Cooling heat exchanger

Abstract

A cooling heat exchanger has first and second heat transfer plates joined to each other. Each of the first and second heat transfer plates has protrusions protruding from a base portion thereof for defining internal fluid passages, a fin portion projecting from the base portion in the same direction as the protrusions and defining a fin inner space, and an aperture on the base portion at a position corresponding to the fin portion. The fin portion includes an offset wall that is offset from the base portion and connected to the base portion at two positions. The aperture of the first heat transfer plate is displaced from the aperture of the second heat transfer plate with respect to a longitudinal direction of the protrusions so that a communication channel that allows communication between the fin inner spaces of the first and second heat transfer plates is provided for draining condensation.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on Japanese Patent Application No. 2006-298691 filed on Nov. 2, 2006, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a cooling heat exchanger having heat transfer plates on which fin portions are integrally formed.

BACKGROUND OF THE INVENTION

[0003] For example, Unexamined Japanese Patent Publication No. 2002-147983 describes a plate-type cooling heat exchanger, such as an evaporator, which is constructed of heat transfer plates without using separate fin members. The heat transfer plates include base portions, which are generally flat, and protrusions protruding from the base portions for defining internal fluid passages therein through which an internal fluid, such as a refrigerant, flows. The protrusions are formed by pressing, such as projecting. The heat transfer plates further have slit fins on the base portions and between the protrusions.

[0004] In the disclosed heat exchanger, heat exchange is performed between an external fluid, such as air, flowing outside thereof and the internal fluid. At this time, a flow of air is disturbed by the protrusions. Namely, since the protrusions serve as turbulent members for causing turbulent flows, a coefficient of heat transfer of the air improves. Further, efficiency of heat transfer improves. Also, the fins have substantially U-shaped cross-sections, and thus the air can flow inside of the fins. Because a heat transfer area for the air increases due to configuration of the fins, the efficiency of heat transfer further improves.

[0005] Although such a plate-type heat exchanger does not have the fin members, such as corrugated fins, which are generally used in a fin and tube type heat exchanger, the efficiency of heat transfer is improved by the slit fins. The plate-type heat exchanger is simply formed by brazing the heat transfer plates, which are formed by pressing.

[0006] In a cooling heat exchanger, condensation is generated due to cooling of the air. Condensation generated on the surfaces of heat transfer plates tends to accumulate in the inside of slit fins. In this case, because water exists between inner surfaces of the slit fins and the air passing through the slit fins, thermal resistance due to the water is likely to increase. As a result, the efficiency of heat transfer reduces. Also, the accumulated condensation will be scattered toward downstream positions with respect to the air flow due to air pressure. Namely, in a cooling heat exchanger, it is required to effectively discharge or drain condensation from the fin portions.

SUMMARY OF THE INVENTION

[0007] The present invention is made in view of the foregoing matter, and it is an object of the present invention to provide a cooling heat exchanger capable of improving drainage of condensation.

[0008] According to an aspect of the present invention, a heat exchanger for cooling air, which flows outside thereof, includes a first heat transfer plate and a second heat transfer plate. Each of the first and second heat transfer plates includes a base portion that defines a plane in a flow direction of the air and protrusions that protrude from the base portion and extend in a direction that intersects with the air flow direction. The first and second heat transfer plates are joined to each other such that the base portions thereof are in contact with each other. Also, the protrusions of the first heat transfer plate protrude in one direction and the protrusions of the second heat transfer plate protrude in an opposite direction. The protrusions provide internal fluid passages therein for allowing the internal fluid to flow. Each of the first and second heat transfer plates further includes a fin portion that projects from the base portion in the same direction as the respective protrusions for defining a fin inner space therein and an aperture on the base portion at a position corresponding to the fin portion. Each of the fin portions includes an offset wall offset from the base portion. The offset wall is connected to the base portion at two locations that are spaced in a direction parallel to a longitudinal direction of the protrusions. The aperture of the first heat transfer plate is displaced from the aperture of the second heat transfer plate with respect to the longitudinal direction of the protrusions, and the fin inner space of the first heat transfer plate is in communication with the fin inner space of the second heat transfer plate, such that a communication channel for draining condensation is provided between the first and second heat transfer plates.

[0009] Accordingly, condensation in the fin inner spaces is smoothly discharged through the communication channel.

[0010] According to another aspect of the present invention, a heat exchanger for cooling air includes a first heat transfer plate and a second heat transfer plate. The first heat transfer plate includes a base portion that defines a plane in a flow direction of the air, a plurality of protrusions that protrudes from the base portion, a fin portion that projects from the base portion in the same direction as the plurality of protrusions such that a fin inner space is defined inside of the fin portion, and a first aperture on the base portion at a position corresponding to the fin portion. The protrusions extend in a direction that intersects with a flow direction of the air and define internal fluid passages therein for allowing the internal fluid to flow. The fin portion includes an offset wall that is offset from the base portion. The offset wall is connected to the base portion at two locations that are separated in a longitudinal direction of the protrusions. The second heat transfer plate includes a base portion that defines a plane in the flow direction of the air, a plurality of protrusions protruding from the base portion, and a second aperture. The protrusions of the second heat transfer plate extend in a direction intersecting with the flow direction of the air and define internal fluid passages therein for allowing the internal fluid to flow. The first heat transfer plate and the second heat transfer plate are joined to each other such that the base portions thereof are in contact with each other. The protrusions of the first heat transfer plate protrude in one direction and the protrusions of the second heat transfer plate protrude in an opposite direction. The first aperture and the second aperture overlap at least at a part with respect to the longitudinal direction of the protrusions.

[0011] Accordingly, since the fin inner space is in communication with outside of the first and second heat transfer plates through the first and second apertures, condensation will be discharged from the fin inner space through the first and second apertures. As such, condensation is effectively drained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

[0013] FIG. 1 is an exploded perspective view of an evaporator according to a first embodiment of the present invention;

[0014] FIG. 2 is an exploded perspective view of the evaporator, for explaining a general flow of a refrigerant therein, according to the first embodiment;

[0015] FIG. 3 is a cross-sectional view of the evaporator taken along a line III-III in FIG. 1;

[0016] FIG. 4 is a perspective view of a part of a heat transfer plate of the evaporator according to the first embodiment;

[0017] FIG. 5 is a cross-sectional view of the heat transfer plates taken along a line V-V in FIG. 4;

[0018] FIG. 6 is a schematic cross-sectional view of heat transfer plates as a comparative example;

[0019] FIG. 7A is a graph showing the amount of accumulation of condensation per fin of the comparative example;

[0020] FIG. 7B is a graph showing the amount of accumulation of condensation per fin of the evaporator according to the first embodiment;

[0021] FIG. 8 is a graph showing a relationship between a fin height and the amount of accumulation of condensation per fin according to the first embodiment and the comparative example;

[0022] FIG. 9 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a second embodiment of the present invention;

[0023] FIG. 10 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a third embodiment of the present invention;

[0024] FIG. 11 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a fourth embodiment of the present invention;

[0025] FIG. 12 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a fifth embodiment of the present invention;

[0026] FIG. 13 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a sixth embodiment of the present invention; and

[0027] FIG. 14 is a schematic cross-sectional view of a part of heat transfer plates of an evaporator according to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0028] First to seventh embodiments of the present invention will now be described with reference to the accompanying drawings. In the second to seventh embodiments, components similar to those of the first embodiment will be indicated by the same reference numerals and will not be described further.

First Embodiment

[0029] Referring to FIGS. 1 to 8, a heat exchanger of the first embodiment is exemplarily employed as an evaporator 10 for a vehicular air conditioner. A general structure of the evaporator 10 can be similar to a heat exchanger described in U.S. Pat. No. 6,047,769 (Japanese Unexamined Patent Publication No. 11-287580). The evaporator 10 generally includes a plurality of heat transfer plates 12.

