bodies, for example, two
channels, that may or may not be in physical contact with each other or
adjacent to
each other but still exchange heat with each other. One body in thermal
contact with
another body may heat or cool the other body.
The term "fluid" may refer to a gas, a liquid, a mixture of a gas and a
liquid, or
3o a gas or a liquid containing dispersed solids, liquid droplets and/or
gaseous bubbles.
The droplets and/or bubbles may be irregularly or regularly shaped and may be
of
similar or different sizes.
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The terms "gas" and "vapor" may have the same meaning and are sometimes
used interchangeably.
The term "partially miscible" may refer to one fluid being soluble in another
fluid to the extent of up to about 90% dissolution of the one fluid in the
another fluid
at 25 C.
The term "residence time" or "average residence time" may refer to the
internal volume of a space within a microchannel processing unit occupied by a
fluid
flowing in the space divided by the average volumetric flow rate for the fluid
flowing
in the space at the temperature and pressure being used.
The term "volume" with respect to volume within a microchannel may include
all volume in the microchannel for which a process fluid may flow-through
orflow-by.
This volume may include the volume within surface features that may be
positioned
in the microchannel.
The terms "upstream" and "downstream" may refer to positions within a
channel (e.g., a process microchannel) that is relative to the direction of
flow of a
fluid stream in the channel. For example, a position within the channel not
yet
reached by a portion of a fluid stream flowing toward that position would be
downstream of that portion of the fluid stream. A position within the channel
already
passed by a portion of a fluid stream flowing away from that position would be
upstream of that portion of the- fluid stream. The terms "upstream" and..
"downstream" do not necessarily refer to a vertical position since the channel
used
herein may be oriented horizontally, vertically or at an inclined angle.
The term "shim" may refer to a planar or substantially planar sheet or plate.
The thickness of the shim may be the smallest dimension of the shim and may be
up
to about 4 mm, and in one embodiment in the range from about 0.05 to about 2
mm,
and in one embodiment in the range of about 0.05 to about 1 mm, and in one
embodiment in the range from about 0.05 to about 0.5 mm. The shim may have any
length and width.
The term "surface feature" may refer to a depression in a microchannel wall
3o and/or a projection from a microchannel wall that disrupts flow within the
microchannel. The surface features may be in the form of circles, spheres,
frustrums, oblongs, squares, rectangles, angled rectangles, checks, chevrons,
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vanes, airfoils, wavy shapes, and the like, and combinations of two or more
thereof.
The surface features may contain subfeatures where the major walls of the
surface
features further contain smaller surface features that may take the form of
notches,
waves, indents, holes, burrs, checks, scallops, and the like. The surface
features
may have a depth, a width, and for non-circular surface features a length. The
surface features may be formed on or in one or more of the interior walls of
the
process microchannels used in accordance with the disclosed process. The
surface
features may be formed on or in one or more of the interior walls of heat
exchange
channels that may be used in the disclosed process. The surface features may
be
1o referred to as passive surface features or passive mixing features. The
surface
features may be used to disrupt laminar flow streamlines and create advective
flow
at an angle to the bulk flow direction.
The term "SFG" may be used to refer to surface feature geometry.
The term "main channel" may refer to an open path for flow having a single
inlet and a single outlet.
The term "channel width" may refer to the largest dimension of the cross
section of a channel.
The term "main channel gap" may refer to the smallest dimension of the cross
section of a channel.
The term "main channel mean bulk flow direction" may refer to the average
direction of flow along a portion of the main channel for flow traveling from
an inlet to
an outlet.
The term "depth of surface feature" may refer to the mean (or average)
distance from the plane where the surface feature intersects the main channel
to the
bottom of the surface feature (the bottom being the plane tangent to the
surface
feature edge which may be farthest from and parallel to the plane where the
surface
feature intersects the main channel).
The term "width or span of surface feature" may be the nominal value of the
shortest dimension of the surface feature in the plane where the surface
feature
intersects the main channel, or distance from surface feature edge to surface
feature
edge.
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The term "run length of surface feature leg" may refer to the nominal value of
the longest dimension of the surface feature leg in the plane where the
surface
feature intersects the main channel.
The term "surface feature leg" may refer to a portion of the surface feature
having no discontinuity or change in slope along the run length relative to
the main
channel mean bulk flow direction.
The term "spacing of repeated surface features" may refer to the distance
between repeated surface features in the direction perpendicular to the run
length of
the feature leg .
The term "angle of surface feature" may refer to the angle between the
direction of the run length of the surface feature leg and the plane
orthogonal to the
mean bulk flow direction in the main channel. A surface feature may have more
than
one angle. The angle may change from one greater than zero to one less than
zero.
The angle may change continuously along the surface feature in either a
continuous
or discontinuous manner. The angle may change fromsurface feature to surface
feature along the length or width of the process microchannel.
The term "orientation of surface feature" may refer to the orientation of a
section of repeated surface features relative to identical surface features on
an
adjacent or opposite wall in the main channel.
The term "flow orientation relative- to surface feature" may refer to the
direction of the mean bulk flow in the main channel relative to the
orientation of a
surface feature recessed in a given wall of the main channel. The designation
A
may be used to designate a mean bulk flow direction in the main channel for
which
the run length of each leg of a two-legged surface feature tend to converge or
come
closer together along the main channel mean bulk flow direction. The
designation B
may be used to designate the opposite flow direction relative to the surface
feature.
For surface features with more than two-legs, an A orientation may refer to a
mean
or average or net feature run length that is more converging than diverging
with
respect to the mean direction of flow. Conversely, a B orientation may refer
to a
mean or average or net feature run length that is more diverging than
converging
with respect to the mean direction of flow.
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The term "heat source" may refer to a substance or device that gives off heat
and may be used to heat another substance or device. The heat source may be in
the form of a heat exchange channel having a heat exchange fluid in it that
transfers
heat to another substance or device; the another substance or device being,
for
example, a channel that is adjacent to and/or in thermal contact with the heat
exchange channel. The heat exchange fluid may be in the heat exchange channel
and/or it may flow through the heat exchange channel. The heat source may be
in
the form of a non-fluid heating element, for example, an electric heating
element or a
resistance heater.
The term "heat sink" may refer to a substance or device that absorbs heat
and may be used to cool another substance or device. The heat sink may be in
the
form of a heat exchange channel having a heat exchange fluid in it that
receives
heat transferred from another substance or device; the another substance
ordevice
being, for example, a channel that is adjacent to and/or in thermal contact
with the
heat exchange channel. The heat exchange fluid may be in the heat exchange
channel and/or it may flow through the heat exchange channel. The heat sink
may
be in the form of a cooling element, for example, a non-fluid cooling element.
The
heat sink may be in the form of a Peltier electronic element.
The term "heat source and/or heat sink" may refer to a substance or a device
that may give off heat and/or absorb heat. The heat source and/or heat sink
may be
in the form of a heat exchange channel having a heat exchange fluid in it that
transfers heat to another substance or device adjacent to and/or in thermal
contact
with the heat exchange channel when the another substance or device is to be
heated, or receives heat transferred from the another substance or device
adjacent
to or in thermal contact with the heat exchange channel when the another
substance
or device is to be cooled. The heat exchange channel functioning as a heat
source
and/or heat sink mayfunction as a heating channel attimes and a cooling
channel at
other times. A part or parts of the heat exchange channel may function as a
heating
channel while another part or parts of the heat exchange channel may function
as a
cooling channel.
The term "heat exchange channel" may refer to a channel having a heat
exchange fluid in it that may give off heat and/or absorb heat. The heat
exchange
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channel may accept heat from or provide heat to an adjacent process
microchannel
and optionally from orto additional process microchannels that are adjacent to
each
other but not adjacent to the heat exchange channel. By this manner, one, two,
three or more process microchannels may be adjacent to each other and
5 interspersed between heat exchange channels.
The term "heat transfer wall" may refer to a common wall between a process
microchannel and an adjacent heat exchange channel where heat transfers from
one channel to the other through the common wall.
The term "heat exchange fluid" may refer to a fluid that may give off heat
1 o and/or absorb heat.
The term "liquid film" may refer to a liquid phase on a solid phase. A gas
phase may overlie the liquid film. The term "liquid film thickness" may refer
to the
distance from the solid phase-liquid film interface to the liquid film-gas
phase
interface.
15 The term "bulk fiow direction" may refer to the vector through which fluid
may
travel in an open path in a channel.
The term "bulk flow region" may refer to open areas within a microchannel. A
contiguous bulk flow region may allow rapid fluid flow through a microchannel
without significant pressure drops. In one embodiment there may be laminar
flow in
the bulk flow region. A bulk flow region may comprise.at least. about 5% of
the
internal volume and/or cross-sectional area of a microchannel; and irr one
embodiment from about 5% to about 100%, and in one embodiment from about 5%
to about 99%, and in one embodiment about 5% to about 95%, and in one
embodiment from about 5% to about 90%, and in one embodiment from about 30%
to about 80% of the internal volume and/or cross-sectional area of the
microchannel.
The terms "open channel" or "flow-by channel" or "open path" may refer to a
channel (e.g., a microchannel) with a gap of at least about 0.01 mm that
extends all
the way through the channel such that fluid may flow through the channel
without
encountering a barrier to flow. The gap may extend up to about 10 mm.
The term "cross-sectional area" of a channel (e.g., process microchannel)
may refer to an area measured perpendicularto the direction of the bulk flow
of fluid
in the channel and may include all areas within the channel including any
surface
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16
features that may be present, but does not include the channel walls. For
channels
that curve along their length, the cross-sectional area may be measured
perpendicular to the direction of bulk flow at a selected point along a line
that
parallels the length and is at the center (by area) of the channel. Dimensions
of
height and width may be measured from one channel wall to the opposite channel
wall. These dimensions may not be changed by application of a coating to the
surface of the wall. These dimensions may be average values that account for
variations caused by surface features, surface roughness, and the like.
The term "open cross-sectional area" of a channel (e.g., process
1o microchannel) may refer to an area open for bulk fluid flow in a channel
measured
perpendicular to the direction of the bulk flow of fluid flow in the channel.
The open
cross-sectional area may not include internal obstructions such as surface
features
and the like which may be present.
The term "superficial velocity" for the velocity of a fluid flowing in a
channel
may refer to the velocity resulting from dividing the volumetric flow rate of
the fluid at
the inlet temperature and pressure of the channel divided bythe cross-
sectional area
of the channel.
The term "free stream velocity" may refer to the velocity of a stream flowing
in
a channel at a sufficient distance from the sidewall of the channel such that
the
velocity is at a maximum value. The velocity of a stream flowing in a channel
is zero
at the sidewall if a no slip boundary condition is applicable, but increases
as the
distance from the sidewall increases until a constant value is achieved. This
constant value is the "free stream velocity."
The term "local velocity" for the velocity of a fluid flowing in a channel may
refer to the volumetric flow rate of the fluid at the inlet temperature and
pressure
divided by the open cross-sectional area of the channel at a specific location
along
the length of the channel.
The term "dynamic pressure" may refer to the energy of a fluid flowing in a
channel and may be defined as the square of the mass flux rate over the cross-
sectional area divided by twice the density of the fluid at the inlet
temperature and
pressure.
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17
The term "capture structure" may refer to a structure positioned within a
channel that captures liquid.
The term "capillary features" may refer to features associated with a
microchannel that are used to hold liquid substances. These features may be
either
recessed within a wall of a microchannel or protrude from a wall of the
microchannel
into the flow path that is adjacent to the microchannel wall. The capillary
features
may create a spacing that is less than about 1 mm, and in one embodiment less
than about 250 microns, and in one embodiment less than about 100 microns. The
capillary features may have at least one dimension that is smaller than any
dimension of the microchannel in which they are situated. The capillary
features
may be referred to as surface features.
The term "wicking material" may refer to a material that draws off liquid by
capillary action.
The term "mm" may refer to millimeter. The term "nm" may refer to
nanometer. The term "ms" may refer to millisecond. The term "ps" may refer to
microsecond. The term "pm" may refer to micron or micrometer. The terms
"micron"
and "micrometer" have the same meaning and may be used interchangeably.
Unless otherwise indicated, all pressures are expressed in terms of absolute
pressure.
The process microchannel may have at least one internal dimension of height-
or width of up to about 50 millimeters (mm), and in one embodiment up to about
10
mm, and in one embodiment up to about 5 mm, and in one embodiment up to about
2 mm, and in one embodiment up to about 1 mm. The height or width may be
referred to as a gap. The bulk flow of fluid in the process microchannel may
proceed
along the length of the microchannel normal to the height and width of the
microchannel. The length of the process microchannel may not be the shortest
dimension of the microchannel. The process microchannel may comprise at least
one inlet and at least one outlet wherein the at least one inlet is distinct
from the at
least one outlet. The process microchannel may not be merely a channel through
a
zeolite or a mesoporous material. The process microchannel may not be merely
an
orifice. An example of a process microchannel that may be used with the
disclosed
process is illustrated in Fig. 1. Referring to Fig. 1, microchannel 100 has a
height
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18
(h), width (w) and length (I). A liquid phase may flow in the microchannel 100
along
the length of the process microchannel in the direction indicated by arrows
102 and
104. Similarly, a gas phase may flow in the process microchannel in the
direction
indicated by arrows 106 and 108. Alternatively, the gas phase and the liquid
phase
may flow in the directions opposite those shown in Fig. 1. In each of these
cases,
the gas phase and the liquid phase are flowing in directions that are counter
current
to one another. Alternatively, the gas phase and the liquid phase may flow in
directions that are cocurrent relative to one another.
The height (h) or width (w) of the process microchannel may be in the range
from about 0.05 to about 50 mm, and in one embodiment from about 0.05 to about
10 mm, and in one embodiment from about 0.05 to about 5 mm, and in one
embodiment from about 0.05 to about 2 mm, and in one embodiment from about
0.05 to about 1.5 mm, and in one embodiment from about 0.05 to about 1 mm, and
in one embodiment about from 0.05 to about 0.75 mm, and in one embodimentfrom
about 0.05 to about 0.5 mm. The other dimension of height or width may be of
any
dimension, for example, up to about 3 meters, and in one embodiment from about
0.01 to about 3 meters, and in one embodiment about 0.1 to about 3 meters. The
length (I) of the process microchannel may be of any dimension, for example,
up to
about 10 meters, and in one embodiment from about 0.2 to about 10 meters, and
in
one embodiment from about 0.2 to about 6 meters, and -in one embodiment from
about 0.2 to about 3 meters. Although the process microchannel 100 illustrated
in
Fig. 1 has a cross section that is rectangular, it is to be understood that
the
microchannel may have a cross section having any shape, for example, a square,
circle, semi-circle, oval, trapezoid, etc. The shape and/or size of the cross
section of
the microchannel may vary over its length. For example, the height or width
may
taperfrom a relatively large dimension to a relatively small dimension, orvice
versa,
over the length of the microchannel.
The process may be described initially with reference to Figs. 2A-2C.
Referring to Figs. 2A-2C, the process may be conducted using microchannel
processing unit 110, which comprises microchannel processing unit core 112,
header 104, and footer 106. The microchannel processing unit core 112 may
comprise one or more repeating units. Each of the repeating units may comprise
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19
one or more of the process microchannels. The header 114 may be used to
provide
for the flow of fluid to or from the process microchannels in the microchannel
processing unit core 112. The footer 116 may also be used to provide for the
flow of
fluid to or from the process microchannels in the microchannel processing unit
core
112. The header 114 and the footer 116 may comprise one or more manifolds for
distributing fluids to the process microchannels or receiving fluids from the
process
microchannels.
