U.S. patent application number 09/918922 was filed with the patent office on 2004-04-29 for folded, bent and re-expanded heat exchanger tube and assemblies.
Invention is credited to Mckay, A. Todd, Paulman, Roger.
Application Number | 20040079522 09/918922 |
Document ID | / |
Family ID | 32110969 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040079522 |
Kind Code |
A1 |
Paulman, Roger ; et
al. |
April 29, 2004 |
Folded, bent and re-expanded heat exchanger tube and assemblies
Abstract
A heat exchanger assembly of the side-entry type includes at
least one fin set and an elongated heat exchanger tube having one
or more collapsed sidewall portions extending substantially the
length of the tube. The folded tube is first bent to form the
return bend portions and then is expanded to engage the fin set.
Methods of making the elongated heat exchanger tube having one or
more collapsed sidewall portion methods of making heat exchanger
assemblies are also disclosed.
Inventors: |
Paulman, Roger; (Barrington,
IL) ; Mckay, A. Todd; (Matteson, IL) |
Correspondence
Address: |
William F. Prendergast
Brinks Hofer Gilson & Lione
P.O. Box 10395
Chicago
IL
60610
US
|
Family ID: |
32110969 |
Appl. No.: |
09/918922 |
Filed: |
July 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09918922 |
Jul 30, 2001 |
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09226908 |
Jan 8, 1999 |
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09226908 |
Jan 8, 1999 |
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08798615 |
Feb 11, 1997 |
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08798615 |
Feb 11, 1997 |
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08572180 |
Dec 13, 1995 |
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5704123 |
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60006655 |
Nov 13, 1995 |
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Current U.S.
Class: |
165/177 |
Current CPC
Class: |
F28F 1/32 20130101; F28F
1/02 20130101; B21D 53/085 20130101; F28F 1/003 20130101 |
Class at
Publication: |
165/177 |
International
Class: |
F28F 001/00 |
Claims
1. For use in the heat exchanger assembly of a side entry type
having at least one fin set, an elongated heat exchanger tube
having at least two collapsed sidewall portions extending
substantially the length of said tube, the elongated heat exchanger
tube being adapted to being bent to form a return bend portion and
then being expanded to engage and secure the tube in a passage in a
fin set.
2. The tube of claim 1 wherein said elongated heat exchanger tube
has a wall thickness of between about 0.010 to 0.030 inches.
3. The tube of claim 1 wherein the one or more collapsed sidewall
portions comprises an elongated recess extending substantially the
length of said heat exchanger tube.
4. The tube of claim 1 wherein the one or more collapsed sidewall
portions comprise a pair of opposed elongated recesses extending
substantially the length of said heat exchanger tube.
5. An elongated heat exchanger tube comprising: an elongated tube
having first and second ends and an internal passageway extending
between the first and second ends, said elongated tube being formed
from a sidewall; at least two collapsed portions of the sidewall of
the elongated heat exchanger tube extending substantially along a
length of the elongated tube, the two collapsed portions contacting
each other within the passageway of the tube; and the at least two
collapsed portions of the sidewall of the elongated tube being
expandable radially outward to push the at least two collapsed
sidewall portions outward so that they no longer contact each other
and the passageway within the tube is opened.
6. The tube of claim 31 wherein the at least two collapsed portions
define at least two elongated recesses extending substantially
along a length of the elongated tube.
7. The tube of claim 31 wherein the at least two collapsed portions
of the side wall of the elongated tube are each form a portion of
the sidewall that is bent into a generally U-shaped configuration
having two sides and a bottom, and the bottoms of the U-shaped
configurations of the at least two collapsed portions contact each
other.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part application from
pending U.S. Ser. No. 08/798,615, filed Feb. 11, 1997, which is a
divisional application of U.S. Ser. No. 08/572,180, filed Dec. 13,
1990, which is based on provisional application U.S. Ser. No.
60/006,655, filed Nov. 13, 1995.
FIELD OF THE INVENTION
[0002] The present invention relates to a novel thin-walled heat
exchanger tube and a method of manufacturing heat exchanger
assemblies utilizing such thin-walled heat exchanger tubes.
