Fin array for heat transfer assemblies and method of making same

Abstract

An improved fin array for use in a heat transfer assembly, such as a condenser for a vehicle air conditioning system, and a method of making the improved fin array, are disclosed. The fin array comprises an elongated one-piece fin member having top and bottom base portions with fin sets extending between adjacent top and bottom base portions. The top and bottom base portions are generally flat for bonding to the heat exchanger tubes, such as by brazing. Each fin set includes a plurality of individual fins extending perpendicularly to a longitudinal length of the fin member and having side edges that are longitudinally offset with respect to each other. The offset fin edges provide increased fresh air flow over the individual fins and thus increase the efficiency of the overall heat exchanger. The method of making the improved fin array includes providing a flat sheet of elongated fin stock, pressing a chisel shape into the fin stock to a depth of between 40 to 90 percent of the thickness of the fin stock in order to produce a cut pattern along the length of the fin stock, bending the fin stock into a serpentine pattern, and then compressing the fin stock to finalize the one-piece fin member.

Description

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 exchanger tubes to maximize heat transfer. This configuration also prevents formation of “passage ways” that could otherwise allow air to pass through the fin without contacting any of the fin or tube surfaces.

The inventive fin array of the present invention can advantageously be manufactured without the use of shearing devices or associated lubrication oils, which otherwise can make the manufacturing process unduly complicated, expensive, and harmful to the environment. In particular, the method of manufacturing the inventive heat array includes providing a flat sheet of fin stock and then positioning the fin stock between chisel and an anvil. The chisel is then press or impacted into the fin stock so that the chisel penetrates the fin stock to between about 40 to 90 percent of the thickness of the fin stock in order to define a cut pattern along the length of the fin stock. In most metallic fin stock materials, the chisel shape need not penetrate entirely through the material since lateral forces applied by the chisel to the fin material will exceed the ultimate strength of the remaining fin material which will then split through completely. The cut pattern thus achieving the plurality of top base portions, bottom base portions, and fin sets extending between the top and bottom base portions.

By using an chiseling method of forming the cut pattern on the fin stock, the method of the present invention avoids use of shears and lubricants such as in the prior art processes of forming fin arrays.

After the cut pattern is formed on the fin stock, the fin stock is bent by passing the fin stock through a pair of star rollers or other similar device. The fin stock is thus bent into a serpentine pattern so that the top base portions extend in a common top plane, the bottom base portions extend in a common bottom plane, and the fin stock extend between and connect adjacent ones at the top and bottom base portions. At this stage in the manufacturing process, the fin extends at an angle greater than 90° with respect to the top and bottom portions to permit the fin stock to roll off of and be removed from the star rollers or other forming device.

After passing through the star rollers, the fin stock is in an uncompressed fin member shape with the fins being angled with respect to the top and bottom base portions. The fin stock is then placed in a compression device where the ends of the fin stock are urged together until the fins extend at an angle of 90° with respect to the top and bottom base portions. The manufacturing of the fin stock into the completed one-piece fin member is then complete.

In addition, to avoiding the complexity, cost, and environmental concerns of prior art manufacturing processes, the method of the present invention provides a further advantage in that the impact step of forming the cut pattern in the fin stock results in the fins having serrated or roughened edges. The roughened or serrated edges on the fins have increased surface area on a microscopic level and thus improve heat flux with the surrounding environment.

Other objects, features and advantages of the present invention will become apparent from the following description and drawings in a vehicle

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art heat exchanger assembly in the form of a condenser for an air conditioning system.

FIG. 2 is a perspective view of a prior art fin array including louvers.

FIG. 3 is a perspective view looking down on the top and side of the improved fin array of the present invention.

FIG. 4 is a front, somewhat perspective view, illustrating the improved fin array of the present invention in an uncompressed condition.

FIG. 5 is a front, somewhat perspective view, illustrating the improved fin array of the present invention in an uncompressed condition.

FIG. 6 is a schematic side view illustrating the step of scoring a sheet of fin stock for forming the improved fin array of the present invention.

FIG. 7 is a schematic side view illustrating the step of scoring a sheet of fin stock for forming the improved fin array of the present invention.

