Note: Descriptions are shown in the official language in which they were submitted.
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
TITLE
Evaporative Heat Exchange Apparatus With Finned Elliptical Tube Coil Assembly
BACKGROUND OF THE INVENTION
100011 The present invention relates to improvements in tubes in a coil
assembly for
use in an evaporative heat exchange apparatus in which the coil assembly is to
be
mounted in a duct or plenum of the apparatus in which external heat exchange
fluids,
typically a liquid, usually water, and a gas, usually air, flow externally
through the coil
assembly to cool an internal heat transfer fluid passing internally through
the tubes of the
coil assembly. The improvements concern the use of tubes or segments of the
tubes
having a generally elliptical cross-section, in combination with tube
orientation,
arrangement and spacing, and fin spacing, height and thickness, all of which
must be
carefully balanced, to provide increased heat transfer coefficients with an
unexpected
relatively low air pressure drop that produces high air volume that together
produces very
high heat exchange capacity.
[0002] Preferably, though not exclusively, the finned tube coil assembly
of the
present invention using tubes that have finned segments with generally
elliptical cross-
sections, is most effectively mounted in a counterflow evaporative heat
exchanger so that
water flows downwardly and externally through the coil assembly while air
travels
upwardly and externally through the coil assembly. The coil assembly of the
present
invention can be used also in a parallel flow evaporative heat exchanger in
which the air
travels in the same direction over the coil assembly as the water, as well as
in a crossflow
evaporative heat exchanger, where air travels over the coil in a direction
transverse to the
flow of the water. The evaporation of the water cools the coil assembly and
the internal
heat transfer fluid inside the tubes forming the coil assembly.
[0003] The tubes may be used in any type of evaporative heat exchange
coil
assembly made of an array of several, and preferably, many tubes that can have
a variety
of arrangements. The tubes are preferably arranged in generally horizontal
rows
extending across the flow path of the air and water which flow externally
through the coil
assembly, whether the air and water are in counterflow, parallel flow or
crossflow
pathways. The ends of the tubes may be connected to manifold or headers for
1
SUBSTITUTE SHEET (RULE 26)
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
appropriate distribution of the internal heat transfer fluid. The internal
heat transfer fluid
may be a heating fluid, a cooling fluid or a processing fluid used in various
types of
industrial processes, where the temperature of the internal heat transfer
fluid needs to be
modified, typically but not exclusively by cooling, and often but not
exclusively by
condensing, as a result of the heat transfer through the walls of the tubes by
the external
heat exchange fluids.
[0004] Typically, evaporative heat exchange apparatus use a number of
serpentine
tubes for the coil assemblies, and such serpentine tubes are often the
preferred type of
tubes used due to the ease of manufacture of effective coil assemblies from
such tubes.
While other types of tubes of the present invention useful for the evaporative
heat
exchange apparatus of the present invention, the tubes and coil assemblies of
the present
invention will primarily be described, without limitation, with respect to the
preferred
serpentine tubes. The following background information is provided to better
understand
the relationship of the tube and coil assembly components using serpentine
tubes. Each
serpentine tube comprises a plurality of two different types of portions,
"segments" and
"return bends." The segments are generally straight tube portions which are
connected
by the return bends, which are the curved portions, sometimes referred to as
"bights," to
give each tube its serpentine structure. In a preferred embodiment of the coil
assembly of
the present invention, the tubes, which may be generally straight in structure
(referred to
hereinafter as "straight tubes"), or the segments of each of the serpentine
tubes, are
generally elliptical in cross-section and the return bends can be any desired
shape and are
typically generally circular, generally elliptical, generally kidney-shaped or
some other
shape in cross-section. The generally horizontal maximum dimension of the
generally
elliptical segments is usually equal to or smaller than the generally
horizontal cross-
sectional dimension of the return bends, especially if the return bends have a
circular
cross-section. If desired, the return bends can have an elliptical cross-
section, or a
kidney-shaped cross-section, but it is usually easier to make the return bends
with a
circular cross-section. The segments of horizontally adjacent serpentine tubes
are spaced
from each other by the larger horizontal cross-section of the return bends
when the return
bends are in contact with each other, or may be spaced by vertically-oriented
spacers
2
CA 02805373 2014-11-24
between the return bends, depending on the design characteristics of the
evaporative heat
exchange apparatus in which the coil assemblies are used.
[0005] In the coil assemblies, the straight tubes or the segments of the
serpentine
tubes are preferably arranged in generally horizontal rows extending across
the flow path
of the air and water which flow externally through the coil assembly, whether
the air and
water are in counterflow, parallel flow or crossflow pathways.
[0006] Evaporative heat exchangers using coil assemblies using
serpentine tubes
having segments with generally elliptical cross-sections are also known, for
example as
disclosed in U.S. Patents 4,755,331 and 7,296,620,
which are assigned to Evapco, Inc., the assignee of
the present invention. These patents do not disclose or contemplate the use of
finned
tubes in the coil assembly in the evaporative heat exchange environment.
[0007] Finned tubes used in coil assemblies of dry (non-evaporative)
heat exchangers
are known and are used in view of the greater surface area provided by the
fins to
dissipate heat by conduction when exposed to air flowing externally through
the coil
assembly of the dry heat exchanger. Generally, the fins in such dry heat
exchangers do
not materially adversely affect the flow of air through the coil assembly of
the dry heat
exchanger. Finned coils are also used extensively in coil assemblies of
products like
home refrigerators to dissipate the heat to the ambient air.
[0008] Examples of coil assemblies for dry heat exchangers made using fins
in the
form of sheets or plates having holes though which segments having generally
elliptical
cross-sections pass are disclosed in Evapco, Inc.'s U.S. Patents 5,425,414,
5,799,725,
6,889,759, and 7,475,719. However, such coil assemblies are not useful with
evaporative
heat exchangers, since the sheets or plates would adversely affect the mixing
and
turbulence of the air and water involved with evaporative heat exchange that
must pass
externally through the coil assembly.
[0009] Evapco, Inc. and others have used finned tube coil assemblies in
evaporative
heat exchangers where the segments of the tubes in the coil assemblies have
circular
cross-sections that include fins extending along the length of the individual
segments of
the tubes. The segments having circular cross-sections are relatively easy to
provide with
fins, such as by spirally wrapping the segments with strips of metal forming
the fins.
3
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
These finned tubes have been used in evaporative heat exchangers, but in
limited
circumstances and with limited success. First, round tube coils with fins have
been
employed in heat exchangers to enhance dry cooling capacity in cold weather
applications when not much capacity is needed and when using water as an
external heat
exchange liquid could result in freezing and other problems. Such uses were
rather rare
and were provided to deal with a problem, as opposed to a way to improve the
primary
function of evaporative cooling according to the present invention. Second,
though round
tube coils with fins have also been employed to improve evaporative cooling,
this has not
been successful. While the presence of the fins increases the heat transfer
coefficient, in
prior attempts the increases were offset because the fins also caused
decreased air flow
over the coil, thus resulting in lower performance.
[0010] The finned tube coil assembly of the present invention provides a
number of
significant advantages. The combination of the shape of the tubes, the spacing
of the
tubes, the height of the fins, and the number of fins per inch have resulted
in exceptional
and unexpected increases in evaporative thermal performance. The geometry of
the tubes
and their orientation and arrangement with a coil assembly play an essential
part in the
turbulent mixing of the air and water. The generally elliptical cross-
sectional shape of
the segments provides the advantages of a large amount of surface area of the
tubes in a
coil assembly, effective flow and heat transfer of process fluid internally
within the tubes
and enhanced external air and water flow characteristics. With the present
invention, the
surprising result of less resistance to the air and water passing externally
through the coil
assembly allows the use of higher air volume that provides additional thermal
capacity
compared to the prior art systems without adding any fan energy. The finned
tubes
provide an enhanced surface area for conductive heat exchange with the tubes
and aid in
turbulent mixing of the air and water externally flowing through the coil
assembly,
enhancing convective heat exchange between the air and the water. The finned
tubes
take up space that may impede the water and air flow and thereby would be
expected to
cause a very significant air side pressure drop, with the need for stronger
motors for fans
to move the air through the coil assembly in the heat exchanger. However, the
finned
tubes with generally elliptical cross-sections having the characteristics of
the present
invention not only provide a careful balance of enhanced coil assembly surface
area for
4
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
conductive heat exchange with any fluid flowing within the interior of the
tubes and
mixing and turbulence of the air and water for the convective heat exchange
but also
provide a surprising reduction in the air side pressure drop through the coil
assembly,
while retaining a very large increase in external heat transfer coefficient.
[0011] The overall capacity of the coil assembly of the present invention
and
evaporative heat exchangers containing it are greatly improved at nominal, or
in certain
circumstances even reduced cost, compared to the increase in capacity. For
example, the
cost per cooling ton may be reduced by, for instance, replacing a coil
assembly using
more non-finned tubes with a coil assembly using fewer finned tubes of the
present
invention. Additionally, an evaporative heat exchanger of a given size using
non-finned
tubes of the prior art could be replaced with a smaller evaporative heat
exchanger
according to the present invention that achieves the same or better thermal
performance.
Moreover, using a coil assembly having the finned tubes of the present
invention could
significantly reduce required fan energy, and therefore overall power
consumption, as
compared to a non-finned coil assembly of the same size.
