Laminated heat exchanger

In a laminated heat exchanger with a pair of tank portions formed at one side of each tube element and intake/outlet portions for heat exchanging medium provided at one end in the direction of the lamination or in the direction running at a right angle to the direction of the lamination, a constricting portion for limiting the flow passage cross section is provided in an area in the tank portions where the flow shifts from an even-numbered pass to an odd-numbered pass in a plurality of passes. This allows the heat exchanging medium to flow in sufficient quantities into the tube elements near the outlet side of the partitioning portion, preventing inconsistency in temperature distribution. This constricting portion, which is formed in the tank group opposite the tank group where the partitioning portion is provided, is provided at the same lamination position as the partitioning portion. The constricting portion may be also formed with a plurality of holes. Thus, by ensuring that heat exchanging medium flows in an even, consistent manner, an improvement in heat exchanging efficiency is achieved.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a laminated heat exchanger used in the
 cooling cycle or the like in an air conditioning system for vehicles. The
 heat exchanger constituted by laminating tube elements and fins
 alternately over a plurality of levels and in particular, the present
 invention relates to a laminated heat exchanger that adopts a structure in
 which a pair of tank portions are formed at one side of the tube elements
 and intake/outlet portions for heat exchanging medium are provided at one
 end in the direction of the lamination or at the end surface of the core
 main body in the direction of the air flow.
 2. Description of the Related Art
 In order to respond to the demand for miniaturization of heat exchangers
 and to improve the heat exchanging efficiency, applicant has developed the
 heat exchanger shown in FIGS. 1 and 2 and has conducted much research
 related to this heat exchanger. In this laminated heat exchanger, a core
 main body is formed by laminating tube elements alternately with fins 2
 over a plurality of levels, a pair of tank portions 12 provided at one
 side of each tube element are made to communicate via a U-shaped passage
 portion 13, a heat exchanging medium flow passage with a plurality of
 passes is formed in the core main body by implementing communication
 between the tank portions 12 of adjacent tube elements as necessary, and
 intake/outlet portions (intake portion 4 and outlet portion 5) for the
 heat exchanging medium are provided at one end of the core main body in
 the direction of the lamination with one of these intake/outlet portions
 (intake portion 4) being made to communicate with a tank block 21, which
 constitutes one end of the heat exchanging medium flow passage through a
 communicating pipe 30 and the other of the intake/outlet portions (outlet
 portion 5) being made to communicate directly with a tank block 22, which
 constitutes the other end of the heat exchanging medium flow passage.
 The applicant has also been conducting various types of research into the
 one-side tank type laminated heat exchanger that is known in the prior
 art, as well as the heat exchanger described above. For instance, FIGS. 10
 and 11A-B show one such heat exchanger. In this heat exchanger, a core
 main body is formed by laminating tube elements alternately with fins 2
 over a plurality of levels, a pair of tank portions 12, provided at one
 side of each tube element (toward the bottom in the figures) are made to
 communicate via a U-shaped passage portion 13 and the tank portions 12 in
 adjacent tube elements are made to communicate as necessary to form a heat
 exchanging medium flow passage with a plurality of passes in the core main
 body. In these aspects, this heat exchanger is similar to the one
 described earlier. However, this heat exchanger is provided with
 intake/outlet portions (intake portion 4, outlet portion 5) for heat
 exchanging medium at the end surface of the core main body in the
 direction of the air flow.
 In these heat exchangers described above, when the heat exchanging medium
 flows in through one of the intake/outlet portions (intake portion 4), the
 heat exchanging medium enters the tank block 21 which constitutes one end
 of the heat exchanging medium flow passage either directly or via the
 communicating pipe 30. After travelling through a plurality of passes, the
 heat exchanging medium reaches the tank block 22, which constitutes the
 other end of the heat exchanging medium flow passage, and it flows out
 through the other of the intake/outlet portions (outlet portion 5), which
 communicates with the tank block 22. In this process, the flow of the heat
 exchanging medium, in which it travels upward or downward through the
 U-shaped passage portions 13 of the tube elements, is counted as one pass
 and, for instance, a heat exchanger in which the heat exchanging medium
 passes through the U-shaped passage portions 13 twice, starting from the
 tank block constituting one end of the heat exchanging medium flow passage
 until it reaches the tank block constituting the other end, is referred to
 as a 4-pass heat exchanger and if it passes through the U-shaped passage
 portions three times, it is referred to as a 6-pass heat exchanger.