Referring to Fig. 2A, a liquid phase may flow through header 114, as indicated
by arrow 120, and from header 114 into the microchannel processing unit core
112
io where it flows through a plurality of process microchannels, contacts a
second fluid
phase flowing counter currently to it in the process microchannels, and then
flows
through footer 116 and out of the microchannel processing unit 110, as
indicated by
arrow 122. Similarly, a second fluid phase may flow through footer 116, as
indicated
by arrow 124, and from footer 116 into the microchannel processing unit core
112
~ s where it flows through a plurality of process microchannels, contacts the
liquid phase
flowing counter currently to it in the process microchannels, and then flows
through
header 114 and out of the microchannel processing unit 110, as indicated by
arrow
126. Mass transfer between the liquid phase and second fluid phase may occur
in
the process microchannels. When mass transfer between the second fluid phase
2o and the liquid phase occurs, one or more parts or components of one or both
of the
phases may transfer to the other phase. In one embodiment, the second fluid
phase
may completely or partially transfer to the liquid phase. In one embodiment,
the
iiquid phase may completely or partially transfer to the gas phase.
Referring to Fig. 2B, a liquid phase may flow through header 114, as indicated
25 by arrow 130, and from header 114 into the microchannel processing unit
core 112.
Similarly, a second fluid phase may flow through header 114, as indicated by
arrow
132, and from header 114 into the microchannel processing unit core 112. tn
fihe
microchannel processing unit core 112, the liquid phase and the second fluid
phase
may flow co-currently through a plurality of process microchannels, and
contact
3o each other in the process microchannels. Mass transfer between the liquid
phase
and the second fluid phase may occur in the process microchannels. The liquid
and
second fluid phases may then flow through footer 116 and out of the
microchannel
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processing unit 110, as indicated by arrow 134. The liquid and second fluid
phases
may combine with each other in the process microchannels to form a fluid
stream.
In one embodiment, the second fluid phase may completely or partially transfer
to
the liquid phase. In one embodiment, the liquid phase may completely or
partially
5 transfer to the second fluid phase. The liquid and second fluid may flow
through
footer 116 and oiat of the microchannel processing unit 110, as indicated by
arrow
134.
Referring to Fig. 2C, a liquid phase may flow through header 114, as
indicated by arrow 140, and from header 114 into the microchannel processing
unit
1o core 112 where it flows through a plurality of process microchannels,
contacts a
second fluid phase flowing counter currently to it in the process
microchannels, and
then flows through footer 116 and out of-the microchannel processing unit 110,
as
indicated by arrow 144. Similarly, a second fluid phase mayflow through footer
116,
as indicated by arrow 142, and from footer 116 into the microchannel
processing unit
15 core 112 where it flows in the plurality of process microchannels and
contacts the
liquid phase flowing counter currently to it in the process microchannels.
Mass
transfer between the liquid phase and the second fluid phase may occur in the
process microchannels. The liquid and second fluid phases may combine to form
a
fluid stream. This fluid stream may flow through footer 116 and out of the
20 microchannel processing unit 110,-as indicated by arrow 144. In one
embodiment,
the second fluid phase may completely or partially transfer to the liquid
phase. In
one embodiment, the liquid phase may completely or partially transferto the
second
fluid phase. In either case, a(iquid phase may flow through footer 116 and
then out
of the microchannel processing unit 110, as indicated by arrow 144, and a
second
fluid phase may flow through header 114 and out of the microchannel processing
unit 110.
The process may be a distillation process which may be described with
reference to Fig. 2D. Referring to Fig. 2D, a microchannel distillation
assembly 150
is provided for distilling a fluid mixture containing components X and Y.
Component
Y is more volatile than component X. The microchannel distillation assembly
150
includes microchannel distillation unit 152, condenser 154, and reboiler 156.
The
condenser may be a microchannel condenser. The reboiler may be a microchannel
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21
reboiler. The microchannel distillation unit 152 contains one or more process
microchannels which are provided for contacting a gas or vapor phase and a
liquid
phase and for separating component X from component Y. In operation, a feed F
comprising a fluid (i.e., gas, liquid, or mixture of gas and liquid)
comprising
components X and Y enters a microchannel distillation unit 152, as indicated
by
arrow 158. Within the microchannel distillation unit 152 a vapor phase flows
in a
direction towards the condenser 154 and a liquid phase flows in a direction
towards
the reboiler 156. In the process microchannels the vapor phase and the liquid
phase
contact each other with the result being a mass transfer between the phases.
The
io vapor phase, which may become enriched with the more volatile component Y,
flows
through microchannel distillation unit 152 towards the condenser 154 and into
the
condenser 154. The liquid phase, which may become enriched with the less
volatile
component X, flows through the microchannel distillation unit 152 towards the
reboiler 156 and into the reboiler 156. The vapor phase may be condensed in
the
condenser 154 to form distillate product D. Part of the distillate product D,
which
may be referred to as an overhead product (sometimes called a head or a make),
may be withdrawn from the system, as indicated by arrow 160. Part of the
distillate
product D may be returned to the microchannel distillation unit 152 where it
flows
through the microchannel distillation unit in the form of a liquid phase. The
liquid
phase, in the form of bottoms product B, flows into the reboiler 156. - Part-
of the
bottoms product B may be withdrawn from the system, as indicated by arrow 162.
Part of the bottoms product may be vaporized in the reboiler 156 and returned
to the
microchannel distillation unit 152 where it flows through the microchannel
distillation
unit 152 in the form of a vapor phase. The ratio between the amount of
distillate
product D that is removed from the system and the amount that is returned to
the
system may be referred to as the reflux ratio. The ratio between the amount of
bottoms product B that is removed from the system and the amount that is
returned
to the system may be referred to as the boil-up ratio. These ratios can vary
and can
be determined by those skilled in the art.
In one embodiment, the microchannel distillation assembly 150 may be
constructed without the condenser 154. In this embodiment, the microchannel
distillation assembly 150 would comprise the microchannel distillation unit
152 and
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22
the reboiler 156. In this embodiment the microchannel distillation assembly
150 may
be used as a stripping column.
In one embodiment, the microchannel distillation assembly 150 may be
constructed without the reboiler 162. In this embodiment, the microchannel
distillation assembly 150 would comprise the microchannel distillation unit
152 and
the microchannel condenser 154. In this embodiment the microchannel
distillation
assembly 150 may be used in operations where a relatively hot fluid is added
in a
lower section or stage. An example of such a use may be a steam stripper.
In addition to the distillation process illustrated in Fig. 2D, there are
other
1 o distillation processes that may be used for separating fluids for which
the disclosed
microchannel distillation process may be employed. For example, distillation
processes with any number of microchannel distillation units or assemblies,
for
example, ten, twenty, thirty, etc., may be employed similarly to those
illustrated.
Distillation processes that may be conducted in accordance with the disclosed
process may include: processes employing partitioned columns; topping and
tailing
processes or tailing and topping processes, which may employ two distillation
columns; easiest separation first processes, which may employ three
distillation
columns; and full thermal coupling processes which employ two distillation
columns.
These distillation processes are described in Becker et al., "The World's
Largest
Partitioned Column with Trays - Experiences from Conceptual Development to
Successful Start-Up," Reports on Science and Technology 62/2000, pages 42-48.
The microchannel distillation units used with the disclosed process may be
employed in these distillation processes. An advantage of using the disclosed
process is that microchannel distillation units disclosed herein can be built
on smaller
scales that consume significantly less energy and still produce the same level
of
product output as conventional distillation systems. Another advantage of
using the
microchannel distillation units disclosed herein relates to the ability to
closely space
partitions within these microchannel distillation units or to closely space
thermally
coupled streams by integration of such thermally coupled streams with adjacent
channels or within adjacent or nearly adjacent layers in the same microchannel
distillation assembly. The close spacing of the thermally coupled streams may
reduce one or more of thermal response times, control feedback times, and
start-up
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23
times needed for achieving steady-state operations for continuous distillation
processes.
The height of an equivalent theoretical plate (HETP) ratio may be used for
calculating the mass transfer efficiency of hardware for effecting gas-liquid
contacting processes. In conventional distillation processes, the HETP is
typically
on the order of about 2 feet (about 61 cm) for trays and packing. On the other
hand,
with the disclosed process the HETP may be less than about 1 foot (about 30.5
cm),
and in one embodiment less than about 6 inches (15.24 cm), and in one
embodiment less than about 2 inches (5.08 cm), and in one embodiment less than
1o about 1 inch (about 2.54 cm), and in one embodiment in the range from about
0.01
to about 1 cm. This provides the disclosed process with the advantage of
employing
more theoretical distillation stages in a more compact system than
conventional
processes and yet achieve similar separation and product throughput results.
In one
embodiment, at least one theoretical distillation stage for separating two or
more
components may be provided in each process microchannel. For example, for the
separation of ethane from ethylene in the production of > 99% by volume pure
ethylene, the microchannel distillation unit used with the disclosed process
may be
less than about 20 meters (about 65 feet) high, and in one embodiment less
than
about 3 meters(about 9.8 feet) high, while with conventional processes the
same
separation may require a distillation column that may be hundreds of feet
high.
The microchannel processing unit core 112 (Figs. 2A-2C) and the
microchannel distillation unit 152 (Fig. 2D) may contain a plurality of
process
microchannels wherein the liquid phase and the second fluid phase contact each
other. In one embodiment, these process microchannels may have the
construction
illustrated in Fig. 3. Referring to Fig. 3, process microchannel 100A
comprises
liquid phase region 170 and second fluid phase region 172. Fig. 3 shows
a"vapor"
flowing in the second fluid phase region 172, however, it is to be understood
that any
second fluid may flow in the region 172. The liquid and second fluid phases
may
contact each other at interface 174. The liquid phase flows counter current to
second fluid phase. Heat and/or mass transfer may occur between the phases.
Mass may be transferred from the second fluid phase to the liquid phase via
the
interface 174, and/or mass may be transferred from the liquid phase to the
second
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24
fluid phase via the interface. A layer of a wicking material at the interface
174 may
be included to assure that the liquid velocity is not impeded by drag from the
flow of
the second fluid phase. The wicking material layer may promote good contact
between the second fluid phase and the liquid phase. Convective mixing induced
by surface features 176 and 178 on the walls 180 and 182, respectively,
opposite
the interface 174 may be used to overcome mass transport resistance in both
the
liquid and second fluid phases and thereby improve mixing between the liquid
and
the second fluid. Different surface feature geometries may be used forthe
liquid and
second fluid phase regions. In an alternate embodiment, the surface features
may
lo be used in only the liquid region 170 or only the second fluid phase region
172.
An alternate embodiment of the process microchannels that may be used is
illustrated in Fig. 4. Referring to Fig. 4, process microchannel 100B
comprises liquid
phase region 190 and second fluid phase region 192 which are separated by
capillary plate 194. Fig. 4 shows a "vapor channel," however it is to be
understood.
that the vapor channel is provided for flowing any second fluid phase. The
capillary
plate 194 may be referred to as a contactor. The capillary plate 194 may be in
the
form of thin porous material such as a thin screen. The capillary plate 194
includes
surface features 196 on the wall of the capillary plate facing the liquid
region 190,
and surface features 198 on the wall of the capillary plate facing the second
fluid
phase region 192. The surface features 196 and 198 are through-surface
features
which permit mass transfer through the surface features. Mass from the liquid
phase
may flow through the surface features 196, then through the capillary plate
194, then
through surface features 198 into the second fluid phase region. Mass
transferfrom
the second fluid phase region 192 to the liquid phase region 190 may flow in
the
reverse path. The liquid phase and the second fluid phase may flow in a co-
current
or counter current direction (counter current is shown in Fig. 4). In an
alternate
embodiment, surfacefeatures may be positioned on process microchannel walls
191
and/or 193. Either or both surface features 196 and 198 may be eliminated, and
surface features on walls 191 and/or 193 may be added. Any combination of
3o surface features on either or both walls of the capillary plate 194 and/or
on either or
both of the microchannel walls 191 and 193 may be used.
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The capillary plate 194 may be used to keep the liquid and the second fluid
phases separate and prevent the formation of a two-phase mixture inside the
process microchannel. The capillary plate may prevent the mixing of liquid and
second fluid by virtue of surface tension forces. The capillary plate may or
may not
5 be required depending upon the application. In the absence of the capillary
plate, a
surface feature wall may be used to separate the liquid and second fluid phase
regions. The surface features on either or both sides of the capillary plate
may
provide for the movement of liquid and second fluid from bulk to the capillary
plate.
This movement of bulk fluid towards the capillary plate may improve mass
transfer
lo between the liquid and second fluid phases.
In one embodiment, the capillary plate may not be used and the at least two
phases may be allowed to mix along the length of the process microchannel. The
resulting intimate mixing may increase the surface area for mass transfer and
the
surface features may enhance mixing. The flow of the two phase may be either
co-
15 current or counter current. For co-current flow and for distillation, the
flow may need
to be phase separated after the mixing and mass transfer in each stage. For
counter
current flow the phase separation may occur near the product draws or outlet
ports
and/or near the feed inlet manifolding region. In one embodiment, the phase
separation for -one or more fluid streams may occur outside the microchannel
20 processing unit or microchannel distillation unit.
Although only one process microchannel is illustrated in Figs. 3 and 4, there
is
practically no upper limit to the number of process microchannels that may be
used
in the microchannel processing unit core (Figs. 2A-2C) or the microchannel
distillation unit 152 (Fig. 2D). For example, one, two, three, four, five,
six, eight, ten,
25 twenty, fifty, one hundred, hundreds, one thousand, thousands, ten
thousand, tens
of thousands, one hundred thousand, hundreds of thousands, millions, etc., of
the
process microchannels may be used. The process microchannels may be aligned
side-by-side or stacked one above another. The process microchannels may be
aiigned to provide for vertical flow through the channels, or they may be
aligned
3o horizontally to provide for horizontal flow through the channels, or they
may be
aligned at an inclined angle from the horizontal.
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26
Repeating units that may be used in the microchannel processing unit core
112 or the microchannel distillation unit 152 may include those illustrated in
Figs. 24-
27. Each of these comprises a process microchannel that contains surface
features
on its interior walls and is used to provide for the contacting of a liquid
phase with a
second fluid phase. Each of the drawings refer to "vapor," but it is to be
understood
that any second fluid may be used. The repeating unit illustrated in Fig. 25
includes
adjacent heat exchange channels. Fig. 28 shows a microchannel wall that
employs
dual depth surface features which may be used in the foregoing process
microchannels.
The process microchannels may contain one or more surface features in the
form of depressions in and/or projections from one or more interior walls of
the
process microchannels. The heat exchange channels discussed below may also
contain such surface features. The surface features may be used to disrupt the
flow
of the liquid phase and/or the second fluid phase flowing in the process
microchannel. These disruptions in flow may enhance mixing and/or mass
transfer
between the liquid and the second fluid phases. The surface features in the
heat
exchange channels may enhance heat exchange between the heat exchange
channels and the process microchannels. Either or both walls of the capillary
plate
may contain surface features. The surface features may be in the form of
patterned
surfaces. The microchannei processing unit core 112 or microchannel
distillation
unit 152 containing the process microchannels may be made by laminating a
plurality of shims together. One or both major surfaces of the shims may
contain
surface features. Alternatively, the microchannel processing unit core 112 or
microchannel distillation unit 152 may be assembled using some sheets (or
shims)
and some strips, or partial sheets to reduce the total amount of metal
required to
construct the device. In one embodiment, a shim containing surface features
may
be paired (on opposite sides of a microchannel) with another shim containing
surface features. Pairing often creates better mixing or heat or mass transfer
enhancement as compared to channels with surface features on only one major
surface. In one embodiment, the patterning may comprise diagonal recesses that
are disposed over substantially the entire width of a microchannel surface.
The
patterned surface feature area of a wall may occupy part of or the entire
length of a
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27
microchannel surface. In one embodiment, surface features may be positioned
over
at least about 10%, and in one embodiment at least about 20%, and in one
embodiment at least about 50%, and in one embodiment at least about 80% of the
length of a microchannel surface. Each diagonal recesses may comprise one or
more angles relative to the flow direction. Successive recessed surface
features
may comprise similaror alternate angles relative to other recessed surface
features.
