Patent Publication Number: US-6209628-B1

Title: Heat exchanger having several heat exchanging portions

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a CIP application of U.S. application Ser. No. 09/039,943, filed on Mar. 16, 1998, now abandoned and is based on Japanese Patent Application No. 9-63237 filed on Mar. 17, 1997, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat exchanger in which different core portions are integrated with each other, and more particularly the present invention relates to a heat exchanger which can be effectively applied to a radiator of an automotive engine and a condenser of an automotive air conditioning apparatus. 
     2. Description of Related Art 
     Conventionally, an automotive air conditioning apparatus is assembled into a vehicle at a car dealer or the like after the vehicle has been completed. Recently, however, the automotive air conditioning apparatus is generally installed in the vehicle during vehicle assembling process. Therefore the automotive air conditioning apparatus is assembled with automotive parts in the assembling process of the vehicle at the manufacturing plant. 
     A heat exchanger in which different core portions such as a radiator and a condenser are integrated is disclosed in Japanese Patent Publication No. 3-177795. In this heat exchanger, cooling fins of first core portion and second core portion are integrated with each other. These cooling fins are connected to each oval flat tube of the first and second core portions by brazing. 
     In the cooling fin, a plurality of slits are formed at the center portion between the first and second core portions for interrupting a heat transmission from a high temperature side core portion (for example, radiator core portion) to a low temperature side core portion (for example, condenser core portion). 
     The required heat exchanging abilities of the first core portion (condenser core portion) and the second core portion (radiator core portion) varies in accordance with the difference of engine type or vehicle type despite the required constitutions of the heat exchanger are the same. When the automotive heat exchanger is constructed by some single heat exchangers, the required heat exchanging abilities thereof are set by tuning fin pitches of the cooling fins respectively in accordance with the engine type or vehicle type. 
     However, in the heat exchanger in which different core portions are integrated and cooling fins of first core portion and second core portion are integrated with each other, each fin pitch cannot be designed independently respectively. Therefore, the above-described method of setting the fin pitches in the first and second core potions respectively cannot be applied to this type heat exchanger. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, it is an object of the present invention to provide a heat exchanger in which different core portions and cooling fins thereof are integrated with each other, while setting the required heat exchanging abilities of each core portion independently respectively. 
     According to a first aspect of the present invention, a ratio, in a first core portion, of the number of louvers to a width of a first cooling fin, and a ratio, in a second core portion, of the number of louvers to a width of a second cooling fin are set to be in such a manner that the ratio in one core portion, out of said first and second core portion, the required radiation amount of which is larger than that of the other core portion is larger than the ratio in the other core portion. 
     Thus, in the core portion having a small required radiation amount, the number of louvers relative to the width of the cooling fin is small thereby decreasing the heat transfer ratio. However, the pressure loss in this core portion decreases thereby increasing the amount of an external fluid. Thus, the radiation amount of the core portion having a large required radiation amount increases. 
     According to a second aspect of the present invention, in one core portion, out of the first and second core portions, the required radiation amount of which is smaller than that of the other core portion, a width of the cooling fin in an external fluid flow direction is shorter than a width of a tube in its cross sectionally longitudinal direction. Further, a ratio, in the first core portion, of the number of louvers to the width of a first tube, and a ratio, in the second core portion, of the number louvers to the width of a second tube are set to be in such a manner that the ratio in one core portion, out of the first and second core portions, the required radiation amount of which is smaller than that of the other core portion is smaller than the ratio in the other core portion. 
     Thus, in the core portion having a small required radiation amount, the width of the cooling fin and the number of louvers relative to the width of the tube in its cross sectionally longitudinal direction are small thereby decreasing the heat transfer ratio. However, by this, the pressure loss in the core portion decreases thereby increasing the amount of an external fluid. Thus, the radiation amount of the core portion having a large required radiation amount increases. 
     According to a third aspect of the present invention, the length of the louver in one core portion, out of the first and second core portions, the required radiation amount of which is smaller than that of the other core portion is shorter than the length of the louver in the other core portion. 
     Thus, in the core portion having a small required radiation amount, the length of the louver is short thereby decreasing the heat transfer ratio. However, by this, the pressure loss in the core portion decreases thereby increasing the flow amount of the external fluid. Thus, the radiation amount of the core portion having a large required radiation amount increases. 
     According to a fourth aspect of the present invention, a tilt angle of the louver in one core portion, out of the first and second core portion, the required radiation amount of which is smaller than that of the other core portion is smaller than the tilt angle of the louver in the other core portion. 