[0012] Various types of heat exchange apparatus are used in a variety of
industries,
from simple building air conditioning to industrial processing such as
petroleum refining,
power plant cooling, and other industries. Typically, in indirect heat
exchange systems, a
process fluid used in any of such or other applications is subject to heating
or cooling by
passing internally through a coil assembly made of heat conducting material,
typically a
metal, such as aluminum, copper, galvanized steel or stainless steel. Heat is
transferred
through the walls of the heat conducting material of the coil assembly to the
ambient
atmosphere, or in a heat exchange apparatus, to other heat exchange fluid,
typically air
and/or water flowing externally over the coil assembly where heat is
transferred, usually
from hot processing fluid internally within the coil assembly to the cooling
heat exchange
fluid externally of the coil assembly, by which the internal processing fluid
is cooled and
the external heat exchange fluid is warmed.
[0013] In evaporative indirect heat exchange apparatus in which the
finned tube coil
assembly of the present invention is used, heat is transferred using indirect
evaporative
exchange, where there are three fluids: a gas, typically air (accordingly,
such gas will
usually be referred to herein, without limitation, as "air"), a process fluid
flowing
5
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
internally through a coil assembly of tubes, and an evaporative cooling
liquid, typically
water (accordingly, such external heat exchange or cooling liquid will usually
be referred
to herein, without limitation, as "water"), which is distributed over the
exterior of the coil
assembly through which the process fluid is flowing and which also contacts
and mixes
with the air or other gas flowing externally through the coil assembly. The
process fluid
first exchanges sensible heat with the evaporative liquid through indirect
heat transfer
between the tubes of the coil assembly, since it does not directly contact the
evaporative
liquid, and then the air stream and the evaporative liquid exchange heat and
mass when
they contact each other, resulting in more evaporative cooling.
[0014] In other embodiments, direct evaporative heat exchange may be used
together
with the indirect evaporative heat exchange involving the finned tube coil
assembly of
the present invention, as explained in more detail hereinafter, to provide
enhanced
capacity. In direct evaporative heat exchange apparatus, air or other gas and
water or
other cooling liquid may be passed through direct heat transfer media, called
wet deck
fill, where the water or other cooling liquid is then distributed as a thin
film over the
extended fill surface for maximum cooling efficiency. The air and water
contact each
other directly across the fill surface, whereupon a small portion of the
distributed water is
evaporated, resulting in direct evaporative cooling of the water, which is
usually collected
in a sump for recirculation over the wet deck fill and any coil assembly used
in the
apparatus for indirect heat exchange.
100151 Evaporative heat exchangers are commonly used to reject heat as
coolers or
condensers. Thus, the apparatus of the present invention may be used as a
cooler, where
the process fluid is a single phase fluid, typically liquid, and often water,
although it may
be a non-condensable gas at the temperatures and pressures at which the
apparatus is
operating. The apparatus of the present invention may also be used as a
condenser,
where the process fluid is a two-phase or a multi-phase fluid that includes a
condensable
gas, such as ammonia or FREON refrigerant or other refrigerant in a condenser
system
at the temperatures and pressures at which the apparatus is operating,
typically as part of
a refrigeration system where the process fluid is compressed and then
evaporated to
provide the desired refrigeration. Where the apparatus is used as a condenser,
the
condensate is collected in one or more condensate receivers or is transferred
directly to
6
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
the associated refrigeration equipment having an expansion valve or evaporator
where the
refrigeration cycle begins again.
[0016] The present invention uses a finned tube coil assembly where the
claimed
combination of factors of tube shape, orientation, arrangement and spacing,
and fin
spacing, height and thickness, all of which must be carefully balanced, to
provide
increased heat transfer coefficients with an unexpected relatively low air
pressure drop
that produces high air volume. The combination of increased heat transfer
coefficients
with high air volume produces very high heat exchange capacity.
DEFINITIONS
[0017] As used herein, the singular forms "a", "an", and "the" include
plural
referents, and plural forms include the singular referent unless the context
clearly dictates
otherwise.
[0018] Certain terminology is used in the following description for
convenience only
and is not limiting. Words designating direction such as "bottom," "top,"
"front,"
"back," "left," "right," "sides," "up" and "down" designate directions in the
drawings to
which reference is made, but are not limiting with respect to the orientation
in which the
invention and its components and apparatus may be used. The terminology
includes the
words specifically mentioned above, derivatives thereof and words of similar
import.
[0019] As used herein, the term "about" with respect to any numerical
value, means
that the numerical value has some reasonable leeway and is not critical to the
function or
operation of the component being described or the system or subsystem with
which the
component is used, and will include values within plus or minus 5% of the
stated value.
[0020] As used herein, the term "generally" or derivatives thereof with
respect to any
element or parameter means that the element has the basic shape, or the
parameter has the
same basic direction, orientation or the like to the extent that the function
of the element
or parameter would not be materially adversely affected by somewhat of a
change in the
element or parameter. By way of example and not limitation, the segments
having a
"generally elliptical cross-sectional shape" refers not only to a cross-
section of a true
mathematical ellipse, but also to oval cross-sections or somewhat squared
corner cross-
sections, or the like, but not a circular cross-section or a rectangular cross-
section.
7
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
Similarly, an element that may be described as "generally normal" to or
"generally
parallel to" another element can be oriented a few degrees more or less than
exactly 900
with respect to "generally normal" and a few degrees more or less than exactly
perfectly
parallel or 00 with respect to "generally parallel," where such variations do
not materially
adversely affect the function of the apparatus.
[0021] As used herein, the term "substantially" with respect to any
numerical value
or description of any element or parameter means precisely the value or
description of the
element or parameter but within reasonable industrial manufacturing tolerances
that
would not adversely affect the function of the element or parameter or
apparatus
containing it, but such that variations due to such reasonable industrial
manufacturing
tolerances are less than variations described as being "about" or "generally."
By way of
example and not limitation, "fins having a height extending from the outer
surface of the
segments a distance of substantially 23.8% to substantially 36% of the nominal
tube
outside diameter" would not allow variations that adversely affect
performance, such that
the fins would be too short or too tall to allow the evaporative heat
exchanger to have the
desired enhanced performance.
[0022] As used herein, the term "thickness" with respect to the
thickness of the fins,
refers to the thickness of the fins prior to treatment after the fins are
applied to the tubes
to make the finned tubes, such as galvanizing the tubes or the coil assembly
using the
finned tubes, as such treatment would likely affect the nominal thickness of
the fins, the
nominal fin height and the nominal spacing of the fins. Thus, all of the
dimensions set
forth herein are of the finned tubes prior to any later treatment of the
finned tubes
themselves or of any coil assembly containing them.
[0023] As used herein, where specific dimensions are presented in
inches and
parenthetically in centimeters (cm), the dimensions in inches controls, as the
centimeter
dimensions were calculated based on the inches dimensions by multiplying the
inches
dimensions by 2.54 cm per inch and rounding the centimeter dimensions to no
more than
three decimal places.
8
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
BRIEF SUMMARY OF THE INVENTION
[0024] The present invention relates to an improvement in an evaporative
heat
exchanger comprising a plenum having a generally vertical longitudinal axis, a
distributor
for distributing an external heat exchange liquid into the plenum, an air
mover for
causing air to flow in a direction through the plenum in a direction generally
countercurrent to, generally parallel to, or generally across the longitudinal
axis of the
plenum, and a coil assembly having a major plane and being mounted within the
plenum
such that the major plane is generally normal to the longitudinal axis of the
plenum and
such that the external heat exchange liquid flows externally through the coil
assembly in
a generally vertical flow direction, wherein the coil assembly comprises inlet
and outlet
manifolds and a plurality of tubes connecting the manifolds, the tubes
extending in a
direction generally horizontally and having a longitudinal axis and a
generally elliptical
cross-sectional shape having a major axis and a minor axis where the average
of the
major axis length and the minor axis length is a nominal tube outside
diameter, the tubes
being arranged in the coil assembly such that adjacent tubes are generally
vertically
spaced from each other within planes generally parallel to the major plane,
the adjacent
tubes in the planes generally parallel to the major plane being staggered and
spaced with
respect to each other generally vertically to form a plurality of staggered
generally
horizontal levels in which every other tube is aligned in the same generally
horizontal
level generally parallel to the major plane, and wherein the tubes are spaced
from each
other generally horizontally and generally normal to the longitudinal axis of
the tube.
[0025] The improvement comprises the tubes having external fins formed
on an outer
surface of the tubes, wherein the fins have a spacing of substantially 1.5 to
substantially
3.5 fins per inch (2.54 cm) along the longitudinal axis of the tubes, the fins
having a
height extending from the outer surface of the tubes a distance of
substantially 23.8% to
substantially 36% of the nominal tube outside diameter, the fins having a
thickness of
substantially 0.007 inch (0.018 cm) to substantially 0.020 inch (0.051 cm),
the tubes
having a center-to-center spacing generally horizontally and generally normal
to the
longitudinal axis of the tubes of substantially 100% to substantially 131% of
the nominal
tube outside diameter, and the horizontally adjacent tubes having a generally
vertical
9
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
center-to-center spacing of substantially 110% to substantially 300% of the
nominal tube
outside diameter.
[0026] Preferably, the tubes are serpentine tubes having a plurality of
segments and a
plurality of return bends, the return bends being oriented in generally
vertical planes, the
segments of each tube connecting the return bends of each tube and extending
between
the return bends in a direction generally horizontally, the segments having a
longitudinal
axis and a generally elliptical cross-sectional shape having a major axis and
a minor axis
where the average of the major axis length and the minor axis length is a
nominal tube
outside diameter, the segments being arranged in the coil assembly such that
the
segments of adjacent tubes are generally vertically spaced from each other
within planes
generally parallel to the major plane, the segments of adjacent tubes in the
planes
generally parallel to the major plane being staggered and spaced with respect
to each
other generally vertically to form a plurality of staggered generally
horizontal levels in
which every other segment is aligned in the same generally horizontal level
generally
parallel to the major plane, and wherein the segments are spaced from each
other
generally horizontally and generally normal to the longitudinal axis of the
segment
connected to the return bend.