In embodiments wherein surface features may be positioned on or in more
than one microchannel wall, the surface features on or in one wall may have
the
same (or similar) pattern as found on a second wall, but rotated about the
centerline
of the main channel mean bulk flow direction. !n embodiments wherein surface
features may be on or in opposite walls, the surface features on or in one
wall may
be approximately mirror images of the features on the opposite wall. In
embodiments wherein surface features are on or in more than one wall, the
surface
features on or in one wall may be the same (or similar) pattern as found on a
second
wall, but rotated about an axis which is orthogonal to the main channel mean
bulk
flow direction. In other words, the surface features may be flipped 180
degrees
relative to the main channel mean bulk flow direction and rotated about the
centerline of the main channel mean bulk flow. The surface features on or in
opposing or adjacent walls may or may not be aligned directly with one
another, but
may be repeated continuously along the wall for at least part of the length-of
the wall.
Surface features may be positioned on three or more interior surfaces of a
microchannel. For the case of microchannel geometries with three or fewer
sides,
such as triangular, oval, elliptical, circular, and the like, the surface
features may
cover from about 20% to about 100% of the perimeter of the microchannel.
In one embodiment, a patterned surface may comprise multiple patterns
stacked on top of each other. A pattern or array of holes may be placed
adjacent to
a heat transfer wall and a second pattern, such as a diagonal array of surface
features may be stacked on top and adjacent to an open channel for flow. A
sheet
adjacent to an open gap may have patterning through the thickness of the sheet
such that flow may pass through the sheet into an underlying pattern. Flow may
occur as a result of advection or diffusion. As an example, a first sheet with
an array
of through holes may be placed over a heat transfer wall, and a second sheet
with
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an array of diagonal through slots may be positioned on the first sheet. This
may
create more surface area for adhering an active material such as an adsorbent,
wick,
etc. In one embodiment, the pattern may be repeated on at least one other wall
of
the process microchannel. The patterns may be offset on opposing walls. The
innermost patterned surfaces (those surfaces bounding a flow channel) may
contain
a pattern such as a diagonal array. The diagonal arrays may be oriented both
"with"
the direction of flow (cis orientation) or one side oriented with the
direction of flow
and the opposing side oriented "against" the direction of flow (trans
orientation). By
varying surface features on opposing walls, different flow fields and degrees
of
vorticity may be created in the fluid that travels down the center and open
gap.
The surface features may be oriented at angles relative to the direction of
flow
through the channels. The surface features may be aligned at an angle from
about
1 to about 89 , and in one embodiment from about 30 to about 75', relative
to the
direction of flow. The angle of orientation may be an oblique angle. The
angled
surface features may be aligned toward the direction of flow or against the
direction
of flow. The flow of fluids in contact with the surface features may force one
or more
of the fluids into depressions in the surface features, while other fluids may
flow
above the surface features. Flow within the surface features may conform with
the
surface feature and be at an angle to the direction of the bulk flow in the
channel. As
fluid exits the surface features it may exert-momentum-in the x and y
direction for an
x,y,z coordinate system wherein the bulk flow is in the z direction. This may
result in
a churning or rotation in the flow of the fluids. This pattern may be helpful
for mixing
a two-phase flow as the imparted velocity gradients may create fluid shear
that
breaks up one of the phases into small and well dispersed droplets.
Two or more surface feature regions within the process microchannels may
be placed in series such that mixing of the process fluids may be accomplished
using a first surface feature region, followed by at least one second surface
feature
region where a different flow pattern may be used. The second flow pattern may
be
used to separate one or more liquids or gases from the fluid mixture. In the
second
surface feature region, a flow pattern may be used that creates a centrifugal
force
that drives one liquid toward the interior walls of the process microchannels
while
another liquid remains in the fluid core. One pattern of surface features that
may
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create a strong central vortex may comprise a pair of angled slots on the top
and
bottom of the process microchannel. This pattern of surface features may be
used
to create a central swirling flow pattern.
The surface features may have two or more layers stacked on top of each
other or intertwined in a three-dimensional pattern. The pattern in each
discrete layer
may be the same or different. Flow may rotate or advect in each layer or only
in one
layer. Sub-layers, which may not be adjacent to the bulk flow path of the
channel,
may be used to create additional surface area. The flow may rotate in the
first level
of surface features and diffuse molecularly into the second or more sublayers
to
promote reaction. Three-dimensional surface features may be made via metal
casting, photochemical machining, laser cutting, etching, ablation, or other
processes where varying patterns may be broken into discrete planes as if
stacked
on top of one another. Three-dimensional surface features may be provided
adjacent to the bulk flow path within the microchannel where the surface
features
have different depths, shapes, and/or locations accompanied by sub-features
with
patterns of varying depths, shapes and/or locations.
An example of a three-dimensional surface feature structure may comprise
recessed oblique angles or chevrons at the interface adjacent the bulk flow
path of
the microchannel. Beneath the chevrons there may be a series of three-
dimensional
structures that connect to the surface features adjacent to-the bulk flow path
but are --
made from structures of assorted shapes, depths, and/or locations. It may be
further
advantageous to provide sublayer passages that do not directly fall beneath an
open
surface feature that is adjacent to the bulk flow path within the microchannel
but
rather connect through one or more tortuous two-dimensional or three-
dimensional
passages. This approach may be advantageous for creating tailored residence
time
distributions in the microchannels, where it may be desirable to have a wider
versus
more narrow residence time distribution.
The length and width of a surface feature may be defined in the same way as
the length and width of a microchannel. The depth may be the distance which
the
3o surface feature sinks into or rises above the microchannel surface. The
depth of the
surface features may correspond to the direction of stacking a stacked and
bonded
microchannel device with surface features formed on or in the sheet surfaces.
The
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dimensions for the surface features may refer the maximum dimension of a
surface
feature; for example the depth of a rounded groove may refer to the maximum
depth,
that is, the depth at the bottom of the groove.
The surface features may have depths that are up to about 5 mm, and in one
5 embodiment up to about 2 mm, and in one embodiment in the range from about
0.01
to about 5 mm, and in one embodiment in the range from about 0.01 to about 2
mm,
and in one embodiment in the range from about 0.01 mm to about 1 mm. The width
of the surface features may be sufficient to nearly span the microchannel
width (for
example, herringbone designs), but in one embodiment (such as fill features)
may
lo span about 60% or less of the width of the microchannel, and in one
embodiment
about 50% or less, and in one embodiment about 40% or less, and in one
embodiment from about 0.1 % to about 60% of the microchannel width, and in one
embodiment from about 0.1 % to about 50% of the microchannel width, and in one
embodiment from about 0.1 /a to about 40% of the microchannel width. The
width of
15 the surface features may be in the range from about 0.05 mm to about 100
cm, and
in one embodiment in the range from about 0.5 mm to about 5 cm, and in one
embodiment in the range from about 1 to about 2 cm.
Multiple surface features or regions of surface features may be included
within a microchannel, including surface features that recess at different
depths into
20 one or more microchannel walls. The spacing between recesses may be in the
range from about 0.01 mm to about 10 mm, and in one embodiment in the range
from about 0.1 to about 1 mm. The surface features may be present throughout
the
entire length of a microchannel or in portions or regions of the microchannel.
The
portion or region having surface features may be intermittent so as to promote
a
25 desired mixing or unit operation (for example, separation, cooling, etc.)
in tailored
zones. For example, a one-centimeter section of a microchannel may have a
tightly
spaced array of surface features, followed by four centimeters of a flat
channel
without surface features, followed by a two-centimeter section of loosely
spaced
surface features. The term "loosely spaced surface features" may be used to
refer
3o to surface features with a pitch or feature to feature distance that is
more than about
five times the width of the surface feature.
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The surface features may be positioned in one or more surface feature
regions that extend substantially over the entire axial length of a channel.
In one
embodiment, a channel may have surface features extending over about 50% or
less of its axial length, and in one embodiment over about 20% or less of its
axial
length. In one embodiment, the surface features may extend over about 10% to
about 100% of the axial length of the channel, and in one embodiment from
about
20% to about 90%, and in one embodiment from about 30% to about 80%, and in
one embodiment from about 40% to about 60% of the axial length of a channel.
Each surface feature leg may be at an oblique angle relative to the bulk flow
1o direction. The feature span length or span may be defined as being normal
to the
feature orientation. As an example, one surface feature may be a diagonal
depression at a 45 degree angle relative to a plane orthogonal to the mean
direction
of bulk flow in the main channel with a 0.015 inch opening or span or feature
span
length and a feature run length of 0.22 inch. The run length may be the
distance
from one end to the other end of the surface feature in the longest direction,
whereas
the span or feature span length may be in the shortest direction (that is not
depth).
The surface feature depth may be the distance way from the main channel. For
surface features with a nonuniform width (span), the span may be the average
span
averaged over the run length.
In one embodiment, the process microchannel-may comprise a mass transfer
system comprising a gas-containing open section connected to a liquid-
containing
microchannel. The liquid-containing microchannel may comprise two major
surfaces
in which the liquid is mixed by flow past surface features on two major
surfaces of
the microchannel. Two major surfaces may be opposite one another and comprise
diagonal recesses positioned substantially across the entire width of both
microchannel surfaces. The microchannel major surfaces may have a length,
which
is the direction of fluid flow, and width, which is perpendicular to the
length.
A surface feature may comprise a recess or a protrusion based on the
projected area at the base of the surface feature or the top of the surface
feature. If
the area at the top of the surface feature is the same or exceeds the area at
the
base of the surface feature, then the surface feature may be considered to be
recessed. If the area at the base of the surface feature exceeds the area at
the top
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of the surface feature, then it may be considered to be protruded. For this
description, the surface features may be described as recessed although it is
to be
understood that by changing the aspect ratio of the surface feature it may be
alternatively defined as a protrusion. For a process microchannel defined by
walls
that intersect only the tops of the surface features, especially for a flat
channel, all
surface features may be defined as recessed and it is to be understood that a
similar
channel could be created by protruding surface features from the base of a
channel
with a cross section that includes the base of the surface features.
The process microchannel may have at least about 20%, and in one
1 o embodiment at least about 35%, and in one embodiment at least about 50%,
and in
one embodiment at least about 70%, and in one embodiment at least about 90% of
the interior surface of the channel (measured in cross-section perpendicular
to
length; i.e., perpendicular to the direction of net flow through the channel)
that
contains surface features. The surface features may cover a continuous stretch
of at
Ieast about 1 cm, and in one embodiment at least about 5 cm. In the case of an
enclosed channel, the percentage of surface feature coverage may be the
portion of
a cross-section covered with surface features as compared to an enclosed
channel
that extends uniformly from either the base or the top of the surface feature
or a
constant value in-between. The latter may be a flat channel. For example, if a
channel has patterned top arid bottom surfaces that are each 0.9 crri across
(wide)
and unpatterned side walls that are 0.1 cm high, then 90% of the surface of
the
channel would contain surface features.
The process microchannel may be enclosed on all sides, and in one
embodiment the channel may have a generally square or rectangular cross-
section
(in the case of rectangular channel, surface feature patterning may be
positioned on
both major faces). For a generally square or rectangular channel, the channel
may
be enclosed on only two or three sides and only the two or three walled sides
may
be used in the above described calculation of percentage surface features. In
one
embodiment, the surface features may be positioned on cylindrical channels
with
3o either constant or varying cross section in the axial direction.
Each of the surface feature patterns may be repeated along one face of the
main channel, with variable or regular spacing between the surface features in
the
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33
main channel bulk flow direction. Some embodiments may have only a single leg
to
each surface feature, while other embodiments may have multiple legs (two,
three,
or more). For a wide-width main channel, multiple surface features or columns
of
repeated surface features may be placed adjacent to one another across the
width
of the main channel. For each of the surface feature patterns, the feature
depth,
width, span, and spacing may be variable or constant as the pattern is
repeated
along the bulk flow direction in the main channel. Also, surface feature
geometries
having an apex connecting two legs at different angles may have alternate
embodiments in which the surface feature legs may not be connected at the
apex.
In one embodiment, it may be desired to hold up liquid in the surface features
in a gravitational field (i.e. in applications such as applying uniform
coatings to the
walls of microchannels). For such embodiments the vertical component (relative
to
gravity) of the run length of each surface feature leg may be less than about
4 mm,
and in one embodiment less than about 2 mm to prevent the.liquid in the
surface
feature from draining out.
The surface feature geometry SFG-0 (see, Fig. 5) comprises an array of
chevrons or v-shaped recesses that may occur along the length of the process
microchannel. The chevrons may be either regularly or irregularly spaced with
equal
or varying distance between successive surface features. Regular (or equal)
spacing of the surface features may be useful since the disruptions to the
bulk flow
in the main channel effected by the presence of each surface feature may
reinforce
the disruptions effected by the other surface features. A one-sided surface
feature
may have surface features on only one side of the microchannel. A two-sided
surface feature may have surface features on two sides of a microchannel
(either on
opposite walls or adjacent walls). In some two-sided orientation embodiments,
surface feature orientation may be either in the cis orientation or the trans
orientation. In the cis orientation with surface features on opposite walls
(see, Fig.
6), the surface features may be mirror images on both channel walls. In the
trans
orientation, the surface features on one face may be symmetric to the surface
features on the opposite face about an axis perpendicular to both that face
and the
main channel bulk flow direction. Flow orientation relative to the surface
features on
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a given wall may be either cis A (flow direction from bottom to top; see, Fig.
7) or cis
B (flow direction from top to bottom; see, Fig. 6).
Fig. 6, which shows the top and bottom of the microchannel with angled
surface features on two walls, shows how the surface features may be aligned
in the
microchannel.
I n Fig. 7, the top and bottom of the microchannel with angled surface
features
on two walls, shows how the surface features may be aligned in the
microchannel.
Typically, the surface features are on opposing walls, but they may be on
adjacent
walls.
SFG-1 (Fig. 8) contains surface features that alternate in orientation or
angle
along each microchannel wall. For this geometry, five or more asymmetric
chevrons
(where one feature leg is longer than a second feature leg) may be placed with
the
apex of the surface feature stationed one-third of the way in along the
microchannel
width. The surface features are then followed by two filler features (noting
that fewer
or more filler features may be used), and then followed by five or more
asymmetric
features where the apex of the chevron is roughly two-thirds along the width
of the
microchannel. This pattern may be repeated several times. As shown in Fig. 8,
the
pattern on the opposing microchannel wall is in the trans-orientation, where
the
surface features are not mirror images.
SFG-2 (Fig. 9) comprises an air foil design; where the angle is continuously
changing along the surface feature run length. The flow in the main channel
adjacent to the surface features may be from left to right or from right to
left as
shown in Fig. 9. Flow disturbance at the leading edge of each surface feature
may
be minimized as a result of the aerodynamic shape of each surface feature.
The SFG-3 surface feature pattern is shown in Fig. 10, which includes a view
of both top and bottom faces, and how the two overlap when seen from above.
This
pattern may be repeated as many times as necessary to fill the desired length.
The
main characteristic of SFG-3 is the repetition of the "checkmark" shape.
The surface feature pattern SFG-4 is a simple diagonal slot with only one
feature leg per surface feature. This is shown in the right hand side of Fig.
17 and is
labeled "45 DEG".
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SEG-5 (Fig. 11) is represented by a series of checks, where the apex of the
check is such that the run length of one leg of the surface feature is roughly
half of
the run length of the other leg. Groups of four or more of these "check"
shaped
surface features may be arranged in many different combinations, including the
5 three shown in Fig. 11. These groups of checks may have different
orientations
relative to one another, or all may have the same orientation, forming a
continuous
pattern of checks along the surface. Each combination or variety of the SFG-5
pattern may yield different mixing characteristics.
SFG-6 (Fig. 12) contains three surface feature legs and has two changes in
10 the angle of orientation from positive to negative with respect to the
direction of flow.
This imparts aspects of both an "A" and a "B" type flow direction to the flow
in the
main channel, as two of the feature legs may converge with respect to each
other
along the bulk flow direction and two of the feature legs may diverge with
respect to
each other along the bulk flow direction.