[0003] Aluminum evaporator coils have been used for decades in
frost-free refrigeration systems. Their adoption and use has been
predicated upon cost-effective manufacturing methods relative to
competing technologies, coupled with continued improvements in
operating efficiencies and the use of less refrigerant material in
the refrigeration system. For example, the tube wall thickness has
typically declined from about 0.035 inches to approximately 0.019
inches over the past twenty years. Additionally, fin thicknesses
have also been typically reduced from 0.010 to 0.00575 inches
during this same period of time. Such savings in material wall
thickness has been possible because the finished evaporator coil
generally requires a burst strength of only about 500 pounds per
square inch maximum while current models even with the thinnest
tube wall-thicknesses possess burst strengths of over 1,000 pounds
per square inch, more than a sufficient safety factor.
[0004] However, the problem facing heat exchanger assembly
manufacturers has been to devise an acceptable method of
manufacturing a coil using thin-walled tubing. The problem of the
known prior art methods is highlighted by the requirement of
bending the thin-walled tubing around a small radius to create the
"return bend." Thin-walled tubing collapses unless properly
supported either internally with a mandrel bend, which is now
uneconomic because of cleanliness requirements of the new
refrigerants, or externally by spacers as has been the case for
many years in the manufacture of this style of evaporator coil. In
addition, some methods of manufacture require that the thin walled
tubing be pushed or pulled through collared fins sets or arrays.
Because thin-walled heat exchanger tubes do not possess sufficient
strength and rigidity, they are generally unsuitable for this type
of handling in manufacture.
[0005] Various means have been suggested for containing the
thin-walled heat exchange tube at the "return bend". One such
method utilizes spacers as the tube is wound around a mandrel
thereby resulting in a controlled collapse of the tubing at the
return bend that is later expanded through internal pressure to
something close to its original size and shape. See for example,
U.S. Pat. No. 5,228,198, assigned to the assignee of the present
invention for a discussion of the technique. Alternately, it has
been suggested that the heat exchanger tubing may be ovalized in
cross-section to fit into keyhole shaped slots in the fin set or
array which are then re-expanded through the use of internal
pressure. See for example, U.S. Pat. Nos. 4,778,004 and 4,881,311
assigned to the assignee of the present invention for such
techniques. However, each of these methods result in return bend
portions that must be externally supported to prevent collapse of
the tube.
SUMMARY OF THE INVENTION
[0006] Therefore, one object of the present invention is to provide
a novel method of making and utilizing a thin-walled elongated heat
exchanger tube having one or more collapsed sidewall portions
extending substantially the length thereof in a heat exchanger
assembly of the side-entry type which may be readily manufactured
and assembled.
[0007] Another object of the present invention is to provide a
thin-walled heat exchanger assembly which is more compact and
rugged than existing heat exchanger assemblies while possessing
increased efficiencies over existing refrigeration systems.
[0008] It is another object of the present invention to permit easy
assembly and positioning of the serpentine tube into the associated
fin set without the use of collars or other devices.
[0009] It is still another object of the present invention to
utilize a novel heat exchanger tube arrangement wherein a thin
walled elongated tube having a collapsed sidewall extending
substantially the length thereof is inserted within a straight tube
of a larger diameter and then reinflated to form a tight bond and
seal with the outside tube to provide a shield for the interior
tube against leakage. This permits the use of such heat exchanger
assemblies in refrigeration systems containing combustible
refrigerants.
[0010] It is yet another object of the present invention to provide
a novel heat exchanger tube wherein a heating wire is positioned
within the elongated opening of the collapsed tube, the tube and
heating wire is inserted within a straight tube of a larger
diameter and then re-inflated to form a tight bond and seal with
the outside tube to provide a structure where the heating wire
contained between the heat exchanger tubes is positioned adjacent
the fin sets or array to readily accomplish defrosting of the heat
exchanger assembly.
