Patent Publication Number: US-6216776-B1

Title: Heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application relates to and claims priority from Japanese Patent Application No. Hei. 10-32505 filed on Feb. 16, 1998, No. Hei. 10-65719 filed on Mar. 16, 1998, No. Hei. 10-95961 filed on Apr. 8, 1998, No. Hei. 10-168700 filed on Jun. 16, 1998, and No. Hei. 10-294163 filed on Oct. 15, 1998, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat exchanger which is typically applied to a condenser or a radiator for a refrigerant cycle in which carbon dioxide is used as refrigerant. 
     2. Related Art 
     Recently, refrigerant cycles without using chlorofluorocarbon (hereinafter referred to as flon) as refrigerant are developed to prevent global warming. A super critical refrigerant cycle in which carbon dioxide (CO 2 ) is used as refrigerant (hereinafter referred to as CO 2  refrigerant cycle) is studied. However, because the CO 2  refrigerant cycle has a high operation internal pressure, heat exchangers used in the CO 2  refrigerant cycle, such as a condenser into which high-pressure refrigerant flows, need to have a high strength. As shown in FIG. 38, JP-A-5-215482 discloses a heat exchanger having plural extruded flat tubes  302 . Each of the flat tubes  302  has plural fluid passages  302   a  having a round-shaped cross-section, so that strength of each flat tube  302  is improved. However, since each fluid passage  302   a  has the round-shaped cross-section, a wall thickness of the flat tube  302  becomes thicker as compared with a flat tube having fluid passages with a square-shaped cross-section. As a result, weight of each flat tube  302  is increased. On the other hand, when the flat tube has the fluid passages having the square-shaped cross-section, wall thickness and weight of the flat tube are decreased, but strength of the flat tube is also decreased. 
     On the other hand, JP-A-2-247498 discloses a heat exchanger in which an inner supporting plate is disposed within a header tank having first and second plates, so that strength of the header tank is enhanced. However, in the heat exchanger, the inner supporting plate and the header tank are connected to each other by an acute angle, and stress tends to be intensively applied to a connection portion between the inner supporting plate and the header tank. As a result, the strength of the heat exchanger may be not resistant to high pressures such as 40 MPa of the CO 2  refrigerant cycle. 
     Further, JP-A-3-260596 discloses a conventional heat exchanger having plural flat tubes  402  through which refrigerant flows, and a pair of substantially cylindrical header tanks  405  connected to both longitudinal ends of the flat tubes  402 , as shown in FIG.  39 . However, high pressure of the CO 2  refrigerant cycle is approximately ten times larger than that of a refrigerant cycle using flon as refrigerant. Therefore, when the conventional heat exchanger is used in the CO 2  refrigerant cycle, thickness of the header tank  405  may need to be greatly increased so that the header tank  405  has a sufficient pressure resistance. As a result, size and weight of the header tank  405  may be increased. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, it is a first object of the present invention to provide a heat exchanger having relatively light weight and high strength. 
     It is a second object of the present invention to provide a heat exchanger having large pressure resistance. 
     It is a third object of the present invention to provide a heat exchanger in which refrigerant is introduced into tubes from each tank passage of a header tank so that heat-exchange performance of the heat exchanger is improved. 
     It is a fourth object of the present invention to provide a heat exchanger in which an amount of refrigerant introduced into tank passages of the header tank is controlled so that heat-exchange performance of the heat exchanger is improved. 
     According to the present invention, a heat exchanger includes a plurality of tubes and a header tank disposed on each longitudinal ends of the tubes. Each of the tubes has a first portion having a first wall portion for forming plural first passages through which a fluid flows, and a second portion disposed on each sides of the first portion. The second portion has a second wall portion for forming a second passage in which no fluid flows. Each of longitudinal ends of the second portion is recessed from each of the longitudinal ends of the first portion, and the second wall portion has a wall thickness thinner than that of the first wall portion. Therefore, a cross-sectional area of the second passage is increased, while a cross-sectional area of the second wall portion is decreased. Thus, weight of each tube is decreased while strength of each tube is improved. 
     Preferably, the first passage of the first portion has a round-shaped cross-section, and the second passage has a polygonal-shaped cross-section. Therefore, each of the tubes has a sufficient strength, while weight thereof is reduced. 
     More preferably, the header tank has therein an inner partition wall extending in a longitudinal direction of the header tank to partition an inner space of the header tank into first and second tank passages. A width of the inner partition wall in a width direction perpendicular to both of a longitudinal direction of the tubes and the longitudinal direction of the header tank is gradually increased toward inner walls of the header tank, so that the first and second tank passages have an oval-shaped cross-section. As a result, pressure resistance of the header tank is improved. 
     Further, the first tank passage is provided on an upstream air side of the second tank passage relative to a flow direction of air passing through between the tubes, and an amount of the fluid flowing through the first tank passage is made larger than an amount of the fluid flowing through the second tank passage. As a result, more fluid flows through the tubes at an upstream air side, thereby improving heat-exchange performance of the heat exchanger. 
     Preferably, the header tank has a first communication hole through which the first and second tank passages communicate with each other, and a second communication hole through which the first tank passage communicates with a pipe for introducing the fluid into the header tank. An opening area of the first communication hole is set to smaller than that of the second communication hole, so that more fluid flows through the first tank passage than the second tank passage. Thus, heat-exchange performance of the heat exchanger can be further improved. 