     Thus, in the core portion having a small required radiation amount, the tilt angle of the louver is small thereby decreasing the heat transfer ratio. However, by this, the pressure loss in the core portion decreases thereby increasing the flow amount of the external fluid. Thus, the radiation amount of the core portion having a large required radiation amount increases. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: 
     FIG. 1 is a perspective view showing a core portion of a heat exchanger according to the first embodiment of the present invention; 
     FIG. 2 is a front view showing a core portion of a heat exchanger according to the first embodiment; 
     FIG. 3 is a plan view showing a core portion of a heat exchanger according to the first embodiment; 
     FIG. 4 is a perspective view showing a shape of the cooling fin; 
     FIG. 5A is a plan view showing tubes and cooling fins according to the first embodiment, 
     FIG. 5B is a cross sectional view taken along line  5 B— 5 B in FIG. 5A; 
     FIG. 6A is a plan view showing tubes and cooling fins according to the second embodiment, 
     FIG. 6B is a cross sectional view taken along line  6 B— 6 B in FIG. 6A; 
     FIG. 7 is a graph showing a relationship between a number of louvers decreasing ratio and a performance ratio; 
     FIG. 8A is a plan view showing tubes and cooling fins according to the third embodiment, 
     FIG. 8B is a cross sectional view taken along line  8 B— 8 B in FIG. 8A; 
     FIG. 9A is a plan view showing tubes and cooling fins according to the fourth embodiment, 
     FIG. 9B is a cross sectional view taken along line  9 B— 9 B in FIG. 9A; 
     FIG. 10A is a plan view showing tubes and cooling fins according to the fourth embodiment, 
     FIG. 10B is a cross sectional view taken along line  10 B— 10 B in FIG. 10A; 
     FIG. 11A is a plan view showing tubes and cooling fins according to the sixth embodiment, 
     FIG. 11B is a cross sectional view taken along line  11 B— 11 B in FIG. 11A; 
     FIG. 12 is a graph showing a relationship between a fin width ratio and a performance ratio; 
     FIG. 13A is a plan view showing tubes and cooling fins according to the seventh embodiment, 
     FIG. 13B is a cross sectional view taken along line  13 B— 13 B in FIG. 13A; 
     FIG. 14A is a plan view showing tubes and cooling fins according to the first comparison example of the seventh embodiment, 
     FIG. 14B is a cross sectional view taken along line  14 B— 14 B in FIG. 14A; 
     FIG. 15A is a plan view showing tubes and cooling fins according to the second comparison example of the seventh embodiment, 
     FIG. 15B is a cross sectional view taken along line  15 B— 15 B in FIG. 15A; 
     FIG. 16 is a graph showing the relations between a number of louvers and a performance ratio; 
     FIG. 17 is a graph showing a flat turning portion length and a performance ratio; 
     FIG. 18 is a graph showing a heat transfer ratio in accordance with a position of the cooling fin along an air flow direction; 
     FIG. 19A is a plan view showing tubes and cooling fins according to the eighth embodiment, 
     FIG. 19B is a cross sectional view taken along line  19 B— 19 B in FIG. 19A; 
     FIG. 20A is a plan view showing tubes and cooling fins according to the ninth embodiment, 
     FIG. 20B is a cross sectional view taken along line  20 B— 20 B in FIG. 20A; 
     FIG. 21A is a plan view showing tubes and cooling fins according to the tenth embodiment, 
     FIG. 21B is a cross sectional view taken along line  21 B— 12 B in FIG. 21A; 
     FIG. 22 is a graph showing relations between a louver cut length ratio and a performance ratio; 
     FIG. 23A is a plan view showing tubes and cooling fins according to the eleventh embodiment, 
     FIG. 23B is a cross sectional view taken along line  23 B— 23 B in FIG. 23A; 
     FIG. 24A is a plan view showing tubes and cooling fins according to the twelfth embodiment, 
     FIG. 24B is a cross sectional view taken along line  24 B— 24 B in FIG. 24A; 
     FIG. 25A is a plan view showing tubes and cooling fins according to the thirteenth embodiment, 
     FIG. 25B is a cross sectional view taken along line  25 B— 25 B in FIG. 25A; 
     FIG. 26 is a graph showing relations between louver a tilt angle reduction ratio and a performance ratio; and 
     FIG. 27 is a graph showing a relationship between a number of louvers decreasing ratio of first cooling fin and a performance ratio of second core portion. 
    
    
     DETAILED DESCRIPTION OF PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS 
     Preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings. 
     (First Embodiment) 
     In an automotive heat exchanger  1  shown in FIGS.  1 , 2 , a condenser core portion  2  of an automotive air conditioning apparatus is used as a first core portion, and a radiator core portion  3  for cooling an engine is used as a second core portion. Generally, because the temperature of refrigerant flowing through the condenser core portion  2  is lower than that of engine cooling water flowing through the radiator core portion  3 , the condenser core portion  2  is disposed at the upstream air side of the radiator core portion  3  in air flow direction and the two core portions  2 ,  3  are disposed in series in the air flow direction at the front-most portion of an engine compartment. The structure of the heat exchanger of the first embodiment is hereinafter described with reference to FIGS. 1 through 5. 