[0030] In the drawings, arrows A1 denote a general flow direction of air for an air conditioning operation as an external fluid, and arrows B denote a general flow direction of an internal fluid, such as a refrigerant, flowing in internal fluid passages formed in heat transfer plates. The flow direction B of the refrigerant intersects the flow direction A1 of the air. In the illustrated example, the evaporator 10 is constructed as a perpendicularly countercurrent heat exchanger in which the flow direction A1 of the air is substantially perpendicular to the flow direction B of the refrigerant. Also, the evaporator 10 is constructed such that refrigerant upstream passages, which are in communication with a refrigerant inlet, is located downstream of refrigerant downstream passages, which are in communication with a refrigerant outlet, with respect to the flow direction A1 of the air.

[0031] The evaporator has a core part 11 for performing heat exchange between the air and the refrigerant. The core part 11 is constructed by stacking a plurality of heat transfer plates 12 in a direction substantially perpendicular to the air flow direction A1. The heat transfer plates 12 include tank parts 20 to 23 at upper and bottom ends thereof. Because the air does not pass through the tank parts 20 to 23, the core part 11 is constructed of middle portions of the heat transfer plates 12 other than the tank parts 20 to 23.

[0032] Each of the heat transfer plates 12 is formed by pressing a thin metallic plate member. The plate member is, for example, a clad plate member that has a base material made of A3000 aluminum, and both surfaces of which are clad with a A4000 aluminum brazing material. The heat transfer plate 12 is a very thin plate, and has a thickness t, as shown in FIG. 3. In the present embodiment, for example, the thickness t of the heat transfer plate 12 is 0.2 mm. The heat transfer plate 12 has a generally rectangular plate shape. All of the heat transfer plates 12 generally have the same outer dimensions.

[0033] As shown in FIG. 3, each of the heat transfer plates 12 has substantially flat base portions 13, which share a plane, and protrusions 14 protruding from the base portions 13. The protrusions 14 are, for example, formed by pressing, such as embossing or projecting. The protrusions 14 are formed as ribs and continuously extend in parallel to a longitudinal direction of the heat transfer plate 12.

[0034] In an example shown in FIG. 3, each of the protrusions 14 has a generally semi-circular shaped cross-section. However, the protrusion 14 can have any other cross-sectional shapes such as a substantially trapezoidal shape having rounded corners or the like.

[0035] The protrusion 14 forms a passage space therein for allowing the refrigerant to flow. In the present embodiment, the protrusions 14 form refrigerant passages 15, 16 through which a low pressure refrigerant that has passed through a decompressing device, such as an expansion valve, of a refrigerant cycle flows.

[0036] For example, the evaporator 10 is disposed such that the longitudinal direction of the heat transfer plates 12 corresponds to a direction of gravitational force when in use, that is, in an up and down direction. Therefore, the protrusions 14 extend in the up and down direction. In other words, the protrusions 14 extend perpendicular to the air flow direction A1.

[0037] The heat transfer plates 12 are disposed in pairs. In each of the pairs, one heat transfer plate (hereafter, a first heat transfer plate) 12 and the other heat transfer plate (hereafter, a second heat transfer plate) 12 have the protrusions 14 at the same positions with respect to the air flow direction A1. The first and second heat transfer plates 12 are disposed such that the protrusions 14 thereof protrude outwardly. The base portions 13 of the first and second heat transfer plates 12 are in contact with and joined to each other. Thus, both sides of the protrusions 14 with respect to the air flow direction A1 are sealed by the base portions 13.

[0038] The refrigerant passages 15, 16 are formed by the spaces defined by the opposed protrusions 14 of the first and second heat transfer plates 12. In the present embodiment, the refrigerant passages 15 are located at a downstream side of the heat transfer plates 12 with respect to the air flow direction A1, and the refrigerant passages 16 are located at an upstream side of the heat transfer plates 12 with respect to the air flow direction A1. Therefore, the refrigerant passages 15 are also referred to as air-downstream-side refrigerant passages 15 and the refrigerant passages 16 are also referred to as air-upstream-side refrigerant passages 16.

[0039] The heat transfer plates 12 are integrally formed with fin portions (hereafter, simply referred to as the fins) 17. The fins 17 are formed on the base portions 13 that are in contact with each other in the pair of heat transfer plates 12. The fins 17 are formed between the protrusions 14 with respect to the air flow direction A1, as shown in FIGS. 3 and 4. In the present embodiment, the fins 17 of the first heat transfer plate 12 are located at the same positions as the fins 17 of the second heat transfer plate 12 with respect to the air flow direction A1.

[0040] Also, the fins 17 are arranged at predetermined intervals in the up and down direction. In the example shown in FIGS. 3 and 4, the fins 17 are formed in one row in the up and down direction, between two of the adjacent protrusions 14. However, the fins 17 can be formed in plural rows or staggered manner between two of the adjacent protrusions 14.

[0041] The fins 17 are formed as slit fins, each of which has an offset wall 17a that is spaced from the plane or a surface of the base portions 13 by a predetermined distance, as shown in FIG. 4. In the slit fin, an opening is provided between the offset wall 17a and the base portion 13 such that the air can pass through, and the offset wall 17a is physically connected to the base portions 13 at least two or more locations.

[0042] In the example shown in FIG. 4, each offset wall 17a is parallel to the plane of the base portions 13. The upper and lower ends of the offset fin 17a are connected to the base portions 13 through side walls 17b, 17c. Thus, each fin 17 has a substantially U-shape.

[0043] As shown in FIG. 3, a projecting height of the offset wall 17a, that is, a fin height Fh of the fin 17 is substantially the same as a rib height Rh of the protrusion 14 or slightly smaller than the rib height Rh, for example.

[0044] Also, the fin 17 has a fin inner dimension Fhi that is defined by subtracting the thickness t of the heat transfer plate 12 from the fin height Fh (i.e., Fhi=Fh-t). The fin inner dimension Fhi corresponds to a width of the space defined between the plane of the base portions 13 and the offset wall 17a for allowing the air to pass through, that is, a dimension between the inner surface of the offset wall 17a and the plane of the base portions 13 in a direction perpendicular to the plane of the base portions 13. The fin 17 has a fin width Fw with respect to the air flow direction A1.

[0045] For example, each of the fins 17 is made in the following manner. First, two slits are formed on the base portion 13 with an interval corresponding to the fin width Fw. Then, a portion between the two slits is projected. Thus, the fin 17 has a substantially U-shape.

[0046] In this case, the portion is projected such that each of the side walls 17b, 17c is inclined by a predetermined angle 0 with respect to the surface of the base portion 13. Also, each of the side walls 17b, 17c has rounded corners, which is so-called R-shapes, with the base portion 13 and the offset wall 17a. Therefore, the fins 17 has a smooth projected shape. That is, the formation of the fins 17 is improved.

[0047] In view of the formation of the fins 17, for example, the fin width Fw is equal to or greater than 0.2 mm, and a fin distance Fd between the adjacent two fins 17 with respect to the air flow direction A1 is equal to or greater than 0.4 mm.

[0048] The substantially U-shape of the fin 17, that is, the shape of the slit fin corresponds to a cut and moved shape that provides a cut-out or opening on the base portion 13. That is, a cut-out opening (hereafter, simply referred to as the aperture) 17d is formed on the base portion 13 at a position corresponding to the fin 17 by forming the fin 17.

[0049] In the present embodiment, for example, a length G of the aperture 17d, that is, a dimension of the aperture 17d in the up and down direction is equal to or greater than 5 mm. Here, the dimension G of the aperture 17d includes dimensions of the rounded corners formed between the base portion 13 and the side walls 17b, 17c, as shown in FIG. 5.

[0050] The fins 17 are formed on the base portions 13, that is, at positions where the first and second heat transfer plates 12 are in contact with each other. Therefore, the formation of the apertures 17d will not cause leakage of the refrigerant from the refrigerant passages 15, 16.