    
    
     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 when taken together with the accompanying drawings, in which: 
     FIG. 1 is a perspective view showing a heat exchanger according to a first preferred embodiment of the present invention; 
     FIG. 2A is a partial top plan view showing a flat tube of the heat exchanger according to the first embodiment, and FIG. 2B is a cross-sectional view taken along line IIB—IIB in FIG. 2A; 
     FIG. 3 is a partial sectional view showing a connection structure between the flat tube and a header tank of the heat exchanger according to the first embodiment; 
     FIG. 4 is a top plan view showing a flat tube according to a modification of the first embodiment; 
     FIG. 5 is a top plan view showing a flat tube according to an another modification of the first embodiment; 
     FIG. 6 is a partial sectional view showing a connection structure between the flat tube and a header tank according to an another modification of the first embodiment; 
     FIG. 7 is a partial sectional view showing a connection structure between the flat tube and a header tank according to an another modification of the first embodiment; 
     FIG. 8 is a perspective view showing a heat exchanger according to a second preferred embodiment of the present invention; 
     FIG. 9A is a cross-sectional view showing a header tank of the heat exchanger according to the second embodiment, FIG. 9B is a side view showing a first plate of the header tank when viewed from a side of a core portion of the heat exchanger according to the second embodiment, and FIG. 9C is a side view showing a second plate of the header tank when viewed from the side of the core portion according to the second embodiment; 
     FIG. 10 is a front view showing a separator within the header tank according to the second embodiment; 
     FIG. 11 is a front view showing a header cap of the header tank according to the second embodiment; 
     FIG. 12 is a cross-sectional view showing the header tank into which the separator is attached according to the second embodiment; 
     FIG. 13A is a cross-sectional view showing a header tank according to a third preferred embodiment of the present invention, and FIG. 13B is a perspective view showing the header tank of the third embodiment; 
     FIG. 14A is a cross-sectional view showing a header tank according to a fourth preferred embodiment of the present invention, and FIG. 14B is a perspective view showing the header tank of the fourth embodiment; 
     FIG. 15A is a cross-sectional view showing a header tank according to a fifth preferred embodiment of the present invention, and FIG. 15B is a perspective view showing the header tank of the fifth embodiment; 
     FIG. 16A is a cross-sectional view showing a header tank according to a sixth preferred embodiment of the present invention, and FIG. 16B is a perspective view showing the header tank of the sixth embodiment; 
     FIG. 17 is a cross-sectional view showing a header tank according to a modification of the second embodiment; 
     FIG. 18 is an exploded sectional view of a header tank according to an another modification of the second embodiment; 
     FIG. 19 is a cross-sectional view showing a header tank according to an another modification of the second embodiment; 
     FIG. 20A is a disassemble view showing an assembling structure of a separator and a header tank according to an another modification of the second embodiment, and FIG. 20B is a perspective view showing an assembled structure between the separator and the header tank in FIG. 20A; 
     FIG. 21A is a disassemble view of a header tank according to an another modification of the second embodiment, and FIG. 21B is a cross-sectional view showing an assembled structure between the header tank in FIG. 21A and a flat tube; 
     FIG. 22 is a cross-sectional view showing a header tank and a flat tube according to an another modification of the second embodiment; 
     FIG. 23 is a partial sectional view showing a connection structure between a header tank and flat tubes according to an another modification of the second embodiment; 
     FIG. 24 is a cross-sectional view showing a header tank and a flat tube according to an another modification of the second embodiment; 
     FIG. 25 is a perspective view showing a header tank of a radiator produced on a trial basis by the inventor of the present invention; 
     FIG. 26 is a front view showing a radiator according to a seventh preferred embodiment of the present invention; 
     FIG. 27 is a perspective view showing a header tank of the radiator according to the seventh embodiment; 
     FIG. 28 is a cross-sectional view of the header tank and a tube according to the seventh embodiment; 
     FIG. 29 is a schematic side view showing a part of the header tank according to the seventh embodiment; 
     FIG. 30 is a perspective view showing a header tank of a radiator according to an eighth preferred embodiment of the present invention; 
     FIG. 31 is a perspective view showing a header tank of a radiator according to a ninth preferred embodiment of the present invention; 
     FIGS. 32A,  32 B are cross-sectional views showing a pipe of a radiator according to a tenth preferred embodiment of the present invention; 
     FIG. 33 is a perspective view showing a part of a radiator according to an eleventh preferred embodiment of the present invention; 
     FIG. 34A is a perspective view showing a supplying member for a header tank according to the eleventh embodiment, FIG. 34B is a cross-sectional view showing the header tank of the eleventh embodiment, and FIG. 34C is a schematic side view showing the header tank according to the eleventh embodiment; 
     FIG. 35 is a perspective view showing a supplying member of a radiator according to a twelfth preferred embodiment of the present invention; 
     FIG. 36A is a perspective view showing a supplying member and a part of a header tank of a radiator according to a thirteenth preferred embodiment of the present invention, and FIG. 36B is a schematic side view showing the header tank of the thirteenth embodiment; 
     FIG. 37 is an exploded perspective view of a header tank according to a modification of the seventh embodiment; 
     FIG. 38 is a top plan view showing a flat tube of a conventional heat exchanger; and 
     FIG. 39 is a perspective view of a header tank of a conventional radiator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
     A first preferred embodiment of the present invention will be described with reference to FIGS. 1-3. In the first embodiment, a heat exchanger  1  shown in FIG. 1 is typically used for a condenser of a refrigerant cycle. As shown in FIG. 1, the heat exchanger  1  has plural flat tubes  2  laminated to each other, corrugated fins  3  disposed between adjacent flat tubes  2 , and a pair of header tanks  4  connected to both end of each flat tube  2 . 
     The flat tube  2  is formed into a flat shape having a relatively small thickness by extrusion. As shown in FIGS. 2A-3, each of the flat tubes  2  has a flow passage portion  2 A inserted into the header tanks  4 , and a pair of non-flow passage portions  2 B disposed at both sides of the flow passage portion  2 A to be exposed outside the header tanks  4 . Further, as shown in FIG. 2B, each longitudinal end of the non-flow passage portions  2 B is formed to be respectively recessed from longitudinal ends of the flow passage portion  2 A in a longitudinal direction of the flat tubes  2 . 
