U.S. patent application number 14/599798 was filed with the patent office on 2016-07-28 for bowed fin for heat exchanger.
The applicant listed for this patent is Hamilton Sundstrand Corporation. Invention is credited to Donald E. Army, George Kan.
Application Number | 20160216046 14/599798 |
Document ID | / |
Family ID | 55174583 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160216046 |
Kind Code |
A1 |
Army; Donald E. ; et
al. |
July 28, 2016 |
BOWED FIN FOR HEAT EXCHANGER
Abstract
A heat exchanger includes a plurality of first fluid passages
configured to receive a first stream and a plurality of second
fluid passages each formed between two first fluid passages. Each
first fluid passage includes a first plate and a second plate
parallel to the first plate. The first plate and second plate are
connected by two closure bars. The first fluid passage also
includes a fin pack having a plurality of fins connected to the
first and second plate, and configured for the first stream to flow
around the fins. The fins have a cross-sectional profile that is
bowed at non-operational temperatures and is configured to flex
under a thermal load without exceeding the tensile or fatigue
strength of the fin. Each second fluid passage is configured to
receive a second stream and is configured to allow heat to
indirectly exchange between the first stream and the second
stream.
Inventors: |
Army; Donald E.; (Enfield,
CT) ; Kan; George; (West Hartford, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hamilton Sundstrand Corporation |
Windsor Locks |
CT |
US |
|
|
Family ID: |
55174583 |
Appl. No.: |
14/599798 |
Filed: |
January 19, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 9/0062 20130101;
F28F 3/025 20130101; F28F 1/12 20130101; F28F 2265/26 20130101 |
International
Class: |
F28F 1/12 20060101
F28F001/12 |
Claims
1. A heat exchanger comprising: a plurality of first fluid passages
configured to receive a first stream, each first fluid passage
comprising: a first plate; a second plate parallel to the first
plate, wherein the first plate and second plate are connected by
two closure bars; a fin pack having a plurality of fins connected
to the first and second plate, and configured for the first stream
to flow around the fins, wherein the fins have a cross-sectional
profile that is bowed at non-operational temperatures and is
configured to flex under a thermal load without exceeding the
tensile or fatigue strength of the fin; and a plurality of second
fluid passages each formed between two first fluid passages,
wherein each second fluid passage is configured to receive a second
stream, and wherein the second fluid passage is configured to allow
heat to indirectly exchange between the first stream and the second
stream.
2. The heat exchanger of claim 1, wherein the fin further
comprises: a plurality of first fin base portions parallel and
adjacent to the first plate; a plurality of second fin base
portions parallel and adjacent to the second plate; a plurality of
first and second bowed fin portions connected between the first and
second fin base portions, wherein the first and second bowed fin
portions are oppositely bowed and are configured to flex under a
thermal load without exceeding the tensile or fatigue strength of
the fin.
3. The heat exchanger of claim 2, wherein each fin extends from a
first end of the first fluid passage to a second end of the first
fluid passage between the first and second plates, and where the
profile of each fin is consistent between the first and second end
of the first fluid passage.
4. The heat exchanger of claim 2, wherein the first and second fin
base portions and first and second bowed fin portions extend from a
first end of the first fluid passage to a second end of the first
fluid passage, and wherein the portions form a plurality of fin
sections that are offset between the first and second end of the
first fluid passage such that adjacent fin sections are offset from
each other moving from the first end of the first fluid passage to
the second end of the first fluid passage.
5. The heat exchanger of claim 1, wherein each fin extends from a
first end of the first fluid passage to a second end of the first
fluid passage between the first and second plates, and wherein the
profile of the fin is consistent between the first and second end
of the fin.
6. The heat exchanger of claim 1, wherein the heat exchanger is a
dual heat exchanger having a primary and a secondary heat
exchanger.
7. The heat exchanger of claim 6, wherein the primary heat
exchanger is configured to receive bleed air from a gas turbine
engine and is configured to receive ram air that has passed through
the secondary heat exchanger.
8. The heat exchanger of claim 7, wherein the heat exchanger
further comprises a second fin disposed in some of the fluid
passages, wherein the second fin has a cross-sectional profile that
is not bowed.
9. The heat exchanger of claim 8, wherein the fins having a profile
that is bowed are only used in first fluid passages near local
areas of the primary heat exchanger subject to a high thermal load
and the second fin is used throughout the remainder of the heat
exchanger.
10. The heat exchanger of claim 9, wherein each fin extends from a
first end of the first fluid passage to a second end of the first
fluid passage, and wherein the profile of the fin is consistent
between the first and second end of the first fluid passage.
11. An environmental control system comprising: a heat exchanger
comprising: a plurality of first fluid passages configured to
receive a first stream, each first fluid passage comprising: a
first plate; a second plate parallel to the first plate, wherein
the first plate and second plate are connected by two closure bars;
a fin pack having a plurality of fins connected to the first and
second plate, and configured for the first stream to flow around
the fins, wherein the fins have a cross-sectional profile that is
bowed at non-operational temperatures and is configured to flex
under a thermal load without exceeding the tensile or fatigue
strength of the fin; and a plurality of second fluid passages each
formed between two first fluid passages, wherein each second fluid
passage is configured to receive a second stream, and wherein the
second fluid passage is configured for heat to indirectly exchange
between the first stream and the second stream. a gas turbine bleed
source for providing the first stream to the heat exchanger; at
least one ram air fan for providing the second stream to the heat
exchanger; and an air cycle machine for receiving the first stream
from the heat exchanger.
