Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ENHANCED CROSSFLOW HEAT TRANSFER
The present invention relates generally to methods and related apparatus for
enhancing heat transfer to or from a fluid flowing cross-wise in contact with
the outer
thermally-conductive shells of a plurality of axially-oriented heat exchange
conduits
capable of acting as heat sources or heat sinks. By channeling cross-wise
fluid flow,
flowing generally orthogonal to the axes of the heat exchange conduits, and
contouring it
upstream, downstream and/or around or alongside the heat exchange conduits
utilizing
slotted or apertured plates, baffles or surrounding sleeve-like elements, a
surprisingly
more effective and efficient heat transfer between the flowing fluid and the
thermally-
conductive surface is realized.
BACKGROUND OF THE INVENTION
It is well known to heat or cool process fluids, which may be liquids or
gases, by
flowing them into contact with a thermal-transfer surface that is maintained
at a
temperature which is different from that of the upstream process fluid thereby
resulting in
heat transfer either to or from the process fluid (depending on whether the
thermal-
transfer surface is maintained at a higher or lower temperature than the
fluid). In one
familiar version of this technology, the thermal-transfer surface that acts as
a heat source
or heat sink is the exterior of a thermally-conductive shell of a thermal-
transfer tube or
pipe, for example, which is heated or cooled by means of a liquid flowing
axially through
the interior of the tube or pipe. In a variation of this technology, heat may
be supplied
directly inside a heat exchange conduit by means of flameless combustion of
fuel gas
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(such as hydrogen or a hydrocarbon) as taught, for example, by U.S. Patent
Nos. 5,255,742
and 5,404,952.
It is also known in the art to flow a process fluid axiaily along a thermal-
#ausfer
sarface, eitixer concurrently or counter-currently relative to the direction
of liquid flow
inside the thermal-transfer tube, or to crossflow the process fluid relative
to the axis of the
thermal-transfer tube, or some combination of the two. Typical applications of
heat
transfer between crossflowing fluid and heat exchanging conduits are found in
air coolers,
economizers associated with fired heaters or fiunaces, and in shell and tube
exchangers.
Various types of so-calIed radial or axial/radial flow reactor designs are
known for various
applications whereby at least a pazt of aluid process stream moves, at some
point, through
the reactor in a radial, crossflow direction (i.e., inward-to-out or outward-
to-in), as
contrasted with the more faaniliar axial flow (i.e., end-to-end) reactor
designs. Examples of
reactor designs embodying at least in part a radial, crossflow of process
fluid relative to a
plurality of axially-disposed heat-transfer tubes are shown in U.S. Patent
Nos, 4,230,669;
4,321,234; 4,594,227; 4,714,592; 4,909,808; 5,250,270; and 5,585,074.
Although cross#low contact of a process fluid with a heat-transfer surface ean
be an
attractive option for many applications, the utility of crossfloru contact for
industrial
applications has been limited by certain heat transfer inefficiencies which
have been
experienced in practice. Typically in crossflow designs, a given portion of
the process fluid
is in contact with the beat-transfer sur&ce for a shorter time than with a
comparable axial
flow design. In addition, the contact between the crossflowing process fluid
and the
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heat-transfer surface is uneven due to process fluid separation and
recirculation. Short
surface contact time, uneven contact, and limited fluid mixing can lead to
inefficient,
insufficient, and/or non-uniform thermal energy transfer.
Thus, in an article entitled "Impingement heat transfer at a circular cylinder
due to
an offset of non-offset slot jet," appearing in Int. J. Heat Mass Transfer.,
vol. 27, no. 12,
pp. 2297-2306 (1984), the authors Sparrow and Alhomoud report experimental
efforts to
vary the heat transfer coefficients associated with crossflow of a process gas
relative to a
heat-transfer tube by positioning a slotted surface some distance upstream of
the heat-
transfer tube to create a gas jet. Sparrow and Alhomoud varied the width of
the jet-
inducing slot, the distance between the slot and the tube, the Reynolds number
(degree of
fluid turbulence), and whether the slot jet was aligned with or offset from
the tube. The
authors concluded that the heat transfer coefficient increased with slot width
and
Reynolds number, but decreased with slot-to-tube separation distance and
offset.