 However, in the first type of heat exchanger, i.e., in a 4-pass cooling
 heat exchanger, in which the heat exchanging medium passes through a tank
 group without a partitioning portion 18 when it moves from the second pass
 to the third pass, as shown in FIG. 9A, the coolant tends to flow in the
 direction that runs at a right angle to the air flow in the structure
 described above, in which the coolant flows out from one end of the core
 main body. This results in the coolant collecting in the tube elements
 close to the outlet (one end in the direction of the lamination). In other
 words, in the area extending from the third pass through the fourth pass,
 the coolant does not readily flow toward the side close to the
 partitioning portion 18 and this has been proved true through testing; the
 results of which are indicated with the broken lines in FIGS. 7 and 8A-B,
 which demonstrate that the tube temperature and the passing air
 temperature in the area of the partitioning portion close to the outlet
 are higher than those in the other areas.
 In this context, the tube temperature (TUBU TEMP.) refers to the
 temperature of the tube element itself and the tube numbers (TUBU No.) in
 FIGS. 7 and 12 refer to the tube element numbers assigned starting from
 the front left side in FIGS. 1 and 10. Also, the passing air temperature
 (AIR TEMP.) refers to the temperature of the air that has passed through
 the area between the tube elements and for which heat exchange has been
 performed with the fins. The air temperature was measured at a position
 that is away from the end surface of the core main body on the downstream
 side by 1.about.2 cm.
 In a 6-pass heat exchanger, too, the heat exchanging medium flow
 concentrates in the area toward the outlet side, away from the
 partitioning portion 18, as shown in FIG. 9B. As a result, it is assumed
 that the tube temperature and the passing air temperature in the area of
 the partitioning portion near the outlet will be different from those in
 the other areas.
 Furthermore, in the latter type of heat exchanger, too, i.e., a 4-pass
 cooling heat exchanger, when the flow speed increases with the coolant
 flow rate per unit time increasing, the coolant will concentrate toward
 the end in the direction of the lamination when it moves from the second
 pass through the third pass, as shown in FIG. 14, and the coolant will not
 readily flow in the area toward the partitioning portion 18 in the area
 extending from the third pass through the fourth pass. The coolant is
 clearly demonstrated to flow in this manner by the test results indicated
 with the broken lines in FIG. 12, which show that the passing air
 temperature is higher in the area near the partitioning portion 18
 compared to the other areas.
 SUMMARY OF THE INVENTION
 Accordingly, the object of the present invention is to provide a laminated
 heat exchanger in which heat exchanging medium can flow evenly throughout
 the tube elements without concentrating in any area and with which it is
 possible to achieve an improvement in heat exchanging efficiency.
 The applicant has discovered that concentration of heat exchanging medium
 in any particular area can be prevented when the heat exchanging medium is
 made to flow sufficiently through the tube elements near the partitioning
 portion, which results in nearly consistent temperature distribution in
 the core main body, by changing the state of the flow of the heat
 exchanging medium travelling from an even-numbered pass to an odd-numbered
 pass in the tank group, and the applicant has completed the present
 invention based upon this observation.
 In order to achieve the object described above, the laminated heat
 exchanger according to the present invention is constituted by laminating
 tube elements, each of which is provided with a pair of tank portions and
 a U-shaped passage portion communicating between the pair of tank
 portions, alternately with fins over a plurality of levels, to form a core
 main body. A heat exchanging medium flow passage with a plurality of
 passes is formed in the core main body by partitioning tank groups
 constituted by bonding the tank portions of the tube elements as
 necessary. Intake / outlet portions for the heat exchanging medium are
 provided at one end of the core main body in the direction of the
 lamination with one of the intake/outlet portions being made to
 communicate with the tank block at one end of the heat exchanging medium
 flow passage via a communicating pipe and the other of the intake/outlet
 portions being made to communicate with the tank block constituting the
 other end of the heat exchanging medium flow passage at one end in the
 direction of the lamination. A constricting portion, which limits the flow
 passage cross section is provided in at least one location in the tank
 group where the flow path shifts from an even-numbered pass to an
 odd-numbered pass in the plurality of passes.
