U.S. patent application number 16/722199 was filed with the patent office on 2020-09-24 for evaporative heat exchange apparatus with finned elliptical tube coil assembly.
The applicant listed for this patent is Evapco, Inc.. Invention is credited to Thomas William BUGLER, III, Davey Joe VADDER.
Application Number | 20200300548 16/722199 |
Document ID | / |
Family ID | 1000004882070 |
Filed Date | 2020-09-24 |
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United States Patent
Application |
20200300548 |
Kind Code |
A1 |
BUGLER, III; Thomas William ;
et al. |
September 24, 2020 |
EVAPORATIVE HEAT EXCHANGE APPARATUS WITH FINNED ELLIPTICAL TUBE
COIL ASSEMBLY
Abstract
An improved finned coil tube assembly enhances evaporative heat
exchanger performance, and includes tubes, preferably serpentine
tubes, in the coil assembly. The tubes have a generally elliptical
cross-section with external fins formed on an outer surface of the
tubes. The fins are spaced substantially 1.5 to substantially 3.5
fins per inch (2.54 cm) along the longitudinal axis of the tubes,
extend substantially 23.8% to substantially 36% of the nominal tube
outside diameter in height from the tubes outer surface and have a
thickness of substantially 0.007 inch (0.018 cm) to substantially
0.020 inch (0.051 cm). The tubes have a center-to-center spacing
generally horizontally and normal to the longitudinal axis of the
tubes of substantially 109% to substantially 125% of the nominal
tube outside diameter, and a generally vertical center-to-center
spacing of substantially 100% to about 131% of the nominal tube
outside diameter.
Inventors: |
BUGLER, III; Thomas William;
(Frederick, MD) ; VADDER; Davey Joe; (Manchester,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Evapco, Inc. |
Taneytown |
MD |
US |
|
|
Family ID: |
1000004882070 |
Appl. No.: |
16/722199 |
Filed: |
December 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15622729 |
Jun 14, 2017 |
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16722199 |
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12838003 |
Jul 16, 2010 |
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15622729 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 1/02 20130101; F28F
1/30 20130101; F28D 5/02 20130101; F28F 1/36 20130101 |
International
Class: |
F28D 5/02 20060101
F28D005/02; F28F 1/02 20060101 F28F001/02; F28F 1/30 20060101
F28F001/30; F28F 1/36 20060101 F28F001/36 |
Claims
1-37. (canceled)
38. An evaporative indirect heat exchanger comprising: a plenum
having a generally vertical axis, a coil assembly, a distributor
for distributing an external heat exchange liquid onto a coil
assembly, an air mover for causing air to flow in a direction
through the plenum, and said coil assembly mounted within the
plenum such that the external heat exchange liquid flows externally
through the coil assembly in a generally downward vertical flow
direction, and the air flows externally through the coil assembly
interacting with the external heat exchange liquid to evaporate and
cool the external heat exchange liquid and internal process fluid
within the coil assembly, wherein the coil assembly comprises inlet
and outlet manifolds and a plurality of tubes connecting the
manifolds, each tube comprising a plurality of horizontally
oriented segments arranged vertically relative to one-another in a
single vertical plane, wherein each segment has 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, and
where the major axis of each segment of a tube is aligned with the
single vertical plane, wherein the tubes are arranged in the coil
assembly in a staggered arrangement of a first and second set of
alternating tubes in which each tube in said first set of tubes is
fixed in the coil assembly at a first vertical position, and each
of said second set of alternating tubes is fixed in the coil
assembly at a second vertical position which is displaced from said
first vertical position, wherein the tubes are serpentine tubes
having a plurality of segments and a plurality of return bends,
wherein the return bends are 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, and wherein all segments in said plurality of
segments for each serpentine tube are vertically aligned with
one-another, wherein the tubes have external elliptical spiral fins
on an outer surface of the tubes, wherein the fins have: a spacing
of 1.5 to 3.5 fins per inch (2.54 cm) along the longitudinal axis
of the tubes, 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, and a thickness of substantially
0.007 inch (0.018 cm) to substantially 0.020 inch (0.051 cm),
wherein each of the tubes of said first or second set of
alternating tubes is horizontally spaced, center-to-center, from an
adjacent tube in a same set of alternating tubes by a distance (DH)
that is substantially 100% to substantially 131% of the nominal
tube outside diameter, and wherein each of the tubes in said first
set of tubes is vertically displaced, center-to-center, relative to
adjacent tubes in said second set of tubes by a distance (DV) that
is substantially 110% to substantially 300% of the nominal tube
outside diameter.
