U.S. patent application number 10/114608 was filed with the patent office on 2003-10-02 for heat exchanger and folded tube used therein.
Invention is credited to Hughes, Gregory G., Memory, Stephen B., Vetter, Frank.
Application Number | 20030183378 10/114608 |
Document ID | / |
Family ID | 28453814 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030183378 |
Kind Code |
A1 |
Memory, Stephen B. ; et
al. |
October 2, 2003 |
Heat exchanger and folded tube used therein
Abstract
A folded, elongated tube (28) is provided for use in a heat
exchanger (10, 11). The tube (28) has a flattened cross section
with a minor dimension (d) and a major dimension (D). The tube (28)
includes a pair of parallel tube runs (36), and a folded section
(40) connecting the pair of tube runs (36). The major dimensions
(D) of the tube runs (36) lie in a common plane. The folded section
(40) includes a U-shaped bend (42), a first twist (44), and a
second twist (46). The U-shaped bend (42) includes a straight
section (48) extending between two curved sections (50, 52), and
has its major dimension (D) extending substantially transverse to
the major dimension (D) of the tube runs (36). The first twist (44)
connects one of the tube runs (36) to the curved section (50), and
the second twist (46) connects the other tube run (36) to the other
curved section (52) of the U-shaped bend (42).
Inventors: |
Memory, Stephen B.;
(Kenosha, WI) ; Vetter, Frank; (Neuhausen, DE)
; Hughes, Gregory G.; (Milwaukee, WI) |
Correspondence
Address: |
WOOD, PHILLIPS, VAN SANTEN,
CLARK & MORTIMER
Suite 3800
500 West Madison Street
Chicago
IL
60661
US
|
Family ID: |
28453814 |
Appl. No.: |
10/114608 |
Filed: |
April 2, 2002 |
Current U.S.
Class: |
165/153 ;
165/176 |
Current CPC
Class: |
F25B 2309/061 20130101;
F28F 1/025 20130101; F25B 9/008 20130101; F28D 1/0478 20130101;
F28D 2021/0073 20130101; F28F 1/128 20130101; F28D 1/0476
20130101 |
Class at
Publication: |
165/153 ;
165/176 |
International
Class: |
F28D 001/02; F28D
007/06 |
Claims
1. A heat exchanger comprising: a pair of elongated headers having
longitudinal axes disposed substantially parallel to each other; a
plurality of elongated tubes spaced in side by side relation along
the longitudinal axes of the headers, each of the tubes having a
first end connected to one of the headers and a second end
connected to the other header to transfer the working fluid between
the headers, each of the tubes having a flattened cross section
with a minor dimension and a major dimension, each of the tubes
including a pair of parallel tube runs connected by a folded
section of the tube, the major dimension of each of the tube runs
extending substantially transverse to the longitudinal axes of the
headers, the folded section of each of the tubes comprising a
U-shaped bend including a straight section of tube extending
between two curved sections of tube, the bend having its major
dimension extending substantially parallel to the longitudinal axes
of the headers, a first twist connecting one of the tube runs to
one of the curved sections of the U-shaped bend, and a second twist
connecting the other tube run to the other curved section of the
U-shaped bend; and serpentine fins extending between adjacent pairs
of said tubes.
2. The heat exchanger of claim 1 wherein for the major dimension of
one of the tube runs of each tube lies in a common plane with the
major dimension of the other tube run of the tube.
3. The heat exchanger of claim 1 wherein the straight section of
each of the U-shaped bends extends transverse to the parallel
legs.
4. The heat exchanger of claim 1 wherein each of the twists is a
90.degree. twist.
5. The heat exchanger of claim 1 wherein each of the tubes further
comprises: a third tube run parallel to the pair of tube runs, the
major dimension of the tube extending transverse to the
longitudinal axes of the headers; and a second folded section of
tube connecting the third tube run to one of the other tube runs of
the tube, the second folded section comprising a second U-shaped
bend including a straight section of tube extending between two
curved sections of tube and having its major dimension extending
substantially parallel to the longitudinal axes of the headers, a
third twist connecting the one of the other tube runs to one of the
curved sections of the second U-shaped bend, and a fourth twist
connecting the third tube run to other curved section of the second
U-shaped bend.