12. The heat exchanger of claim 11, wherein the fin further
comprises: a plurality of first fin base portions parallel and
adjacent to the first plate; a plurality of second fin base
portions parallel and adjacent to the second plate; a plurality of
first and second bowed fin portions connected between the first and
second fin base portions, wherein the first and second bowed fin
portions are oppositely bowed and are configured to flex under a
thermal load without exceeding the tensile or fatigue strength of
the fin.
13. The heat exchanger of claim 12, wherein each fin extends from a
first end of the first fluid passage to a second end of the first
fluid passage between the first and second plates, and where the
profile of the fin is consistent between the first and second end
of the first fluid passage.
14. The heat exchanger of claim 12, wherein the first and second
fin base portions and first and second bowed fin portions extend
from a first end of the first fluid passage to a second end of the
first fluid passage, and wherein the portions form a plurality of
fin sections that are offset between the first and second end of
the first fluid passage such that adjacent fin sections are offset
from each other moving from the first end of the first fluid
passage to the second end of the first fluid passage.
15. The environmental control system of claim 14, wherein the
secondary heat exchanger is configured to receive ram air from a
ram air inlet, and discharge ram air into the primary heat
exchanger, and wherein the primary heat exchanger is configured to
receive bleed air from a gas turbine engine and discharge the bleed
air into the air machine.
Description
BACKGROUND
[0001] Heat exchangers are devices configured to allow for heat to
be exchanged between two or more fluids or reservoirs. Indirect
heat exchangers allow for heat to be exchanged between fluids
indirectly, or without contact between the fluids. To enable
efficient heat transfer, many variables of indirect heat exchangers
are manipulated to obtain optimum heat transfer. Variables of heat
transfer efficiency such as the material of the heat exchanger, the
heat exchanger's shape and size, and the flow rates and pressures
of the fluids are all manipulated to optimize heat exchanger
efficiency.
[0002] One way to increase heat exchanger efficiency is through the
use of fins. Thermally efficient fins are often thin in one
direction and frequently occurring in order to increase heat
transfer while minimizing pressure drop. Thermally efficient heat
exchangers are often composed of copper, aluminum, or a combination
thereof, because these materials are good thermal conductors. More
recently, many industries have begun using heat exchangers formed
of only aluminum to save weight and cost, as aluminum is both less
expensive and lighter than copper.
[0003] In an effort to increase thermal efficiency and decrease
cost and weight, heat exchangers have become much more lightweight
and often less robust. Though increasing heat exchanger thermal
efficiency is desirable, premature component failure is costly.
SUMMARY
[0004] In an embodiment, a heat exchanger includes a plurality of
first fluid passages configured to receive a first stream and a
plurality of second fluid passages each formed between two first
fluid passages. Each first fluid passage includes a first plate and
a second plate parallel to the first plate. The first plate and
second plate are connected by two closure bars. The first fluid
passage also includes a fin pack having a plurality of fins
connected to the first and second plate, and configured for the
first stream to flow around the fins. The fins have a
cross-sectional profile that is bowed at non-operational
temperatures and is configured to flex under a thermal load without
exceeding the tensile or fatigue strength of the fin. Each second
fluid passage is configured to receive a second stream and is
configured to allow heat to indirectly exchange between the first
stream and the second stream.
[0005] In another embodiment, an environmental control system
includes a heat exchanger, a gas turbine bleed source for providing
a first stream to the heat exchanger, at least one ram air fan for
providing a second stream to the heat exchanger, and an air cycle
machine for receiving the first stream from the heat exchanger.
Each heat exchanger includes a plurality of first fluid passages
configured to receive a first stream and a plurality of second
fluid passages each formed between two first fluid passages. Each
first fluid passage includes a first plate and a second plate
parallel to the first plate. The first plate and second plate are
connected by two closure bars. The first fluid passage also
includes a fin pack having a plurality of fins connected to the
first and second plate, and configured for the first stream to flow
around the fins. The fins have a cross-sectional profile that is
bowed at non-operational temperatures and is configured to flex
under a thermal load without exceeding the tensile or fatigue
strength of the fin. Each second fluid passage is configured to
receive a second stream and is configured to allow heat to
indirectly exchange between the first stream and the second
stream.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic view illustrating an embodiment of an
aircraft environmental control system including a dual heat
exchanger.
[0007] FIG. 2 is a partially exploded isometric view of a heat
exchanger.
[0008] FIG. 3 is a of a close-up, partially exploded isometric view
of a working fluid passage of the heat exchanger of FIG. 2.
[0009] FIGS. 4A and 4B are cross-sectional views of a portion of a
bleed flow path of the heat exchanger of FIG. 2.
[0010] FIG. 5 is a close-up, partially exploded isometric view of
another embodiment of a working fluid passage.
DETAILED DESCRIPTION
[0011] FIG. 1 is a schematic view illustrating an embodiment of
aircraft environmental control system 10 including dual heat
exchanger 12, gas turbine engine 13, air cycle machine 14, ram air
inlet duct 16, ram air outlet duct 18, ram air fan 20, and ram air
fan shaft 22. Dual heat exchanger 12 includes primary heat
exchanger 24, and secondary heat exchanger 26. Aircraft
environmental control system 10 also includes aspirator 28, bleed
inlet duct 30, bleed primary outlet duct 34, secondary inlet duct
36, secondary outlet duct 38, and conditioned process outlet duct
40. Also illustrated in FIG. are bleed stream B, ram air RA, and
process air stream P.