39. An evaporative heat exchanger according to claim 38, wherein
the fins have a spacing of substantially 2.75 to substantially 3.25
fins per inch (2.54 cm) along the longitudinal axis of the
tubes.
40. An evaporative heat exchanger according to claim 39, wherein
the fins have a spacing of substantially 3 fins per inch (2.54 cm)
along the longitudinal axis of the tubes.
41. An evaporative heat exchanger according to claim 38, wherein
each of the tubes of said first or second set of alternating tubes
is horizontally spaced, center-to-center, from an adjacent tube in
a same set of alternating tubes by a distance (DH) that is
substantially 106% to substantially 118% of the nominal tube
outside diameter.
42. An evaporative heat exchanger according to claim 41, wherein
each of the tubes of said first or second set of alternating tubes
is horizontally spaced, center-to-center, from an adjacent tube in
a same set of alternating tubes by a distance (DH) that is
substantially 112% of the nominal tube outside diameter.
43. An evaporative heat exchanger according to claim 38, wherein
each of the tubes in said first set of tubes is vertically
displaced, center-to-center, relative to adjacent tubes in said
second set of tubes by a distance (DV) that is substantially 150%
to substantially 205% of the nominal tube outside diameter.
44. An evaporative heat exchanger according to claim 43, wherein
each of the tubes in said first set of tubes is vertically
displaced, center-to-center, relative to adjacent tubes in said
second set of tubes by a distance (DV) that is substantially 179%
of the nominal tube outside diameter.
45. An evaporative heat exchanger according to claim 38, wherein
the nominal tube outside diameter is substantially 1.05 inches
(2.67 cm).
46. An evaporative heat exchanger according to claim 38, wherein
the fins have a spacing of substantially 2.75 to substantially 3.25
fins per inch (2.54 cm) along the longitudinal axis of the tubes, a
height of substantially 28% to substantially 33% of the nominal
tube outside diameter, a thickness of substantially 0.009 inch
(0.023 cm) to substantially 0.015 inch (0.038 cm), wherein each of
the tubes of said first or second set of alternating tubes is
horizontally spaced, center-to-center, from an adjacent tube in a
same set of alternating tubes by a distance (DH) that is
substantially 106% to substantially 118% of the nominal tube
outside diameter, and wherein each of the tubes in said first set
of tubes is vertically displaced, center-to-center, relative to
adjacent tubes in said second set of tubes by a distance (DV) that
is substantially 150% to substantially 205% of the nominal tube
outside diameter.
47. An evaporative heat exchanger according to claim 46, wherein
the nominal tube outside diameter is substantially 1.05 inches
(2.67 cm).
48. An evaporative heat exchanger according to claim 38, wherein
the fins have a spacing of substantially 3 fins per inch (2.54 cm)
along the longitudinal axis of the tubes, a height of substantially
29.76% of the nominal tube outside diameter, a thickness of
substantially 0.01 inch (0.025 cm) to substantially 0.013 inch
(0.033 cm), and wherein each of the tubes of said first or second
set of alternating tubes is horizontally spaced, center-to-center,
from an adjacent tube in a same set of alternating tubes by a
distance (DH) that is about 112% of the nominal tube outside
diameter, and wherein each of the tubes in said first set of tubes
is vertically displaced, center-to-center, relative to adjacent
tubes in said second set of tubes by a distance (DV) that is about
179% of the nominal tube outside diameter.
49. An evaporative heat exchanger according to claim 48, wherein
the nominal tube outside diameter is substantially 1.05 inches
(2.67 cm).
50. An evaporative heat exchanger according to claim 38, wherein
the nominal tube outside diameter is substantially 1.05 inches
(2.67 cm), wherein the fins have a center-to-center spacing of
substantially 0.286 inch (0.726 cm) to substantially 0.667 inch
(1.694 cm), a height of substantially 0.25 inch (0.635 cm) to
substantially 0.375 inch (0.953 cm), and wherein each of the tubes
of said first or second set of alternating tubes is horizontally
spaced, center-to-center, from an adjacent tube in a same set of
alternating tubes by a distance (DH) that is substantially 1.05
inches (2.67 cm) to substantially 1.38 inches (3.51 cm), and
wherein each of the tubes in said first set of tubes is vertically
displaced, center-to-center, relative to adjacent tubes in said
second set of tubes by a distance (DV) that is substantially 1.15
inches (2.92 cm) to substantially 3.15 inches (8.00 cm).