 Consequently, in this structure, the heat exchanging medium flowing in
 through one of the intake/outlet portions, enters the tank block
 constituting one end of the heat exchanging medium flow passage via the
 communicating pipe, reaches the tank block constituting the other end of
 the heat exchanging medium flow passage after passing through the core
 main body a plurality of times and flows out from one end of this tank
 block in the direction of the lamination via the other of the
 intake/outlet portions. In this process, in the area where the flow shifts
 from an even-numbered pass to an odd-numbered pass, the heat exchanging
 medium tends to flow in greater quantity toward the outlet. However, since
 a constricting portion for limiting the flow passage cross section is
 provided in the area of the tank group where the flow shifts from an
 even-numbered pass (even-numbered path) to an odd-numbered pass
 (odd-numbered path), the heat exchanging medium flows in sufficient
 quantity through the tube elements near the outlet in the partitioning
 portion as through the other tube elements, due to the reduced flow speed
 caused by the constricting portion and the like. With this, as indicated
 with the solid lines in FIGS. 7 and 8, large discrepancies in temperature
 distribution are eliminated, thus achieving the object described above.
 Alternatively, another laminated heat exchanger which achieves the same
 object may be constituted by laminating tube elements, each of which is
 provided with a pair of tank portions at one side and a U-shaped passage
 portion communicating between the pair of tank portions, alternately with
 fins over a plurality of levels to form a core main body, with a heat
 exchanging medium flow passage that includes a plurality of passes formed
 in the core main body by partitioning tank groups constituted by bonding
 adjacent tank portions as necessary. Intake/outlet portions through which
 the heat exchanging medium flows in and out are provided in the tank
 blocks constituting the two ends of this heat exchanging medium flow
 passage in the direction running at a right angle to the direction of the
 lamination and a constricting portion for limiting the flow passage cross
 section is provided in at least one location in the tank group where the
 flow shifts from an even-numbered pass to an odd-numbered pass in the
 plurality of passes. Specifically, in this structure, the intake/outlet
 portion may be provided at the end surface of the tank block in the
 direction of the air flow (the front surface of the core main body, for
 instance).
 In this structure, too, the heat exchanging medium which has flowed in
 through one of the intake/outlet portions, enters the tank block
 constituting one end of the heat exchanging medium flow passage, reaches
 the tank block constituting the other end of the heat exchanging medium
 flow passage after passing through the core main body a plurality of times
 and flows out via the other of the intake/outlet portions. During this
 process, in the area where the flow shifts from an even-numbered pass to
 an odd-numbered pass, the heat exchanging medium tends to flow in a
 concentrated manner away from the even-numbered pass if the flow speed is
 high. However, since the constricting portion for limiting the flow
 passage cross section is provided in the area of the tank group where the
 flow shifts from an even-numbered pass (even-numbered path) to an
 odd-numbered pass (odd-numbered path), the heat exchanging medium flows in
 sufficient quantity through the tube elements near the partitioning
 portion as through the other tube elements due to the reduced flow speed
 caused by the constricting portion and the like. Thus, as indicated with
 the solid lines in FIG. 12, there is no great discrepancy in the
 temperature distribution, thus achieving the object described earlier.
 In this structure, the constricting portion is formed in the tank group
 opposite the tank group which is provided with the partitioning portion
 and it is desirable to provide the constricting portion at the position
 which corresponds to the position in the lamination where the partitioning
 portion is provided in the tank group. In addition, the constricting
 portion may be constituted with a plurality of holes.
 While the form of the constricting portion may include many variations, it
 has been confirmed that, in a given area, a two-hole configuration rather
 than one hole, provides greater consistency in temperature distribution
 and, by adjusting the number of holes, their shape and size as necessary,
 it is possible to achieve subtle adjustments while maintaining a
 temperature distribution that is practically consistent. In addition, it
 is necessary to set an appropriate constricting portion in relation to the
 pressure loss and the quantity of heat discharge from the core main body.
 If the cross section area of the constricting portion is too small, it
 results in a greater pressure loss with reduced quantity of heat
 discharge, while if the cross section area of the constricting portion is
 too large, the pressure loss is reduced but uneven distribution of the
 heat exchanging medium, which is the problem in the prior art, becomes
 more pronounced. Because of this, it is desirable that the cross section
 area S1 of the constricting portion and the cross section area S2 of the
 through holes communicating between the tank portions maintain a
 relationship expressed as 0.25.ltoreq.S1/S2.ltoreq.s 0.80.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The following is an explanation of embodiments of the present invention in
 reference to the drawings. In FIGS. 1 and 2, a laminated heat exchanger 1
 is a 4-pass type evaporator, for instance, with its core main body formed
 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 provided at one end in the direction of the lamination of the tube
 elements 3. All the tube elements 3, except for tube elements 3a and 3b at
 the two ends in the direction of the lamination, the tube element 3c
 provided with an extended tank portion which is to be explained later, the
 tube element 3d located approximately at the center and the tube element
 3e, which is adjacent to the tube element 3d, are each constituted by
 bonding two formed plates 6a, one of which is shown in FIG. 3A.