     FIG. 1 is a partial enlarged cross-sectional view of a heat exchanger  1  of the present invention. As shown in FIG. 1, a condenser core portion  2  and a radiator core portion  3  are disposed in series in the air flow direction so as to form predetermined clearances  46  between each pair of a condenser tube  21  and a radiator tube  31  described later to interrupt heat transmission. 
     The condenser core portion  2  includes flat shaped condenser tubes  21  in which a plural refrigerant passages are formed, and corrugated (wave-shaped) cooling fins  22  in which a plurality of folded portions  22   a  brazed to the condenser tube  21  are formed. 
     The radiator core portion  3  has a similar structure with the condenser core portion  2 . The radiator core portion  3  includes the radiator tubes  31 , in which a single coolant passage is formed, disposed in parallel with the condenser tubes  21  and radiator cooling fins  32 . The tubes  21  and  31  and the cooling fins  22 ,  32  are alternately laminated and are brazed to each other. A plurality of louvers  220  and  320  are formed in the two cooling fins  22 ,  32  to facilitate heat exchange. The two cooling fins  22 ,  32  and a plurality of connecting portions  45  are integrally formed with the louvers  220 ,  320  by a roller forming method or the like. 
     The connecting portions  45  are formed between the two cooling fins  22 ,  32  for connecting the two cooling fins  22 ,  32 . At both sides of the connecting portion  45 , adiabatic slits  47  are provided for interrupting heat transmission from the radiator core portion  3  to the condenser core portion  2 . The width of the connecting portion  45  is set to be smaller enough than the height of the cooling fins  22 ,  32  (the distance between a pair of adjacent flat tubes  21 ,  31 ) to suppress the heat transmission from the radiator core portion  3  to the condenser core portion  2 . 
     Side plates  23 ,  33  are reinforcement member of the two heat exchanging core portions  2 ,  3 . The side plates  23 ,  33  are respectively disposed in upper and lower end portions of the two heat exchanging core portions  2 ,  3  as shown in FIG.  2 . As shown in FIG. 1, the side plates  23 ,  33  are integrally formed from a sheet of aluminum plate to a general U-shape in cross section. Connecting portions  4  for connecting the side plate  23  and the side plate  33  are formed in two end portions of the longitudinal direction of the two side plates  23 ,  33 . A Z-shaped bent portion  41  of the side plate  23  and a Z-shaped bent portion  42  of the side plate  33  are connected to each other at a top end portion  43  so that the connecting portion  4  is formed. The width of the connecting portion  4  is set to be small enough as compared with the dimension of the side plate  23  or  33  in the longitudinal direction to suppress the heat transmission. Further, a recess portion is formed in the top end portion  43  of the connecting portion  4  to reduce the thickness of the plate wall of the connecting portion  4 . 
     Further, as shown in FIG. 2, a first header tank  34  for distributing cooling water to each radiator tube  31  is disposed at an end (left end) side of the radiator core portion  3 . The front shape of first header tank  34  is nearly a triangular, the cross-sectional shape is ellipsoid as shown in FIG.  3 . An inlet  35  of cooling water flowing to the radiator is formed at an upper side of the first header tank  34  having a nearly triangular shape. Further, a pipe  35   a  for connecting a pipe (not shown) of cooling water is brazed to the inlet  35 . 
     Further, a second header tank  36  for receiving the cooling water having been heat-exchanged is disposed in an opposite end (right end) of the first header tank  34 . The second header tank  36  has a similar shape with the first header tank  34 . As shown in FIG. 2, the second header tank  36  and the first header tank  34  are point-symmetrical with reference to the center of the radiator core portion  3 . Further, an outlet  37  for discharging the cooling water is formed at the bottom side of the second header tank  36 . With the tubes and the cooling fins and the like, a pipe  37   a  for connecting the pipe (not shown) of cooling water is brazed to the outlet  37 . 
     A first header tank  24  is disposed at an end side of the condenser core portion  2  for distributing the refrigerant into each condenser tube  21 , and the body of the first header tank  24  is cylindrically formed as shown in FIG.  3 . The first header tank  24  of the condenser is disposed to have a predetermined clearance with the second header tank  36  of the radiator. Further, a joint  26   a  for connecting a refrigerant pipe (not shown) is brazed to the body of the first header tank  24 , and an inlet  26  of refrigerant is formed in the joint  26   a.    
