U.S. patent application number 14/957821 was filed with the patent office on 2016-03-24 for heat exchanger perforated fins.
This patent application is currently assigned to AIR PRODUCTS AND CHEMICALS, INC.. The applicant listed for this patent is AIR PRODUCTS AND CHEMICALS, INC.. Invention is credited to Vladimir Yliy Gershtein, Patrick Alan Houghton, George Amir Meski, Swaminathan Sunder.
Application Number | 20160084589 14/957821 |
Document ID | / |
Family ID | 55525450 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160084589 |
Kind Code |
A1 |
Sunder; Swaminathan ; et
al. |
March 24, 2016 |
Heat Exchanger Perforated Fins
Abstract
A plate fin heat exchanger comprises a folded fin sheet
comprising fins wherein the fin sheet comprises a plurality of
perforations, such plurality of perforations are positioned on the
fin sheet in parallel rows when such fin sheet is in an unfolded
state, such parallel rows of perforations on the fin sheet comprise
a first spacing between the parallel rows of perforations (S1), a
second spacing between sequential perforations within the parallel
row of perforations (S2), a third spacing (or offset) between the
perforations in adjacent parallel rows of perforations (S3), and a
perforation diameter (D), wherein the ratio of the first spacing
between the parallel rows of perforations to the perforation
diameter (S1/D) is in the range of 0.75 to 2.0, and wherein the
angle between the fins and the parallel rows of perforations is
less than or equal to five degrees (.ltoreq.5.degree.).
Inventors: |
Sunder; Swaminathan;
(Allentown, PA) ; Gershtein; Vladimir Yliy;
(Allentown, PA) ; Meski; George Amir; (Allentown,
PA) ; Houghton; Patrick Alan; (Emmaus, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AIR PRODUCTS AND CHEMICALS, INC. |
Allentown |
PA |
US |
|
|
Assignee: |
AIR PRODUCTS AND CHEMICALS,
INC.
Allentown
PA
|
Family ID: |
55525450 |
Appl. No.: |
14/957821 |
Filed: |
December 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13823147 |
Mar 14, 2013 |
|
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14957821 |
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Current U.S.
Class: |
62/643 ;
165/185 |
Current CPC
Class: |
F28F 13/12 20130101;
F28F 3/027 20130101; F25J 5/002 20130101 |
International
Class: |
F28F 3/02 20060101
F28F003/02; F25J 5/00 20060101 F25J005/00 |
Claims
1. A plate fin heat exchanger, comprising: a folded fin sheet
comprising fins having a height, a width, and a length, the folded
fin sheet being positioned between a first parting sheet and a
second parting sheet; and a first side bar and a second side bar,
wherein the first side bar is positioned between the first parting
sheet and the second parting sheet and adjacent to a first side of
the folded fin sheet, and wherein the second side bar is positioned
between the first parting sheet and the second parting and adjacent
to a second side of the folded fin sheet thereby forming at least a
part of a plate fin passage; wherein the fin sheet comprises a
plurality of perforations, such plurality of perforations are
positioned on the fin sheet in parallel rows when such fin sheet is
in an unfolded state, such parallel rows of perforations on the fin
sheet comprise a first spacing between the parallel rows of
perforations (S1), a second spacing between sequential perforations
within the parallel row of perforations (S2), a third spacing (or
offset) between the perforations in adjacent parallel rows of
perforations (S3), and a perforation diameter (D), wherein the
ratio of the first spacing between the parallel rows of
perforations to the perforation diameter (S1/D) is in the range of
0.75 to 2.0, and wherein the angle between the fins and the
parallel rows of perforations is less than or equal to five degrees
(.ltoreq.5.degree.); wherein the adjacent parallel rows of
perforations are offset such that the position of the parallel rows
of perforations on the fins of the folded fin sheet repeat exactly
at least once every 10 fin wavelengths and more preferably at least
once every 5 fin wavelengths, in at least 50% of the heat exchanger
plate fin passages containing such perforated fins, more preferably
in at least 80% of the plate fin passages and most preferably in
100% of the plate fin passages.
2. The plate fin heat exchanger of claim 1, wherein the angle
between the fins and the parallel rows of perforations is zero
degrees (0.degree.).
3. The plate fin heat exchanger of claim 1, wherein the ratio of
the first spacing between the parallel rows of perforations to the
perforation diameter (S1/D) is in the range of 0.75 to 1.0.
4. The plate fin heat exchanger of claim 1, wherein the ratio of
the third spacing (or offset) between perforations in adjacent
parallel rows of perforations (S3) and the second spacing between
sequential perforations within the parallel row of perforations
(S2) is in the range of 0.25 to 0.75.
5. The plate fin heat exchanger of claim 1, wherein 5% to 25% of
the area of the folded fin sheet in the unfolded state is occupied
by the perforations.
6. The plate fin heat exchanger of claim 1, wherein the perforation
diameter (D) is in the range of 1 mm to 4 mm.
7. The plate fin heat exchanger of claim 1, wherein the
perforations are circular.
8. The plate fin heat exchanger of claim 1, wherein the
perforations are in the shape of ellipses, rectangles, or
parallelograms.
9. The plate fin heat exchanger of claim 1, wherein the adjacent
parallel rows of perforations are offset in alternating fashion
such that the position of the parallel rows of perforations repeats
every other row of perforations.