FIG. 8 is a top view of a scored piece of fin stock used for forming the improved fin array of the present invention and includes an enlarged view of some of the scored pattern.

FIG. 9 is a schematic side view showing the step of passing the fin stock through a pair of star rollers to form the fin array of the present invention.

FIG. 10 is a schematic top view of the star rollers shown in FIG. 9 and used to form the fin stock into the improved fin array of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 3-5 , the numeral 30 generally designates the improved fin array of the present invention. The fin array 30 comprises an elongated one-piece fin member 31 having a longitudinal axis or length L. The fin array 30 can advantageously be used as a more efficient substitute to the fin array 20 or 21 shown in the prior art condenser structures in FIGS. 1 and 2 . While the inventive fin array 30 can advantageously be used in such condensers, it will be understood by those skilled in the art that the improved fin array can be used in a variety of different heat exchanger assemblies within the scope of this invention.

The one-piece fin member 31 is comprised of a serpentine pattern of alternating top and bottom base portions 32 and 33 . A plurality of fin sets generally designated at 34 extend between and connect adjacent ones of the top and bottom base portions 32 and 33 . Each of the fin sets 34 includes a plurality of individual fins 35 to maximize heat transfer with ambient air.

The top base portions 32 are all positioned in a common flat top plane and the bottom base portion 33 are also disposed in a common flat bottom plane. The flat construction of the top and bottom base portions 32 and 33 , as compared to the rounded crests 22 of a traditional fin array, permit a solid bond to be formed within an adjacent heat exchanger tube 14 . The top and bottom base portions 32 and 33 also maximize surface area contact with the tube 14 due to their flat (as opposed to rounded) configuration, which further maximizes heat transfer between the fins and the tubes.

A shown in the figures, the top and bottom base portions 32 and 33 comprise elongated flat sections that extend transversely at an angle with respect to the longitudinal length of the one piece fin member 31 . Generally, the angle designated with an X in FIG. 3 is about 45° but may fall generally within a range of about 15° to 18°. Along this generally transverse line, the top and bottom base portions 32 and 33 comprise a plurality of staggered segments 36 generally having a quadrilateral configuration such as in the form of either a rectangle or a square. The segments 36 are connected to each other in a staggered fashion to form the top and bottom bases 32 and 33 . The segments 36 also include ends 36 a that merge into fins 35 and the segments 36 generally have a width equal to the width of two of said fins 35 . The fins 35 can then project downwardly from opposed ends 36 on each side of each of the segments 36 in a staggered fashion as shown in the drawings.

In the embodiment given in the drawings, each of the fin sets 34 comprises eight individual fins 35 extending between the adjacent ones of the top and bottom base portion 32 and 33 . However, the fin sets 34 may generally include between one and twenty individual fins 35 or more depending upon the application. It will be also understood by those skilled in the art that the number of fins contained within each fin set may be varied considerably depending upon the size and nature of the particular application for which the fin array 30 is used.

Each of the fins 35 includes top and bottom edges 35 a and 35 b respectively merged with top and bottom base portions 32 and 33 . The fins 35 also include a pair of top and bottom faces 35 c and 35 d and a pair of side edges 35 e and 35 f . The side edges 35 e and 35 f extend between and connect the top and bottom base portions 32 and 33 .

Due to the angled transverse alignment of the top and bottom base portions 32 and 33 , each of the fins 35 within a fin set 34 has its side edges 35 e and 36 f longitudinally offset with respect to the edges 35 e and 35 f of all of the other fins 35 in each fin set 34 . The offset positioning of the fins 35 and side edges 35 e and 35 f maximizes heat transfer of the fins 35 with the ambient air because the offset fin edges provide maximum exposure to the air and the fins do not block air with respect to each other. The edges 35 e and 35 f of the fins 35 , as well as the front and rear faces 35 c and 35 d , are preferably perpendicular to the longitudinal length L of the fin member to maximize air flow and to keep air side pressure drop to a minimum across the fins 35 . However, it will be understood by those skilled in the art that the fins 35 could be angled with respect to how each fin 35 presents itself to the air depending upon the particular application for which the fin array 30 is intended.

