Patent Publication Number: US-2004050531-A1

Title: Heat exchanger

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application is an application filed under 35 U.S.C. §111(a) claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing data of Provisional Application No. 60/302,371 filed Jul. 3, 2001 pursuant to 35 U.S.C. §111(b). 
    
    
     
       TECHNICAL FIELD  
       [0002] The present invention relates to heat exchangers for use in motor vehicles or for industrial use, for example, to heat exchangers for use as evaporators, condensers, oil coolers, intercoolers, heater cores, etc.  
       [0003] Generally aluminum heat exchangers are conventionally in wide use as heat exchangers, especially as evaporators for motor vehicle air conditioners, from the viewpoint of lightweightness and workabiliy.  
       [0004] At present, evaporators for motor vehicle air conditioners are chiefly those of the laminate type (layered type). In fabricating evaporators of this type, heat exchange fins for air and a tube portion for evaporating the refrigerant are joined together by brazing, so that such evaporators are superior to heat exchangers of the fin tube enlarged type which were previously in use, for example, with respect to performance and productivity. These evaporators are exceedingly superior to the fin tube enlarged type especially in performance characteristics since louver fins of high heat transfer efficiency are usable as air fins for this type of evaporators to ensure an increased quantity of heat exchange and low resistance to the flow of air.  
       [0005] Accordingly, more lightweight and compact heat exchangers are made available to meet the market demand for smaller sizes and reduced weight. Especially recently, many evaporators are provided with a filter on the front side in view of problems involved in the vehicle compartment, and it has been strongly required that heat exchangers be reduced in thickness to provide space for the installation of the filter.  
       [0006] For example as shown in FIG. 25, conventional heat exchangers for use as evaporators comprise generally rectangular aluminum plates  62  each having formed in one surface thereof front and rear refrigerant channel forming recessed porions  66  divided by a vertically elongated partition ridge  64 , and header forming recessed portions (not shown) respectively continuous with the upper and lower ends of these recessed portions  66  and having a larger depth than these portions  66 . Each pair of adjacent plates  62  are fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges  64 ,  64  of the plates  62 ,  62  to each other and opposed peripheral edges  63 ,  63  thereof to each other and to thereby form a flat tube portion  61  having front and rear flat refrigerant channels  68  and upper and lower header portions continuous with the respective channels  68 . A multiplicity of such flat tube portions  61  are arranged in parallel with a fin interposed therebetween for air to provide the heat exchanger. Each of the plates  62  is prepared from an aluminum sheet by press forming.  
       [0007] The conventional heat exchanger for use as an evaporator encounters the following problems in fulfilling the commercial demand for a reduced thickness.  
       [0008] (1) The plates  62  for forming the flat tube portion  61  are made from an aluminum sheet by drawing with use of a press, so that the partition ridge  64  and the peripheral edge  63  have an increased width. Accordingly, the joints between the two plates  62 ,  62 , i.e., the joint of the opposed partition ridges of the plates  62 ,  62  and the joint of the opposed peripheral edges  63 ,  63  which are useless portions not passing the refrigerant have a relatively great area, which consequently reduces the cross sectional area of the refrigerant channel when the evaporator has a given volume, offering increased resistance to the flow of the refrigerant and resulting in impaired performance.  
       [0009] To meet this problem, it appears useful to give an increased height to the refrigerant channel and thereby assure the channel of a sufficient cross sectional area, whereas the volume to be occupied by the air-side fin in the given volume will then decrease. Thus, the fin has a smaller area for heat transfer and is impaired in performance, while a diminished air passage produces increased resistance to the flow of air, failing to afford a proper rate of air flow.  
       [0010] (2) On the other hand, the joint between the peripheral edges  63 ,  63  of the two plates  62 ,  62  is out of direct contact with the fin for the air side to exhibit a low heat transfer efficiency, so that a reduction in the thickness of the heat exchanger including such useless portions increases the relative ratio in area of the useless portions not participating in the passage of the refrigerant.  
       [0011] (3) The header forming recessed portions of the plate  62  are given a greater depth than the front and rear refrigerant channel forming recessed portions  66 ,  66  on opposite sides of the partition ridge  64  by being worked by drawing, and are therefore made smaller in wall thickness than the recessed portions  66 . Although the flat tube portion  61  having a great proportion is given an allowance for pressure resistance, the header portions are weakest against pressure. With the conventional heat exchanger, the flat tube portion  61  and the header portions are made from an integral plate material, and that by press work, so that there are limitations in further reducing the header portions in wall thickness and weight.  
       [0012] An object of the present invention is to overcome the foregoing technical problems of the prior art and to provide a heat exchanger which is fabricated from plates having ridges and recessed portions formed in one surface thereof as by forging or cutting work instead of using plates formed by press work and in which headers are formed from a member separate from the plate to make a flat tube having a reduced front-to-rear width, a diminished wall thickness (layer of diminished thickness) and an increased heat transfer area, the heat exchanger thus being adapted to achieve a higher heat transfer efficiency and greatly improved heat exchange performance.  
       DISCLOSURE OF THE INVENTION  
       [0013] First, the present invention provides a heat exchanger which is characterized in that the heat exchanger comprises pairs of plates with each plate of the pairs having a peripheral ridge provided on one side of the plate along a periphery thereof and a central ridge provided on said one side of the plate at a center of the width thereof and extending downward from an upper end of the plate to a position where a return channel can be formed, the ridges being formed by forging or cutting, each plate of said pairs having a U-shaped channel recess formed inwardly of the peripheral ridge and comprising a front and a rear channel recess portion formed on opposite sides of the central ridge and a return channel recess portion positioned under the central ridge, the channel recess having one of two fluid inlet-outlet through holes formed at one end thereof and the other through hole formed at the other end thereof, each plate of said pairs having a flat surface on the other side thereof, each of said pairs of plates being fitted together with their U-shaped channel recesses opposed to each other to join the opposed peripheral ridges to each other end-to-end and the opposed central ridges to each other end-to-end and to thereby form a flat tube having a U-shaped fluid channel inside thereof so that a plurality of flat tubes are arranged in parallel with a header member interposed between upper ends of each pair of adjacent flat tubes to provide a front and a rear header in communication with the upper ends of the said pair of adjacent flat tubes, the header member comprising a pair of front and rear fluid passing tube portions in communications with the respective inlet-outlet through holes of the plates of said pair of adjacent flat tubes and a connecting portion between the tube portions.  
