Patent Publication Number: US-6032729-A

Title: Laminated heat exchanger

Description:
This is a divisional application of Ser. No. 08/862,173, filed May 22, 1997, now U.S. Pat. No. 5,881,804. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a laminated heat exchanger employed in a cooling cycle or the like in an air conditioning system for vehicles, which is constituted by laminating tube elements and fins alternately over a plurality of levels and, in particular, relates to a laminated heat exchanger with a structure in which a pair of tank portions are formed on one side of each tube element and an intake portion and an outlet portion for heat exchanging medium are provided at one end in the direction of lamination. 
     2. Description of the Related Art 
     In order to respond to the need for further miniaturization of heat exchangers and for improvement in heat exchanging efficiency, the applicant of the present invention developed a heat exchanger whose external shape is as shown in FIG. 1A and has been conducting various research into this heat exchanger. In this heat exchanger, with its core main body formed by laminating tube elements alternately with fins over a plurality of levels, a pair of tank portions provided at one side of each tube element are made to communicate with each other through a U-turn passage portion, and a heat exchanging medium flow path with a plurality of continuous passes is formed in the core main body, as shown in FIG. 15, by making the tank portions of adjacent tube elements communicate as appropriate, an intake portion 4 and an outlet portion 5 for heat exchanging medium are provided at one end in the direction of lamination. In heat exchangers of the existing type, the intake portion 4 is made to communicate with the most upstream pass via a communicating pipe 20, and the outlet portion 5 is made to communicate directly with the most downstream pass. 
     In the heat exchanger described above, after the heat exchanging medium flows in through the intake portion 4, the heat exchanging medium enters the most upstream pass via the communicating pipe 20 and after going through a plurality of passes it reaches the most downstream pass before it flows out through the outlet portion 5 which is in communication with the most downstream pass. In the heat exchanger, the unidirectional flow in which the heat exchanging medium moves from the tank side toward the non-tank side or from the non-tank side toward the tank side is considered to be one pass, so that a heat exchanger in which the heat exchanging medium passes through the U-turn passage portions twice during the course of its travel from the intake portion to the outlet portion is referred to as a 4-pass heat exchanger, whereas a heat exchanger in which the heat exchanging medium passes through the U-turn passage portions three times is referred to as a 6-pass heat exchanger. 
     However, in a laminated heat exchanger with 4 passes as described above, since it is structured so that coolant flows out through one end of the core main body, the coolant tends to concentrate at the tube elements that are located closer to the outlet side (toward one end in the direction of lamination) when it travels from the second pass to the third pass, as shown in FIG. 16A. In other words, from the third pass through the fourth pass, the coolant does not flow readily in the area that is close to a partitioning portion α, which partitions the first pass from the fourth pass. This point is substantiated by measured data that are represented with the broken lines in FIGS. 5A and 5B and FIGS. 10A and 10B, which indicate that the temperature of the passing air in this area is higher than that in other areas. It is to be noted that in FIGS. 5A and 5B and FIGS. 10A and 10B, tube numbers (TUBE No.) refer to the tube element number that is obtained by counting from the end where the intake portion and the outlet portion are provided to a specific tube element. In addition, the passing air temperature (AIR TEMP.) refers to the temperature of air with which heat exchange has been performed at the fins when the air passed between the tube elements, measured at a position 1˜2 cm from the downstream side end surface of the core main body. 
     Moreover, in a 6-pass heat exchanger, too, as shown in FIG. 16B, the heat exchanging medium tends to flow while concentrating toward the outlet side away from the partitioning portion α and, as a result, it can be easily deduced that the temperature of the tube elements at the partitioning portion a in the vicinity of the outlet side and the passing air temperature will be different from those in other areas. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a laminated heat exchanger that achieves an improvement in heat exchanging efficiency by causing the heat exchanging medium to flow almost consistently without becoming concentrated in any particular area so that it flows evenly through all the tube elements. 
     The applicant of the present invention has observed that, in order to achieve near consistency in temperature distribution at the core main body by causing the heat exchanging medium to flow sufficiently through the tube elements that are located in the vicinity of the partitioning portion as well, the heat exchanging medium may be forcefully supplied to an odd-numbered pass apart from the main flow of the heat exchanging medium to improve the flow, and has conducted vigorous research into structures for heat exchangers based upon this finding which has culminated in the present invention. 