51. An evaporative heat exchanger according to claim 50, wherein
the fins have a center-to-center spacing of substantially 0.308
inch (0.782 cm) to substantially 0.364 inch (0.925 cm), a height of
substantially 0.294 inch (0.747 cm) to substantially 0.347 inch
(0.881 cm), a thickness of substantially 0.009 inch (0.023 cm) to
substantially 0.015 inch (0.038 cm), and wherein each of the tubes
in said first set of tubes is vertically displaced,
center-to-center, relative to adjacent tubes in said second set of
tubes by a distance (DV) that is substantially 1.57 inches (3.99
cm) to about 2.15 inches (5.46 cm).
52. An evaporative heat exchanger according to claim 51, wherein
the fins have a center-to-center spacing of substantially 0.333
inch (0.846 cm), a height of substantially 0.3125 inch (0.794 cm),
a thickness of substantially 0.01 inch (0.025 cm) to substantially
0.013 inch (0.033 cm), and wherein each of the tubes of said first
or second set of alternating tubes is horizontally spaced,
center-to-center, from an adjacent tube in a same set of
alternating tubes by a distance (DH) that is substantially 1.175
inches (2.985 cm), and wherein each of the tubes in said first set
of tubes is vertically displaced, center-to-center, relative to
adjacent tubes in said second set of tubes by a distance (DV) that
is substantially 1.88 inches (4.78 cm).
53. An evaporative heat exchanger according to claim 38, wherein
the major axes of the tubes are generally parallel to the vertical
axis of the plenum.
54. An evaporative heat exchanger according to claim 38, wherein
the return bends have a circular cross-section with an outside
diameter of substantially 1.05 inches (2.67 cm) and wherein the
nominal tube outside diameter is substantially 1.05 inches (2.67
cm).
55. An evaporative heat exchanger according to claim 38, wherein
the return bends have a generally elliptical cross-section and the
nominal tube outside diameter of substantially 1.05 inches (2.67
cm).
56. An evaporative heat exchanger according to claim 38, wherein
the major axes of the segments are generally parallel to the plane
of the return bends.
57. An evaporative heat exchanger according to claim 38, the fins
having a spacing of substantially 2.75 to substantially 3.25 fins
per inch (2.54 cm) along the longitudinal axis of the segments, the
fins having a height of substantially 28% to substantially 33% of
the nominal tube outside diameter, the fins having a thickness of
substantially 0.009 inch (0.023 cm) to substantially 0.015 inch
(0.038 cm), wherein each of the tubes of said first or second set
of alternating tubes is horizontally spaced, center-to-center, from
an adjacent tube in a same set of alternating tubes by a distance
(DH) that is substantially 106% to substantially 118% of the
nominal tube outside diameter, and wherein each of the tubes in
said first set of tubes is vertically displaced, center-to-center,
relative to each of said tubes in said second set of tubes by a
distance (DV) that is 150% to substantially 205% of the nominal
tube outside diameter.
58. An evaporative heat exchanger according to claim 38, the fins
having a spacing of substantially 3 fins per inch (2.54 cm) along
the longitudinal axis of the segments, the fins having a height of
substantially 29.76% of the nominal tube outside diameter, the fins
having a thickness of substantially 0.01 inch (0.025 cm) to
substantially 0.013 inch (0.033 cm), wherein each of the tubes of
said first or second set of alternating tubes is horizontally
spaced, center-to-center, from an adjacent tube in a same set of
alternating tubes by a distance (DH) that is substantially 112% of
the nominal tube outside diameter, and wherein each of the tubes in
said first set of tubes is vertically displaced, center-to-center,
relative to each of said tubes in said second set of tubes by a
distance (DV) that is substantially 179% of the nominal tube
outside diameter.
Description
BACKGROUND OF THE INVENTION
[0001] 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 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 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.
Pat. Nos. 4,755,331 and 7,296,620, the disclosures of which are
hereby incorporated herein in their entireties, 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. Pat. Nos. 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. 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
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 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.
[0015] 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.RTM. 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 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.
[0021] 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 90.degree. with
respect to "generally normal" and a few degrees more or less than
exactly perfectly parallel or 0.degree. with respect to "generally
parallel," where such variations do not materially adversely affect
the function of the apparatus.
[0022] 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.
[0023] 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.
[0024] 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.
BRIEF SUMMARY OF THE INVENTION
[0025] 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.
[0026] 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 center-to-center spacing of substantially 110%
to substantially 300% of the nominal tube outside diameter.
[0027] 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.