[0027] Where the tubes are serpentine tubes, the improvement comprises
the
segments having external fins formed on an outer surface of the segments,
wherein the
fins have a spacing of substantially 1.5 to substantially 3.5 fins per inch
(2.54 cm) along
the longitudinal axis of the segments, the fins having a height extending from
the outer
surface of the segments a distance of substantially 23.8% to substantially 36%
of the
nominal tube outside diameter, the fins having a thickness of substantially
0.007 inch
(0.018 cm) to substantially 0.020 inch (0.051 cm)%, the segments having a
center-to-
center spacing generally horizontally and generally normal to the longitudinal
axis of the
segments of substantially 100% to substantially 131% of the nominal tube
outside
diameter, and the horizontally adjacent segments having a generally vertical
center-to-
center spacing of substantially 110% to substantially 300% of the nominal tube
outside
diameter.
10
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0028] The foregoing summary, as well as the following detailed
description of the
preferred embodiments of the invention, will be better understood when read in
conjunction with the appended drawings. For the purpose of illustrating the
invention,
there are shown in the drawings embodiments which are presently preferred. It
should be
understood, however, that the invention is not limited to the precise
arrangements and
instrumentalities shown.
[0029] Fig. 1 is an isometric view of one embodiment of a serpentine
finned tube
according to the present invention used with other such finned tubes in a coil
assembly of
an evaporative heat exchange apparatus.
[0030] Fig. 2 is an enlarged view of a portion of the serpentine tube of
Fig. 1,
showing the area in Fig. 1 within the circle designated "Fig. 2."
[0031] Fig. 3 is a vertical cross-section view taken along lines 3--3 of
the
embodiment of Fig. 2.
[0032] Fig. 4 is an end elevation view taken along the left-hand end of
Fig. 1,
showing a serpentine tube having a generally vertical plane extending 900 into
the plane
of the drawing sheet.
[0033] Fig. 5A is a first embodiment view, partly in end elevation and
partly in
vertical cross-section, of a portion of four tubes of a plurality of
serpentine tubes of a coil
assembly, taken along lines 5--5 of the embodiment of Fig. 1, showing the
generally
elliptical segments having their major axes generally vertically aligned and
generally
parallel to the plane of the return bends when the tubes are generally
vertically oriented
as shown with respect to the tube in Fig. 4.
[0034] Fig. 5B is a second embodiment view, partly in end elevation and
partly in
vertical cross-section, of a portion of four tubes of a plurality of
serpentine tubes of a coil
assembly, taken along lines 5--5 of the embodiment of Fig. 1, showing
generally elliptical
segments having their major axes of adjacent tubes on different levels angled
in opposite
directions with respect to each other and to the plane of the return bends as
shown in Fig.
4.
[0035] Fig. 6 is an isometric view of one embodiment of an exemplary coil
assembly
made using the finned tubes of the present invention.
11
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
[0036] Fig. 6A is a schematic side elevation drawing of the embodiment
of the
exemplary coil assembly of Fig. 6 made using serpentine finned tubes of the
present
invention.
[0037] Fig. 6B is a schematic side elevation drawing of an alternative
embodiment of
an exemplary coil assembly made using the finned tubes of the present
invention.
[0038] Fig. 6C is a schematic side elevation drawing of another
alternative
embodiment of an exemplary coil assembly made using the finned tubes of the
present
invention.
[0039] Fig. 7 is a schematic, vertical cross-section view of a first
embodiment of an
induced draft, counterflow, evaporative heat exchanger including an
arrangement of two
finned tube coil assemblies of the present invention within the evaporative
heat
exchanger.
[0040] Fig. 8 is a schematic, vertical cross-section view of an
embodiment of a forced
draft, counterflow, evaporative heat exchanger including an arrangement of two
finned
tube coil assemblies of the present invention within the evaporative heat
exchanger, with
some typical components removed for the sake of clarity.
[0041] Fig. 9 is a schematic, vertical cross-section view of an
embodiment of an
induced draft evaporative heat exchanger including an arrangement of a finned
tube coil
assembly of the present invention located directly below a direct contact heat
transfer
media section including wet deck fill within the evaporative heat exchanger,
with some
typical components removed for the sake of clarity.
[0042] Fig. 10 is a schematic, vertical cross-section view of another
embodiment of
an induced draft evaporative heat exchanger including an arrangement of a
finned tube
coil assembly of the present invention located directly above a direct contact
heat transfer
media section including wet deck fill within the evaporative heat exchanger,
with some
typical components removed for the sake of clarity.
[0043] Fig. 11 is a schematic, vertical cross-section view of an
embodiment of an
induced draft, counterflow evaporative heat exchanger including an arrangement
of a
finned tube coil assembly of the present invention located in a spaced
configuration
below fill within the evaporative heat exchanger, with some typical components
removed
for the sake of clarity.
12
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
[0044] Fig. 12 is a graph of results of testing of various embodiments
of an
evaporative heat exchanger using coil assemblies of the present invention as
compared to
other types of coil assemblies under equivalent conditions using test
procedures as
explained hereinafter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] The present invention will be described with reference to the
drawings, where
like numerals indicate like elements throughout the several views, and
initially with
reference to Figs. 1-4, 5A and 5B showing embodiments of a finned tube,
together with
Figs. 6, 6A, 6B and 6C, showing various embodiments of a coil assembly made
using a
number of the finned tubes, as well as Fig. 7, showing one embodiment of an
exemplary
evaporative heat exchange apparatus containing the coil assembly of the finned
tubes of
the present invention.
[0046] While the preferred embodiments of the invention use finned tubes
of the
present invention for all of the tubes in a coil assembly of an evaporative
heat exchange
apparatus to provide the greatest advantages and benefits of the invention,
and are the
embodiments described in detail hereinafter, other embodiments of the
invention include
using at least one finned tube of the present invention in a coil assembly
together with
other, non-finned tubes in such a coil assembly. Preferably a plurality of
finned tubes,
such that at least some, more preferably the majority, and most preferably as
mentioned
above, all of the tubes in a coil assembly for an evaporative heat exchange
apparatus are
the finned tubes of the present invention. When finned tubes are used in such
a coil
assembly together with non-finned tubes, the finned tubes are used in any
desired
arrangement of finned and non-finned tubes, but preferably and without
limitation, the
finned tubes may usually be arranged to be on the top portion of a coil
assembly and the
non-finned tubes may be on the bottom portion of the coil assembly.
[0047] The basic component of the present invention is a finned tube 10,
preferably
but not exclusively in the form of a serpentine tube best seen in Figs. 1-4,
formed to
provide the advantages of the invention when combined with other such finned
tubes into
a coil assembly 24 (see Figs. 6 and 6A). The coil assembly 24 has a major
plane 25, that
in turn is used in an evaporative heat exchange apparatus, such as evaporative
heat
13
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
exchanger 26, for example (see Fig. 7). When the finned tube 10 is in the
preferred form
of a serpentine tube, it has a plurality of generally straight segments 12
that have a
longitudinal axis 13 and which are interconnected by return bends 16. The
tubes 10 may
be made of any heat-conductive metal, such as galvanized steel, stainless
steel, copper,
aluminum or the like. Stainless steel and galvanized steel, where the zinc is
applied to
the steel to form galvanized steel after tubes are assembled into a coil
assembly 24, are
the presently preferred materials for the tubes 10 for most evaporative heat
exchange
applications.
[0048] The return bends 16 may be integrally and unitarily formed with
the segments
12 to form the tubes 10. Alternatively, the fins can be included on the
segments 12 and
the return bends 14, having connector end portions 16 can be connected to
connector end
portions 18 of the segment 12 after fins 20 are formed on the outer surface of
the
segments 12. The connecting end portions 16 of the return bend 14 match the
shape and
are typically slightly larger in cross-sectional area than the connecting end
portions 18 of
the segments 12, such that the connecting end portions 18 of the segments fit
within the
connecting end portions 16 of the return bend 14, and may be conveniently
substantially
sealed in a substantially liquid-tight and preferably substantially gas-tight
manner, such
as by welding the connecting end portions 16 and 18 together. Alternatively,
the
connecting end portions 16 of the return bends 14 match the shape and may be
slightly
smaller in cross-sectional area than the connecting end portions 18 of the
segments 12,
such that the connecting end portions 18 of the segments fit over the
connecting end
portions 16 of the return bend 14, and may be conveniently substantially
sealed in a
substantially liquid-tight and preferably substantially gas-tight manner, such
as by
welding the connecting end portions 16 and 18 together. The connecting end
portions 16
and 18 may have a generally elliptical or other cross-sectional shape.
Preferably, for ease
of manufacture and handling, the connecting end portions 16 and 18 have a
generally
circular cross-sectional shape, such that it is easier to orient and connect
together the
connecting end portions 16 and 18, and so that uniform return bends 14 can be
used that
preferably have a generally circular cross-sectional shape throughout their
curved length
from one connecting end portion 16 to the opposite connecting end portion 16.
However,
if desired, such as for creating a more tightly packed coil assembly of a
plurality of
14
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
generally horizontally arranged tubes 10, the return bends may have a
generally elliptical
cross-sectional shape, where major axes of the ellipses of the body of the
return bends 14
between the connector end portions 16 are oriented in a generally vertical
direction, for
most applications within an evaporative heat exchanger. Alternatively, the
return bends
14 may have a kidney-shaped cross-section throughout their length, with or
without
kidney-shaped connecting end portions 16 if the connecting end portions 18 of
the
segments 12 have matching kidney-shaped cross-sections. It is preferred to
connect the
return bends 14 to the segments 12 after the fins 20 have been applied to the
segments,
for ease of manufacture.