       [0014] Second, the present invention provides a heat exchanger which is characterized in that the heat exchanger comprises pairs of plates with each plate of the pairs having an edge ridge U-shaped in its entirety and provided on one side of the plate along opposite side edges and a lower edge thereof and a central ridge provided on said one side of the plate at a center of the width thereof and having a bifurcated upper end, the central ridge extending from the upper end downward to a position where a return channel can be formed, the ridges being formed by forging or cutting, each plate of said pairs having a U-shaped channel recess formed inwardly of the U-shaped edge ridge and comprising a front and a rear channel recess portion formed on opposite sides of the central ridge and a return channel recess portion positioned under the central ridge, each plate of said pairs having a flat surface on the other side thereof, each of said pairs of plates being fitted together with their U-shaped channel recesses opposed to each other to join the opposed U-shaped edge ridges to each other end-to-end and the opposed central ridges including the bifurcated upper ends to each other end-to-end and to thereby form a flat tube having bifurcated open upper ends and a U-shaped fluid channel inside thereof, a pair of front and rear header members being each in the form of a pipe having a rectangular cross section, each of the header members having slits formed in a lower wall thereof and arranged at a predetermined spacing, a plurality of flat tubes being arranged in parallel by inserting the bifurcated open upper ends thereof into the respective slits in the front and rear header members to join the flat tubes to the header members and to provide a front and a rear header in communication with the bifurcated open upper ends of the flat tubes.  
       [0015] With the heat exchanger having the first or second feature described, a plurality of channel dividing U-shaped ridges are formed in the U-shaped channel recess of each plate by forging or cutting, and a pluralty of U-shaped divided fluid passageways are formed in the U-shaped fluid channel in the interior of each flat tube. The invention provides several modes of channel dividing ridges.  
       [0016] As a first mode, a plurality of channel dividing U-shaped ridges are formed in the U-shaped channel recess of each plate by forging or cutting, and each said pair of plates are fitted together with the recesses thereof opposed to each other and with each of opposed pairs of channel dividing U-shaped ridges joined to each other end-to-end to form a plurality of U-shaped divided fluid passageways in the U-shaped fluid channel inside the flat tube.  
       [0017] A second mode of channel dividing ridges is as follows. Each plate of said pairs has formed in the channel recess thereof front and rear channel dividing ridges having a height twice the depth of the channel recess and each comprising a straight portion positioned in the front or rear straight channel recess portion of the channel recess and a quarter circular-arc portion extending from a lower end of the straight portion and positioned in the return portion of the channel recess, the channel dividing ridges being formed by forging or cutting and positioned alternately when each of said pairs of plates are fitted together with their channel recesses opposed to each other, each of said pairs of plates being fitted together with their channel recesses opposed to each other to join top ends of the front and rear channel dividing ridges to a bottom wall flat surface of the plate providing the channel recess and opposed thereto and to thereby form U-shaped divided fluid passageways in the U-shaped fluid channel inside the flat tube.  
       [0018] A third mode of channel dividing ridges is as follows. Each plate of said pairs has formed in the channel recess thereof channel dividing ridges having a height twice the depth of the channel recess and formed by forging or cutting so as to be positioned alternately, when each of said pairs fitted together with the recesses thereof opposed to each other, each of said pairs of plates being fitted together to join top ends of the channel dividing ridges on each plate of the pair to a flat surface of bottom wall of the channel recess of the other plate opposed to said each plate and to thereby form U-shaped divided fluid passageways in the U-shaped fluid channel inside the flat tube.  
       [0019] A fourth mode of channel dividing ridges is as follows. Each plate of said pairs has formed in a rear half of the channel recess thereof channel dividing ridges having a height twice the depth of the channel recess and formed by forging or cutting, the channel recess of each plate having a front half in the form of a flat surface provided by a bottom wall thereof and having no channel dividing ridges, each of said pairs of plates being fitted together with the recesses thereof opposed to each other to join top ends of the channel dividing ridges thereof to the bottom wall flat surface of the channel recess of the plate opposed to the dividing ridges and to thereby form U-shaped divided fluid passageways in the U-shaped fluid channel inside the flat tube.  
       [0020] With the heat exchanger having the first feature of the invention, one of each pair of plates may be replaced by a flat plate.  
       [0021] More specifically, the heat exchanger in this case comprises ridged plates each having a peripheral ridge provided on one side of the plate along a periphery thereof and a central ridge provided on said one side of the plate at a center of the width thereof and extending downward from an upper end of the plate to a position where a return channel can be formed, the ridges being formed by forging or cutting, each of the ridged plates having a U-shaped channel recess formed inwardly of the peripheral ridge and comprising a front and a rear channel recess portion formed on opposite sides of the central ridge and a return channel recess portion positioned under the central ridge, the channel recess having one of two fluid inlet-outlet through holes formed at one end thereof and the other through hole formed at the other end thereof, each of the ridged plates having a flat surface on the other side thereof and being fitted to each of flat plates face-to-face, each of said flat plates having the same contour and the same size as the ridged plate and two fluid inlet-outlet through holes corresponding to said through holes, the peripheral ridge of the ridged plate having a top end thereof joined to a peripheral edge of the flat plate, the central ridge of the ridged plate having a top end thereof joined to a flat surface of a corresponding central portion of the flat plate, whereby a flat tube having a U-shaped fluid channel inside thereof is formed so that a plurality of flat tubes are arranged in parallel with a header member interposed between upper ends of each pair of adjacent flat tubes to provide a front and a rear header in communication with the upper ends of the said pair of adjacent flat tubes, the header member comprising a pair of front and rear fluid passing tube portions in communications with the respective inlet-outlet through holes of the plates of said pair of adjacent flat tubes and a connecting portion between the tube portions.  