[0051] However, if corrosion of the base portions 13 advances, the refrigerant will leak from the fin 17. To restrict the leakage of the refrigerant due to the corrosion, a difference of a dimension Bw of the base portion 13 with respect to the air flow direction A1 and the fin width Fw is equal to or greater than 0.3 mm (i.e., Bw-Fw.gtoreq.0.3 mm).

[0052] In other words, when the dimension of the base portion 13 on each side of the fin 17 with respect to the air flow direction A1 (i.e., a width of each of side sections of the base portion 13 on opposite sides of the fin 17) is equal to or greater than 0.15 mm as a margin for corrosion, the leakage of refrigerant due to corrosion of the base portions 13 is sufficiently reduced.

[0053] Also, to sufficiently maintain brazing of the base portion 13, the difference of the dimension Bw of the base portion 13 and the fin width Fw is equal to or greater than 1.0 mm, for example. That is, when the overlapping dimension (e.g., contact dimension or a margin for brazing) of the base portions 13 on each side of the fin 17 with respect to the air flow direction A1 is equal to or greater than 0.5 mm, the base portions 13 are sufficiently brazed.

[0054] In the present embodiment, the length of the fin 17, that is, a dimension of the fin 17 with respect to the up and down direction is greater than the fin width Fw with respect to the air flow direction A1. That is, the fins 17 have the length in the up and down direction.

[0055] As shown in FIG. 5, the positions of the fins 17 are displaced or staggered between the first and second heat transfer plates 12 with respect to the up and down direction such that the apertures 17d of the first heat transfer plate 12 partly overlap with the apertures 17d of the second heat transfer plate 12. That is, the apertures 17d of the first heat transfer plate 12 are partly in communication with the apertures 17d of the second heat transfer plate 12.

[0056] Due to mutual overlapping of the apertures 17d of the first and second heat transfer plates 12, a communication channel P that allows continuous communication between the inner spaces of the fins 17 in the up and down direction is formed. In the example shown in FIG. 5, the communication channel P is continuously formed in the up and down direction. However, it is not always necessary that the communication channel P is continuous across the length of the heat transfer plates 12. The communication space P may be suitably separated in the up and down direction.

[0057] In FIGS. 1 and 2, the fins 17 are not illustrated for the sake of simplification of the illustration. In the example shown in FIGS. 1 to 3, each of the heat transfer plates 12 as five protrusions 14. However, the number of the protrusions 14 of each heat transfer plate 12, that is, the number of the refrigerant passages 15, 16 can be modified according to conditions in use, such as a required performance, an outer shape, and the like.

[0058] Also, each of the heat transfer plates 12 has two upper tank parts 20, 22 at the upper end and two lower tank parts 21, 23 at the lower end. The upper tank parts 20, 22 are aligned generally in the air flow direction A1. Likewise, the lower tank parts 21, 23 are aligned generally in the air flow direction A1. The upper tank parts 20, 22 and the lower tank parts 21, 23 are separated in the refrigerant flow direction B. Hereafter, the upper tank part 20 is also referred to as the air-downstream-side upper tank part 20, the lower tank part 21 is also referred to as the air-downstream-side lower tank part 21, the upper tank part 22 is also referred to as the air-upstream-side upper tank part 22, and the lower tank part 23 is also referred to as the air-upstream-side lower tank part 23.

[0059] The tank parts 20 to 23 are formed such as by projecting. The tank parts 20 to 23 project in the same direction as the protrusions 14. A projection height of the tank parts 20 to 23, that is, a dimension of the tank parts 20 to 23 in a direction perpendicular to the plane of the base portions 13 is half of tube pitch Tp. Thus, when the pairs of the heat transfer plates 12 are stacked, ends of the tank parts 20 to 23 of one heat transfer plate 12 are in contact with ends of the tank parts 20 to 23 of opposed heat transfer plate 12 of the adjacent pair of heat transfer plates 12. The adjacent pairs of heat transfer plates 12 can be joined to each other at the ends of the tank parts 20 to 23.

[0060] Here, the projection height of the tank parts 20 to 23 includes the thickness t of the heat transfer plate 12. As shown in FIG. 3, the tube pitch Tp is arrangement intervals of the pairs of the heat transfer plates 12. Also, a space pitch Sp is a value that is defined by subtracting the thicknesses t of two heat transfer plates 12 from the tube pitch Tp (i.e., Sp=Tp-2t).

[0061] In FIG. 3, the rib height Rh of the protrusions 14 is smaller than a half of the tube pitch Tp, that is, smaller than the projection height of the tank parts 20 to 23, as an example. However, the rib height Rh can be modified. For example, the rib height Rh of the protrusions 14 can be substantially equal to or slightly larger than the projection height of the tank parts 20 to 23.

[0062] The tank parts 20 to 23 project in the same direction as the protrusions 14, and define spaces therein. Also, the longitudinal ends, such as upper and lower ends, of the protrusions 14 connect to the tank parts 20 to 23. That is, the spaces defined by the protrusions 14 are in communication with the spaces defined by the tank parts 20 to 23. Therefore, the ends of the air-upstream-side refrigerant passage 16 are in communication with the spaces defined by the air-upstream-side upper and lower tank parts 22, 23, respectively. Likewise, the ends of the air-downstream-side refrigerant passage 15 are in communication with the spaces defined by the air-downstream-side upper and lower tank parts 20, 21, respectively.

[0063] The spaces defined by the air-upstream-side upper tank part 22 and the air-downstream-side upper tank part 20 are separated from each other. Namely, the air-upstream-side upper tank part 22 and the air-downstream-side upper tank part 20 provide portions of the refrigerant passages separately. Likewise, the spaces defined by the air-upstream-side lower tank part 23 and the air-downstream-side lower tank part 21 are separated from each other. Namely, the air-upstream-side lower tank part 23 and the air-downstream-side lower tank part 21 provide portions of the refrigerant passages separately.

[0064] Each of the tank parts 20 to 23 is formed with a communication opening 20a to 23a at a substantially middle portion thereof. When the pairs of the heat transfer plates 12 are stacked such that the ends of the tank parts 20 to 23 are in contact with each other between the adjacent pairs of the heat transfer plates 12, the spaces defined by the respective tank parts 20 to 23 are communicated with each other through the openings 20a to 23a.

[0065] Therefore, the refrigerant passages defined by the tank parts 20 to 23 are communicated with each other between the adjacent heat transfer plates 12 with respect to the plate stacking direction, such as, a substantially right and left direction of FIGS. 1 and 2. In other words, four tank spaces are provided by the tank parts 20 to 23 in the plate stacking direction, respectively.

[0066] Also, as shown in FIG. 3, the positions of the protrusions 14 are staggered in the air flow direction A1 between the adjacent pairs of the heat transfer plates 12. Therefore, the protrusions 14 of one of the pairs of the heat transfer plates 12 are opposed to the base portions 13 of the adjacent pair of the heat transfer plates 12. In the example shown in FIG. 3, the protrusions 14 of one pair of the heat transfer plates 12 are located to correspond to middle positions of the base portions 13 of the adjacent pair of the heat transfer plates 12. That is, the protrusions 14 of one pair of the heat transfer plates 12 are located to correspond to the center of the rib pitch Rp of the adjacent pair of the heat transfer plates 12.

[0067] As described above, the rib height Rh of the protrusions 14 is generally half of the tube pitch Tp. Therefore, a clearance is provided between top portions of the protrusions 14 of one pair of the heat transfer plates 12 and the base portions 13 of the adjacent pair of heat transfer plates 12, in the plate stacking direction.

[0068] As such, an air passage 18 is provided between the adjacent pairs of the heat transfer plates 12 continuously across the width of the heat transfer plates 12 in the air flow direction A1. As shown by an arrow A2 in FIG. 3, the air can flow through the air passage 18 in a meandering or serpentine manner. The fins 17 are located adjacent to the protrusions 14, within the air passage 18.