Because the Sparrow and Alhomoud study concluded that the heat transfer
coefficient increased with slot width, the general utility of an upstream slot
to increase
heat transfer is at best ambiguous based on these results. It can only be
concluded that, in
the experimental design used by Sparrow and Alhomoud, a relatively wider slot
led to a
higher heat transfer coefficient than a relatively narrower slot, and no
upstream slot at all
might yield the highest value. No testing was performed utilizing a plurality
of heat-
transfer tubes, or using upstream and downstream pairs, or around or alongside
flow
constriction means to preferentially contour crossflow fluid paths in contact
with the outer
surface of each of a plurality of heat-transfer tubes, and no reasonable
extrapolations can
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be made to such very different alternative designs and configurations based on
the
extremely limited data presented.
These and other drawbacks with and limitations of the prior art crossflow heat
exchanged designs are overcome in whole or in part with the enhanced crossflow
heat
transfer methods and designs of this invention.
OBJECTS OF THE INVENTION
Accordingly, a principal object of this invention is to provide methods and
designs
for enhanced crossflow heat transfer between a process fluid and a heat-
transfer surface.
It is a general object of this invention to provide methods and designs for
specially
directing and shaping fluid crossflow paths in contact with one or more heat-
transfer
surfaces so as to enhance heat transfer between the fluid and the heat-
transfer surfaces.
A specific object of this invention is to provide fluid flow-constriction
means
upstream, downstream and/or around or alongside a heat-transfer surface so as
to
preferentially contour a process fluid stream flowing cross-wise past the heat-
transfer
surface to enhance heat transfer between the fluid stream and the heat-
transfer surface.
A further specific object of this invention is to provide curved or flat
apertured
plates or apertured sleeves disposed relative to each conduit in an array of
heat exchange
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conduits so as to preferentiallv contour the flow path of the fluid stream
flowing cross-
wise past the outside of each of the conduits to realize improved heat
transfer.
Still another object of this invention is to provide heat-transfer conduit
arrays of
varying sizes and configurations wherein each conduit of the array is
associated with its
own fluid flow-constriction means upstream, downstream and/or around or
alongside of
the conduit so as to preferentially contour the portion of the fluid stream
flowing cross-
wise past the outside of the conduit to realize improved heat transfer.
Other objects and advantages of the present invention will in part be obvious
and
will in part appear hereinafter. The invention accordinglv comprises, but is
not limited to,
the methods and related apparatus, involving the several steps and the various
components, and the relation and order of one or more such steps and
components with
respect to each of the others, as exemplified by the following description and
the
accompanying drawings. Various modifications of and variations on the method
and
apparatus as herein described will be apparent to those skilled in the art,
and all such
modifications and variations are considered within the scope of the invention.
SUMMARY OF THE INVENTION
In the present invention, a baffle structure comprising at least a paired set
of fluid
flow constructors is utilized to preferentially contour the flow path of a
process fluid
flowing cross-wise, or substantially cross-wise, in contact with a heat-
transfer surface in
order to enhance heat transfer between the fluid and the surface. The
apparatus is
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designed so as to substantially restrict the bypassing of fluid flow such that
a predominant
portion of the process fluid is forced to flow past the heat-transfer surface.
The heat-
transfer surface will typically be one or a configured array of heat exchange
conduits,
oriented to have parallel axes disposed in an axial direction which is
generally orthogonal
to the direction of fluid flow, and having a thermally-conductive shell. The
exterior
surface of the shell of each such conduit is maintained at a temperature
different from that
of the upstream process fluid so that thermal energy is transferred to or from
the process
fluid by means of conduction, convection, radiation or some combination
thereof, as the
fluid flows past and contacts the exterior surfaces of the heat exchange
conduits.
The heat exchange conduits or ducts of this invention may broadly comprise
tubes, pipes, or any other enclosures with heat sources or heat sinks. The
exterior
surfaces of the heat exchange conduits may be bare or, as discussed below, may
be finned
or any combination of the two. The cross-section of the conduits or ducts may
be
circular, elliptical, or any other closed shapes. Where a plurality of such
heat exchange
conduits are used, they will typically be arrayed in some predetermined
configuration
such as in a triangular array, a square array, a circular array, an annular
array, or other
such patterns depending on design choice and/or the requirements of a
particular
application. Relative to the direction of fluid flow, adjacent conduits may be
aligned,
staggered or otherwise positioned, again depending on design choice and/or
application
requirements.