10. (canceled)
11. The plate fin heat exchanger of claim 1, wherein the folded fin
sheet comprises a surface texture.
12. The plate fin heat exchanger of claim 1, wherein the fin height
is in the range of 0.25 inches to 1 inch, more preferably in the
range of 0.4 inches to 0.75 inches, and most preferably in the
range of 0.5 inches to 0.6 inches.
13. The plate fin heat exchanger of claim 1, wherein the folded fin
sheet is an easyway heat transfer fin or distributor fin.
14. The plate fin heat exchanger of claim 1, wherein the plate-fin
passages are adapted to accept a fluid stream, and wherein the
fluid stream undergoes heat transfer without phase change over at
least 80%, more preferably over at least 90%, and most preferably
over 100% of the length of the plate-fin passages.
15. A process for exchanging heat between at least two streams in a
plate fin heat exchanger constructed in accordance with claim 1,
wherein at least one stream undergoes heat transfer without phase
change over at least 80% of the length of the plate-fin passages,
and wherein the Reynolds Number of the at least one stream is in
the range of 800 to 100,000 and more preferably in the range of
1,000 to 10,000.
16. A process for separating nitrogen, oxygen and/or argon from air
by cryogenic distillation, which utilizes the plate fin heat
exchanger of claim 1, wherein at least one stream undergoes heat
transfer without phase change over at least 80% of the length of
the plate-fin passages, more preferably over at least 90% of the
length of the plate-fin passages, and most preferably over 100% of
the length of plate-fin passages.
17.-18. (canceled)
Description
BACKGROUND
[0001] Plate fin heat exchangers are generally used for exchanging
heat between process streams for the purpose of heating, cooling,
boiling, evaporating, or condensing the process streams. The
process conditions in these heat exchangers may involve single
phase or two phase flow and heat transfer. While some plate fin
exchangers contain only two streams, others contain multiple
streams in multiple sets of plate fin passages. Individual streams
may be fed into and withdrawn from the heat exchanger using nozzles
and headers. Each stream flows into specific plate-fin passages
allocated within the bank of adjacent plate-fin passages. The
individual plate-fin passages are contained between pairs of
parting sheets, which are spaced apart by the fins and the
plate-fin passages are enclosed on the outer periphery by sidebars
and endbars so they can be isolated from each other and can contain
the fluids of interest. When streams at different temperatures flow
in the plate-fin passages that are adjacent to each other, they
exchange heat through the parting sheets which are referred to as
primary heat transfer surfaces as well as the fin legs that
separate them, which are referred to as secondary heat transfer
surfaces.
[0002] Plate fin exchangers may be formed by using many different
types of fins such as plain, perforated, serrated and wavy. One
embodiment of the current invention deals with perforated fins
which have been employed in the industry, but in an inefficient
manner. The plate fin heat exchangers having perforated fins,
according to the present invention, have particular application in
cryogenic processes such as air separation, although these plate
fin heat exchangers may be used in other heat transfer
processes.
[0003] When a stream or fluid enters a plate fin heat exchanger
channel it exhibits high heat transfer coefficients due to the
well-known entrance effect. Post entrance effect, the stream or
fluid will soon reach a steady state condition with a much lower
heat transfer coefficient. In particular when the flow is
characterized as being in a turbulent state or in a transition
state between laminar and turbulent states, laminar and viscous
boundary layers are known to form adjacent to all the surfaces that
the fluid flows along. The overall effect is to lower the average
heat transfer coefficients in such an exchanger. The lower heat
transfer coefficient condition can be at least partially reversed
by periodically disturbing this boundary layer through a variety of
means such as, for example, introduction of perforations or
serrations in the fins. Introduction of perforations or serrations
in the fins will increase the heat transfer performance, however,
such introduction will also increase pressure losses and,
therefore, the geometry and arrangement of the perforations or
serrations in the fins is critical for achieving improved
performance. It is particularly important in the case of perforated
fins because while they disturb the flow leading to an increase in
the local heat transfer coefficient proximate to the perforations,
introduction of perforations in the fins also results in a loss of
surface area from the original material which would otherwise have
been beneficial for the overall heat transfer from the heat
exchanger. Also removal of metal, for example, in the form of
perforations can greatly reduce the strength of the remaining
material. Thus, the problem of improving the performance of plate
fin heat exchangers by using perforated fins is complicated and it
is particularly important to organize the geometry and arrangements
of using such perforations to achieve improved performance.
[0004] Historically, publications concerning plate fin heat
exchangers provided general descriptions of the overall geometry
and the elementary methods for the manufacture of plate fin heat
exchangers. While these publications discuss the many constituent
parts of plate fin heat exchangers, their relationship to one
another, and how they are assembled and brazed together, the
publications are brief in their description of the perforated fins
that may be utilized in such plate fin heat exchangers. Even in
cases where some nominal details are disclosed, the publications
simply fail to discuss any preferred geometry and patterns to
use.