[0012] Dual heat exchanger 12 is shown as one heat exchanger;
however, dual heat exchanger 12 may comprise two heat exchangers,
12a and 12b (not numbered in FIG. 1), where dual heat exchanger 12a
includes primary heat exchanger 24a and secondary heat exchanger
26a, and dual heat exchanger 12b includes primary heat exchanger
24b and secondary heat exchanger 26b (also not shown in FIG.
1).
[0013] In the ram air system of aircraft environmental control
system 10, ram air inlet duct 16 connects to the inlet of dual heat
exchanger 12, which is the inlet of secondary heat exchangers 26.
The outlet of secondary heat exchangers 26 connects to the inlet of
primary heat exchanger 24. The outlet of primary heat exchanger 24
connects to the inlet of ram air outlet duct 18. Within ram air
outlet duct 18 is ram air fans 20. Ram air fan 20 is connected to
ram air fan shaft 22, which connects to a component within air
cycle machine 14, such as a compressor and turbine (not shown).
Aspirator 28 is mounted within ram air inlet duct 16 near the inlet
of secondary heat exchanger 26.
[0014] In the bleed air system of aircraft environmental control
system 10, bleed inlet duct 30 connects to the inlet of primary
heat exchanger 24. Bleed inlet duct 30 also connects to bleed
balancing duct 32 upstream of its connection to primary heat
exchanger 24. Bleed primary outlet duct 34 connects to the bleed
air discharge of primary heat exchanger 24. Bleed primary outlet
duct 34 connects to an inlet of air cycle machine 14. Connected to
an outlet of air cycle machine is secondary inlet duct 36.
Downstream, secondary inlet duct 36 also connects to the inlet of
secondary heat exchangers 26. The outlet of secondary heat
exchanger 26 is connected to secondary outlet duct 38, which also
connects to an inlet of air cycle machine 14. Conditioned process
air outlet 40 connects to an outlet of air cycle machine 14.
[0015] In this embodiment, fan 20 is driven by shaft 22, which is
driven by compressors and turbines (not shown) within air cycle
machine 14. Fan 20 draws ram air RA into ram air inlet duct 16. Ram
air RA is sprayed with a liquid and vapor mixture by aspirator 28.
The liquid of the mixture evaporates into ram air RA, lowering the
temperature of ram air RA. Ram air RA then travels to secondary
heat exchanger 26. There, ram air RA will be heated up by process
fluids traveling from secondary inlet duct 36, through secondary
heat exchanger 26, to secondary outlet duct 38.
[0016] After traveling through secondary heat exchanger 26, ram air
RA will exit secondary heat exchanger 26 and enter primary heat
exchanger 24. In primary heat exchanger 24 ram air RA will be
further heated by bleed air entering the heat exchanger from bleed
inlet duct 30. Following the heat exchanges, ram air RA travels
through ram air fan 20 and is propelled through ram air outlet duct
18 and is then exhausted overboard from the aircraft. Though
primary heat exchanger 24 and secondary heat exchanger 26 are shown
in a parallel configuration, a series configuration may be used in
alternate embodiments.
[0017] Bleed stream B (process air), which is supplied by a
component of gas turbine engine 13, such as a compressor, enters
the inlet of bleed inlet duct 30 and travels through primary heat
exchanger 24. In primary heat exchanger 24, the process air is
cooled by ram air RA passing through primary heat exchanger 24. The
process air then exits primary heat exchanger 24 and travels
through primary outlet 34, before entering air cycle machine 14
where it will encounter a process component, such as a compressor.
Following being subjected to at least one process, the process air
can travel to secondary heat exchanger 26 by way of secondary inlet
duct 36. The process air is then cooled by ram air RA through
secondary heat exchanger 26, and enters air cycle machine 14.
Following its entry into air cycle machine 14, the process air may
be subjected to another process component such as a condenser or
water collector. Then, the process air stream P may reenter the
turbine or another process component of air cycle machine 14, or
may be exhausted from air cycle machine 14 via conditioned process
outlet duct 40. Thereafter, process air stream P may be sent to
various components within the aircraft to perform heating or
cooling functions. Additionally, process air stream P may be
recirculated to any of the locations previously mentioned.
[0018] FIG. 2 is a partially exploded isometric view of dual heat
exchanger 12a, which includes primary heat exchanger 24a and
secondary heat exchanger 26a. Dual heat exchanger 12a includes end
sheets 42a and 42b, working passages 43a-43n, bleed closure bars
44a-44n, cooling passages 45a-45n, parting sheets 46a-46n, ram
closure bars 48a-48n, core bands 50, core framing 52, primary fin
packs 56a-56n, and cold fin packs 60a-60n. Also illustrated in FIG.
2 are bleed stream B, conditioned bleed stream CB, and ram air RA.
Further illustrated in FIG. 2 are ends E1, E2, E3, and E4. Included
in dual heat exchanger 12a, but not shown are secondary hot fin
packs.
[0019] Cold fin packs 60a-60n are disposed in cooling fluid
passages 45a-45n, between every other set of parting sheets
46a-46n. For example, cold fin pack 60b is disposed between parting
sheets 46c and 46d, but not between parting sheets 46b and 46c.
Disposed between parting sheets 46b and 46c in working fluid
passage 43b are primary fin pack 56b and secondary hot fin packs
(not shown), where primary hot fin pack 56b is separated from the
secondary hot fin packs (not shown).
[0020] Parting sheets 46a-46n are parallel and consistently spaced
between end sheet 42a and 42b. Parting sheets 46a-46n are also
parallel to end sheets 42a and 42b. Parting sheets 46a-46n are
connected to bleed closure bars 44a-44n and ram closure bars
48a-48n. Ram closure bars 48a-48n connect parting sheets 46a-46n at
two ends opposite from each other to form cooling passages 45a-45n.