 This formed plate 6a is formed by press machining an aluminum plate with
 two bowl-like distended portions for tank formation 7 and 7 formed at one
 end, a distended portion for passage formation 8 formed continuous to
 them, an indented portion 9 for mounting a communicating pipe, which is to
 be explained later, formed between the distended portions for tank
 formation and a projection 10 extending from the area between the two
 distended portions for tank formation 7 and 7 to the area close to the
 other end of the formed plate 6a, formed in the distended portion for
 passage formation 8. In addition, at the other end of the formed plate 6,
 a projected tab (shown in FIG. 1) 11 for preventing the fins 2 from
 falling out during assembly preceding brazing, are provided.
 The distended portions for tank formation 7 are made to distend more than
 the distended portion for passage formation 8 and the projection 10 is
 formed so as to lie on the same plane as the bonding margin at the edge of
 the formed plate. When two formed plates 6a are bonded at their edges,
 their projections 10 are also bonded so that a pair of tank portions 12
 are formed with the distended portions for tank formation 7 that face
 opposite each other and a U-shaped passage portion 13 for communicating
 between the tank portions is formed with the distended portions for
 passage formation 8 that face opposite each other.
 The tube elements 3a and 3b at the two ends in the direction of the
 lamination are each constituted by bonding a flat plate 15 to a plate 6a,
 illustrated in FIG. 3A.
 In the formed plates 6b and 6c constituting the tube element 3c, one of the
 distended portions for tank formation extends so as to approach the other
 distended portion for tank formation. As a result, in the tube element 3c,
 a tank portion 12, the size of which is the same as that in the tube
 element 3 mentioned earlier, and a tank portion 12a, which is made to
 extend into and fill the indented portion, are formed. Other structural
 features, i.e., the distended portion for passage formation 8 formed
 continuous to the distended portions for tank formation, the projection 10
 formed extending from the area between the distended portions for tank
 formation to the area close to the other end of the formed plate and the
 projected tab 11 for preventing the fins 2 from falling out provided at
 the other end of the formed plate are identical to those in the formed
 plate 6 shown in FIG. 3A and their explanation is omitted here.
 In the heat exchanger, as shown in FIG 1, adjacent tube elements are
 abutted at the tank portions to form two tank groups, i.e., a first tank
 group 15 and a second tank group 16 which extend in the direction of the
 lamination (at a right angle to the direction of the air flow) and in the
 one tank group 15, which includes the extended tank portion 12a, all the
 tank portions are in communication via the through holes 17 formed in the
 distended portions for tank formation 9, except for the formed plate 6d,
 located at approximately the center in the direction of the lamination. In
 the other tank group 16, all the tank portions are in communication via
 the through holes 17, without any partition.
 The tube element 3d is constituted by combining the formed plate 6a shown
 in FIG. 3A and the formed plate 6d shown in FIG. 3B with the formed plate
 6d, not provided with a through hole in one of its distended portions for
 tank formation 7a, and a partitioning portion 18 to partition one of the
 tank groups, i.e., the tank group 15, which is formed with this
 non-communicating portion. Note that the partitioning portion 18 may be
 constituted by having the adjacent tube element 3e, too, as a blind tank,
 which does not have a through hole, and by bonding the distended portions
 for tank formation without through holes in order to increase the strength
 or it may have a structure in which, instead of a blind tank, a thin plate
 is enclosed between the tube element 3d and the tube element 3e to close
 off the through holes communicating between the tank portions.
 In addition, the tube element 3e is constituted by combining the formed
 plate 6a shown in FIG. 3A and the formed plate 6e shown in FIG. 3C, with a
 constricting portion 19, for limiting the communicating portion of the
 tank group 16 located opposite from the tank group 15 where the
 partitioning portion 18 is provided, in the formed plate 6e, which is on
 the side where it is bonded with the tube element 3d. As a result, the
 first tank group 15 is partitioned into a first tank block or first tank
 subgroup 21 that includes the extended tank portion 12a, and a second tank
 block or fourth tank subgroup 22 that communicates with the outlet portion
 5 by the partitioning portion 18, while the non-partitioned second tank
 group 16 constitutes a third tank block 23 that includes a second tank
 subgroup and a third tank subgroup, which is provided with the
 constricting portion 19. Note that the first and second subgroups are
 disposed on opposite sides of the heat exchanger and fluidly communicate
 via the U-shaped passage portions 13. Note that in this embodiment, the
 tube elements are laminated over 27 levels with the tube element 3c
 positioned at the 6th level, the tube element 3d positioned at the 14th
 level and the tube element 3e positioned at the 15th level, counting from
 the right in the figure.