       [0022] With the heat exchanger having the second feature of the invention, one of each pair of plates may be replaced by a flat plate.  
       [0023] Stated more specifically, the heat exchanger in this case comprises ridged plates each having an edge ridge U-shaped in its entirety and provided on one side of the plate along opposite side edges and a lower edge thereof and a central ridge provided on said one side of the plate at a center of the width thereof and having a bifurcated upper end, the central ridge extending from the upper end downward to a position where a return channel can be formed, the ridges being formed by forging or cutting, each of the ridged plates having a U-shaped channel recess formed inwardly of the U-shaped edge ridge and comprising a front and a rear channel recess portion formed on opposite sides of the central ridge and a return channel recess portion positioned under the central ridge, each of the ridged plates having a flat surface on the other side thereof and being fitted to each of flat plates face-to-face, each of said flat plates having the same contour and the same size as the ridged plate, the peripheral ridge of the ridged plate having a top end thereof joined to a peripheral edge of the flat plate, the central ridge of the ridged plate including the bifurcated upper ends having a top end thereof joined to a flat surface of a corresponding central portion of the flat plate, whereby a flat tube having bifurcated open upper ends and a U-shaped fluid channel inside thereof is formed, a pair of front and rear header members being each in the form of a pipe having a rectangular cross section, each of the header members having slits formed in a lower wall thereof and arranged at a predetermined spacing, a plurality of flat tubes being arranged in parallel by inserting the bifurcated open upper ends thereof into the respective slits in the front and rear header members to join the flat tubes to the header members and to provide a front and a rear header in communication with the bifurcated open upper ends of the flat tubes.  
       [0024] In a heat exchanger having such flat plates, a plurality of channel dividing U-shaped ridges are formed in the U-shaped channel recess of each ridged plate by forging or cutting, and each ridged plate and each flat plate are fitted together face-to-face with the channel dividing U-shaped ridges of the ridged plate joined to the flat surface of the corresponding central portion of the flat plate to form a plurality of U-shaped divided fluid passageways in the U-shaped fluid channel inside the flat tube.  
       [0025] Third, the present invention provides a heat exchanger which is characterized in that the heat exchanger comprises pairs of plates with each plate of the pairs having a peripheral ridge provided on one side of the plate along a periphery thereof and a central ridge provided on said one side of the plate at a center of the width thereof and extending vertically, the ridges being formed by forging or cutting, each plate of said pairs having a front and a rear channel recess portion formed inwardly of the peripheral ridge on opposite sides of the central ridge, each of the front and rear channel recess portions having a through hole formed in each of upper and lower ends thereof, each plate of said pairs having a flat surface on the other side thereof, each of said pairs of plates being fitted together with their channel recess portions opposed to each other to join the opposed peripheral ridges to each other end-to-end and the opposed central ridges to each other end-to-end and to thereby form a flat tube having a front and a rear fluid channel inside thereof so that a plurality of flat tubes are arranged in parallel with an upper and a lower header member interposed respectively between upper ends of each pair of adjacent flat tubes and between lower ends thereof to provide an upper and a lower header in communication with the upper ends and the lower ends of said pair of adjacent flat tubes, each of the header members comprising a pair of front and rear fluid passing tube portions in communications with the corresponding through holes of the plates of said pair of adjacent flat tubes and a connecting portion between the tube portions.  
       [0026] Fourth, the present invention provides a heat exchanger which is characterized in that the heat exchanger comprises pairs of plates with each plate of the pairs having a side edge ridge provided on one side of the plate along each of opposite side edges thereof and a central ridge provided on said one side of the plate at a center of the width thereof and having a bifurcated upper and a bifurcated lower end, the ridges being formed by forging or cutting, each plate of said pairs having a front and a rear channel recess portion formed inwardly of the side edge ridges on opposite sides of the central ridge, each plate of said pairs having a flat surface on the other side thereof, each of said pairs of plates being fitted together with their channel recess portions opposed to each other to join the opposed side edge ridges to each other end-to-end and the opposed central ridges including the bifurcated upper and lower ends to each other end-to-end and to thereby form a flat tube having bifurcated open upper and lower ends and a front and a rear fluid channel inside thereof, an upper pair of front and rear header members and a lower pair of front and rear header members being each in the form of a pipe having a rectangular cross section, each of the header members having slits formed in an upper wall or a lower wall thereof and arranged at a predetermined spacing, a plurality of flat tubes being arranged in parallel by inserting the bifurcated upper or lower ends thereof into the respective slits in the header members to join the flat tubes to the header members and to provide an upper pair of front and rear headers and a lower pair of front and rear headers in communication with the bifurcated upper and lower ends of the flat tubes respectively.  
       [0027] With the heat exchanger having the third or fourth feature described, a plurality of channel dividing ridges are formed in the front and rear channel recesses of each plate by forging or cutting, and a pluralty of divided fluid passageways are formed in the front and rear fluid channels in the interior of each flat tube. The invention provides several modes of channel dividing ridges.  
       [0028] As a first mode, a plurality of channel dividing ridges are formed in the front and rear channel recess portions of each plate by forging or cutting, and each of said pairs of plates are fitted together with their recess portions opposed to each other to join each of opposed pairs of the channel dividing ridges to each other end-to-end and form divided fluid passageways in the front and rear fluid channels inside thereof.  