     Further, as shown in FIG. 3, a second header tank  25  of the condenser for receiving the refrigerant having been heat-exchanged is disposed at an opposite end of the first header tank  24  of the condenser core portion  2 . The second header tank  25  is disposed to have a predetermined clearance with the first header tank  34  of the radiator. The body of the second header tank  25  is cylindrically formed. Further, as shown in FIG. 2, a joint  27   a  for connecting a refrigerant pipe (not shown) is brazed to the body of the second header tank  25 . An outlet  27  of refrigerant is formed in the joint  27   a.    
     Next, the condenser cooling fin  22  and the radiator cooling fin  32  will be described. 
     The width Lc of the condenser cooling fin  22  and the width Lr of the radiator cooling fin  32  have the same length as the width of the tubes  21 ,  31  in the cross sectional longitudinal direction thereof. Here, the widths Lc, Lr are the dimension of the cooling fins  22 ,  32  along the cross sectionally longitudinal direction of the tubes  21 ,  31  (air flow direction). 
     The louver  220  of the condenser cooling fin  22  is constructed by a first louver group  221 , a second louver group  222 , and a turning louver  223  arranged between both louver groups  221 ,  222 . The turning louver  223  turns the air flow. The first louver group  221  and the second louver group  222  tilt toward the opposite side to each other. 
     Similarly, a first louver group  321 , a second louver group  322 , and a turning louver  323  are provided in the radiator cooling fin  32 . 
     The numbers of both louvers  220 ,  320  are set as follows to improve the heat transmitting ability (heat transmitting amount). In the condenser cooling fin  22 , each first and second louver groups  221 ,  222  has three louvers  220 . In the radiator cooling fin  32 , each first and second louver groups  321 ,  322  has five louvers  320 . 
     That is, the number Nc of the louvers  220  in the condenser cooling fin  22  is six (Nc=6), and the number Nr of the louvers  320  in the radiator cooling fin  32  is ten (Nr=10). 
     Accordingly, the ratio of the Nc and Lc in the condenser cooling fin  22  (Nc/Lc) and the ratio of the Nr and Lr in the radiator cooling fin  32  (Nr/Lr) satisfy the following relation: 
     
       
         (Nc/Lc)&lt;(Nr/Lr). 
       
     
     Here, the condenser cooling fin  22  has six louvers although ten louvers can be provided thereon if desired. Therefore, the area of air introducing portions  224 ,  225  provided in front and rear of the louvers  220  can be wide relative to the area where the louvers  220  are formed. 
     Accordingly, the ratio of the sum of the lengths of the air introducing portions  224 ,  225  in the air flow direction (L 1 +L 2 ) to the length of the space where the louvers  220  are formed in the air flow direction L 3 , [(L 1 +L 2 )/L 3 ], and the ratio of the sum of the lengths of the air introducing portions  324 ,  325  in the air flow direction (L 4 +L 5 ) to the length of the space where the louvers  320  are formed in the air flow direction L 6 , [(L 4 +L 5 )/L 6 ], satisfy the following relation: 
     
       
         [(L 1 +L 2 )/L 3 ]&gt;[(L 4 +L 5 )/L 6 ]. 
       
     
     Next, an operation of the above-described structure will be explained. 
     When a cooling fan (not illustrated) which is disposed at the air downstream side of the radiator core portion  3  operates, the cooling air passes through the condenser core portion  2  and the radiator core portion  3 , as shown in FIGS. 1 and 2. 
     At the same time, a gas phase refrigerant flowing out of a compressor flows into the first header tank  24  through the refrigerant inlet  26 . The gas phase refrigerant flows in the condenser tubes  21  from the right side to the left side in FIGS. 2 and 3 while being heat exchanged with the cooling air to be condensed. The condensed liquid phase refrigerant is collected in the second header tank  25  and flows out of the condenser core portion  2  through the refrigerant outlet  27 . 
     A hot engine coolant flows from an engine into the first header tank  34  through the engine coolant inlet  35 . The engine coolant flows in the radiator tube  31  from the left side to the right side in FIGS. 2 and 3 while being heat exchanged with the cooling air to be cooled. The cooled engine coolant is collected in the second header tank  36  and flows out of the radiator core portion  3  through the engine coolant outlet  37 . 
     The heat exchanging abilities of the condenser core portion  2  and the radiator core portion  3 , if the constitutions thereof are the same, depend on the heat transmitting ratio and the air flow resistance thereof. The heat transmitting ratio and the air flow resistance decrease in accordance with a decrease in the number of the louvers  220 ,  320 . 
     According to the first embodiment, in the condenser cooling fin  22 , six louvers are provided although ten louvers can be provided thereon if desired. While, in the radiator cooling fin  32 , ten louvers are provided by using the most of the space thereof. 