 The constricting portion 19 is constituted of, for instance, one round hole
 with the flow passage cross section area (the size of the through hole 17)
 reduced compared to that in the other areas, as shown in FIG. 4A. In this
 embodiment, the diameter of the regular through hole 17 is set at
 .PHI.15.7 mm and the diameter of the constricting portion is set at
 .PHI.12 mm, and the constricting portion 19 is provided in the formed
 plate 6e. However, the constricting portion may be provided at the formed
 plate 6d, where the partitioning portion 18 is formed, as shown in FIG.
 4B, or it may be provided at both the formed plates 6d and 6e in order to
 achieve increased strength.
 It must be born in mind, however, that if the cross section area of the
 constricting portion 19 is too small, the passage resistance becomes
 great, increasing the pressure loss .DELTA.Pr and resulting in reduced
 heat discharge (heat exchange quantity) Q due to the reduction in the flow
 rate of the heat exchanging medium (see FIG. 13) and that if, in order to
 avoid this, the cross section area of the constricting portion 19 is made
 too large, inconsistency in the distribution of the heat exchanging
 medium, which is the problem in the prior art, becomes more pronounced.
 Thus, in order to avoid these problems, it is desirable to set the size of
 the constricting portion 19 within a range in which the cross sectional
 area S1 of the constricting portion 19 and the cross sectional area S2 of
 the through holes 17 maintain the relationship expressed as
 0.25.ltoreq.S1/S2.ltoreq.0.80. Consequently, when the size of the through
 hole is at .PHI.15.7, as in this embodiment, it is desirable to form the
 constricting portion within the range of approximately
 .PHI.8.about..PHI.14.
 Now, the intake portion 4 and the outlet portion 5, which are provided at
 one end in the direction of the lamination on the side which is further
 from the extended tank portion 12a, are constituted by bonding a plate for
 intake/outlet passage formation 24 to the flat plate 15 mentioned earlier,
 which constitutes an end plate, and are provided with an intake passage 25
 and an outlet passage 26 respectively, formed to extend from approximately
 the middle of the plate 15 in the direction of the length toward the tank
 portions.
 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 extended tank portion 12a are in communication with each other through
 a communicating passage constituted with a communicating pipe 30, which is
 secured in the indented portion 9 and is bonded to the hole formed in the
 plate 15 and a hole formed in the formed plate 6b. The second tank block
 22 and the outlet passage 26 communicate with each other via a hole formed
 in the plate 15.
 Thus, in the heat exchanger structured as described above, heat exchanging
 medium which has flowed in through the intake portion 4 enters the
 extended tank portion 12a through the communicating pipe 30, is then
 dispersed over the entirety of the first tank block 21 and then travels
 upward through the U-shaped passage portions 13 of the tube elements that
 correspond to the first tank block 21 along the projections 10 (first
 pass). Then, the heat exchanging medium makes a U-turn above the
 projections 10 before starting to travel downward (second pass) and it
 reaches the tank group on the opposite side (third tank block 23). After
 that, the heat exchanging medium moves horizontally to the remaining tube
 elements which constitute the third tank block 23 and travels upward
 through the U-shaped passage portions 13 of the tube elements along the
 projections 10 (third pass). Next, it makes a U-turn above the projections
 10 before travelling downward (fourth pass) and is then led to the tank
 portions constituting the second tank block 22 before flowing out through
 the outlet portion 5. Because of this, the heat of the heat exchanging
 medium is communicated to the fins 2 during the process in which it flows
 through the U-shaped passage portions 13 constituting the
 first.about.fourth passes, so that heat exchange is performed with the air
 passing between the fins.