[0069] In the example shown in FIG. 3, the fins 17 are located at the center of the rib pitch Rp of the base portions 13, that is, located at middle portions between the protrusions 14 adjacent in the air flow direction A1. Therefore, an outer surface of the offset wall 17a of each fin 17 is opposed to the outer surface of the protrusion 14, which is adjacent to the offset wall 17a across the air passage 18, across a predetermined distance X.

[0070] Although not illustrated, the heat transfer plates 12 have contact ribs that project from the base portions 13 toward the adjacent heat transfer plates 12 across the air passages 18. The contact ribs are in the form of small projection having smooth semi-circular shapes, and project from the base portions 13 and at positions between the fins 17.

[0071] The contact ribs have a projection height that is substantially the same as the rib height Rh of the protrusions 14. The contact ribs of one heat transfer plate 12 are in contact with the tops of the protrusions 14 of another heat transfer plates 12 that is adjacent across the air passage 18. The evaporator 10 is integrally brazed in the condition that the contact ribs are in contact with the tops of the protrusion 14 of the adjacent heat transfer plates and a pressing force is exerted to the contact portions between the contact ribs and the protrusions 14 in the plate stacking direction.

[0072] Since the brazing is performed in a condition that the adjacent heat transfer plates 12 contact at the middle portions where the refrigerant passages 15, 16 are formed, in addition to the tank parts 20 to 23, the base portions 13 are sufficiently brazed. Since the heat transfer plates 12 are sufficiently brazed, it is less likely that the refrigerant will leak from the refrigerant passages 15, 16 due to insufficient brazing.

[0073] To sufficiently contact the base portions 13 of the heat transfer plates 12, the contact ribs are formed separately and at plural locations in the longitudinal direction of the heat transfer plates 12.

[0074] Next, structures of inlet and outlet parts of the refrigerant will be described. As shown in FIGS. 1 and 2, the evaporator 10 has first and second end plates 24, 25 at the ends of the stacked heat transfer plates 12. The first and second end plates 24, 25 have the same size as the heat transfer plates 12. Each of the first and second end plates 24, 25 has a generally flat plate shape. The first and second end plates 24, 25 are joined to the end heat transfer plates 12 such that inner surfaces thereof contacts the surfaces of the first and second end plates 24, 25 on which the tank parts 20 to 23 are formed.

[0075] The first end plate 24, which is disposed on a left end in FIG. 1, has openings adjacent to its upper end. A refrigerant inlet pipe 24a and a refrigerant outlet pipe 24b are coupled to and joined to the openings of the first end plate 24. The refrigerant inlet pipe 24a is disposed on a downstream side of the refrigerant outlet pipe 24b with respect to the air flow direction A1. The refrigerant inlet pipe 24a is in communication with the opening 20a of the air-downstream-side upper tank part 20 of the leftmost heat transfer plate 12, which is located at the left end in FIG. 1. The refrigerant outlet pipe 24b is in communication with the opening 22a of the air-upstream-side upper tank part 22 of the leftmost heat transfer plate 12.

[0076] The first end plate 24 is made of an aluminum clad plate, both surfaces of which are clad with the brazing material, similar to the heat transfer plates 12. Thus, the first end plate 24 is joined to the refrigerant inlet and outlet pipes 24a, 24b and the heat transfer plate 12 by brazing. On the other hand, the second end plate 25 is made of a clad plate in which only one surface to be joined with the heat transfer plate 12 is clad with the brazing material.

[0077] A gas and liquid two-phase, low pressure refrigerant, which has been decompressed by the decompressing device (not show), flows in the refrigerant inlet pipe 24a. On the other hand, the refrigerant outlet pipe 24b is in communication with a suction side of a compressor (not shown). Thus, a gas phase refrigerant, which has been evaporated in the evaporator 10, is introduced to the compressor from the refrigerant outlet pipe 24b.

[0078] The air-downstream-side refrigerant passages 15, which are defined between the protrusions 14 of the paired heat transfer plates 12, are in communication with the refrigerant inlet pipe 24a. The refrigerant flows in the air-downstream-side refrigerant passages 15 from the refrigerant inlet pipe 24a. Thus, the air-downstream-side refrigerant passages 15 provide inlet-side refrigerant passages in the whole of the evaporator 10.

[0079] On the other hand, the air-upstream-side refrigerant passages 16 are in communication with the refrigerant outlet pipe 24b. The refrigerant that has passed through the air-downstream-side refrigerant passages 15, that is, the inlet-side refrigerant passages, flows in the air-upstream-side refrigerant passages 16, and then flows out from the evaporator 10 from the refrigerant outlet pipe 24b. Therefore, the air-upstream-side refrigerant passages 16 provide outlet-side refrigerant passages.

[0080] The refrigerant generally flows through the evaporator 10 as shown by arrows Pa through Pk in FIG. 2. In this case, the air-downstream-side upper tank parts 20 provide a refrigerant inlet-side upper tank space, and the air-downstream-side lower tank parts 21 provide a refrigerant inlet-side lower tank space. Also, the air-upstream-side upper tank parts 22 provide a refrigerant outlet-side upper tank space, and the air-upstream-side lower tank parts 23 provide a refrigerant outlet-side lower tank space.

[0081] Although not illustrated, a separation part is provided at a middle portion of the stack of the heat transfer plates 12 such that the stack of the heat transfer plates 12 is generally divided into a left section (first section) Y1 and a right section (second section) Y2. Thus, the refrigerant inlet-side upper tank space, which is provided by the air-downstream-side upper tank parts 20, is separated into a left passage space and a right passage space by the separation part. Likewise, the refrigerant outlet-side tank space, which is provided by the air-upstream-side upper tank parts 22, is separated into a left passage space and a right passage space by the separation part.

[0082] For example, the separation part is constructed by closing the openings 20a, 22a of the middle heat transfer plate 12 that is located at the middle of the stack of the heat transfer plates 12.

[0083] In the evaporator 10, first, the gas and liquid two-phase refrigerant flows in the refrigerant inlet-side tank space from the refrigerant inlet pipe 24a, as shown by the arrow Pa. Since the refrigerant inlet-side tank space is separated into the left passage space and the right passage space by the separation part, the refrigerant only flows in the left passage space of the refrigerant inlet-side tank space.

[0084] Then, the refrigerant flows through the inlet-side refrigerant passages 15 of the left section Y1 in a downward direction as shown by the arrow Pb, and flows in the refrigerant inlet-side lower tank space, which is provided by the air-downstream-side lower tank parts 21. In the refrigerant inlet-side lower tank space, the refrigerant flows in a rightward direction, that is, toward the right section Y2, as shown by the arrow Pc.

[0085] Then, the refrigerant flows through the inlet-side refrigerant passages 15 of the right section Y2 in an upward direction as shown by the arrow Pd, and flows in the right passage space of the refrigerant inlet-side upper tank space. The opening 20a of the air-downstream-side upper tank part 20 of the rightmost heat transfer plate 12 is in communication with the opening 22a of the air-upstream side upper tank part 22 through a communication passage (not shown) formed on an upper portion of the second end plate 25.

[0086] Therefore, the refrigerant flows in the rightward direction in the right passage space of the refrigerant inlet-side upper tank space as shown by the arrow Pe, and then flows in the right passage space of the refrigerant outlet-side upper tank space through the communication passage of the right end plate 25 as shown by the arrow Pf.

[0087] Since the refrigerant outlet-side upper tank space is separated into the left passage space and the right passage space by the separation part, the refrigerant only flows in the right passage space of the refrigerant outlet-side upper tank space from the communication passage, as shown by the arrow Pg. Then, the refrigerant flows through the outlet-side refrigerant passages 16 of the right section Y2 in the downward direction as shown by the arrow Ph. The refrigerant flows in the refrigerant outlet-side lower tank space and moves in the rightward direction as shown by the arrow Pi.

