AU2002343716A1

AU2002343716A1 - Split fin for a heat exchanger

Info

Publication number: AU2002343716A1
Application number: AU2002343716A
Authority: AU
Inventors: Rifiquat Cheema; Frank M. Grippe; Gregory G. Hughes; William Markusen; Stephen Memory; Kenneth Ritt; James C. Rogers
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 2001-12-12
Filing date: 2002-11-13
Publication date: 2003-06-23
Anticipated expiration: 2022-11-13
Also published as: BR0213723A; AU2002343716B2; WO2003050468B1; TW200303409A; KR100628793B1; JP3965387B2; WO2003050468A1; RU2287755C2; RU2004115398A; CN1650143A; DE02780677T1; US20030106677A1; MXPA04004922A; EP1459028A1; ZA200403169B; AR037710A1; CA2464686A1; JP2005512013A; KR20040063966A; CN100445687C

Description

WO 03/050468 PCT/US02/36635 -1 SPLIT FIN FOR A HEAT EXCHANGER FIELD OF THE INVENTION This invention relates to a split fin construction for use in heat exchangers, and more particularly, for a heat exchanger having a 5 plurality of rows of tube runs from front to back and wherein it is desir able to minimize heat transfer through the fin from one row of tubes to another. BACKGROUND OF THE INVENTION There are a variety of applications wherein it is important 10 to limit heat conduction between the front and rear side of a heat exchanger. Such applications are typified by those wherein the fluid temperature entering the heat exchanger is at a significantly different level than the temperature of the fluid exiting the heat exchanger. One such application is in a refrigeration system heat exchanger such as a 15 condenser, or more specifically, a gas cooler and a refrigeration system utilizing a transcritical refrigerant. CO 2 is an example of such a refriger ant. Another application occurs where two or more heat exchanger cores, each receiving a separate fluid, are located in series 20 in the flow path for another heat exchange fluid such as a gas as air. An example of such an application would be one usually found in a vehicular context wherein, for example, the core of a condenser or gas cooler for an air conditioning system is located upstream or down stream of a core for engine coolant. 25 In the former case, in order to decrease the refrigerant exit temperature as much as possible, it is desired to limit the conduction WO 03/050468 PCT/US02/36635 -2 path across the depth of the heat exchanger such that the relatively much hotter entering refrigerant dissipates its heat to the coolant pass ing through the heat exchanger rather than to the exiting refrigerant via conduction through fins extending from front to back in the heat 5 exchanger. In the latter case, it is desirable that heat from the radiator and the engine coolant therein is not conveyed to the condenser via common fins to impede the efficiency of operation of the condenser or vice versa. In a typical gas cooled heat exchanger, cross conduction 10 paths may exist both in the metal tubes as well as the metal fins. To avoid the formation of a cross conduction path in the metal tubes, the tubes in adjacent rows from front to back of the heat exchanger are spaced from one another. To minimize cross conduction through the fins, heat interrupters, typically in the form of slots, are located in the 15 fins in alignment with the spaces between the rows of tubes in the heat exchanger. Examples of the latter are shown, for example, in Shinmura 5,000,257 and its reissue patent Re. 35,710; Sugimoto 5,992,514; Watanabe 5,720,341 and Yamanaka 6,000,460. In each of the foregoing patents, a slot is formed wherein 20 material is removed from the fin to form the slot which provides an interruption in the heat conduction through the fin. While these con structions are believed to be operative for their intended purpose, the fact that material is removed from the fin reduces the surface area of the fin. As is apparent from Fourier's law, a reduction in area reduces 25 heat transfer and thus the slots proposed by the above patentees, while providing the desired reduction in heat conduction through the fin from one side of the heat exchanger to the other, also increase gas side thermal resistance, reducing the efficiency of heat exchange from the WO 03/050468 PCT/US02/36635 -3 fluid contained within the tubes to a gas which passes through the fins. As, in typical gas/fluid heat exchangers, gas side thermal resistance can account for as much as 95% of the total resistance to heat exchange from the gas to the fluid flowing within the tubes, it is highly desirable 5 that reduction of heat conduction through the fin from one side of the heat exchanger to the other not be accompanied by an increase in gas side thermal resistance. The present invention is directed to achieving that desire. SUMMARY OF THE INVENTION 10 It is a principal object of the invention to provide a new and improved gas side fin for use in heat exchangers having plural rows of tube runs from front to back of the heat exchanger. More specifi cally, it is an object of the invention to provide such a fin wherein heat conduction through the fin from one side of the heat exchanger to the 15 other is minimized while at the same time is not accompanied by an increase in gas side thermal resistance. An exemplary embodiment of the invention accomplishes the foregoing in a heat exchanger having a front and a back with a plurality of spaced rows of flattened tubes from front to back which 20 define aligned tube runs in each row. Serpentine fins are abutted to adjacent tube runs in each row and extend from front to back so that each fin is common to each of the rows. The serpentine fins have heat flow interrupters in each fin at a location in the space between the aligned tube runs in each row. The invention contemplates the im 25 provement wherein the heat flow interrupter is defined by a slit extend ing completely through the fin and which is characterized by the ab- WO 03/050468 PCT/USO2/36635 -4 sence of the removal of any material of which the fin is made at the slit. In a preferred embodiment, the edges of the slit are dis placed from the remainder of the fin. 5 In one embodiment, the edges of the slit extend at an acute angle to the remainder of the fin. Even more preferably, the edges of each slit are displaced in opposite directions from the remainder of the fin at the acute angle. In another embodiment of the invention, the edges of each 10 slit are displaced into offset, spaced planes. In still another embodiment of the invention, the slits in each fin defining the heat flow interrupters in each fin are separated by short joining sections and the edges of each slit are spaced from one another by deforming the joining sections. 15 Preferably, the joining sections are made thinner than the remainder of the fins. By way of example only, a coining operation may be utilized on the joining sections to make them thinner thereby displacing the edges of the slit into spaced relation. In a preferred embodiment, the aligned ones of the tube 20 runs are connected in hydraulic series so as to be useable as a gas cooler or a gas cooler/evaporator in a refrigeration system or in a heat pump system. Other objects and advantages will become apparent from the following specification taken in connection with the accompanying 25 drawings.