     Therefore, the heat transfer ratio in the condenser core potion  2  decreases in accordance with the decreasing the number of the louvers  220 . Thus, the heat transmitting ability of the condenser core portion  2  decreases. However, the air flow resistance in the condenser core portion  2  decreases thereby increasing the amount of the cooling air passing through the radiator core portion  3 . Thus, the heat transmitting ability of the radiator core portion  3  increases. 
     (Second Embodiment) 
     According to the second embodiment, as shown in FIGS. 6A,  6 B, in the condenser cooling fin  22 , ten louvers  220  are provided by making the most of the space thereof. While, in the radiator cooling fin  32 , six louvers  320  are provided although ten louvers can be provided thereon if desired. That is, the relation: (Nc/Lc)&gt;(Nr/Lr) is satisfied. Thereby, the radiation amount in the radiator core portion  3  decreases, while the radiation amount in the condenser core portion  2  increases with the air flow amount increasing. 
     FIG. 7 shows the relations between the number of louvers decreasing ratio and the performance ratios of the core portions  2 ,  3  under the condition that air flow speed of the cooling air is constant. Here, the number of louvers decreasing ratio is defined as a ratio of the number of louvers decreased relative to the number of louvers which can be provided within the predetermined fin width Lc, Lr. For example, in the condenser cooling fin  22  shown in FIG. 5A, six louvers is provided although ten louvers can be provided, thus the number of louvers decreasing ratio is 40%. Similarly, in the radiator cooling fin  32  shown in FIG. 6A, the number of louvers decreasing ratio is 40%. 
     As is understood from FIG. 7, when the number of louvers decreasing ratio is set to 50% in one of the condenser core portion  2  and the radiator core portion  3 , the radiation amount in this core portion decreases by about 10% and the pressure loss therein decreases by about 30%. In this way, as the pressure loss decreases in one core portion, the flow amount of the air passing through these core portions increases thereby increasing the radiation amount in the other core portion by about 5%. 
     Further, as is understood from FIG. 7, it is necessary to set the number of louvers decreasing ratio to 30% or more for decreasing the pressure loss by about 20%. 
     FIG. 27 shows a relationship between a number of louvers decreasing ratio of the first core portion which is required smaller radiation amount and a performance ratio of the second core portion which is required larger radiation amount. It is necessary to set the number of louvers decreasing ratio of the first core larger than 30% for significant increasing the radiation amount of the second core by about 3%. Preferably, the first core portion is the condenser with decreased number of louvers. The second portion is the radiator with the full number of louvers which can be provided within the fin width. The number of louvers in the first core as the condenser is decreased by 30% or more relative to the number of louvers in the second core as the radiator. Therefore, the density of the louvers on the first fin area is less than the density of the louvers on the second fin area. 
     (Third Embodiment) 
     According to the third embodiment, as shown in FIGS. 8A,  8 B, a projection portion  326  is formed at the air upstream side end (the end facing the condenser core portion  2 ) of the radiator cooling fin  32 . This projection portion  326  protrudes from the end of the radiator tube  31  toward the air upstream side. Thereby, the number of louvers Nr in the radiator cooling fin  32  is increased more than that in the first embodiment. 
     For example, as shown in FIGS. 8A,  8 B, the radiator cooling fin  32  has twelve louvers  320 . Thus, a radiation amount difference between in the condenser core portion  2  and in the radiator core portion  3  is expanded more than in the first embodiment. 
     (Fourth Embodiment) 
     According to the forth embodiment, as described in the first embodiment, the condenser cooling fin  22  has six louvers in spite of ten louvers can be provided thereon if making the most of the space thereof. In the fourth embodiment, as shown in FIGS. 9A,  9 B, the louver pitch Lpc of the louver  220  is set to be wider than the louver pitch Lpr of the louver  320 . Here, the louver pitch Lpc is defined as a distance between a pair of adjacent louvers  220 ,  320 . This distance is same as the length of each louver  220 ,  320  in the air flow direction. 
     In this way, the louver pitch in the condenser cooling fin  22  is set to be wider than in the first embodiment. Thus, the length of the air introducing portions  224 ,  225  (L 1 +L 2 ) can be decreased more than in the first embodiment. 
     In the first embodiment, the area L 3  where the louvers  220  are formed is partial to the center portion of the condenser cooling fin  22 . Thus, the air flowing along the tilted surface of the louvers  220  is collected in the center portion of the cooling fin  22 , and the reduction ratio of the heat transmitting ratio can be made remarkable. However, in the fourth embodiment, as the louver pitch Lpc is set to be larger than in the first embodiment, the air flowing along the tilted surface of the louvers  220  is spread entirely. Thus, the reduction ratio of the heat transmitting ratio can be decreased. 