     Namely, in the laminated heat exchanger according to the present invention, which is constituted by laminating tube elements that are each provided with a pair of tank portions at one side and a U-turn passage portion communicating between of tank portions in each pair alternately with fins over a plurality of levels, a heat exchanging medium flow path with an even number of passes that are continuous to one another is formed with each pass constituted of a flow in which the heat exchanging medium flows in one direction by making the tank portions of adjacent tube elements communicate with each other as appropriate, an intake portion and an outlet portion for the heat exchanging medium are provided at one end in the direction of lamination, the intake portion is made to communicate with the pass at the most upstream level of the heat exchanging medium flow path via a communicating passage, the outlet portion is made to communicate with the pass at the most downstream level of the heat exchanging medium flow path at one end in the direction of lamination and the communicating passage is made to communicate with a pass at an odd-numbered level, with the communicating area where the pass at the odd-numbered level communicates with the communicating passage provided in the vicinity where the pass at the odd-numbered level changes from the pass at the even-numbered level that immediately precedes it. 
     While, in this explanation, a laminated heat exchanger provided with a heat exchanging medium flow path constituted of an even number of passes may be a 4-pass or a 6-pass heat exchanger, it goes without saying that in some cases, the present invention may be adopted in a 2-pass heat exchanger or a heat exchanger with 8 passes or more. In addition, the pass at an odd-numbered level that communicates with the communicating passage refers to the pass at the third level in the case of a heat exchanger with four passes and refers to either the pass at the third level or the pass at the fifth level or both of these in the case of a heat exchanger with six passes, for instance. 
     Consequently, in the structure described above, the heat exchanging medium that has flowed in through the intake portion, flows into the pass at the first level in the heat exchanging medium flow path via the communicating passage and, after having traveled through a plurality of passes, reaches the pass at the last level in the heat exchanging medium flow path and is then finally allowed to flow out through the outlet portion from the pass at the last level. Concurrently with this flow, the heat exchanging medium inside the communicating pipe enters the pass at the odd-numbered level directly and subsequently reaches the pass at the last level after flowing through the passes on the downstream side before it is allowed to flow out through the outlet portion from the pass at the last level. 
     The flow of the heat exchanging medium that travels from the pass at an even-numbered level to a pass at an odd-numbered level tends to concentrate in an area that is distanced from the partitioning portion as explained earlier, due to the force with which it is supplied from the pass at the even-numbered level combined with the fact that the outlet portion and the pass at the most downstream level are in communication with each other at one end in the direction of lamination. However, since the communicating passage communicates with the pass at the odd-numbered level and moreover, since this communicating area is provided in the vicinity where the pass at the odd-numbered level changes from the pass at the even-numbered level that immediately precedes it, the heat exchanging medium flows in a sufficient quantity through tube elements where the flow rate of the coolant would otherwise tend to be low (the tube elements located in the vicinity where the pass at the odd-numbered level changes from the pass that immediately precedes it among the tube elements constituting the pass at the odd-numbered level) as well as the remaining tube elements. Thus, as indicated with the solid lines in FIGS. 5A and 5B, any significant inconsistency in temperature distribution is eliminated, achieving the object mentioned above. 
     Alternatively, in order to achieve consistency in temperature distribution at the core main body, the heat exchanger may be constituted by laminating tube elements that are each provided with a pair of tank portions at one side and a U-turn passage portion communicating between the tank portions in each pair alternately with fins over a plurality of levels, making tank portions of adjacent tube elements communicate as appropriate to form a heat exchanging medium flow path with an even number of continuous passes with each of the passes constituted of a flow in which the heat exchanging medium flows in one direction, providing an intake portion and an outlet portion for the heat exchanging medium at one end in the direction of lamination, making the intake portion communicate with the pass at the most upstream level of the heat exchanging medium flow path via a communicating pipe, making the outlet portion communicate with the pass at the most downstream level of the heat exchanging medium flow path at one end in the direction of lamination and making the intake portion communicate with the pass that immediately precedes the pass at the most downstream level at one end in the direction of lamination. 