[0011] In accordance with the present invention, a thin-walled heat
exchanger tube extruded to final cross-section or is passed through
a folding mechanism or Yoder style rolling mill to provide an
elongated tube having one or more collapsed side-wall portions
extending substantially the length of the tube. The cross-section
of the collapsed elongated tube provides one or more elongated
recesses, channels or openings extending substantially the length
of the heat exchanger tube. The one or more collapsed sidewall
portions may be of equal or unequal lengths and are formed at
multiple angles around the circumference of the tube. In exemplar
embodiments, the tube may include two opposed recesses or three,
four or five recesses equidistantly spaced about a circumference of
the tube and extending substantially the length thereof.
[0012] The effect of compressing or collapsing the tubing to create
recesses or openings extending the length of the tubing and around
the circumference at any angle reduces the effective diameter of
the heat exchanger tube while increasing the effective tube-wall
thickness. Such a tube structure permits the bending of the
resilient tube having a smaller diameter about a mandrel in
multiple orientations circumferentially with the folded wall
preventing the collapse of the tubing in the bend area. Thus, by
reducing the effective diameter of the tube while increasing the
effective wall thickness of the tube, smaller mandrels and multiple
directions circumferentially may be used for bending the heat
exchanger tube into the serpentine coil. This structure permits the
bending of the collapsed tube having a wall thickness of as little
as 0.012 inches (generally in the range of 0.010-0.025 inches)
around mandrels of 1/2 inch or less (generally from 3/8 to 11/2
inches or more) to provide a finish coil containing tubes as close
together in the plane of bending of 1/2 inch or less instead of the
5/8 inches or greater, as is true of existing heat exchanger
assemblies. This structure provides an increase of tube density in
a given coil configuration of up to 20 to 50 percent over existing
structures, a significant factor in making heat exchanger
assemblies.
[0013] Additionally, in accordance with the present invention, the
inward folding of the elongated tube to provide collapsed sidewall
portions extending substantially the length of the tube and at
multiple angles circumferentially provides a collapsed tube where
the interior surfaces of the folds actually touch or come very
close to touching or engaging the opposite wall of the tube or the
opposing fold. Such a structure prevents the portion of the tube
that is in actual contact with the mandrels during the bending
operation from forming a "cave" or "dent" by moving away from the
mandrel. Such "caves" or "dents" generally do not reround
themselves during the reinflation of the tubing process. The
opposite sidewall of the tube or opposing fold being in contact
with the sidewall which engages the mandrel, has an effect of
reinforcing the tube wall against such "caving" or "denting" during
wrapping and, thus, increases the effective wall thickness for the
purpose of bending.
[0014] During the manufacture of heat exchanger tubes in accordance
with the present invention, at least one end of the heat exchanger
tube for a distance of approximately 6 to 12 inches from the end is
not collapsed during engagement with the folding mechanism or means
and remains in the as-extruded round cross-sectional configuration.
The round end structure facilitates ready attachment or connection
with a pressure fitting when the time for reinflation occurs.
[0015] Thus, the present invention discloses a manufacturing method
for making heat exchanger assemblies that eliminates the use of
spacers during the bending operation of the heat exchanger tube
around multiple diameter mandrel assemblies. Additionally, the
present invention, utilizing a collapsed thin-walled heat exchanger
tube, provides for a heat exchanger assembly having a more dense
spacing of the tube utilizing smaller mandrel sizes than is
presently available under existing prior art structures.
Additionally, mandrels of differing sizes and greater design
opportunities exist for use with the refrigeration industry thereby
providing increased evaporator efficiency of the refrigerating
system. Also, in accordance with the present invention, thinner
fins and tube walls may be utilized than had previously been
possible for use in making heat exchanger assemblies containing a
serpentine elongated heat exchanger tube and results in a more
efficient tube having a substantial lower cost in
manufacturing.
[0016] Thus, the present invention significantly simplifies the
tube bending mechanism utilized in serpentine-type heat exchanger
assemblies while providing an initial lower investment in equipment
costs to make heat exchanger assemblies in accordance with the
present invention.