WO 03/050468 PCT/USO2/36635 -5 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a somewhat schematic perspective view of a heat exchanger made according to the invention; Fig. 2 is an enlarged, fragmentary sectional view taken 5 approximately along the line 2-2 in Fig. 1; Fig. 3 is a fragmentary sectional view taken approximately along the line 3-3 in Fig. 2; Fig. 4 is a fragmentary sectional view taken approximately along the line 4-4 in Fig. 2 and showing a modified embodiment of the 10 invention; Fig. 5 is a fragmentary sectional view taken approximately along the line 5-5 in Fig. 2 and showing still another modified embodi ment of the invention; Fig. 6 is a view similar to that taken along the line 5-5 in 15 Fig. 2 but showing still a further modified embodiment; and Fig. 7 is a schematic of a refrigeration system, specifically a heat pump system, in which a heat exchanger having a fin made according to the invention may be employed. DESCRIPTION OF THE PREFERRED EMBODIMENT 20 The following description will describe the invention gener ally in the terms of a refrigeration system which is intended to encom pass heat pump systems as well. The context of the description will be that of a vehicular heating/cooling system but it is to be specifically understood that the invention is not limited to use in vehicular systems. 25 The invention will also be described in the context of a gas cooler wherein a gas, typically air, is utilized to cool and/or condense a single fluid such as a refrigerant; and the term "gas cooler" is intended to WO 03/050468 PCT/US02/36635 -6 include both condensers and coolers which cool refrigerant without condensing it. However, the invention is also applicable to heat exchangers having a plurality of cores, each receiving a different work ing fluid as, for example, a plural core heat exchanger for cooling both 5 the refrigerant from a gas cooler and the coolant for an engine or the like. Similarly, while the invention will be described in the context of a gas, typically air, cooling another working fluid within the heat exchanger, it should be appreciated that the heat exchanger can be employed wherein the gas is heated by the working fluid as well. In 10 short, the invention is not to be limited by the following description except in so far as stated in the appended claims. Referring to Fig. 1, a heat exchanger made according to the invention is illustrated and is seen to include a pair of spaced, paral lel, tubular headers 10,12. Of course, header plates fitted with tanks 15 could be employed in lieu of the tubular headers 10,12 if desired. In the illustrated embodiment, the header 10 is provided with an outlet schematically illustrated at 14 while the header 12 is provided with an inlet, schematically indicated at 16. A direction of air flow through the heat exchanger is illustrated by an arrow 18 and it will 20 be seen that the just described arrangement of the inlet 16 and outlet 14 provide a counter/cross flow heat exchange regime. However, in some instances the air flow direction 18 can be reversed. When the heat exchanger is intended to be used as a gas cooler or gas cooler/evaporator in a refrigeration system, the foregoing 25 counter/cross flow arrangement is preferred. That is also true of the use of tubular headers 10,12 because of their high pressure resistance. A plurality of flattened tubes 20 extend between the head ers 10,12 that are in fluid communication with the interior of each.