     In this structure, the heat exchanging medium that has flowed in through the intake portion, flows into the pass at the most upstream level of the heat exchanging medium flow path via the communicating pipe and after completing a plurality of passes, reaches the pass at the most downstream level of the heat exchanging medium flow path, finally flowing out through the outlet portion from the pass at the most downstream level. Concurrently with this, the heat exchanging medium at the intake portion flows into the pass that immediately precedes the pass at the most downstream level from the one end in the direction of lamination and after this, it flows through the passes on the downstream side to reach the pass at the most downstream level before it is allowed to flow out through the outlet portion from the pass at the most downstream level. 
     Because of this, at the pass that immediately precedes the pass at the most downstream level, the heat exchanging medium delivered from the immediately preceding even-numbered pass and the heat exchanging medium that flows in directly from the intake portion conflux to be distributed almost consistently through the tube elements constituting this pass, and thus, as indicated with the solid lines in FIGS. 10A and 10B, any significant inconsistency in the temperature distribution in a 4-pass heat exchanger is eliminated. 
     If, on the other hand, there are a greater number of passes, as in a heat exchanger with 6 passes or more, or if there are many tube elements constituting each pass, as in a heat exchanger with two passes, consistency in the distribution of heat exchanging medium is still a cause for concern, even with the intake portion being made to communicate with the pass immediately preceding the pass at the most downstream level. However, in such a case, the problem can be precluded by combining the structure described above, in which the communicating passage is made to communicate with a pass at an odd-numbered level with the communicating portion of the pass at the odd-numbered level and the communicating passage located in the vicinity where the pass at an odd-numbered level changes from the pass at an even-numbered level that immediately precedes it. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features of the invention and the concomitant advantages will be better understood and appreciated by persons skilled in the field to which the invention pertains in view of the following description given in conjunction with the accompanying drawings which illustrate preferred embodiments. In the drawings: 
     FIG. 1 shows the laminated heat exchanger according to the present invention, with FIG. 1A showing an end surface which forms a right angle relative to the direction of airflow and FIG. 1B showing a side surface where the intake portion and the outlet portion are provided; 
     FIG. 2A is a bottom view of the 4-pass laminated heat exchanger shown in FIG. 1 and FIG. 2B is a conceptual diagram that illustrates the flow of heat exchanging medium in the laminated heat exchanger shown in FIG. 1; 
     FIG. 3 shows a standard formed plate that is employed in the greatest number to constitute the heat exchanger shown in FIG. 1; 
     FIG. 4 shows the formed plates that are employed in a tube element provided with an extended tank portion, with FIG. 4A showing a formed plate provided with an extended distended portion for tank formation with a through hole for inserting the communicating pipe formed therein and FIG. 4B showing a formed plate provided with an extended distended portion for tank formation without the through hole for inserting the communicating pipe; 
     FIG. 5 shows the temperature of discharge air when the laminated heat exchanger shown in FIG. 1 is utilized, with FIG. 5A presenting a characteristics diagram representing the temperature of air that has passed through the upper level of the laminated heat exchanger (representative temperature of air having passed through the upper half between the tube elements) and FIG. 5B presenting a characteristics diagram representing the temperature of air that has passed through the lower level of the laminated heat exchanger (representative temperature of air having passed through the lower half between the tube elements); 
     FIG. 6A is a bottom view of a 6-pass laminated heat exchanger showing the structure adopted when heat exchanging medium is allowed to flow into the first and the third passes, whereas FIG. 6B is a conceptual diagram illustrating the flow of the heat exchanging medium in this 6-pass laminated heat exchanger; 
     FIG. 7A is a bottom view of a 6-pass laminated heat exchanger showing the structure adopted when heat exchanging medium is allowed to flow into the first, third and fifth passes, whereas FIG. 7B is a conceptual diagram illustrating the flow of the heat exchanging medium in this 6-pass laminated heat exchanger; 
     FIG. 8 shows another embodiment of the laminated heat exchanger according to the present invention, with FIG. 8A showing an end surface that forms a right angle relative to the direction of airflow and FIG. 8B showing a side surface where the intake portion and the outlet portion are provided; 