     Further, the flow passage portion  2 A has plural flow passages  2   a  through which refrigerant flows, and the flow passages  2   a  are equally spaced in a lateral direction of the flat tube  2 . The non-flow passage portion  2 B has two non-flow passages  2   b  in which no refrigerant flows. In FIGS. 2A,  2 B, two non-flow passages  2   b  are indicated; however, the non-flow passage portion  2 B may have at least one non-flow passage  2   b.  Each of the flow passages  2   a  has a round-shaped cross-section. On the other hand, one of the non-flow passage  2   b  has a square-shaped cross-section, and the other non-flow passage  2   b  has a substantially semicircular-shaped cross-section. The non-flow passage  2   b  may have any polygonal-shaped cross-section. Therefore, a cross-sectional area of a single flow passage  2   a  is smaller than that of a single non-flow passage  2   b.  That is, a first wall portion for forming each of the flow passages  2   a  is formed thicker than a second wall portion for forming each of the non-flow passage  2   b.    
     Referring back to FIG. 1, each of the corrugated fins  3  is formed into a corrugated shape by bending thin metal plate having a large heat conductivity such as aluminum plate. The corrugated fins  3  are attached between each adjacent flat tubes  2 , and are bonded to outer surfaces of the flat tubes  2  through brazing or the like. 
     Each of the header tanks  4  has a cylindrical body  4 A formed into an oval-shape in cross-section, and a pair of header caps  4 B attached to both longitudinal ends of the cylindrical body  4 A to close the longitudinal ends of the cylindrical body  4 A. Each of the header tanks  4  is disposed at each of longitudinal ends of the flat tubes  2 . As shown in FIG. 3, plural oblong holes  4   a  are formed in a side surface of the header tank  4 . Each of the longitudinal end portions of the flat tubes  2  is inserted into the corresponding oblong hole  4   a  so that the flow passages  2   a  of the flat tubes  2  communicate with the header tank  4 . 
     Next, operation of the heat exchanger  1  according to the first embodiment will be described. When the refrigerant cycle starts operating, high-pressure high-temperature gas refrigerant is introduced into one of the header tanks  4  and is distributed into each flat tubes  2 . While the gas refrigerant flows through the flow passages  2   a  in the flat tubes  2  toward the other header tank  4 , the refrigerant is cooled through heat exchange between the refrigerant and air passing through the heat exchanger  1 . As a result, the gas refrigerant is condensed and liquefied. The condensed liquid refrigerant flows into the other header tank  4  through the flow passages  2   a  in the flat tubes  2 , and is discharged from the other header tank  4  through an outlet (not shown) connected to the other header tank  4 . 
     According to the first embodiment of the present invention, each of the flow passages  2   a  has a round-shaped cross-section, and each of the non-flow passages  2   b  has a polygonal-shaped cross-section. Therefore, the first wall portion for forming each of the flow passages  2   a  is formed thicker than the second wall portion for forming each of the non-flow passage  2   b.  That is, each of the flow passages  2   a  has a cross-sectional area smaller than that of each of the non-flow passages  2   b.  Therefore, the weight of the non-flow passage portion  2 B is decreased, thereby decreasing weight of each flat tube  2 . On the other hand, the flow passage portion  2 A has a sufficient strength, because each of the flow passages  2   a  has a round-shaped cross-section. Thus, in the first embodiment, weight of the flat tube  2  is decreased, while the flat tube  2  has a sufficient strength. 
     Next, modifications of the first embodiment will be described with reference to FIGS. 4-7. In the modifications of the first embodiments, components which are similar to those in the first embodiment are indicated with the same reference numerals, and the explanation thereof is omitted. 
     As shown in FIG. 4, a tube  12  may have a non-flow passage  12   b  formed into a single passage having an oblong-shaped cross-section extended in the lateral direction of the flat tube  2 . As shown in FIG. 5, a tube  22  may have a pair of non-flow passage portions  2 B respectively having three non-flow passages  22   b.  Both the flat tubes  12 ,  22  shown in FIGS. 4,  5  have a cross-sectional area of wall portion, smaller than that of a comparison tube having a non-flow passage portion in which each of non-flow passages has a round-shaped cross-section similarly to the flow passages (hereinafter referred to as comparison tube). That is, each weight of the flat tubes  12 ,  22  shown in FIGS. 4,  5  is smaller than that of the comparison tube. 
     For example, each of dimensions of the flat tubes  12 ,  22  shown in FIGS. 4,  5  and the comparison tube is set as follows, and each cross-sectional area of wall portions of the flat tubes  12 ,  22  and the comparison tube is calculated and compared therebetween. That is, each lateral width Wt of the flat tubes  12 ,  22 , and the comparison tube is 24 mm, thickness T of the flat tubes in a flattened direction thereof is 1.2 mm, inner diameter d of the flow passage  2   a  is 0.7 mm, a dimension t 1  between the adjacent flow passages  2   a  in the lateral direction of the flat tubes is 0.43 mm, a dimension t 2  between a most-external non-flow passage and a lateral end of the flat tubes in the lateral direction of the flat tubes is 0.35 mm, a dimension t 3  between the passages and a flattened end of the flat tubes in the flattened direction of the flat tubes is 0.25 mm, a lateral dimension n 1  of a non-flow passage  12   b  of the flat tube  12  in FIG. 4 is 2.96 mm, a lateral dimension n 2  of a non-flow passage  22   b  of the flat tube  22  in FIG. 5 is 0.7 mm, and an inner diameter of a non-flow passage (not shown) of the comparison tube is 0.7 mm. In this case, a cross-sectional wall area of a wall portion of the flat tube  12  shown in FIG. 4 is 18.68 mm 2 , and a cross-sectional area of a wall portion of the flat tube  22  shown in FIG. 5 is 19.88 mm 2 , and a cross-sectional area of a wall portion of the comparison tube is 20.41 mm 2 . Thus, each wall portion of the flat tubes  12 ,  22  shown in FIGS. 4,  5  has a cross-sectional area smaller than that of the comparison tube. As a result, the flat tubes  12 ,  22  shown in FIGS. 4,  5  have a decreased weight as compared with the comparison tube. 