[0005] For example, in "Aluminum Brazed Plate Fin Heat Exchangers
for Process Industries," a chapter of Compact Heat Exchangers for
the Process Industries, edited by R. K. Shah, proceedings of the
International Conference for the Process Industries, held at Cliff
Lodge and Conference Center, Snowbird, Utah, Jun. 22-27, 1997, by
Shozo Hotta from Sumitomo Precision Products (SPP), a general
description of plate fin heat exchangers by SPP, a major supplier
of such heat exchangers, is disclosed. Specifically, FIG. 4 on page
181 of such reference provides photographic evidence of the common
fin types including perforated fins. As described and taught
therein, the perforated fins are formed by folding a sheet with
regularly perforated small round apertures or perforations at some
large angle relative to a major axis of perforations on the flat
sheet. No further details, however, are presented.
[0006] This method of manufacture is very common in the industry to
minimize the overall cost. A few standard perforated sheet
materials may be used to produce a wide range of finished fins with
varying dimensions. This type of method of manufacture of
perforated fins, however, leads to an irregular arrangement of the
perforations on the fins resulting in poor performance of the
perforated fins.
[0007] U.S. Pat. No. 6,834,515 B2, entitled "Plate Fin Exchangers
with Textured Surfaces," to Sunder et al., also discloses various
perforated fins. The Sunder patent teaches use of surface texture
to enhance the performance of other perforated fins. FIG. 2B of the
Sunder patent illustrates exemplary fins with a row of perforations
along the top and sides of the fins where the perforations are
laterally aligned. Example 1 of the Sunder patent states that the
perforated fins have an open area of about 10%. No other details,
however, are provided regarding the perforations.
[0008] U.S. Pat. No. 5,603,376, entitled "Heat Exchanger for
Electronics Cabinet," to Hendrix, describes a heat exchanger for
passive heat exchange between a weather-tight, sealed electronics
cabinet, and the outside environment. FIG. 2 of the Hendrix patent
shows heat generation side fins 21 with perforations 25 contained
therein. The Hendrix patent teaches that fins 21 are formed by
pleating or folding perforated sheet material. The perforations are
said to be perpendicular to the direction of the folds. FIG. 2 of
the Hendrix patent illustrates that the perforations are a single
row of perforations along the sides of fins 21, however, no
perforations are shown on the underside where the valleys or crests
of the waves would form. Further, the Hendrix patent provides no
teaching regarding the position of the perforations.
[0009] In "Three-dimensional numerical simulation on the laminar
flow and heat transfer in four basic fins of plate-fin heat
exchangers", by Y. Zhu and Y. Li, Journal of Heat Transfer,
November 2008, vol. 130, 111801-1 to 8, a Computational Fluid
Dynamics (CFD) based calculation is performed concerning the
performance of four samples (plain, perforated, strip offset (which
is another term for serrated) and wavy fins) is disclosed. The Zhu
and Li paper lists many major publications on compact heat
exchangers that have appeared since they were first introduced, and
goes on to state that, "[t]o the best of the authors' knowledge,
complete three-dimensional flow and heat transfer in the perforated
fins have received scant attention in literature."
[0010] Such statement is significant and appears to support and
lead to the conclusion of Applicants, namely that what is known in
the art concerning perforated fins is suboptimal.
[0011] As part of comparing the four types of fins, the authors of
the Zhu and Li paper conducted CFD calculations on one specific
exemplary perforated fin geometry. To keep the computation size and
time reasonable, the authors only included a minimum repeating
structure as illustrated in FIGS. 2a and 2b on page 2 of the paper.
The cross section modeled for the perforated fin represents one
half of a wavelength of a fin, which includes a half each of the
top and bottom fin lengths and one full fin height. These in turn
include a series of half perforations on the top and bottom and a
series of full perforations on the fin height all along the flow
length. The full structure, also as illustrated in FIG. 1D,
corresponds to exactly one row of perforations along the top,
bottom, and side of each fin channel along the flow length, all of
which are laterally aligned. The diameter of the perforations is
0.8 mm as illustrated in Table 1 and the spacing of the
perforations along the fins appears to be approximately 1.4 mm from
center to center as can be inferred from FIGS. 6C and 7C. This
frequency of perforations represents approximately 16% open area on
only the sides of the plate fin passages (i.e., the Zhu and Li
paper does not count or consider the perforations on the top or the
bottom of the fins for determining open area because fins
perforations on the top and bottom of the fins are covered by the
parting sheets). This open area determination is illustrated in
Table 1 under the column on specifications. Such a pattern would
work out to approximately 20% open area on the flat perforated
sheet prior to its being formed into fins. It appears that this
geometry represents a typical case the authors chose to model with
no indication or teaching as to what they might consider preferred
in terms of perforation patterns and geometry.
[0012] Thus, the one specific exemplary perforated fin geometry
described above is merely a representative perforated fin that the
authors used to compare against the four types of fins (plain,
perforated, strip offset and wavy types). The pattern and geometry
the authors modeled are different from those taught under the
current application.
[0013] In summary, prior descriptions concerning perforated fins
were brief in the details concerning the geometry of the perforated
fins used in plate fin exchangers. And even when aspects of the
geometry such as open area were cited, there is no teaching on how
to position the perforations or how to select the best geometry for
the perforations to obtain the best performance so that the overall
capital and operating costs of the plate fin heat exchangers may be
minimized.
[0014] It is desired to increase the efficiency and improve the
performance of plate-fin heat exchangers.
[0015] It is further desired to improve the turbulence
characteristics of a single phase stream within the plate-fin
passages of a plate-fin exchanger in order to improve the heat
transfer efficiency.