     FIG. 9A is a bottom view of the 4-pass laminated heat exchanger shown in FIG. 8, and FIG. 9B is a conceptual diagram illustrating the flow of heat exchanging medium in the laminated heat exchanger in FIG. 8; 
     FIG. 10 shows the temperature of discharge air when the laminated heat exchanger shown in FIG. 8 is utilized, with FIG. 10A presenting a characteristic diagram representing the temperature of air that has passed through the upper level of the laminated heat exchanger (representative temperature of air having passed through the upper half between the tube elements) and FIG. 10B presenting a characteristic diagram representing the temperature of air that has passed through the lower level of the laminated heat exchanger (representative temperature of air having passed through the lower half between the tube elements); 
     FIG. 11A is a bottom view of a 6-pass laminated heat exchanger in which heat exchanging medium is made to flow in through the intake portion to the first pass via a communicating pipe and heat exchanging medium is also made to flow directly into the fifth pass and FIG. 11B is a conceptual diagram illustrating the flow of heat exchanging medium in this 6-pass laminated heat exchanger; 
     FIG. 12A is a bottom view of a 6-pass laminated heat exchanger in which heat exchanging medium is made to flow directly from the intake portion to the fifth pass and heat exchanging medium is also made to flow into the first and third passes via a communicating pipe, and FIG. 12B is a conceptual diagram illustrating the flow of the heat exchanging medium in this 6-pass laminated heat exchanger; 
     FIG. 13A is a bottom view of a 2-pass laminated heat exchanger in which heat exchanging medium is made to flow in through the intake portion to the first pass via a communicating pipe and heat exchanging medium is also made to flow directly through a small hole, and FIG. 13B is a conceptual diagram illustrating the flow of heat exchanging medium in this 2-pass laminated heat exchanger; 
     FIG. 14A is a bottom view of a 2-pass laminated heat exchanger in which heat exchanging medium is made to flow directly in through the intake portion to the first pass and heat exchanging medium is made to flow to the first pass from the end portion and the middle portion of the communicating pipe, and FIG. 14B is a conceptual diagram illustrating the flow of the heat exchanging medium in this 2-pass laminated heat exchanger; 
     FIG. 15 shows a schematic structure of a 4-pass laminated heat exchanger in the prior art in perspective; and 
     FIG. 16A is a conceptual diagram illustrating the flow of heat exchanging medium in the laminated heat exchanger shown in FIG. 15, and FIG. 16B is a conceptual diagram illustrating the flow of heat exchanging medium in a 6-pass laminated heat exchanger. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is an explanation of preferred embodiments according to the present invention. In FIGS. 1 and 2, a laminated heat exchanger 1 is, for instance, a 4-pass type evaporator in which a core main body is constituted by laminating fins 2 and tube elements 3 alternately over a plurality of levels and an intake portion 4 and an outlet portion 5 for heat exchanging medium are provided at one end in the direction of lamination of the tube elements 3. Each of the tube elements 3 is constituted by bonding two formed plates 6a, one of which is shown in FIG. 3, except for tube elements 3a and 3b at the two ends in the direction of lamination, tube elements 3c and 3d provided with enlarged tank portions and a tube element 3e located approximately at the center, which are to be detailed later. 
     The formed plate 6a is formed by press machining an aluminum plate, and is provided with two roughly hemispherical distended portions for tank formation 7 and 7 at one end with a distended portion for passage formation 8 formed continuously to them and an indented portion 9 for mounting a communicating pipe, to be detailed later, formed between the distended portions for tank formation. In addition, at the distended portion for passage formation 8, a projection 10, which extends from the area between the distended portions for tank formation 7 and 7 to the vicinity of the free end of the formed plate 6a is formed. It is to be noted that reference number 11 indicates circular beads that are formed in the formed plate in order to improve the heat exchanging efficiency and when two formed plates are bonded to each other, each bead 11 becomes bonded with the bead formed at the position facing opposite it. 
     The distended portions for tank formation 7 are formed to distend to a greater degree than the distended portion for passage formation 8, and the projection 10 is formed so that it is on the same plane as the bonding margin at the circumferential edges of the formed plate. Thus, when two formed plates 6a are bonded to each other at their circumferential edges, their projections 10 also become bonded, a pair of tank portions 12 and 12 are formed with the distended portions for tank formation 7 that face opposite each other and a U-turn passage portion 13 that connects the two tank portions is formed by the distended portions for passage formation 8 that face opposite each other. 