     In the above-described first embodiment, each header tank  4  is formed into a oblong shape in cross section, as shown in FIG.  3 . However, as shown in FIG. 6, a header tank  14  may have a round-shaped cross-section. Further, as shown in FIG. 7, a header tank  24  may have a 8-shaped cross-section. That is, the header tank  24  may be formed into a shape approximately corresponding to numerical letter eight in cross-section. 
     The flow passages  2   a  may have an oval-shaped cross-section instead of the round-shaped cross-section. The non-flow passages  2   b  may have a cross-section of any shape besides the shapes shown in FIGS. 2A,  4 ,  5 , provided that the cross-sectional area of the wall portion forming the non-flow passage  2   b  is smaller than that of the wall portion forming the flow passage  2   a.  For example, the non-flow passage  2   b  may have a circular-shaped cross-section having a larger passage area than that of each flow passage  2   a.    
     A second preferred embodiment of the present invention will be described with reference to FIGS. 8-12. 
     In the second embodiment, the present invention is typically applied to a radiator  100  of a CO 2  refrigerant cycle. As shown in FIG. 8, the radiator  100  has plural laminated flat tubes  111  through which CO 2  refrigerant flows, and plural corrugated fins  112  attached between each adjacent tubes  111 . The flat tubes  111  are formed through extrusion using aluminum alloy. The corrugated fins  112  are made of aluminum, and are formed into a corrugated shape through a roller forming method. A core portion  110  of the radiator  100  is composed of the flat tubes  111  and the corrugated fins  112 . Heat exchange between refrigerant flowing through the flat tubes  111  and air passing through the core portion  110  of the radiator  100  is performed in the radiator  100 . 
     A pair of side plates  113  are attached to the core portion  110  to enhance strength of the core portion  110 . The side plates  113  and the flat tubes  111  are bonded to the corrugated fins  112  through brazing, using brazing material coated on both sides of the corrugated fins  112 . Further, a pair of header tanks  120  are disposed on both longitudinal ends of the flat tubes  111 . The header tanks  120  extend in a direction perpendicular to a longitudinal direction of the flat tubes  111 , and communicates with the flat tubes  111 . Refrigerant is distributed into the flat tubes  111  from the header tank  120  on the right side in FIG. 8, and is collected into the header tank  120  on the left side in FIG. 8 from the flat tubes  111 . The radiator  100  is connected to a compressor (not shown) of the CO 2  refrigerant cycle through a connection block  131 , and is connected to a decompressor (not shown) of the CO 2  refrigerant cycle through a connection block  132 . 
     As shown in FIGS. 9A-9C, the header tank  120  is composed of a first plate  121  and a second plate  122 . The first and second plates  121 ,  122  are connected to each other to form the header tank  120 . The first plate  121  has plural first insertion holes  121   a  formed into an oblong shape. The flat tubes  111  are respectively inserted into the first insertion holes  121   a.  The second plate  122  has an inner partition wall  123  protruding toward the first plate  121  and extending in a longitudinal direction of the header tank  120 . The inner partition wall  123  is formed integrally with the second plate  122 . A protruding end of the inner partition wall  123  is bonded to an inner wall of the first plate  121 , so that the first plate  121  and the second plate  122  are connected with each other by the inner partition wall  123 . 
     That is, the inner partition wall  123  is disposed inside the header tank  120  to extend in the longitudinal direction of the header tank  120 . Therefore, an inner space within the header tank  120  is divided into a first space  120   a  and a second space  120   b  extending in the longitudinal direction of the header tank  120  by the inner partition wall  123 . Thus, the first and second spaces  120   a,    120   b  are defined by the first and second plates  121 ,  122  and the inner partition wall  123 . 
     Further, as shown in FIG. 9C, plural communication passages  123   a  are formed on the protruding end portion of the inner partition wall  123  by milling, so that the first and second spaces  120   a,    120   b  communicate with each other through the communication passages  123   a.  The communication passages  123   a  are provided at positions corresponding to the first insertion holes  121   a.    
     The inner partition wall  123  has a substantially hourglass-shaped cross-section, as shown in FIG.  9 A. That is, the inner partition wall  123  is formed to have a width W being increased toward both the inner walls of the first and second plates  121 ,  122 . Therefore, each of the first and second spaces  120   a,    120   b  has a substantially circular-shaped cross-section. The width W of the inner partition wall  123  is a dimension in a width direction parallel to a longer diameter of the oval-shaped cross-section of the header tank  120 . That is, the width direction is perpendicular to both of the longitudinal direction of the flat tubes  111  and the longitudinal direction of the header tank  120 . 
     The first plate  121  is formed by pressing an aluminum material (A3003), and the second plate  122  is formed by extrusion of an aluminum material (A3003). The first plate  121 , the second plate  122  including the inner partition wall  123 , and the flat tubes  111  are integrally bonded to each other by brazing, using a brazing material (A4004) coated on both sides of the first plate  121 . 
     Further, a separator  130  is disposed within each header tank  120  so that the first and second spaces  120   a,    120   b  are divided into plural spaces in the longitudinal direction of the header tank  120 . Refrigerant flows through the core portion  110  along a S-shaped route indicated by arrow in FIG. 8 due to the separator  130 . As shown in FIG. 10, the separator  130  includes first and second plate portions  131 ,  132  having a substantially circular shape, a connection portion  133  for partially connecting the first and second plate portions  131 ,  132 , and a protruding portion  134  protruding toward the first plate  121 . The first and second plate portions  131 ,  132  air-tightly separate the first and second spaces  120   a,    120   b,  respectively, into several spaces in the longitudinal direction of the header tank  120 . The portions  131 - 134  of the separator  130  are integrally formed by pressing an aluminum plate (A3003). 