For example, ram closure bar 48b connects parting sheets 46c and
46d and encloses cold fin pack 60b, at end E2. Another ram closure
bar 48b connects parting sheets 46c and 46d at end E4 (not shown)
to create cooling passage 45b. Similarly, bleed closure bar 44b
connects parting sheets 46b and 46c, which surround primary fin
pack 56b, at end E1. Another bleed closure bars 44a connects
parting sheets 46b and 46c at end E3 (not shown) to create working
passage 43a.
[0021] Core framing 52 is connected to end sheets 42a and 42b and
contacts the sides of parting sheets 46a-46n, bleed closure bars
44a-44n, and ram closure bars 48a-48n. Core band 50 is located on
ends E2 and E4 of dual heat exchanger 12a. Core band 50 contacts
the sides of parting sheets 46a-46n, and bleed closure bars
44a-44n, and ram closure bars 48a-48n. Further, core band 50 can be
welded, or otherwise secured, to ram closure bars 48a-48n. For
example, core bands 50 can be welded to dual heat exchanger 12a
following the brazing of heat exchanger 12a. Although two of core
bands 50 are shown, more may be used. Core framing 52 and core band
50 secures the components of heat exchanger 12a.
[0022] Dual heat exchanger 12a and all of its components are
composed of aluminum. This allows dual heat exchanger 12a to be
brazed together as a single assembly in an oven brazing process.
However, other methods of securing and sealing the components, such
as tack-welding and caulking, or fastening may be used. Also, heat
exchangers of other materials such as copper or steel can be
used.
[0023] Working passages 43a-43n contain both primary fin packs
56a-56n and secondary hot fin packs (not shown). The portion of
working passages 43a-43n which contain primary fin packs 56a-56n,
create primary flow paths for bleed air to travel through the
process or working fluid side of primary heat exchanger 24a within
dual heat exchanger 12a. In this embodiment, bleed air enters
primary heat exchanger 24a at the surface of dual heat exchanger
12a between ends E1 and E3 and perpendicular to end E2. Bleed air
exits primary heat exchanger 24a between ends E1 and E3 and
perpendicular to end E4.
[0024] The portion of working passages 43a-43n containing secondary
hot fin packs (not shown) create secondary flow paths for
conditioned bleed stream CB to travel through the process or
working fluid side of secondary heat exchanger 26a within dual heat
exchanger 12a. In this embodiment, conditioned bleed stream CB
enters secondary heat exchanger 26a on the surface of dual heat
exchanger 12a between ends E1 and E3 and perpendicular to end E4.
Conditioned bleed stream CB doubles back, turning its flow
direction 180 degrees, and exits secondary heat exchanger 26a on
the surface of dual heat exchanger 12a between ends E1 and E3 and
perpendicular to end E4. While in dual heat exchanger 12a, bleed
stream B and conditioned bleed stream CB are physically
separated.
[0025] Also, cooling passages 45a-45n, which contain cold fin packs
60a-60n, create a flow path for ram air RA to travel through
cooling fluid side of primary heat exchanger 24a and secondary heat
exchanger 26a within dual heat exchanger 12a. In this embodiment,
ram air RA enters secondary heat exchanger 26a on the surface of
dual heat exchanger 12a between ends E2 and E4 and perpendicular to
end E3. Ram air RA continues through secondary heat exchanger 26a
and enters primary heat exchanger 24a without exiting its flow
paths. Ram air RA then exits primary heat exchanger 24a between
ends E2 and E4 and perpendicular to end E1.
[0026] In the operation of one embodiment, ram air RA enters
cooling passages 45a-45n from ram air inlet duct 16 (of FIG. 1),
bleed stream B enters the working fluid passages 43a-43n from bleed
inlet duct 30a (of FIG. 1), and conditioned bleed stream CB enters
the secondary flow path of working fluid passages 43a-43n from
secondary inlet duct 36 (of FIG. 1). As conditioned bleed stream CB
enters the secondary flow paths within secondary heat exchanger 26a
it is cooled through indirect heat transfer by ram air RA that is
traveling in adjacent ram air flow paths of secondary heat
exchanger 26a. After being cooled by ram air RA, conditioned bleed
stream CB exits secondary heat exchanger 26a. However, after
cooling the conditioned bleed stream CB, ram air RA continues
through cooling passages 45a-45n to primary heat exchanger 24a
where cooling passages 43a-45n are adjacent to the portion of
working passages 45a-45n containing bleed stream B. At this point,
heat is indirectly exchanged between bleed stream B and ram air RA.
This process cools bleed stream B as it travels through primary
heat exchanger 24a, while heating ram air RA. Following this heat
exchange, ram air RA exits primary heat exchanger 24a and enters
ram air outlet duct 18a (of FIG. 1). Also, bleed stream B exits
primary heat exchanger 24a and enters primary outlet duct 34 (of
FIG. 1). The result is that bleed stream B has been cooled,
conditioned bleed stream CB has been cooled, and ram air RA has
been heated.
[0027] Within dual heat exchanger 12a, parting sheets 46a-46n
transfer heat between the streams passing through the passages. For
example parting sheet 26b transfers heat between bleed stream B and
ram air RA. Within each passage, fin packs transfer heat from the
streams to the parting sheets. For example, primary fin pack 56b,
between parting sheets 46b and 46c, transfers heat from bleed
stream B to parting sheet 46c. Then, from parting sheet 46c, heat
can be transferred into ram air RA in cooling passage 45b between
parting sheets 46c and 46d. Further, heat from parting sheet 46c
can be transferred to cold fin pack 60b and then into ram air
RA.
