Heat exchanger

Abstract

A flow inlet and a flow outlet are provided at one lateral end of a core. A second communication passage is provided at the other lateral end of the core to communicate between an interior of a downstream side lower tank, which is connected to a furthermost downstream side passage row that is furthermost from the flow inlet, and an interior of an upstream side lower tank, which is connected to a furthermost upstream side passage row that is furthermost from the flow outlet. The second communication passage is placed at a location that projects from a body of the core in a lateral direction or a top-to-bottom direction of the core.

1 . A heat exchanger comprising:
 a core that includes:
 a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and 
 a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow; 
   a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes:
 at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and 
 at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows; 
   a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes:
 at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and 
 at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows; 
   a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;   a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;   at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;   at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and   a communicating means that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, wherein:   the communicating means is placed at a location that projects from a body of the core in one of the lateral direction and the up-to-bottom direction of the core;   a portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core; and   a rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.   
   
   
       2 . The heat exchanger according to  claim 1 , wherein:
 the communicating means includes a lower communication passage that communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core;   the heat exchanger further comprises an upper communication passage that communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core; and   the rest of the refrigerant, which remains in the furthermost one of the at least one downstream side lower tank, flows upwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side upper tank and then flows into the furthermost one of the at least one upstream side upper tank through the upper communication passage and is merged with the portion of the refrigerant, which flows from the furthermost one of the at least one downstream side lower tank into the furthermost one of the at least one upstream side lower tank through the lower communication passage and then flows into the furthermost one of the at least one upstream side upper tank thorough the furthermost one of the upstream side flow passage rows.   
   
   
       3 . The heat exchanger according to  claim 1 , wherein:
 the communicating means includes an upper communication passage that communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core;   the heat exchanger further comprises a lower communication passage that communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core; and   the rest of the refrigerant, which remains in the furthermost one of the at least one downstream side upper tank, flows downwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side lower tank and then flows into the furthermost one of the at least one upstream side lower tank through the lower communication passage and is merged with the portion of the refrigerant, which flows from the furthermost one of the at least one downstream side upper tank into the furthermost one of the at least one upstream side upper tank through the upper communication passage and then flows into the furthermost one of the at least one upstream side lower tank thorough the furthermost one of the upstream side flow passage rows.   
   
   
       4 . The heat exchanger according to  claim 1 , wherein:
 the communicating means includes at least one communication passage forming member that has a communication passage therein; and   each of the at least one communication passage forming member is formed as a separate component, which is separate from the plurality of downstream side header tanks and the plurality of upstream side header tanks and is assembled integrally to a corresponding one of the plurality of downstream side header tanks and the plurality of upstream side header tanks.   
   
   
       5 . The heat exchanger according to  claim 4 , wherein at least a portion of each of the at least one communication passage forming member is placed laterally inward of a lateral end of the core in the lateral direction of the core. 
   
   
       6 . The heat exchanger according to  claim 5 , wherein one of the plurality of downstream side tubes and the plurality of upstream side tubes, which is located at the lateral end of the core, or a side plate, which supports the core, has a longitudinal end portion that is inserted into an interior of a corresponding one of the at least one communication passage forming member. 
   
   
       7 . The heat exchanger according to  claim 5 , wherein one of the plurality of downstream side tubes and the plurality of upstream side tubes, which is located at the lateral end of the core, or a side plate, which supports the core, has a longitudinal end portion that is inserted into an interior of a corresponding one of the plurality of downstream side header tanks and the plurality of upstream side header tanks. 
   
   
       8 . The heat exchanger according to  claim 4 , further comprising a lateral end tube, which is placed at a lateral end of the core and does not conduct the refrigerant therethrough, wherein the lateral end tube or a side plate, which supports the core, has a longitudinal end portion that is bent and contacts a corresponding one of the at least one communication passage forming member. 
   
   
       9 . The heat exchanger according to  claim 1 , wherein at least one communication hole is formed through a wall that partitions between an interior of another furthermost one of the downstream side header tanks and another furthermost one of the upstream side header tanks to communicate therebetween. 
   
   
       10 . The heat exchanger according to  claim 1 , wherein:
 the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area SI;   the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S 2 ; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S 1 /S 2 .   
   
   
       11 . The heat exchanger according to  claim 10 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S 1 /S 2 .   
   