[0016] It is still further desired to have a plate-fin exchanger
that exhibits high performance characteristics for cryogenic
applications, such as those used in air separation, and for other
heat transfer applications.
[0017] It is still further desired to have a more efficient air
separation process utilizing a plate-fin exchanger which is more
compact and/or more efficient than previously disclosed.
[0018] It is still further desired to have a plate-fin exchanger
design which minimizes the size, weight, and/or cost of the heat
exchangers, which would result in an air separation process more
efficient and/or less expensive per unit quantity of product
produced.
[0019] It also is further desired to have a method for assembling a
plate-fin heat exchanger which uses fins with perforation patterns
and geometry that affords better performance than the fins
previously disclosed, and which overcomes the disadvantages of the
fins previously disclosed to provide better and more advantageous
results.
SUMMARY
[0020] The disclosed embodiments satisfy the need in the art by
providing novel patterns and novel geometry of fin perforations for
use in plate fin heat exchangers to maximize the overall heat
transfer performance within the allowable pressure drop
constraints. The benefits of such novel patterns and novel geometry
of fin perforations over previously disclosed fin patterns and
geometry include: (1) a significant reduction in the volume; (2) a
significant increase in heat transfer efficiency; (3) a significant
reduction in pressure drop losses; or (4) some judicious
combination of factors (1) to (3) such that the overall capital and
operating cost of the heat exchanger system is reduced, thereby
also reducing the capital and operating cost of the process that
utilizes such a heat exchanger system.
[0021] While the disclosed embodiments contained herein are mainly
aimed at easyway fins, wherein the flow is largely parallel to the
fin flow channels, the teachings may also be applicable to
distribution fins, which simultaneously perform some heat transfer
function and wherein the flow is predominantly, but not
exclusively, parallel to the fin flow channels. The embodiments
disclosed herein are particularly suitable for applications in
which the fluid streams experience heat transfer without any phase
change over at least 80% of the flow length, more preferably over
at least 90% of the flow length, and most preferably over 100% of
the flow length within the plate-fin passages of the plate fin
exchanger, for example, containing fin channels with the
perforation patterns and geometry disclosed herein.
[0022] In a first embodiment a plate fin heat exchanger is
disclosed comprising a folded fin sheet comprising fins having a
height, a width, and a length, the folded fin sheet being
positioned between a first parting sheet and a second parting
sheet; and a first side bar and a second side bar, wherein the
first side bar is positioned between the first parting sheet and
the second parting sheet and adjacent to a first side of the folded
fin sheet, and wherein the second side bar is positioned between
the first parting sheet and the second parting and adjacent to a
second side of the folded fin sheet thereby forming at least a part
of a plate fin passage; wherein the fin sheet comprises a plurality
of perforations, such plurality of perforations are positioned on
the fin sheet in parallel rows when such fin sheet is in an
unfolded state, such parallel rows of perforations on the fin sheet
comprise a first spacing between the parallel rows of perforations
(S1), a second spacing between sequential perforations within the
parallel row of perforations (S2), a third spacing (or offset)
between the perforations in adjacent parallel rows of perforations
(S3), and a perforation diameter (D), wherein the ratio of the
first spacing between the parallel rows of perforations to the
perforation diameter (S1/D) is in the range of 0.75 to 2.0, and
wherein the angle between the fins and the parallel rows of
perforations is less than or equal to five degrees
(.ltoreq.5.degree.).
[0023] In a second embodiment a process for exchanging heat between
at least two streams in a plate fin heat exchanger in accordance
with the first embodiment is disclosed, wherein at least one stream
undergoes heat transfer without phase change over at least 80% of
the length of the plate-fin passages, and wherein the Reynolds
Number of the at least one stream is in the range of 800 to 100,000
and more preferably in the range of 1,000 to 10,000.
[0024] In a third embodiment, a process for separating nitrogen,
oxygen and/or argon from air by cryogenic distillation, which
utilizes the plate fin heat exchanger in accordance with the first
embodiment is disclosed, wherein at least one stream undergoes heat
transfer without phase change over at least 80% of the length of
the plate-fin passages, more preferably over at least 90% of the
length of the plate-fin passages, and most preferably over 100% of
the length of plate-fin passages.