[0028] The fin packs increase the thermal efficiency of dual heat
exchanger 12a by allowing more heat to be transferred between the
streams flowing through the heat exchangers. Fins are typically
comprised of a very thin, relative to the other fin dimensions,
thickness of metal. This allows for the pressure drop of air
flowing over the fins to be reduced while still increasing the
effective heat transfer surface area of the heat exchanger. Thin
fins are also desirable, because a smaller fin thickness allows for
more fins to fit into a given space, further increasing surface
area for heat transfer. In other words, the amount of heat
exchanged is increased due to the increase in heat transfer surface
area that fins provide, while the increase in pressure drop caused
by the fins is maintained at a reasonable magnitude by using fins
having a small cross-sectional area.
[0029] When fins are thin and are subjected to thermal cycling, a
fin's fatigue stress may be reached more quickly than desired.
Modification of the profile of a fin to increase the fin's ability
to withstand thermal cycling increases the life of the heat
exchanger. This is further discussed below.
[0030] FIG. 3 is a close-up partially exploded isometric view of
cooling passage 45b, which includes closure bar 48b, parting sheets
46c and 46d, and cold fin pack 60b. Cold fin pack 60b includes fins
F, which include bowed fin portion 62 and 64 and fin base portions
66 and 68. Also shown in FIG. 3 are ends E1 and E2 and ram air
stream RA.
[0031] Cold fin pack 60b is comprised of several of fins F between
ram air closure bars 48b and span between ends E2 and E4. Bowed fin
portion 62 and 64 and fin base portions 66 and 68 extend between
ends E1 and E3 in a consistent profile, meaning these portions do
not change shape between ends E1 and E3. This is also known as a
flat fin type.
[0032] Bowed fin portion 62 is bowed in shape between parting
sheets 46c and 46d (which are flat), and connects at its end near
parting sheet 46d to fin base portion 68. Bowed fin portion 62
connects at its other end near parting sheet 46c to fin base
portion 66. Connected to the other end of fin base portion 66 is
bowed fin portion 64, which connects to another fin base portion
68. All of fins F have the same portions, creating a repeating fin
profile when viewed from end E1, which repeats consistently between
bleed closure bars 48b.
[0033] Cold fin pack 60b and parting sheets 46c and 46d connect to
closure bar 48b at end E2 of cooling passage 45b. Parting sheets
46c and 46d mate to fin portions 66 and 68, respectively. Cold fin
pack 60b and parting sheets 4cb and 46d connect to the other
closure bar 48b at end E4 of cooling passage 45b (not shown). This
encloses cold fin pack 60b on all but two surfaces. The open
surfaces of cold fin pack 60b are at ends E1 and E3.
[0034] These surfaces are open to allow ram air stream RA to pass
through cooling passage 45b and heat exchanger 24a as described
above. Further, ram air stream RA passes over all exposed surfaces
of cold fin pack 60b, as shown in FIG. 3. Though only cooling
passage 45b is shown, similar fin patterns may be used for any
working or cooling passage of heat exchanger 12a.
[0035] FIGS. 4A and 4B are discussed concurrently to more
accurately convey the operation of the illustrated components. FIG.
4A is a cross-sectional view of a portion of a cooling flow path of
primary heat exchanger 24a. FIG. 4A illustrates cold fin pack 60b
in a relative low temperature state. This may be when cold fin pack
60b is not in operation and exposed to ambient conditions of -100
to 120 degrees Fahrenheit (-73 C to 49 C), or during operation when
exposed to similar temperatures. FIG. 4B is the same
cross-sectional view of cold fin pack 60b' within primary heat
exchangers, but FIG. 4B illustrates cold fin pack 60b' in relative
high temperature state. This may be when cold fin pack 60b' is
exposed to conditions similar to that of operational temperatures
of up to (or over) 1000 degrees Fahrenheit (538 C) when steel type
materials are used, or temperatures of up to (or over) 500 degrees
Fahrenheit (26 C) when aluminum materials are used.
[0036] Illustrated in FIG. 4A are cold fin pack 60b, which includes
fins F. Fins F each includes bowed fin portions 62 and 64 and fin
base portions 66 and 68. Also illustrated in FIG. 4A are fin height
fh, fin thickness t, fin base width bw, fin width w, and parting
sheet height ph. Illustrated in FIG. 4B is cold fin pack 60b',
which includes bowed fin portions 62' and 64' and fin base portions
66 and 68. Also illustrated in FIG. 4B are fin height fh, fin
thickness t, fin base width bw, fin width w', parting sheet height
ph, bowed fin portions 62 and 64 (shown in phantom in FIG. 4b), and
fin base portions 66 and 68. The connection and operation of cold
fin pack 60b is consistent with FIGS. 1-3. Cold fin pack 60b is
disposed between parting sheets 46c and 46d, as described in FIG.
3.
[0037] The views illustrated in FIGS. 4A and 4B are
cross-sectional, meaning cold fin packs 60b and 60b' extend into
the cavity created by parting sheets 46c and 46d. Fin height fh,
fin thickness t, fin base width bw, fin width w, fin width w', and
parting sheet height ph are all dimensions. Fin height fh is the
dimension of bowed bowed fin portions 62 and 64 and 62'and 64'. Fin
thickness t is the dimension of the thickness of fin F, otherwise
known as the fin material thickness. Fin base width bw is the
distance of fin base portions 66 and 68. Fin width w is the largest
distance between bowed fin portions 62 and 64. Fin width w' is the
largest distance between bowed fin portions 62' and 64'. Parting
sheet height ph is the distance between parting sheets 46c and 46d.