       [0029] A second mode of channel dividing ridges is as follows. Each plate has formed in the respective front and rear channel recess portions thereof front and rear channel dividing ridges having a height twice the depth of the recess portion, the front and rear channel dividing ridges being formed by forging or cutting and positioned alternately when each of said pairs of plates are fitted together with their recess portions opposed to each other, each of said pairs of plates being fitted together face-to-face to join top ends of the front and rear channel dividing ridges to a bottom wall flat surface of recess portion of the plate opposed thereto and to thereby form divided fluid passageways in the front and rear fluid channels inside the flat tube.  
       [0030] A third mode of channel dividing ridges is as follows. Each plate of the pairs has formed in each of the front and rear channel recess portions thereof a channel dividing ridge having a height twice the depth of the recess portion, the channel dividing ridge being so formed by forging or cutting that the front and rear channel dividing ridges of each pair of plates as fitted together face-to-face are positioned alternately, each pair of plates being fitted together with their recess portions opposed to each other to join top ends of the front and rear channel dividing ridges of each plate of the pair to a bottom wall flat surface of the recess portion of the other plate of the pair opposed thereto and to thereby form divided fluid passageways in the front and rear fluid channels inside the flat tube.  
       [0031] A fourth mode of channel dividing ridges is as follows. Each plate has formed in one of the front and rear channel recess portions thereof a plurality of channel dividing ridges having a height twice the depth of the recess portion, the channel dividing ridges being formed by forging or cutting, the other channel recess portion having a bottom wall flat surface having no channel dividing ridges, each of said pairs of plates being fitted together with their recess portions opposed to each other to join top ends of the channel dividing ridges to the bottom wall flat surface of the recess portion of the plate opposed thereto and to thereby form divided fluid passageways in the front and rear fluid channels inside the flat tube.  
       [0032] With the heat exchanger having the third feature of the invention, one of each pair of plates may be replaced by a flat plate.  
       [0033] Stated more specifically, the heat exchanger in this case comprises ridged plates each having a peripheral ridge provided on one side of the plate along a periphery thereof and a central ridge provided on said one side of the plate at a center of the width thereof and extending vertically, the ridges being formed by forging or cutting, each the ridged plates having a front and a rear channel recess portion formed inwardly of the peripheral ridge on opposite sides of the central ridge, each of the front and rear channel recess portions having a through hole formed in each of upper and lower ends thereof, each of the ridged plates having a flat surface on the other side thereof and being fitted to each of flat plates face-to-face, each of said flat plates having the same contour and the same size as the ridged plate and fluid inlet-outlet through holes corresponding to said through holes, the peripheral ridge of the ridged plate having a top end thereof joined to a peripheral edge of the flat plate, the central ridge of the ridged plate having a top end thereof joined to a flat surface of a corresponding central portion of the flat plate, whereby a flat tube having a front and a rear fluid channel inside thereof is formed so that a plurality of flat tubes are arranged in parallel with an upper and a lower header member interposed respectively between upper ends of each pair of adjacent flat tubes and between lower ends thereof to provide an upper and a lower header in communication with the upper ends and the lower ends of said pair of adjacent flat tubes, each of the header members comprising a pair of front and rear fluid passing tube portions in communications with the corresponding through holes of the plates of said pair of adjacent flat tubes and a connecting portion between the tube portions.  
       [0034] In the above heat exchanger, the connecting portion of one of the upper and lower header members interposed between the upper ends and lower ends of each pair of adjacent flat tubes may have a passage interconnecting the fluid passing tube portions of the header member.  
       [0035] With the heat exchanger having the fourth feature of the invention, one of each pair of plates may be replaced by a flat plate.  
       [0036] Stated more specifically, the heat exchanger then comprises ridged paltes each having a side edge ridge provided on one side of the plate along each of opposite side edges thereof and a central ridge provided on said one side of the plate at a center of the width thereof and having a bifurcated upper and a bifurcated lower end, the ridges being formed by forging or cutting, each of the ridged plates having a front and a rear channel recess portion formed inwardly of the side edge ridges on opposite sides of the central ridge, each of the ridged plates having a flat surface on the other side thereof and being fitted to each of flat plates face-to-face, each of said flat plates having the same contour and the same size as the ridged plate, the side edge ridges of the ridged plate having top ends thereof joined to side edges of the flat plate, the central ridge of the ridged plate including the bifurcated upper and lower ends having a top end thereof joined to a flat surface of a corresponding central portion of the flat plate, whereby a flat tube having bifurcated open upper and lower ends and a front and a rear fluid channel inside thereof is formed, an upper pair of front and rear header members and a lower pair of front and rear header members being each in the form of a pipe having a rectangular cross section, each of the header members having slits formed in an upper wall or a lower wall thereof and arranged at a predetermined spacing, a plurality of flat tubes being arranged in parallel by inserting the bifurcated upper or lower ends thereof into the respective slits in the header members to join the flat tubes to the header members and to provide an upper pair of front and rear headers and a lower pair of front and rear headers in communication with the bifurcated upper and lower ends of the flat tubes respectively.  
       [0037] In a heat exchanger wherein flat plates are used, each of the ridged plates has channel dividing ridges formed in the respective front and rear channel recess portions thereof by forging or cutting, and each ridged plate is fitted to each flat plate face-to-face to join top ends of the channel dividing ridges to a flat surface of a corresponding portion of the flat plate and to thereby form divided fluid passageways in the front and rear fluid channels inside the flat tube.  
       [0038] In a heat exchanger which has the first or third feature, the header member interposed between the ends of each pair of adjacent flat tubes has its fluid passing tube portions joined at their opposite end faces to the flat surfaces on the other sides of the opposed plates of the pair of flat tubes. Preferably, tacks for temporarily holding the header member are provided on respective edges defining the inlet-outlet through holes in the end of each plate.  
       [0039] In a heat exchanger according, a plurality of cutouts are formed in the channel dividing ridges on each plate to cause the adjacent divided fluid passageways inside the flat tube to communicate with each other through the cutouts.  