[0025] In a fourth embodiment, a method for manufacturing a plate
fin heat exchanger is disclosed, which comprises the steps of:
providing at least one perforated sheet, the at least one
perforated sheet comprising a plurality of perforations arranged in
parallel rows, wherein such parallel rows of perforations on the
perforated sheet comprise a first spacing between the parallel rows
of perforations (S1), a second spacing between sequential
perforations within the parallel row of perforations (S2), a third
spacing (or offset) between the perforations in adjacent parallel
rows of perforations (S3), and a perforation diameter (D), wherein
the ratio of the first spacing between the parallel rows of
perforations to the perforation diameter (S1/D) is in the range of
0.75 to 2.0; folding the at least one perforated sheet into fins to
form a folded perforated sheet such that the angle between the fins
and the parallel rows of perforations is less than or equal to five
degrees (.ltoreq.5.degree.); positioning a first side bar adjacent
to a first side of the at least one folded perforated sheet, a
second side bar adjacent to a second side of the at least one
folded perforated sheet, a first distributor fin adjacent to a
first end of the at least one folded perforated sheet, a second
distributor fin adjacent to a second end of the at least one folded
perforated sheet, a first endbar adjacent to the first distributor
fin, and a second endbar adjacent to the second distributor fin to
form a preliminary plate fin passage; placing the preliminary plate
fin passage of step (c) between a first parting sheet and a second
parting sheet thereby forming a plate fin passage therebetween;
combining the plate fin passage of step (d) with other plate fin
passages to form the plate fin heat exchanger; and brazing the
plate fin heat exchanger.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0026] The foregoing summary, as well as the following detailed
description of exemplary embodiments, is better understood when
read in conjunction with the appended drawings. For the purpose of
illustrating embodiments, there is shown in the drawings exemplary
constructions; however, the invention is not limited to the
specific methods and instrumentalities disclosed. In the
drawings:
[0027] FIG. 1 is an exploded perspective view of a basic element or
sub-assembly of a plate-fin heat exchanger with fins having a
perforation pattern and geometry according to one embodiment of the
present invention;
[0028] FIG. 2 is a schematic diagram illustrating an embodiment of
the perforation pattern on a flattened plate prior to their being
formed into fins according to the present invention; and
[0029] FIG. 3 is a graph illustrating the relative heat transfer
and pressure loss performance of perforated fins as a function of
S1/D with an indication of the preferred range.
DETAILED DESCRIPTION
[0030] One embodiment of the current invention relates to plate fin
exchangers that comprise perforated fins in at least a portion of
the plate-fin passages and to the methods for assembling such plate
fin exchangers. The perforated fins are assembled using flat
perforated sheets. The formed fins have a special relationship to
the perforation pattern on the flat sheet. While some plate-fin
passages have the aforesaid fins, other plate-fin passages may have
different types of fins, including plain, perforated, strip offset
and wavy types, for example. Plate-fin heat exchangers that
comprise such perforated fins have particular application in
cryogenic processes such as air separation, although they may also
be used in other heat transfer processes.
[0031] Referring to FIG. 1, a plate-fin heat exchanger of the
current invention comprises several plate fin passages, some of
which are made by placing at least one fin sheet in between parting
sheets or plates 30,40 sidebars 50,60, distributing fins (not shown
but generally known in the art) and endbars (not shown but
generally known in the art). These plate-fin passages comprise
special patterns of perforations 20 in at least some portion of
such plate-fin passages.
[0032] Prior to being formed into the fin sheet 10 as illustrated
in FIG. 1, the fin sheet 10 is a flattened sheet made of a metal
such as aluminum, copper, another alloy, or any other heat
conducting material known in the art for fabrication of fins. The
flattened fin sheet 10, as illustrated in FIG. 2, comprises the
perforations 20. The flattened sheet has special perforation
patterns comprising several parallel rows of perforations
100,200,300 with each parallel row 100,200,300 comprising
perforations 1A,1B,1C; 2A,2B,2C; and 3A,3B,3C. In one embodiment,
the rows of perforations 1A,1B,1C; 2A,2B,2C; and 3A,3B,3C will
align in a direction that is parallel to the desired direction of
the fins when the flattened sheet is folded to form the fin sheet
10 as depicted in the FIG. 1. When the fins are employed as easyway
fins, the nominal stream lines of the flow will be parallel to the
direction of perforations as illustrated in FIG. 2.
[0033] As illustrated in FIG. 2, the perforations have a diameter
(D). The spacing between parallel rows of perforations 100, 200,
300 is designated S1 while the spacing between sequential
perforations (i.e., between perforation 2A and 2B) in the stream
flow direction is designated as S2. The offset between perforations
in adjacent parallel rows 100, 200, 300 (i.e. between 2A and 3A) is
designated as S3.
[0034] In one embodiment, Applicants found with surprising result
that when the following parameters are held within the following
ranges: (1) perforation diameters D in the range of 1 mm to 4 mm;
(2) open area in the range of 5% to 25%; (3) the ratio S3/S2 in the
range of 0.25-0.75; (4) and the ratio S1/D in the range of 0.75 to
2.0 with a most preferred range of 0.75 to 1.0, the plate-fin heat
exchangers exhibited higher efficiencies and improved the
performance compared with traditional heat exchangers not designed
accordingly.
[0035] In the most preferred arrangement/embodiment, the fluid flow
direction is parallel to the parallel rows of perforations
100,200,300, but in a preferred arrangement/embodiment the
direction of fluid flow is within five degrees (5%) to the
direction of the parallel rows of perforations 100,200,300. This
means that as the fins are formed, the fin sheet 10 should be
folded such that the angle between the fin folds and such parallel
rows of perforations 100,200,300 is less than or equal to five
degrees, while the most preferred arrangement is where such angle
is zero degrees (0.degree.).
[0036] The fin sheets 10 may comprise perforations 20 that are
circular as illustrated in FIGS. 1 and 2, however, those skilled in
the art will recognize that non-circular perforations may also be
used including, but not limited to perforations in the shape of
ellipses, rectangles, parallelograms, and other such shapes.