[0017] Also, the present invention allows for a much greater
flexibility in the configuration and placement of heat exchanger
tubes relative to the fin set and enables the designer to change
concentration of tubes and fins within the same finished
product.
[0018] The present invention consists of certain novel features and
structural details hereinafter fully described, illustrated in the
accompanying drawings, and particularly pointed out in the appended
claims, it being understood that various changes in the details may
be made without departing from the spirit, or sacrificing any of
the advantages of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a perspective view of an extruded thin-walled heat
exchanger tube in Accordance with the present invention.
[0020] FIG. 1A is a cross-section of the thin-walled heat exchanger
tube shown in FIG. 1.
[0021] FIG. 2 is a perspective view of a collapsed thin walled heat
exchanger tube during rolling down through a folding mechanism or
means of the exchanger tube of FIG. 1 to provide the elongated
collapsed heat exchanger tube in accordance with the present
invention.
[0022] FIG. 2A is a front view of the heat exchanger tube passing
through the folding mechanism as shown in FIG. 2.
[0023] FIG. 3 illustrates a set of multiple diameter mandrels used
for bending the various radii bends in a continuous wrapping motion
for making the serpentine tube in accordance with the present
invention.
[0024] FIG. 4 is the heat exchanger tube of FIG. 2 continuously
wrapped on the mandrels of FIG. 3 in accordance with the present
invention.
[0025] FIG. 5 illustrates the collapsed serpentine-type heat
exchanger tube formed in FIG. 4 during insertion into openings in a
fin set or array in accordance with the present invention.
[0026] FIG. 6 illustrates the serpentine heat exchanger tube of
FIG. 5 after expansion to engage the fin set or array using
internal pressure means in accordance with the present
invention.
[0027] FIG. 7 is a tube within a tube cross-section illustrate the
insertion of the collapsed tube within a round tube of a larger,
diameter in accordance with a further embodiment of the present
invention.
[0028] FIG. 7A is the tube within a tube as depicted in FIG. 7
after expansion of the inner collapsed tube using internal pressure
means in accordance with the present invention.
[0029] FIG. 8 is a tube within a tube as shown in FIG. 7 further
including an elongated heating wire positioned within the elongated
opening provided by the collapsed thin-walled heat exchanger tube
in accordance with a further embodiment of the present
invention.
[0030] FIG. 8A is the tube within a tube and heating wire as
depicted in FIG. 8 after expansion of the inner collapsed tube
using internal pressure means in accordance with the present
invention.
[0031] FIG. 9 is a perspective view of the collapsed or folded heat
exchanger tube of FIG. 2 being inserted through individual fin sets
or arrays associated with each pipe of a heat exchanger
assembly.
[0032] FIG. 9A illustrates a heat exchanger assembly of the heat
exchanger tube of FIG. 9 continuously arranged on mandrels in
accordance with the present invention.
[0033] FIG. 9B illustrates the finished heat exchanger assembly of
FIG. 9A after air expansion utilizing internal pressure means to
expand the collapsed tube to engage and be locked to the fin sets
or arrays in accordance with the present invention.
[0034] FIG. 10A is an end view of one embodiment of the heat
exchanger tube including two opposed collapsed sidewall
portions.
[0035] FIG. 10B is an end view of one embodiment of the heat
exchanger tube including three collapsed sidewall portions.
[0036] FIG. 10C is an end view of one embodiment of the heat
exchanger tube including four collapsed sidewall portions.
[0037] FIG. 10D is an end view of one embodiment of the heat
exchanger tube including five collapsed sidewall portions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Referring now to the drawings wherein like numerals have
been used throughout the several views to identify the same or
similar parts, the heat exchanger assembly 10 (FIG. 6) includes a
one piece length of heat exchanger tubing 12 (FIGS. 1 and 1A) in
the as-extruded round condition. The tubing 12 used for heat
exchangers of the type used in home refrigerator systems typically
have outside diameters of 1/4 to 1/2 inch, with wall thicknesses 14
of between about 0.010 to 0.030 inches and calculated to provide a
minimum burst strength. The wall thickness 14 will depend on the
material selected for extrusion, such as AA1050 grade aluminum, and
the tolerances allowed by the aluminum extrusion process. The
tubing 12 at this stage is in the as-extruded round configuration
or "F" state typically with a fine-grained structure.