       [0040] In any of the heat exchangers of the invention described, a fin is provided between each pair of adjacent flat tubes included in the flat tubes arranged in parallel, and the fin has opposite sides edges thereof joined to the flat surfaces on the other sides of the plates of the pair of flat tubes.  
       [0041] For use in any of the heat exchangers of the invention described, the plates are those having recesses and ridges formed on one side thereof by forging or cutting, in place of conventional plates which are formed by press work, and the header members are members separate from the plate for providing headers. These features provide flat tubes having a reduced front-to-rear width, a diminished wall thickness (layer of diminished thickness) and an increased heat transfer area to result in the advantages of a higher heat transfer efficiency and greatly improved heat exchange performance. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0042]FIG. 1 is a perspective view of a heat exchanger according to a first embodiment of the invention.  
     [0043]FIG. 2 is an enlarged front view of a plate of the heat exchanger of FIG. 1.  
     [0044]FIG. 3 is an enlarged fragmentary perspective view of the plate.  
     [0045]FIG. 4 is an enlarged exploded fragmentary perspective view of the heat exchanger of FIG. 1.  
     [0046]FIG. 5 is an enlarged cross sectional view of a plate tube of the heat exchanger.  
     [0047]FIG. 6 is an enlarged fragmentary perspective view partly broken away and showing the heat exchanger.  
     [0048]FIG. 7 is an enlarged fragmentary cross sectional view showing a modification of dividing ridges of plate of the heat exchanger of FIG. 1.  
     [0049]FIG. 8 is an enlarged front view showing a modified plate of the heat exchanger.  
     [0050]FIG. 9 is an enlarged fragmentary perspective view showing another modified plate of the heat exchanger.  
     [0051]FIG. 10 is an enlarged cross sectional view of a flat tube for the heat exchanger wherein the plate of FIG. 9 is used.  
     [0052]FIG. 11 is an enlarged exploded fragmentary perspective view of a heat exchanger according to a second embodiment of the invention.  
     [0053]FIG. 12 is an enlarged fragmentary front view of the plate of the heat exchanger of FIG. 11, with headers also shown.  
     [0054]FIG. 13 is a perspective view of a heat exchanger according to a third embodiment of the invention.  
     [0055]FIG. 14 is an enlarged front view of the plate of the heat exchanger plate shown FIG. 13.  
     [0056]FIG. 15 is an enlarged fragmentary perspective view of the heat exchanger plate.  
     [0057]FIG. 16 is an enlarged exploded perspective view of an upper end portion of the heat exchanger.  
     [0058]FIG. 17 is an enlarged exploded perspective view of a lower end portion of the heat exchanger.  
     [0059]FIG. 18 is an enlarged front view of a plate for use in the heat exchanger of FIG. 1 to show a second modification of diving ridges.  
     [0060]FIG. 19 is an enlarged cross sectional view of a flat tube for the heat exchanger wherein the plate of FIG. 18 is used.  
     [0061]FIG. 20 is an enlarged front view of a plate for use in the heat exchanger of FIG. 1 to show a third modification of diving ridges, the plate being one of a pair of plates in combination.  
     [0062]FIG. 21 is an enlarged front view of the other plate of the pair.  
     [0063]FIG. 22 is an enlarged front view of a plate for use in the heat exchanger of FIG. 1 to show a fourth modification of diving ridges.  
     [0064]FIG. 23 is an enlarged cross sectional view of a flat tube for the heat exchanger wherein the plate of FIG. 22 is used.  
     [0065]FIG. 24 is an enlarged cross sectional view of a flat tube of heat exchanger of the invention, wherein one of a pair of plates in combination is replaced by a flat plate as a modification.  
     [0066]FIG. 25 is an enlarged cross sectional view of a flat tube of an example of conventional heat exchanger. 
    
    
     BEST MODE OF CARRYING OUT THE INVENTION  
     [0067] Embodiments of the present invention will be described below with reference to the drawings.  
     [0068] The terms “front,” “rear,” “left,” “right,” “upper” and “lower” as used herein are based on FIG. 2; “front” refers to the left-hand side of FIG. 2, “rear” to the right-hand side thereof, “left” to the front side of the plane of the drawing, “right” to the rear side of the plane thereof, “upper” to the upper side of the drawing, and “lower” to the lower side thereof.  
     [0069] The drawings show heat exchangers of the invention for use as evaporators for motor vehicle air conditioners.  
     [0070] FIGS.  1  to  6  show a first embodiment of the present invention. A heat exchanger  1  for use as an evaporator is made from aluminum (including aluminum alloys).  
     [0071] A generally rectangular plate  2  made of an aluminum plate has a peripheral ridge  3  provided on one side of the plate  2  along a periphery thereof and a central ridge  4  provided on the same side of the plate  2  at the center of the width thereof and extending downward from the upper end of the plate to a position where a refrigerant return channel can be formed. Formed in the plate  2  internally of the peripheral ridge  3  is a U-shaped refrigerant channel recess  6  comprising front and rear straight refrigerant channel recess portions  6   a ,  6   b  positioned on opposite sides of the central ridge  4  and a refrigerant return channel recess portion  6   c  positioned under the central ridge.  
     [0072] According to this first embodiment, the plate  2  is provided in the widthwise midportion of its upper end with a notch  14  which is U-shaped when seen from the front. The central ridge  4  is joined at its upper end to the peripheral ridge  3  at the lower end of this notch  14 .  
     [0073] The channel recess  6  has one of refrigerant inlet-outlet through holes  10 ,  10  formed at one end thereof and the other through hole  10  formed at the other end thereof. The plate  2  has a plurality of channel diving U-shaped ridges  5  formed inside the channel recess  6  and extending over the approximate entire length thereof.  
     [0074] The presence of the notch  14  in the widthwise midportion of upper end of the plate  2  positions the though holes  10 ,  10  as spaced apart from each other by the width of the notch  14 . This serves to prevent unnecessary heat exchange between an incoming portion of refrigerant having a low temperature and an outgoing portion of refrigerant having a high temperature, and to prevent the refrigerant introduced into an inlet header to be described later from flowing into an outlet header through a short path.  
