Heat exchanger

Abstract: The present invention is directed to a heat exchanger (15A) which forms a part of a refrigeration circuit into which a refrigerant of a non-azeotropic mixture of a plurality of HFC (hydrofluorocarbon) based substances is charged. The heat exchanger comprises a pipe member (151) having a plurality of straight portions (151a), a plurality of curved turn portions (151b) connected to the straight portions, and a plurality of fin plate members (152) fixedly disposed about the straight portions of the pipe member such that the fin members (152) function to increase the surface area of the straight portions (151a) of the pipe member that is substantially exposed to the air which flows along an exterior surface of the heat exchanger. The pipe member (151) and the fin plate members (152) form a heat exchange region (153) of the heat exchanger (15A). A flow path of the refrigerant is defined when the refrigerant flows through the pipe member. The heat exchange region (153) of the heat exchanger comprises a first section (153a) which includes a first portion of the refrigerant flow path continuing from an inlet port (151c) of the heat exchanger, and a second section (151b) which includes a second portion of the refrigerant flow path continuing to an outlet port (151d) of the heat exchanger. The second section (153b) of the heat exchanger has a greater surface area than the first section that is substantially exposed to the air, relative to the unit length of the flow path of the first fluid.

Description: BACKGROUND OF THE INVENTION Technical Field of the Invention This invention relates to a heat exchanger, and more particularly to a heat exchanger used in a refrigeration circuit which is employed in a refrigerator-freezer display case, vending machine or the like. Description of the Prior Art The US 4 438 808 discloses a heat exchanger according the preamble of claim 1. Referring to Figure 1, a refrigeration circuit 10 as generally employed in a refrigerator-freezer display case (not shown), vending machine (not shown) or the like includes a compressor 11, a condenser 12, an expansion device 14 and an evaporator 15' which are connected to one another in series. A heat medium, such as a refrigerant is charged into the refrigeration circuit under vacuum therein. Referring to Figure 2 in addition to Figure 1, evaporator 15' includes a heat medium conducting circular pipe 151 which comprises a plurality of straight portions 151a and a plurality of curved turn portions 151b alternately connecting the ends of straight portions 151a with the ends of adjacent straight portions 151a to form a continuous flow path. The straight portions 151a are arranged to be parallel to one another in approximately equal spaced intervals. A plurality of fin plates 152 are fixedly disposed about the heat medium conducting pipe 151 as illustrated in Figure 3. The fin plates 152 are arranged to be parallel to one another in approximately equal spaced intervals, and to intersect with the straight portions 151a of the heat medium conducting pipe 151 at right angles. The fin plates 152 extend from conducting pipe 151 to be parallel to a flow direction "B" of air which passes through evaporator 15', as indicated by arrow B in Figure 3. Furthermore, the thickness of the fin plates 152 is designed to be sufficiently smaller than an outer diameter of the heat medium conducting pipe 151. The heat medium conducting pipe 151 and fin plates 152 form a heat exchange region 153 of the evaporator 15'. The fin plates 152 function to increase the area of the heat medium conducting pipe 151 that is substantially exposed to the air which moves along an exterior surface of the evaporator 15'. As a result, the efficiency of the heat exchange operation which is carried out between the refrigerant flowing through the pipe 151 and the air moving along the exterior surface of the evaporator 15' is increased. Furthermore, later-mentioned fan 16 is associated with the evaporator 15' and operates to move the air in the direction which is perpendicular to a parallel plane of the heat exchange region 153 of the evaporator 15'. Accordingly, with respect to a drawing sheet of Figure 2, the air passes perpendicularly therethrough. The evaporator 15' is provided with inlet and outlet ports 151c and 151d which are fixedly disposed at opposite ends of the heat medium conducting pipe 151. The inlet port 151c is connected to an outlet (not shown) of the condenser 12 via the expansion device 14, and the outlet port 151d is connected to a suction chamber (not shown) of the compressor 11. The refrigerant flows through the heat medium conducting pipe 151 along a continuous single line from the inlet port 151c to the outlet port 151d during operation of the refrigeration circuit 10. The heat exchange region 153 of the evaporator 15' includes a first section 153a which comprises a part of the heat medium conducting pipe 151 continuing from the inlet port 151c to an interim location along the flow path of the refrigerant, and a second section 153b which comprises a part of the heat medium conducting pipe 151 