[0088] Thereafter, the refrigerant flows through the outlet-side refrigerant passages 16 of the left section Y1 in the upward direction as shown by the arrow Pj, and flows in the left passage space of the refrigerant outlet-side upper tank space. The refrigerant flows toward the refrigerant outlet pipes 24b as shown by the arrow Pk, and flows out from the evaporator 10.

[0089] In manufacturing the evaporator 10, the component parts, such as the heat transfer plates, 12, the first and second end plates 24, 25 and the refrigerant inlet and outlet pipes 24a, 24b, are assembled to make contact at predetermined portions thereof. The assembled component parts are held in the above condition by predetermined jigs and placed in a furnace. When the assembled component parts are heated to a melting point of the brazing material, the component parts are integrally brazed. Thus, the evaporator 10 is integrally brazed.

[0090] Next, an operation of the evaporator 10 will be described. For example, the evaporator 10 is housed in an air conditioning unit case (not shown) such that the up and down direction in FIGS. 1 and 2, that is, the longitudinal direction of the heat transfer plates 12 corresponds to the vertical direction. When a blower (not shown) for the air conditioning operation is operated, the air passes through the evaporator as shown by the arrow A1.

[0091] When the compressor of the refrigerant cycle is operated, the gas and liquid two-phase refrigerant is introduced to the evaporator 10 from the decompression device, such as the expansion valve. Thus, the refrigerant passes through the evaporator 10 as shown by the arrows Pa through Pk.

[0092] Since the air passages 18 are formed between the heat transfer plates 12, the air blown by the blower flows through the air passages 18 in the meandering manner, as shown by the arrow A2. At this time, the refrigerant is evaporated by receiving latent heat of evaporation from the air, and the air is cooled.

[0093] In this case, the inlet-side refrigerant passages 15 are disposed downstream of the outlet-side refrigerant passages 16 with respect to the air flow direction A1. Therefore, the arrangement of the inlet and outlet of the refrigerant is opposed to the flow of the air. Namely, the general flow direction of the refrigerant is opposed to the general air flow direction.

[0094] The air flow direction A1 is substantially perpendicular to the longitudinal direction of the protrusions 14. The protrusions 14 provide heat transfer surfaces protruding from the base portions 13 and intersecting with the air flow direction A1. Thus, the flow of the air is obstructed and disturbed by the protrusions 14. Accordingly, a coefficient of heat transfer of the air is improved on the heat transfer surfaces of the protrusions 14.

[0095] In a plate-type heat exchanger in which a core part is constructed of heat transfer plates, heat transfer surfaces of air are smaller than that of a fin and tube-type heat exchanger in which a core part is constructed of tubes and fins. Therefore, it is generally difficult to sufficiently maintain a necessary heat transfer performance.

[0096] In the evaporator 10 of the present embodiment, the fins 17 are formed on the heat transfer plates 12. The fins 17 have the substantially U-shapes and disposed between the adjacent protrusions 14 and in the air passages 18. Since the air flows along both inner surfaces and outer surfaces of the offset walls 17a, the heat transfer surface area increases, as compared with a plate-type heat exchanger without having the fins.

[0097] Further, the coefficient of heat transfer of the air is improved at the base portions 13 due to the fins 17. For example, in the case where the fins are not formed on the base portions 13, a temperature boundary layer progresses and becomes thick toward downstream positions with respect to the air flow direction A1. Thus, the coefficient of heat transfer of the air on the base portions 13 is likely to reduce.

[0098] On the other hand, in the present embodiment, since the fins 17 are formed on the base portions 13 between the adjacent protrusions 14, the thickness of the temperature boundary layer on the flat surfaces of the base portions 13 is reduced. Therefore, the coefficient of heat transfer of the air at the base portions 13 improves, as compared with the base portions 13 without having the fins 17.

[0099] Accordingly, even in the plate-type heat exchanger, the heat transfer efficiency is effectively improved while suppressing an increase in resistance to flow of the air.

[0100] In the present embodiment, the side walls 17b, 17c of the fins 17 are inclined at predetermined angles .theta. relative to the plane of the base portions 13 so as to ease the formation of the fins 17. However, the length FL of the offset wall 17a in the up and down direction is reduced, as compared with a case in which the side walls of the fin are perpendicular to the base portion. Therefore, the heat transfer efficiency will be reduced due to the decrease of the length FL of the offset wall 17a.

[0101] Thus, to improve the formation of the fins 17 as well as to improve the heat transfer efficiency, for example, the predetermined angle .theta. of the inclination of each side wall 17b, 17c can be set in a range between equal to or greater than 30 degrees and equal to or less than 60 degrees.

[0102] Here, the length FL of the offset wall 17a is a dimension of a flat portion of the inner surface of the offset wall 17a in the up and down direction. That is, the length FL of the offset wall 17a does not include the dimensions of the rounded corners formed between the offset wall 17a and the side walls 17b, 17c.

[0103] Next, an effect of draining condensation of the evaporator 10 will be described. In the evaporator 10, moisture in the air is condensed due to a cooling effect, and hence condensation is generated. The condensation tends to accumulate on an inner portion of the fin 17, in particular, an inner area of the lower side walls 17c, as shown by an area M in FIG. 5.

[0104] FIG. 6 shows a comparative example in which the fins 17 of the first and second heat transfer plates 12 are disposed at the same positions with respect to the up and down direction. In the comparative example, the condensation is blocked by the lower side walls 17c. Thus, the drainage of the condensation is restricted. In other words, the condensation is received by the lower side walls 17c.

[0105] In the present embodiment shown in FIG. 5, on the other hand, the positions of the fins 17 are staggered between the paired heat transfer plates 12 in the up and down direction such that the continuous communication channel P is formed within the fins 17. Therefore, the condensation generated on the inner side of the fins 17 smoothly flows downwardly as shown by the arrow N through the communication channel P, without being blocked by the lower side walls 17c. In other words, a drainage channel for draining the condensation is provided by the communication channel P. Accordingly, the condensation is effectively discharged.

[0106] Further, in a case that the dimension G of the aperture 17d of the fin 17 is 5 mm or more in the up and down direction, the condensation is more effectively discharged.

[0107] Since the side walls 17b, 17c and the base portions 13 form the rounded corners, the communication space P is formed into a smoothly curved shape. Therefore, the condensation is smoothly discharged.

[0108] FIG. 7A is a graph showing the amount of accumulation of condensation per fin of the comparative example. FIG. 7B is a graph showing the amount of accumulation of condensation per fin of the present embodiment. As shown in FIGS. 7A and 7B, the amount of accumulation of condensation per fin of the present embodiment is generally half of or one-third of that of the comparative example.

[0109] FIG. 8 is a graph showing a relationship between the fin height Fh and the amount of accumulation of condensation per fin. A horizontal axis represents the fin height Fh and a vertical axis represents the amount of accumulation of condensation per fin. In this case, the fin width Fw is 1.5 mm.

[0110] As shown by two curves of FIG. 8, when the fin height Fh is smaller than 0.35 mm, the amount of accumulation of condensation per fin 17 of the present embodiment is larger than that of the comparative example. This is caused by the following reasons.

[0111] In the present embodiment, a width of the communication channel P defined between the base portion 13 and the offset wall 17a, that is, a dimension of the communication channel P in the direction perpendicular to the plane of the base portion 13, is substantially equal to the fin height Fh, as shown in FIG. 5. In the comparative example, on the other hand, a width of a space defined between the fins 17, that is, a space where the condensation stays (hereafter, condensation accumulating space) in the direction perpendicular to the plane of the base portion 13 is twice of the fin height Fh, as shown in FIG. 6.