[0039] The tubing 12 is cut to length for the particular serpentine
configuration desired in the finished heat exchanger assembly with
one length for each assembly. This length may vary typically from
as little as 15 feet to as much as 50 feet, depending on the total
heat transfer required by the refrigeration system.
[0040] Preferably, about 6-12 inches on the ends of the tubing are
preserved in their as-extruded "round" state, as will hereinafter
be discussed. One end of each individual tube is then inserted 6-12
inches from the end into a compression means or Yoder style rolling
mill 15, as shown in FIGS. 2 and 3.
[0041] In FIG. 2, the thin-walled heat exchanger tube 12 is passed
through a forming mechanism compressing means or Yoder style
rolling mill 15 having a forming cavity in the die which cooperates
with a compression wheel to provide an elongated tube 13 having a
collapsed side-wall 16 (FIG.2A) extending substantially the length
of the tube 13. The cross-section of the collapsed elongated tube
13 provides an elongated recess, channel or opening 18 extending
substantially the length of the heat exchanger tube, as also shown
in FIG. 2A. The effect of compressing and collapsing the tubing 12
to create an elongated recess or opening 18 within the folded tube
13 extending the length of the tubing provides that the effective
diameter of the collapsed heat exchanger tube 13 has been reduced
while at the same time the effective wall thickness 14 has been
increased. Such a tube structure permits the bending of the folded
tube 13 having a smaller diameter, about a multiple diameter
mandrels 20 with the sidewall 16 preventing the collapse of the
tubing in the bend area. Accordingly, by reducing the effective
diameter of the tube 13 while increasing the effective 20 wall
thickness of the tube, smaller mandrels 20 may be used for bending
the heat exchanger tube into the desired serpentine coil. Also,
such a structure permits the bending of collapsed tubes having a
wall thickness of as little as 0.012 inches (generally in the range
of 0.010-0.025 inches) around mandrels of 1/2 inch or less
(generally from 3/8 to 11/2 inches or more). This provides a coil,
according to the method of the present invention, containing tubes
as close together in the plane of bending of 1/2 inch or less
instead of the 5/8 inches or greater, as is true of existing heat
exchanger assemblies, as the mandrel set 20 turns in a rotary
fashion, as shown in FIG. 3. The folded tubing 13 exiting from the
rolling mill 15 possessing the structural shape shown in FIG. 2A,
and is then wrapped about the mandrels 20 with the open space 18 of
the collapsed tube away from the mandrel surfaces 20A, as shown in
FIG. 4. The rolling mill predeterminately controls the location of
the open space on the collapsed tube so that the tube is properly
positioned relative to the mandrel it will be wound around during
the manufacture of the serpentine heat exchanger tube.
[0042] In effect, as shown in FIG. 4, the collapsed tube 13 having
the elongated opening 18 therein is fed onto the multiple diameter
mandrel assembly 20, with the opening 18 always on the outside of
the mandrel surface 20A because the bending of heavier walled tubes
having a smaller diameter becomes easier to do without collapse of
the tubing in the bend area. By reducing the effective diameter and
increasing the effective wall thickness in this manner, smaller
mandrels may be used for bending. Typically, under previous methods
of manufacture, a {fraction (5/16)} inch outside diameter tube with
a {fraction (0.022)} inch wall thickness would collapse and be
unusable. As pointed out above, the method of the present invention
achieves an increase of tube density in a given coil of up to 20
percent over conventional available coils. Also, it should be noted
in accordance with the present invention, given dimensions are
proportionate for various tube diameters and wall thicknesses of
tubing and that this invention covers all ranges of diameters and
wall thickness.
[0043] It is an aspect of the present invention that at least one
end of the heat exchanger tubing 12 not be folded in the manner
heretofore described. The purpose for leaving at least one end in
the as-extruded round shape is that it permits for the simple
hookup with a pressure fitting when the time for reinflation
occurs.