continuing from the interim location to the outlet port 151d. In operation, as indicated by arrows "A" in Figure 1, the refrigerant circulates through the refrigeration circuit 10 while undergoing the following processes. The refrigerant is compressed within the compressor 11 under a gaseous state, and then the compressed gaseous refrigerant flows into the condenser 12. The gaseous refrigerant is condensed in condenser 12 by virtue of a heat exchanging operation between the refrigerant in condenser 12 and the air which moves along an exterior surface of the condenser 12. The movement of the air which flows along the exterior surface of the condenser 12 is generated by a fan 13 associated with the condenser 12. The condensed refrigerant flowing from the condenser 12 flows through the expansion device 14 such that the condensed refrigerant is expanded, and then flows into evaporator 15'. The expanded refrigerant in evaporator 15' is vaporized by virtue of a heat exchanging operation between the refrigerant in evaporator 15' and the air which flows along the exterior surface of the evaporator 15'. A movement of the air which moves along the exterior surface of the evaporator 15' is generated by a fan 16 associated with evaporator 15'. Thereafter, the vaporized refrigerant returns to the compressor 11 to once again be compressed. The above-mentioned processes are cyclically carried out during operation of the refrigeration circuit 10. In recent years, since regulations of using CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) have come into force, a non-azeotropic mixture of a plurality of HFC (hydrofluorocarbon) based substances, for example, a mixture of HFC-32, HFC-125 and HFC-134a (20/40/40 wt%), i.e., so called R407A refrigerant, has been charged into a refrigeration circuit employed in the refrigerator-freezer display case, vending machine or like as the refrigerant therein, in place of an azeotropic mixture of HCFC-12 and CFC-115 (48.8/51.2 wt%), i.e., so called R502. During the vaporizing operation within evaporator 15', the percentages of the components of the R502 refrigerant do not vary. As a result, as indicated by a solid line in Figure 4, the temperature of the R502 refrigerant is substantially uniform at any part of the refrigerant flow path in the evaporator. On the other hand, during the vaporizing operation within evaporator 15', the percentages of the components of the R407A refrigerant do vary. As a result, as indicated by a broken line in Figure 4, the temperature of the R407A refrigerant gradually rises toward the outlet port side of the refrigerant flow path in the evaporator 15'. Therefore, as illustrated in Figure 4, the temperature differential between the R407A refrigerant and the air outside the evaporator 15' becomes gradually smaller toward the outlet port side of the refrigerant flow path in the evaporator 15'. Accordingly, when a heat exchange between the R407A refrigerant flowing through the heat medium conducting pipe 151 of the evaporator 15' and the air moving along the exterior surface of the evaporator 15' is carried out, the amount of heat absorbed from the air moving along the exterior surface of the evaporator 15' gradually decreases in the second section 153b of the heat exchange region 153 of the evaporator 15'. Therefore, the refrigeration circuit 10 including the evaporator 15' may operate inefficiently when R407A refrigerant is charged therein. Furthermore, during the condensing operation in the condenser, as indicated by the other broken line in Figure 4, the temperature of R407A refrigerant gradually drops toward the outlet port side of the refrigerant flow path in the condenser. Therefore, as illustrated in Figure 4, the temperature differential between the R407A refrigerant and the air outside the condenser becomes gradually smaller toward the outlet port side of the refrigerant flow path in the condenser. Accordingly, when a heat exchange between the R407A refrigerant flowing through the heat medium conducting pipe of the condenser and the air moving along the exterior surface of the condenser is carried out, the amount of heat radiating from the R407A refrigerant which flows through the heat medium conducting pipe of the condenser gradually decreases toward the outlet port side of the refrigerant flow path of the condenser. Thus, the above-mentioned drawback may also arise in the condensing operation of a condenser having a similar construction to that of the above-mentioned evaporator 15' if R407A refrigerant is charged into a refrigeration circuit which includes the above condenser. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a heat exchanger, which forms a part of a refrigeration circuit, that can effectively compensate for a decrease in the amount of the heat exchanging carried out between the refrigerant in the heat exchanger and the air moving along the exterior surface of the heat exchanger, even if R407A is the refrigerant charged in the refrigeration circuit. A heat exchanger in accordance with the present invention forms a part of a refrigeration circuit into which a first fluid, such as a mixture of HFC-32, HFC-125 and HFC-134a (20/40/40 wt%) is charged. The heat exchanger includes conducting means, such as a pipe member for conducting the first fluid therethrough so that a flow path of the first fluid is defined, and exposed area increasing means, such as a plurality of fin plate members for increasing the area of the pipe member that is substantially exposed to a second fluid, such as air which flows along an exterior surface of the heat exchanger. The fin plate members have an exposed area that is in contact with the air. The heat exchanger further includes a heat exchange region which is formed by the pipe member and the fin plate members. An inlet port is provided at one end of the pipe member so as to conduct the first fluid into the pipe member, and an outlet port is provided at the other end of the pipe member so as to conduct the first fluid out from the pipe member. The heat exchange region of the heat exchanger has a first section which includes a first portion of the flow path of the first fluid continuing from the inlet port to an interim location along the flow path, and a second section which includes a second portion of the flow path of the first fluid continuing from the interim location to the outlet port. The second section of the heat exchanger has a greater area than the first section that is substantially exposed to the air, relative to the unit length of the flow path of the first fluid. BRIEF DESCRIPTION OF THE DRAWINGS The novel features of the present invention are set out with particularity in the appended claims, but the invention will be understood more fully and clearly from the following detailed description of the invention as set forth in the accompanying drawings, in which: Figure 1 is a block diagram of a refrigeration circuit in accordance with one prior art embodiment; Figure 2 is a schematic elevation of the evaporator illustrated in Figure 1; Figure 3 is an enlarged partial plan view of the evaporator illustrated in Figure 2; Figure 4 is a graph illustrating relationships between the temperature and the flow path of the refrigerant which flows through the heat exchanger shown in Figure 1. In the graph, the solid lines illustrate relationships between the temperature and the flow path of the refrigerant of R502 which flows through the evaporator or condenser shown in Figure 1, and the broken lines illustrate relationships between the temperature and the flow path of the refrigerant of R407A which flows through the evaporator or condenser shown in Figure 1; Figure 5 is a schematic elevation of an evaporator in accordance with a first embodiment of the present invention; Figure 6 is an enlarged partial plan view of the evaporator illustrated in Figure 5; Figure 7 is an enlarged partial plan view of an evaporator modified from the first embodiment of the present invention; Figure 8 is a schematic elevation of an evaporator in accordance with a second embodiment of the present invention; and Figure 9 is a schematic elevation of an evaporator in accordance with a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 5, 8 and 9 illustrate schematic elevations of the evaporators in accordance with the first, second and third embodiments of the present invention, respectively. The same numerals are used in Figures 5, 8 and 9 to denote the corresponding elements shown in Figure 2, and a detailed explanation thereof is therefore omitted. Figure 5 illustrates a heat exchanger, such as an evaporator 15A in accordance with a first embodiment of the present invention. Evaporator 15A includes a plurality of additional fin plates 152a which are, as illustrated in Figure 6, fixedly disposed about the heat medium conducting pipe 151 at a location within the second section 153b of the heat exchange region 153 of the evaporator 15A. The additional fin plates 152a are arranged to be parallel to fin plates 152. The additional fin plates 152a extend from heat conducting pipe 151 to be parallel to the flow direction "B" of air which passes through evaporator 15A as well as fin plates 152, as indicated by arrow B in Figure 6. The thickness of the additional fin plates 152a is designed to be about equal to that of fin plates 152. Each of the additional fin plates 152a is located at about the center of a space which is defined between the adjacent fin plates 152. Furthermore, in this embodiment, the second section 153b is designed to occupy about one-third of the area of the heat exchange region 153 of the evaporator 15A. That is, in other words, the first section 153a is designed to occupy about two-thirds of the area of the heat exchange region 153 of the evaporator 15A. Moreover, fin plates 152 and additional fin plates 152a can be replaced with cylindrical fins 162 and additional cylindrical fins 162a as illustrated in Figure 7. Cylindrical fins 162 and additional cylindrical fins 162a are arranged to be located on a downstream or far side of straight portions 151a of heat medium conducting pipe 151 with respect to the flow of air which passes through evaporator 15A. By providing the additional fin plates 152a within the