15 Cis A refers to an alignment of a two or more sided microchannel with
surface
features where the surface features on both top and bottom are aligned in the
same
direction with respect to flow, and the surface feature legs may converge
along the
flow direction.
Cis B refers to an alignment of a two or more sided microchannel with surface
20 features where the surface features on both top and bottom are aligned in
the same
direction with respect to flow, and the surface feature legs diverge along the
flow
direction.
Trans refers to an alignment of a two or more sided microchannel with surface
features where the surface features on opposite walls are not aligned, but
rather a
25 second wall is first taken as a mirror image and then rotated 180 degrees
(so that
the top view of the pattern appears upside down relative to the first wall) to
create
offsetting features. The second and opposing wall may not be a perfectly
rotated
mirror image, as filler features may be added to create more net area of the
microchannel that contains surface features, and since the surface features on
30 opposite walls may be somewhat offset from one another along the direction
of bulk
flow.
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36
Fanelli (see, Fig. 13) refers to a discontinuity or small disconnection of the
legs of the surface features that are otherwise connected. The discontinuity
may be
less than about 20% of the surface feature run length. Fig. 13 shows a Fanelli
for a
SFG-0 feature pattern, where the apex is removed to help alleviate either dead
spots
or reduced velocity regions in the main channel flow path that result from a
change
in angle.
House (see, Fig. 14) refers to an entrance leg to a surface feature where one
or more legs runs parallel with the main channel bulk flow direction before
turning at
an oblique angle to the direction of flow. The angle may optionally be more
rounded
lo than that shown in Fig. 14.
A sharks tooth pattern (Fig. 15) represents a single legged surface feature
with a varying span from one end to the other. The leg may be at any angle
relative
to the main channel bulk flow direction, and multiple teeth at different
angles may
populate a microchannel wall.
Fig. 16 shows a surface feature with 45 degree angle, where the angle is
defined relative to a horizontal plane that bisects the microchannel cross
section
orthogonal to the main flow direction.
Fig. 17 shows surface features with a 60 degree angle forthe SFG-0 pattern,
a 75 degree angle for the SFG-0 pattem, and a 45 degree angle for the SFG-4
pattern.
Other embodiments of multiple-legged surface feature geometries may have
different angles and or lengths for each leg, or for some of the legs, or
groupings of
five or more identical surface features as shown in Fig. 18. Repetition of
groupings
of surface features also provides potential advantages during fabrication. For
example, when stamping features from thin sheets, stamping tools can be made
to
stamp multiple features at once.
Layered surface features may be formed in one or more walls of a main
channel. The layered surface feature wall may be formed by stacking adjacent
layers with different surface feature geometries in them (see, Fig. 19), and
aligning
the columns of surface features such that the two stacked together make a more
complex three dimensional feature. Fig. 19 shows a top view of different
surface
feature patterns which, when stacked in adjacent layers, form a layered
surface
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37
feature. For layered surface features, the surface features in all layers
except the
layer farthest from the main channel may be through surface features.
Alternately,
the identical surface features made as through surface features in a thin
sheet may
be made deeper by stacking sheets of identical surface features directly on
top of
one other and aligning the surface features in each sheet.
The surface features shown on the left in each of Figs. 20 and 21 may be
positioned in the vapor phase region of the process microchannel, and the
surface
features shown, on the right may be positioned in the liquid phase region.
Next to
each of these figures are schematic illustrations showing the surface features
as
1o they may overlap and complement one another. Figs. 22 and 23 show alternate
embodiments of these surface features. Each of these figures show the
complementing nature of these surface features.
The shim illustrated in Fig. 29 may be used to form a major surface of a
process microchannel. This surface may be paired (on opposite sides of the
microchannel) with a shim of the same or substantially similar structure with
diagonal
strips (the strips may be recessed) that are either aligned, staggered or
crossed with
respect to the opposing surface. Pairing may create better mixing than in
channels
where surface features are only on one major surface. The patterning of the
surface
features may comprise diagonal recesses that are positioned over substantially
the
entire width of the microchannel surface.
The pattern of surface features shown in Fig. 30 introduces a spatially
varying
depth for the surface features. This may be advantageous for some applications
where changing the depth of the surface feature within a surface feature may
create
more flow rotation or vorticity such that the external mass transfer
resistance
between fluids may be reduced.
The surface feature pattern shown in Fig. 31 may be advantageous as an
underlayer surface pattern that sits beneath at least one or more other
surface
pattern sheets to increase the available surface area for a mass exchange
agent.
The surface feature pattern shown in Fig. 32 may be advantageous for
inducing flow rotation in a center channel adjacent to a surface pattern
sheet.
Greater flow rotation may further reduce external mass transfer resistance.
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The surface feature pattern shown in Fig. 33 introduces both angled features
and a horizontal feature. The surface feature geometry may vary along the
length of
the process microchannel. This design may be advantageous as an underlayer
surface pattern sheet that is used to both hold more mass exchange agent while
also creating more depth to angled surface features that may sit adjacent to
this
sheet. A second and angled sheet may be adjacent to the flow path and induce
flow
rotation. The varying depths of angled surface features may create more
turbulence
or apparent turbulence in the flow paths.
The surface features shown in Fig. 34 may provide for convective flow in the
process microchannel in a direction perpendicular to the direction of bulk
flow and
thereby improve mass transfer.
Fig. 35 shows surface features in the form of inter-connected oblique angles
that may project from one or more interior walls of the process microchannel.
The surface features when added to the walls of a microchannel, may modify
the laminar flow pattern that is typically formed within a microchannel. The
creation
of regular flow patterns with rotation, swirling, vorticity, and other
movement
orthogonal or angled with the direction of bulk flow may be advantageous for
increasing heat transfer efficiency, reducing mass transport resistance,
enhancing
mixing, enhancing mass and/or energy transport between phases, and/or
promoting
separation of phases such as separating a gas from a liquid or liquid from a
gas.
The process microchannels and/or heat exchange channels (discussed
below) may have their interior walls coated with a lipophobic coating (the
same
coating may also provide hydrophobic properties) to reduce surface energy.
Teflon
may be an example of a coating material that may exhibit both lipophobic and
hydrophobic tendencies. In one embodiment, fluids may not wet surfaces coated
with the lipophobic coating. As such, the fluids may slip past the surface and
thus
negate or reduce the usual no-slip boundary condition of fluids against a
wall. As
the fluids slip, the local friction factor may decrease as a result of reduced
drag and
the corresponding pressure drop may be reduced per unit length of the
channels.
3o The local heat transfer rate may increase as a result of forced convection
over a
coated surface as opposed to conductive heat transferthrough a stagnantfilm.
The
effect of the coating may have a different impact on different types of non-
Newtonian
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39
fluids. For the case of pseudoplastic (power law) fluid without yield may
appear
Newtonian above shear rates that are fluid dependent. The viscosity of the
fluid may
be higher when the shear rate is below a certain value. If the shear rate is
locally
larger because of the coated wall, then the fluid may be able to shear
droplets more
easily, move with less energy (lower pumping requirements), and have better
heat
transfer properties than if the coating were not used. For the case of
pseudoplastic
(power law) fluid with yield may still have a yield stress, at the wall the
yield stress
may be greatly reduced with the use of the lipophobic coating. Heat transfer
and
frictional properties may be enhanced if the apparent yield is low when the
coating
1 o is used as compared to when the coating is not used. The shear-related
effects may
be more pronounced for non-Newtonian fluids than for Newtonian fluids.
The microchannel processing unit core 112 and the microchannel distillation
unit 152 may further comprise a heat source and/or heat sink in thermal
contact with
the process microchannels. The heat source and/or heat sink may comprise one
or
more heat exchange channels adjacent to and/or in thermal contactwith the
process
microchannels. The heat exchange channels may be microchannels. The heat
source and/or heat sink may be used to provide cooling and/or heating to the
process microchannels. Various combinations of heating and cooling may be
employed to provide for desired temperature profiles within the process
microchannels and along the length of the process microchannels:
The heat source and/or heat sink may comprise one or more heat exchange
channels containing a heat exchange fluid. The heat source may comprise a non-
fluid heating element such as an electric heating element or a resistance
heater.
The heat sink may comprise a non-fluid cooling element such as a Peltier
electronic
element. A heat exchange fluid may flow in and through heat exchange channels
in
the microchannel processing unit core 112 orthe microchannel distillation unit
152.
Heat transfer between the process fluids and the heat source and/or heat sink
may
be effected using convective heat transfer. In one embodiment, heat transfer
may
be enhanced using a heat exchange fluid wherein the heat exchange fluid
undergoes an exothermic or endothermic reaction and/or a full or partial phase
change. Multiple heat exchange zones may be employed along the length of the
process microchannels to provide for different temperatures at different
points along
6
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the lengths of the process microchannels. This may provide the advantage of
tailoring the heating and/or cooling profile in the process microchannels.
The heat exchange channels may be microchannels or they may have larger
dimensions. Each of the heat exchange channels may have a cross section having
5 any shape, for example, a square, rectangle, circle, semi-circle, etc. Each
of the
heat exchange channels may have an internal height or gap of up to about 10
mm,
and in one embodiment in the range from about 0.05 to about 10 mm, and in one
embodiment from about 0.05 to about 5 mm, and in one embodiment from about
0.05 to about 2 mm. The width of each of these channels may be of any
dimension,
i o for example, up to about 3 meters, and in one embodiment from about 0.01
to about
3 meters, and in one embodiment from about 0.1 to about 3 meters. The length
of
each of the heat exchange channels may be of any dimension, for example, up to
about 10 meters, and in one embodiment from about 0.01 to about 10 meters, and
in
one embodiment from about 0.01 to about 5 meters, and in one embodiment from
15 0.01 to about 2.5 meters, and in one embodiment from about 0.01 to about 1
meter,
and in one embodiment from about 0.02 to about 0.5 meter, and in one
embodiment
from about 0.02 to about 0.25 meter. The length may be in the range from about
15
cm to about 15 m. The heat exchange channels may have cross sections that are
rectangular, or alternatively they may have cross sections having any shape,
for
2o example, a square, circle, semi-circle;-trapezoid, etc. The-shape and/or-
size of-the-
cross section of the heat exchange channel may vary over its length. For
example,
the height or width may taper from a relatively large dimension to a
relatively small
dimension, or vice versa, over the length of the microchannel.
The separation between adjacent process microchannels, heat exchange
25 channels may be in the range from about 0.05 mm to about 50 mm, and in one
embodiment about 0.1 to about 10 mm, and in one embodiment about 0.2 mm to
about 2 mm.
The heat exchange fluid may be any fluid. These may include air, steam,
liquid water, steam, gaseous nitrogen, other gases including inert gases,
carbon
30 monoxide, molten salt, oils such as mineral oil, and heat exchange fluids
such as
Dowtherm A and Therminol which are available from Dow-Union Carbide.
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The heat exchange fluid may comprise a stream of the first and/or second
reactant. This may provide process pre-heat and increase in overall thermal
efficiency of the process.
The heat exchange channels may comprise process channels wherein an
endothermic process or an exothermic process is conducted. These heat exchange
process channels may be microchannels. Examples of endothermic processes that
may be conducted in the heat exchange channels include steam reforming and
dehydrogenation reactions. Steam reforming of an alcohol that occurs at a
temperature in the range from about 200 C to about 300 C is an example of an
1o endothermic process suited for an exothermic reaction such as an FT
synthesis
reaction in the same temperature range. The incorporation of a simultaneous
endothermic reaction to provide an improved heat sink may enable a typical
heat flux
of roughly an order of magnitude above the convective cooling heat flux.
Examples
of exothermic processes that may be conducted in the heat exchange channels
include water-gas shift reactions, methanol synthesis reactions and ammonia
synthesis reactions. The use of simultaneous exothermic and endothermic
reactions
to exchange heat in a microchannel reactor is disclosed in U.S. Patent
Application
Serial No. 10/222,196, filed August 15, 2002, which is incorporated herein by
reference.
The heat exchange fluid may undergo a partial or full phase change as- it
flows in the heat exchange channels. This phase change may provide additional
heat removal from the process microchannels beyond that provided by convective
cooling. For a liquid heat exchange fluid being vaporized, the additional heat
being
transferred from the process microchannels may result from the latent heat of
vaporization required by the heat exchange fluid. An example of such a phase
change may be an oil or water that undergoes boiling or partial boiling. In
one
embodiment, about 80% by weight of the heat exchange fluid may be vaporized,
and
in one embodiment about 50% by weight may be vaporized, and in one embodiment
about 30% by weight may be vaporized, and in one embodiment about 3% by weight
may be vaporized. In one embodiment, from about 5% to about 50% by weight may
be vaporized.
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The microchannel processing unit 110 and the microchannel distillation
assembly 150 may be used in combination with one or more storage vessels,
pumps, valves, manifolds, microprocessors, flow control devices, and the like,
which
are not shown in the drawings, but would be apparent to those skilled in the
art.
The microchannel processing unit 110 and the microchannel distillation
assembly 150 may contain a plurality of process microchannels and heat
exchange
channels aligned side by side or stacked one above the other. The process
microchannels and/or heat exchange channels may be provided in layers of each,
with each layer containing a plurality of channels. For each heat exchange
channel,
one or more process microchannels may be used. Thus, for example, one, two,
three, four, five, six or more process microchannels may be employed with a
single
heat exchange channel. Alternatively, two or more heat exchange channels may
be
employed with each process microchannel. The heat exchange channels may be
used for heating and/or cooling. In one embodiment, each process microchannel
may be positioned between adjacent heat exchange channels. In one embodiment,
two or more process microchannels may be positioned adjacent each other to
form a
vertically or horizontally oriented stack of process microchannels, and a heat
exchange channel may be positioned on one or both sides of the stack. Each
combination of process microchannels and heat exchange channels may be
referred
to as a repeating unit.
The microchannel processing unit 110 and the microchannel distillation
assembly 150 may be constructed of any material that provides sufficient
strength,
dimensional stabiiity and heat transfer characteristics for carrying out the
inventive
process. Examples of suitable materials may include steel (e.g., stainless
steel,
carbon steel, and the like), aluminum, titanium, nickel, and alloys of any of
the
foregoing metals, plastics (e.g., epoxy resins, UV cured resins, thermosetting
resins,
and the like), monel, inconel, ceramics, glass, composites, quartz, silicon,
or a
combination of two or more thereof. The microchannel processing unit 110 and
the
microchannel distillation assembly 150 may be fabricated using known
techniques
including wire electrodischarge machining, conventional machining, laser
cutting,
photochemical machining, electrochemical machining, molding, water jet,
stamping,
etching (for example, chemical, photochemical or plasma etching) and
combinations
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thereof. The microchannel reactor may be constructed by forming layers or
sheets
with portions removed that allow flow passage. A stack of sheets may be
assembled
via diffusion bonding, laser welding, diffusion brazing, and similar methods
to form
an integrated device. The microchannel reactor may have appropriate manifolds,
valves, conduit lines, etc. to control flow of the reactants and product, and
the flow of
heat exchange fluid. These are not shown in the drawings, but can be readily
provided by those skilled in the art.
The microchannel processing unit core 112 and the microchannel distillation
unit 152 may be made by a process that includes laminating or diffusion
bonding thin
sheets or shims of any of the above-indicated materials (e.g., metal, plastic
or
ceramic) so that each layer has a defined geometry of channels and openings
through which to convey fluids. After the individual layers are created, they
may be
stacked in a prescribed order to build up the lamination. The layers may be
stacked
side-by-side or one above the other. The completed stack may then be diffusion
bonded to prevent fluids from leaking into or out of the microchannel reactor
or
between streams. After bonding, the device may be trimmed to its final size
and
prepared for attachment of pipes and manifolds. An additional step for the
process
microchannels that contain the catalyst may be to integrate the catalyst into
the
device prior to final assembly.
Feature creation methods may include photochemical etching, milling, drilling,
electrical discharge machining, laser cutting, and stamping. A useful method
for
mass manufacturing is stamping. In stamping, care should be taken to minimize
distortion of the material and maintain tight tolerances of channel
geometries, for
example, less than about 0.5 mm displacement of feature location. Preventing
distortion, maintaining shim alignment and ensuring that layers are stacked in
the
proper order are factors that should be controlled during the stacking
process.