   
       12 . The heat exchanger according to  claim 10 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S 1 /S 2 .   
   
   
       13 . The heat exchanger according to  claim 10 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S 1 /S 2 .   
   
   
       14 . The heat exchanger according to  claim 10 , wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three. 
   
   
       15 . The heat exchanger according to  claim 1 , wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows. 
   
   
       16 . The heat exchanger according to  claim 1 , wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core. 
   
   
       17 . The heat exchanger according to  claim 1 , wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm. 
   
   
       18 . The heat exchanger according to  claim 1 , wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows. 
   
   
       19 . The heat exchanger according to  claim 1 , wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows. 
   
   
       20 . The heat exchanger according to  claim 1 , wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows. 
   
   
       21 . A heat exchanger comprising:
 a core that includes:
 a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and 
 a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow; 
 a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes: 
 at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and 
 at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows; 
   a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes:
 at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and 
 at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows; 
   a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;   a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;   at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;   at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall;   a lower communication passage that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and communicates between an interior of a furthermost one of the at least one downstream side lower tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side lower tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side lower tank into the furthermost one of the upstream side flow passage rows, wherein:   the portion of the refrigerant from the furthermost one of the at least one downstream side lower tank flows into the furthermost one of the at least one upstream side lower tank through the lower communication passage and then flows into the furthermost one of the at least one upstream side upper tank after flowing upwardly thorough the furthermost one of the upstream side flow passage rows;   a rest of the refrigerant, which remains in the furthermost one of the at least one downstream side lower tank, flows upwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side upper tank and then flows into the furthermost one of the at least one upstream side upper tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side upper tank; and   a refrigerant inflow opening of the lower communication passage is an inlet of the lower communication passage and opens to an interior of the furthermost one of the at least one downstream side lower tank at a location that is below lower end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.   
   
   
       22 . The heat exchanger according to  claim 21 , wherein:
 the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area SI;   the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area  52 ; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S 1 /S 2 .   
   
   
       23 . The heat exchanger according to  claim 22 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S 1 /S 2 .   
   
   
       24 . The heat exchanger according to  claim 22 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S 1 /S 2 .   
   
   
       25 . The heat exchanger according to  claim 22 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S 1 /S 2 .   
   
   
       26 . The heat exchanger according to  claim 22 , wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three. 
   
   
       27 . The heat exchanger according to  claim 21 , wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows. 
   
   
       28 . The heat exchanger according to  claim 21 , wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core. 
   
   
       29 . The heat exchanger according to  claim 21 , wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm. 
   
   
       30 . The heat exchanger according to  claim 21 , wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows. 
   
   
       31 . The heat exchanger according to  claim 21 , wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows. 
   
   
       32 . The heat exchanger according to  claim 21 , wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows. 
   
   
       33 . A heat exchanger comprising:
 a core that includes:
 a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and 
 a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow; 
   a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes:
 at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and 
 at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows; 
   a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes:
 at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and 
 at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows; 
   a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;   a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;   at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;   at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and   an upper communication passage that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and communicates between an interior of a furthermost one of the at least one downstream side upper tank, which is furthermost from the refrigerant inlet in the lateral direction of the core and is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of a furthermost one of the at least one upstream side upper tank, which is furthermost from the refrigerant outlet in the lateral direction of the core and is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, to conduct a portion of the refrigerant in the furthermost one of the at least one downstream side upper tank into the furthermost one of the upstream side flow passage rows, wherein:   the portion of the refrigerant from the furthermost one of the at least one downstream side upper tank flows into the furthermost one of the at least one upstream side upper tank through the upper communication passage and then flows into the furthermost one of the at least one upstream side lower tank after flowing downwardly thorough the furthermost one of the upstream side flow passage rows;   a rest of the refrigerant, which remains in the furthermost one of the at least one downstream side upper tank, flows downwardly through the furthermost one of the downstream side flow passage rows into the furthermost one of the at least one downstream side lower tank and then flows into the furthermost one of the at least one upstream side lower tank and is merged with the portion of the refrigerant in the furthermost one of the at least one upstream side lower tank; and   a refrigerant inflow opening of the upper communication passage is an inlet of the upper communication passage and opens to an interior of the furthermost one of the at least one downstream side upper tank at a location that is above upper end openings of the downstream side tubes of the furthermost one of the downstream side flow passage rows in the vertical direction.   
   