     As shown in FIG. 9B, the first plate  121  of the header tank  120  has a second insertion hole  121   b  into which the protruding portion  134  of the separator  130  is inserted. The separator  130  is brazed to the inner walls of the first and second plates  121 ,  122  and the inner partition wall  123 , while the protruding portion  134  of the separator  130  is inserted into the second insertion hole  121   b.    
     Further, as shown in FIG. 8, a pair of header caps  140  (hereinafter referred to as caps  140 ) made of aluminum are bonded to the longitudinal ends of each header tanks  120  to close the longitudinal ends of the first and second spaces  120   a,    120   b.  As shown in FIG. 11, the cap  140  has a pair of cylindrical protruding portions  141  which are inserted into the first and second spaces  120   a,    120   b  of the header tank  120 , respectively. Each of the cylindrical protruding portions  141  has a substantially-hemispherical recess portion  142 , as shown in FIG.  11 . The caps  140  are brazed to the first and second plates  121 ,  122  of the header tank  120  using brazing material sprayed on the caps  140 . 
     According to the second embodiment of the present invention, each of the first and second spaces  120   a,    120   b  has a substantially circular-shaped cross-section. Therefore, stress is prevented from being intensively applied to the first and second plates  121 ,  122  including the connection portion between the inner partition wall  123  and the first plate  121 . As a result, pressure tightness (pressure resistance) of the header tank  120  is improved. 
     Further, the cross-section of the inner partition wall  123  is a hourglass shape in which the width W of the inner partition wall  123  in the width direction is gradually increased toward the inner walls of the first and second plates  121 ,  122 , so that each of the first and second spaces  120   a,    120   b  have a substantially circular-shaped cross-section. Therefore, a bonding area between the inner partition wall  123  and the first plate  121 , and a cross-sectional area of the connection portion between the inner partition wall  123  and the second plate  122  are increased. As a result, bonding strength between the inner partition wall  123  and the first plate  121 , and strength of the connection portion between the inner partition wall  123  and the second plate  122  are improved, thereby improving pressure resistance of the header tank  120 . Further, the separator  130  is bonded to the first and second plates  121 ,  122  and the inner partition wall  123 , thereby improving pressure tightness of both the header tank  120  and the separator  130 . 
     Further, the separator  130  is brazed to the inner walls of the first and second plates  121 ,  122  and the inner partition wall  123 , while the protruding portion  134  of the separator  130  is inserted into the second insertion hole  121   b  formed on the first plate  121 . Therefore, bonding strength between the separator  130  and the header tank  120  is further increased, and the separator  130  is readily attached to the first plate  121 . 
     Furthermore, each the cylindrical protruding portions  141  of the cap  140  has the hemispherical recess portion  142  at a protruding end. Therefore, pressure inside the header tank  120  is applied to the hemispherical recess portion  142  of the cap  140 , thereby preventing stress from being intensively applied to the cap  140  and the bonding area between the cap  140  and the header tank  120 . As a result, pressure resistance of the header tank  120  can be further improved. 
     Further, the connection portion  133  of the separator  130  is formed to partially connect the first and second plate portions  131 ,  132 . Therefore, as shown in FIG. 12, the separator  130  is disposed inside the header tank  120  in such a manner that the separator  130  partially pierces the inner partition wall  123 , not fully. Therefore, strength of the inner partition wall  123  is prevented from being greatly decreased due to the separator  130 . Thus, the separator  130  can be disposed inside the header tank  120 , while it can prevent pressure resistance of the header tank  120  from being reduced. 
     A third preferred embodiment of the present invention will be described with reference to FIGS. 13A,  13 B. In the third embodiment, the header tank  120  is provided so that brazing errors between the inner partition wall  123  and the first plate  121  are readily found. 
     As shown in FIGS. 13A,  13 B, the first plate  121  has a communication hole  125  through which inside and outside of the header tank  120  communicate with each other. The inner partition wall  123  is bonded to the inner wall of the first plate  121  through brazing, so that the communication hole  125  is closed by the inner partition wall  123 . 
     According to the third embodiment of the present invention, when the header tank  120  is filled with an inspection fluid (e.g., inactive gas such as helium) with a predetermined pressure, the inspection fluid leaks from the communication hole  125  if any brazing errors is caused between the inner partition wall  123  and the first plate  121 . Thus, any brazing error between the inner partition wall  123  and the first plate  121  is readily found. In the third embodiment, the other portions are similar to those in the second embodiment, and the explanation thereof is omitted. 
     A fourth preferred embodiment of the present invention will be described with reference to FIGS. 14A,  14 B. In the fourth embodiment, as shown in FIGS. 14A,  14 B, a protruding portion  126  protruding outside of the header tank  120  through the communication hole  125  is formed integrally with the inner partition wall  123 . The protruding portion  126  contacts the corrugated fins  112 , while the first plate  121  and the corrugated fins  112  are disposed with a predetermined gap (not shown) therebetween. 
     If the corrugated fins  112  contacts the first plate  121  of the header tank  120 , brazing material coated on the first plate  121  is readily drawn toward the corrugated fins  112  due to surface tension of the brazing material on the first plate  121 . Therefore, brazing errors between the first plate  121  and the inner partition wall  123 , and between the first plate  121  and the flat tubes  111  may be caused. 
     According to the fourth embodiment of the present invention, because the protruding portion  126  contacts the corrugated fins  112 , the protruding portion  126  prevents the corrugated fins  112  from contacting the first plate  121 . Therefore, brazing material coated on the first plate  121  is prevented from being drawn toward the fins  112  during brazing. Thus, the first plate  121  and the inner partition wall  123 , and the first plate  121  and the flat tubes  111  are securely bonded to each other through brazing, thereby improving pressure resistance of the header tank  120 . In the fourth embodiment, the other portions are similar to those in the second embodiment, and the explanation thereof is omitted. 