The size of the heat exchange conduits will be dictated, at least in part, by
process
requirements for the rate of heat transfer. In general, conduits having larger
cross-
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sections (for any given conduit geometry) will provide larger surface areas
and therefore
more heat transfer capacity. Fin elements, baffles or other heat-transfer
enhancing
structures may be provided on the outside surface of some or all of the heat
exchange
conduits to further increase surface area and improve heat transfer
characteristics. A
preferred embodiment utilizes closely spaced circumferential fins applied in a
spiral along
the exterior length of the conduit. This arrangement increases the heat-
transfer surface
area exposed to the crossflow without impeding the flow. It will be understood
that the
nature and flowrate of the process fluid, and the desired temperature change
in the fluid
between upstream of the heat exchange conduits and downstream of the conduits,
will
also affect these design choices.
The fluid flow constriction means for contouring the cross-wise flow of the
process fluid may comprise inlets, outlets and openings of various shapes and
sizes in
baffle structures located upstream, downstream and/or around or alongside the
heat
exchange conduits. In a further preferred embodiment, each heat exchange
conduit has
its own associated pair of upstream and downstream fluid flow constrictors or
its own
around or alongside flow constrictors as described below. The apertured baffle
structures
which function as fluid flow constriction means may comprise plates, sleeves
or other
baffles which comprise substantially flat surfaces, or curved surfaces, or a
combination of
flat and curved surfaces. Apertured structures of this type positioned in
pairs upstream
and downstream of an array of heat exchange conduits have been found to
enhance heat
transfer by a factor of about one and one-half to about two times. In a
particularly
advantageous embodiment for certain applications, the fluid flow constriction
structure is
a larger, generally concentric sleeve-like structure at least partially
surrounding each
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conduit in an array of tubular heat exchange conduits, each such sleeve
structure having
apertures upstream and downstream of the centrally-located heat exchange tube.
Apertured sleeves of this type at least partially surrounding individual heat
exchange
conduits in an array of such conduits have been found to enhance heat transfer
by a factor
of about five rimes or more.
The apertures in the fluid flow constriction structure preferably comprise any
combination of perforated holes or axial slots (i.e., elongated apertures
having a longer
axis generally parallel to the axial orientation of the heat exchange
conduits). The holes
or slots in different portions of the apparatus mav be the same or differ in
curvature, size
and shape. The edges around the inlets and outlets may be straight, rounded,
jagged, or
some combination thereof.
The fluid flow constriction structure is preferably positioned relative to an
associated heat exchange conduit such that the distance between the centerline
of an
upstream or downstream aperture and the associated heat exchange conduit
centroid
ranges from about 0 to about 2.0, preferably from about 0.50 to about 1.00,
times the
outer diameter (or largest cross-sectional dimension of a non-circular
conduit) of the
conduit. In any case, the spacing between aperture and conduit must be
sufficiently close
to realize substantially enhanced heat transfer. The width (shortest side) of
an elongated
flow constriction aperture or the diameter of a generally circular hole
constriction
aperture may preferably range from about 0.02 to about 1.5, preferabl_y from
about 0.05 to
about 0.25, times the outside diameter (or largest cross-sectional dimension
of a non-
circular conduit) of the conduit. The fluid flow constriction structure is
preferably
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positioned relative to an associated heat exchange conduit such that the
offset between the
center of the aperture and the centroid of the heat exchange conduit ranges
from 0 to 0.5,
preferably 0, times the outside diameter (or largest cross-sectional dimension
of a non-
circular conduit) of the conduit.
The enhanced crossflow heat exchange apparatus of this invention enhances heat
transfer between the crossflowing fluid and the plurality of heat exchange
conduits by one
or more of the following mechanisms: (a) increasing the fluid velocity around
the heat
exchange conduits; (b) preferentially directing the fluid to closely follow
the outer surface
of the heat exchange conduits; (c) restricting the fluid from flowing into or
through areas
that are distant from the outer surface of a heat exchange conduit; (d)
reducing "dead"
regions and flow recirculation around heat exchange conduits; (e) enhancing
fluid
turbulence; and (f) enhancing mixing between colder and hotter portions of the
fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. I is a schematic top sectional view of a first embodiment of a crossflow
heat
exchange apparatus, with heat transfer enhancement according to the present
invention,
wherein a substantially circular array of axially-disposed heat exchange
conduits is
positioned inside a fluid flow-constricted annulus.