     (Fifth Embodiment) 
     According to the fifth embodiment, as shown in FIGS. 10A,  10 B, the fin width Lc of the condenser cooling fin  22  is smaller than the width Ltc of the condenser oval flat tube  21 . While, in the radiator cooling fin  32 , the fin width Lr is same as the width Ltr of the radiator oval flat tube  31 . Here, the width Ltc of the condenser tube  21  is same as the width Ltr of the radiator tube  31 . 
     Accordingly, the ratio of the number of louvers  220  Nc (in FIGS. 10A,  10 B, Nc=6) to the condenser tube width Ltc (Nc/Ltc) and the ratio of the number of louvers  320  Nr (in FIGS. 10A,  10 B, Nr=10) to the radiator tube width Ltr (Nr/Ltr) satisfy the following relation: 
     
       
         (Nc/Ltc)&lt;(Nr/Ltr). 
       
     
     Here, in FIGS. 10A,  10 B, L F  denotes a width of an entire fin constructed by the condenser cooling fin  22  and the radiator cooling fin  32 , and L denotes the distance between both ends of both oval flat tubes  21 ,  31  (the width of the heat exchanger). 
     According to the fifth embodiment, because in the condenser core portion  2 , the fin width Lc relative to the tube width Ltc is small in comparison with in the radiator core portion  3 , the radiation area in the condenser core portion  2  decreases thereby decreasing the radiation amount. However, by decreasing the fin width Lc and the number Nc of the louvers  220  decreases, the air flow resistance in the condenser core portion  2  decreases thereby increasing the air flow amount passing through these heat exchanging core portions  2 ,  3 . Consequently, the radiation amount in the radiator core portion  3  increases. 
     (Sixth Embodiment) 
     According to the sixth embodiment, as shown in FIGS. 11A,  11 B, the fin width Lr of the radiator cooling fin  32  is smaller than the width Ltr of the radiator oval flat tube  31 . While, in the condenser cooling fin  22 , the fin width Lc is same as the width Ltc of the condenser oval flat tube  21 . Here, the width Ltc of the condenser tube  21  is same as the width Ltr of the radiator tube  31 . 
     Accordingly, the ratio of the number Nc of louvers  220  (in FIGS. 11A,  11 B, Nc=10) to the condenser tube width Ltc (Nc/Ltc) and the ratio of the number Nr of louvers  320  (in FIGS. 11A,  11 B, Nr=6) to the radiator tube width Ltr [Nr/Ltr] satisfy the following relation: 
     
       
         (Nc/Ltc)&gt;(Nr/Ltr). 
       
     
     Thus, the radiation amount in the radiator core portion  3  decreases. However, the air flow resistance in the radiator core portion  3  decreases thereby increasing the air flow amount passing through these heat exchanging core portions  2 ,  3 . Consequently, the radiation amount in the condenser core portion  2  increases. 
     FIG. 12 is a graph showing the experimented results based on the fifth and the sixth embodiments. The graph shows relations between the ratio of the fin width Lc, Lr to the tube width Ltc, Ltr (Lc/Ltc, Lr/Ltr) and the radiation performance ratio of the condenser core portion  2  and the radiator core portion  3 . Here, the experimented results are under the condition that the air flow speed is constant. 
     As is understood from FIG. 12, when the fin width Lc or Lr is set to 80% of the tube widths Ltc, Ltr in one of the condenser core portion  2  and the radiator core portion  3 , the radiation amount in this core portion decreases by about 10% and the pressure loss therein decreases by about 20%. In this way, as the pressure loss decreases in one core portion, the flow amount of the air passing through these core portions increases thereby increasing the radiation amount in the other core portion by about 3%. Further, as is understood from FIG. 12, it is necessary to set the fin width Lc, Lr to 80% or less of the tube width Ltc, Ltr. 
     (Seventh Embodiment) 
     According to the seventh embodiment, as shown in FIGS. 13A,  13 B, the length L T  of the flat turning surface  223   a,    323   a  of the turning louver  223 ,  323  is set to be three times or more as the louver pitch Lp. Here, for example, the length of the flat turning surface  223   a,    323   a  is set to be about 5.5 times as the louver pitch Lp. The object of the seventh embodiment is to suppress the reduction of heat transfer ratio in the cooling fin  22 ,  32 . 
     FIGS. 14 and 15 show a first and a second comparison examples being compared with the seventh embodiment. The first and second comparison examples are all the same except for the number of louvers  220 ,  320 . 
     According to the experimented results and studies about the first and second comparison examples, when the number of louvers is simply decreased from both front and rear side in the air flow direction, both air pressure loss and heat transfer ratio are decreased proportionally, as shown in FIG.  16 . 