[0037] In yet another embodiment, the arrangement of the offset
rows of perforations will repeat every two rows as illustrated in
FIG. 2 (i.e., Row 100 shall be offset similar to Row 300, 500 (not
shown), 700 (not shown), etc.). Further, when the flat perforated
sheets are folded into fins in a finning operation, the structure
of perforations that result on the finished fin sheet 10 tend to
have a complex relationship because of the mechanical details of
how the material flows in the finning dies. In one embodiment, the
flattened sheet is folded such that the perforation patterns on the
finished fin sheet 10 repeat at least once every ten (10) fin
wavelengths and more preferably at least once every five (5) fin
wavelengths, in at least fifty percent (50%) of the heat exchanger
platefin passages containing such perforated fins, more preferably
in at least eighty percent (80%) of the plate-fin passages and most
preferably in one-hundred percent (100%) of the plate-fin
passages.
[0038] In a further embodiment, surface texture may be applied to
the perforated sheets prior to the material being folded into fins
as taught by U.S. Pat. No. 6,834,515 B2, entitled "Plate Fin
Exchangers with Textured Surfaces," to Sunder et al., that is
incorporated by reference in its entirety. Alternatively the
surface texture may be created in the process of creating the fins
from the flat perforated sheets.
[0039] The embodiments described herein are suitable for plate fin
heat exchangers wherein at least a portion of the fins have a
height in the range of 0.25 inches to 1 inch (0.635 centimeters to
2.54 centimeters), more preferably in the range of 0.40 inches to
0.75 inches (1.016 centimeters to 1.905 centimeters) and most
preferably in the range of 0.5 inches to 0.6 inches (1.27
centimeters to 1.524 centimeters). The embodiments are
advantageously applied when the fluid flow conditions in such plate
fin passages are in a transition state between laminar and
turbulent states or in a turbulent state. This may be expressed as
a Reynolds Number range of 800 to 100,000 and more preferably a
range of 1,000 to 10,000. The Reynolds Number is calculated as
follows:
Re=.rho.VD/.mu., where
Where,
[0040] Re=Reynolds number;
[0041] .rho.=fluid density;
[0042] V=fluid velocity;
[0043] .mu.=fluid viscosity;
[0044] D=4 A/P;
[0045] A=fluid flow cross sectional area; and
[0046] P=fluid flow perimeter
For plate-fin passages, it is common to calculate the hydraulic
diameter D based on individual plate-fin passages and the current
calculations are based on using the base metal sheets without
adjusting for the perforations for their contributions to the A
(fluid flow cross sectional area) and P (fluid flow perimeter).
[0047] Embodiments of the present invention have significant value
because plate fin heat exchangers may be made more compact relative
to conventional plate-fin exchangers, thus, saving combined capital
and operating costs of the plant, such as an air separation
plant.
Example 1
[0048] To better understand the influence of the perforations
within the fin geometry, several sample problems were solved using
Computational Fluid Dynamics (CFD). In using this technique, it is
common to restrict the computation to some repeating structure in
order to limit the computational size of the problem. But when one
tries to quantify the effect of specific perforation patterns, the
overall geometry of the heat exchanger is very complicated, even
when one limits the problem to a single subchannel within plate-fin
passages. For this reason a different type of approximation was
used.
[0049] In most plate fin exchangers the secondary surface area
tends to be the dominant fraction of the total area. As noted
before, this is the area represented by the fin legs that span and
separate the parting sheets or plates 30,40 that represent the
primary surface area. To understand the effect of the positioning
of the perforations, a representative periodic area of two infinite
parallel plates was modeled to quantify the heat transfer and
pressure losses that occur when air flows between them. The general
scheme of the perforations on the flattened sheet is illustrated in
FIG. 2.
[0050] Example 1 concerns easyway fins that are used for heat
transfer and/or distribution purposes, wherein, as previously
stated, the direction of flow is generally parallel to the fin
direction as indicated in FIG. 2.
[0051] A number of exemplary cases were solved using CFD, wherein
the various spacings (S1, S2, and S3) were varied while keeping the
diameter (D) of the perforations and the overall open area
constant. Specifically, spacings S1 and S2 were varied
simultaneously, while the offset S3 was set equal to one-half of
the spacing S2. In these exemplary cases, there was only one
independent parameter and the results are listed in Table 1 and
illustrated in FIG. 3.
TABLE-US-00001 TABLE 1 Relative Relative heat pressure Parameter
S1/S2 S1/D transfer loss Case 1 0.037 0.5417 1.2626 1.2140 Case 2
0.071 0.7500 1.2469 1.1806 Case 3 0.127 1.0000 1.2465 1.1789 Case 4
0.224 1.3292 1.2162 1.1689 Case 5 0.348 1.6583 1.1951 1.1554 Case 6
0.500 1.9875 1.1881 1.1505 Case 7 0.679 2.3167 1.1347 1.1031 Case 8
0.886 2.6458 1.0632 1.0483 Case 9 1.120 2.9750 1.0000 1.0000
[0052] The exemplary calculations show the relative values of the
pressure losses and heat transfer rates that are obtained merely by
changing the pattern of perforations. The exemplary data was
plotted after scaling relative to the values that occur when the
ratio of spacing to the perforation dimension was approximately 3.