second section 153b of the heat exchange region 153 of the evaporator 15A, the second section 153b gains an increased area that is substantially exposed to the air moving along the exterior surface of the evaporator 15A. The second section thereby achieves a greater exposed area than the first section 153b relative to the unit length of the straight portions 151a of the heat medium conducting pipe 151. As a result, during operation of the refrigeration circuit 10, the second section 153b becomes higher than the first section 153a in the efficiency of the heat exchanging which is carried out between the refrigerant flowing through the heat medium conducting pipe 151 and the air moving along the exterior surface of the evaporator 15A. Accordingly, even though the temperature differential between the R407A refrigerant and the air outside the evaporator gradually decreases within the second section 153b of the heat exchange region 153 of the evaporator 15A, the present invention effectively prevents a decease in the amount of heat absorbed from the air moving along the exterior surface of the evaporator 15A at the second section 153b of the heat exchange region 153 of the evaporator 15A. Therefore, the inefficient operation of the refrigeration circuit can be substantially eliminated even when R407A refrigerant is charged therein. Figure 8 illustrates a heat exchanger, such as an evaporator 15B in accordance with a second embodiment of the present invention. Evaporator 15B includes the heat medium conducting pipe 151 having a plurality of straight portions 151a which are arranged such that the distance D 2 , as measured between adjacent straight portions 151a of the heat medium conducting pipe 151 within the second section 153b of the heat exchange region 153 of the evaporator 15B, is greater than the distance D 1 , as measured between adjacent straight portions 151a of the heat medium conducting pipe 151 within the first section 153a of the heat exchange region 153 of the evaporator 15B. Preferably, the distance D 2 is designed to be about one and one-half (1.5) times as long as the distance D 1 . Furthermore, the second section 153b is designed to occupy about one-third of the area of the heat exchange region 153 of the evaporator 15B. That is, in other words, the first section 153a is designed to occupy about two-thirds of the area of the heat exchange region 153 of the evaporator 15B. According to the second embodiment, with respect to the unit length of the straight portions 151a of the heat medium conducting pipe 151, the second section 153b achieves a greater area than the first section 153a which is substantially exposed to the air moving along the exterior surface of the evaporator 15B. As a result, during operation of refrigeration circuit 10, the second section 153b becomes more efficient than the first section 153a in the heat exchanging which is carried out between the refrigerant flowing through the heat medium conducting pipe 151 and the air moving along the exterior surface of the evaporator 15B. Thus, an effect and advantage similar to those of the first embodiment are obtained. Figure 9 illustrates a heat exchanger, such as an evaporator 15C in accordance with a third embodiment of the present invention. In the third embodiment, straight portions 151a of the heat medium conducting pipe 151 are arranged such that the distance D 2 , as measured between adjacent straight portions 151a of the heat medium conducting pipe 151 within the second section 153b of the heat exchange region 153 of the evaporator 15C, is greater than the distance D 1 , as measured between adjacent straight portions 151a of the heat medium conducting pipe 151 within the first section 153a of the heat exchange region 153 of the evaporator 15C, similar to the arrangement of the second embodiment discussed above. In the third embodiment of the present invention, however, the distance D 2 is preferably designed to steppedly increase toward the outlet port 151d, and the maximum distance D 2 is designed to be about one and one-half (1.5) times the distance D 1 . Furthermore, the second section 153b is designed to occupy about one-third of the area of the heat exchange region 153 of the evaporator 15C. That is, in other words, the first section 153a is designed to occupy about two-thirds of the area of the heat exchange region 153 of the evaporator 15C. The effects and advantages of this embodiment are similar to those of the second embodiment such that a detailed explanation thereof is therefore omitted. Of course, the constructions disclosed in the first through third embodiments of the present invention are applicable to the condenser of the refrigeration circuit as well as the evaporator. With respect to application to a condenser, a decease in the amount of heat which radiates from the air moving along the exterior surface of the condenser within the second section of the heat exchange region of the condenser is effectively prevented. Therefore, the inefficient operation of the refrigeration circuit can be substantially eliminated even when R407A refrigerant is charged therein.