[0044] As pointed out above, FIG. 4 shows the preferred manner of
wrapping of the folded tube about the mandrel surfaces 20A. The
opening 18 of the folded tube 13 should be oriented away from the
mandrel itself to permit the tube in the inflation mode to "open"
back outwardly to its original round or nearly round state. Also,
in accordance with the present invention, the elongated inwardly
folded sidewall, identified as 16 in the drawings, preferably
touches or comes in close contact with the opposite sidewall 16a of
the tube 13. The purpose for this is to prevent the portion of the
tube that is in actual contact with the mandrel during bending from
forming a "cave" or "dent" by displacement away from the mandrel.
Such "caves" or "dents" will generally not re-round themselves
during reinflation of the tubing process. The inward folded
sidewall 16 of the tube 13 being in contact with the sidewall 16a
which touches the mandrel surfaces 20A has the effect of
reinforcing the tube wall against such caving or denting during
wrapping and thus increases the apparent or effective wall
thickness for the purpose of bending.
[0045] As shown in FIGS. 3 and 4, some of the return bends have
different radii than others of the return bends. The purpose for
these differing sized bend radii is to allow the tubing to be
positioned in latter processing for variable tube spacing or for
"jumpers" or other reasons to allow the finished coil to have tubes
in almost any position within the finished heat exchanger assembly.
FIG. 4 also shows a proposed tube layout that might use variable
tube spacing for the purpose of catching frost in a frost-free
refrigerator, for example.
[0046] FIG. 5 illustrates the spirally wrapped serpentine type tube
17 containing the elongated opening 18 therein having been removed
from the mandrels and being inserted into slots or fin holes 22 in
the fin set or array 24. Unlike the prior art, the uninflated
folded serpentine-type tube 17 of the present invention has a
smaller diameter than the slots or fin holes 22 of the fin set or
array 24 into which it is being inserted. Consequently, it is
unnecessary to have collars or any other devices to facilitate the
easy slippage or positioning of the serpentine-type tube 17 into
the slots or fin holes, as is necessary with previously known
methods of manufacture. Thus, in accordance with the present
invention, the elongated folded or collapsed serpentine-type tube
17 may more easily be inserted into the fin set array than with
other methods of manufacture. It is a further part of this
invention that the "dog-bone" slots or fin holes 22 (FIG. 5)
through which the serpentine return bends must be slid may be
narrower than has previously been required, thus yielding greater
fin surface area in the finished heat exchanger assembly. Also, the
folded serpentine-type tube 17 being stiffer because of cold
working may be more easily slid into the fin slots or fin holes
22.
[0047] FIG. 6 illustrates the serpentine-type tube 12 and resultant
heat exchanger assembly 10 after reinflated to a new configuration,
in this case, substantially round. In this process, the expanded
tube sidewall 16 comes into intimate contact with the fin sets or
array 24 and locks the array into contact with the expanded tube to
produce an excellent tube-to-fin bond and consequently excellent
heat transfer properties. The reinflation process is extremely fast
and inflation of the collapsed serpentine tube 13 at one point will
not move the fin sets or array away from the tubing because there
is not enough time for the mass of the fin to accelerate and
produce movement away from the expanding tube. When the folded tube
is positioned and held in the proper orientation with respect to
the slots or fin holes 22 in the fin sets or array 24, the
inflation of the folded tube 13 causes the expanded tube to conform
to the geometry 20 of the fin slots or fin holes.
[0048] FIGS. 7 and 7A shows a further embodiment of the present
invention where a tube-in-tube arrangement is illustrated wherein
the collapsed tube 13 has been inserted into a straight tube 25
having a larger surface diameter and then re-inflated to form a
good tight bond between the outside of the collapsed tube and the
inner surface of the straight tube 25. Both tubes together can then
be serpentined and finned by conventional methods. This embodiment
provides a shield for the interior tube, which has heretofore not
been possible in manufacturing shielded interior tubes. Thus, an
important aspect of the present invention is that upon
re-inflation, the elongated opening 18 of the tube 13 does not
fully re-expand to the round shape, thus providing a small
elongated port 26 between the walls of the two tubes. This
elongated port 26 may be used by escaping gases should the interior
refrigerant containing tube 13 develop a leak. This design is of
particular value in the design of refrigeration systems using
combustible refrigerants.