The fins 35 preferably each form an angle of about 90° with respect to the fin ends 35 a and 35 b merge with the side edges 36 a of the segments 36 of the top and bottom connecting portions 32 and 33 . This angle at the juncture between the base portions and the fins 35 is generally designated with a Y in the drawings. The angle Y between the base portions 32 and 33 and fins 35 is preferably perpendicular or 90° so that the fins 35 extend completely between the top and bottom base portions and the adjacent tubes brazed or otherwise connected to the base portions 32 and 33 . This maximizes heat transfer between the fins 35 and the heat exchanger tubes 14 . Because the fins 35 extend completely between the adjacent tubes 14 , the fins 35 also do not define bypass portions such as found at the top and bottom of the louvered fins shown in FIG. 2 and described above.

FIG. 4 shows the fin array 30 in an uncompressed state just prior to completion of manufacture of the fin array 30 . In such uncompressed condition, the fin array 30 is substantially complete as described in connection with FIG. 3 except that the fins 35 form an angle greater than 90° with the top and bottom connecting portions 32 and 33 . However, FIG. 4 makes it easier to see the individual components that make up the final fin array structure 30 .

The fin array 30 is preferably made of a metallic material such as aluminum or copper. In condenser application such as shown in FIG. 1 , the fin array 30 may be comprised of rolled aluminum fin stock or other suitable materials. While these materials are believed to be desirable, it will be understood by those skilled in the art that other suitable or appropriate heat exchanger materials could be used to form the fin array 30 .

FIGS. 4-10 generally show the method of making the inventive fin array 30 . Referring to FIG. 8 , the method involves first providing an elongate piece of fin stock generally designated at 40 in FIGS. 6-8 . The fin stock 40 is positioned between a chisel 41 and an anvil 42 as show in FIG. 6 . The chisel 42 is then pressed or impacted into the fin stock 40 over the anvil 42 so that the chisel 42 penetrates the fin stock 40 to between about 40 to 90 percent of its thickness T to a depth D. This chiseling action fractures the remaining thickness of fin stock 40 as designated at 43 . The chisel 41 and anvil 42 are used to define a cut pattern 44 on the flat fin stock 40 as shown in FIG. 8 . It should be understood that the term “chisel” refers to various forms of rotary dies on which a pattern of chisel-like edges have been machined. The cut pattern 44 defines the top base portions 32 , the bottom base portions 33 , and the fin sets 34 comprised of individual fins 30 therebetween on the fin stock.

Advantageously, during the above-described impacting process of forming the cut pattern 44 on the fin stock 40 , the chisel 41 and anvil 42 never come into contact. Thus, no lubrication is required such as in prior art shearing processes. Thus, this manufacturing method avoids the expensive use of lubricants, the expensive step of removing the lubricant from the heat exchanger components and the expense associated with the environment and any dangerous byproducts from the lubrication removal process. Tool life is also expected to be greater since close tolerance of shearing edges are not required in this type of cutting.

After the cut pattern 45 is formed on the fin stock 40 , the fin stock 40 is bent to form the fin array in the uncompressed state shown in FIG. 4 by passing the fin stock 40 through a pair of star rollers 45 shown in FIG. 8 . The star rollers 45 are generally known in the art for forming serpentine patterns in pieces of fin stock 40 . The star rollers 45 used in conjunction with the present method are different in that they are comprised of a plurality of individual star rollers 46 that include offset portions 47 for forming the offset fins 35 in the fin stock 40 . The star rollers 45 are designed to create an angle Y between the fins 35 and the top and bottom base portions 32 and 33 that is greater than 90° so that the fin stock 40 will easily roll off of the star rollers 45 during the manufacturing process. If the star rollers were designed to impart an angle of 90° between the fins 35 and the top and bottom base portion 32 and 33 , it is believed that the star rollers could become trapped within the 90° angle of the components.

After passing through the star rollers 45 , the fin stock 40 is in the uncompressed shape of a semi-complete fin member 31 shown in FIG. 4 . Thereafter, the fin member 31 is placed in a compression device 48 , which includes platform 49 and a pair of presses 50 . The presses 50 are used to compress the ends of the fin member 31 until the fins 35 are all extending at an angle of approximately 90° with respect to the top and bottom base portions 32 and 33 .