Fig. 2A is a schematic plan view of a second embodiment of a crossflow heat
exchange apparatus, with heat transfer enhancement according to the present
invention,
showing a substantially circular array of axially-disposed heat exchange
conduits, each
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surrounded by a substantially concentric, fluid flow-constricted tubular
sleeve, and also
showing the several fluid flow-constricted sleeves joined together in a first
ring-like
structure. Fig. 2B is a side view of one conduit-sleeve combination
illustrating a
preferred staggered offset slot configuration.
Fig. 3 illustrates a variation of the structure of Fig. 2 showing a double,
concentric
circular array of heat exchange conduits with radially adjacent conduits shown
in
alignment such that the fluid flow-restriction apertures of the respective
flow-restricted
sleeves associated with these radiallv aligned conduits are also in radial
alignment.
Fig. 4 is a schematic top sectional view of another embodiment of a crossflow
heat exchange apparatus, with heat transfer enhancement according to the
present
invention, showing a double row of axially-disposed heat exchange conduits
arranged in a
substantially rectangular array with a first, upstream fluid flow-restricted
baffle, a second,
intermediate fluid flow-restricted baffle separating the first and second rows
of conduits,
and a third, downstream fluid flow-restricted baffle following the second row
of conduits,
with the corresponding apertures of the first, second and third baffles shown
substantially
in alignment with the respective conduits and with each other.
Fig. 5 illustrates still another embodiment of an enhanced crossflow heat
transfer
apparatus according to this invention showing an array of multiple (i.e.,
three or more)
rows of heat exchange conduits arranged in a triangular pitch and showing two
alternative
fluid flow paths through the array.
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Fig. 6 illustrates another embodiment of an enhanced crossflo , heat transfer
apparatus according to this invention showing an array of multiple (i.e.,
three or more)
rows of heat exchange conduits arranged in a square pitch and showing two
altemative
fluid flow paths through the array.
Fig. 7 illustrates still another embodiment of an enhanced crossflow heat
transfer
apparatus according to this invention showing how one or a plurality of plates
can be
positioned alongside two sides of each heat exchange conduit to cause
preferential
contouring of a crossflowing fluid stream to achieve enhanced heat transfer
characteristics.
Fig. 8 illustrates yet another embodiment of an enhanced crossflow heat
transfer
apparatus according to this invention showing an alternative type of sleeve
structure
formed by positioning curved plates having a contour corresponding to two
sides of a
conduit around two sides of each heat exchange conduit to cause preferential
contouring
of a crossflowing fluid stream to achieve enhanced heat transfer
characteristics.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows a crossflow heat exchange apparatus 10 according to this
invention
having a generally circular array of axially-disposed heat exchange conduits
12
distributed around the interior of an annular region 28 defined by an inner
cylindrical wall
20 and an outer cylindrical wall 22, each having a common centerpoint 14. As
shown in
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Fig. 1, conduits 12 are of substantially the same diameter, which is less than
the radial
width of the annular region, and spaced substantially equidistant from one
another.
Associated with each heat exchange conduit 12 is an upstream aperture 24 in
inner
wa1120 and a downstream aperture 26 in outer wall 22. As shown in Fig. 1,
respective
pairs of upstream apertures 24 and downstream apertures 26 are substantially
in radial
alignment with the associated conduit 12 and with each other. Thus, in Fig. 1,
a process
fluid 30 is flowed axially into the inner cylindrical region 16 of the heat
exchange
apparatus 10 and then directed radially outward through upstream apertures 24,
flowing
cross-wise into contact with the heat exchange conduits 12, as denoted by the
fluid flow
arrows in Fig. 1, thereby heating or cooling the process stream to form a
thermally-
conditioned fluid stream 32 which exits annular region 28 through downstream
apertures
26.
It will be understood that whereas Fig. 1 illustrates a radially-outward fluid
flow
path, the same apparatus could be utilized for thermally treating a process
stream flowing
radially inward to center region 16 and thereafter being axially withdrawn
from region 16.
In this variation, apertures 26 in the outer wa1122 would be the upstream
apertures and
apertures 24 in inner wall 20 would be the downstream apertures.