Claims: A heat exchanger forming a part of a refrigeration circuit into which a first fluid is charged, said heat exchanger comprising: conducting means (151) for conducting said first fluid therethrough so that a flow path of said first fluid is defined; exposed area increasing means (152,152a) for increasing a substantially exposed area of said conducting means (151) to a second fluid which flows along an exterior surface of said heat exchanger, said exposed area increasing means (152,152a) having an area which is in contact with said second fluid; and a heat exchange region (153) which is formed by said conducting means (151) and said exposed area increasing means (152,152a); said conducting means (151) including a first port (151c) through which said first fluid flows thereinto, and a second port (151d) through which said first fluid flows out therefrom; characterised by said heat exchange region (153) of said heat exchanger comprising a first section (153a) which includes a first portion of said flow path of said first fluid continuing from said first port (151c) to an interim location along said flow path of said first fluid, and a second section (153b) which includes a second portion of said flow path of said first fluid continuing from said interim location to said second port (151d), said second section (153b) of said heat exchanger having a greater substantially exposed area than said first section (153a) of said heat exchanger with respect to the unit length of said flow path of said first fluid. The heat exchanger of claim 1, wherein, said conducting means includes a pipe member (151) through which said first fluid flows, said pipe member (151) has a plurality of straight portions (151a) and a plurality of curved turn portions (151b) connecting one end of adjacent said straight portions and the other end of adjacent said straight portions (151a) alternately; said exposed area increasing means includes a plurality of fin members (152) fixedly disposed about said straight portions (151a) of said pipe member (151) such that said fin members (152) function to increase a surface area of said straight portions (151a) of said pipe member (151) that is substantially exposed to said second fluid, said fin members (152) having an area which is in contact with said second fluid. The heat exchanger of claim 2, wherein said first port (151c) is provided at one end of said pipe member (151) so as to conduct said first fluid into said pipe member (151), and said second port (151d) is provided at the other end of said pipe member (151) so as to conduct said first fluid out from said pipe member (151); and a plurality of additional fin members (152a) are fixedly disposed about said straight portions (151a) of said pipe member (151) in said second section (153b) of said heat exchange region (153) of said heat exchanger. The heat exchanger of claim 2 or 3 wherein said straight portions (151a) of said pipe member (151) are arranged to be parallel to one another with generally equal intervals. The heat exchanger of claim 3 or 4 wherein said additional fin members (152a) are arranged to be parallel to said fin members (151) or are arranged to be parallel to a direction of said second fluid which moves through said heat exchanger. The heat exchanger of one of claims 2 to 5 wherein said fin members (152,152a) are cylindrical rod members. The heat exchanger of claim 2, wherein said straight portions (151a) of said pipe member (151) are arranged to be generally parallel to one another. The heat exchanger of claim 7, wherein said first port (151c) is provided at one end of said pipe member (151) so as to conduct said first fluid into said pipe member (151), and said second port (151d) is provided at the other end of said pipe member (151) so as to conduct said first fluid outside said pipe member (151); said straight portions (151a) in said first section (153a) of said heat exchange region of said heat exchanger are spaced one from another in approximately first equal intervals, and said straight portions (151a) in said second section (153b) of said heat exchange region (153) of said heat exchanger are spaced one from another in approximately second intervals which are greater than said first equal intervals. The heat exchanger of claim 8 wherein said second intervals are generally equal or steppedly increase toward the second port (151d) of said heat exchanger. The heat exchanger of one of claims 2 to 9 wherein said fin members (152,152a) are arranged to be parallel to one another with generally equal intervals, and to intersect with said straight portions (151a) of said pipe member (151) at right angles. The heat exchanger of one of claims 7 to 10 wherein said fin members (152,152a) are plate members, said plate members extending preferably from said pipe (151) to be parallel to a direction of said second fluid which moves through said heat exchanger. The heat exchanger of one of claims 1 to 11 wherein said second section (153b) of said heat exchange region (153) of said heat exchanger occupies one-third of the area of said heat exchange region (153) of said heat exchanger. The heat exchanger of one of claims 1 to 12 wherein said first fluid is a non-azeotropic mixture of a plurality of HFC (hydrofluorocarbon) based substances, is preferably a mixture of HFC-32, HFC-125 and HFC-134a (20/40/40 wt%). The heat exchanger of one of claims 1 to 13 wherein said heat exchanger is an evaporator or a condenser. The heat exchanger of one of claims 1 to 14 wherein said second fluid is air.

Inventors: KOMATSU SHUNJI, KOMATSU, SHUNJI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1996
Main classification: F25B39
IPC codes: F28F1, F25B39, F25B1