As this ratio is lowered to approximately 2, significant
improvement occurs in heat transfer. As noted in Table 1, the
increase in heat transfer is higher than the increase in the
corresponding pressure loss. Thus, a heat exchanger designed at a
ratio of 2 may be shorter by a factor of about 1.2 compared to a
heat exchanger designed at a ratio of 3, while the overall pressure
loss will also be lower. This is a significant reduction in length
and thereby the volume. If the ratio is reduced below 2, the
improvement continues and particularly good values are obtained
between the values of the ratio between 0.75 and 1. In this range
of ratios there is an improvement in heat transfer by a factor of
about 1.25. The length or volume required will be the reciprocal of
this ratio namely 0.80 or eighty percent (80%). This represents a
substantial size reduction by twenty percent (20%) while the
pressure loss will also be reduced by the ratio of 1.18/1.25 which
is equal to 0.94 or ninety-four percent (94%). Thus, there can be a
twenty percent (20%) reduction in length or volume while there is
also a six percent (6%) reduction in pressure loss.
[0053] These are significant improvements that can be obtained by
arranging the perforation positions as disclosed herein which was
not known or disclosed previously. In fact, either through express
statements, implication, or illustrations, some previous
disclosures taught away from such arrangements. As illustrated in
FIG. 3, the range of ratios from 0.75 to 2.0 is preferred wherein
the range from 0.75 to 1.0 is particularly preferred.
Example 2
[0054] Example 2 illustrates an exemplary improvement obtained
using the teaching contained herein. As noted before, traditional
teachings concerning perforated fins in plate fin heat exchangers
did not discuss preferred geometry or perforation patterns as
outlined herein. The CFD paper by Zhu et al., cited earlier,
however, did study the effect of a specific perforated fin in
comparison with other forms of fins such as plain, serrated and
wavy fins. The current example has been generated by applying the
perforation pattern used in the CFD paper by Zhu et al. in the same
manner as described in Example 1.
[0055] The parameters of the perforation pattern on the flat sheets
before being folded into fins are as follows: perforation diameter
(D)=0.8 mm; open area=20%; S1=1.81 mm; S2=1.39 mm; and S3=0. The
calculated relative performance of a heat exchanger that utilizes
such prior art fins is shown in Table 2.
TABLE-US-00002 TABLE 2 Disclosed CFD exemplary Parameter Paper
embodiment Perforation diameter, mm 0.8 2.4 Open area, % 20 10 S1,
mm 1.81 2.4 S2, mm 1.39 18.96 S3, mm 0.0 9.48 S1/D 2.26 1.0 S3/S2
0.0 0.5 Relative heat transfer 1.00 1.26 coefficient Relative
pressure gradient 1.00 1.26 Relative length of exchanger 1.00 0.79
Relative volume of exchanger 1.00 0.79 Relative pressure loss in
1.00 1.00 exchanger
[0056] As illustrated in Table 2, because the Relative heat
transfer coefficient and Relative pressure gradient of the
disclosed exemplary embodiment are 26% higher than the CFD paper
heat exchanger, a heat exchanger constructed according to the
teachings of the disclosed exemplary embodiment can have a lesser
relative length (21% less) and a lesser relative volume (21% less)
compared with a heat exchanger constructed based on the teachings
of the CFD paper where both heat exchangers have equal or matching
heat transfer duty and pressure drop. This is a substantial benefit
for utilizing fins made in accordance with the teachings of the
disclosed exemplary embodiment over the teachings of the CFD
paper.
[0057] While aspects of the present invention has been described in
connection with the preferred embodiments of the various figures,
it is to be understood that other similar embodiments may be used
or modifications and additions may be made to the described
embodiment for performing the same function of the present
invention without deviating therefrom. For example, the following
aspects should also be understood to be a part of this
disclosure:
[0058] Aspect 1. A plate fin heat exchanger, comprising:
[0059] a folded fin sheet comprising fins having a height, a width,
and a length, the folded fin sheet being positioned between a first
parting sheet and a second parting sheet; and
[0060] a first side bar and a second side bar, wherein the first
side bar is positioned between the first parting sheet and the
second parting sheet and adjacent to a first side of the folded fin
sheet, and wherein the second side bar is positioned between the
first parting sheet and the second parting and adjacent to a second
side of the folded fin sheet thereby forming at least a part of a
plate fin passage;
[0061] wherein the fin sheet comprises a plurality of perforations,
such plurality of perforations are positioned on the fin sheet in
parallel rows when such fin sheet is in an unfolded state, such
parallel rows of perforations on the fin sheet comprise a first
spacing between the parallel rows of perforations (S1), a second
spacing between sequential perforations within the parallel row of
perforations (S2), a third spacing (or offset) between the
perforations in adjacent parallel rows of perforations (S3), and a
perforation diameter (D), wherein the ratio of the first spacing
between the parallel rows of perforations to the perforation
diameter (S1/D) is in the range of 0.75 to 2.0, and wherein the
angle between the fins and the parallel rows of perforations is
less than or equal to five degrees (.ltoreq.5.degree.).
[0062] Aspect 2. The plate fin heat exchanger of Aspect 1, wherein
the angle between the fins and the parallel rows of perforations is
zero degrees (0.degree.).
[0063] Aspect 3. The plate fin heat exchanger of Aspect 1 or Aspect
2, wherein the ratio of the first spacing between the parallel rows
of perforations to the perforation diameter (S1/D) is in the range
of 0.75 to 1.0.
[0064] Aspect 4. The plate fin heat exchanger of any one of Aspects
1 to Aspect 3, wherein the ratio of the third spacing (or offset)
between perforations in adjacent parallel rows of perforations (S3)
and the second spacing between sequential perforations within the
parallel row of perforations (S2) is in the range of 0.25 to
0.75.