Figs. 2A and 2B show a particularly preferred crossflow heat exchange
apparatus
110 according to this invention having a generally circular array of axially-
disposed heat
exchange conduits 112, each surrounded by an apertured sleeve 120 having
either an
upstream aperture 124 and a downstream aperture 126 or offset aperture pairs
174, 176
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and 184, 186 as described below. The individual sleeves 120 are joined
together into a
larger ring-like or cylindrical structure by connecting walls 122. Apertures
124 and 126
mav comprise columns of axially-oriented perforation holes or elongated slots
which are
radially aligned with the conduits 112. Alternatively, in a preferred
embodiment also
illustrated in one portion of Fig. 2A, aperture pairs 174, 176 and 184, 186
are slightly
offset from radial alignment in a staggered slot arrangement. The staggered
slot
arrangement for aperture pairs 174, 176 and 184, 186 is illustrated in Fig.
2A, with
additional detail in Fig. 2B, where offset slot pairs 174, 176 and 184, 186
(replacing
apertures pairs 124, 126) are staggered in elevation and offset slightly from
the radial line
from centerpoint 114 by equal angles 0. Fig. 2B shows a side view taken along
the line
2B-2B in Fig. 2A of a heat exchange conduit 112 having a cylindrical sleeve
120 with the
preferred staggered slot arrangement. The plan view of this staggered slot
conduit/sleeve
combination as shown in Fig. 2A is taken along the line 2A-2A in Fig. 2B. The
ends of
the slots from alternating offset slot pairs can be slightly overlapped or at
equal elevation
so there is no interruption of flow along the axial direction of the heat
exchange
apparatus. This design with separation and overlap of the offset slots also
leaves
connection regions between the axially overlapped portions of adjacent offset
slots,
indicated generally by the reference numeral 190 in Fig. 2B, to provide the
sleeves 120
with better circumferential mechanical integrity without blocking any fluid
flow. For
simplified illustration, Fig. 2A shows one apertured sleeve 120 having the two-
pair offset
aperture configuration while the other sleeves have the one-pair aligned
aperture
configuration. In practice, however, all of the apertured sleeves for a
particular apparatus
110 will typically have the same aperture configuration.
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Thus, in Fig. 2A, a process fluid 130 is flowed axially into the inner
cylindrical
region 116 having centerpoint 114 of the heat exchange apparatus 110 and then
directed
radially outward through upstream apertures 124, flowing cross-wise into
contact with the
heat exchange conduits 112, as denoted by the fluid flow arrows in Fig. 2A,
thereby
heating or cooling the process stream to form a thermally-conditioned fluid
stream 132
which exits the interior regions defined by the sleeves 120 through downstream
apertures
126. In the staggered slot embodiment, fluid flowing radially outward would
either flow
through upstream aperture 174, into contact with conduit 112, and exit through
downstream aperture 176, or, depending on the axial elevation, instead flow
through
aperture pair 184, 186. It will be understood that whereas Fig. 2A illustrates
a radially-
outward fluid flow path, the same apparatus could be utilized for thermally
treating a
process stream flowing radially inward to center region 116 and thereafter
being axially
withdrawn from region 116. In this variation, apertures 126 (or 176 and 186)
would be
the upstream apertures, and apertures 124 (or 174 and 184) would be the
downstream
apertures.
Fig. 3 shows a crossflow heat exchange apparatus 160 which is a variation of
the
crossflow heat exchange apparatus 110 shown in Fig. 2. Apparatus 160 differs
from
apparatus 110 in the use of a double, concentric circular array of heat
exchange conduits
instead of the single circular array of Fig. 2. As seen in Fig. 3, there is a
second circular
array of heat exchange conduits 142, each in radial alignment with a
corresponding
conduit 112 of the first circular array. Each conduit 142 is surrounded by an
apertured
sleeve 150 having an upstream aperture 164 and a downstream aperture 166.
Apertures
164 and 166 for a given sleeve 150 associated with a particular conduit 142
are shown
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substantiallv in radial alignment with the apertures 124 and 126 in the sleeve
120 of the
corresponding radially adjacent conduit 112. The individual sleeves 150 are
joined
together into a larger ring-like or cylindrical structure by walls 152.
Although Fig. 3
shows only a single conduit 142 of the second circular array of heat exchange
conduits, it
will be understood that each conduit 112 of the first circular array is
associated with a
corresponding conduit 142 of the second circular array.
Thus, in Fig. 3, a partially ther,mally-conditioned fluid stream 132 exiting
first
downstream apertures 126 in sleeves 120 is directed radially outward through
second
upstream apertures 164, flowing cross-wise into contact with the second array
of heat
exchange conduits 142, thereby further heating or cooling the process stream
to form a
fully thermally-conditioned fluid stream 162 which exits the interior region
defmed by the
sleeves 150 through second downstream apertures 166. It will be understood
that
whereas Fig. 3 illustrates a radially-outward fluid flow path, the same
apparatus could be
utilized for thermally treating a process stream flowing radially inward to
center region
116 and thereafter being axially withdrawn from region 116. In this variation,
apertures
166 and 126 would be respectively the first and second upstream apertures, and
apertures
164 and 124 would be respectively the first and second downstream apertures.