The stack may be bonded through a diffusion process. In this process, the
stack may be subjected to elevated temperatures and pressures for a precise
time
period to achieve the desired bond quality. Selection of these parameters may
3o require modeling and experimental validation to find bonding conditions
that enable
sufficient grain growth between metal layers.
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The next step, after bonding, may be to machine the device. A number of
processes may be used, including conventional milling with high-speed cutters,
as
well as highly modified electrical discharge machining techniques. A full-
sized
bonded microchannel reactor unit or sub-unit that has undergone post-bonding
machining operations may comprise, for example, tens, hundreds or thousands of
shims.
The process microchannels and heat exchange channels may have
rectangular cross sections and be aligned in side-by-side vertically oriented
planes
or horizontally oriented stacked planes. These planes may be tilted at an
inclined
angle from the horizontal. These configurations may be referred to as parallel
plate
configurations. Various combinations of process microchannels and heat
exchange
channels may be employed. Combinations of these rectangular channels may be
arranged in modularized compact repeating units for scale-up.
The cross-sectioned shape and size of the process microchannels may vary
along their axial length to accommodate changing hydrodynamics within the
channel. For example, with mass transport between phases, the fluidic
properties of
each phase may change over the course of a process run. Surface features may
be
used to provide a different geometry, pattern, angle, depth, or ratio of size
relative to
the cross-section of the process microchannel along its axial length to
accommodate
these hydrodynamic changes.
The process microchannel and the heat exchange channel may comprise
circular tubes aligned concentrically. The process microchannel may be in an
annular space and the heat exchange channel may be in the center space or an
adjacent annular space. The process microchannel may be in the center space
and
the heat exchange channel may be in an adjacent annular space.
The process microchannels may be assembled using shims A, B, C and D
which are illustrated in Figs. 36-39. The shims may be assembled (and
subsequently bonded) using the following sequence: D, A, B, C, D, and so
forth. A
useful repeating unit may follow the sequence A, B, C, D; and a microchannel
processing unit core or a microchannel distillation unit may contain 1, 2, 4,
6, 8,10 or
more of these repeating units. Solid sheets can be used as end plates. These
may
also be interspersed between repeating units (for example, between sets of at
least
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three repeating units). A liquid may flow from right to left along shim D and
between
the two surface pattern sheets C and A. The liquid may be held in these
regions by
capillary forces. The width of the liquid filled channel created by shim D may
be
such that capillary forces are sufficiently strong enough to retain the fluid
in the liquid
5 flow regions of shim D. Liquid may not flow into the central second fluid
flow
channel. Shim D may have a thickness of about 2 mm or less, and in one
embodiment about 1 mm or less. The second fluid may contact the liquid along
shim
D and may also flow in adjacent shims. The second fluid may flow through the
central portion, for example, only the second fluid may flow through shim B.
10 Liquid may be pulled through the channels by suction. Surface features may
not be needed for the second fluid flow channel when the second fluid is a gas
since
diffusion in a gas may be about 1000 times faster. However, surface feature
patterns for the second fluid path may be useful (see, for example, modified
shim C
(Fig. 41) as one embodiment). The surface feature patterns may take the form
of
15 recessed zones along the second fluid flow channel in shims A, B and/or C.
The
recessed zones may be aligned between shims A, B and C such that there may be
an angle (albeit created in a step-wise fashion) oblique to the direction of
flow to
assist in fluid mixing.
Figs. 42-46 show the creation of different shaped surface features within
20 successively stacked shims such that, when stacked, the resulting channel
walls
have indentations or protuberances, i.e., surface features. These surface
features
on the channel walls may be in the form of a desired geometric pattern that
may
produce a desired enhancement of heat and/or mass transfer within the
microchannel. These drawings have an open top to the microchannel only for
ease
25 of visualization. The features within a single shim may have identical or
different
shapes as desired.
When the shims are stacked, the resulting surface features that are created
may be diagonal grooves/fins. Since these surface features are created by
straight-
sided openings in adjacent shims, the resulting surface features in the
assembled
3o microchannel (Fig. 46) may have stepwise discontinuities. These may be
referred to
as "digital" diagonals instead of true, continuous fins or grooves. However,
the
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46
surface features thus formed may not be limited to diagonal features. They may
also
form pockets within which coatings may hold up when coated on a vertical wall.
Referring to Figs. 42-45, shim 1(Fig. 42) shows a small tab (protuberance)
extending leftward from the upper right side of the channel. In the drawing of
shim 2
(Fig. 43), the tab is still present and extends the same distance leftward
into the
channel, but its vertical position has shifted downward. In shim 3 (Fig. 44),
the same
tab is shifted down even further. Finally, in shim 4 (Fig. 45) the tab has
shifted
completely to the bottom of the channel and therefore appears only as a stair
step in
the bottom right corner of the channel. These shims have a finite thickness
and thus
when they are stacked in successive numerical order, the effect is to create a
protuberance or recess that appears to be at a diagonal along the right hand
wall.
The finite shim thickness means that the diagonal surface feature appears not
as a
continuous feature with smooth edges but appears as a stair-step, or digitized
diagonal. This design and manufacturing technique may be used to create
surface
features on the walls of channels. These surface features alter the shape and
texture of the channel walls and create flow-disturbance features. The concept
can
be extended to the idea of making indentation features in the channel walls as
opposed to protuberance-type features. By varying the thickness of the shims,
these
types of surface features may be made to appear curved.
Flow is into the page (Fig. 46)- into the main channel, and- recessed or--
protruded sections create a structure that approaches a true diagonal feature
in a
digital or incremental way. The surface features may be formed on one, two or
more
channel walls, including side walls with this method.
In an alternate embodiment, this digital diagonal approach to creating surface
features may be used in a non-orthogonal flow arrangement, where flow is along
the
shim lines or grains such that depressions in the floor in a digital diagonal
manner
may emulate a true diagonal surface feature.
In another embodiment, either a digitally diagonal ora layered surface feature
groove may be covered for a portion of the length of the channel, thus
allowing flow
to enter and exit the legs of the surface features, but separating the flow
from the
main channel during a portion of the run length of the surface feature leg.
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As shown in Figs. 47-49, surface features may be cut into channels formed by
shims and then stacked and joined or bonded. A look at one wall of the
microchannel as shown in Figs. 47-49 represents a diagonal surface feature
that is
formed in discontinuous parts. The angle of an individual leg is zero and
horizontal to
the direction of bulk flow. An adjacent leg also has an angle of zero but is
off set in
lateral position within the channel such that the difference approximates an
overall
angle when the two or more features are evaluated together. The number of legs
in
the digital diagonal may be two, three or more. The legs may overlap each
other to
allow flow to move at a net oblique angle relative to the bulk flow path when
the legs
1o are working together.
The second fluid phase may comprise a gas, a liquid, or a mixture thereof.
The gas may comprise any gas. In one embodiment, the gas may comprise one or
more of air, oxygen, nitrogen, carbon dioxide, steam, ammonia, ozone, chlorine
gas,
hydrogen, and the like. The gas may comprise one or more oxides of carbon,
nitrogen and sulfur. The gas may comprise H2S, 02, N2 and/or one or more noble
gases. The gas may comprise one or more gaseous hydrocarbons, for example,
hydrocarbons containing 1 to about 5 carbon atoms. These include saturated and
unsaturated hyrocarbons. The hydrocarbons include methane, ethane, ethylene,
propane, isopropane, propylene, the butanes, the butylenes, the pentanes,
cyclopentane, the pentylenes, cyclopentylene, and the like.
The liquid phase and the second fluid phase may comprise any liquid. The
liquid and the second fluid phase liquid may be immiscible or partially
miscible with
each other. One of the liquids may comprise a phase transfer catalyst. The
liquid
may comprise water, an organic liquid, or a combination thereof. The liquid
may
comprise one or more liquid hydrocarbons. These may include hydrocarbon
compounds containing from 1 to about 24 carbon atoms, and in one embodiment
about 5 to about 24 carbon atoms, and in one embodiment about 6 to about 18
carbon atoms, and in one embodiment about 6 to about 12 carbon atoms. The term
"hydrocarbon" denotes a compound having a hydrocarbon or predominantly
3o hydrocarbon character. These hydrocarbon compounds may include the
following:
(1) Purely hydrocarbon compounds; that is, aliphatic compounds, (e.g.,
alkane or alkylene), alicyclic compounds (e.g., cycloalkane, cycloalkylene),
aromatic
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48
compounds, aliphatic- and alicyclic-substituted aromatic compounds, aromatic-
substituted aliphatic compounds and aromatic-substituted alicyclic compounds,
and
the like. Examples include hexane, 1-hexene, dodecane, cyclohexene,
cyclohexane, ethyl cyclohexane, benzene, toluene, the xylenes, ethyl benzene,
styrene, etc.
(2) Substituted hydrocarbon compounds; that is, hydrocarbon compounds
containing non-hydrocarbon substituents which do not alter the predominantly
hydrocarbon character of the compound. Examples of the non-hydrocarbon
substituents include hydroxy, acyl, nitro, halo, etc.
(3) Hetero substituted hydrocarbon compounds; that is, hydrocarbon
compounds which, while predominantly hydrocarbon in character, contain atoms
other than carbon in a chain or ring otherwise composed of carbon atoms. The
hetero atoms include, for example, nitrogen, oxygen and sulfur.
The liquid may be a natural oil, synthetic oil, or mixture thereof. The
natural
oils include animal oils and vegetable oils (e.g., castor oil, lard oil) as
well as mineral
oils such as liquid petroleum oils and solvent treated or acid-treated mineral
oils of
the paraffinic, naphthenic or mixed paraffinic-naphthenic types. The natural
oils
include oils derived from coal or shale. The oil may be a saponifiable oil
from the
family of triglycerides, for example, soybean oil, sesame seed oil, cottonseed
oil,
safflower oil, and the like. The oil may be a silicone oil (e.g:;
cyclomethicone; silicon
methicones, etc.). The oil may be an aliphatic or naphthenic hydrocarbon such
as
Vaseline, squalane, squalene, or one or more dialkyl cyclohexanes, or a
mixture of
two or more thereof. Synthetic oils include hydrocarbon oils such as
polymerized
and interpolymerized olefins (e.g., polybutylenes, poiypropylenes, propylene
isobutylene copolymers, etc.); poly(1-hexenes), poly-(1-octenes), poly(1-
decenes),
etc. and mixtures thereof; alkylbenzenes (e.g., dodecylbenzenes,
tetradecylbenzenes, dinonylbenzenes, di-(2-ethylhexyl)benzenes, etc.);
polyphenyis
(e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.); alkylated diphenyl
ethers
and alkylated diphenyl sulfides and the derivatives, analogs and homologs
thereof
3o and the like. Alkylene oxide polymers and interpolymers and derivatives
thereof
where the terminal hydroxyl groups have been modified by esterification,
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49
etherification, etc., are synthetic oils that may be used. The synthetic oil
may
comprise a poly-alpha-o(efin or a Fischer-Tropsch synthesized hydrocarbon.
The liquid may comprise a normally liquid hydrocarbon fuel, for example, a
distillate fuel such as motor gasoline as defined by ASTM Specification D439,
or
diesel fuel or fuel oil as defined by ASTM Specification D396.
The liquid may comprise one or more oxygenates, for example, fatty alcohols,
fatty acid esters, or mixtures thereof. The fatty alcohol may be a Guerbet
alcohol.
The fatty alcohol may contain from about 6 to about 22 carbon atoms, and in
one
embodiment about 6 to about 18 carbon atoms, and in one embodiment about 8 to
lo about 12 carbon atoms. The fatty acid ester may be an ester of a linear
fatty acid of
about 6 to about 22 carbon atoms with linear or branched fatty alcohol of
about 6 to
about 22 carbon atoms, an ester of a branched carboxylic acid of about 6 to
about
13 carbon atoms with a linear or branched fatty alcohol of about 6 to about 22
carbon atoms, or a mixture thereof. Examples include myristyl myristate,
myristyl
paimitate, myristyl stearate, myristyl isostearate, myristyl oleate, myristyl
behenate,
myristyl erucate, cetyl myristate, cetyl palmitate, cetyl stearate, cetyl
isostearate,
cetyl oleate, cetyl behenate, cetyl erucate, stearyl myristate, stearyl
paimitate, stearyl
stearate, stearyl isostearate, stearyl oleate, stearyl behenate, stearyl
erucate,
isostearyl myristate, isostearyl palmitate, isostearyl stearate, isostearyl
isostearate,
isostearyl oleate, isostearyl behenate,- isostearyl- oleate,- oleyl myristate,
oleyl
paimitate, oleyl stearate, oleyl isostearate, oleyl oleate, oleyl behenate,
oleyl erucate,
behenyl myristate, behenyl paimitate, behenyl stearate, behenyl isostearate,
behenyl
oleate, behenyl behenate, behenyl erucate, erucyl myristate, erucyl paimitate,
erucyl
stearate, erucyl isostearate, erucyl oleate, erucyl behenate and erucyl
erucate. The
fatty acid ester may comprise: an ester of alkyl hydroxycarboxylic acid of
about 18 to
about 38 carbon atoms with a linear or branched fatty alcohol of about 6 to
about 22
carbon atoms (e.g., dioctyl malate); an ester of a linear or branched fatty
acid of
about 6 to about 22 carbon atoms with a polyhydric alcohol (for example,
propylene
glycol, dimer diol or trimer triol) and/or a Guerbet alcohol; a triglyceride
based on one
or more fatty acids of about 6 to about 18 carbon atoms; a mixture of mono-,
di-
and/or triglycerides based on one or more fatty acids of about 6 to about 18
carbon
atoms; an ester of one or more fatty alcohols and/or Guerbet alcohols of about
6 to
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about 22 carbon atoms with one or more aromatic carboxylic acids (e.g.,
benzoic
acid); an ester of one or more dicarboxylic acids of 2 to about 12 carbon
atoms with
one or more linear or branched alcohols containing 1 to about 22 carbon atoms,
or
one or more polyols containing 2 to about 10 carbon atoms and 2 to about 6
5 hydroxyl groups, or a mixture of such alcohols and polyols; an ester of one
or more
dicarboxylic acids of 2 to about 12 carbon atoms (e.g., phthalic acid) with
one or
more alcohols of 1 to about 22 carbon atoms (e.g., butyl alcohol, hexyl
alcohol); an
ester of benzoic acid with linear and/or branched alcohol of about 6 to about
22
carbon atoms; or mixture of two or more thereof. The liquid may comprise: one
or
1 o more branched primary alcohols of about 6 to about 22 carbon atoms; one or
more
linear and/or branched fatty alcohol carbonates of about 6 to about 22 carbon
atoms;
one or more Guerbet carbonates based on one or more fatty alcohols of about 6
to,
about 22 carbon atoms; one or more dialkyl (e.g., diethylhexyl) naphthalates
wherein
each alkyl group contains 1 to about 12 carbon atoms; one or more linear or
15 branched, symmetrical or nonsymmetrical dialkyl ethers containing about 6
to about
22 carbon atoms per alkyl group; one or more ring opening products of
epoxidized
fatty acid esters of about 6 to about 22 carbon atoms with polyols containing
2 to
about 10 carbon atoms and 2 to about 6 hydroxyl groups; or a mixture of two or
more thereof.
20 The water may be taken from any convenient source. The water may be...
deionized or purified using osmosis or distillation.
In one embodiment, the liquid phase or the second fluid phase may comprise
a critical fluid.
The phase transfer catalyst may comprise one or more crown ethers. These
25 may contain one or more alkali metal cations useful for catalysis. Crown
ethers may
be heterocyclic compounds that may be referred to as cyclic oligomers of
ethylene
oxide. A repeating unit of any crown ether is ethyleneoxy, i.e., -CH2CH2O-,
which
repeats twice in dioxane and six times in 18-crown-6. The nine-membered ring
1, 4,
7-trioxonane (9-crown-3) may be called a crown and can interact with cations.