WO 03/050468 PCT/US02/36635 -7 Each flattened tube is configured in a serpentine configuration so as to have three runs 22, 24 and 26 which are parallel with each other and which are aligned with each other from the front 28 of the heat exchanger to the rear 30 thereof. Consequently, the runs 22 form a 5 front row of runs within the heat exchanger, the runs 24 form an inter mediate row of runs within the heat exchanger and the runs 26 form a rear row of runs within the heat exchanger. The runs 22, 24 and 26 are spaced by a small gap 27 (Fig. 2) so as to prevent or otherwise minimize heat conduction between the runs 22, 24 and 26 as would 10 result if they were in contact with one another. The various runs are connected by arcuate sections 32. In the usual case, the arcuate sections 32 will be approximately in line with one or the other of the headers 10,12 in the direction of air flow 18 through the heat exchanger. Preferably, the tubes making up the 15 runs 22,24,26 and the arcuate sections 32 are flattened tubes having a major dimension DM and a minor dimension Dm transverse thereto. Desirably, to maximize the cross sectional area of the gas flow path through the heat exchanger, the runs 22,24,26 are oriented so that the major dimension DM is parallel to the direction of air flow 18 through 20 the heat exchanger. At the same time, in high pressure applications, such as gas coolers used in transcritical refrigeration systems, it is desirable that the diameter of the headers 10,12, be as small as possible. Thus, it is conceivable, and even likely that the tube major dimension DM will 25 be greater than the diameter of either of the headers 10 or 12. In such a case, the ends of the runs 22,26, shown collectively at 34, are re ceived in elongated slots 36 in the respective headers 10,12 which extend in the direction of elongation of the respective header 10,12.

WO 03/050468 PCT/USO2/36635 -8 To achieve this relation along with the relation requiring the tube major dimensions DM to be parallel to the direction of air flow 18, immediately adjacent to the ends 34, the tubes are provided with a twist 38, typi cally, but not always, 900. Similar twists are also provided at the ends 5 of each arcuate section 32 and are schematically illustrated by dotted lines 40. The twists 40 facilitate bending of the tubes to include the arcuate sections 32. Serpentine fins, generally designated 42, are disposed between adjacent ones of the tubes with each fin 42 extending be 10 tween an aligned pair of the runs 22, the runs 24 and the runs 26 from the front 28 to the back 30 of the heat exchanger. Alternatively plate or other fins may be used. Thus, there exists a heat conductive flow path between the runs 22, 24 and 26 through the fins 42. As generally alluded to previously, it is undesirable in many 15 applications that such a heat conduction path exists. As mentioned previously, those applications include ones where a sizable temperature differential exists between the runs 22 and 26 as would be the case in a gas cooler or gas cooler/evaporator when being operated as a gas cooler in a transcritical refrigeration system. Another typical example 20 would be where certain of the runs are being employed in a condenser for a refrigerant and others of the runs are being employed as a radiator for coolant such as engine coolant. In the case of the latter, of course, additional headers to separate the refrigerant stream from the coolant stream would be employed. As seen in Fig. 1, each of the fins 42 25 includes a plurality of generally flat sections 44, which are connected to each other by crests 46, which, in turn, are metallurgically bonded as by brazing, soldering or welding, to the flat side of each of the tube runs 22,24,26 between which the fin 42 is located.