Parting sheet height ph is primarily determined by bleed closure
bar 44b, which determine the spacing of parting sheets 46c and 46d
for the fin packs disposed within each pair of parting sheets.
[0038] When cold fin pack 60b is exposed to a relatively low
temperature, for example, 60 degrees Fahrenheit (15.6 C), the
cross-sectional profile of fin F will appear as it does in FIG. 4A.
In this condition, bowed fin portions 62 and 64 are curved or bowed
in opposite directions. This bowing provides fin width w and fin
height fh, where fin width w is wider than fin base width bw, and
where fin height fh is equal to parting plate height ph.
[0039] When cold fin pack 60b is exposed to operational
temperatures, similar to when exposed to bleed air (through heat
transfer), the temperatures seen may reach 500 degrees Fahrenheit
(260 C). At these temperatures the cross-sectional profile of the
fin will appear as it does in FIG. 4B. In the condition of FIG. 4B,
bowed fin portions 62' and 64' have a greater bow than bowed fin
portions 62 and 64 (shown in phantom in FIG. 4B). This bowing
provides a fin width w', but fin height fh remains constant, as fin
height fh is constrained by parting sheets 46c and 46d (and
therefore closure bar 48b). Fin width w' becomes larger than fin
width w, due to thermal expansion of fins F. The thermal expansion
is caused by the thermal load applied by the high temperatures of
bleed air flowing over fins F. The bowing of fins F may not be
uniform, as is shown in FIGS. 4A and 4B. Regardless, the result is
fin F has a fatigue strength that is greater than an un-bowed fin,
as described below in greater detail.
[0040] The improved fin design is obtained through specific
manufacturing processes. To manufacture a bowed fin at the
appropriate height, several processes may be used. In one
embodiment, an effective process is to form a fin 0.001 to 0.005
inches (0.025 to 0.127 mm) above parting sheet height ph. Then, the
fin may be spanked to match parting sheet height ph (or the closure
bar height). Spanking is a process where a compressive force
controllably alters the height of a component through pressure
applied to plates on either side of the fin. Thereafter, the fin
can be placed inside its heat exchanger so that it may be brazed
into the heat exchanger. This results in, for example, cold fin
pack 60b that have fins F having a height equivalent to parting
sheet height ph and a bow in bowed fin portions 62 and 64, which
allows for width w to increase to width w'.
[0041] After this manufacturing process cold fin pack 60b is
configured so that if it were outside of parting sheets 46c and
46d, it would be allowed to straighten, or unbow and increase in
fin height fh due to thermal expansion when exposed to a thermal
load similar to the design conditions. The increase in fin height
fh may be, for example between 0.0005 inches and 0.005 inches
(0.0127 to 0.127 mm) when placed under the thermal load. Typically,
the increase in fin height fh is small relative to the dimensions
of the fin. For example, the fin height may be 0.5 inches (12.7 mm)
and the increase in fin height may be 0.005 inches (0.127 mm).
[0042] When cold fin pack 60b is placed between parting sheets 46c
and 46d it is not free to fully expand. In the prior art, when a
fin pack is under thermal load and not free to expand, the thermal
expansion causes both stress and strain on the fin pack (where
strain is a measurement of deformation experienced by a material,
and stress is a measurement of potentially deforming force to
cross-sectional area). Both thermally induced stress and strain of
the fin pack can cause adverse effects to the fin pack.
Specifically, cyclical stress caused by the thermal expansion and
contraction discussed above can lead to cracking of fins within a
heat exchanger when the fatigue strength or fatigue limit of the
fin material is reached. This cracking quickly propagates in
subsequent thermal cycles, and ultimately leads to failure of the
fins within the heat exchanger. This issue is particularly common
where thin fins are used to increase thermal efficiency and
decrease weight and cost, because thin fins are less able to
withstand the thermally induced strains. Vibrations have been known
to create or worsen these problems. These issues are prevalent in
aircraft heat exchangers, which may use (relatively) thin fins,
experience high thermal variance, are frequently cycled (due to
starting and stopping of engines associated with flight), and
frequently encounter vibrations.
[0043] The methods of this disclosure address these problems. Cold
fin pack 60b helps to reduce this issue, because fins F have a
bowed profile which allows cold fin pack 60b to absorb the stress
and strain better than an unbowed fin. For example, cold fin pack
60b is placed in dual heat exchanger 12a in areas susceptible to
thermal expansion and high deformation. For example, near the bleed
inlet, the incoming bleed stream B temperature may be 1000 degrees
Fahrenheit (538 C) when steel type materials are used, or
temperatures of up to (or over) 500 degrees Fahrenheit (26 C) when
aluminum materials are used. At this time of operation, ram air RA
may have an inlet temperature ranging from -100 to 200 degrees
Fahrenheit (-73 C to 93 C). Regardless, this is a large temperature
difference between the cooling fluids (ram air RA) and the process
or working fluid (bleed stream B). In this location, cold fin pack
60b will encounter this temperature range and may experience
frequent expansion and contraction.
[0044] When cold fin pack 60b is between parting sheets 46c and
46d, cold fin pack 60b will not be free to expand to its full
height when exposed to bleed stream B at a high temperatures.