 During this process, since the outlet portion 5 is connected to the second
 tank block 22 via the end of the core main body in the direction of the
 lamination, the flow of the heat exchanging medium moving from the second
 pass to the third pass would tend to concentrate toward the outlet portion
 as described earlier, and this might be of concern. However, with the
 constricting portion 19 formed in the communicating area in the third tank
 group 23, the heat exchanging medium is made to flow in sufficient
 quantity into the tube elements near the partitioning portion, too, among
 all the tube elements constituting the third and fourth passes. Such a
 change in the flow of coolant effected by providing the constricting
 portion 19 is assumed to be caused by the fact that the flow speed of the
 heat exchanging medium moving to the third pass is restricted by the
 constricting portion 19 and also the complex flow pattern being created
 with the prevention of a linear flow of the heat exchanging medium inside
 the second tank group 16. In any case, according to the results of tests
 in which the tube temperature and the passing air temperature were
 measured, shown in FIG. 7 and FIGS. 8A-B, the temperature of the tube
 elements in the partitioning portion near the outlet (in particular TUBU
 Nos. 9.about.13) and the temperature of the air passing through the upper
 level of the tube elements (in particular TUBU Nos. 5.about.13) are lower
 than those in a heat exchanger without a constricting portion in the prior
 art, as indicated with the solid lines, achieving a consistent temperature
 distribution overall, and this proves that heat exchanging medium
 (coolant) flow is practically consistent over the entirety of the core
 main body without significant concentration in any particular area.
 It has been confirmed that the temperature distribution changes subtly
 depending upon the shape of, and the number of holes in the constricting
 portion 19 mentioned above, whereby the flow passage area is made smaller
 relative to the other through holes 17. Even when the constricting portion
 19 in the distended portion for tank formation 7 of the formed plate 6d
 provided with the partitioning portion 18 or the formed plate 6e adjacent
 to it, as shown in FIG. 4C or D, is made by forming holes symmetrically at
 two positions, in an upper area and a lower area, for instance, with the
 total area of the constricting portion remaining the same, the temperature
 in the partitioning portion near the outlet (the tube temperature and the
 passing air temperature) can be further kept down, further smoothing the
 temperature distribution in core main body.
 In addition, the constricting portion 19 is not limited to those described
 above and it may be constituted by forming two symmetrical holes at two
 locations, left and right in the distended portion for tank formation in
 the formed plate 6d provided with the partitioning portion 18 or the
 formed plate 6e adjacent to it, as shown in FIG. 5A, or it may be
 constituted by forming two symmetrical holes relative to a hypothetical
 line which inclines at approximately 45.degree., as shown in FIG. 5B.
 The structure in which the constricting portion 19 is constituted with two
 holes also may include a configuration in which the two holes formed at
 the left and right in the distended portion for tank formation in the
 formed plate provided with the partitioning portion 18 or the formed plate
 adjacent to it, are not equal in size, as shown in FIG. 5C or FIG. 5D, or
 two holes of different sizes may be formed above and below each other at
 two positions in the distended portion for tank formation, as shown in
 FIG. 5E or FIG. 5F.
 Further variations in the shape of the constricting portion 19 for limiting
 the flow passage area are conceivable and, as shown in FIG. 6A, the hole
 may be cross-shaped or, as shown in FIG. 6B, the constricting portion 19
 may take a form in which small holes are provided at four locations, up,
 down, left and right. Furthermore, as shown in FIG. 6C, holes may be
 provided at three positions, i.e., in the upper, middle and lower parts of
 the distended portion for tank formation or, as shown in FIG. 6D, the
 constricting portion 19 may be constituted with three holes that are three
 sections of a circle created by dividing a circular hole into three
 approximately equal segments with their central angles approximately the
 same. Moreover, as shown in FIG. 6E, it may be constituted with four holes
 that are four sections of a circle divided into four equal segments with
 their central angles approximately the same.
 In any of these forms, as long as the cross sectional area (when the
 constricting portion is constituted with a plurality of holes, the total
 area of the cross sectional areas of all the holes) S1 of the constricting
 portion 19 and the cross sectional area S2 of the through holes 17 retain
 the relationship expressed as 0.25.ltoreq.S1/S2.ltoreq.0.80, the
 advantages described earlier are achieved.
 Another embodiment of the present invention is shown in FIGS. 10 and 11A-B
 and mainly, the aspects of it that are different from those in the
 previous embodiment are explained below, with the same reference numbers
 assigned to components which are identical to those in all the drawings.
 This laminated heat exchanger is a 4-pass type evaporator, for instance,
 with an intake portion 4 and an outlet portion 5 for heat exchanging
 medium provided at an end surface of the core main body in the direction
 of the air flow, specifically at the end surface on the upstream side. All
 the tube elements 3, except for the tube elements 3a and 3b at the two
 ends in the direction of the lamination, the tube element 3d located at
 approximately the center, the tube element 3e adjacent to it and tube
 elements 3f, each of which is formed as a unit with the intake portion 4
 or the outlet portion 5, are constituted by bonding together two formed
 plates 6a, one of which is shown in FIG. 3A
 As all the tube elements except for the tube elements 3f are structured
 identically to those described earlier, their explanation is omitted here.