[0049] FIGS. 8 and 8A illustrate a further embodiment of the
present invention of the tube-in-tube arrangement as shown in FIGS.
7 and 7A, wherein an elongated heating wire 27 is positioned within
the elongated opening 18 of the collapsed or folded tube 13. As set
forth above with respect to FIGS. 7 and 7A, upon reinflation, the
elongated opening 18 of the collapsed tube 13 does not fully
re-expand to the round shape, thus depositing the heating wire 27
within the elongated port 26 between the walls of the tubes. Such a
structure permits placing the heating wire within the heat
exchanger tubes to position the heat adjacent the fin sets or
array, the source of the frost. This structure readily accomplishes
defrosting of such heat exchanger assembles while utilizing reduced
power consumption.
[0050] FIGS. 9-9B illustrates an alternate type of finished heat
exchanger assembly 10 wherein individual folded fin sets or arrays
24 have been predeterminately positioned on the elongated folded
tube 13 (FIG. 9) by inserting the elongated collapsed tube through
fin holes 22 in the arrays 24 and then having the tubes containing
fin sets bent around mandrels 20 (FIG. 9A) prior to reinflation of
the tubes. The process of reinflation captures and secures the
individual fins to the tubes, as shown in FIG. 9B, to complete the
heat exchanger assembly 10. In this embodiment of the present
invention, it is also possible to have various forms of "collars"
to increase the tube to fin contact thus decreasing the resistance
of the heating flux between the tube and the fin. The method of
using the folded and reinflated tube containing fin sets therein
permits the heat exchanger designer greatly increased flexibility
not only in design of the tube layout but also the fin shape and
placement of the array within the finished coil. Also, in such
assemblies, both thinner fins and thinner tube walls are possible
than have been used in the prior art because the fins do not
support the expanded tubes or pipes.
[0051] In each of the foregoing embodiments, the tube 12 can be
formed to include one or more collapsed sidewall portions or
recesses 16. FIGS. 10A-10D illustrate alternate embodiments of the
tube 12 having a plurality of collapsed sidewall portions or
recesses 30-33. In each of the embodiments, the tube 12 and the
multiple collapsed sidewall portions or recesses 30-33 can be
formed by extrusion or using a conventional compression means or
Yoder style rolling mill as in known in the art.
[0052] In the embodiment shown in FIG. 10A, the tube 12 includes a
pair of opposed collapsed sidewall portions or recesses 30 that
extend substantially the length of the tube 12. In the embodiment
shown in FIG. 10B, the tube 12 includes three collapsed sidewall
portions or recesses 31 that are equidistantly spaced about the
circumference of tube 12 and extend substantially along the length
of the tube 12. FIG. 10C illustrates the tube 12 with four recesses
32 that are positioned equidistantly about the circumference of the
tube 12 and extend substantially along the length of the tube 12.
FIG. 10D illustrates the tube 12 with five recesses 33 that are
positioned equidistantly about the circumference of the tube 12 and
extend substantially along the length of the tube 12.
[0053] As shown in FIGS. 10A-10D, each of the collapsed sidewall
portions or recesses 30-33 come very close to touching or actually
touch the opposed or adjacent fold. The close proximity of the
collapsed wall portions prevents those portions of the tube from
forming a "cave" or "dent" during the bending operation. In that
regard, the multiple collapsed sidewall portions or recesses 30-33
are preferably equidistantly spaced about the circumference of the
tube 12 to facilitate such positioning of the opposed or adjacent
folds. In addition, the close positioning of the collapsed sidewall
portions or recesses 30-33 also permits the tube 12 to be wound
onto the mandrel in a variety of orientations. In contrast, the
tube 12 with one collapsed sidewall portion 16 is preferably
positioned in a preselected orientation with the collapsed portion
16 facing away from the mandrel.