Instead, while between parting sheets 46c and 46d, the bowed fin
will change shape as shown in FIG. 4B, increasing from width w to
width w'. This flexing of fins F are designed to withstand stresses
and strains created by the fin tensile load, by changing shape in a
controlled and predetermined manner. The bowed configuration is
analogous to a spring, in that it is capable of handling repetitive
thermally induced loads without failing.
[0045] To obtain a fatigue strength of cold fin pack 60b even
higher than that induced by the high operational temperature caused
by bleed air, straight fins F may be used. Straight fins have a
lower moment of inertia than wavy or corrugated fins, allowing
straight fins to flex more easily. The use of a bowed straight fin
provides the fins with significantly higher fatigue strength and
reduces the stresses and strains on cold fin pack 60b. This allows
for the heat exchanger to last for significantly more thermal or
operational cycles, saving material cost, labor cost, and reducing
risks associated with component failure during aviation flight.
[0046] In some embodiments, bowed fins may be used throughout dual
heat exchanger 12a. In other embodiments, some fin packs may
contain unbowed fins and some fin packs may contain bowed fins. For
example, bowed fins may be strategically placed in dual heat
exchanger 12a in areas that are most susceptible to thermal
expansion induced fatigue stress failures, such as the fin packs
most near the entrance of bleed air B into primary heat exchanger
24a where the largest thermal gradient between bleed air B and ram
air RA will be exist within heat exchanger 12a. Then, a second type
of fin that is not bowed, such as a fin type created by electrical
discharge machining (EDM), can be used in all other locations of
heat exchanger 24a. These fins are often optimized for thermal
performance, whereas bowed fins are optimized to avoid failure.
This strategy allows for bowed fins to be used sparingly, which can
reduce the cost of the heat exchanger as bowed fins require more or
different steps of manufacturing, thus increasing their cost
relative to unbowed fins.
[0047] Because use of bowed fins in only some areas is effective to
increase the life of the heat exchanger, bowed fins may be replaced
for other fin styles in existing heat exchangers in areas most
susceptible to failure due to thermal loads and cycling. For
example, bowed fins or fin packs may be substituted for fins or fin
packs most near the entrance of bleed air in a heat exchanger
already existing in an aircraft.
[0048] FIG. 5 is a close-up partially exploded isometric view of
cooling passage 45b', which includes closure bar 48b, parting
sheets 46c and 46d, and cold fin pack 60b. Cold fin pack 60b
includes fins F. Each fin includes several of fin section f. Each
fin section f includes bowed fin portion 62 and 64 and fin base
portions 66 and 68. Also shown in FIG. 5 are ends E1 and E2 and ram
air stream RA. Elements of FIG. 5 that are similar to elements of
FIG. 3 are identified by similar character reference numbers.
[0049] Cold fin pack 60b is comprised of several fins F between
bleed closure bars 48b. Fins F are connected to one another (as
described below and above) and span between ends E1 and E2. Fin
sections f are small in dimension relative to the dimension of fin
F between ends E1 and E3. Each fin F includes several fin sections
f, which include bowed fin portion 62 and 64 and fin base portions
66 and 68. Each fin section f is offset from adjacent fin sections
f within its own fin F, and is offset from fin sections f of nearby
fins F. This is also known as a serrated fin type. The remainder of
the connections of cooling passage 45b' are consistent with FIG.
3.
[0050] As in cooling passage 45b, all but two surfaces of cooling
passage 45b' are closed. The open surfaces of cooling passage 45b
are at ends E1 and E3. These surfaces are open to allow ram air
stream RA to pass through cooling passage 45b and heat exchanger
24a as described above. Further, ram air stream RA passes over all
exposed surfaces of cold fin pack 60b, as shown in FIG. 3. However,
unlike cooling passage 45b, ram air stream RA flowing through cold
fin pack 60b of cooling passage 45b' will continuously split as it
encounters staggered fin section f, specifically encountering bowed
fin portions 62 and 64 as ram air stream stream RA passes through
cooling passage 45b'. Though only cooling passage 45b' is shown,
similar fin patterns may be used for any working or cooling
passage.
[0051] Parting sheets 46a-46n are comprised of a thermally
conductive material, such as aluminum, to allow for heat to
indirectly transfer between the adjacent streams within dual heat
exchanger 12a. Similarly, cold fin packs 60a-60n, primary fin packs
56a-56n, and secondary hot fin packs are comprised of a thermally
conductive material, such as aluminum, to allow for heat to
indirectly transfer between the adjacent streams within dual heat
exchanger 12a. However, materials other than aluminum, such as
copper, stainless steel, cupronickel, or any other thermally
conductive materially may be used.
[0052] Dual heat exchanger 12a is shown as having two heat
exchangers, primary heat exchanger 24a and secondary heat exchanger
26a; however, the present disclosure may apply to single heat
exchangers. Additionally, dual heat exchanger 12a is shown having
the flow direction of ram air RA being orthogonal to the flow
direction of bleed stream B; however, the present disclosure may
apply to heat exchangers having any relative flow directions. For
example, the present disclosure may apply to heat exchangers
arranged in a thermal counter flow arrangement, a thermal co-flow
arrangement, or a thermal cross-flow arrangement. Similarly, the
present disclosure may apply to heat exchangers with varying
passes. For example, a single pass heat exchanger may be used;
however, a multi-pass heat exchanger may also be used.
[0053] The bowing of fins may be applied to fins of many shapes.
Straight fins, as shown in FIGS. 4A and 4B as well as serrated fins
are examples of some shapes where bowing provides benefits.