WO 03/050468 PCT/US02/36635 -9 As seen in Fig. 2, each section 44 is defined by three segments including a first segment 48 extending between the tube runs 22, a second segment 50 extending between the tube runs 24 and a third segment 52 extending between the tube runs 26. Each of the 5 segments 48,50,52 is typically provided with louvers 54 which may be of conventional construction. Between each of the segments 48,50,52 is a flow inter rupter. Two such flow interrupters are shown in Fig. 2 which are made according to different embodiments of the invention. A first flow inter 10 rupter is generally designated 56 while a second is generally designated 58. According to the invention, each flow interrupter is defined by an elongated slit that runs continuously through each fin 44 and is posi tioned to be located in alignment with the spaces 27 between the runs 22, 24 and 26. The slits are illustrated at 62 in Fig. 2 and each is 15 interrupted by connecting sections 64 that may be a few millimeters in length and which are positioned at intervals in the corresponding slit 62. The connecting sections 64 need not be present at each section 44 of each fin 42 and typically will not be. They only need be provided with such frequency as to maintain the integrity of a fin 42 so that it 20 will not separate into individual parts at each slit 62. The slits 62 are generally straight line and have opposed edges. As illustrated in Fig. 3, the opposed edges are shown at 66 and 68, face one another and are generally transverse to the direction of air flow 18. In the embodiment of the invention illustrated in Fig. 3, the 25 edges 66 and 68 are virtually in abutment, but not quite in abutment, with each other, and, because of the interruption in the continuity of the fin 42 at this location, interrupt the flow of heat from one segment 48,50,52 to the other. It is to be particularly noted that the slits 62 are WO 03/050468 PCT/USO2/36635 -10 formed without the removal of any material from the fin 42 itself. As a consequence, the surface area of each fin 42 is not diminished in any way by the presence of the slits 62 and as a consequence, each fin 42 has a maximum surface area for heat exchange of air flowing in the 5 direction 18. Consequently, the greater surface area of each fin that results provides improved heat transfer. In the embodiment shown in Fig. 3, it is desirable, though not absolutely necessary, that if braze material is employed, that braze material be located on the side walls 70 of the tube runs 22,24,26 as 10 opposed to being on the fin 42. This assures that the slit 62 will re main continuous after it is formed as a result of the prevention of flow of brazed metal into the slit 62 that might braze the edges 66,68 to gether. The embodiment of Fig. 4 provides further assurance that 15 there will be no brazing together of the edges 66,68 of each slit 62. In this embodiment, the segments 50 of each fin 42 which extend be tween the tube runs 24 are displaced in the direction of elongation of the tube runs 22,24,26 from segments 48,52 without the removal of any material from the fin 42. As a result, gaps 70 in a plane generally 20 transverse to the plane of each segment 48,50,52 are provided to define the flow interrupters 56. Still another alternative is illustrated in Fig. 5. In the em bodiment of Fig. 5, one of the flow interrupters 58 is illustrated. One edge 72 of the slit 62 is bent upwardly while another edge 74 is bent 25 downwardly so that the two edges 72,74 are spaced as illustrated in Fig. 5. Again, a gap between the edges 72,74, is formed as in the embodiment of Fig. 4 as well, and again, without the removal of any material from the fin 42 which would reduce its surface area.