   
       34 . The heat exchanger according to  claim 33 , wherein:
 the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area S 1 ;   the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S 2 ; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S 1 /S 2 .   
   
   
       35 . The heat exchanger according to  claim 34 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S 1 /S 2 .   
   
   
       36 . The heat exchanger according to  claim 34 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S 1 /S 2 .   
   
   
       37 . The heat exchanger according to  claim 34 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S 1 /S 2 .   
   
   
       38 . The heat exchanger according to  claim 34 , wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three. 
   
   
       39 . The heat exchanger according to  claim 33 , wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows. 
   
   
       40 . The heat exchanger according to  claim 33 , wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core. 
   
   
       41 . The heat exchanger according to  claim 33 , wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm. 
   
   
       42 . The heat exchanger according to  claim 33 , wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows. 
   
   
       43 . The heat exchanger according to  claim 33 , wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows. 
   
   
       44 . The heat exchanger according to  claim 33 , wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows. 
   
   
       45 . A heat exchanger comprising:
 a core that includes:
 a plurality of downstream side flow passage rows, wherein each of the plurality of downstream side flow passage rows is formed with a plurality of downstream side tubes, which extend in a top-to-bottom direction of the core and are placed one after another in a lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of refrigerant therethrough and are arranged in a row to form the downstream side flow passage row, and the downstream side flow passage rows are placed side-by-side in the lateral direction of the core on a downstream side in a direction of an air flow, which exchanges heat with the refrigerant; and 
 a plurality of upstream side flow passage rows, wherein each of the plurality of upstream side flow passage rows is formed with a plurality of upstream side tubes, which extend in the top-to-bottom direction of the core and are placed one after another in the lateral direction of the core to form a plurality of flow passages, respectively, that conduct a flow of the refrigerant therethrough and are arranged in a row to form the upstream side flow passage row, and the upstream side flow passage rows are placed side-by-side in the lateral direction of the core on an upstream side of the downstream side flow passage rows in the direction of the air flow; 
   a plurality of downstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the downstream side tubes of each corresponding one of the downstream side flow passage rows, wherein the plurality of downstream side header tanks includes:
 at least one downstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the downstream side flow passage rows; and 
 at least one downstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the downstream side flow passage rows; 
   a plurality of upstream side header tanks, each of which supplies the refrigerant to or receives the refrigerant from the upstream side tubes of each corresponding one of the upstream side flow passage rows, wherein the plurality of upstream side header tanks includes:
 at least one upstream side upper tank, each of which is connected to upper ends of the flow passages of each corresponding one of the upstream side flow passage rows; and 
 at least one upstream side lower tank, each of which is connected to lower ends of the flow passages of each corresponding one of the upstream side flow passage rows; 
   a refrigerant inlet that is located at one lateral side of the core and is communicated with an interior of a corresponding one of the downstream side header tanks to supply the refrigerant to the flow passages of a corresponding one of the downstream side flow passage rows;   a refrigerant outlet that is located at the one lateral side of the core and is communicated with an interior of a corresponding one of the upstream side header tanks to output the refrigerant from the flow passages of a corresponding one of the upstream side flow passage rows;   at least one downstream side partition wall, each of which is provided in a corresponding one of the downstream side header tanks to partition an interior of the corresponding one of the downstream side header tanks, so that one of the downstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the downstream side partition wall, and another one of the downstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the downstream side partition wall;   at least one upstream side partition wall, each of which is provided in a corresponding one of the upstream side header tanks to partition an interior of the corresponding one of the upstream side header tanks, so that one of the upstream side flow passage rows forms an upflow passage row, in which the flow of the refrigerant becomes an upflow, on one lateral side of the upstream side partition wall, and another one of the upstream side flow passage rows forms a downflow passage row, in which the flow of the refrigerant becomes a downflow, on the other lateral side of the upstream side partition wall; and   a communicating means that is provided at the other lateral side of the core opposite from the refrigerant inlet and the refrigerant outlet and is for communicating between an interior of each corresponding one of the downstream side header tanks, which is connected to a furthermost one of the downstream side flow passage rows that is furthermost from the refrigerant inlet in the lateral direction of the core, and an interior of each corresponding one of the upstream side header tanks, which is connected to a furthermost one of the upstream side flow passage rows that is furthermost from the refrigerant outlet in the lateral direction of the core, wherein:   the core has an upstream side lateral plane and a downstream side lateral plane, which are located on the upstream side and the downstream side, respectively, in the direction of the air flow;   the core is tilted toward the upstream side in the direction of the air flow such that the upstream side lateral plane is closer to an imaginary horizontal plane, which is placed vertically below the at least one upstream side lower tank, in comparison to the downstream side lateral plane;   a portion of the refrigerant in a furthermost one of the downstream side header tanks, which is furthermost from the refrigerant inlet in the lateral direction of the core, is conducted toward the upstream side of the air flow into a furthermost one of the upstream side header tanks located on an upstream side thereof in the direction of the air flow after flowing through the communicating means and then flows through the furthermost one of the upstream side flow passage rows into an opposed one of the upstream side header tanks, which is opposed to the furthermost one of the upstream side header tanks in the top-to-bottom direction of the core; and   a rest of the refrigerant, which remains in the furthermost one of the downstream side header tanks, flows through the furthermost one of the downstream side flow passage rows into an opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks where the rest of the refrigerant is merged with the portion of the refrigerant supplied through the communicating means.   
   