     A fifth preferred embodiment of the present invention will be described with reference to FIGS. 15A,  15 B. In the fifth embodiment, as shown in FIGS. 15A,  15 B, the protruding portion  126  is partially deformed plastically so that the first plate  121  is clamped by the protruding portion  126  of the inner partition wall  123  to be secured to the inner partition wall  123 . Therefore, the inner partition wall  123  and the first plate  121  are assuredly bonded to each other through brazing, thereby further improving pressure resistance of the header tank  120 . In the fifth embodiment of the present invention, the other portions are similar to those in the second embodiment, and the explanation thereof is omitted. 
     A sixth preferred embodiment of the present invention will be described with reference to FIGS. 16A,  16 B. In the above-described second through fifth embodiment, a milling step for forming the communication passage  123   a  is necessary. However, in the sixth embodiment, the milling step for forming the communication passages  123   a  on the end surface of the inner partition wall  123  is omitted. 
     As shown in FIGS. 16A. 16B, the first plate  121  is formed to have a W-shaped cross-section having two semicircular portions  121   c  which protrude toward the flat tube  111 . Further, the first plate  121  has a connection portion  121   d  disposed between the two semicircular portions  121   c,  and the second plate  122  has a protruding portion  122   b  which protrudes toward the first plate  121 . The connection portion  121   d  of the first plate  121  is bonded to a top end of the protruding portion  122   b  of the second plate  122 . Thus, in the sixth embodiment, the protruding portion  122   b  of the second plate  122  and the connection portion  121   d  of the first plate  121  correspond to the inner partition wall  123  in the second through fifth embodiments. 
     Further, the first insertion holes  121   a  are formed in the first plate  121  by pressing or stamping to penetrate through the first plate  121 . When the flat tubes  111  are inserted into the first insertion holes  121   a,  gaps  121   e  are defined between each of the longitudinal ends of the flat tubes  111  and the protruding portion  122   b  of the second plate  122 . Therefore, the first and second spaces  120   a,    120   b  communicate with each other through the gaps  121   e.    
     The first plate  121  is formed into a W-shape in cross-section by pressing an aluminum plate during a first pressing step. Then, the first insertion holes  121   a  are formed in the W-shaped first plate  121  by stamping during a second pressing step. 
     According to the sixth embodiment, the gaps  121   e  (i.e., communication passage  123   a ) through which the first and second spaces  120   a,    120   b  communicate with each other are simultaneously formed while the first insertion holes  121   a  are formed in the first plate  121 , without a milling step. As a result, manufacturing steps of the second plate  122  can be reduced, and the radiator  100  is manufactured in low cost. 
     In the above-described second through sixth embodiments, the second plate  122  and the inner partition wall  123  are formed integrally. However, as shown in FIG. 17, the inner partition wall  123  may be separately formed from the second plate  122 , and may be brazed to the inner walls of the first and second plates  121 ,  122  of the header tank  120 . In this case, preferably, a protruding portion  124  for determining a connection position is formed on the first and second plates  121 ,  122 , and a recess portion  124   a  into which the protruding portion  124  is inserted is formed on the inner partition wall  123 . On the contrary, the protruding portion  124  may be formed on the inner partition wall  123 , and the recess portion  124   a  may be formed on the first and second plates  121 ,  122 . In FIG. 18, the protruding portion  124  is formed on the first and second plates  121 ,  122 , and the recess portion  124   a  is formed on the inner partition wall  123 . 
     Further, as shown in FIG. 19, the first and second plates  121 ,  122  and the inner partition wall  123  may be integrally formed through a method such as extrusion. 
     Further, as shown in FIGS. 20A,  20 B, the inner partition wall  123  may have an insertion groove  123   b  formed by milling, into which the connection portion  133  of the separator  130  is inserted. In this case, the second insertion hole  121   b  of the first plate  121  and the protruding portion  134  of the separator  130  can be omitted. 
     Furthermore, as shown in FIGS. 21A,  21 B, a recess portion  121   f  may be formed in the first plate  121  at a position where the inner partition wall  123  is bonded. In this case, the first and second plates  121 ,  122  are brazed to each other, while the inner partition wall  123  is fitted in the recess portion  121   f.  Therefore, the second plate  122  is readily positioned on the first plate  121 , and a contacting area between the first and second plates  121 ,  122  is increased. As a result, the first and second plates  121 ,  122  are more securely brazed to each other. Further, each of the cross-section of the first and second spaces  120   a,    120   b  is formed into an almost genuine circular shape, thereby preventing stress from being intensively applied to the first and second plates  121 ,  122 . 
     Further, as shown in FIG. 22, the communication passage  123   a  may be formed on a side adjacent to the flat tube  111  with respect to a portion of the inner partition wall  123  with a minimum width W, while a recess portion  135  is formed at one longitudinal end of the flat tube  111  to be recessed toward the other longitudinal end of the flat tube  111 . The recess portion  135  is also formed at the other longitudinal end of the flat tube  111 . As a result, a cut-out portion of the inner partition wall  123  is decreased relatively, thereby improving pressure resistance of the header tank  120 . Further, since the flat tube  111  has the recess portions  135  at both longitudinal ends, a fluid-flowing area of the communication passage  123   a  is prevented from being reduced even when the cut-out portion of the inner partition wall  123  is decreased. Further, when flux including silicon powder is applied to only a portion of the second plate  122  to which the first plate  121  is bonded, and one longitudinal end of the flat tube  111  is shifted by a predetermined distance toward the other longitudinal end of the flat tube  111 , the flow passages of the flat tube  111  are prevented from being blocked by brazing material. In this case, the forming step of the recess portion  135  at the longitudinal end of the flat tube  111  is omitted. 
     Further, as shown in FIG. 23, the communication passages  123   a  may be formed by cutting the inner partition wall  123  so that each of the communication passages  123   a  has a U-shaped cross-section. 