6. The heat exchanger of claim 1 wherein the straight section of
each of the tubes has a length that at least doubles the minor
dimension of the flattened tube cross section.
7. The heat exchanger of claim 1 wherein the parallel legs of each
of the tubes are spaced from each other.
8. The heat exchanger of claim 1 wherein the major dimension of
each of the tube ends extends parallel to the longitudinal axes of
the headers at the location where the tube end is connected to the
header.
9. The heat exchanger of claim 1 wherein one of the twists of each
of the tubes is a left handed twist and the other twist of the tube
is a right handed twist.
10. The heat exchanger of claim 1 wherein one of the twists of each
of the tubes is a left handed twist and the other twist of the tube
is a left handed twist.
11. The heat exchanger of claim 1 wherein one of the twists of each
of the tubes is a right handed twist and the other twist of the
tube is a right handed twist.
12. A folded, elongated tube for use in a heat exchanger, the tube
having a flattened cross section with a minor dimension and a major
dimension, the tube comprising: a pair of parallel tube runs, the
major dimensions of the tube runs lying in a common plane; and a
folded section of tube connecting the pair of tube runs, the folded
section comprising a U-shaped bend including a straight section of
tube extending between two curved sections of tube and having its
major dimension extending substantially transverse to the major
dimensions of the tube runs, a first 90.degree. twist connecting
one of the tube runs to one of the curved sections of the U-shaped
bend, and a second 90.degree. twist connecting the other tube run
to the other curved section of the U-shaped bend.
13. The tube of claim 12 wherein the straight section of the tube
has a length that at least doubles the minor dimension of the
flattened tube cross section.
14. The tube of claim 12 wherein the straight section of the
U-shaped bend extends transverse to the parallel legs.
15. The tube of claim 12 further comprising: a third tube run
parallel to the pair of tube runs, the major dimension of the tube
run lying in the common plane; and a second folded section of tube
connecting the third tube run to one of the other tube runs, the
second folded section comprising a second U-shaped bend including a
straight section of tube extending between two curved sections of
tube and having its major dimension extending substantially
transverse to the major dimensions of the tube runs, a third
90.degree. twist connecting the one of the other tube runs to one
of the curved sections of the second U-shaped bend, and a fourth
90.degree. twist connecting the third tube run to other curved
section of the second U-shaped bend.
16. The tube of claim 12 wherein the parallel legs are spaced from
each other.
17. The tube of claim 12 wherein one of the twists is a left handed
twist and the other twist is a right handed twist.
18. The tube of claim 12 wherein one of the twists is a left handed
twist and the other twist is a left handed twist.
19. The tube of claim 1 wherein one of the twists is a right handed
twist and the other twist is a right handed twist.
Description
FIELD OF THE INVENTION
[0001] This invention relates to heat exchangers and tubes
therefor, and more particularly, to heat exchangers including a
core made up of elongated, flat tubes and interconnecting fins.
BACKGROUND OF THE INVENTION
[0002] One common form of a heat exchanger includes a so called
"core" made up of tubes and interconnecting fins. One fluid is
passed through the tubes of the core while a second fluid is passed
through the core itself in the spaces between the fins and tubes.
Typically, the opposite ends of the tubes are connected to a pair
of parallel manifolds or "tanks", with one of the manifolds being
an inlet manifold and the other manifold being an outlet manifold
which direct one of the fluids into and out of the tubes,
respectively.
[0003] Heat exchangers of this general type are used for a large
variety of purposes, such as radiators, condensers, evaporators,
charge air coolers, oil coolers, etc., all of which may be utilized
in a vehicle. One common form of this type of heat exchanger is
known as a parallel flow heat exchanger wherein flat, multi-port
tubes direct a refrigerant through the heat exchanger. Typically,
the flat tubes are straight and the manifolds are spaced on
opposite sides of the heat exchanger to receive the opposite ends
of the tubes. However, it is known to bend the flat tubes so that
the each tube is shaped as a so called "hair pin" tube having two
parallel legs, with the inlet and outlet manifold positioned next
to each other to receive the ends of the tubes. Examples of such a
construction are shown in U.S. Pat. No. 5,531,268 issued to Hoshino
et al. and EP 0 659 500 B1. While these constructions may be
suitable for their intended purpose, there is always room for
improvement. For example, these constructions may not be suitable
or optimum for use in some air conditioning systems that rely on a
higher operating pressure, such as a transcritical cooling cycle
that requires a gas cooler for providing supercritical cooling of a
refrigerant such as carbon dioxide (CO.sub.2).