 In each tube element 3f the distended portion for tank formation 7 on the
 upstream side projects out and opens in the direction of the air flow and,
 as a result, in the tube elements 3f, the intake portion 4 or the outlet
 portion 5 is formed by bonding this portion that projects out and opens,
 face-to-face. The other structural features, i.e., the distended portion
 for passage formation formed continuous to the distended portions for tank
 formation, the projection formed extending from the area between the
 distended portions for tank formation through the area near the other end
 of the formed plate and the projected tab for preventing the fins 2 from
 falling out provided at the other end of the formed plate are identical to
 those in the formed plate 6 shown in FIG. 3A and their explanation is
 omitted here.
 In addition, the partitioning portion 18 and the constricting portion 19
 provided on the opposite side from the partitioning portion 18, are
 structured identically to those described earlier. However, in this heat
 exchanger, the tube elements are laminated over 26 levels with the intake
 portion 4 formed at the 7th level and the outlet portion formed at the
 20th level from the left in the figure, and the partitioning portion 18
 and the constricting portion 19 formed between the 7th level (tube element
 3e) and the 14th level (tube element 3d) counting from the left. In this
 heat exchanger, the partitioning portion 18 and the constricting portion
 19 may be formed between the 14th level and the 15th level from the left
 instead.
 As shown in FIG. 4A, the constricting portion 19 may be constituted by
 forming one round hole whose flow passage cross section is constricted in
 the formed plate 6e, for instance. Alternatively, this round hole may be
 provided in the formed plate 6d, where the partitioning portion 18 is
 formed, as shown in FIG. 4B, or a round hole may be provided in both of
 the formed plates 6d and 6e for increased strength. In addition, while the
 diameter of the round hole is set at .PHI.12 mm against the diameter of
 the regular through hole 17 which is set at .PHI.15.7 mm, it is desirable
 to set the cross sectional area of this constricting portion within the
 range in which the cross sectional area S1 of the constricting portion 19
 and the cross sectional area S2 of the through hole 17 retain the
 relationship expressed as 0.25.ltoreq.S1/S2.ltoreq.0.80 by taking into
 consideration the relationship illustrated in FIG. 13, as explained
 earlier and when the size of the through hole is at .PHI.15.7 as in this
 embodiment, the constricting portion 19 may be formed within the range of
 approximately .PHI.8.about.14.
 Consequently, in the heat exchanger structured as described above, heat
 exchanging medium which has flowed in through the intake portion 4 is
 distributed over the entirety of the first tank block 21 and it then
 travels upward through the U-shaped passage portions 13 of the tube
 elements that correspond to the first tank block 21 along the projections
 10 (first pass). Then, it makes a U-turn above the projections 10 before
 travelling downward (second pass) to reach the tank group (third tank
 block 23) on the opposite side. After this, the heat exchanging medium
 moves horizontally to the remaining tube elements constituting the third
 tank block 23 and travels upward through the U-shaped passage portions 13
 of the tube elements along the projections 10 (third pass). Then it makes
 a U-turn above the projections 10 before travelling downward (fourth pass)
 and is then led to the tank portions constituting the second tank block 22
 before flowing out through the outlet portion 5. Because of this, the heat
 of the heat exchanging medium is communicated to the fins 2 during the
 process in which it flows through the U-shaped passage portions 13
 constituting the first.about.fourth passes so that heat exchange is
 performed with the air passing between the fins.
 During this process, the flow of the heat exchanging medium moving from the
 second pass to the third pass tends to concentrate toward the outlet
 portion as described earlier and this might be of concern. However, with
 the constricting portion 19 formed in the communicating area in the third
 tank group 23, the heat exchanging medium is made to flow in sufficient
 quantity into the tube elements near the partitioning portion, too, among
 all the tube elements constituting the third and fourth passes. Such a
 change in the flow of coolant effected by providing the constricting
 portion 19 is assumed to be caused by fact that the flow speed of the heat
 exchanging medium moving to the third pass is reduced by the constricting
 portion 19 and also the complex flow pattern being created with the
 prevention of a linear flow of the heat exchanging medium inside the
 second tank group 16. In any case, according to the results of tests in
 which the passing air temperature was measured, shown in FIG. 12, the
 temperature of the air passing between the tube elements of the
 partitioning portion near the outlet (in particular TUBU Nos. 14.about.20)
 is lower than that in a heat exchanger without a constricting portion in
 the prior art, as indicated with the solid line, achieving consistent
 temperature distribution overall. This proves that the flow of heat
 exchanging medium (coolant) is practically consistent over the entirety of
 the core main body without concentrating much in any particular area.