Fig. 4 shows a portion of another crossflow heat exchange apparatus 210
according to this invention. In Fig. 4 a double row of axially-disposed heat
exchange
conduits, comprising a first upstream row of conduits 212 and second
downstream row of
conduits 216, are disposed in a generally rectangular array in conjunction
with: a first,
upstream apertured plate 220 having apertures 226; a second, intermediate
apertured plate
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222 having apertures 228, plate 222 separating the first and second rows of
conduits; and,
a third, downstream apertured plate 224 having apertures 230. Each set of
apertures 226,
228 and 230 associated with an upstream-downstream adjacent pair of conduits
212 and
216 is shown substantially in linear alignment with each other and with the
associated
pair of upstream and downstream conduits 212 and 216 respectively.
Thus, in Fig. 4, a process fluid 232 is directed, as denoted by the fluid flow
arrows
in Fig. 4, through apertures 226 and flowed cross-wise into contact with
first, upstream
heat exchange conduits 212, thereby partially heating or cooling the process
stream to
form a partially thermally-conditioned fluid stream 234. Stream 234 is then
directed
through apertures 228 and flowed cross-wise into contact with second,
downstream heat
exchange conduits 216 thereby further heating or cooling the process stream to
form a
fully thermally-conditioned fluid stream 236 which is flowed out of the
apparatus 210
through exit apertures 230.
Fig. 5 illustrates two alternative possible fluid flow paths through a multi-
row set
of heat exchange conduits 312 arranged in an offset or triangular array in
accordance with
another embodiment of a crossflow heat exchange apparatus 310 according to
this
invention. Thus, in Fig. 5, alternate rows of heat exchange conduits are
offset from
adjacent rows instead of having conduits in adjacent rows substantially in
linear
alignment as shown in Figs. 4 and 6. In this configuration, the centerpoints
of three
adjacent conduits in two adjacent rows form an equilateral triangle 340.
Although not
shown in Fig. 5, it is understood that the apparatus of Fig. 5 includes
upstream and
downstream apertured plates respectively located before the first row of
conduits and
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after the last row of conduits, as well as intermediate apertured plates
separating adjacent
rows of conduits. Alternativelv, each conduit 312 may be surrounded with an
apertured
sleeve-like structure as previouslv described for other figures.
Fluid flow arrows 332 in Fig. 5 illustrate a first possible fluid flow
orientation
which can be utilized with the triangular conduit array of apparatus 310.
Fluid flow
arrows 334 in Fig. 5 illustrate a second possible fluid flow orientation which
can be
utilized with the triangular conduit array of apparatus 310. Although Fig. 5
shows four
rows of heat exchange conduits in the triangular array, a smaller or larger
number of
conduit rows in this configuration may be utilized as appropriate.
Fig. 6 illustrates two alternative possible fluid flow paths through a multi-
row set
of heat exchange conduits 412 arranged in a square array in accordance with
still another
embodiment of a crossflow heat exchange apparatus 410 according to this
invention.
Thus, in Fig. 6, conduits 412 in adjacent rows are substantially in linear
alignment. In
this configuration, the centerpoint of four adjacent conduits in two adjacent
rows form a
square 440. Although not shown in Fig. 6, it is understood that the apparatus
of Fig. 6
includes upstream and downstream apertured plates respectively located before
the first
row of conduits and after the last row of conduits, as well as intermediate
apertured plates
separating adjacent rows of conduits. Alternatively, each conduit 412 may be
surrounded
with an apertured sleeve as previously described.
Fluid flow arrows 432 in Fig.6 illustrate a first possible fluid flow
orientation
which can be utilized with the square conduit array of apparatus 410. Fluid
flow arrows
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434 in Fig. 6 illustrate a second possible fluid flow orientation which can be
utilized with
the square conduit array of apparatus 410. Although Fig. 6 shows five rows of
heat
exchange conduits in the square array, a smaller or larger number of conduit
rows in this
configuration may be utilized as appropriate.