[0112] In the present embodiment, if the fin height Fh is smaller than necessary, the condensation cannot easily flow through the communication channel P. As a result, the flow of the condensation will be stagnated throughout the communication channel P, although the condensation will not accumulated only at the uppermost portion of the communication channel P.

[0113] In the comparative example, since the width of the condensation accumulating space is larger than the width of the communication channel P of the present embodiment. Therefore, the condensation does not accumulate at the upper portion of each condensation accumulating space. As a result, the amount of accumulation of condensation per fin of the comparative example is relatively smaller than that of the present embodiment.

[0114] Therefore, when the fin height Fh is smaller than 0.35 mm, the amount of accumulation of condensation per fin of the present embodiment is larger than that of the comparative example. On the other hand, when the fin height Fh is equal to or greater than 0.35 mm, the amount of accumulation of condensation per fin of the present embodiment is smaller than that of the comparative example. Thus, the draining effect of the present embodiment is improved.

[0115] In the present embodiment, the thickness t of the heat transfer plates 12 is 0.2 mm. Therefore, when the fin height Fh is 0.35 mm or more, the fin inner height Fhi is equal to or greater than 0.15 mm. In other words, when the width of the space defined between the offset wall 17a and the base portion 13 is equal to or greater than 0.15 mm, the amount of accumulation of condensation per fin of the present embodiment is smaller than that of the comparative example. Thus, the draining effect is improved.

[0116] The above idea can be applied to set the clearance between the offset wall 17a of the fin 17 and the surface of the heat transfer plate 12. For example when the distance X between the outer surface of the offset wall 17a and the outer surface of the protrusion 14 that is opposed to the fin 17 across the air passage 18 is equal to or greater than 0.15 mm, the amount of accumulation of condensation in the clearance will be reduced. As such, the draining effect is improved.

[0117] In FIGS. 7A, 7B and 8, the amount of accumulation of condensation is measured in the following conditions.

[0118] (1) Outer size of the evaporator of the present embodiment and the comparative example: width is 260 mm; height is 215 mm; and depth is 38 mm. Here, the width is a dimension in the plate stacking direction, as shown by an arrow W in FIG. 2. The height is a dimension as shown by an arrow H in FIG. 2. Also, the depth is a dimension in the air flow direction A1, as shown by an arrow D in FIG. 2.

[0119] (2) The volume of air is 500 m.sup.3/h. Resistance of air flow at the core part is equal between the evaporator of the present embodiment and the comparative example.

[0120] (3) Regarding the comparative example, the thickness t of the heat transfer plate is 0.15 mm; the space pitch Sp is 2.6 mm; the rib pitch Rh is 7.1 mm; and the protrusion height Rh is 1.45 mm.

[0121] (4) Regarding the evaporator of the present embodiment, the thickness t of the heat transfer plate 12 is 0.15 mm; the space pitch Sp is 3.0 mm; the rib pitch Rp is 7.1 mm; the protrusion height Rh is 1.45 mm, the fin height Fh is 1.0 mm; and the fin width Fw is 0.8 mm. Here, the fin pitch Fp is a half of the rib pitch Rp.

[0122] In the example shown in FIG. 3, the heat transfer plates 12 have the fins 17 downstream of the most downstream protrusions 14 with respect to the air flow direction A1. However, it is not always necessary to have the fin 17 downstream of the most downstream protrusion 14 with respect to the air flow direction A1.

[0123] In a case that the fins 17 are not provided downstream of the most downstream protrusions 14 with respect to the air flow direction A1, even if the condensation in the fins 17 is blown by the air pressure, the blown condensation will adhere to the protrusion 14 that is located downstream of the fins 17 and discharged along the protrusions 14 in the downward direction. Therefore, scattering of the condensation in the fins 17 will be reduced.

[0124] In the present embodiment, the heat transfer plate 12 has a basically flat shape and the protrusions 14, the fins 7, the tank parts 20 to 23 and the like are formed to project from the flat wall. That is, the base portions 13 are coplanar. However, it is not always necessary that the base portions 13 are coplanar. Alternatively, the middle portions of the heat transfer plates 12 other than the tank parts 20 to 23, that is, portions of the heat transfer plates 12 forming the core part 11 may have the wave shape, which includes smoothly curves walls, instead of the flat wall. Also in this case, the similar effects as the present embodiment will be provided.

Second Embodiment

[0125] The evaporator 10 according to the second embodiment is similar to the evaporator 10 of the first embodiment except a configuration of the offset wall 17a. In the first embodiment, the offset walls 17a are parallel to the plane of the base portions 13. In the second embodiment, on the other hand, the offset walls 17a are inclined relative to the plane of the base portions 13, with respect to the up and down direction.

[0126] As shown in FIG. 9, each of the offset walls 17a is inclined at a predetermined angle .theta.a relative to the plane of the base portion 13 such that a distance between the offset wall 17a and the plane of the base portion 13 increases toward an upper position. As such, the condensation in the fin 17 of one heat transfer plate 12 is smoothly introduced into the fin 17 of the opposite heat transfer plate 12, as shown by the arrow N. Accordingly, the condensation is further smoothly drained.

Third Embodiment

[0127] The evaporator 10 according to the third embodiment is similar to the evaporator 10 of the first embodiment except a configuration of the offset wall 17a. In the third embodiment, the offset walls 17a are inclined relative to the plane of the base portions 13, with respect to the air flow direction A1, as shown in FIG. 10.

[0128] For example, each of the offset walls 17a is inclined in the same direction as a downstream side curved wall of the semi-circular-shaped protrusion 14. In other words, the off set wall 17a is inclined toward a downstream position with respect to the air flow direction A1. Specifically, the offset wall 17a forms an angle .theta.b of inclination relative to the plane of the base portion 13 such that a distance between the offset wall 17a and the plane of the base portion 13 increases toward an upstream position with respect to the air flow direction A1.

[0129] In this case, the flow of the air is aligned along the downstream side curved wall of the protrusion 14 due to a guide effect of the inclined offset walls 17a. Therefore, separation of the air flow from the surface of the heat transfer plate 12 at a position downstream of the protrusion 14 is reduced, as shown by an arrow Q1 in FIG. 10. Namely, a decrease of the coefficient of heat transfer due to the separation of the air flow is reduced. Accordingly, the heat transfer efficiency further improves. Also in this case, the offset wall 17a can be further inclined with respect to the up and down direction, in a manner similar to the second embodiment.

Fourth Embodiment

[0130] The evaporator 10 according to the fourth embodiment is similar to the evaporator 10 of the third embodiment, but is different because the offset wall 17a has a curved shape to align the air flow along the meandering shape of the air passage 18.

[0131] As shown in FIG. 11, the offset wall 17a is curved inwardly such that a distance between the offset wall 17a and the plane of the base portion 13 reduces toward a middle portion with respect to the air flow direction A1. Therefore, the air flow can be aligned along the curved surfaces of the protrusions 14 due to a guide effect of the curved shape of the offset wall 17a, as shown by the arrow A2. Therefore, it is less likely that the air flow will be separated from the surface of the heat transfer plate 12 at the upstream and downstream positions of the protrusions 14 with respect to the air flow direction A1, as shown by arrows Q1, Q2. Accordingly, the decrease of the coefficient of heat transfer due to the separation of the air flow is further reduced than that of the third embodiment. Therefore, the heat transfer efficiency further improves.

Fifth Embodiment

[0132] The evaporator according to the fifth embodiment 10 is similar to the evaporator 10 of the first embodiment except the shape of the fins 17. The shape of the fins 17 is not limited to the substantially U-shape as illustrated in FIG. 5, but may be modified.

[0133] For example, the fin 17 is formed to project in a smoothly curved shape, as shown in FIG. 12. In this case, the offset wall 17a is a curved wall projecting from the base portion 13 in the form of a substantially semi-circular or semi-elliptical shape. Both ends of the curved wall connects to the base portions 13. Since the shape of the fin 17 is smooth or gentle, the formation of the fin 17 by projecting improves.