30 Macrocycles of the (-CH2CH2O-)n type in which n _ 4 may be referred to as
crown
ethers rather than by their systematic names.
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The disclosed distillation process may be used to separate any two or more
fluids that have different volatilities. The fluids may have boiling points
that vary by
up to about 100 C, and in one embodiment up to about 20 C, and in one
embodiment up to about 10 C, and in one embodiment up to about 5 C, and in one
embodiment up to about 2 C, and in one embodiment up to about 1 C. The process
may be suitable for handling difficult separations such as ethane from
ethylene
wherein the fluids being separated have very similar volatilities. Examples of
the
separations that may be effected using the disclosed process may include, in
addition to ethane from ethylene; styrene from ethylbenzene separation and
1o associated purification of styrene monomer in an ethylbenzene
dehydrogenation
plant; separation of oxygen from nitrogen in the cryogenic towers of an air
separation
plant; separation of cyclohexane from cyclohexanol/cyclohexanone in a nylon
monomers plant; deisobutanizers in a gasoline alkylation plant; naphtha
splitters
upstream from a naphtha reforming plant; and the like. The process may be used
to
separate hexane from cyclohexane. The process may be used to separate benzene
from toluene, methanol from water, or isopropanol from isobutanol.
The mass transfer of the liquid phase to the second fluid phase in the process
microchannel may be at least about 1 % by weight based on the weight of the
liquid
phase entering the process microchannel, and in on embodiment at least about
5%
by weight, and in one embodiment at least about 10% by weight, and in one
embodiment at least about 15% by weight, and in one embodiment at least about.
20% by weight, and in one embodiment at least about 25% by weight.
In one embodiment, a chemical reaction between the liquid phase and the
second fluid phase may be conducted in the process microchannels.
The mass transfer of the second fluid phase to the liquid phase in the process
microchannel may be at least about 1% by weight based on the weight of the
second
fluid phase entering the process microchannel, and in on embodiment at least
about
5% by weight, and in one embodiment at least about 10% by weight, and in one
embodiment at least about 15% by weight, and in one embodiment at least about
3o 20% by weight, and in one embodiment at least about 25% by weight.
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The heat flux for heat exchange in the microchannel reactor may be in the
range from about 0.01 to about 500 watts per square centimeter of surface area
of
the one or more process microchannels (W/cm2) in the microchannel reactor, and
in
one embodiment in the range from about 0.1 to about 250 W/cm2, and in one
embodiment from about 1 to about 125 W/cm2. The heat flux for convective heat
exchange in the microchannel reactor may be in the range from about 0.01 to
about
250 W/cm2 , and in one embodiment in the range from about 0.1 to about 50
W/cm2,
and in one embodiment from about 1 to about 25 W/cm2, and in one embodiment
from about 1 to about 10 W/cm2. The heat flux for phase change and/or an
exothermic or endothermic reaction of the heat exchange fluid may be in the
range
from about 0.01 to about 500 W/cm2, and in one embodiment from about 1 to
about
250 W/cm2, and in one embodiment, from about 1 to about 100 W/cm2, and in one
embodiment from about 1 to about 50 W/cm2, and in one embodiment from about 1
to about 25 W/cm2 , and in one embodiment from about I to about 10 W/cm2.
In a scale up device, for certain applications, it may be required that the
mass of the process fluid be distributed uniformly among the microchannels.
Such
an application may be when the process fluid is required to be heated or
cooled
down with adjacent heat exchange channels. The uniform mass flow distribution
may
be obtained by changing the cross-sectional area from one parallel
microchannel to
2o another microchannel. The uniformity of mass flow distribution may
be.defined by
Quality Index Factor (Q-factor) as indicated below. A Q-factorof 0% means
absolute
uniform distribution.
Q= M. - m'"' x 100
A change in the cross-sectional area may result in a difference in shear
stress on the
wall. In one embodiment, the Q-factor for the process microchannels may be
less
than about 50%, and in one embodiment less than about 20%, and in one
embodiment less than about 5%, and in one embodiment less than about 1 /a.
In one embodiment, the Q-factor for the process microchannel may be less
than about 50%. In one embodiment, the Q-factor may be less than about 5%. In
one embodiment, the Q-factor may be less than about 1%.
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53
The superficial velocity for the liquid flowing in the process microchannels
may be at least about 0.1 meters per second (m/s), and in one embodiment at
least
about 0.2 m/s, and in one embodiment at least about 0.5 m/s, and in one
embodiment at least about I m/s, and in one embodiment in the range from about
0.1 to about 100 m/s, and in one embodiment in the range from about 0.1 to
about
20 m/s, and in one embodiment in the range from about 0.1 to about 10 m/s, and
in
one embodiment in the range from about 0.1 to about 5 m/s.
The superficial velocity for the gas flowing in the process microchannels may
be at least about 0.1 m/s, and in one embodiment at least about 1 m/s, and in
one
lo embodiment at least about 10 m/s, and in one embodiment in the range from
about
0.1 to about 250 m/s, and in one embodiment in the range from about 0.1 to
about 5
m/s, and in one embodiment in the range from about I to about 20 ms, and in
one
embodiment in the range from about 10 to about 250 m/s.
In one embodiment, the superficial velocity for the liquid may be at least
about
0.01 m/s, and in one embodiment in the range from about 0.01 to about 100 m/s,
while the superficial velocity for the gas may be at least about 0.1 m/s, and
in one
embodiment in the range from about 0.1 to about 250 m/s.
The dynamic pressure for the liquid in the process microchannels may be at
least about 0.1 Pa (9.87 x 10-' atm) , and in one embodiment at least about 5
Pa
(4.93 x 10"5 atm), and in one embodiment at least about 25 Pa (0.000248 atm),
and
in one embodiment in the range from about 0.1 to about 100,000 Pa (9.87 x
10"7to
0.987 atm) . The dynamic pressure for the gas in the process microchannels may
be at least about 0.5 Pa (4.93 x 10"6 atm), and in one embodiment at least
about 5
Pa (4.93 x 10"5 atm), and in one embodiment at least about 10 Pa (9.87 x 10-5
atm),
and in one embodiment in the range from about 0.5 to about 200 Pa (4.93 x 10-6
to
0.00197 atm).
The liquid may have a viscosity in the range from about 0.001 to about 1000
centipoise, and in one embodiment in the range from about 0.1 to about 500
centipoise. The gas may have a viscosity in the range from about 0.001 to
about 1
centipoise, and in one embodiment from about 0.01 to about 0.1 centipoise.
The space velocity (or gas hourly space velocity (GHSV)) for the flow of the
process fluid in the process microchannels may be at least about 10 hr l
(normal
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liters of feed/hour/liter of volume within the process microchannels). The
space
velocity may be in the range from about 100 to about 1,000,000 hr l, and in
one
embodiment from 10,000 to about 100,000 hr l.
The temperature of the fluids entering the process microchannels may be in
the range from about -200 C to about 950 C, and in one embodiment about 0 C to
about 600 C, and in one embodiment about 20 C to about 300 C, and in one
embodiment in the range from about 150 C to about 270 C.
The temperature of the fluids within the process microchannels may range
from about -200 C to about 950 C, and in one embodiment from about 0 C to
about
600 C, and in one embodiment from about 20 C to about 300 C, and in one
embodiment in the range from about 150 C to about 270 C.
The temperature of the fluids flowing out of the process microchannels may
be in the range from about -200 C to about 950 C, and in one embodiment about
0 C to about 600 C, and in one embodimentfrom about 20 C to about 300 C, and
in one embodiment in the range from about 150 C to about 270 C.
The pressure within the process microchannels may be at least about 5
atmospheres, and in one embodiment at least about 10 atmospheres, and in one
embodiment at least about 15 atmospheres, and in one embodiment at least about
atmospheres, and in one embodiment at least about 25 atmospheres, and in one
2o embodiment at least about 30 atmospheres. In one embodiment the pressure
may '
range from about 5 to about 250 atmospheres, and in one embodiment from about
10 to about 50 atmospheres, and in one embodiment from about 10 to about 30
atmospheres, and in one embodiment from about 10 to about 25 atmospheres, and
in one embodiment from about 15 to about 25 atmospheres.
The pressure drop of the process fluid as it flows in the process
microchannels may range up to about 15 atmospheres per meter of length of the
process microchannel (atm/m), and in one embodiment up to about 10atm/m, and
in
one embodiment up to about 5 atm/m.
The Reynolds Number for the flow of gas or vapor in the process
microchannels may be in the range from about 10 to about 8000, and in one
embodiment from about 100 to about 2000. The Reynolds Number for the flow of
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liquid in the process microchannels may be in the range from about 10 to about
4000, and in one embodiment from about 100 to about 2000.
The heat exchange fluid entering the heat exchange channels may be at a
temperature in the range from about -200 C to about 950 C, and in one
5 embodiment from about 0 C to about 600 C. The heat exchange fluid exiting
the
heat exchange channels may be at a temperature in the range from about -200 C
to
about 950 C, and in one embodiment about 0 C to about 600 C. The residence
time of the heat exchange fluid in the heat exchange channels may be in the
range
from about 50 to about 5000 ms, and in one embodiment from about 100 to about
1o 1000 ms. The pressure drop for the heat exchange fluid as it flows in the
heat
exchange channels may range up to about 10 atm/m, and in one embodiment from
about 0.01 to about 10 atm/m, and in one embodiment from about 0.02 to about 5
atm/m. The heat exchange fluid may be in the form of a vapor, a liquid, or a
mixture
of vapor and liquid. The Reynolds Number for the flow of vapor in the heat
15 exchange channels may be from about 10 to about 8000, and in one embodiment
from about 100 to about 2000. The Reynolds Number for the flow of liquid in
heat
exchange channels may be from about 10 to about 8000, and in one embodiment
about 100 to about 2000.
A disadvantage of conventional hardware used for vapor-liquid contacting unit
20 operations is that conventional trays and packing may be difficult to
operate or
operate less efficiently when the process is operated at feed rates below
about 50%
design capacity. An advantage of the disclosed process relates to an ability
to
operate the process in a modular fashion for effective operation at a wide
range of
capacities. The disclosed process may be designed with numerous modules and
25 sections of modules. Turndown operation can be achieved with directing
flows to
active modules and sections of modules, where the process channels are
operating
efficiently at close capacity. For example, an overall process may be
operating at
50% capacity, but the active process microchannels may be operating at 80-90%
capacity.
30 In one embodiment, the disclosed process may provide for the separation of
ethylene from a fluid mixture comprising ethylene and ethane in a distillation
unit
having a height of up to about 20 meters, and in one embodiment up to about 10
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meters, and in one embodiment up to about 5 meters, and in one embodiment up
to
about 3 meters, with purity levels of ethylene of at least about 95% by
volume, and in
one embodiment at least about 98% by volume, and in one embodiment at least
about 99% by volume.
Example I
A microchannel processing unit is used to separate ethane from ethylene.
The processing unit is made out of stainless steel 304 plates and stainless
steel 304
shims. Fig. 50 shows an exploded view of the assembly of various shims and
plates
in the processing unit. The overall size of the end plate is 9.563" X 6.033" X
0.605".
1 o On either end of the plate is a machined manifold for the distribution of
fluid in to the
liquid channel. The manifold opening is 0.5" wide and 0.1" deep. The inlet and
the
outlet of the manifold are at diagonally opposite corners of the end plate.
The plate is
chamfered at 45 on the edges for weldment of the assembly. Slots and holes
are
designed for alignment of shims and plates during assembly. The end plate next
to
the vapor surface feature shim has the same dimensions.
The overall size of the liquid channel shim is 9.375" X 5.845" X 0.005".
There are 20 through slots made in the shim to make the channel shim as shown
in
Fig. 50. Each channel slot is 0.2" wide and 5.5" long and separated from the
other
slot by 0.050" wall. The vapor channel shim is the same in overall design
except the
thickness of the shim is 0.010" instead of 0.005".
The overall size of the surface feature shim is the same as that of liquid
channel shim except that the thickness of the shim is 0.015". The serpentine
shaped features on the upper section of the shim are designed to achieve
uniform
flow distribution in the channels and are referred to as flow distribution
features.
Each flow channel has a flow distribution feature. All the flow distribution
features
are identical in design. The overall of span of the feature (from left bend to
right
bend ) is the same as the width of the channel (0.2"). The flow channel in
every
distribution feature is 0.030" wide and 0.015" deep (same as the shim
thickness).
More details of the flow distribution section are shown in Fig. 51. Below the
flow
3o distribution features section is the surface feature section. The
connection between
the flow distribution feature and surface feature section is made as shown in
Fig. 51.
The overall size of the surface feature section is big enough to cover the
channel
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section in the liquid channel shim. Three different types of surface feature
design
details are shown in Fig. 52, types (a) and (b), and Fig. 53, type (c). There
are a
total of 2120 surface features of type (a), 8480 surface features of type (b)
and 7360
surface features of type (c). Below the surface feature section is a liquid
exit section.
The vapor surface feature shim is the same as liquid surface channel shim in
dimensions.
The capillary plate is an electroformed wire cloth made out of nickel. The
number of meshes is 1000 X 1000 and wire diameter is 0.00029". The thickness
of
the capillary plate is 0.0002". The overall dimension of the screen is 5.47" X
5.375".
The surface feature section from the additional surface feature shims are cut
and
attached to both sides of the capillary plate to make the capillary plate
assembly.
All the shims are made by a photochemical machining method. After
fabrication all the shims and plates are arranged in the way shown in Fig. 50.
The
final assembly is welded together.
The operation of the device is as follows. The liquid flows from the liquid
inlet,
into the manifold in the liquid end plate, then enters the flow distribution
features in
the liquid surface feature shim, into the liquid channel in liquid channel
shim. In liquid
channel shim, it contacts the surface features on the surface feature shim and
the
surface features on the capillary plate assembly. Mass is transferred through
the
capillary plate to the vapor side. Then the liquid-flows out to exit channels
in surface
feature shim to the other manifold in liquid end plate and out of the device
through
an outlet tube. The vapor flows in the same way through the shims and plates.
The flow distribution features create a pressure drop through frictional
losses
between the fluid and wall that are higher (>2x, >5x, or even > 10x) than the
pressure drop of the process channel. As such, the restriction in the flow
distribution
features maintains a nearly uniform flow distribution between all the
channels, where
the quality index Q (defined below) is less than 30%, and in one embodiment,
less
than 15%, and in one embodiment, less than 10%. The pressure drop in the
process channels is on the order of 0.01 psi to 1 psi for flow lengths in the
range of 1
to 50 cm and residence times from 0.1 to 10 seconds. The pressure drop in the
flow
distribution features is on the order of 0.1 to 10 psi. In a commercial
distillation unit,
the total channel length may be on the order of 10 to 200 cm.
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Q- 7h~X - YiZ~n X100
m.
where: fia n,aX= Maximum mass flow rate in the channel, kg/s
ria m;,,= Minimum mass flow rate in the channel, kg/s
Q = Quality index
In one embodiment, the surface feature sheet may be placed on either side of
the contactor sheet such that mass preferentially spends more time in the
active
surface features and near the mass transfer interface. In one embodiment,
there
would be no surface feature on any other wall except where mass is exchanged
between the two phases.
In one embodiment, active surface features may be placed on the top and
bottom of the microchannels and the two phases allowed to freely mix while
flowing
in a countercurrent manner to increase the interfacial surface area for mass
transfer.
The gas and liquid may be disengaged in a small axial distance- relative to
the
overall length of the distillation unit to prevent back mixing.
Enhanced contact time between liquid and vapor phases may be important for
maximizing mass transfer. Effective application of microchannel technology to
large-
capacity production processes may call for good performance at intermediate to
high
laminar Reynolds numbers (ranging from about 50 to about 2200). By placing
surface features near the interfacial contact region bulk mixing and
interfacial contact
time may be enhanced.