   
       46 . The heat exchanger according to  claim 45 , wherein:
 the portion of the refrigerant in the furthermost one of the downstream side header tanks is conducted toward the upstream side of the air flow into the furthermost one of the upstream side header tanks through a branching passage having a total passage cross sectional area S 1 ;   the rest of the refrigerant in the furthermost one of the downstream side header tanks flows through the furthermost one of the downstream side flow passage rows into the opposed one of the downstream side header tanks, which is opposed to the furthermost one of the downstream side header tanks in the top-to-bottom direction of the core, and then flows toward the upstream side of the air flow into the opposed one of the upstream side header tanks through a merging passage having a total passage cross sectional area S 2 ; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.41≦S 1 /S 2 .   
   
   
       47 . The heat exchanger according to  claim 46 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as six; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.71≦S 1 /S 2 .   
   
   
       48 . The heat exchanger according to  claim 46 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as five; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.47≦S 1 /S 2 .   
   
   
       49 . The heat exchanger according to  claim 46 , wherein:
 the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as four; and   the branching passage and the merging passage are constructed to satisfy a relationship of 0.66≦S 1 /S 2 .   
   
   
       50 . The heat exchanger according to  claim 46 , wherein the flow of the refrigerant in the furthermost one of the downstream side flow passage rows and the flow of the refrigerant in the furthermost one of the upstream side flow passage rows are directed in a common direction and are thereby counted as one refrigerant flow path, and the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, and the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows, are counted as the number of refrigerant flow paths in the remaining downstream side flow passage rows and the remaining upstream side flow passage rows, so that the total number of the refrigerant flow paths in the core is counted as three. 
   
   
       51 . The heat exchanger according to  claim 45 , wherein the number of the remaining downstream side flow passage rows, which are other than the furthermost one of the downstream side flow passage rows, is larger than the number of the remaining upstream side flow passage rows, which are other than the furthermost one of the upstream side flow passage rows. 
   
   
       52 . The heat exchanger according to  claim 45 , wherein each of the plurality of downstream side header tanks and the plurality of upstream side header tanks is formed by integrally joining a plurality of constituent members, which are stacked one after another in the lateral direction of the core. 
   
   
       53 . The heat exchanger according to  claim 45 , wherein a total thickness of one of the plurality of downstream side header tanks and of an adjacent one of the plurality of upstream side header tanks, which is measured in the direction of the air flow, is equal to or less than 48 mm. 
   
   
       54 . The heat exchanger according to  claim 45 , wherein a lateral size of the furthermost one of the upstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the downstream side flow passage rows. 
   
   
       55 . The heat exchanger according to  claim 45 , wherein a lateral size of the furthermost one of the downstream side flow passage rows, which is measured in the lateral direction of the core, is larger than that of the furthermost one of the upstream side flow passage rows. 
   
   
       56 . The heat exchanger according to  claim 45 , wherein a thickness of the downstream side flow passage rows, which is measured in the direction of the air flow, is larger than that of the upstream side flow passage rows.