[0049] The tubes 10 are assembled into a coil assembly 24, best seen in
Figs. 6 and
6A, where the tubes 10 are serpentine tubes. Typically, a coil assembly 24 has
a
generally rectangular overall shape retained in a frame 28, and is made of
multiple
serpentine tubes 10, where the segments 12 are generally horizontal and
closely spaced
and arranged in levels in planes generally parallel to the major plane 25 of
the coil
assembly 24. The coil assembly 24 has an inlet 30 connected to an inlet
manifold or
header 32, which fluidly connects to inlet ends of the serpentine tubes 10 of
the coil
assembly, and an outlet 34 connected to an outlet manifold or header 36, which
fluidly
connects to the outlet ends of the serpentine tubes 10 of the coil assembly.
Although the
inlet 30 is shown at the top and the outlet 34 is shown at the bottom of the
coil assembly
24, the orientation of the inlet and outlet could be reversed, such that the
inlet is at the
bottom and the outlet is at the top, if desired. The assembled coil assembly
24 may be
moved and transported as a unitary structure such that it may be dipped, if
desired, if its
components are made of steel, in a zinc bath to galvanize the entire coil
assembly.
[0050] Fig. 6B is a schematic side elevation drawing of another
alternative
embodiment of an exemplary coil assembly 24 made using the finned tubes 10 of
the
present invention, where the finned tubes 10 are generally straight tubes that
extend
across the major plane 25 (not shown). In this embodiment, an inlet 30 for the
internal
heat transfer or process fluid is connected to an inlet manifold or header 32.
The internal
fluid flows from the inlet manifold or header 32 into a plurality of finned
tubes 10 that
are fluidly connected at one end to the inlet manifold or header 32 at an
upper level and
into a second, upper manifold or header 33A to which the opposite ends of the
upper
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
level finned tubes 10 are fluidly connected. The internal fluid then flows
from the
second, upper manifold or header 33A through a lower level of finned tubes 10
fluidly
connected at one end to the second, upper manifold or header 33A into a third,
intermediate manifold or header 33B to which the opposite ends of the finned
tubes 10
are fluidly connected. From the third, intermediate manifold or header 33B,
the internal
fluid flows into a still lower level of finned tubes 10 which are fluidly
connected at one
end to the third, intermediate manifold or header 33B to a fourth, lower
manifold or
header 33C to which the opposite ends of the finned tubes 10 are fluidly
connected. Then
the internal fluid flows from the fourth, lower manifold or header 33C to
which the one
end of the lowest level of the finned tubes 10 are fluidly connected to an
outlet manifold
or header 36 to which the opposite ends of the finned tubes 10 are fluidly
connected. An
outlet 34 for the internal heat transfer or process fluid is connected to the
outlet manifold
or header 36. As described above regarding the embodiment of Figs. 6 and 6A,
if desired
for particular uses, the flow of the internal fluid can be reversed, such that
the described
inlet 30 would be an outlet and the described outlet 34 would be the inlet.
[0051] Fig. 6C is a schematic side elevation drawing of an alternative
embodiment of
an exemplary coil assembly 24 made using the finned tubes 10 of the present
invention,
where the finned tubes 10 are generally straight tubes that extend across the
major plane
(not shown) and fluidly connect directly at respective opposite ends to an
inlet
20 manifold or header 32 and to an outlet manifold or header 36. An inlet
30 for the internal
heat transfer or process fluid is connected to the inlet manifold or header
32. An outlet
34 for the internal heat transfer or process fluid is connected to the outlet
manifold or
header 36. As described above regarding the embodiment of Figs. 6, 6A and 6B,
if
desired for particular uses, the flow of the internal fluid can be reversed,
such that the
25 described inlet 30 would be an outlet and the described outlet 34 would
be the inlet.
[0052] The segments 12 of the finned tubes 10 shown in Figs. 6 and 6A
and the
generally straight finned tubes 10 as shown in Figs. 6B and 6C have external
fins 20,
which are preferably spiral fins, that contact the outer surface of the
segments 12. The
fins may be serrated, may have undulations or corrugations or may be of any
other
desired well-known structure. If desired, collars 22 may be integrally and
unitarily
formed with the fins 20, where the collars 22 provide a direct and secure
contact with the
16
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
surface of the tubes 10 or segments 12 over a greater surface area than if
only the edges
of the fins 20 were in contact with the outer surface of the tubes 10 or
segments 12. The
fins 20 and collars 22 may be formed simultaneously on the tubes 10 or
segments 12
using commercially available equipment in a manner known to those involved
with
producing finned tubes, and especially spiral finned tubes. Alternatively, the
fins 20,
with or without collars 20 may be applied individually onto the outer surface
of the tubes
or segments 12, and then secured, such as by welding, into place, but this is
an
expensive and labor intensive manner of applying the fins 20 to the tubes 10
or segments
12.
10 [0053] Preferably, the fins 20 are applied spirally in a
continuous manner to the tubes
10 or segments 12 by conventional equipment. The fins 20 are formed from a
band of
metal of the same type as used in for the tubes 10, and the band is fed from a
source of
the band at a rate and in a manner to spirally wrapped around the tube 10 or
segment 12
as the tube 10 or segment 12 is advanced longitudinally along and rotated
around its
longitudinal axis 13 through the spiral fin forming equipment. As the fins 20
are
wrapped around the tube 10 or segment 12, the inner radius of the fins 20
buckles while
the outer radius does not, which creates minor corrugations or indentations in
the fins
themselves. This buckling occurs in a regular, repeating process in a left-to-
right pattern,
to form undulations in and out of the plane of the =material used to form the
fins, not
shown in Figs. 2 and 3.
100541 If collars 22 are desired, the band of metal of the same type as
used in for the
tubes 10, is fed from a source of the band at a rate and in a manner to be
bent
longitudinally to provide a flat portion that becomes the collars 22 and an
upstanding
portion that becomes the fins 20. The bent metal band is spirally wrapped
around the
segments 12 as the segments 12 are advanced longitudinally along and rotated
around
their longitudinal axis 13 through the spiral fin forming equipment. When the
strip of
metal is spirally applied to the segments to form the fins 20 with collars 22,
the fins 20
typically have undulations in and out of their plane, rather than straight as
shown in Figs.
2 and 3 for the ease of illustration, while the collars 22 are flat against
the surface of the
segments 12, resulting from the metal deformation during the application of
the strip of
metal to the advancing and rotating segments.
17
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
[0055] Figs. 5A and 5B show respective first and second embodiments,
partly in end
elevation and partly in vertical cross-section, of a portion of four
serpentine tubes 10A or
10B, for Figs. 5A and 5B, respectively, of a plurality of tubes 10 of a coil
assembly 24,
taken along lines 5--5 of the embodiment of Fig. 1. As shown, starting from
the left-hand
= side of each of Figs. 5A and 5B, the second and fourth tubes are shown in a
preferred
orientation as being staggered in height, or vertically (as shown, lower),
with respect to
their next generally horizontally adjacent first and third tubes. Figs. 5A and
5B also
illustrate alternative embodiments of orientations of the major axes of the
generally
elliptical segments 12A of serpentine tubes 10A in Fig. 5A and the generally
elliptical
segments 12B of serpentine tubes 10B in Fig. 5B. Otherwise, the embodiments of
Figs.
5A and 5B are similar to each other. In Figs. 5A and 5B, the cross-section of
Fig. 1 was
selected such that the fins are not shown or described for the sake of
clarity, but the
orientations of the major and minor axes of the generally elliptical segments
should be
understood as relating to the entire length of the finned segments 12 until
they connect
with or are unitarily formed with the return bends 14A and 14B. Although each
of the
return bends 14A and 14B is shown as having a circular cross-sectional shape,
as
explained above, the return bends 14A and 14B may alternatively have a
generally
elliptical cross-sectional shape, a generally kidney-shaped cross-sectional
shape, or other
cross-sectional shape. For ease of explanation, the orientation of the major
axes of the
generally elliptical finned segments 12A and 12B will be described in the
preferred
embodiment of the serpentine tubes 10 as shown in the embodiment illustrated
in Figs. 6
and 6A, but in principle, the same orientation can be and, preferably, is
provided for the
generally straight and generally elliptical finned tubes 10 used in a coil
assembly such as
the coil assemblies shown in Figs. 6B and 6C.
[0056] In both Figs. 5A and 5B, the segments 12A or 12B of adjacent tubes
are
generally vertically spaced from each other within planes generally parallel
to the major
plane 25 of the coil assembly 24 at respective upper generally horizontal
levels LlA and
L 1 B and respective lower generally horizontal levels L2A and L2B. Thus, the
segments
12A or 12B of adjacent tubes 10A or 10B are in planes generally parallel to
the major
plane 25 and are staggered and spaced with respect to each other generally
vertically to
18
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
form a plurality of staggered generally horizontal levels in which every other
segment is
aligned in the same generally horizontal level generally parallel to the major
plane 25.
[0057] In the first embodiment of Fig. 5A, the generally elliptical
segments 12A have
their major axes generally vertically aligned and generally parallel to the
plane of the
return bends 14A when the tubes 10A are generally vertically oriented as shown
with
respect to the tube 10 in Fig. 4. This alignment or orientation is regardless
of whether the
segments are on an upper generally horizontal vertical level LlA or a lower
horizontal
level, such as the next adjacent generally horizontal level L2A.