     The tube elements 3a and 3b located at the two ends in the direction of lamination are each constituted by bonding a flat plate 15 to the outside of the formed plate 6a shown in FIG. 2. In addition, the tube elements 3c and 3d are each provided with a tank portion 12 which is the same size as those in the tube elements 3 and tank portions 12a and 12b respectively that are enlarged to fill in the indented portion. Of these, the tube element 3c is constituted by combining formed plates 6b and 6c shown in FIGS. 4A and 4B respectively, and in each of the formed plates 6b and 6c, one of the distended portions for tank formation, i.e., a distended portion for tank formation 7a or 7b, is formed enlarged so that it approaches the other distended portion for tank formation 7. A through hole 14 through which a communicating pipe 20, to be detailed later, is to be inserted and bonded, is formed at the distended portion for tank formation 7a, which is formed enlarged in the formed plate 6b. The tube element 3d, on the other hand, is constituted by combining the formed plate 6b described earlier shown in FIG. 4A and a formed plate that has a shape symmetrical to the formed plate 6b, for instance, and bonded with the communicating pipe 20, which passes through the through hole 14. 
     Since other structural features of the formed plates 6b and 6c are identical to those in the formed plate 6a shown in FIG. 3, i.e., in that the distended portion for passage formation 8 is formed continuous to the distended portions for tank formation, that the projection 10 is formed extending from the area between the distended portions for tank formation 7 to the vicinity of the free end of the formed plate and the like, their explanation is omitted. 
     As shown in FIGS. 1 and 2, in the heat exchanger 1, adjacent tube elements are abutted with each other at their tank portions to form two tank groups, i.e., a first tank group 16 and a second tank group 17 that extend in the direction of lamination (perpendicular to the direction of airflow), and in one of the tank groups, i.e., the tank group 16, which includes the enlarged tank portion 12a, the individual tank portions are in communication via the through holes 18 formed at the distended portions for tank formation 7 except for in the formed plate 6e that is located approximately at the center in the direction of lamination whereas, in the other tank group 17, all the tank portions are in communication via the through holes 18 without any partitioning. 
     As for the tube element 3e, which is constituted by combining the formed plate 6a shown in FIG. 3 and a formed plate 6e, whose external shape is identical to that of the formed plate 6a but with no through hole formed at the distended portion for tank formation on one side, this non communicating portion forms a partitioning portion 19 that partitions one of the tank groups, i.e., the tank group 16. The partitioning portion 19 may be constituted by blocking off the through hole with a thin plate inserted between the tube element 3e and the adjacent tube element, instead of blocking off the distended portion for tank formation. 
     As a result, the first tank group 16 is partitioned into a first tank block 21 that includes the enlarged tank portion 12a, and a second tank block 22 that communicates with the outlet portion 5, by the partitioning portion 19, whereas the non-partitioned second tank group 17 constitutes a third tank block 23. It is to be noted that in this embodiment, the tube element 3d is provided at the 11th level, the tube element 3e is provided at the fourteenth level and the tube element 3c is provided at the twenty second level counting from the right end in the figure (the end where the intake portion 4 and the outlet portion 5 are provided). 
     The intake portion 4 and the outlet portion 5, which are provided at one end in the direction of lamination, are constituted by bonding an intake and outlet passage plate 24 with the flat plate 15 of the tube element 3a, with an intake passage 25 and an outlet passage 26 formed between these plates extending from a position approximately half way along the lengthwise direction of the flat plate 15 toward the tank portion. 
     At the upper portion of the intake passage 25 and the outlet passage 26, an inflow port 28 and an outflow port 29 respectively are provided via a coupling 27 which secures an expansion valve. The intake passage 25 and the enlarged tank portion 12a are made to communicate with each other through a communicating passage that is constituted of the communicating pipe 20 secured at the indented portions 9. The outlet passage 26 is made to communicate with the second tank block 22 via a hole formed at the plate 15. 
     In addition, the communicating pipe 20 mounted at the indented portions 9 is mounted by passing through the through holes 14 in the individual plates constituting the tube element 3d and is brazed so that no gap is formed between itself and the through holes 14 thereby forming a circumferential wall hole at the area where it is inserted in the tank portion 12b to allow coolant to flow out into the tank portion 12b. 
