Heat exchange – Radiator core type – Deformed sheet forms passages between side-by-side tube means
Reexamination Certificate
1999-04-19
2003-07-29
Flanigan, Allen (Department: 3743)
Heat exchange
Radiator core type
Deformed sheet forms passages between side-by-side tube means
C165SDIG005, C165SDIG005, C029S890046
Reexamination Certificate
active
06598669
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to heat exchanger assemblies and more particularly to an improved fin array design for use in a variety of heat exchanger assemblies and a method of making the fin array.
FIG. 1
illustrates a prior art heat exchanger assembly in the form of a condenser typically used in air conditioning units for vehicles. The heat exchanger assembly
10
includes a pair of opposed, spaced, generally parallel headers
11
and
12
. The headers
11
and
12
each define a series of generally parallel slots or openings
13
for receiving the ends
14
a
and
14
b
of tubes
14
that extend in fluid communication between the headers
11
and
12
. Each of the headers
11
and
12
includes a fitting
15
and a cap
16
. The fittings
15
operate as either an inlet or outlet for circulation of fluid through the headers
11
and
12
and tubes
14
. The fittings
15
can be operatively connected, such as by tube
17
or other appropriate tubing, to a heat exchanger system such as for a air conditioning unit for a vehicle. The heat exchanger assembly
10
also includes channels or flanges
18
and
19
in order to provide rigidity to the structure.
A plurality of elongated serpentine fins
20
extend between the headers
11
and
12
along each of the heat exchanger tubes
14
. Each of the fins
20
follows a serpentine pattern and has rounded crests that are alternately connected to the top and bottom tubes
14
by a process such as brazing.
It is well known in the art that the efficiency of a heat exchanger assembly is mainly limited by the heat flux between the fins and the ambient air, which receives the heat from the system or transmits heat into the system depending upon the application. For example, in the case of mechanical refrigeration systems, it is known that the heat flux per unit of area between the tube walls and refrigerant or between the tube walls and fins is very high relative to the heat flux per unit area between the surrounding air and the fin and tube surfaces. It is also known in the art that the portion of the fin that first cuts through the air has the highest heat flux per unit area.
To improve heat flux between the fins and the ambient air, many heat transfer systems employ a fan to move more air per unit of time across the fins. As another example, moving vehicles such as automobiles typically position the air conditioning condenser on the front of the car to provide maximum air flow across the fin and tube surfaces.
In another system to improve heat flux between the fins and ambient air, the fins are manufactured to include small louvers in each fin that catch the air and force the air to flow past or over the heated or cooled fin surfaces. A fin array
21
including louvers on the fins is shown in the prior art fin assembly of FIG.
2
. The fin array
21
is folded in a serpentine pattern to form a series of alternating upper and lower crests
22
and a plurality of individual fins
23
. Each of the individual fins
23
includes a plurality of louvers
24
.
The elongated fin array
21
is typically manufactured from strips of metal, such as copper or aluminum, that are run through rotary cutting dies that shape the openings in a strip, shape the louvers by pushing them inward or outward from the strip, and then fold the fins using a “star wheel” style roller which imparts a rounded bend to the fin stock. The fin array
21
including louvers
24
on the fins
23
improves the heat flux as compared to traditional non-louvered fins. However, the louvered fins are less than optimal for maximizing heat flux between the fins and ambient air and are difficult and expensive to manufacture.
For example, the louvers
24
on the fins
23
do not extend across the entire length of the individual fins due to the rounded bend area at crests
22
and thus form bypass passageways labeled
25
in FIG.
2
. Air can thus pass entirely through the fins
22
at bypass portions
25
without encountering the louvers
24
or substantially contacting the fins
23
.
In the louvered fin array
21
, the louvers
24
are also aligned directly behind each other such that the air tends substantially to contact only the first row or two of the louvers
24
. Thus, the louvers
24
toward the back of the fin set do not “see” fresh air since they are in the shadow of the first louvers.
The louvered fin array shown in
FIG. 2
is typically manufactured by cutting the fins in a traditional shearing die technique. With most metals such as copper or aluminum, those skilled in the art know that large amounts of lubrication are required for shear cutting of the material in order to prevent heat build-up in the cutting tools. However, the lubricating oils must be substantially removed from the fins after the cutting process so that the fins are clean for brazing the fins to the tubes. The process of removing the lubricating oils from the fins is an expensive process and may result in environmentally dangerous byproducts.
This manufacturing process also commonly results in relatively large fin height variations that can lead to poor bonding between the fins and tubes. As a consequence of tolerance build up, added to run by run in the full assembly process, the rounded upper and lower crests of the fin array may not allow for complete fin to tube contact if the tubes are thinner than normal or if the fins have been folded with too small of a height. Poor bonding between the fins and tubes can dramatically decrease the efficiency of the entire heat exchanger assembly. If, on the other hand, fins have been folded with too great a height and/or tubes are thicker than normal, then some runs of the fins may be crushed out of shape allowing increased (or decreased) by-pass (or breakage). Both of which are detrimental to heat transfer.
SUMMARY OF THE INVENTION
An important aspect of this invention lies in providing an improved fin array for a heat transfer assembly that provides improved heat flux between the fins and the ambient air and that permits more efficient and economical manufacturing than prior art fin arrays including louvers. The fin array of the present invention comprises an elongated serpentine one-piece fin member having top and bottom base portions connected together by fin sets extending between adjacent ones of the top and bottom base portions. The fin sets each include a plurality of individual fins having side edges facing generally perpendicular to a longitudinal length of the one piece fin member. The side edges of the fins are also longitudinally offset with respect to each other to improve heat flux with the passing air.
The fin sets are divided into a plurality of individual fins that have offset sides edges which greatly increase the heat flux of the entire fin member. The side edges of the fins typically provide the greatest amount of heat flux and the offset nature of the side edges of the fins maximizes this heat flux since each of the edges sees fresh air.
The top and bottom base portions of the fin unit extend respectively in top and bottom planes and are generally flat. The flat nature of the top and bottom base portions permits solid bonding and increased surface area in contact with the heat exchanger tube to increase overall heat transfer. The flat configuration of the top and bottom base portions or crests also provides a better and more stable connection than prior art fins having rounded crests.
The top and bottom base portions generally comprise elongated, flat sections that extend transversely at an angle with respect to the longitudinal length of the fin member. The base portions are formed of staggered sections, that may comprise either rectangles or squares, in order to longitudinally offset the side edges of the fins. This permits dense packaging of the fins and their side edges to fully meet and engage oncoming air in order to improve heat flux.
In that regard, the fins preferably extend at an angle of 90° with respect to the top and bottom base portions. The fins then extend completely between the top and bottom heat exc
Brinks Hofer Gilson & Lione
Flanigan Allen
Peerless of America
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