[0004] Increasing environmental concerns over the use of many
conventional refrigerants such as CFC12 and, to a lesser extent
HFC134a, has led to consideration of transcritical CO.sub.2
systems, particularly for use in vehicular applications. For one,
the CO.sub.2 utilized as a refrigerant in such systems could be
claimed from the atmosphere at the outset with the result that if
it were to leak from the system back to the atmosphere, there would
be no net increase in atmospheric CO.sub.2 content. Moreover, while
CO.sub.2 is undesirable from the standpoint of a greenhouse effect,
it does not affect the ozone layer and would not cause an increase
in the greenhouse effect since there would be no net increase in
the atmospheric CO.sub.2 content as a result of leakage.
SUMMARY OF THE INVENTION
[0005] It is the principle object of the invention to provide a new
and improved heat exchanger and tube constructions.
[0006] An exemplary embodiment of the invention achieves at least
some of the foregoing objects in a heat exchanger including a pair
of elongated headers having longitudinal axes disposed
substantially parallel to each other, a plurality of elongated
tubes spaced in side-by-side relation along the longitudinal axes
of the headers, each of the tubes having a first end connected to
one of the headers and a second end connected to the other header
to transfer the working fluid between the headers, and serpentine
fins extending between adjacent pairs of the tubes. The tubes each
have a flattened cross section with a minor dimension and a major
dimension, and include a pair of parallel tube runs connected by a
folded section of the tube. The major dimension of each of the tube
runs extends substantially transverse to the longitudinal axes of
the headers. The folded section of each of the tubes includes a
U-shaped bend having a straight section of tube extending between
two curved sections of tube, a first twist connecting one of the
tube runs to one of the curved sections of the U-shaped bend, and a
second twist connecting the other tube run to the other curved
section of the U-shaped bend. Each of the U-shaped bends has its
major dimension extending substantially parallel to the
longitudinal axes of the headers.
[0007] In one form, the major dimension of one of the tube runs of
each tube lies in common plane with the major dimension of the
other tube run of the tube.
[0008] In one form, each of the twists is a 90.degree. twist.
[0009] In one form, the major dimension of each of the tube runs
extends parallel to the longitudinal axes of the headers at the
location where the tube end is connected to the header.
[0010] In one form of the invention, a folded, elongated tube is
provided for use in a heat exchanger. The tube has a flattened
cross section with a minor dimension and a major dimension. The
tube includes a pair of parallel tube runs, and a folded section
connecting the pair of tube runs. The major dimensions of the tube
runs lie in a common plane. The folded section includes a U-shaped
bend, a first 90.degree. twist, and a second 90.degree. twist. The
U-shaped bend includes a straight section of tube extending between
two curved sections of tubes. The U-shaped bend has its major
dimension extending substantially transverse to the major
dimensions of the tube runs. The first 90.degree. twist connects
one of the tube runs to one of the curved sections of the U-shaped
bend, and the second 90.degree. twist connects the other tube run
to the other curved section of the U-shaped bend.
[0011] In one form, the straight section of the U-shaped bend
extends transverse to the parallel tube runs.
[0012] Other objects and advantages will become apparent from the
following specification and claims taken in connection with the
accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a somewhat diagrammatic elevation view of a
cooling system including a pair of heat exchangers embodying the
present invention;
[0014] FIG. 2 is an elevation view of one of the heat exchangers
shown in FIG. 1;
[0015] FIG. 3 is a side view of the heat exchanger shown in FIG.
2;
[0016] FIG. 4 is a top view of the heat exchanger shown in FIG.
2;
[0017] FIG. 5 is an enlarged, partial section view taken along line
5-5 in FIG. 3;
[0018] FIG. 6 is an enlarged, partial view of a tube embodying the
invention and employed in the heat exchangers shown in FIG. 1;
[0019] FIG. 7 is a perspective view showing a tube and a fin
utilized in the heat exchangers shown in FIG. 1;
[0020] FIG. 8 is an elevation view of the other heat exchanger
shown in FIG. 1;
[0021] FIG. 9 is a top view of the heat exchanger shown in FIG. 8;
and
[0022] FIG. 10 is a side view of the heat exchanger shown in FIG.