     In the structure described above, the coolant that has flowed in through the intake portion 4 enters the enlarged tank portion 12a through the communicating pipe 20, becomes dispersed throughout the entirety of the first tank block 21 and travels upward along the projections 10 through the U-turn passage portions 13 of the tube elements that corresponds to the first tank block 21 (first pass). Then, it makes a U-turn above the projections 10 before traveling downward (second pass) and reaches the tank group on the opposite side (third tank block 23). After this, it travels horizontally to the remaining tube elements that constitute the third tank block 23 before traveling upward again along the projections 10 through the U-turn passage portion 13 of the tube elements (third pass). Next, it travels downward after making a U-turn above the projections 10 (fourth pass) is led to the tank portions constituting the second tank block 22 and finally flows out through the outlet portion 5. 
     Concurrently with this main flow, the coolant that has been led into the communicating pipe 20 enters the third tank block 23 from the enlarged tank portion 12b of the tube element 3d via a side wall hole and flows through the U-turn passage portions 13 of the tube elements constituting the third pass while joining the main flow delivered from the second pass and then finally flows out through the outlet portion 5. 
     During this process, since the outlet portion 5 is connected to the second tank block 22 via an end portion of the core main body in the direction of lamination, it is a cause for concern that the coolant traveling from the second pass to the third pass may concentrate in the tube elements close to the outlet portion, as explained earlier. However, since the communicating pipe 20 is in communication with the third pass in the vicinity where it changes from the second pass, the coolant will flow in sufficient quantity through the tube elements in the vicinity of the partitioning portion 19 of the tube elements constituting the third and fourth passes. This flow is substantiated by the temperature distribution, which is made consistent overall with the temperature of the air passing through in the vicinity of partitioning portion 19 in the vicinity of the outlet (in particular, among TUBE Nos. 7˜13) being reduced compared to that in a heat exchanger in the prior art, as indicated by the solid lines in FIGS. 5A and 5B. 
     FIGS. 6 and 7 show structures that are achieved when the technical concept described above is adopted in a 6-pass heat exchanger. In FIG. 6, an example in which tube elements are laminated over 26 levels is shown, with tube elements 3e, which are not provided with a through hole, positioned at the ninth and seventeenth levels counting from the end where the intake portion 4 and the outlet portion 5 are provided a partitioning portion 30 that partitions the first tank group 16, is constituted of the tube element 3e at the ninth level and a partitioning portion 31, which partitions the second tank group 17 is constituted of the tube element 3e at the seventeenth level. In addition, the tube element 3d and the tube element 3c respectively are provided at the fifteenth level and the twenty third level. In the tube element 3c, the tank portion 12a is enlarged to extend toward the first tank group 16 and, in the tube element 3d, the tank portion 12b is enlarged to extend toward the second tank group 17. Moreover, in correspondence to this structure, the position of the peripheral wall hole of the communicating pipe 20, too, is set in accordance with the position of the tube element 3d. 
     As a result, the first tank group 16 is divided by the partitioning portion 30 into two blocks, i.e., a first tank block 32 that includes the enlarged tank portion 12b, and a second tank block 33 that communicates with the outlet portion 5, whereas the second tank group 17 is divided by the partitioning portion 31 into two blocks, i.e. a third tank block 34 that includes the enlarged tank portion 12a and a fourth tank block 35 constituted of the remaining tube elements. 
     In such a structure, the coolant that has flowed in through the intake portion 4 becomes dispersed throughout the entirety of the third tank block 34 after traveling through the communicating pipe 20, and reaches the tank group on the opposite side (first tank block 32) by traveling through the U-turn passage portions 13 of the tube elements that correspond to the third tank block 34 (first and second passes). After that, the coolant travels horizontally to the remaining tube elements that constitute the first tank block 32, is then led to the tank portions constituting the fourth tank block 35 by traveling through the U-turn passage portions 13 of those tube elements (third and fourth passes), then further travels horizontally to the remaining tube elements constituting the fourth tank block 35 and is then led to the tank portions constituting the second tank block 33 after traveling through the U-turn passage portions 13 again (fifth and sixth passes) and finally, it flows out through the outlet portion 5. In addition, concurrently with this main flow, the coolant that has been led into the communicating pipe 20, flows into the first tank block 32 via the enlarged tank portion 12b of the tube element 3d and, as it joins the coolant in the main flow that is delivered from the second pass, flows through the third and subsequent passes before flowing out through the outlet portion 5. 