Sixth Embodiment

[0134] The evaporator 10 according to the sixth embodiment is similar to the evaporator 10 of the first embodiment except the following structures. In the first embodiment, both the first and second heat transfer plates 12 have the fins 17. Alternatively, in the sixth embodiment, only one of the first and second heat transfer plates 12 has the fins 17.

[0135] For example, as shown in FIG. 13, the first heat transfer plate (left heat transfer plate) 12 has the fins 17. However, the second heat transfer plate (right heat transfer plate) 12, which is paired with the first heat transfer plate 12, does have the fins 17. Instead, the second heat transfer plate 12 is formed with apertures 13a at the positions corresponding to the fins 17 of the first heat transfer plate 12. The apertures 13a is, for example, formed by punching. Also in this case, the fins 17 and the apertures 13a are disposed at plural locations in the up and down direction.

[0136] In the example shown in FIG. 13, the aperture 13a is located within an area of the aperture 17d of the fin 17 with respect to the up and down direction. In other words, the aperture 17d and the aperture 13a are disposed to overlap at least at a part between the first and second heat transfer plates 12.

[0137] As such, the inner space of the fin 17 of the first heat transfer plate 12 is in communication with an outer space of the heat transfer plates 12 through the aperture 13a. Therefore, the condensation in the inner space of the fin 17 can be introduced to the outside of the heat transfer plates 12. The condensation will further flows in the downward direction, as shown by an arrow T. In other words, a drainage channel for draining the condensation can be provided by the inner spaces of the fins 17. Accordingly, the condensation will be effectively discharged.

[0138] For example, in a case that the dimension G of the aperture 17d of the fin 17 in the up and down direction is equal to or greater than 5, the condensation is further effectively drained. In a case that a dimension K of the aperture 13a in the up and down direction is equal to or grater than the fin width Fw of the fin 17, the condensation can be effectively discharged to the outside of the heat transfer plates 12 through the apertures 13a. Therefore, the draining effect further improves. Further, in a case that a dimension of the aperture 13a with respect to the air flow direction A1 is equal to or greater than the fin width Fw of the fin 17, the draining effect further improves.

Seventh Embodiment

[0139] The evaporator 10 according to the seventh embodiment is similar to the evaporator 10 of the sixth embodiment, but positions of the apertures 13a and the fins 17 are modified.

[0140] As shown in FIG. 14, the respective aperture 13a is located slightly lower than the corresponding apertures 17d of the fin 17. Specifically, a lower end 13b of each aperture 13a is located lower than a lower end 17e of the corresponding aperture 17d, with respect to the up and down direction.

[0141] Since the lower end 17e of the aperture 17d overlaps with the aperture 13a, the condensation can be smoothly discharged from the lower end 17e of the fin 17 to the outside of the heat transfer plates 12 through the aperture 13a. As such, the condensation will be effectively drained.

[0142] In the example shown in FIG. 14, an upper end 13c of the aperture 13a is located lower than an upper end 17f of the aperture 17d, with respect to the up and down direction. Alternatively, the upper end 13c of the aperture 13a can be at the same height as the upper end 17f of the aperture 17d or located higher than the upper end 17f of the aperture 17d.

[0143] (Modifications)

[0144] In the above embodiments, the protrusions 14 are located at the same positions between the paired heat transfer plates 12 with respect to the air flow direction A1. Alternatively, the protrusions 14 can be located at different positions with respect to the air flow direction A1 between the paired heat transfer plates 12. For example, the protrusions 14 can be disposed in a staggered manner between the paired heat transfer plates 12 with respect to the air flow direction A1.

[0145] In the above embodiments, the protrusions 14 extend in the up and down direction, that is, in the direction of gravitational force. Here, "the up and down direction" and "the direction of gravitational force" should not mean exactly a direction of gravitational force, but may be slightly inclined. That is, the meaning of "the up and down direction" and "the direction of gravitational force" include directions that are slightly inclined from the exact direction of the gravitational force.

[0146] In the above embodiments, the protrusions 14 extend to the up and down direction. However, it is not always necessary that the longitudinal direction of the protrusions 14 correspond to the up and down direction. The protrusions 14 can extend in a direction that intersect with the air flow direction A1. For example, the protrusions 14 can extend diagonally with respect to the up and down direction.

[0147] In the second embodiment shown in FIG. 9, the offset wall 17a is inclined relative to the plane of the base portion 13, with respect to the up and down direction. In the third embodiment shown in FIG. 10, the offset wall 17a is inclined relative to the plane of the base portion 13, with respect to the air flow direction A1. Alternatively, the offset wall 17a can be configured by combination of the structures of the second and third embodiments. That is, the offset wall 17a can be inclined with respect to the up and down direction and the air flow direction A1.

[0148] In the fourth embodiment, the offset wall 17a has the curved shape to align the air flow along the serpentine shape of the air passage 18. Alternatively, the offset wall 17a can have a shape combined with the shape of the second embodiment and the shape of the fourth embodiment.

[0149] In the above embodiments, the core part 11 and the tank spaces are integrally formed by the stack of the heat transfer plates 12. Alternatively, the core part 11 can be formed by the stack of the heat transfer plates 12 and the tank spaces can be formed separately from the core part 11.

[0150] In the above embodiments, two separate heat transfer plates 12 are paired and joined to each other, and the refrigerant passages 15, 16 are formed inside of the protrusions 14 of the heat transfer plates 12. Alternatively, the pair of heat transfer plates 12 can be formed by folding a single plate member on which protrusions for the refrigerant passages are formed into two and joining the folded plate at the base portions, in a manner similar to the plates shown in FIG. 36 of U.S. Pat. No. 6,401,804 (Japanese Unexamined Patent Publication No. 2001-41678).

[0151] Further, the pairs of the heat transfer plates 12 can be connected through connecting members, in a similar manner as a structure shown in FIG. 35 of U.S. Pat. No. 6,401,804.

[0152] In the above embodiments, "the pair of heat transfer plates 12" and "the paired heat transfer plates 12" include both the case in which two separate plates 12 are joined and the case in which a single plate is folded and joined at predetermined portions.

[0153] In the sixth and seventh embodiments, the fins 17 are formed on the first heat transfer plate 12 and the apertures 13a are formed on the second heat transfer plate 12. However, the fins 17a and the apertures 13a can be formed on both of the first and second heat transfer plates 12. For example, the fins 17 and the apertures 13a are formed on the first heat transfer plate 12 alternately in rows, and the fins 17 and the apertures 13a are formed on the second heat transfer plate 12 alternately in rows. The first and second heat transfer plates 12 are joined such that the rows of the fins 17 and the rows of the apertures 13a of the first heat transfer plate 12 respectively correspond to the rows of the apertures 13a and the rows of the fins 17 of the second heat transfer plate 12. Also in this case, the similar effects are provided.

[0154] In the sixth and seventh embodiments, the fins 17 can have any shapes and arrangement structures as those of the fins 17 of the first to fifth embodiments.

[0155] In the above embodiments, the heat exchanger 10 is exemplarily employed to the evaporator in which a low pressure, low temperature refrigerant of the refrigerant cycle flows through the refrigerant passages 15. However, the fluid flowing through the refrigerant passages (internal fluid passages) are not limited to the refrigerant, but may be any other cooling fluid, such as a cool water or the like. Namely, the heat exchanger of the above embodiments can be employed as any cooling heat exchangers used for any other purposes.