 As in the previous embodiment, it has been confirmed that when the flow
 passage area of the constricting portion 19 mentioned above is made
 smaller relative to the other through holes 17, the temperature
 distribution changes subtly, depending upon its shape and the number of
 holes in it. Even when the constricting portion 19 is made by forming
 holes symmetrically at two positions above and below each other, or in the
 upper area and lower area of the distended portion for tank formation 7 of
 the formed plate 6d provided with the partitioning portion or the formed
 plate 6e adjacent to it, as shown in FIG. 4C or FIG. 4D, and the flow
 passage area remains constant, the temperature in the partitioning portion
 18 near the outlet portion (the tube temperature and the passing air
 temperature) can be further kept down, providing an even smoother
 temperature distribution in the core main body.
 In addition, the constricting portion 19 is not limited to those described
 above and may be constituted by forming two symmetrical holes at two
 locations, left and right, in the distended portion for tank formation in
 the formed plate 6d provided with the partitioning portion 18 or the
 formed plate 6e adjacent to it, as shown in FIG. 5A, or it may be
 constituted by forning two symmetrical holes relative to a hypothetical
 line which inclines at approximately 45.degree., as shown in FIG. 5B.
 The structure in which the constricting portion 19 is constituted with two
 holes also may include one in which two holes of different size are formed
 at the left and right in the distended portion for tank formation in the
 formed plate provided with the partitioning portion 18 or the formed plate
 adjacent to it, as shown in FIG. 5C or FIG. 5D, or two holes of different
 size may be formed above and below each other at two positions in the
 distended portion for tank formation, as shown in FIG. 5E or FIG. 5F.
 Further variations in the shape of the constricting portion 19 for limiting
 the flow passage area are conceivable and, as shown in FIG. 6A, the hole
 may be a cross-shaped or, as shown in FIG. 6B, the constricting portion 19
 may take a form in which small holes are provided at four locations, up,
 down, left and right. Furthermore, as shown in FIG. 6C, holes may be
 provided at three positions, i.e., in the upper, middle and lower parts of
 the distended portion for tank formation or, as shown in FIG. 6D, the
 constricting portion 19 may be constituted with three holes that are three
 sections created by dividing a circular hole into three approximately
 equal segments with their central angles approximately the same. Moreover,
 as shown in FIG. 6E, it may be constituted with four holes that are four
 sections of a circle divided into four equal segments with their central
 angles approximately the same.
 In any of these forms, as long as the cross section area (when the
 constricting portion is constituted with a plurality of holes, the total
 area of the cross section areas of all the holes) S1 of the constricting
 portion 19 and the cross section area S2 of the through holes 17 retain
 the relationship expressed as 0.25.ltoreq.S1/S2.ltoreq.0.80, the
 advantages described earlier are achieved.
 Note that while the state of the flow of heat exchanging medium is
 presumably also affected by the positions of the intake portion 4 and the
 outlet portion 5 and in particular by the position of the outlet portion
 5, since the heat exchanging medium will tend to flow near the
 partitioning portion even without a constricting portion 19, as long as
 the outlet portion 5 is located close to the partitioning portion 18, this
 mode of the present invention is effective, specifically, when the outlet
 portion 5 is provided at a position within 3/4 of the distance from the
 end to the partitioning portion 18 (in this embodiment, at any one of the
 tube elements TUBU Nos. 18.about.26).
 As has been explained, according to the present invention, whether in a
 heat exchanger with the intake/outlet portions for heat exchanging medium
 provided at one end of the core main body in the direction of the
 lamination or in a heat exchanger with its intake/outlet portions provided
 in the direction running at a right angle to the direction of the
 lamination in the core main body, since a constricting portion is provided
 in the area where the flow of the heat exchanging medium shifts from an
 even-numbered pass to an odd-numbered pass where the flow tends to become
 uneven, more specifically, at a position which corresponds to the position
 of the partitioning portion which is partitioned to form a plurality of
 passes relative to the direction of the lamination in the tank group that
 is opposite the tank group in which the partitioned portion is provided to
 ensure that the heat exchanging medium flows in sufficient quantity into
 the tube elements near the partitioned portion, the uneven flow of the
 heat exchanging medium is prevented, achieving an improvement in heat
 exchanging efficiency.