[0058] In the second embodiment of Fig. 5B, the generally elliptical
segments 12B
have their major axes of the tubes 10B on the different, next adjacent
generally horizontal
levels L1B and L2B, angled in opposite directions with respect to the plane of
the return
bends 14B when the tubes 10B are generally vertically oriented as shown with
respect to
the tube 10 in Fig. 4. As shown in Fig. 5B, in a preferred embodiment where
the major
axes of the segments 12 are oriented in opposite directions on adjacent
horizontal levels,
the angle of all of the major axes on a first generally horizontal level L1B
is about 20
from the plane of the return bends and the angle of all of the major axes on
the next
adjacent generally horizontal level L2B is about 340 from the plane of the
return bends.
In this configuration, each horizontal level L1B, the major axes of all of the
segments
12B are oriented in the same angled direction and on the next adjacent lower
level L2B,
the major axes of all the segments are oriented in the same angled direction,
but in an
opposite angled orientation from the angled orientation of the major axes in
level L1B.
Where the major axes are angled in opposite directions on adjacent horizontal
levels, they
are sometimes known as a "ric-rac" arrangement or orientation, and this term
is used in
the Table below to designate this type of arrangement or orientation. If
desired, however,
on each level L1B or L2B, the major axes of the segments within the same
generally
horizontal level may be angled in opposite directions.
[0059] Thus, as represented in Figs. 5A and 5B, the major axes of the
finned
segments 12A or 12B on a first generally horizontal level LlA or LIB,
respectively, may
be 0 to about 25 degrees from the plane of the return bends and the angle of
the major
axes of the finned segments 12B or 12A, respectively, on the next adjacent
generally
horizontal level L2B or L2A, respectively, may be about 335 to 360 from the
plane of
19
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
the return bends. Fig. 4 shows the oppositely angled major axes of the finned
segments
12 as described with respect to Fig. 5B for a complete serpentine tube 10.
[0060] The return bends 14, 14A and 14B are shown as being generally
circular in
cross-section. The outside diameter of the circular cross-section of the
return bends
substantially equals the nominal tube outside diameter that is an average of
the lengths of
the major and minor axes of the segments 12, 12A and 12B having a generally
elliptical
cross-section. Preferably, but without limitation, the outside diameter of the
return bends
and the nominal tube outside diameter are about and preferably substantially
1.05 inches
(2.67 cm), where the wall thickness of the tubes forming the segments 12 and
the return
bends 14 is about 0.055 inch (0.14 cm). The minor axis of the generally
elliptical tube 10
or segments 12, 12A and 12B is about 0.5 to about 0.9 times, and preferably
about 0.8
times the nominal tube outside diameter. Thus, the generally elliptical
straight tubes 10
and segments 12, 12A and 12B having a nominal tube outside diameter of 1.05
inches
(2.67 cm), would have a minor axis length of about and preferably
substantially
0.525 inch (1.334 cm) to about and preferably substantially 0.945 inch (2.4
cm), and
preferably about and preferably substantially 0.84 inch (2.134 cm). Tubes 10
with these
dimensions have been found to have a good balance among an appropriate inner
diameter
or dimensions to allow the processing fluid in the form of any desired gas or
liquid to
easily flow within the tubes 10, proximity of such processing fluid to the
tube wall for
good heat transfer through the walls of the tubes with the elliptical cross-
sectional shape
that has a large effective surface area, and ability to provide an appropriate
number of
tubes 10 to be packed into a coil assembly 24. The tubes are strong, durable
and when in
serpentine form, able to be readily worked, including connecting the segments
12 and
return bends 14 and placement within a coil assembly 24. Depending on the
environment
and intended use of the evaporative heat exchangers, such as the evaporative
heat
exchanger 26, in which the finned tubes 10 of the present invention are
placed, the
dimensions and cross-sectional shape of the tubes 10 may be varied
considerably.
[0061] The spacing and orientation of the tubes 10 having the generally
elliptical
cross-sectional shape or segments having the generally elliptical cross-
sectional shape
within a coil assembly 24 are important factors for the performance of the
evaporative
heat exchanger containing the coil assembly 24. If the spacing between
segments 12 is
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
too tight, air and water flow through and turbulent mixing within the coil
assembly will
be adversely affected and fans with greater horsepower will be needed and
there will be
an increased pressure drop. If the spacing between segments 12 is too great,
then there
will be less tubes per surface area of the major plane 25 of the coil assembly
24, reducing
the heat transfer capacity, and there may be inadequate, as in insufficient
for example,
mixing of the air and water, adversely affecting the degree of evaporation,
and thereby
heat exchange. The orientation of the segments 12, particularly with respect
to the angle
of the major axes of the segments, also affects the heat exchange ability of
an evaporative
heat exchanger with which they are used.
[0062] The spacing of the fins 20 around the outer surface of the segments
12 is
critical. If the fin spacing is too close (too many fins per inch, for
example), the ability of
the external heat exchange liquid and the air to effectively mix turbulently
is adversely
affected and the fins 20 may block the space externally of the coil assembly
24, such that
greater air mover power is needed. Similar concerns involve the critical
determination of
the height of the fins (the distance from the proximal point where the base of
the fins 20
contact the outer surface of the segments 12 and the distal tip of the fins).
While higher
fins have greater surface area which the evaporating water may coat, longer
fins may
block the air passage. Thicker fins 20 also have similar critical concerns.
Thicker fins
are more durable and are better able to withstand the forces of water and air,
as well as
other material that may be entrained in either as they pass through a coil
assembly, but
thicker fins may also block the flow of water or air through the coil assembly
and would
be more expensive to manufacture. All of these factors adversely affect
performance.
[0063] If the fin spacing is too great (not enough fins per inch, for
example), the
advantages of a sufficient number of fins 20 for the evaporative water to coat
would not
be present and there may be an adverse effect on the desired mixing of the
water and air
responsible for efficient evaporation. Similar concerns are present when the
fin height is
too low, as there is not enough structure of the fins to be coated with the
water, and there
may be less mixing of the water and air. Thinner fins may not be sufficiently
durable to
withstand the hostile environment to which they are subject in evaporative
heat
exchangers and if the fins are too thin, they could be bent during operation
as they are
21
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
subject to the forces of both' the water and air impacting them, adversely
affecting flow of
both the water and air. In addition, and more significantly, thinner fins
transfer less heat.
[0064] The present invention was conceived and developed in view of the
foregoing
factors of tube shape, orientation, arrangement and spacing, and fin spacing,
height and
thickness, all of which must be carefully balanced, and which was a difficult
task
requiring considerable testing and experimentation. Based on such work, the
appropriate
parameters of tube shape, arrangement, orientation and spacing, as well as fin
spacing,
height and thickness were determined.
[0065] The orientation and spacing, within a coil assembly 24 and an
evaporative
heat exchanger, of the tubes 10 with their segments 12 and return bends 14
will be
described primarily with reference to Figs. 5A and 5B. The center-to-center
spacing DH
generally horizontally (which will be generally parallel to the major plane 25
in Fig. 6)
and generally normal to the longitudinal axis 13 of the segments 12, 12A and
12B is
substantially 100% to substantially 131%, preferably substantially 106% to
substantially
118%, and more preferably substantially 112% of the nominal tube outside
diameter.
The vertical straight tube or segment spacing Dv generally is not as critical
to the
performance of an evaporative heat exchanger as the horizontal tube or segment
spacing
DH. The segments 12, 12A and 12B have a generally vertical center-to-center
spacing of
substantially 110% to substantially 300% of the nominal tube outside diameter,
preferably substantially 150% to substantially 205% of the nominal tube
outside
diameter, and more preferably, substantially 179% of the nominal tube outside
diameter.
This generally vertical center-to center spacing is indicated by the distance
Dv between
the upper generally horizontal levels LlA and L1B and the lower generally
horizontal
levels L2A and L2B, respectively.
[0066] These parameters may be applied as follows to the presently
preferred
embodiment, where the nominal tube outside diameter is substantially 1.05
inches
(2.67 cm). The center-to-center spacing DH of the finned straight tubes 10 or
segments
12, 12A and 12B of the serpentine finned tubes 10 would be substantially 1.05
inches
(2.67 cm) to substantially 1.38 inches (3.51 cm), preferably substantially
1.11 inches
(2.82 cm) to substantially 1.24 inches (3.15 cm), and more preferably
substantially
1.175 inches (2.985 cm). The finned tubes 10 or the finned segments 12, 12A
and 12B
22
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
would have a generally vertical center-to-center spacing Dv of substantially
1.15 inches
(2.92 cm) to substantially 3.15 inches (8.00 cm), preferably substantially
1.57 inches
(3.99 cm) to substantially 2.15 inches (5.46 cm), and more preferably
substantially
1.88 inches (4.78 cm). In some embodiments, the major axes of the finned tubes
10 or
the finned segments 12, 12A are oriented substantially vertically, so that
they are
generally parallel to the plane of the return bends 14 as shown in Fig. 4. In
other
embodiments, the major axes of the finned tubes 10 or the finned segments 12B
may be
greater than 0 to about 25 , and preferably about 20 , from the plane of the
return bends
14 and the angle of the major axes of the finned tubes 10 or the finned
segments 12B on
the next vertically adjacent generally horizontal level, may be about 335 to
less than
360 , and preferably about 340 from the plane of the return bends 14, such
that the major
axes of the finned tubes 10 or the finned segments 12 are oriented in opposite
directions
on vertically adjacent horizontal levels.
[0067] The parameters relating to the fins 20, namely fin spacing along
the
longitudinal axis 13 of the segments 12, the fin height from the outer surface
of the
segments 12 and the fin thickness are as follows according to the present
invention.