[0156] Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader term is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

Claims

1. A heat exchanger for performing heat exchange between air flowing outside thereof and an internal fluid flowing inside thereof, thereby cooling the air, comprising: a first heat transfer plate; and a second heat transfer plate, wherein each of the first and second heat transfer plates includes a base portion defining a plane in a flow direction of the air and a plurality of protrusions protruding from the base portion and extending in a direction that intersects with the flow direction of the air, the protrusions defining internal fluid passages therein for allowing the internal fluid to flow, the first and second heat transfer plates are joined to each other such that the base portions are in contact with each other, the protrusions of the first heat transfer plate protrude in one direction and the protrusions of the second heat transfer plate protrude in an opposite direction, each of the first and second heat transfer plates further includes a fin portion projecting from the base portion in the same direction as the protrusions thereof and an aperture on the base portion at a position corresponding to the fin portion, the fin portion includes an offset wall that is offset from the base portion and defines a fin inner space therein, the offset wall is connected to the base portion at two locations that are spaced in a direction parallel to a longitudinal direction of the protrusions, and the aperture of the first heat transfer plate is displaced from the aperture of the second heat transfer plate with respect to the longitudinal direction of the protrusions, and the fin inner space of the first heat transfer plate is in communication with the fin inner space of the second heat transfer plate through the apertures, such that a communication channel for draining condensation is provided between the first and second heat transfer plates.

2. The heat exchanger according to claim 1, wherein the fin portion has a fin height in a direction perpendicular to the plane of the base portion, the fin height being equal to or greater than 0.35 mm.

3. The heat exchanger according to claim 1, wherein each of the first and second heat transfer plates has a plurality of fin portions including the fin portion, the plurality of fin portions is disposed in the flow direction of the air such that a plurality of communication channels including the communication channel is disposed in the flow direction of the air.

4. A heat exchanger for performing heat exchange between air flowing outside thereof and an internal fluid flowing inside thereof, thereby cooling the air, the heat exchanger comprising: a first heat transfer plate including a base portion that defines a plane in a flow direction of the air, a plurality of protrusions that protrudes from the base portion and extends in a direction intersecting with the flow direction of the air, a fin portion that projects from the base portion in a same direction as the protrusions and defines a fin inner space therein, and a first aperture on the base wall at a position corresponding to the fin portion, the fin portion including an offset wall that is offset from the base portion, the offset wall connected to the base portion at two locations that are separated in a longitudinal direction of the protrusions; and a second heat transfer plate including a base portion that defines a plane in the flow direction of the air, a plurality of protrusions that protrudes from the base portion and extends in a direction intersecting with the flow direction of the air, and a second aperture, wherein the first heat transfer plate and the second heat transfer plate are joined to each other such that the base portions thereof are in contact with each other, the protrusions of the first heat transfer plate protrude in one direction and the protrusions of the second heat transfer plate protrude in an opposite direction, the protrusions of the first and second heat transfer plates define internal fluid passages therein for allowing the internal fluid to flow, and the first aperture and the second aperture overlap at least at a part.

5. The heat exchanger according to claim 4, wherein the first heat transfer plate includes a plurality of fin portions including the fin portion and a plurality of first apertures including the first aperture, the plurality of fin portions being disposed in the longitudinal direction of the protrusions, the plurality of first apertures being disposed in the longitudinal direction of the protrusions, and the second heat transfer plate includes a plurality of second apertures including the second aperture, the plurality of second apertures being disposed in the longitudinal direction of the protrusions.

6. The heat exchanger according to claim 4, wherein a dimension of the second aperture in the longitudinal direction of the protrusions is equal to or greater than a width of the fin portion in the flow direction of the air.

7. The heat exchanger according to claim 4, wherein a dimension of the second aperture in the flow direction of the air is equal to or greater than a width of the fin portion in the flow direction of the air.

8. The heat exchanger according to claim 4, wherein the second aperture is disposed such that a lower end thereof is located lower than a lower end of the first aperture.

9. The heat exchanger according to claim 4, wherein the first heat transfer plate includes a plurality of fin portions including the fin portion and a plurality of first apertures including the first aperture, the plurality of fin portions being disposed in the flow direction of the air, the plurality of first apertures being disposed in the flow direction of the air, the second heat transfer plate includes a plurality of second apertures including the second aperture, the plurality of second apertures being disposed in the flow direction of the air, and each of the plurality of first apertures overlaps with a corresponding one of the plurality of second apertures, at least, at a part.

10. The heat exchanger according to claim 3, wherein the plurality of fin portions is spaced in the flow direction of the air, and a distance between adjacent two fin portions is equal to or greater than 0.4 mm.

11. The heat exchanger according to claim 1, wherein a dimension of each aperture in the longitudinal direction of the protrusions is equal to or greater than 5 mm.

12. The heat exchanger according to claim 1, wherein the offset wall is parallel to the plane of the base portion.

13. The heat exchanger according to claim 1, wherein the offset wall is inclined relative to the plane of the base portion such that a distance between the offset wall and the plane of the base portion reduces toward a lower position.

14. The heat exchanger according to claim 1, wherein each of the protrusions includes a curved outer surface, the fin portion is disposed downstream of one of the protrusions with respect to the flow direction of the air, the offset wall is inclined relative to the plane of the base portion such that a distance between the offset wall and the plane of the base portion reduces toward a downstream position with respect to the flow direction of the air.

15. The heat exchanger according to claim 1, wherein each of the protrusions includes a curved outer surface, the fin portion is disposed between two of the protrusions that are disposed in the flow direction of the air, and the offset wall is curved toward the plane of the base portion such that a distance between the offset wall and the plane of the base portion reduces toward a middle position with respect to the flow direction of the air.

16. The heat exchanger according to claim 1, wherein the fin portion includes a first connecting wall that connects an upper end of the offset wall to the base portion and a second connecting wall that connects a lower end of the offset wall to the base portion.

17. The heat exchanger according to claim 16, wherein the first connecting wall and the second connecting wall are respectively inclined relative to the plane of the base portion, and an angle of inclination of each of the first connecting wall and the second connecting wall is at least 30 degrees and at most 60 degrees.

18. The heat exchanger according to claim 16, wherein the upper end of the offset wall and the first connecting wall form a rounded corner therebetween, and the lower end of the offset wall and the second connecting wall form a rounded corner therebetween.

19. The heat exchanger according to claim 1, wherein the offset wall has a semi-circular shape in a cross-section defined in the longitudinal direction of the protrusions, and ends of the offset wall connect to the base portion.

20. The heat exchanger according to claim 1, wherein the fin portion has a width equal to or greater than 0.2 mm with respect to the flow direction of the air.

21. The heat exchanger according to claim 20, wherein the base portion includes side sections on opposite sides of the fin portion with respect to the flow direction of the air, and a width of each of the side sections with respect to the air flow direction is equal to or greater than 0.15 mm.

22. The heat exchanger according to claim 1, wherein the protrusions of the first heat transfer plate and the protrusions of the second heat transfer plate are disposed at the same positions with respect to the flow direction of the air such that each of the internal fluid passages is provided by one of the protrusions of the first heat transfer plate and one of the protrusions of the second heat transfer plate.

23. The heat exchanger according to claim 1, further comprising: a plurality of first heat transfer plates including the first heat transfer plate; and a plurality of second heat transfer plates including the second heat transfer plate, wherein the plurality of first heat transfer plates and the plurality of second heat transfer plates are disposed in pairs, and the pairs of the first and second heat transfer plates are stacked in a direction perpendicular to the planes of the base portions such that clearances for allowing the air to flow are provided between the adjacent pairs of the first and second heat transfer plates.

24. The heat exchanger according to claim 23, wherein a dimension of each clearance at a position between the offset wall of one heat transfer plate and a surface of another heat transfer plate that is opposed to the one heat transfer plate across the clearance is equal to or greater than 0.15 mm.

25. The heat exchanger according to claim 1, wherein the fin portion is disposed upstream of an end protrusion with respect to the flow direction of the air, the end protrusion being one of the plurality of protrusions and located at a downstream-most position in the plurality of protrusions with respect to the flow direction of the air.