     Further, according to the experimented results and studies about relations between the length L T  of the flat turning surface  223   a,    323   a  of the turning louver  223 ,  323  and the performance ratio of the core portion  2 ,  3 , when the length L T  of the flat turning surface  223   a,    323   a  becomes large, both heat transfer ratio and pressure loss ratio of the fin increase as shown in FIG.  17 . Here, FIG. 17 shows the relations between the length L T  and the performance ratio of the core portion  2 ,  3  under the condition that the air flow speed is constant. The length L T  is expressed as a multiple of the louver pitch Lp. 
     As is understood from FIG. 17, the heat transfer ratio and the pressure loss ratio of the fin increase as the length L T  becomes large, and are saturated as the length L T  is more than 3×Lp. Therefore, it is preferable to set the length L T  to be three times or more as the louver pitch Lp. 
     The heat transfer ratio of the fin increases in accordance with that the length L T  of the flat turning surface  223   a,    323   a  becomes large because the following reason. That is, as the length L T  becomes large, the flow speed of the air passing through the second louver group  222 ,  322  which is disposed at the air downstream side of the turning louver  223 ,  323  recovers. Thus, the air passes through the second louver group  222 ,  322  at high speed. 
     Accordingly, in the seventh embodiment, the length L T  of the flat turning surface  223   a,    323   a  of the turning louver  223 ,  323  is set to be three times or more as the louver pitch Lp. 
     In FIG. 18A, the axis of abscissa denotes the cross sectional shape of the fin in the comparison example shown in FIG. 14B in the air flow direction. In FIG. 18B, the axis of abscissa denotes the cross sectional shape of the fin in the seventh embodiment shown in FIG. 13B in the air flow direction. 
     In the comparison example, the turning louver  223 ,  323  is formed into a V-shape, i.e., the turning louver  223 ,  323  has no flat turning surface. Thus, the flow speed of the air passing through the second louver group  222 ,  322  does not recover and is still low. Therefore, as denoted by {circle around (1)} in FIG. 18A, the heat transfer ratio in the second louver group  222 ,  322  is lower than that in the first louver group  221 ,  321 . 
     Contrary to this, in the seventh embodiment, the length L T  of the flat turning surface  223   a,    323   a  is set to be 5.5 times as the louver pitch Lp. That is, the length L T  is large enough to make the speed of the air passing through the second louver group  222 ,  322  recover. Thus, because the air passes through the second louver group  222 ,  322  at high speed, the heat transfer ratio in the second louver group  222 ,  322  is approximately the same as in the first louver group  221 ,  321  as denoted by {circle around (2)} in FIG.  18 B. 
     According to the inventor&#39;s research and study, it is preferable that the length L T  of the flat turning surface  223   a,    323   a  in one cooling fin in which the number of louvers is smaller than that in the other cooling fin is set to be longer than the length Li of the air introducing portion  224 ,  324  disposed at the air upstream side of the louvers  220 ,  320  for making the flow speed of the air passing through the second louver group  222 ,  322  recover. 
     (Eighth Embodiment) 
     According to the eighth embodiment, as shown in FIGS. 19A,  19 B, a length (cut length) Ec of the condenser louver  220  and a length (cut length) Er of the radiator louver  320  are set to be different from each other. The length Ec, Er is defined as a length of the louver  220 ,  320  in a direction perpendicular to the air flow direction, and influences the heat transfer ratio and the air flow resistance. 
     That is, when the length Ec, Er of the louver  220 ,  320  is decreased, the heat transfer ratio and the air flow resistance are also decreased. 
     In the eighth embodiment, the length Ec of the condenser louver  220  is set to be shorter than the length Er of the radiator louver  320  for improving the performance of the radiator core portion  3 . 
     Thus, though the performance of the condenser core portion  2  is decreased by shortening the length Ec of the condenser louver  220 , the air resistance is decreased by shortening the length Ec of the condenser louver  220  thereby increasing the air flow amount. Therefore, the performance of the radiator core portion  3  is improved. 
     Here, for example, the fin height Hf of the cooling fin  22 ,  32  (distance between a pair of adjacent tubes) is 8 mm, the length Er of the radiator louver  320  is 7 mm, and the length Ec of the condenser louver  220  is 5 mm. 
     (Ninth Embodiment) 
     According to the ninth embodiment, as shown in FIGS. 20A,  20 B, the length Er of the radiator louver  320  is set to be shorter than the length Ec of the condenser louver  220  for improving the performance of the condenser core portion  2 . 