[0054] Though the heat exchanger disclosed herein is described as
mounting to a bleed system of an aircraft, any heat exchanger may
make use of fin bowing to increase the life of the heat exchanger.
For example, bowed fins may be used in an outdoor air to exhaust
air heat exchanger in a home. Bowed fins may also be used in a
cross-flow type heat exchanger in commercial, industrial, or
process type HVAC applications.
[0055] Further, bowed fins may be applied to other types of heat
exchangers aside from air-to-air heat exchangers. For example,
bowed fins may be used on refrigerant to air, or water to air heat
exchangers.
[0056] Although bowing is described in the methods of this
disclosure, other shapes of the fin profile or cross-section may be
used that increase the fatigue strength of the fin.
DISCUSSION OF POSSIBLE EMBODIMENTS
[0057] The following are non-exclusive descriptions of possible
embodiments of the present invention.
[0058] A heat exchanger includes a plurality of first fluid
passages configured to receive a first stream and a plurality of
second fluid passages each formed between two first fluid passages.
Each first fluid passage includes a first plate and a second plate
parallel to the first plate. The first plate and second plate are
connected by two closure bars. The first fluid passage also
includes a fin pack having a plurality of fins connected to the
first and second plate, and configured for the first stream to flow
around the fins. The fins have a cross-sectional profile that is
bowed at non-operational temperatures and is configured to flex
under a thermal load without exceeding the tensile or fatigue
strength of the fin. Each second fluid passage is configured to
receive a second stream and is configured to allow heat to
indirectly exchange between the first stream and the second
stream.
[0059] The heat exchanger of the preceding paragraph can optionally
include, additionally and/or alternatively, any one or more of the
following features, configurations and/or additional
components.
[0060] The fin can include a plurality of first fin base portions
parallel and adjacent to the first plate, a plurality of second fin
base portions parallel and adjacent to the second plate, and a
plurality of first and second bowed fin portions connected between
the first and second fin base portions. The first and second bowed
fin portions are oppositely bowed and are configured to flex under
a thermal load without exceeding the tensile or fatigue strength of
the fin.
[0061] The fins can extend from a first end of the first fluid
passage to a second end of the first fluid passage between the
first and second plates, and the profile of the fins can be
consistent between the first and second end of the first fluid
passage.
[0062] The first and second fin base portions and the first and
second bowed fin portions can extend from a first end of the first
fluid passage to a second end of the first fluid passage, and the
portions can form a plurality of fin sections that are offset
between the first and second end of the first fluid passage such
that adjacent fin sections can be offset from each other moving
from the first end of the first fluid passage to the second end of
the first fluid passage.
[0063] The heat exchanger can be a dual heat exchanger having a
primary and a secondary heat exchanger.
[0064] The primary heat exchanger can be configured to receive
bleed air from a gas turbine engine and can be configured to
receive ram air that has passed through the secondary heat
exchanger.
[0065] The heat exchanger can include a second fin disposed in some
of the fluid passages. The second fin can have a cross-sectional
profile that is not bowed.
[0066] The fins can be only used in first fluid passages near local
areas of the primary heat exchanger subject to a high thermal load
and the second fin can be used throughout the remainder of the heat
exchanger.
[0067] An environmental control system includes a heat exchanger, a
gas turbine bleed source for providing a first stream to the heat
exchanger, at least one ram air fan for providing a second stream
to the heat exchanger, and an air cycle machine for receiving the
first stream from the heat exchanger. Each heat exchanger includes
a plurality of first fluid passages configured to receive a first
stream and a plurality of second fluid passages each formed between
two first fluid passages. Each first fluid passage includes a first
plate and a second plate parallel to the first plate. The first
plate and second plate are connected by two closure bars. The first
fluid passage also includes a fin pack having a plurality of fins
connected to the first and second plate, and configured for the
first stream to flow around the fins. The fins have a
cross-sectional profile that is bowed at non-operational
temperatures and is configured to flex under a thermal load without
exceeding the tensile or fatigue strength of the fin. Each second
fluid passage is configured to receive a second stream and is
configured to allow heat to indirectly exchange between the first
stream and the second stream.
[0068] The system of the preceding paragraph can optionally
include, additionally and/or alternatively, any one or more of the
following features, configurations and/or additional
components.
[0069] The fin can include a plurality of first fin base portions
parallel and adjacent to the first plate, a plurality of second fin
base portions parallel and adjacent to the second plate, and a
plurality of first and second bowed fin portions connected between
the first and second fin base portions. The first and second bowed
fin portions are oppositely bowed and are configured to flex under
a thermal load without exceeding the tensile or fatigue strength of
the fin.
[0070] The fins can extend from a first end of the first fluid
passage to a second end of the first fluid passage between the
first and second plates, and the profile of the fins can be
consistent between the first and second end of the first fluid
passage.
[0071] The first and second fin base portions and the first and
second bowed fin portions can extend from a first end of the first
fluid passage to a second end of the first fluid passage, and the
portions can form a plurality of fin sections that are offset
between the first and second end of the first fluid passage such
that adjacent fin sections can be offset from each other moving
from the first end of the first fluid passage to the second end of
the first fluid passage.
[0072] The secondary heat exchanger can be configured to receive
ram air from a ram air inlet, and discharge ram air into the
primary heat exchanger, and the primary heat exchanger can be
configured to receive bleed air from a gas turbine engine and
discharge the bleed air into the air machine.
[0073] While the invention has been described with reference to an
exemplary embodiment(s), it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment(s) disclosed, but that the invention will
include all embodiments falling within the scope of the appended
claims.
* * * * *