WO 03/050468 PCT/USO2/36635 -11 Fig. 6 illustrates still another embodiment of the invention. In this embodiment, the joining sections 64 are compressed by a suit able operation as, for example, by coining. This results in the edges of the slits 72,74 being driven away from one another even though occu 5 pying the same plane so as to form a gap 76 between adjacent ones of the segments 48,50,52. Since the coining operation does not cause removal of any material from the fin, fin surface area is again maxi mized to improve heat transfer. Fig. 7 illustrates a preferred environment of use of heat 10 exchanger made according to the invention. Specifically illustrated is a refrigeration system as may be used for refrigeration or air condition ing purposes, and more specifically, a heat pump system which may be employed for both heating and cooling. Two heat exchangers, gener ally designated 80 and 82, respectively, and made according to the 15 invention are employed as gas cooler/evaporators with one acting as a gas cooler when the other is acting as an evaporator, and vice versa. The two are connected in a conventional heat pump circuit with valves 84 as is a conventional compressor 86 and an expansion valve 88. Typically a suction line heat exchanger (not shown) will be located on 20 the inlet side 90 of the compressor 86 along with an accumulator (also not shown). When the system in Fig. 7 is employed for cooling pur poses, the heat exchanger 80 will be acting as a gas cooler and will receive compressed refrigerant from the outlet side 92 of the compres 25 sor 86 via the heat pump connected plumbing and valves 84 on a line 94. The compressed, hot refrigerant will exit the heat exchanger 80, now acting as a gas cooler on a line 96 to ultimately be passed through the expansion valve 88 which discharges on a line 98 connected to the WO 03/050468 PCT/US02/36635 -12 heat exchanger 82. The refrigerant will be expanded in the heat exchanger 82, now acting as an evaporator, and ultimately returned to the inlet side 90 of the compressor 86 via the previously mentioned suction line heat exchanger, if present. Conventional fans 100 are 5 employed to drive air through both of the heat exchangers 80,82. When the system of Fig. 7 is employed for heating pur poses, the heat exchanger 82 will be employed as a gas cooler and the heat exchanger 80 as an evaporator. In this case, hot compressed refrigerant from the outlet side 92 of the compressor 86 will be pro 10 vided to the heat exchanger 82 on the line 98 to exit therefrom on a line 102 which will be connected by the heat pump connected plumb ing and valves 84 to the expansion valve 88. From the expansion valve 88, the refrigerant will enter the heat exchanger 80 on the line 94 and expand therein as the heat exchanger 80 will be acting as an evapora 15 tor at this time. The refrigerant exiting the heat exchanger 80 will exit on the line 96 to be returned via the heat pump connected plumbing and valves 84 to the inlet side 90 of the compressor 86. From the foregoing, it will be appreciated that a heat exchanger made according to the invention is ideally suited for those 20 applications where heat conduction through fins common to several rows of runs of tubing is highly undesirable. The provision of the slits 62 in the fins 54 between the segments 48, 50 and 52 to act as heat interrupters achieves that function without the removal of any of the material of which the fins 42 are made. Consequently, the fins 42 25 retain their original surface area which then is available for heat trans fer, making the fins 42 more efficient that those fins heretofore known which involve the removal of material from the fins to provide the heat interrupters.

WO 03/050468 PCT/US02/36635 -13 The invention is not only applicable to those heat exchang ers wherein a large temperature differential from one run to the next is encountered where all of the runs contain a single working fluid such as a refrigerant, but may be used with efficacy in combination heat 5 exchangers such as common core condensers and radiators wherein the fins are common to both the condensing section and the radiator section. The heat interrupters 56,58 are easily fabricated during the typical roll forming operation used to provide the serpentine fins 42 10 which provides a simple and economical way to accomplish the desired result without the necessity of removing material from the fins 52 and disposing of the scrap constituted by such removed material. Finally, it will be appreciated that in some instances, the principles of the invention are not limited to serpentine fin heat 15 exchangers but may be employed in plate fin heat exchangers as well.

Claims

1. In a heat exchanger having a front and a back, a plurality of spaced rows of flattened tubes from fmront to back and defining aligned tube runs in each row, and fins abutted to adjacent tube runs in each row and extending from front to back so that each fin is common to each of said rows and having heat flow interrupters in each fin at a location in the space between the aligned tube runs in each row, the improvement wherein each said heat flow interrupter is defined by a slit extending completely through the fin and is characterized by the absence of the removal of any material of which the fin is made at the slit, and each edge of each slit is not displaced with respect to opposite edge of the slit.

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled) WO 03/050468 PCT/US02/36635 20

7. (canceled)

8. In a heat exchanger having a front and a back, a plurality of spaced rows of flattened tubes from front to back and defining aligned tube runs in each row, and serpentine fins abutted to adjacent tube runs in each row and extending from front to back so that each fin is common to each of said rows and having heat flow interrupters in each fin at a location in the space between the aligned tube runs in each row, the improvement wherein each said heat flow interrupter is defined by a slit extending completely through the fin and is characterized by the absence of the removal of any material of which the fin is made at the slit, each edge of each slit is not displaced with respect to opposite edge of the slit, and the aligned ones of said tube runs being connected in hydraulic series.

9. In a heat exchanger having a front and a back, a plurality of spaced rows of flattened tubes from front to back and defining aligned tube runs in each row, and serpentine fins abutted to adjacent tube runs in each row and extending from front to back so that each fin is common to each of said rows and having heat flow interrupters in each fin at a location in the space between the aligned tube runs in each row, the improvement wherein each said heat flow interrupter is defined by a slit extending completely through the fin and is characterized by the absence of the removal of any material of which the fin is