The studies described below involve numerical simulations of flow through
channels. All analyses are performed using the CFD package Fluent. The example
that follows shows enhanced performance at higher Reynolds numbers. A
comparison with an alternate design option is included to clarify the benefit
of the
disclosed configuration. The same fluid density and viscosity are used in all
cases,
480 kg/m3 and 8.3x10"5 kg/m-s, respectively.
The two cases considered focus on comparing the residence time of the liquid
in the main channel with its residence time in the surface features. Both
cases
assume that liquid flows through a modified rectangular channel that is in
contact
with a vapor phase on one side. In the first case, the side of the channel in
contact
with the vapor is open, and the liquid flowing past the open sidewall
experiences no-
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59
stress; all other sidewalls are assumed to be no slip boundaries. In the
second
case, all four channel sidewalls are assumed to be no slip boundaries, whether
corresponding to solid walls or potentially permeable screens. Figs. 54 and 55-
56
show representative system flow configurations.
Fig. 55 is a schematic illustration of the first channel configuration,
including a
liquid flow path open to the vapor phase. The modeled channel section has a
total
width of 1.14 mm, a height of 0.51 mm, and a length 24.8 mm. 61 surface
features
are included in the total channel length. For ease of viewing, the schematic
illustration does not reflect the number of surface features included in the
model. An
1o expanded view of the channel inlet cross section is shown for reference.
The dotted
cross marks the initial position of the particle tracers monitored for the
analysis.
Figs. 55 and 56 show schematic illustrations of the second channel
configuration, including a liquid flow path separated from the vapor phase by
a
porous screen. The modeled channel section has a total width of 13.17 mm, a
height of 0.42 mm (including a 0.16 mm main channel height and a 0.25 mm
surface
feature region thickness), and a length of 32.58 mm (surface features are not
to
scale). 24 surface feature sequences are included in the total channel length,
as
shown in the expanded view in Fig. 56. Each surface section sequence has a
0.33
mm separation distance. The 10 connected chevrons that span the width of the
channel have a width of 0.43 mm; their sides are inclined 45 relative to
the main
channel flow direction. The expanded view of the channel inlet cross section
is also
shown for reference. The dotted lines mark the initial positions of the
particle tracers
monitored for the analysis.
Fig. 54 shows the configuration for a 24.8 mm long channel with an inlet
cross-section that is 0.51 mm (in the direction perpendicular to the open
wall) by
0.38 mm. Surface features are incorporated in the two opposing, no slip
sidewall of
the channel, starting 2.54 mm downstream of the inlet plane. The surface
features
consist of grooves that extend out from the main flow channel, 0.38 mm in the
direction perpendicular to the main axis of flow. The grooves are straight and
perpendicular to the surface from which they protrude, but incline 45
relative to the
open surface. The surface features of one wall are positioned at 90 with
respect to
the surface features on the opposing wall. Viewed from the channel side, the
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opposing surface features form a perfect cross. The span of the surface
features
and their width is 0.127 mm.
Fig. 55 shows the configuration for a 32.5 mm long channel with an inlet cross
section that is 13.17 mm by 0.419 mm. 1.75 mm downstream of the inlet plane,
one
5 of the two 13.17 mm sidewalls is expanded by 0.254 mm to include connected
surface features that span the entire wall width. The surface features have a
0.43
mm width and a 0.33 mm span; they are angled 45 relative to the inlet
plane, 90
relative to each other. Inserts in Fig. 55 detail the surface feature
configuration.
Analysis for the first configuration involves comparison of the residence time
10 for uniform inlet flow velocities of 0.1 and 0.6 m/s; these correspond to
Reynolds
numbers of 220 and 1322, respectively. Analysis of the second configuration
involves residence time comparisons for inlet flow velocities of 0.1 and 0.2
m/s;
these correspond to Reynolds numbers of 95 and 191, respectively. All Reynolds
numbers are calculated based on the minimum gap dimension at the inlet plane.
15 Residence times are calculated for representative tracer particles assumed
to enter
the flow channel at the beginning of the simulation. Their position is
monitored and
their cumulative residence time in the main channel and surface feature
regions are
calculated over the course of the simulation. To obtain a representative
measure of
the behavior of the fluid entering through the whole main channel cross-
section,
20 tracer particles are released at the center lines of the inlet planes, as
shown in the
inserts of Figs. 54 and 55. For data manageability, results that pertain to
the second
configuration are limited to tracer particles released in a 2.5 mm section of
the 13.2
mm channel width.
Figs. 57 through 60 show the relative residence time of tracer particles in
the
25 surface features for all velocities and configurations considered. The
abscissa
marks the initial position of the tracer particles relative to the overall
inlet channel
dimension in the gap direction or perpendicular to the gap direction, as
noted.
As Figs. 57 and 58 show, the first configuration leads to no penetration into
the surface features for particle tracers that originate at the center of the
30 microchannel and some penetration for the particles that originate at the
edges of
the channel inlet. Tracer particles released along the center line that marks
the
symmetry plane of the system penetrate the surface features to a greater
extent than
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61
the particles released along the perpendicular center line. The lower Reynolds
number leads to slightly better surface feature penetration.
As Figs. 59 and 60 highlight, in contrast to the first configuration, the
second
configuration leads to significant penetration into the surface features for
particle
released from all sections of the inlet plane. Improved penetration is also
noted at
the higher Reynolds numbers.
Overall, when the transfer surface (whether mass or energy) is integrated as
the surface feature backwall and processes involve moderately high laminar
Reynolds numbers, transfer can be more efficiently promoted to provide
enhanced
1 o performance.
For the case of a liquid flow velocity of 0.1 m/s and a gaseous flow velocity
of
0.58 m/s, a 2.5 cm length distillation unit for the separation of ethane and
ethylene at
28 bar, and 0.3 stages of separation it may be possible to achieve a Liquid
Height
Equivalent of a Theoretical Plate (HETP) that is less than 8.6 cm. Improved
designs
with mass transfer occurring within the active surface features may achieve a
HETP
less than about 5 cm, and in one embodiment less than about 1 cm.
Example 2
The impact of surface features on the mixing of bulk fluid flowing through
open and closed channels may be significant. Hence, surface features can be
introduced on channel sidewalls to promote either interaction between the bulk
fluid
and the lateral walls or interaction between the bulk fluid and a free
interface (typical
of mass transfer processes relevant to distillation, absorption, extraction,
and the
like.)
The factors that may play a role on the extent of the mixing improvement
relative to non-surface-feature modified channels may include:
= channel configuration,
~ open (e.g., a rectangular channel with only 3 walls),
= closed;
= surface feature positioning,
= one surface,
~ two opposing surfaces;
= rib design, where a rib is defined as a single surface feature
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~ all cases use a single leg diagonal surface feature configuration (see,
"45 DEG" design in Fig. 17),
~ size and location of rib interruptions,
~ cis (ribs aligned on opposing sides - mirror symmetry) and trans (ribs
criss-crossed on opposing sides, e.g., rotationally symmetric)
configurations;
= rib dimensions,
~ angle relative to the flow and/or the free surface,
~ depth,
~ width,
= rib frequency,
= flow direction with respect to the ribs,
= fluid velocity;
= main channel gap size.
The current investigation involves a series of computational fluid dynamics
(CFD)
simulations of flow through micro-channels intended to highlight some of the
key
effects. All analyses, performed using the CFD package FluentTM, are presented
in
terms of visualized flow patterns. Extent of conversion is also calculated and
presented for each case as an approximate means of quantifying differences in
2o behavior. The cases considered are listed in Table 1, below. Key parameters
and settings are noted for each case. Italicized bold values and cell borders
are
indicative of comparative sets.
run no. of channel din:ensions (mm) rib dimensions (mm) velocity
id flow slip SF ribs gap tot length SF length angle depth span separation
(m/s)
1 -- y - ~ -- 0.38 27.5 -- -- -- -- -- 0.2
2 -- yn trans 60 0.38 24.8 22.2 450 0.38 0.127 0.127 0.2
3 -- trans61 0.38 24.8 22.2 450 0.38 10.127 0.127 0.2
4 -- y trans 61 0.38 24.8 22.2 45 0.38 0.127 0.127 0.6
5 -- y trans 31 0.38 27.5 22.2 450 0.38 0.254 0.254 0.2
6 -- y trans 46 0.38 27.9 25.1 450 0.38 0.254 _ 0.127 0.2
7 -- y trans 44 0.38 25.5 23.0 60 0.38 0.127 ~ 0.127 0.2
8 -- y trans 44 0.38 25.5 23.0 L60 0.38 0.127 0.127 0.6
9 A y cis 61 0.38 24.8 22.2 450 0.38 0.127 0.127 0.2
10 B y cis 61 0.38 24.8 22.2 450 0.38 0.127 0.127 0.2
11 A y 1 sided 61 0.38 24.8 22.2 450 0.38 0.127 0.127 0.2
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12 -- y trans 31 0.76 16.5 11.5 45 0.38 0.127 0.127 0.2
13 -- y trans 31 0.38 16.5 11.5 45 0.38 0.127 0.127 0.2
14 -- y trans 30 0.38 14.011.5 45 0.19 10.127 0.127 0.2
The above-indicated Table I shows parameter settings for the comparative
CFD cases considered. The main channel gap is held constant at 0.51 mm for all
cases. For clarity, cases for direct comparison are differentiated by
corresponding
cell borders and italicized bold writing. SF refers to surface feature;
velocity refers
to the uniform fluid velocity at the channel inlet. All configurations are as
shown in
Fig. 17 (45 DEG) and include an initial 2.54 mm without surface features. Slip
refers
to the upper, wall boundary condition. The rib angle is taken with respect to
the
channel floor.
As indicated in Table 1, in all cases, except Run 2, the upper channel wall is
assumed to have a no stress boundary condition. All other surfaces are assumed
to
be no slip boundaries for all runs. In all cases, fluid density and viscosity
are set to
480 kg/m3 and 0.083 cP, respectively. A uniform inlet fluid velocity is
imposed
throughout. The onset of surface features is consistently held 2.54 mm from
the inlet
to avoid entrance effects and obtain a well-established flow profile upstream
of the
surface features. Additional channel details defining flow direction and 1-
sided and..
2-sided cis and trans configurations are described above.
The results for each case listed in Table 1 are presented in Figs. 61-74 in
terms of path line evolution along channel length. Path-lines originating from
the
inlet vertical and horizontal center-lines are shown for reference. Front and
side
views are presented for clarification. Figs. 75 and 76 show extent of
conversion
along normalized channel length. Fig. 75 presents Runs I through 11; Fig. 76
presents Runs 12 through 14 as well as Run 1 results, for reference. The
extent of
conversion is taken as a representative measure of the extent of interaction
of the
bulk flow with the upper channel wall where a mass transfer with an adjacent
or
other phase stream is present. The fluid is assumed to include a single
component,
material A, at the channel entrance. Upon contact with the upper wall, the
entering
component is assumed to be immediately converted to a second component,
material B, with the same properties as the first component. The zero order,
isothermal reaction is defined by a pre-exponential factor of 1x106. A 300 K
temperature and an activation energy of 10 J/kmol are assumed. The components
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64
inter-diffuse with a diffusion coefficient of 1x10"8 m2/sec. Although the
extent of
conversion becomes less sensitive as conversion increases, it still provides a
simple
measure by which to estimate and compare configuration performance. However,
it
is not an absolute indicator of mixing.
Figs. 61 a through 61 d show representative flow profiles for Run 1(Table 1).
Results are shown in terms of path-lines released from the vertical and
horizontal
inlet center-lines, a and c and b and d, respectively. Figures a and b show
the path-
lines viewed from the channel side; Figures c and d show the path-lines viewed
from the exit plane of the channel. All views are orthographic. The channel
inlet is
1o shown for reference. Figs. 62-74 show similar flow profiles for Runs 2-14,
respectively.
Fig. 75 shows concentration measurements indicating degree of conversion
of material A in response to contact with the upper channel wall. Measurements
begin after the initial 2.54 mm featureless section, which is taken as the
zero point of
the normalized channel length. The channel length is normalized upon division
by
25.4 mm. Legend numbers correspond to the run numbers of Table 1.
Fig. 76 shows concentration measurements indicating degree of conversion
of material A in response to contact with the upper channel wall. Measurements
begin after the initial 2.54 mm straight, which is taken as the zero point of
the
2o normalized channel length. The channel length is normalized upon division
by 25.4.
Legend numbers correspond to the run numbers of Table 1.
As shown in Fig. 75, the performance of all cases considered is bound by the
baseline case of Run1, which contains no surface features, and Run 7, the more
steeply inclined trans surface feature configuration involving low fluid
velocity, 0.2
m/sec. Conversion increases relatively linearly as the material proceeds down
the
channel even for the worst case, which involves no path-line intertwining, as
is
evident in Fig. 61. This effect is indicative of diffusional mass transfer in
a direction
perpendicular to the channel flow axis. As profiies for Cases 7 and 3 and 8
and 4
indicate, the effect of surface feature angle between 45 degrees and 60
degrees is
rather small for these low velocity (< 1 m/s), narrow gap (0.38 mm) cases. The
greater effect in extent of mixing may be attributed to flow speed. The impact
can
also be seen from comparison of Figs. 63, 64, 67 and 68. For the evaluated
velocity
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difference of 0.2 m/s and 0.6 m/s, improved extent of reaction is calculated
for the
lower velocity cases. It is easier to mix a lower velocity stream than a
higher velocity
stream. As the stream velocity increases in the open microchannel,
modifications to
the surface feature geometry, angle relative to the plane orthogonal to the
flow, and
5 depth are particularly useful to increase flow rotation in the bulk flow
path. A
comparison of Figs. 62 and 63 and their corresponding profiles in Fig. 75 also
shows
that the presence of the free surface leads to slightly less orderly motion
that
enhances interaction and transfer with the upperwall. The free surface implies
a slip
boundary condition as found when two fluids are moving past each other as
opposed
1o to a fluid moving past a stationary wall; a slip boundary condition may
also be
created if a wall chemistry is changed such that it repels the bulk fluid -
such as a
hydrophobic coating for an aqueous solution flowing in a microchannel.
According to the curves for Runs 3, 5, and 6, relatively little effect is
evident
when the rib span and separation are doubled or when the frequency of the ribs
is
15 doubled, leaving the rib span unchanged. However, as the corresponding path-
line
profiles attest, much greater rotation is imparted for both increased rib
frequency and
decreased surface feature span. Such differences in conclusions highlight the
need
to identify more sensitive quantitative measures of mixing effectiveness. A
comparison of Runs 3, 9, 10, and 11 shows, the trans configuration appears to
20 enhance mixing effectiveness relative to the other alternatives. A
significant impact
of gap size is noted by comparing Runs 12 and 13, a shorter equivalent of Run
3.
The larger the gap, the less the mixing enhancement for a given fixed geometry
of
surface feature. An increased surface feature depth may increase mixing for
larger
gap microchannels. Decreasing surface feature depth has a detrimental effect
on
25 mixing, although it appears less significant than main channel gap size. As
is
evidenced by Fig. 76, an initial lag in the onset of mixing appears to exist;
in the
cases considered it extends approximately 0.2 normalized channel heights past
the
onset of the surface features.
Example 3
30 This example is a simulation which shows flow rotation and mixing for gas
mixtures; open channel with diagonal recesses on two sides. The addition of
surface features to two sides of a microchannel to induce a change from
laminar flow
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in the channel to a strongly mixing flow in the channel is investigated via
computational fluid dynamics (CFD) simulations using Fluent. For the
simulation,
fluid properties are assumed to be constant, with a density of 5.067 kg/m3,
and a
viscosity of 3.62 x 10-5 kg/m-s. A uniform inlet velocity of 12.13 m/s and a
no-slip
flow condition at all walls were imposed as boundary conditions. A grid size
of
315,174 cells is used.