     [0075] The corners of return channel recess portion  6   c  of the channel recess  6  have short circular-arc ridges  9  for achieving an improved heat exchange efficiency at the corner portions.  
     [0076] Each plate  2  is formed, for example, by forging or cutting. Plates  2  are provided in pairs, and each pair of plates  2  are fitted together with their U-shaped channel recesses  6 ,  6  opposed to each other to join the opposed peripheral ridges  3 ,  3  of the plates  2 ,  2  to each other end-to-end, the opposed central ridges  4 ,  4  thereof to each other end-to-end and each of the opposed pairs of channel dividing rides  5 ,  5  to each other end-to-end and to thereby form a flat tube  12  having a U-shaped refrigerant channel  8  inside thereof, with a plurality of U-shaped divided refrigerant passageways  7  formed in the refrigerant channel  8  inside the flat tube  12 .  
     [0077] A clad material is used for each plate  2  which has a brazing sheet affixed to one surface thereof, preferably each of the inner and outer surfaces thereof. Such components can then be joined together easily.  
     [0078] The evaporator  1  of the present invention has headers  23 ,  23  which interconnect flat tubes  12 ,  12  providing a refrigerant circuit and which are formed in the following manner.  
     [0079] A plurality of flat tubes  12  are arranged in parallel, with a spectacle-shaped header member  20  interposed between the upper ends of each pair of adjacent flat tubes  12 ,  12  to provide front and rear headers  23 ,  23  in communication with the upper ends of the pair of adjacent flat tubes  12 . The header member  20  comprises a pair of front and rear refrigerant passing tube portions  21 ,  21  in communications with the respective inlet-outlet through holes  10 ,  10  of the plates  2  and a connecting portion  22  between the tube portions. Opposite end faces of front and rear tube portions  21 ,  21  of the header member  20  are joined to flat surfaces provided by the other sides of respective opposed plates  2 ,  2  of the pair of flat tubes  12 .  
     [0080] Below the headers  23 ,  23 , a corrugated louver fin  24  for effecting heat exchange with air is provided between the adjacent flat tubes  12 ,  12 . The fin  24  is joined at left and right sides thereof to the flat surfaces of the plates  2 ,  2 .  
     [0081] The corrugated louver fin  24  has louvers formed simultaneously with bending for improved heat transfer.  
     [0082] The bottom of the U-shaped notch  14  formed in the widthwise midportion of the upper end of each plate  2  needs to be positioned below the connecting portion  22  of the spectacle-shaped header member  20  so as to drain condensation water collecting in the notch.  
     [0083] Tacks  13 ,  13  for temporarily holding the header member  20  are provided at the midportions of the lower edges defining the respective inlet-outlet through holes  10 ,  10  in the upper end of the plate  2 . The header member  20  can be prevented from shifting by these tacks  13 ,  13  during brazing.  
     [0084] With reference to FIGS. 1 and 4, a pair of side plates  25 ,  25  are arranged respectively at left and right ends of the evaporator  1 . The left side plate  25  of the pair is provided with an inlet-outlet pipe connecting block  27  joined to the upper end thereof. The side plate  25  has a pair of front and rear through holes  26 ,  26  formed in the upper end thereof and communicating respectively with a pair of front and rear through holes  28 ,  28  formed in the block  27 . The holes  26 ,  26  of the side plate  25  communicate respectively with the tube portions  21 ,  21  of the header member  20 .  
     [0085] Incidentally, the side plate  25  need not be provided in the case where the block  27  is attached directly to the plate  2  at the left or right outer end of the evaporator  1 . The block  17  may alternatively be provided at an intermediate portion of the height of the side plate  25 . The block  27  may further be provided at the midportion of length of the evaporator  1 , or may comprise an inlet pipe connecting block and an outlet pipe connecting block which are provided respectively at the left and right ends of the evaporator so as to position an inlet and an outlet individually at the left and right ends.  
     [0086] The evaporator components described are assembled and thereafter joined together by brazing to fabricate the essential portion of the evaporator  1 .  
     [0087] The assembly is brazed in a vacuum, or in a furnace with use of a fluorine-containing flux.  
     [0088] It is desirable to use a material of relatively high strength for the header member  20  and the side plates  25  in view of pressure resistance. It is especially desirable to use an aluminum alloy containing magnesium added thereto.  
     [0089] In the case where the fluorine-containing flux is used, it is desirable to use an aluminum alloy material having a magnesium content preferably of up to 0.4% since this results in improvements in bondability and strength.  
     [0090] The surfaces of the plate  2  and the corrugated fin  24  are approximately flat so that the fin  24  can be joined to the flat tube  12  nearly 100% to achieve highly efficient heat exchange between the interior of the circuit of flat tubes  12  and the corrugated fins  24 .  
     [0091] The header member  20  providing the headers  23 ,  23  has a generally spectacle-shaped section with two refrigerant channels, one of which has the function of collecting or distributing an incoming portion of refrigerant, with the other serving to collect or distribute an outgoing portion of refrigerant.  
     [0092] When the heat exchanger of the present invention is used as an evaporator  1 , the refrigerant is introduced into the flat tubes  12  in the form of a mixture of a liquid and a gas. At this time, the liquid refrigerant has a higher density than the gas and is more readily subjected to an inertial force. The liquid refrigerant has higher properties to advance straight than the gas. For this reason, the liquid refrigerant tends to collect in a greater amount at a header end remote from the inlet header. An uneven flow of the liquid refrigerant upsets the balance of latent heat of vaporization in various portions, contributing greatly to impairment of performance. This can be precluded effectively by causing the flat tube  12  to project into the header  23  to serve as a baffle and diminish the properties of the liquid refrigerant to advance straight.  