8.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring to FIG. 1, heat exchangers 10 and 11 embodying the
present invention are shown in connection with a cooling system 12
that operates a transcritical cooling cycle. The heat exchanger 10
is shown in the form of a gas cooler that provides supercritical
cooling to the working fluid or refrigerant, such as CO.sub.2, of
the cooling system 12 by rejecting heat to a medium, such as an air
flow, on the fin side of the heat exchanger 10. The heat exchanger
11 is shown in the form of an evaporator that transfers heat from
one medium, such as an airflow on the fin side of the heat
exchanger 11 to the refrigerant in the system 12 to change the
refrigerant from the liquid phase to the gaseous phase. The cooling
system 12 further includes a compressor 14 that compresses gaseous
phase refrigerant to a supercritical pressure for delivery to the
heat exchanger 10, an expansion device 16 that reduces the pressure
in the refrigerant received from the heat exchanger 10 so at least
some of the refrigerant enters the liquid phase, an accumulator 18
(optional), and a suction line heat exchanger 19 that transfers
heat from the refrigerant exiting the gas cooler 10 to the
refrigerant exiting the evaporator 11, or accumulator 18 if used.
While the heat exchangers 10 and 11 are shown in connection with a
transcritical cooling cycle, it should be understood that the heat
exchangers 10 and 11 may find uses in other types of cooling and/or
heating systems, and in other configuration of cooling systems that
perform a transcritical cooling cycle, and are not limited to use
with the specific cooling system shown in FIG. 1 unless
specifically recited in the claims. Further, it should be
understood that the heat exchangers 10 and 11 can be adapted for a
large variety of purposes, such as for use as radiators,
condensers, charge air coolers, oil coolers, etc.
[0024] Having described a typical operating environment for the
heat exchangers 10 and 11, a more detailed description will now be
provided for the heat exchangers 10 and 11, with a focus on the
heat exchanger 11 for the purpose of brevity.
[0025] With reference to FIGS. 2-4, the heat exchanger 11 includes
a pair of elongated tubular headers 20 and 22 having longitudinal
axes 24 and 26, respectively, disposed substantially parallel to
each other; a plurality of elongated tubes 28 spaced in
side-by-side relation along the longitudinal axes 24, 26 of the
headers 20, 22; and serpentine fins 30 extending between adjacent
pairs of the tubes 28. It should be understood that in the
illustrated embodiment, each fin 30 extends over a length L of the
tubes 28, but the middle portions of the lengths are not shown in
FIG. 2 for convenience of illustration. Preferably, the fins 30 are
louvered. As seen in FIG. 3, each of the tubes 28 has a first end
31 connected to the header 20, and a second end 32 connected to the
header 22 to transfer the refrigerant between the headers 20,
22.
[0026] Each of the tubes 28 has a flattened cross-section with a
major dimension D and a minor dimension d, as best seen in FIG. 5.
Each of the tubes 28 is preferably a multi-port tube. In this
regard, it should be understood that while FIG. 5 shows six ports
34, it may be beneficial in some applications to include more than,
or less than, six ports 34 in each of the multi-port tubes 28. For
example, in one preferred embodiment each of the tubes has four
ports 34. Additionally, it should be understood that the hydraulic
diameter of the tubes 28 will be highly dependent upon the specific
parameters of each particular application, such as, for example, of
the particular working fluid used within the heat exchanger and the
flow rate of the working fluid to the heat exchanger.
[0027] In one preferred embodiment, the tubes are configured to
withstand a burst pressure of at least 6500 PSI, such as may be
required for a heat exchanger in a transcritical CO.sub.2 cooling
system. Further, in some preferred embodiments for use in a
transcritical CO.sub.2 cooling system, the hydraulic diameter of
the tube is preferably in the range of 0.015 inch to 0.045 inch,
the major dimension D of each of the tubes 28 is preferably no
greater than 0.500 inch, and the minor dimension d is preferably no
greater than 0.100 inch, while in some highly preferred embodiments
the minor dimension d is nominally no greater than 0.060 inch and
the major dimension D is nominally no greater than 0.320 inch.