     (Tenth Embodiment) 
     According to the tenth embodiment, as shown in FIGS. 21A,  21 B, the projection portion  326  described in FIG. 8A is provided at the air upstream side end of the radiator cooling fin  32 , and a projection portion  327  facing the projection portion  326  is provided at the air downstream side end of the condenser cooling fin  22  also. By this, the number of condenser louvers  220  in the second louver group  222  and the number of radiator louvers  320  in the first louver group  321  are increased. 
     Further, the length Ec of the condenser louver  220  is set to be shorter than the length Er of the radiator louver  320 . 
     FIG. 22 is a graph showing relations between the length of the louver in the eighth through tenth embodiments and the performance of the core portion under the condition that the flow speed of the air passing through the core portion is constant. The louver length ratio placed on the axis of abscissa is a ratio of the louver length which is shortened intently (for example, condenser louver length Ec in the eighth embodiment) to the louver length which is defined by the fin height Hf (for example, radiator louver length Er in the eighth embodiment). 
     That is, the louver length ratio is defined as follows: 
     (Louver length which is shortened intently)/(Louver length which is defined by a fin height). 
     As is understood from FIG. 22, when the louver length ratio is set to be 50%, the radiation amount in the core portion in which the louver length is shorten decreases by about 10%, and the pressure loss therein decreases by about 30%. By this, pressure loss decreases by about 30%, the radiation amount in the core portion in which the louver length is defined by the fin height is improved by about 5%. 
     (Eleventh Embodiment) 
     According to the eleventh embodiment, as shown in FIGS. 23A,  23 B, a tilt angle θc of the condenser louver  220  and a tilt angle θr of the radiator louver  320  are set to be different from each other. The tilt angles θc, θr influence the heat transfer ratio and the air flow resistance. 
     That is, when the tilt angle θc, θr of the louver  220 ,  320  is decreased, the speed of the air passing through the louvers is decreased, and the heat transfer ratio and the air flow resistance are also decreased. 
     In the eleventh embodiment, the tilt angle θc of the condenser louver  220  is set to be smaller than the tilt angle θr of the radiator louver  320  for improving the radiation performance of the radiator core portion  3 . 
     Thus, though the performance of the condenser core portion  2  decreases by reducing the tilt angle θc of the condenser louver  220 , the air resistance decreases by reducing the tilt angle θc of the condenser louver  220  thereby increasing the air flow amount. Therefore, the performance of the radiator core portion  3  is improved. 
     For example, the tilt angle θc of the condenser louver  220  is 18°, and the tilt angle θr of the radiator louver  320  is 25°. 
     (Twelfth Embodiment) 
     According to the twelfth embodiment, as shown in FIGS. 24A,  24 B, the tilt angle θr of the radiator louver  320  is set to be smaller than the tilt angle θc of the condenser louver  220  for improving the performance of the condenser core portion  2 . 
     (Thirteenth Embodiment) 
     According to the thirteenth embodiment, as shown in FIGS. 25A,  25 B, the projection portion  326  described in FIG. 21 is provided at the air upstream side end of the radiator cooling fin  32 , and a projection portion  327  facing the projection portion  326  is provided at the air downstream side end of condenser cooling fin  22  also. By this, the number of condenser louvers  220  in the second louver group  222  and the number of radiator louvers  321  in the first louver group  322  are increased. 
     Further, the tilt angle θc of the condenser louver  220  is set to be larger than the tilt angle θr of the radiator louver  320 . 
     FIG. 26 is a graph showing relations between the tilted angle of the louver in the eleventh through thirteenth embodiments and the performance of the core portion under the condition that the flow speed of the air passing through the core portion is constant. 
     Here, a louver tilt angle reduction ratio which is placed on the axis of abscissa is defined as a ratio of the tile-angle reduced intently to the common tilt-angle for attaining a high heat transfer ratio. 
     That is, the louver tilt angle reduction ratio is defined as follows: 
     
       
         (tile-angle reduced intently)/(common tilt-angle for attaining a high heat transfer ratio)×100. 
       
     
     As is understood from FIG. 26, for example, when the tilt angle reduction ratio is set to be 20%, the radiation amount in the core portion in which the tilt-angle is reduced decreases by about 10%, and the pressure loss therein decreases by about 25%. By this decreasing pressure loss decreasing by about 25%, the radiation amount in the core portion in which the tile-angle of the louver is the common angle for attaining the high heat transfer ratio is improved about 4%. 
     In the above described embodiments, the present invention is applied to the heat exchanger in which the condenser core portion  2  and the radiator core portion  3  are integrated. However, it is to be noted that the present invention can be applied to various heat exchangers in which two heat exchanging core portions, to carry out heat exchanges between two kinds of fluid and the air, are integrated. 
     Although the present invention has been fully described in connection with preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.