[0065] Aspect 5. The plate fin heat exchanger of any one of Aspects
1 to Aspect 4, wherein 5% to 25% of the area of the folded fin
sheet in the unfolded state is occupied by the perforations.
[0066] Aspect 6. The plate fin heat exchanger of any one of Aspects
1 to Aspect 5, wherein the perforation diameter (D) is in the range
of 1 mm to 4 mm.
[0067] Aspect 7. The plate fin heat exchanger of any one of Aspects
1 to Aspect 6, wherein the perforations are circular.
[0068] Aspect 8. The plate fin heat exchanger of any one of Aspects
1 to Aspect 6, wherein the perforations are in the shape of
ellipses, rectangles, or parallelograms.
[0069] Aspect 9. The plate fin heat exchanger of any one of Aspects
1 to Aspect 8, wherein the adjacent parallel rows of perforations
are offset in alternating fashion such that the position of the
parallel rows of perforations repeats every other row of
perforations.
[0070] Aspect 10. The plate fin heat exchanger of any one of
Aspects 1 to Aspect 8, wherein the adjacent parallel rows of
perforations are offset such that the position of the parallel rows
of perforations on the fins of the folded fin sheet repeat exactly
at least once every 10 fin wavelengths and more preferably at least
once every 5 fin wavelengths, in at least 50% of the heat exchanger
plate fin passages containing such perforated fins, more preferably
in at least 80% of the plate fin passages and most preferably in
100% of the plate fin passages.
[0071] Aspect 11. The plate fin heat exchanger of any one of
Aspects 1 to Aspect 10, wherein the folded fin sheet comprises a
surface texture.
[0072] Aspect 12. The plate fin heat exchanger of any one of
Aspects 1 to Aspect 11, wherein the fin height is in the range of
0.25 inches to 1 inch, more preferably in the range of 0.4 inches
to 0.75 inches, and most preferably in the range of 0.5 inches to
0.6 inches.
[0073] Aspect 13. The plate fin heat exchanger of any one of
Aspects 1 to Aspect 12, wherein the folded fin sheet is an easyway
heat transfer fin or distributor fin.
[0074] Aspect 14. The plate fin heat exchanger of any one of
Aspects 1 to Aspect 13, wherein the plate-fin passages are adapted
to accept a fluid stream, and wherein the fluid stream undergoes
heat transfer without phase change over at least 80%, more
preferably over at least 90%, and most preferably over 100% of the
length of the plate-fin passages.
[0075] Aspect 15. A process for exchanging heat between at least
two streams in a plate fin heat exchanger constructed in accordance
with any one of Aspects 1 to Aspect 13, wherein at least one stream
undergoes heat transfer without phase change over at least 80% of
the length of the plate-fin passages, and wherein the Reynolds
Number of the at least one stream is in the range of 800 to 100,000
and more preferably in the range of 1,000 to 10,000.
[0076] Aspect 16. A process for separating nitrogen, oxygen and/or
argon from air by cryogenic distillation, which utilizes the plate
fin heat exchanger of any one of Aspects 1 to Aspect 13, wherein at
least one stream undergoes heat transfer without phase change over
at least 80% of the length of the plate-fin passages, more
preferably over at least 90% of the length of the plate-fin
passages, and most preferably over 100% of the length of plate-fin
passages.
[0077] Aspect 17. A method for manufacturing a plate fin heat
exchanger which comprises the steps of: [0078] (a) providing at
least one perforated sheet, the at least one perforated sheet
comprising a plurality of perforations arranged in parallel rows,
wherein such parallel rows of perforations on the perforated sheet
comprise a first spacing between the parallel rows of perforations
(S1), a second spacing between sequential perforations within the
parallel row of perforations (S2), a third spacing (or offset)
between the perforations in adjacent parallel rows of perforations
(S3), and a perforation diameter (D), wherein the ratio of the
first spacing between the parallel rows of perforations to the
perforation diameter (S1/D) is in the range of 0.75 to 2.0; [0079]
(b) folding the at least one perforated sheet into fins to form a
folded perforated sheet such that the angle between the fins and
the parallel rows of perforations is less than or equal to five
degrees (.ltoreq.5.degree.); [0080] (c) positioning a first side
bar adjacent to a first side of the at least one folded perforated
sheet, a second side bar adjacent to a second side of the at least
one folded perforated sheet, a first distributor fin adjacent to a
first end of the at least one folded perforated sheet, a second
distributor fin adjacent to a second end of the at least one folded
perforated sheet, a first endbar adjacent to the first distributor
fin, and a second endbar adjacent to the second distributor fin to
form a preliminary plate fin passage; [0081] (d) placing the
preliminary plate fin passage of step (c) between a first parting
sheet and a second parting sheet thereby forming a plate fin
passage therebetween; [0082] (e) combining the plate fin passage of
step (d) with other plate fin passages to form the plate fin heat
exchanger; and [0083] (f) brazing the plate fin heat exchanger.
[0084] Aspect 18. A method for manufacturing a plate fin heat
exchanger according to Aspect 17, further comprising applying a
surface texture to at least one perforated sheet prior to folding
the at least one perforated sheet in step (b).
[0085] The claimed invention, therefore, should not be limited to
any single embodiment or aspect, but rather should be construed in
breadth and scope in accordance with the appended claims.
* * * * *