     Furthermore, as shown in FIG. 24, each of the first and second plates  121 ,  122  may be formed by pressing a plate. In this case, when at least one of the first and second plates  121 ,  122  is coated with brazing material, brazing error between the first and second plates  121 ,  122  is decreased. Further, the second plate  122  formed by a pressing step has a higher mechanical strength as compared with a case where the second plate  122  is formed by extrusion or drawing, thereby improving pressure resistance of the header tank  120 . 
     The second through sixth embodiments may be applied to a radiator without the separator  130 , in which refrigerant flows through the core portion in one-way. Further, the second through sixth embodiments are not limited to a radiator of the CO 2  refrigerant cycle, but may be applied to any heat exchanger with a high operating internal pressure. 
     A seventh preferred embodiment of the present invention will be described with reference to FIGS. 25-28. In the seventh embodiment, the present invention is applied to a radiator of the CO 2  refrigerant cycle, similarly to the second embodiment. 
     As shown in FIG. 25, the inventors of the present invention experimentally produced and studied a radiator having a header tank  205  in which a partition wall  205   c  is provided so that the header tank  205  has a sufficient pressure resistance without increasing size of the header tank  205 . The partition wall  205   c  extends in a longitudinal direction of the header tank  205 , and divides the header tank  205  into first and second tank spaces  205   a,    205   b  communicating with flat tubes  202 . 
     However, the inventors of the present invention found that the radiator having the header tank  205  including the first and second spaces  205   a,    205   b  has insufficient radiation performance. Further, since the header tank  205  is divided into the first and second spaces  205   a,    205   b,  refrigerant may not be introduced into all of the first and second spaces  205   a,    205   b.    
     The seventh embodiment is invented to overcome the above-mentioned problems. FIG. 26 shows a radiator  201  when viewed from an upstream air side thereof. The radiator  201  has plural flat tubes  202  made of aluminum alloy, through which CO 2  refrigerant flows. As shown in FIG. 28, each of the flat tubes  202  has plural flow passages  221  extending in a longitudinal direction of the flat tubes  202 . Further, plural aluminum corrugated fins  203  are attached between each adjacent flat tubes  202  to facilitate heat exchange between refrigerant and air. A heat-exchange core portion  204  is composed of the flat tubes  202  and the corrugated fins  203 . 
     Each of the flat tubes  202  is integrally formed by extrusion or drawing. The corrugated fins  203  are formed by a roller forming method or the like. The flat tubes  202  and the corrugated fins  203  are brazed to each other using brazing material coated on both sides of the corrugated fins  203 . 
     Further, a header tank  251  for distributing refrigerant into each of the flat tubes  202  is disposed on one longitudinal end side of the flat tubes  202  (i.e., on the left side in FIG.  26 ), and a header tank  252  into which refrigerant flowing from the flat tubes  202  is collected is disposed on the other longitudinal end side of the flat tubes  202  (i.e., on the right side in FIG.  26 ). The header tanks  251 ,  252  extend in a direction perpendicular to the longitudinal direction of the flat tubes  202 . 
     Further, a connection block  261  is attached to an upper part of the header tank  251 , and a connection block  262  is attached to a lower part of the header tank  252 . The header tank  251  communicate with an outlet pipe (not shown) of a compressor (not shown) of the CO 2  refrigerant cycle through the connection block  261 . The header tank  252  communicates with an outlet pipe (not shown) of a decompressor (not shown) of the CO 2  refrigerant cycle through the connection block  262 . Hereinafter, both of the header tanks  251 ,  252  are generically referred to as the header tank  205 , and both of the connection blocks  261 ,  262  are generically referred to as the connection block  206 . 
     As shown in FIG. 27, the header tank  205  has an inner partition wall  205   c  for partitioning an inside space of the header tank  205  into first and second spaces  205   a,    205   b.  The inner partition wall  205   c  is integrally formed with the header tank  205  and extends in the longitudinal direction of the header tank  205 . The inner partition wall  205   c  has an inner communication hole  205   d  through which the first and second spaces  205   a,    205   b  communicates with each other. The inner communication hole  205   d  is provided at a position corresponding to the connection block  206 . That is, the inner communication hole  205   d  is in alignment with the connection block  206 . The first space  205   a  is disposed at an upstream air side of the second space  205   b  in the header tank  205 . 
     Further, an outer communication hole  206   a  through which the first space  205   a  and the connection block  206  communicate with each other is formed in the header tank  205 . In the seventh embodiment, an opening area S 1  of the inner communication hole  205   d  is set to be smaller than an opening area S 2  of the outer communication hole  206   a,  so that an amount of refrigerant flowing in the first space  205   a  becomes larger than an amount of refrigerant flowing in the second space  205   b.  As shown in FIG. 27, when diameter of the inner communication hole  205   d  is set to “B”, and diameter of the outer communication hole  206   a  is set to “A”, S 1 , S 2  are defined as πB 2 / 4 , πA 2 / 4 , respectively. Further, as shown in FIG. 28, the inner partition wall  205   c  is formed in such a manner that a communication passage  205   e  is formed between the flat tubes  202  and the inner partition wall  205   c.  As a result, refrigerant in the header tank  205  can be introduced into a flow passage  221  which is positioned to be opposite to the inner partition wall  205   c.    
     According to the seventh embodiment of the present invention, the amount of refrigerant flowing through the first space  205   a  disposed on the upstream air side of the second space  205   b  is larger than the amount of refrigerant flowing through the second space  205   b.  Therefore, more refrigerant flows through the flow passages  221  disposed on the upstream air side, where temperature of air is relatively low. As a result, refrigerant is cooled more efficiently, thereby improving radiation performance of the radiator  201 . Thus, in the seventh embodiment, both of pressure resistance and radiation performance of the radiator  201  are improved without increasing size of the radiator  201 . 
     An eighth preferred embodiment of the present invention will be described with reference to FIGS. 29-30. 