Fig. 7 illustrates still another variation of an enhanced crossflow heat
transfer
apparatus 510 according to this invention. In Fig. 7, each heat exchange
conduit 512 is
associated with one or more lateral flow-constriction plates 520, 522, 524,
526, and 528
positioned alongside conduit 512 and oriented generally orthogonal to the
direction of
fluid flow, as indicated by arrows 530 and 532. The edges of the lateral
plates 520, 522,
524, 526 and 528 closest to conduit 512 are spaced apart from the exterior
walls of
conduit 512 so as to create two fluid openings or channels between the plate
edges and
the conduit wall, one along each side of each conduit 512. The spacing between
the plate
edges and the conduit wall may be adjusted by routine experimentation to
optimize the
contouring of the fluid flow path to maximize heat transfer. Where two or more
lateral
flow-constriction plates are utilized for each conduit 512, the spacing
between the plate
edges and the conduit wall may be the same or different in order to optimally
contour the
fluid flow path.
As seen in Fig. 7, the lateral flow-constriction plates may be positioned
alongside
conduit 512 such that the plane of the plate passes through the centroid 518
of conduit
512 (such as plate 524), or else be positioned such that the planes of the
plates intersect
conduit 512 upstream (such as plates 520 and 526) of centroid 518, or
downstream (such
as plates 522 and 528) of centroid 518, or any combination thereof. The
distance 542
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WO 01/07857 PCTIUSOO/40401
between the aperture and the conduit centroid 518 may be less than one-half of
the
diameter 544 as shown, with a distance approaching zero as a limit, for
example plate
524. This differs from the baffle structures shown in Figs. 1 and 4 where the
distance
between the apertures and the conduit centroid is greater than one-half the
diameter of the
conduit. As used herein, the phrase "lateral plate positioned alongside a heat
exchange
conduit" is meant to refer to plates such as 520, 522, 524, 526 and 528 in
Fig. 7, oriented
generally orthogonal to the direction of fluid flow, wherein the plane of the
plate
intersects any part of the heat exchange conduit.
Fig. 8 illustrates another variation of an enhanced crossflow heat transfer
apparatus 610 according to this invention showing a variation of the apertured
sleeve
configuration shown in Fig. 2. In Fig. 8, each heat exchange conduit 612 is
partially
surrounded by a pair of oppositely curved plates 620 generally conforming to
the
curvature of the outer wall of conduit 612 in a clam-shell configuration. Each
curved
plate 620 is joined to a wall or lateral plate 622 positioned generally
orthogonal to the
direction of fluid flow, as indicated by arrows 630 and 632.
The pair of curved plates 620 around either side of a given conduit 612 do not
touch each other and do not extend either upstream or downstream of the outer
wall of
conduit 612. Thus, as shown for illustration purposes in Fig. 8, a line or
plane connecting
the upstream or downstream edges of a pair of curved plates 620 would
intersect conduit
612. The upstream and downstream openings between the pairs of curved plates
620 are
the apertures through which the process fluid stream is directed to realize
preferential
contouring of the fluid stream. The distance 642 between the aperture and the
conduit
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centroid 618 mav be less than one-half of the diameter 644 as shown, with a
distance
approaching zero as a limit, for example, as the lengths of curved plates 620
approach
zero leaving only lateral plate 622, a configuration corresponding to Fig. 7
with a single
plate 524. This differs from the baffle structures shown in Figs. 1 and 4
where the
distance between the apertures and the conduit centroid is greater than one-
half the
diameter of the conduit.
The clam-shell configuration of Fig. 8 with each pair of curved plates 620
around
the sides of each conduit 612, differs from the slotted sleeve configuration
of Fig. 2 in
that in Fig. 8 a line or plane connecting the edges of the upstream and
downstream fluid
openings intersects the conduit 612, which is not the case for the slotted
sleeves shown in
Fig. 2A. In a sense, the embodiment of Fig. 8 may be viewed as an extreme
version of the
embodiment of Fig. 7 wherein the individual lateral plates positioned
alongside the heat
exchange conduit are not spaced apart, as seen in Fig. 7, but instead are
positioned face-
to-face with one another such that their conduit-side edges form the curved
plates 620 of
Fig. 8.
It will be apparent to those skilled in the art that other changes and
modifications
may be made in the above-described apparatus and methods for enhancing
crossflow heat
transfer without departing from the scope of the invention herein, and it is
intended that
all matter contained in the above description shall be interpreted in an
illustrative and not
a limiting sense.
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