[0028] 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.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0029] 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.
[0030] 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.
[0031] 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."
[0032] FIG. 3 is a vertical cross-section view taken along lines
3-3 of the embodiment of FIG. 2.
[0033] 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 90.degree. into the plane of the drawing
sheet.
[0034] 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.
[0035] 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.
[0036] FIG. 6 is an isometric view of one embodiment of an
exemplary coil assembly made using the finned tubes of the present
invention.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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
[0046] 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.
[0047] 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.
[0048] 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 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.
[0049] 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
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.
[0050] 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.
[0051] 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 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.
[0052] 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 25 (not shown) and fluidly connect directly at respective
opposite ends to an inlet 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 described inlet 30 would be an outlet and the
described outlet 34 would be the inlet.
[0053] 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 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 filmed 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 10 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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 L1A and L1B 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 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.
[0058] 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 L1A or a lower horizontal level, such as
the next adjacent generally horizontal level L2A.
[0059] 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.degree. 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.degree.
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.
[0060] Thus, as represented in FIGS. 5A and 5B, the major axes of
the finned segments 12A or 12B on a first generally horizontal
level L1A or L1B, respectively, may be 0.degree. to about
25.degree. 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.degree. to 360.degree. from the
plane of 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.
[0061] 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.
[0062] 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 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.
[0063] 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.
[0064] 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 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.
[0065] 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.
[0066] 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 D.sub.H 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 D.sub.V generally is
not as critical to the performance of an evaporative heat exchanger
as the horizontal tube or segment spacing D.sub.H. 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 D.sub.V between the upper generally horizontal levels L1A
and L1B and the lower generally horizontal levels L2A and L2B,
respectively.
[0067] 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
D.sub.H 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
would have a generally vertical center-to-center spacing D.sub.V 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.degree. to about
25.degree., and preferably about 20.degree., 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.degree. to less than
360.degree., and preferably about 340.degree. 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.
[0068] 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.
[0069] 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).
[0070] 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 0.294 inch (0.747 cm) to substantially 0.347 inch
(0.881 cm), and more preferably 0.3125 inch (0.794 cm).
[0071] 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.
[0072] The coil assembly 24 of any desired configuration, such as
shown in any of FIG. 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. Pat. No. 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.
[0073] 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 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.
[0074] 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.
[0075] 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 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.
[0076] 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. Pat. No. 6,315,804, the
disclosure of which is hereby incorporated by reference herein in
its entirety.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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 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.
[0081] 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 fill 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.RTM. PVC fill, disclosed in Evapco, Inc.'s U.S. Pat. No.
5,124,087, the disclosure of which is hereby incorporated by
reference herein, in its entirety. When wet deck fill 64 is used,
it may be located above the coil assembly 24B as shown in FIG. 9,
or below the coil assembly 24C as shown in FIG. 10, since in 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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 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.
[0086] 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.
[0087] 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.
[0088] 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 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. Pat. No. 6,598,862, the disclosure of which is hereby
incorporated by reference herein, in its entirety, 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.
[0089] 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).
[0090] 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
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.
[0091] 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.
[0092] 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.
[0093] 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,
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 D.sub.H 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 D.sub.V 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 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:
TABLE-US-00001 Major Axes D.sub.H Tube Fin Spacing Fin Height Test
ID Orientation Spacing Fins (Fins/Inch) (Inch) A 20.degree. &
340.degree. Wide No -- -- Ric-rac B 0.degree. Wide Yes 3 0.25 C
20.degree. & 340.degree. Wide Yes 1.5 0.3125 Ric-rac D
0.degree. Narrow Yes 3 0.3125 E 20.degree. & 340.degree. Wide
Yes 3 0.3125 Ric-rac F 0.degree. Wide Yes 3 0.3125 G 20.degree.
& 340.degree. Wide Yes 1.5 0.5 Ric-rac H 20.degree. &
340.degree. Wide Yes 3 0.5 Ric-rac
[0094] 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.
[0095] With reference to FIG. 12, the baseline performance of Curve
A relates to coil assembly A, with a 20.degree. to 340.degree.
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.
[0096] Test ID "G" and "H" with a 20.degree.-340.degree. 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 (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.
[0097] In general, the test results show that an orientation of the
major axes of the generally elliptical finned segments in a
generally vertical direction (0.degree.) 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.
[0098] The practical effect of the results shown in FIG. 12 is that
coil assemblies 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.times.100=18.3%).
[0099] 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 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 spirit and scope of the present invention
as defined by the appended claims.
* * * * *