[0028] As best seen in FIGS. 3 and 6, each of the tubes 28 is
folded upon itself to define at least two parallel tube runs 36 of
the tube 28 so that the refrigerant flows serially through at least
two parallel fluid passes 38 from the header 20 to the header 22.
In this regard, it is preferred that the inlet and outlet headers
20, 22 be selected so that the heat exchanger 11 operates in a
cross-counterflow configuration relative to the fluid flow A on the
fin side of the heat exchanger 11. Each pair of the parallel tube
runs 36 is joined by a fold 40 that is twisted 90.degree. relative
to the tube runs 36 at the location of the fold 40 so that the
major dimension D extends parallel to the axes 26, 24 at the
location of the fold 39, rather than transverse.
[0029] As best seen in FIG. 6, each of the folds 40 includes a
U-shaped bend 42, a first 90.degree. twist 44, and a second
90.degree. twist 46. Each U-shaped bend 42 includes a straight
section 48 extending between two curved sections 50 and 52. The
twist 44 connects one of the tube runs 36 to one of the curved
sections 50, and the twist 46 connects the other parallel tube run
36 to the other curved section 52.
[0030] Preferably, the fold 40 is formed by first twisting the tube
runs 36 90.degree. relative to the portion of the tube 28 that will
form the straight section 48 and then bending the tube 28 at each
end of the straight section 48 through approximately 90.degree. to
form the curved sections 50 and 52. In this regard, it should be
understood that the 90.degree. twist of each of the tube runs 36
relative to the fold 40 can be in the same direction as shown in
FIGS. 3 and 6, or in opposite directions, depending upon which
configuration offers the most advantage for a particular
application of the heat exchanger 11.
[0031] As best seen in FIG. 6, the parallel tube runs 36 of each of
the tubes 28 are preferably spaced from each other by a distance X,
with the major dimension D of each of the parallel tubes 36 lying
in a common plane, illustrated by dashed line P in FIGS. 2 and 5,
that is substantially transverse to the longitudinal axes 24, 26 of
the headers 20, 22. This allows the major dimension D to extend
parallel to the direction A of the flow of the medium through the
fins 30. The spacing X reduces heat conduction from one tube run 36
to the other, which can be advantageous when the heat exchanger 10
is providing supercritical cooling because the temperature of the
refrigerant can vary substantially as it flows through the tube 28
from one header 20 to the other header 22. Preferably, the distance
X is sufficient to minimize or prevent the closing of the space
between adjacent parallel tube runs 36 by braze material during
brazing of the heat exchanger 10, but not so large so as to unduly
increase the depth of the heat exchanger 10. While it is preferred
that the adjacent parallel tube 36 of each tube 28 be spaced from
each other, in some applications this spacing may not be required
and/or desirable.
[0032] In one preferred embodiment, the straight section 48 of each
of the tubes 28 has a length L1 that at least doubles the minor
dimension of the flattened tube cross section. However, it should
be appreciated that the length L1 of the straight section 48 can
vary from application to application depending upon the particular
parameters of each application, such as, for example, the
acceptable bend radius R for the curved sections 50 and 52 of the
bends 42 and the desired spacing X between each of the tube runs
36.
[0033] As best seen in FIG. 3, the illustrated heat exchanger 11
includes 6 parallel tube runs 36 for each of the tubes 28. However,
it should be understood that the optimum number of parallel tube
runs for each application of the heat exchanger 10 will be highly
dependent upon the specific parameter for the particular
application such as, for example, the working fluid of the system
12, the envelope and environment into which the heat exchanger 11
must be packaged, and the function of the heat exchanger, i.e. as a
gas cooler, condenser, or evaporator for use in an AC or heat pump
system. For example, in some applications it may be desirable to
have as few as two or three parallel tube runs 36 for each of the
tubes 28, or 12 or more tube runs 36 for each of the tubes 28. By
way of further example, FIGS. 8, 9 and 10 show the heat exchanger
10 having two parallel tube runs 36 for each of the tubes 28.
[0034] As seen in FIGS. 1 and 5, each of the fins 30 has a fin
height H equal to the spacing between adjacent tubes 28, i.e. a fin
height H extending from one of the tubes 28 to an adjacent tube 28
parallel to the longitudinal axes 24, 26 of the headers 20, 22.