[0068] The fins 20 are preferably spiral fins and have a spacing of
substantially 1.5 to
substantially 3.5 fins per inch (2.54 cm) along the longitudinal axis 13 of
the segments
12, preferably substantially 2.75 to substantially 3.25 fins per inch (2.54
cm) and more
preferably substantially 3 fins per inch (2.54 cm). Expressed alternatively,
the center-to-
center distance between the =fins is therefore, respectively, substantially
0.667 inch
(1.694 cm) to substantially 0.286 inch (0.726 cm), preferably substantially
0.364 inch
(0.925 cm) to substantially 0.308 inch (0.782 cm), and more preferably
substantially
0.333 inch (0.846 cm).
[0069] The fins 20 have a height of substantially 23.8% to substantially
36% of the
nominal tube outside diameter, preferably substantially 28% to substantially
33% of the
nominal tube outside diameter, and more preferably substantially 29.76% of the
nominal
tube outside diameter. These parameters may be applied as follows to the
presently
preferred embodiment, where the nominal tube outside diameter is substantially
1.05 inches (2.667 cm). In this embodiment, the fins 20 have a height of
substantially
0.25 inch (0.635 cm) to substantially 0.375 inch (0.953 cm), preferably
substantially
23
CA 02805373 2013-01-11
WO 2012/009221 =
PCT/US2011/043351
0.294 inch (0.747 cm) to substantially 0.347 inch (0.881 cm), and more
preferably
0.3125 inch (0.794 cm).
[0070] The fins 20 have a thickness of substantially 0.007 inch (0.018
cm) to
substantially 0.020 inch (0.051 cm), preferably substantially 0.009 inch
(0.023 cm) to
substantially 0.015 inch (0.038 cm), and more preferably substantially 0.01
inch (0.025
cm) to substantially 0.013 inch (0.033 cm). As noted above in the
"Definitions" section,
dimensions for the thickness of the fins are for the fins on the finned tubes
prior to any
later treatment of the finned tubes themselves or of any coil assembly
containing them.
Where the finned tubes or coil assembly are subjected to a later treatment,
typically by
galvanizing steel finned tubes or more typically, galvanizing the entire coil
assembly
containing them, the thickness of the fins increases by the thickness of the
zinc coating
applied during galvanization. Also typically, the fins after galvanization are
thicker at a
base proximal to the outer surface of the tube than at a tip of the fins
distal from the outer
surface of the tube. Because the fins are thicker after galvanizing, the
spacing between
the fins is reduced accordingly. Usually this is not of concern concerning the
thermal
performance or heat capacity of the evaporative heat exchangers and the rust
or other
corrosion inhibition of the galvanizing is important in providing the finned
tubes and coil
assemblies with greater longevity than if they were not galvanized.
[0071] The coil assembly 24 of any desired configuration, such as shown
in any of
Figs. 6, 6A, 6B or 6C, is then installed into an evaporative heat exchanger
apparatus, such
as evaporative heat exchanger 26, as shown in Fig. 7. Evaporative heat
exchangers have
many varied configurations, and several are shown schematically in Figs. 7-11.
Typical
evaporative heat exchangers in which the coil assembly 24 of the present
invention may
be used are, for example without limitation, any of several available from
Evapco, Inc.,
such as Models ATWB or ATC, which may include the components and operate as
disclosed in Evapco, Inc.'s U.S. Patent 4,755,331. Evaporative heat exchange
apparatus,
though they many variations, have the basic structure and operation described
below,
initially with reference to Fig. 7.
[0072] Fig. 7 is a schematic, vertical cross-section view of an
embodiment of an
induced draft, counterflow, evaporative heat exchanger 26, where water flows
generally
vertically downwardly and air flows generally vertically upwardly through the
plenum
24
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
and coil assembly, including an arrangement of two finned tube coil assemblies
24 of the
present invention within the evaporative heat exchanger. The evaporative heat
exchanger
26 has a housing 38 enclosing a plenum 40 having a generally vertical
longitudinal axis
42. One or more coil assemblies 24 are mounted within the plenum 40 such that
the
major plane 25 of each coil assembly is generally normal to the longitudinal
axis 42 of
the plenum. In this way, the generally vertical plane of the return bends 14
in the
preferred embodiment using serpentine tubes 10, as shown in Fig. 4 and as
indicated by
the generally vertical alignment of the tubes 10 in the coil assemblies as
shown in Fig. 7,
are also generally normal to the major plane 25 of the coil assemblies 24 and
parallel to
the longitudinal axis 42 of the plenum. Based on this alignment, the finned
segments 12,
with their longitudinal axes 13, of the tubes 10 are also in generally
horizontal staggered
planes parallel to the major plane 25 of the coil assemblies 24 and generally
normal to the
longitudinal axis 42 of the plenum 40. If generally straight finned tubes 10
are used as
shown in Figs. 6B and 6C, then the finned tubes with their longitudinal axes
also are in
generally horizontal staggered planes parallel to the major plane 25 of the
coil assemblies
24 and generally normal to the longitudinal axis 42 of the plenum 40.
100731 Air flows from the ambient atmosphere around the heat exchanger
26 via air
inlets 44 which may, and preferably do, have louvers, or more preferably,
selectively
openable and closeable air inlet dampers 45 that may be closed or partially or
fully
opened based on various atmospheric and operating conditions, in a well-known
manner,
and to protect the plenum 40 from inclusion of unwanted objects. In the
embodiment of
Fig. 7, air is drawn into the plenum 40, passes though the coil assemblies 24
and exits an
air outlet 46 by the action of an air mover located in an air outlet housing
50. The air
mover in this embodiment is shown as a fan 48, in the form of a propeller fan,
which is
preferred for use as an induced draft fan to draw air from the ambient
atmosphere. Other
types of fans, such as centrifugal fans, could be, but usually are not used as
induced draft
fans. A grating or screen (not shown) is placed over the fan 48 for safety and
to keep
debris away from the fan 48 and out of the evaporative heat exchanger 26.
[0074] A bottom wall of the evaporative heat exchanger 26, together
with the
adjoining front, back and side walls, defines a sump 52 for the water or other
external
heat exchange liquid. If desired, a drain pipe with an appropriate valve and a
fill pipe
CA 02805373 2014-11-24
with an appropriate valve (none of which is shown) may be included for
draining and
filling or replenishing the sump 52. Water in the sump 52 is circulated to a
liquid
distributor assembly 54, which when turned on distributes, via spray nozzles,
orifices in a
pipe or via other known devices and techniques, the water as the evaporative
heat transfer
liquid above the coil assemblies 24. The distributor assembly 54 is connected
to one end
of a conduit 56 in fluid connection at the other end to the water in the sump.
The
distributor assembly 54 is activated or turned on typically when a pump 58 is
turned on to
pump water from the sump 52 to the distributor assembly 54 through the conduit
56.
[0075] The evaporative heat exchanger 26 also preferably includes drift
eliminators
60 above the liquid distributor assembly 54 and below the fan 48 and air
outlet 46. The
drift eliminators very significantly reduce water droplets or mist entrained
in the air
exiting the outlet 46. Many drift eliminators of various materials are
available
commercially. The presently preferred drift eliminators are PVC drift
eliminators
available from Evapco, Inc. as disclosed in Evapco, Inc.'s U.S. Patent
6,315,804=
[0076] In operation, as air is drawn into the plenum 40 through the air
inlets 44 and
any associated louvers or dampers 45, it is also drawn through the coil
assemblies 24.
Water is distributed over the coil assemblies 24 by the liquid distributor 54.
As the air
travels upwardly through the coil assemblies 24 it is mixed with the water,
with an
appropriate degree of turbulence as provided by the orientation and
arrangement of the
finned segments 12 having the fins 20 with the characteristics, dimensions and
parameters disclosed above. The water coats the outer surfaces of the tubes
10, including
the segments 12 having the generally elliptical cross-sectional shape, as well
as the fins
20. The air causes the water to evaporate, thereby cooling the water, such
that the cooled
water exchanges heat with the tubes 10 of the coil assembly and the process
fluid
contained internally within the tubes 10. Water ultimately passes through the
coil
assemblies 24 and is collected in the sump 52, and recycled into the liquid
distributor 54
through the conduit 56 by the pump. The air with any entrained water is drawn
upwardly
through the drift eliminators 60, whereby most, and preferably almost all, of
the water is
removed from the air stream, before the air is exhausted through the air
outlet 46 by the
fan 48.
26
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
[0077] As noted above, the coil assemblies 24 having the finned tubes 10
of the
present invention may be used in a large variety and types of evaporative heat
exchange
apparatus. Figs. 8-11 schematically illustrate a small sample of such various
evaporative
heat exchangers, with some typical components shown in Fig. 7 removed for the
sake of
clarity. In Figs. 8-11, components that are shown and that are the same as
those in Fig. 7
are not described again, but are identified by like numerals used in Fig. 7,
except that a
letter designation common to the embodiments of each of Figs. 8-11 is used,
where, for
example, the coil assemblies 24A are used in the evaporative heat exchanger
26A of Fig.
8, the coil assembly 24B is used in the evaporative heat exchanger 26B of Fig.
9, the coil
assembly 24C is used in the evaporative heat exchanger 26C of Fig. 10 and the
coil
assembly 24D is used in the evaporative heat exchanger 26D of Fig. 11. Any new
components not used in a previous Fig. are identified by a different numeral.