     Thus, since the communicating pipe 20 is connected to the third pass in the vicinity where it changes from the second pass, the coolant flows in sufficient quantity into the tube elements that are close to the partitioning portion 31 of the tube elements constituting the third and fourth passes. This achieves a more consistent temperature distribution compared to heat exchangers in the prior art, at least at the central area of the core main body. 
     Now, in the 6-pass heat exchanger described above, while it is obvious that the flow of coolant is improved in the third and fourth passes, it is still a cause for concern that the coolant may concentrate toward the outlet portion in the fifth and sixth passes. In order to eliminate this problem, in the heat exchanger shown in FIG. 7, a structure is achieved in which coolant is made to flow directly into the fifth pass in the vicinity where it changes from the fourth pass. In other words, the tube element 3d, whose enlarged tank portion 12b is set toward the second tank group 17, is positioned at the seventh level in the heat exchanger shown in FIG. 6 and a peripheral wall hole that opens within this tank portion 12b is formed at the communicating pipe 20 which passes through the tank portion 12b at the seventh level. 
     In this structure, as shown in FIG. 7B, the coolant flows in sufficient quantity through the tube elements in the vicinity of the downstream side of the partitioning portion 30 as well as in the vicinity of the downstream side of the partitioning portion 31, making it possible to disperse the coolant almost consistently throughout the tube elements and achieving a further consistency in the temperature of the air passing through the heat exchanger. 
     FIGS. 8 and 9 show another embodiment according to the present invention, and an explanation will be given below mainly of components that are different, from the previous embodiment. The same reference numbers are assigned to components identical to those in the previous drawings with their explanations being omitted. 
     In this laminated heat exchanger, which is a 4-pass exchanger, as is the case with the heat exchanger shown in FIGS. 1 and 2, the communicating pipe 20 is employed only to communicate between the intake portion 4 and the enlarged tank portion 12a of the tube element 3c and the intake passage 25 constituting the intake portion 4 is expanded in the direction away from the outlet passage 26 so that it can communicate with the third pass, i.e., the pass that immediately precedes the most downstream pass via a small hole 36 formed in the flat plate 15. This small hole 36 is formed so that its diameter is smaller than that of the communicating pipe 20 to ensure that the coolant does not flow into the third pass from the intake portion 4 in great quantity. 
     In this structure, the coolant that has flowed in through the intake portion 4 enters the enlarged tank portion 12a after traveling through the communicating pipe 20, becomes dispersed throughout the entirety of the first tank block 21 and then travels upward along the projections 10 through the U-turn passage portions 13 of the tube elements that correspond to the first tank block 21 (first pass). After that, it makes a U-turn above the projections 10 and travels downward (second pass) reaching the tank group on the opposite side (third tank block 23). Next, it travels horizontally to the remaining tube elements that constitute the third tank block 23, and travels upward again along the projections 10 through the U-turn passage portions 13 of those tube elements (third pass). Then, it makes a U-turn above the projections 10 before traveling downward (fourth pass), is led to the tank portions constituting the second tank block 22 and finally flows out through the outlet portion 5. 
     While the coolant travels in this main flow, the coolant at the intake portion 4 enters the third tank block 23 via the small hole 36, joins the coolant in the main flow that is delivered from the second pass and, together, they travel upward along the projections 10 through the U-turn passage portions 13 of the tube elements constituting the third pass. Then, it makes a U-turn above the projections 10 before traveling downward (fourth pass) and finally flows out through the outlet portion 5. 
     Thus, the coolant delivered from the second pass and the coolant flowing in through the intake portion 4 both gather in the tank group constituting the third pass in the third tank block and, furthermore, the coolant delivered from the second pass and the coolant flowing in through the intake portion 4 conflux in directions that are opposite each other to inhibit the force with which the coolant delivered from the second pass would otherwise flow toward the outlet, ensuring that the coolant flows in a sufficient quantity into the tube elements in the vicinity of the outlet side of the partitioning portion 19 of the tube elements constituting the third and fourth passes. As a result, as indicated with the solid lines in FIGS. 10A and 10B, the temperature of the air that has traveled between the tube elements in the vicinity of the outlet side of the partitioning portion 19 (in particular, TUBE Nos. 7˜13) becomes lower compared to that in heat exchangers in the prior art, achieving a temperature distribution with overall consistency. 