As shown in FIG. 8 , the cut pattern 44 includes slices or cuts 51 between the fins 35 and the top and bottom base portions 32 and 33 . The cuts or slices 51 ensure a square bend between the fins 35 and the top and bottom bases 32 and 33 and avoid formation of rounded crests such as in the prior art. The cuts or slices 51 may be to the same depth as the cuts used to form the fins 35 but do not cover the entire width of fins 35 . Instead, the cuts or slices 51 may be 40% to 60% of the width of the fins 35 . The purpose for this partial cut is to cause the material to bend at that point (in the star roller) but not to break apart, thus maintaining the interior of the fin set.

After the compression device 48 is used to form 90° bends between the fins 35 and the top and bottom base portions 32 and 33 , the fin array 30 is then complete as shown in FIG. 3 . The fin array 30 can then be brazed or otherwise bonded to tubes 14 to form a completed heat exchanger assembly.

The process of using the chisel 41 and anvil 42 to create fractured cuts between the fins 35 results in the fins 35 having serrated or otherwise rough edges 35 e and 35 f . The serrated or rough edges 35 e and 35 f , at least on a microscopic level, have a greater surface area than shear cut fin edges. Thus, the serrated edges with the greater surface area provide for increased heat transfer between the fin edges and the ambient air.

The design of the fin array 30 of the present invention maximizes heat transfer by providing a plurality of offset fin cutting edges to maximize contact with the air and to maximize heat flux with the ambient air. The flat configuration of the top and bottom base portions 32 and 33 also improves heat transfer by increasing the surface area and contact with the tube and by permitting the fins 35 to run completely between the adjacent tubes. Because the fin array 30 of the present invention maximizes heat transfer, the fin array permits smaller overall size of the completed heat exchanger, which thus saves on material, space and cost. The method of manufacturing the inventive fin array 35 is also advantageous in that it avoids the expensive and complex shearing operations and lubrications required in forming prior art fin arrays.

Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.

Claims

1. A fin array for a heat exchanger assembly comprising:an elongated serpentine one-piece fin member having top and bottom base portions, with a fin set extending between adjacent ones of said top and bottom base portions; each of said fin sets including a plurality of fins having a flat planar surface and each having side edges facing generally perpendicular to a longitudinal length of said one-piece fin member and being longitudinally offset with respect to each other, said fins having a length substantially greater than a width thereof; and said top and bottom base portions each comprising flat staggered segments that extend transversely at a generally uniform angle with respect to the longitudinal length of the one-piece fin member, said flat staggered segments forming a generally stair-shaped pattern.

2. The fin array of claim 1 in which said segments comprise either a rectangle or a square.

3. The fin array of claim 1 in which said segments each have a width substantially equal to a width of two of the fins in the fin sets.

4. The fin array of claim 1 in which each of said segments includes ends merging into ends of respective ones of said fins in said fin sets, and in which a juncture between said segments and said fins includes a score line to facilitate bending between the segments and the fins.

5. The fin array of claim 4 in which said junction between said segments and said fins forms an angle of about 90°.

6. A heat transfer assembly comprising:a pair of tubular headers defining a plurality of slots; a plurality of tubes extending between said headers and having ends inserted into said slots on said headers; a plurality of elongated one-piece fin members extending between said headers and being positioned along said plurality of tubes, each of said elongated one-piece fin members defining a serpentine pattern of alternating top and bottom base portions connected together by fin sets extending between adjacent ones of said top and bottom base portions, said fin sets each including a plurality of individual fins having a continuous, flat planar surface area; and said top and bottom base portions each comprising a plurality of flat staggered segments that extend transversely at a generally uniform angle with respect to the longitudinal length of the one-piece fin member, said segments include ends merging into ends of respective ones of said fins in said fins sets, and in which a juncture between said segments and said fins includes a score line to facilitate bending between said segments and said fins.

7. The heat transfer assembly claim 6 in which said segments comprise either a rectangle or a square.

8. The heat transfer assembly of claim 6 in which said segments each have a width substantially equal to a width of two of the fins in the fin sets.

9. The heat transfer assembly of claim 8 in which said junction between said segments and said fins forms an angle of about 90°.