The assumed geometry is a rectangular cross section for the continuous
channel, with a width of 4.06 mm, a (gap) height of 0.318 mm (which does not
include recess depth), and a length of 63.5 mm. The section from 0 to 3.5 mm
downstream from the inlet and the section 5.0 to 0 mm upstream of the outlet
contain no surface features (simple rectangular microchannel). The surface
features
(or grooves) are cut into two opposing walls, each feature being approximately
rectangular in cross section. The middle section of the microchannel (from 3.5
mm
to 58.5 mm downstream of the inlet) contain the surface features. The surface
features span one of the channel walls diagonally at an angle of 63 from the
direction of the mean bulk laminar flow, as shown in Figs. 86 and 87. Each
surface
feature is about 0.25 mm deep by 0.48 mm wide, by 9 mm long. Surface features
are placed parallel to one another with a spacing of 0.48 mm between surface
features. The surface features on the opposing wall are exactly the same as
those
one the first wall, rotated 180 about the channel centerline. The channel
geometry
is symmetric about the axis of flow extending from the centerpoint of the
inlet plane
to the centerpoint of the outlet plane.
Fig. 77 shows a plan view of the geometry of surface features simulated by
CFD where surface features on both upper and lower walls are superimposed.
Fig.
78 shows an isometric view of the microchannel with mixing features simulated
by
CFD, showing the direction of flow entering the channel. Fig. 79 shows typical
pathlines of flow beginning along the horizontal centerline (running between
the
arrows) of the inlet plane looking down the axis of flow from the inlet plane.
In
classical laminar flow, pathlines flow in a straight line between the inlet
and outlet
planes (for the view shown in Fig. 79, a classical laminar flow pathlines
would not
deviate from the centerline between the arrows. In Fig. 80, a side view of the
same
pathlines of flow beginning along the horizontal centerline of the inlet plane
(arrow
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shows direction of flow) is shown. In Fig. 80, the spread of the flow
pathlines from
the centerline and the swirling motion in the surface features shows improved
mixing
and decreased heat and mass transport resistance relative to laminar flow.
Fig. 81
shows the pathlines of flow beginning along the vertical centerline of the
inlet plane
(running between the arrows) looking down the axis of flow from the inlet
plane. In
Fig. 81, the swirling motion of the flow indicates enhanced mixing and
decreased
heat and mass transport resistance relative to classical laminar flow.
The results of the CFD simulations show that, unlike laminar flow in a
microchannel, the surface features cause the pathlines of the flow in the
continuous
1o channel to twist and swirl, spreading toward the walls much faster than
would be
expected in the case of laminar flow. The calculated pressure drop is 5.2 kPa.
Example 4
Another CFD simulation of surface features was run with a geometry identical
to Example 3 except that the surface features on one of the two walls are
removed
and replaced with a solid wall. The geometry for this case is shown in Fig.
82. As in
Example 3, fluid properties are assumed to be constant, with a density of
5.067
kg/m3, and a viscosity of 3.62 x 10"5 kg/m-s. An outlet pressure of 1.01 bar
is
imposed. A uniform inlet velocity of 12.13 m/s and a no-slip flow condition at
all
walls were imposed as boundary conditions. The CFD simulation mesh size for
this
2o Example is 264,948 cells.
Figs. 83-85 show the flow pathlines predicted for this Example. Fig. 83 shows
pathlines of flow beginning along the horizontal centerline of the inlet plane
for this
example (arrow shows direction of flow) as viewed from the side. Fig. 84
depicts
pathlines of flow for this example beginning along the horizontal centerline
(beginning on the inlet plane between the arrows) of the inlet plane looking
down the
axis of flow from the inlet plane. Fig. 85 shows the predicted pathlines of
flow forthis
example beginning along the vertical centerline (beginning on the inlet plane
between the arrows) of the inlet plane looking down the axis of flow from the
inlet
plane. The mixing and potential mass and heat transport enhancement
performance
3o are less significant for this examples as compared to Example 3.
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Example 5
The studies described below involve numerical simulations of flow through
channels. All analyses are performed using the CFD package Fluent. Channels
with a constant inlet cross-section, 0.5 mm tall by 1.3 mm wide, are
referenced for
the study. The upper channel wall is assumed to have a no stress boundary
condition; all other surfaces are assumed to be no slip boundaries. A case
involving
no slip boundary conditions at all channel walls is also analyzed for
reference. In all
cases, fluid density and viscosity are set to 480 kg/m3 and 0.083 cP,
respectively.
Unless otherwise noted, a uniform inlet fluid velocity of 0.2 m/sec is
imposed. Runs
probe the effect of rib width, surface feature configuration and inlet
velocity; all
results are referenced for completeness. Some visualized flow patterns are
included
for clarity.
Representative one-sided and two-sided surface feature configurations are
shown in Figs. 86a and b. In these figures the top surface is an open wall;
surface
features are on the left and right walls (surface features not shown). Surface
features corresponding to straight ribs, 0.38 mm deep, oriented at a 45 angle
relative to the channel floor, are introduced 0.25 mm from the fluid inlet
plane. The
orientation of the surface features relative to the flow is varied as shown in
Figs. 87
through 87c. Cis configurations correspond to matching orientation of the
surface
features on both sides of the wall (there is a mirror plane of symmetry
through the
horizontal plane parallel to the featured walls); the trans configuration
corresponds to
a 180 difference in the orientation angle of the ribs on opposing walls. A
and B
designations indicate the orientation of the ribs relative to the flow: A
refers to the
direction of inclination the ribs would assume if they were fixed to the lower
channel
surface but allowed to move in response to the flowing fluid. B refers to the
opposite
inclination. Rib width and rib separation are equivalent in all cases
considered; it is
recognized that rib frequency can also affect mixing effectiveness.
Results are presented in terms of path line evolution along channel length.
3o Path lines originating from the inlet vertical and horizontal center-lines
are shown for
reference. Front and side views are also presented for clarification.
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Simulations of fluid flowing through a 2.5 mm long channel with 0.13 mm wide
surface feature ribs, placed on both channel side walls, in a trans
configuration,
show a difference in flow pattern between the closed channel configuration and
one
in which a no stress boundary condition exists at the upper wall. These are
summarized in Figs. 88 and 89. Uniform wall boundary conditions lead to more
uniform and consistent path-lines along the channel length considered.
Figs. 88 and 89 shown representative results for flow through a 2.5 mm long
closed rectangular micro-channel, modified to include lateral surface features
consisting of 0.127 mm wide ribs angled at 45 relative to the channel bottom.
The
1o 2-sided trans configuration includes 0.38 mm deep ribs. Results,
corresponding to a
uniform inlet fluid velocity of 0.2 m/s, are shown in terms of path-lines
released from
the vertical and horizontal inlet center-lines, a and b and c and d,
respectively.
Figures a and c show the path-lines viewed from the exit plane of the channel;
Figures b and d show the path-lines viewed from the channel side. All views
are
orthographic. The channel inlet is shown for reference. Fig. 88 shows the
trans
configuration and closed channel.
Simulation results of the fluid flowing through the 2.5 mm long open channel
(one side wall is missing) with 0.127 mm wide surface feature ribs, in a two-
sided
trans configuration, can be compared to results obtained when the rib
thickness is
increased to 0.254 mm. These are shown in Figs. 90a through d. The wider ribs -
capture more of the flow than the thinner ribs; a tighter vortex flow develops
for the
thinner rib configuration.
Figs. 90a through d. Representative results for flow through a 2.5 mm long
open rectangular micro-channel, modified to include lateral surface features
consisting of 0.254 mm wide ribs angled at 45 relative to the channel bottom.
The
open side of the micro-channel, the upper wall, is defined as a no-stress
boundary
condition. The 2-sided trans configuration includes 0.38 mm deep ribs.
Results,
corresponding to a uniform inlet fluid velocity of 0.2 m/s, are shown in terms
of path-
lines released from the vertical and horizontal inlet center-lines, a and b
and c and d,
3o respectively. Figures a and c show the path-lines viewed from the exit
plane of the
channel; Figures b and d show the path-lines viewed from the channel side. All
views are orthographic. The channel inlet is shown for reference.
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The effect of modifying flow rate can be seen by contrasting results obtained
at 0.2 and 0.6 m/sec inlet velocities. Figs. 91 and 92 show profiles obtained
for the
0.127 mm rib width, with the two-sided trans configuration, in a 1.6 mm long
channel.
For the cases considered, less effective mixing is apparent at the higher flow
rates.
5 Figs. 91 a through d show representative results for flow through a 1.6 mm
long open
rectangular micro-channel, modified to include lateral surface features
consisting of
0.127 mm wide ribs angled at 45 relative to the channel bottom. The open side
of
the micro-channel, the upper wall, is defined as a no-stress boundary
condition. The
2-sided trans configuration includes 0.38 mm deep ribs. Results, corresponding
to a
10 uniform inlet fluid velocity of 0.2 m/s, are shown in terms of path-lines
released from
the vertical and horizontal inlet center-lines, a and b and c and d,
respectively.
Figures a and c show the path-lines viewed from the exit plane of the channel;
Figures b and d show the path-lines viewed from the channel side. All views
are
orthographic. The channel inlet is shown for reference. Here the rib density
is two
15 times higher, resulting in more revolutions.
Figs. 92 a through d show representative results for flow through a 1.6 mm
long open rectangular micro-channel, modified to include lateral surface
features
consisting of 0.127 mm wide ribs angled at 45 relative to the channel bottom.
The
open side of the micro-channel, the upper wall, is defined as a no-stress
boundary
20 condition. The 2-sided trans configuration includes 0.38 mm deep-ribs.
Results,-
corresponding to a uniform inlet fluid velocity of 0.6 m/s, are shown in terms
of path-
lines released from the vertical and horizontal inlet center-lines, a and b
and c and d,
respectively. Figures a and c show the path-lines viewed from the exit plane
of the
channel; Figures b and d show the path-lines viewed from the channel side. All
25 views are orthographic. The channel inlet is shown for reference.
The effect of surface feature positioning and orientation is evident in Figs.
93
through 96. These contrast the profiles obtained for a 0.2 m/sec fluid
velocity in the
1.6 mm long channel, with 0.127 mm thick ribs placed on one channel sidewall,
with
an A flow patfern, and on both sidewalls, in trans, cis A, and cis B
configurations.
30 Two circulating patterns are evident in the cis configurations. A single
vortex
develops in the other two (trans) cases. The cis orientation creates two
vortices -
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one on each side of the center line; however, flow at the center plane is
essentially
unmixed (see Fig. 95). The trans configuration mixes throughout the
microchannel.
Fig. 93a through d shows representative results for flow through a 1.6 mm long
open
rectangular micro-channel, modified to include lateral surface features
consisting of
0.127 mm wide, 0.38 mm deep ribs, angled at 45 relative to the channel
bottom.
The open side of the micro-channel, the upper wall, is defined as a no-stress
boundary condition. All results correspond to a uniform inlet fluid velocity
of 0.2 m/s.
Path-lines released from the horizontal inlet center-line are viewed from the
exit
plane of the channel for one-sided, trans, cis A and cis B surface feature
configurations. All views are orthographic. The channel inlet is shown for
reference.
Figs. 94a through d show representative results for flow through a 1.6 mm long
open
rectangular micro-channel, modified to include lateral surface features
consisting of
0.127 mm wide, 0.38 mm deep ribs, angled at 450 relative to the channel
bottom.
The open side of the micro-channel, the upper wall, is defined as a no-stress
boundary condition. All results correspond to a uniform inlet fluid velocity
of 0.2 m/s.
Path-lines released from the horizontal inlet center-line are viewed from the
side of
the channel for one-sided, trans, cis A and cis B surface feature
configurations. All
views are orthographic. The channel inlet is shown for reference.
Fig. 95a through d shows representative results for flow through a 1.6 mm
long open rectangular micro-channel,-modified to include lateral surface
features
consisting of 0.127 mm wide, 0.38 mm deep ribs, angled at 45 relative to the
channel bottom. The open side of the micro-channel, the upperwall, is defined
as a
no-stress boundary condition. All results correspond to a uniform inlet fluid
velocity
of 0.2 m/s. Path-lines released from the vertical inlet center-line are viewed
from the
exit plane of the channel for one-sided, trans, cis A and cis B surface
feature
configurations. All views are orthographic. The channel inlet is shown for
reference.
Fig. 96a through d shows representative results for flow through a 1.6 mm
long open rectangular micro-channel, modified to include lateral surface
features
consisting of 0.127 mm wide, 0.38 mm deep ribs, angled at 45 relative to the
channel bottom. The open side of the micro-channel, the upper wall, is defined
as a
no-stress boundary condition. All results correspond to a uniform inlet fluid
velocity
of 0.2 m/s. Path-lines released from the vertical inlet center-line are viewed
from the
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side of the channel for one-sided, trans, cis A and cis B surface feature
configurations. AII views are orthographic. The channel inlet is shown for
reference.
Example 6
The location and dimensions of contiguous surface feature (chevron
configurations) impact both the size and location of the vortical path of a
fluid. As
shown in Fig. 97a through 97c, in some instances, a vortex forms within each
chevron leg in the contiguous surface feature configuration. As can be
inferred from
Fig. 98 a through 98c, in other instances, vortices form about the apex of
each
chevron.
In Fig. 97, the channel geometry is shown in a. The path-line profile is shown
in b and c. These figures show the formation of vortices spanning the chevron
legs
in each surface feature. Fig. 97b shows path lines released at the center line
of the
inlet plane gap viewed from an angle. Fig. 97c shows the same path lines
viewed
from the exit plane.
In Fig. 98, the channel geometry is shown in a, and path line profiles are
shown in b and c. The path line profiles show the formation of vortices
centered
about the chevron apex in each surface feature. Fig. 98b shows path lines
released
at the center line of the inlet plane gap viewed from an angles. Fig. 98c
shows the
same path lines viewed from the exit plane.
Additional contiguous surface features in the form of chevron configurations
may be devised. All of these except Fig. 99b, have a 90 subtending angle.
Fig.
99b has a subtending angle of 60 . These configurations allow consideration of
the
impact of changing the subtended chevron angle, Figs. 99a and b, the alignment
of
the surface feature chevrons. Fig. 99 a, c, d and e the variation in chevron
size
along the main flow path, Fig. 99 d, e and g, and the orientation of the
contiguous
chevrons relative to the flow direction, Fig. 99f and g. As shown, the surface
features cover the same cross sectional area (approximately 12.7 mm across and
25.4 mm in length) and are 0.25 mm deep. All of these chevron shaped surface
features have a 0.38 mm span. The inter-chevron distance varies locally.
These configurations provide enhanced shearing to a flowing fluid (whether it
enters the surface features from the main channel or from a partially or
completely
porous substrate in the rear of the surface features). In all but one case,
the
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subtended angle, between the chevron legs is 900. In the case shown in Fig.
99b,
the subtended angle is 60 , leading to a steeper chevron leg configuration.
The
steeper chevron leg is intended to more easily thrust high speed/momentum
fluid
forward and enhance the effectiveness of the mixing as the fluid moves axially
along
the main channel gap. The undulating position of the chevron apex, shown in
Fig.
99b, is intended to shift the fluid laterally and enhance mixing effectiveness
and
contacting with the wall (shifting the axial momentum slightly to the sides).
The
changes in the size of the succeeding chevrons, shown in Figs. 99d and e, may
lead
to repeated vortex separation and enhanced mixing and intersection of
otherwise
non-intersecting fluid paths. The offsetting of Fig. 99e relative to 99d may
lead to
additional flow disruption and mixing. The fishbone-like chevron
configurations of
Fig. 99f and g may lead to repeated diversion of the fluid path-lines to form
relatively
randomly intertwining paths for otherwise nonintersecting fluids. Where the
alternating chevron orientation may shift - vortex center-points laterally,
the
unidirectionally directed chevron may lead to successive vortex splitting.
While the invention has been explained in relation to specific embodiments, it
is to be understood that various modifications thereof will become apparent to
those
skilled in the art upon reading the specification. Therefore, it is to be
understood that
the invention disclosed herein is intended to cover such modifications as fall
within
the scope of the appended claims.