Preferably, the major dimension D of the tubes 28 is either no
greater than the fin height H, or no greater than the sum of the
fin height H and the minor dimension d. This allows a construction
wherein each of the tube ends 31, 32 can be twisted 90.degree.
relative to the parallel tube runs 36 from which they extend so
that the major dimension D of the ends 31, 32 extends parallel to
the longitudinal axes 24, 26 of the headers 20, 22 at the location
where the tube ends 31 and 32 are connected to the headers 20 and
22, as seen in FIG. 2. This can be important in high pressure
applications, such as heat exchangers used in transcritical
refrigeration systems, where it is desirable that the diameter of
the headers 20, 22 be as small as possible. It is conceivable, even
likely, in such constructions that the major dimension D will be
greater than the inner diameter of either of the headers 20, 22. By
allowing the major dimension D to extend parallel to the
longitudinal axis 24, 26 of the headers 20, 22 where the tube ends
31, 32 are connected to the headers 20, 22, the major dimension D
of each of the tubes 28 can be greater than the inner diameter of
either of the headers 20, 22.
[0035] As previously discussed, each of the serpentine fins 30 has
a length L extending parallel to the parallel tube runs 36 of the
adjacent tubes 28, and as best seen in FIG. 4, a transverse width W
extending across the parallel tube runs 36 of the adjacent tubes
28. For purposes of illustration, FIG. 5 shows three tube runs 36
of the tubes 28 and FIG. 7 shows a fin 30 for use with a heat
exchanger construction 10 wherein each of the tubes 28 has only two
parallel runs 36. With reference to FIG. 7, each of the fins 30
includes a plurality of alternating tabs 60 and elongated
separations 62 extending parallel to the parallel tube runs 36 and
located between the parallel tube runs 36 of the adjacent tubes 28
to divide the width W of each fin 30 into two or more discrete fin
strips or elements 64 that are connected to each other by the tabs
60. Each of the fin elements 64 corresponds to and extends along
one of the parallel tube runs 36 of each of the adjacent tubes 28.
The separations 62 are generally straight line and have opposed
edges 65 that face one another and are generally transverse to the
direction of the medium flow through the fins 30. While FIG. 7
illustrates the fin 30 for tubes 28 having two parallel tube runs
36, it should be understood that the above construction including
the tabs 60, separations 62 and fin elements 64 is utilized in
constructions of the heat exchanger 10 having more than two
parallel tube runs 36 in each of the tubes 28, such as the
constructions shown in FIGS. 2-5. In such constructions, each of
the fins 30 preferably extends across all of the parallel tube runs
36 with a fin element 64 corresponding to and extending along each
of the parallel tube runs 36 of each of the adjacent tubes 28, and
the tabs 60 and separations 62 provided between each of the fin
elements 64.
[0036] The alternating tabs 60 in each of the fins 30 serve to
restrict movement of the fin elements 64 relative to each other so
that each fin 30 remains a unitary component during the assembly of
the heat exchanger 10 and, furthermore, to better maintain the fin
elements 64 in alignment with each other to minimize the pressure
drop on the fin side of the heat exchanger. The purpose of the
elongated separations 62 is to minimize the heat conduction from
each of the parallel tube runs 36 to any adjacent parallel tube
runs 36 of each tube 28 by interrupting, and thus minimizing, the
heat conduction between the fin elements 44 associated with each of
the parallel legs 36. Thus, it is desirable for each of the
elongated separations 62 to extend uninterrupted as far as possible
along the length of the fin 30 and for the number and size of the
tabs 60 to be minimized to that which is required to prevent each
of the fin elements 64 from separating during assembly and to
maintain an acceptable degree of alignment between the fin elements
64 of each of the fins 30 during assembly.
[0037] From the foregoing, it should be understood that a number of
configurations are possible for the tabs 60 and the elongated
separations 62. For example, in one embodiment of a fin 30 made of
aluminum, with the fin 30 in an unfolded state, each of the tabs 60
extends approximately 0.020 inch along the length of the unfolded
fin 30 and each of the elongated separations 62 of a fin 30 extends
approximately 8.0 inches along the length of the unfolded fin 30.