[0078] Fig. 8 is a schematic, vertical cross-section view of an
embodiment of a forced
draft, counterflow, evaporative heat exchanger 26A including an arrangement of
two
finned tube coil assemblies 24A of the present invention within the plenum 40A
of the
evaporative heat exchanger. Here, compared to the induced draft evaporative
heat
exchanger 26 of Fig. 7, instead of using a propeller fan 48 mounted in an air
outlet
housing 50, the forced draft evaporative heat exchanger 26A of Fig. 8 uses a
centrifugal
fan 62 type of air mover to force air, entering the plenum 40A within the
housing 38A
through a screen 47 covering the air inlet. The air is then forced generally
vertically
upwardly and through the coil assemblies 24A, through which water is flowing-
generally
vertically downwardly. Thereafter, the air moves through the drift eliminators
60A and
out of the evaporative heat exchanger 26A through the air outlet 46A. The
centrifugal
fan 62 is typically mounted within a lower portion at one side of the housing
38A
adjacent an air inlet typically covered by a screen 47. The sump for the water
is not
shown in Fig. 8, but would be present below the coil assemblies 24A such that
the water
in the sump is blocked from reaching the centrifugal fan 62.
[0079] Fig. 9 is a schematic, vertical cross-section view of an
embodiment of an
induced draft evaporative heat exchanger 26B including an arrangement of a
finned tube
coil assembly 24B of the present invention located directly below a direct
contact heat
transfer media section including wet deck fill 64, described below, within the
plenum
27
CA 02805373 2014-11-24
40B of the evaporative heat exchanger. In the evaporative heat exchanger 26B
of Fig. 9,
air is drawn into the plenum 40B through an air inlet 44B and any associated
louvers or
dampers 45B, where the air inlet 44B is laterally adjacent to the coil
assembly 24B. The
evaporative heat exchanger 26B of Fig. 9 differs in a first respect from the
evaporative
heat exchanger 26 of Fig. 7, in that the air is drawn through the coil
assembly 24B in a
direction generally normal, transverse or horizontally with respect to the
generally
vertical downwardly flow of water externally through the coil assembly 24B,
known in
the industry as a crossflow arrangement. The mixing and turbulence of the air
and water
externally through the coil assembly 24B in a crossflow arrangement is
somewhat
different than but still quite effective, compared to the mixing and
turbulence of the air
and water externally through the coil assembly 24 of Fig. 7 in a counterflow
arrangement.
[0080] The evaporative heat exchanger 26B of Fig. 9 differs in a second
respect from
the evaporative heat exchanger 26 of Fig. 7 in that the evaporative heat
exchanger 26B of
Fig. 9 includes a direct contact heat exchange section containing wet deck
fill 64 below
the liquid distributor 54B and above the coil assembly 24B, which provides
direct,
evaporative heat exchange when the air flow and the evaporative water or other
cooling
liquid come into direct contact with each other and are mixed with some
desired degree
of turbulence within the wet deck filI 64 resulting in additional evaporative
cooling. The
turbulent mixing of the air and water in the wet deck fill 64 allows for
greater heat
transfer between the air and water, but the benefits of the increased
turbulent mixing in
the wet deck fill 64 should not be overcome by potential adverse effects on
the energy
requirements of a larger fan motor or fan size or air flow reduction. As noted
above,
there is a fine balance among these factors when deciding whether and what
type of wet
deck fill heat transfer media to use. That is why the use of the wet deck fill
64 is optional
in evaporative heat exchangers using the coil assembly of the present
invention. The wet
deck fill may be any standard fill media, such as plastic fill, typically PVC,
as well as
wood or ceramic fill media, or any other fill media known in the art. The
presently
preferred fill media is Evapco, Inc.'s EVAPAK PVC fill, disclosed in Evapco,
Inc.'s
U.S. Patent 5,124,087.
When wet deck fill 64 is used, it may be located above the coil assembly
24B as shown in Figs. 9, or below the coil assembly 24C as shown in Fig. 10,
since in
28
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
either location, the additional heat transfer in the wet deck fill 64 will
further
evaporatively cool the water draining into the sump 52B or 52C.
[0081] In the embodiment of Fig. 9, louvers 65 are built into the inlet
side of the wet
deck fill 64, such that the air may be drawn through the louvers 65 into the
wet deck fill
in a crossflow manner as described above with respect to the crossflow
arrangement
concerning the coil assembly 24B.
[0082] The embodiment of the evaporative heat exchanger 26B of Fig. 9
operates as
follows. Ambient air in the environment of the evaporative heat exchanger is
drawn into
the plenum 40B through the air inlets 44B and any associated louvers or
dampers 45B,
and in a crossflow manner externally through the coil assembly 24B, though
which water,
pre-cooled in the wet deck fill 64 of the direct contact heat exchange
section, externally
flows generally vertically downwardly. Ambient air is also drawn into the wet
deck fill
64 in a crossflow manner with respect to the water flowing generally
vertically
downwardly through the louvers 65, where the water is evaporatively cooled
before it
contacts the coil assembly 24B below the wet deck fill 64. The air is then
drawn from the
wet deck fill 64 into the plenum 40B.
[0083] Water is distributed over the wet deck fill 64 by the liquid
distributor 54B
where it is initially cooled evaporatively by mixing with the air flowing
through the wet
deck fill 64 before draining into the coil assembly 24B where it is
turbulently mixed with
the air and thereafter is drained from the coil assembly 24B and collected in
the sump
52B. The water is recycled from the sump 52B into the liquid distributor 54B
through
the conduit 56B by the pump 58B. The air, with any entrained water, in the
plenum 40B
is drawn upwardly through drift eliminators 60 (not shown in Fig. 9) by the
fan 48B in
the air outlet housing 50B, before the air is exhausted through the air outlet
46B.
[0084] Fig. 10 is a schematic, vertical cross-section view of another
embodiment of
an induced draft evaporative heat exchanger 26C including an arrangement of a
finned
tube coil assembly 24C of the present invention located directly above a
direct contact
heat transfer media section including wet deck fill 64C within the plenum 40C
of the
evaporative heat exchanger. The embodiment of the evaporative heat exchanger
26C of
Fig. 10 operates as follows. One portion of ambient air in the environment of
the
evaporative heat exchanger is drawn into the apparatus through an inlet 44C at
the top of
29
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
the apparatus aligned above the coil assembly 24C and flows downwardly
externally
through the coil assembly in a generally vertical direction concurrent with
the flow of
water distributed over the coil assembly by the liquid distributor 54C.
Another portion of
ambient air is also drawn into apparatus through the direct contact heat
exchange section
containing the wet deck fill 64C through the optional louvers 65C. The air
traveling
through the wet deck fill 64C moves in a crossflow manner to water draining
generally
vertically from the coil assembly 24C.
[0085] Water is distributed over the coil assembly 24C by the liquid
distributor 54C
where it is mixed with the concurrently flowing air, thereby being cooled
evaporatively in
the coil assembly, exchanging heat with the coil assembly 24C, before draining
into and
through the wet deck fill 64C. In the wet deck fill 64C, the water is further
turbulently
mixed with the cross-flowing air where it is further evaporatively cooled, and
thereafter is
drained from the wet deck fill 64C and collected in the sump 52C. The water is
recycled
from the sump 52C into the liquid distributor 54C through the conduit 56C by
the pump
58C. The air with any entrained water is drawn into the plenum 40C and then
upwardly
through drift eliminators 60 (not shown in Fig. 10) by the fan 48C in the air
outlet
housing 50C, before the air is exhausted through the air outlet 46C.
[0086] Fig. 11 is a schematic, vertical cross-section view of an
embodiment of an
induced draft, counterflow, evaporative heat exchanger 26D including an
arrangement of
a finned tube coil assembly 24D located in a spaced configuration below wet
deck fill
64D within the plenum 40D in the housing 38D in the evaporative heat
exchanger.
[0087] The embodiment of the evaporative heat exchanger 26D of Fig. 11
operates as
follows. Air in the environment of the evaporative heat exchanger is drawn
into the
plenum 40D through the air inlets 44D and any associated louvers or dampers
45D, and
then is drawn into the wet deck fill 64D in a counterflow manner with respect
to the
water flowing generally vertically downward through the wet deck fill 64D. The
liquid
distributor 54 (not shown in Fig. 11), located above the wet deck fill 64D and
below the
drift eliminators (not shown in Fig. 11), distributes the water over the wet
deck fill 64D
where it is turbulently mixed with the air, thereby being cooled
evaporatively. Then, the
cooled water drains over the coil assembly 24D, exchanging heat with the coil
assembly
24D, before draining into and being collected in the sump 52D. If desired, the
water
CA 02805373 2014-11-24
draining from the wet deck fill 64D may be concentrated to flow directly over
the coil
assembly 24D as disclosed in Evapco, Inc.'s U.S. Patent 6,598,862,
to more efficiently direct
the cooled water to the coil assembly 24D. The water is recycled from the sump
52D into
the liquid distributor 54 through the conduit 56 (not shown in Fig. 11) by the
pump 58
(not shown in Fig. 11). The air with any entrained water is drawn upwardly
through drift
eliminators by the fan 48D in the air outlet housing 50D, before the air is
exhausted
through the air outlet 46D.
[0088] The performance of evaporative heat exchange apparatus is
measured by the
amount of heat transfer, typically but not exclusively during cooling. The
measurements
are affected by several factors. First, the measurements are affected by the
amount and
temperature of the process fluid flowing internally though the tubes 10 of the
apparatus
coil assembl(ies) 24 and the water or other cooling liquid flowing externally
through the
coil assembly. The flow rates are measured using flow meters and the
temperature is
measured using thermometers. The rate and temperature of the air flowing
through the
system is also significant, as well as the force required to drive the air
mover 48 that
moves the air through the apparatus. The air flow is typically measured by an
anemometer in feet per minute through a tube, although other well-known air
flow
measuring devices could also be used, and is typically determined by the
rating of the
motor driving the fan of the air mover, usually expressed in horsepower (HP).