     In the above-described seventh embodiment, as shown in FIG. 28, the header tank  205  has a substantially oblong-shaped cross-section similarly to that of the flat tube  202 , because the first and second spaces  205   a,    205   b  are formed within the header tank  205 . Therefore, as shown in FIG. 29, when the opening area S 2  of the outer communication hole  206   a  is increased, the outer communication hole  206   a  becomes in an oblong or oval shape extending in the longitudinal direction of the header tank  205 . However, when the outer communication hole  206   a  is formed into an oblong or oval shape, pressure resistance of the header tank  205  is lowered. 
     In the eighth embodiment of the present invention, as shown in FIG. 30, plural outer communication holes  206   a  communicating with the single external pipe through the single connection block  206  is formed in the header tank  205 . Further, the opening area S 1  of the inner communication hole  205   d  is set to be smaller than the total opening area S 2  of the outer communication holes  206   a.    
     According to the eighth embodiment of the present invention, each opening area or opening diameter of the plural outer communication holes  206   a  is decreased. Therefore, pressure resistance of the header tank  205  is prevented from being greatly decreased, while the opening area S 1  of the inner communication hole  205   d  is set to be smaller than the total opening area S 2  of the outer communication holes  206   a.  In the eighth embodiment, the other portions are similar to those in the seventh embodiment, and the explanation thereof is omitted. 
     A ninth preferred embodiment of the present invention will be described with reference to FIG.  31 . 
     As shown in FIG. 31, an aluminum pipe  207  is integrally brazed to the connection block  206 . The aluminum pipe  207  is disposed in the header tank  205  to penetrate through the first space  205   a  and the inner partition wall  205   c  and to reach to the second space  205   b.  The connection block  206  is integrally connected to the header tank  205  through the pipe  207 . Further, the pipe  207  has a first opening  207   a  opened into the first space  205   a,  and a second opening  207   b  opened into the second space  205   b.  An opening area of the first opening  207   a  is set to be larger than that of the second opening  207   b  so that the amount of refrigerant flowing into the first space  205   a  becomes larger than the amount of refrigerant flowing into the second space  205   b.    
     According to the ninth embodiment of the present invention, the pipe  207  enhances strength of the header tank  205 , thereby improving pressure resistance of the header tank  205 . In the ninth embodiment, the other portions are similar to those in the seventh embodiment, and the explanation thereof is omitted. 
     A tenth preferred embodiment of the present invention will be described with reference to FIGS. 32A,  32 B. 
     As shown in FIGS. 32A,  32 B, in the tenth embodiment, the pipe  207  has plural flow passages  207   c  extending in a longitudinal direction of the pipe  207 , thereby improving pressure resistance of the pipe  207 . In the tenth embodiment, the other portions are similar to those in the ninth embodiment, and the explanation thereof is omitted. 
     An eleventh preferred embodiment of the present invention will be described with reference to FIGS. 33-34C. 
     As shown in FIG. 33, in the eleventh embodiment, a supplying member  208  for supplying refrigerant into first and second spaces  205   a,    205   b  of the header tank  205  is disposed on a side surface of the header tank  205 . That is, the supplying member  208  is disposed on an outer surface of the header tank  205  in the longitudinal direction of the flat tubes  202 . The supplying member  208  includes the connection block  206  and the pipe  207 . 
     As shown in FIG. 34A, the pipe  207  has a first communication portion  271  communicating with the first space  205   a  and a second communication portion  272  communicating with the second space  205   b.  A cross-sectional area of the first communication portion  271  is set to be larger than that of the second communication portion  272 , so that the amount of refrigerant flowing through the first space  205   a  is larger than the amount of refrigerant flowing through the second space  205   b.  Further, as shown in FIGS. 34B,  34 C, the header tank  205  has a first hole  271   a  into which the first communication portion  271  is inserted, and a second hole  272   a  into which the second communication portion  272  is inserted. The connection block  206 , the pipe  207  and the header tank  205  are integrally connected through brazing. In the eleventh embodiment, the same effect in the seventh through tenth embodiments can be obtained. 
     A twelfth preferred embodiment of the present invention will be described with reference to FIG.  35 . In the above-described eleventh embodiment, the connection block  206  and the pipe  207  are connected through brazing to form the supplying member  208 . However, in the twelfth embodiment, the connection block  206  and the pipe  207  having the first and second communication portions  271 ,  272  are integrally formed through cutting and casting such as die-casting. 
     A thirteenth preferred embodiment of the present invention will be described with reference to FIGS. 36A. 36B. In the thirteenth embodiment, the cross-sectional area of the first hole  271   a  is set to be equal to that of the second hole  272   a.  In this case, refrigerant is introduced into both the first and second spaces  205   a,    205   b  of the header tank  205  without fail, even though the header tank  205  is divided into the first and second spaces  205   a,    205   b.    
     In the above-mentioned seventh through thirteenth embodiments, the header tanks  251 ,  252  on both sides of the core portion have the same structure. However, only the header tank  251  may have the above-mentioned structure. 
     Further, in the above-described ninth and tenth embodiments, the pipe  207  is inserted from the first space  205   a.  However, the pipe  207  may be inserted from the second space  205   b.    
     The seventh through thirteenth embodiments are not limited to a radiator of the CO 2  refrigerant cycle, but may be also applied to any heat exchanger having a high internal pressure. 
     In the seventh through thirteenth embodiments, refrigerant flows through the tubes of the heat exchanger in one way; however, refrigerant may flow through the tubes of the heat exchanger along a U-shaped or a S-shaped route. 
     Further, in the seventh through thirteenth embodiments, the header tank  205  is integrally formed through extrusion or drawing. However, as shown in FIG. 37, the header tank  205  may be formed by connecting a core plate  501  adjacent to the flat tubes  202  and a tank portion  502 . The first and second spaces  205   a,    205   b  are formed by the core plate  501  and the tank portion  502 . 
     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.