[0054] As shown in FIGS. 10A-10D, the tube 12 can include from two
folds or recesses 30 to five folds or recesses 33 that gradually
decrease the ultimate collapsed diameter of the tube 12. The
smaller diameters of the collapsed tubes 12 shown in FIGS. 10A-10D
permit the tube to be bent about smaller mandrels to form smaller
return bends and thus increase tube density in the final heat
exchanger assembly. The smaller diameter of the tubes 12 also
permits the return bends to have a smaller radius, which also
permits an the increase in the tube density in the final heat
exchanger assembly. Further, the tube 12 can be collapsed to a
desired diameter with multiple folds so that the tube has a
sufficiently small diameter to fit within a tube array, or into the
slots of an accordion type fin array prior to inflation of the
tube. The particular number of folds or recesses used with the tube
12 can be selected depending upon the particular application for
which the tube 12 is intended.
[0055] By forming the tube 12 with multiple recesses or folds, the
tube 12 is increasingly work hardened to greater degrees to result
in a tube having a higher bending, reinflation, and burst strength
when the tube 12 is thin-walled aluminum material. This permits the
use of even thinner tubing in the heat exchanger which increases
the heat exchanger efficiently while reducing material costs.
[0056] In accordance with the present invention, a novel method for
making a heat exchanger assembly is disclosed which includes the
steps of passing a thin-walled heat exchanger tube through a
folding mechanism to provide an elongated tube having one or more
collapsed sidewall portions extending substantially the length of
the tube. The elongated collapsed heat exchanger tube is then
rotated about either a multiple diameter or constant diameter
forming mandrel to provide a spirally wrapped serpentine heat
exchanger tube. The spirally wrapped serpentine heat exchanger tube
is aligned with a heat transfer array having first and second
parallel fin surfaces with each paralleled surface having aligned
openings therein. The spirally wrapped and formed serpentine heat
exchanger tube is then inserted into the openings in the heat
transfer array and then re-expanded to move the collapsed heat
exchanger tube outwardly to cause the tube to engage and contact
with the fin surfaces to capture and secure the individual fins to
the expanded tube to complete the heat exchanger assembly.
[0057] Additionally, it is within the scope of the present
invention that the method of making heat exchanger assemblies
includes individual folded fin sets or arrays having openings
therein that are specifically positioned on the elongated collapsed
heat exchanger tube. The specifically mounted fin sets and
corresponding tube are then bent around the mandrel to provide a
serpentine-type like heat exchanger assembly. The formed elongated
serpentine-type collapsed heat exchanger tube is then reinflated to
engage and be secured to the individual fin surfaces of the fin set
array to complete the heat exchanger assembly. This method permits
the heat exchanger designer increased flexibility in the design of
the tube layout as well as the placement of the placement of the
array within the finished coil assembly.
[0058] Also, the method of making heat exchanger assemblies
includes the use of single or multiple heat transfer fin sets or
arrays, that are accordion-like sheets of heat radiating material
folded back and forth upon itself. The junction between the folded
sheets of the array material may include slots or notches which
cooperate to be engaged by a single length of collapsed heat
exchanger tube that is spirally wrapped around the array to engage
the slots or notches to form the heat exchanger assembly. The heat
exchanger assembly is completed by reinflating the collapsed tube
to secure the tube to the array or arrays, to provide a heat
exchanger assembly, substantially in accordance with the teachings
of U.S. Pat. No. 4,778,004, assigned to the assignee of the present
invention, which teaching is incorporated herein.
[0059] Although the present invention has been disclosed as
utilizing a multiple diameter forming mandrel to provide the
spirally wrapped serpentine-type heat exchanger tube, the forming
mandrel may also be of a constant diameter to provide the wrapped
heat exchange tube. Moreover, the forming mandrel may have a
configuration that is rectangular in form or multiple-sided in form
to permit the manufacture of various geometric coil configurations,
as desired.
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