     FIGS. 11 through 14 show other embodiments of the heat exchanger in which a small hole 36 that is similar to the hole described earlier is formed at an end of the core main body, with FIGS. 11 and 12 showing 6-pass heat exchangers and FIGS. 13 and 14 showing 2-pass heat exchangers. 
     In the heat exchanger shown in FIG. 11, the pass that immediately precedes the most downstream pass, i.e., fifth pass, communicates with the intake portion 4 and, as a result, the coolant that has flowed in through the intake portion 4 flows into the first tank block 32 via the communicating pipe 20, and flows out through the outlet portion 5 after traveling through a plurality of passes, and at the same time, coolant flows in directly to the fifth pass via the small hole 36, which then joins with the coolant flowing from the fourth pass so that the coolant becomes dispersed throughout all the tube elements constituting the fifth pass to pass through the U-turn passages. Because of this, of the tube elements constituting the fifth and sixth passes, the tube elements in the vicinity of the downstream side of the partitioning portion 30 will also have a flow of coolant in sufficient quantity, achieving an improvement in the temperature distribution. 
     While the structure described above at least improves the flow in the fifth and sixth passes and the improvement in temperature distribution is achieved within that limit, it is still a cause for concern that the coolant may concentrate toward the downstream side in the third and fourth passes. Thus, the heat exchanger shown in FIG. 6 is modified so that the intake portion 4 and the fifth pass communicate directly through the small hole 36, as shown in FIG. 12. By adopting this structure, the coolant is made to disperse almost consistently in the third and fourth passes as well as in the fifth and sixth passes, achieving an overall temperature distribution without any inconsistency. 
     In addition, in the 2-pass heat exchanger shown in FIG. 13, which is constituted by laminating over 27 levels, the intake portion 4 is connected to an enlarged tank portion of the tube element 3c at the twenty-second level via the communicating pipe 20, and the intake portion 4 is made to communicate with the pass that immediately precedes the most downstream pass, i.e., the first pass, via the small hole 36. Thus, coolant that has flowed in through the intake portion 4 enters the second tank group 17 after traveling through the communicating pipe 20 and also it flows directly into the second tank group via the small hole 36 so that the two flows will join and travel together through the U-turn passage of each tube element to flow out to the outlet portion 5 from the first tank group 16. In this structure, too, by adjusting the size of the small hole 36 as appropriate, it becomes possible to adjust the flow of the coolant that flows into the second tank group 17 from the communicating pipe 20 and the flow of coolant that flows into the second tank group from the small hole 36, thereby achieving an almost consistent temperature distribution by causing the coolant to become dispersed almost consistently throughout. 
     In particular, in the case of a 2-pass heat exchanger, although it is expected to be difficult to disperse the coolant consistently throughout all the elements, since the number of tube elements comprising each pass is great, this concern may be eliminated by adopting a structure in which, as shown in FIG. 14, the tube element 3d with the enlarged tank portion 12b is provided at the central portion of the core main body so that coolant can flow into the second tank group 17 from the middle of the communicating pipe 20 as well. 
     As has been explained, according to the present invention, in a heat exchanger provided with an intake portion and an outlet portion for heat exchanging medium at one end of the core main body in the direction of lamination, since the heat exchanging medium is made to flow readily into the vicinity where the odd-numbered pass changes from the even-numbered pass, it is possible to cause the heat exchanging medium to flow in sufficient quantity to the tube elements in the vicinity of the downstream side of the partitioning portion. Thus, an unbalanced flow of the heat exchanging medium is prevented, thereby improving the temperature distribution in the heat exchanger and achieving an improvement in heat exchanging efficiency. 
     Moreover, in a heat exchanger in the prior art, in which heat exchanging medium flows unevenly, the passage resistance is greater, since the heat exchanging medium flows in a concentrated manner into tube elements at specific locations. According to the present invention, however, heat exchanging medium flows almost equally to each tube element, achieving a reduction in passage resistance.