     [0093] The present invention is adapted to readily provide a baffle structure, for example, by making the height b1 of the through hole  10  at the inlet side of the flat tube  12  smaller than the inside diameter b2 of the refrigerant passing tube portion  21  of the header member  20 . The effect of a baffle is available alternatively by reducing the cross sectional area of the front and rear tube portions  21  of the header member  20  at one location or at a plurality of locations and thereby producing flows of varying cross sectional areas.  
     [0094] Such a procedure diminishes the property of the liquid refrigerant of advancing straight through the headers  23 ,  23 , permitting the refrigerant to flow into the flat tubes  12  in equally divided quantities.  
     [0095] When the percentage of projection of the flat tube  12  into the header  23  in the evaporator  1  of the invention is defined as:  
     ( b 2 −b 1)/ b 2  
     [0096] wherein b1 is the height of the through hole  10  at the inlet side of the flat tube  12 , and b2 is the inside diameter of the tube portion  21  of the header member  20 , the percentage of projection is in the range of 10 to 60% to be suitable. If the percentage of projection is less than 10%, no effect of baffle plate is available, readily permitting occurrence of an uneven flow, whereas if the percentage of projection is over 60%, the header  23  offers increased resistance to the flow to entail impaired performance undesirably.  
     [0097] As shown in detail in FIG. 5, it is especially desirable that the U-shaped divided refrigerant passageways  7  formed in the refrigerant channel  8  in the interior of each flat tube  12  be made generally hexagonal in cross section by tapering the peripheral ridges  3 ,  3  on the pair of the plates  2 ,  2  of the tube  12  toward inward, tapering the central ridges  4 ,  4  thereon inward and tapering the channel dividing ridges  5 ,  5  inward. The reason is that it is advantageous to spread the liquid refrigerant into a thin layer over the inner surface of the refrigerant channel  8  of the flat tube  12  for heat transfer.  
     [0098] Among the U-shaped divided refrigerant passageways  7  formed in the channel  8  inside the flat tube  12 , the passageway  7   a  between the peripheral ridge  3  and the channel dividing U-shaped ridge  5  has a hexagonal cross section with a large width, and the passageways  7   b  between the ridges  5 ,  5  have a hexagonal cross section with a small width.  
     [0099] On the other hand, when the U-shaped divided refrigerant passageways  7  formed in the inside refrigerant channel  8  of the flat tube  12  have a rectangular cross section, for example, as shown in FIG. 7, the liquid refrigerant is liable to collect in wall corners of the flat tube  12  if the circuit width is diminished to give an increased surface area to the refrigerant because the liquid refrigerant which flows at a lower rate than the gas is forced toward the passageway ends. With the liquid refrigerant required for evaporation forced toward end portions, the liquid refrigerant will not adhere to the inner walls of the peripheral ridges  3 ,  3 , central ridges  4 ,  4  and channel dividing ridges  5 ,  5  in the flat tube  12  and will not be subjected to effective heat exchange, so that the heat exchanger fails to exhibit the desired performance.  
     [0100] When the divided refrigerant passageways  7  are made generally hexagonal in cross section as seen in FIG. 5, the liquid refrigerant collects in the recessed parts of intermediate portions of the passageways  7  with the greatest ease, adhering to the tapered surfaces of the peripheral ridges  3 ,  3 , those of the central ridges  4 ,  4  and those of the dividing ridges  5 ,  5  on the pair of plates  2 ,  2  for effective heat transfer and enabling these ridges to act effectively as interior fins to exhibit improved heat transfer performance. As a result, the heat transfer portions in the interior of the refrigerant passageways  7  are increased in the area of effective parts to cool air to assure comfort.  
     [0101] However, the evaporator  1  of the invention may be so shaped as shown in either one of FIGS. 5 and 7 because the entire width of the channel for passing cold refrigerant is equal to the width of contact of the corrugated fin  24  for the heat exchanger of the invention to achieve a higher heat exchange efficiency than the conventional one.  
     [0102] According to the first embodiment of the invention described, the plate  2  is, for example, 10 to 40 mm in width and 0.25 to 1.0 mm in thickness.  
     [0103] The peripheral ridge  3  on the plate  2  is, for example, 0.25 to 1.0 mm in thickness and 0.5 to 2.0 mm in width. The central ridge  4  on the plate  2  is, for example, 0.25 to 1.0 mm in thickness and 0.5 to 2.0 mm in width. The channel dividing U-shaped ridge  5  on the plate  2  is, for example, 0.25 to 1.0 mm in thickness and 0.25 to 1.0 mm in width.  
     [0104] With the evaporator  1  described above, the refrigerant introduced into the front header  23  through one of the through holes  28 , i.e., the inlet hole  28 , in the pipe connecting block  27  flows into divided refrigerant passageways  7  from one end of the U-shaped refrigerant channel  8  of each flat tube  12 , flows through the U-shaped passageways  7  to the other end of the channel  8 , further passes through the rear header  23  and the other through hole  28 , i.e., the outlet hole  28 , in the block  27  and flows out of the evaporator.  
     [0105] On the other hand, air flows through the evaporator  1  from the front rearward through the spaces each having the corrugated louver fin  24  therein and formed between the adjacent flat tubes  12  and between the tube  12  and each end plate  25  to undergo efficient heat exchange with the refrigerant through the walls of the flat tube  12 , the end plates  25  and the louver fins  24 .  
     [0106] The evaporator  1  according to the first embodiment is fabricated from plates which have recesses and ridges formed on one side thereof as by forging or cutting and which are used in place of conventional plates formed by press work. The front and rear headers are formed by header members which are separate from the plates. These features give the flat tubes  12  a reduced front-to-rear width and a decreased thickness (thinner layers) and afford a greater area of heat transfer, enabling the evaporator to achieve a higher heat transfer efficiency and exhibit greatly improved heat exchange performance.  