In one preferred embodiment of the fin 30, the tabs 60 and the
separations 62 have lengths extending parallel with the length of
the fin 30 in the unfolded state, and the ratio of the length of
the separations 62 to the length of the tabs 60 is in the range of
200 to 600. In another example, such as shown in FIG. 7, each of
the elongated separations 62 extends uninterrupted from one of the
tabs 60 over 10 to 14 of the folds 66 to the next tab 60 with the
fin 30 in the folded condition.
[0038] While the tabs 60 and the separations 62 can be formed in a
number of ways, it is preferred that the separations 62 be formed
as cuts or slits in the fin material that do not require removal of
fin material during formation in the fin 30. One way of achieving
such slits or cuts is to use a splitter disk in the fin roll die to
create a simple cut in the fin 30 as the fin 30 is formed from a
strip of sheet material. The split can be eliminated for a small
portion of the disk in every revolution to form the tabs 60 to
ensure that each fin element 64 stays attached to the adjoining fin
element 64 of the fin 30. This provides a physical cut or slit in
the fin 30, with no loss of fin surface. In one such construction,
the edges 65 are virtually, but not quite, in abutment with each
other. One concern is that the fin elements 64 might braze together
during the brazing process. One approach to minimize this concern
is to locate the braze material on the side walls of the tube runs
36 that abut the fins 30, rather than cladding the braze material
onto the fins 30. Another approach to minimize this concern is to
offset adjacent fin elements 64 of the fin 30 at locations remote
from the tab 60, which may allow for clad fins. Another approach
would be to bend the edges 65 formed by the slits slightly apart,
forming a very small louver, which may also allow for clad fins.
Yet another approach is to coin each of the tab portions 60 to
further separate the fin elements 64 from each other. Again, this
last approach may allow for clad fins. While slits are preferred,
in some applications it may be advantageous for the separations 62
to be formed as slots that do require removal of fin material when
formed in the fins 30. In this regard, it would probably be
sufficient for the slots to have a width of a few thousands of an
inch parallel to the width W of the fin 30.
[0039] While it is preferred that the fins 30 include the tabs 60
and separations 62, in some applications the tabs 60 and
separations 62 may not be desirable and/or required.
[0040] It is preferred that the fins 30 be louvered, many forms of
which are known. The exact configuration of the louvers will be
highly dependent on the parameters of the particular application
such as, for example, the fluid on the fin side of the heat
exchanger 10, the available pressure drop on the fin side of the
heat exchanger 10, the number of parallel tube runs 36 in each of
the tubes 28, and whether there is an odd or even number of
parallel tube runs 36 in each of the tubes 28.
[0041] In one preferred embodiment the headers 20, 22, tubes 28,
and fins 30 are all made of aluminum and brazed with an appropriate
braze material. However, it should be understood that in some
applications other suitable materials made be employed for these
components as dictated by the parameters of the particular
application.
[0042] It should also be understood that while the heat exchanger
11 illustrated in FIGS. 1-3 is shown so that the longitudinal axes
24, 26 of the headers 20, 22 extend in a horizontal direction, and
the parallel tube runs 36 of the tubes 28 extend in a vertical
direction, it may be desirable in some applications for a heat
exchanger 11 to have a different orientation, such as, for example,
an orientation wherein the axes 24, 26 extend in a vertical
direction and the parallel tube runs 36 extend in a horizontal
direction. Further, while the headers 20, 22 of the heat exchanger
11 illustrated in FIGS. 1-3 are located on the same side of the
heat exchanger 11, it may be desirable in some applications for the
headers 20, 22 to be located on opposite sides of the heat
exchanger 11. A construction with the headers 20, 22 on the same
side of the heat exchanger will typically result in an even number
of parallel tube runs 36 for each of the tubes 28, while a
construction with the headers 20, 22 on opposite sides of the heat
exchanger 10 will typically result in a odd number of parallel tube
runs 36 for each of the tubes 28. Of course, header plates fitted
with tanks could be employed in lieu of the tubular headers 20, 22
if desired for a particular application.
[0043] It should be appreciated that by providing the straight
section 48 in the U-shaped bend 42, the dimension L2 of the heat
exchanger is minimized, as well as the portion Z of the tubes 28
that are not provided with fins 30.
* * * * *