100891 In one embodiment of the evaporative heat exchange apparatus
using the coil
assemblies 24 having the finned tubes 10 of the present invention, typically,
but without
limitation, the process fluid, in the form of water, is pumped into the inlet
30 and flows
internally through the coil assembly at a rate of approximately 0.75 gpm to
approximately
16.5 gpm per tube present in the coil assemblies, and preferably approximately
10 gpm
per tube. The amount and rate of water that passes externally through the coil
assembl(ies) 24 supplied through the water supply conduit 56 as distributed by
the liquid
distributor 54 is approximately 1.5 gpm/sq. ft. to approximately 7 gpm/sq. ft.
of coil plan
area determined with respect to the major plane 25, and is preferably
approximately 3
gpm/sq. ft. to approximately 6 gpm/sq. ft. Evaporative heat exchange apparatus
using the
coil assemblies 24 having the finned tubes 10 of the present invention
typically, but
31
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
without limitation, have an air flow rate of approximately 300 feet per minute
to
approximately 750 feet per minute, and preferably approximately 600 feet per
minute to
approximately 650 feet per minute. The power of the fan motors is dependent
upon the
size of the evaporative heat exchanger housing, the size of the coil
assemblies used, the
number and configuration of tubes in the coil assemblies, the number of coil
assemblies
used, the presence and orientation of any optional wet deck fill, the size and
type of fan
used, and several other factors, so no absolute values can be presented for
the power of
the fan motors required. In general, and without limitation, the power of the
fan motors
varies within a very broad range, such as approximately 0.06 HP to
approximately 0.5 HP
per square foot of plan area of the coil assemblies used in the evaporative
heat
exchangers, corresponding to the area of the major plane 25 coextensive with
the length
and width of the coil assembly.
[0090] In evaporative heat exchange apparatus using the finned tube
coil assemblies
24 of the present invention, performance has been shown to be enhanced by an
increased
air flow rate even compared to similar coil assemblies using tubes having
segments 12
with a generally elliptical cross-sectional shape but not containing fins 20
as in the
present invention. In view of the space occupied by the fins 20 on the
segments 12 of the
tubes 10 used in coil assemblies 24 of the present invention, it would have
been expected
that the air flow rate would have decreased, as the fins 20 would have been
expected to
block the flow of both air and water, so that it was unexpected and surprising
when the
air flow rate increased. The increase in air flow rate provided a surprising
enhancement
of the thermal performance in evaporative heat exchange apparatus using the
coil
assemblies with the finned tubes 10 of the present invention.
[0091] The enhanced thermal performance of evaporative heat exchange
apparatus
using the coil assemblies 24 having finned tubes of the present invention will
be
described in greater detail with respect to the following non-limiting test
procedure
whereby various coil assemblies were tested, including those of the present
invention,
under equivalent test conditions.
[0092] The test procedure included mounting various single coil
assemblies in an
Evapco, Inc. Model ATWB induced draft, counterflow, evaporative cooler in a
test
facility. The general arrangement of the Model ATWB induced draft,
counterflow,
32
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
evaporative cooler is shown in Fig. 7, except that only one coil assembly 24
was used,
instead of two coil assemblies 24 as shown in Fig. 7. The tested coil
assemblies all had a
plan area of 6 feet (1.83 m) long (corresponding to serpentine tubes having
segments with
return bends fitting within frames of this length with the appropriate
spacing) by 4 feet
(1.22 m) wide (corresponding to 37 adjacent tubes that were packed within
frames of this
width with the appropriate spacing) and had ten generally horizontal rows of
segments 12
with generally elliptical cross-sectional shapes connected by return bends
having a
circular cross-sectional shape, where the major axes of segments were arranged
in
various orientations. All tested coil assemblies used tubes with return bends
having an
outside diameter of substantially 1.05 inches (2.67 cm) and segments having a
nominal
tube outside diameter of substantially 1.05 inches (2.67 cm), with a
substantially
horizontal center-to-center spacing DH of 1.0625 inches (2.699 cm) (designated
"Narrow"
in the Table below) or 1.156 inches (2.936 cm) (designated "Wide" in the Table
below)
and a substantially vertical center-to-center spacing Dv of about 1.875 inches
(4.763 cm).
One tested coil assembly had no fins 20 on the segments (Test ID "A" in the
Table below
and the graph of Fig. 12) and represented a base line against which other
finned coil
assemblies were compared. Other tested coil assemblies identified in the Table
below
and the graph of Fig. 12 had spiral fins 20 with the parameters of fin spacing
and height
as described and claimed herein, and some had spiral fins 20 but not having
the
parameters of fin spacing and height as described and claimed herein. All of
the coil
assemblies including fins used fins of the same thickness, namely, 0.013 inch
(0.033 cm),
which is within the range of fin thickness described and claimed herein.
Certain other
coil assemblies, namely, those having the parameters associated with the Test
ID "B" and
"C" (tested in a different rig) and Test ID "D" (tested using 5 HP motor) in
the Table
below and the graph of Fig. 12, were tested in a different manner, but the
performance
data presented in the graph of Fig. 12 were derived using industry
calculations for
standardizing performance data from apparatus of different configurations. The
performance of the coil assemblies was tested over varying water flow rates
internally
through the coils of 60 gpm to 360 gpm, water flow rates externally through
the coils of
approximately 5.9 gpm per square foot, and air flow rates of 300 feet per
minute (91.44
meters per minute) to 750 feet per minute (228.6 meters per minute), generated
by a fan
33
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
driven by a 3 HP motor (except as noted above regarding Test ID "C"). The coil
assemblies tested had the parameters as set forth in the following Table:
Test ID Major Axes Dll Tube Fins Fin Spacing Fin Height
Orientation Spacing (Fins/Inch) (Inch)
A 20 & 3400 Wide No
Ric-rac
00 Wide Yes 3 0.25
20 & 340 Wide Yes 1.5 0.3125
Ric-rac
0 Narrow Yes 3
0.3125
20 & 340 Wide Yes 3 0.3125
Ric-rac
0 Wide Yes 3
0.3125
20 & 340 Wide Yes 1.5 0.5
Ric-rac
20 & 340 Wide Yes 3 0.5
Ric-rac
[0093] Fig. 12 is a graph of results of testing of the coil assemblies
identified in the
Table in the evaporative heat exchanger under the same conditions set forth in
the
procedure described above, with respect to preferred internal process fluid
(water) flow
rates from 6 to 9.8 gpm per tube (where each tube is identified as a "circuit"
in the x-axis
legend on the graph. The graph show curves based on the heat transferred as
measured in
thousands of BTU/hour (MBH) versus the water flow internally through the coil
assembly in gallons/minute/tube (GPM). Each curve A to H in Fig. 12
corresponds to the
respective coil assembly A to H of the above Table.
[0094] With reference to Fig. 12, the baseline performance of Curve A
relates to coil
assembly A, with a 20 to 340 ric-rac major axes segment orientation and no
fins.
Curves B to F above Curve A indicate that at the indicated internal water flow
rate along
the X-axis, such curves have a better thermal performance than the baseline
performance,
with increasingly better thermal performance from Curve B to Curve F.
[0095] Test ID "G" and "H" with a 20 - 340 ric-rac major axes
orientation,
respective fin spacing of 1.5 and 3 fins/inch (2.54 cm) and fin height of 0.5
inch
34
CA 02805373 2013-01-11
WO 2012/009221
PCT/US2011/043351
(1.27 cm) (outside the fin height parameter of the present invention) had
consistently
lower thermal performance (MBH) as indicated by Curves G and H, respectively.
[0096] In general, the test results show that an orientation of the
major axes of the
generally elliptical finned segments in a generally vertical direction (00)
provides better
thermal performance than a ric-rac orientation of the major axes for tubes
having the
same fin height and fin spacing. Nevertheless arranging the major segments in
a ric-rac
orientation still provides a very considerable increase in thermal performance
of a coil
assembly having all of the other parameters within the scope of the present
invention.
For tubes having the same angle of orientation, namely a ric-rac or generally
vertical
orientation of the generally elliptical segments, fins having a height of
0.3125 inch
(0.794 cm) provided the better thermal performance. For tubes having the same
orientation angle of their major axes and fin height, less spacing within the
parameters of
the present invention provide better thermal performance.
[0097] The practical effect of the results shown in Fig. 12 is that
coil as emblies
made using the finned tubes of the present invention, having the combination
of factors
of tube shape, orientation, arrangement and spacing, and fin spacing, height
and
thickness, all of which must be carefully balanced, provide a dramatic
increase in thermal
capacity and performance compared to other coil assemblies having the same
footprint
(plan area). Thus, based on the present invention, among the other benefits
and
advantages described above, a significantly more cost-effective coil assembly
can be
produced by providing a smaller coil assembly that results in the same heat
capacity
demand. This is important not only for increased initial commercial sales, but
also for
later more cost-effective operation of evaporative heat exchange apparatus
using the coil
assemblies of the present invention. For coil assemblies of the same plan
area, the graph
of Fig. 12 very significantly shows enhanced thermal performance, for the
embodiments
tested and the results shown in Fig. 12, up to about an 18.3% increase in MBH,
comparing the results of Curve F to the baseline Curve A, as measured at a
rate of flow of
internal process fluid (water) of 8 gpm per tube (calculated as 504-426 =
78/426 x 100 =
18.3%).
[0098] It will be appreciated by those skilled in the art that changes
could be made to
the embodiments described above without departing from the broad inventive
concept
CA 02805373 2014-11-24
= thereof. It is understood, therefore, that this invention is not limited
to the particular
embodiments disclosed, but it is intended to cover modifications within the
scope of the present invention as defined by the appended claims.
36