     [0107] To assure the refrigerant of improved heat transfer in the flat tube  12 , it is desired that a plurality of cutouts  15  be formed in the channel dividing U-shaped ridges  5  on each plate  2  at a predetermined spacing, for example as shwon in FIG. 8, the cutouts  15  in the adjacent ridges  5  being in a staggered arrangement, so as to cause the divided adjacent refrigerant passageways  7 ,  7  in the interior of the tube  12  to communicate with each other through the cutouts  15 .  
     [0108] Alternatively, the flat tube  12  may have turbulence promoting members (projections)  16  in a staggered arranged for producing turbulent flows of refrigerant for improved heat transfer, for example, as shown in FIGS. 9 and 10.  
     [0109]FIGS. 11 and 12 show a second embodiment of the invention. This embodiment differs from the first in that a pair of front and rear header members  41 ,  42  each in the form of a pipe having a rectangular cross section are used.  
     [0110] Stated more specifically, an evaporator  1  is fabricated from generally rectangular plates  2  which are aluminum plates. Each of these plates  2  has an edge ridge  33  provided on one side of the plate along opposite side edges and a lower edge thereof and U-shaped in its entirety, and a central ridge  34  provided on the same side of the plate  2  at the center of the width thereof and having a bifurcated upper end  34   a , the central ridge  34  extending from the upper end  34   a  downward to a position where a refrigerant return channel can be formed. The plate  2  has a U-shaped refrigerant channel recess  36  formed internally of the U-shaped edge ridge  33  and comprising front and rear straight refrigerant channel recess portion  36   a ,  36   a  formed on opposite sides of the central ridge  34  and a refrigerant return channel recess portion  36   c  positioned under the central ridge. The plate  2  has a plurality of channel diving U-shaped ridges  35  formed inside the channel recess  36  and extending over the approximate entire length thereof.  
     [0111] The corners of return channel recess portion  36   c  of the channel recess  36  has short circular-arc ridges  39  for achieving an improved heat exchange efficiency at the corner portions.  
     [0112] According to this second embodiment, the plate  2  is provided in the widthwise midportion of its upper end with a notch  37  which is U-shaped when seen from the front. The central ridge  34  has the bifurcated upper end  34   a.    
     [0113] Each plate  2  is formed, for example, by forging or cutting. Plates  2  are provided in pairs, and each pair of plates  2  are fitted together with their U-shaped channel recesses  36 ,  36  opposed to each other to join the opposed U-shaped edge ridges  33 ,  33  of the plates  2 ,  2  to each other end-to-end, the opposed central ridges  34 ,  34  including the bifurcated upper ends  34   a  to each other end-to-end and each of the opposed pairs of channel dividing rides  5 ,  5  each other end-to-end and to thereby form a flat tube  32  having upper ends  32   a ,  32   a  which are bifurcated and opened, with a plurality of U-shaped divided refrigerant passageways formed inside the flat tube  32 .  
     [0114] On the other hand, a pair of front and rear header members  41 ,  42  are each in the form of a pipe rectangular in cross section and having a lower wall  43 , front wall  45 , rear wall  46  and upper wall  47 . The header members  41 ,  42  have slits  44 ,  44  formed in the respective lower walls  43 ,  43  thereof and arranged at a predetermined spacing. Flat tubes  32  are arranged in parallel laterally, with a front and a rear header provided in communication with the bifurcated open upper ends  32   a ,  32   a  of the flat tubes  32 , by inserting the bifurcated open upper ends  32   a ,  32   a  thereof into the respective slits  44 ,  44  of the juxtaposed header members  41 ,  42  and thereby joining the flat tubes to the header members. At this time, the rear wall  46  and the front wall  45  of the respective juxtaposed front and rear header members  41 ,  42  are fitted as joined together into U-shaped notches  37 ,  37  in the upper ends of the opposed plates  2 ,  2  of each flat tube  32 .  
     [0115] Below the headers, a corrugated fin  24  is provided between the adjacent flat tubes  32 ,  32 . The fin  24  is joined at left and right sides thereof to the flat surfaces provided by the other sides of the plates  2 ,  2 .  
     [0116] The evaporator  1  of the second embodiment is fabricated in the same manner as the first in that the assembly of components is brazed in a vacuum, or in a furnace with use of a fluorine-containing flux, so that throughout the drawings concerned, like parts are designated by like reference numerals.  
     [0117] Although not shown, the pair of front and rear header members  41 ,  42  each in the form of rectangular pipe may be replaced by a single aluminum extrudate having two refrigerant channels generally rectangular in cross section and partitioned by a central wall for use in the evaporator  1  according to the second embodiment described. The extrudate has slits  44 ,  44  formed in the respective portions of a lower wall thereof which define the refrigerant channels and arranged at a predetermined spacing. A front and a rear header are provided in communication with the bifurcated open upper ends  32   a ,  32   a  of the juxtaposed flat tubes  32  by inserting the bifurcated open upper ends  32   a ,  32   a  the tubes into the respective slits  44 ,  44  and thereby joining the tubes to the lower wall.  
     [0118] FIGS.  13  to  17  show a third embodiment of the present invention, which differs from the first in that headers  57  and headers  58  are provided respectively at the top and bottom of an evaporator  1 .  
     [0119] With reference to these drawings, a generally rectangular plate  2  made of an aluminum plate has a peripheral ridge  3  provided on one side of the plate  2  along a periphery thereof and a central ridge  4  provided on the same side of the plate  2  at the center of the width thereof and extending vertically. Formed in the plate  2  internally of the peripheral ridge  3  are front and rear refrigerant channel recess portions  6   a ,  6   b  positioned on opposite sides of the central ridge  4  and through holes  10 ,  10  formed in the upper and lower ends of the recess portions  6   a ,  6   b . The plate  2  has straight channel diving ridges  5  formed inside the channel recess portions  6   a ,  6   b  and extending over the approximate entire length of the portions  6   a ,  6   b.    
     [0120] The plate  2  is formed, for example, by forging or cutting. Such plates  2  are provided in pairs, and each pair of plates  2  are fitted together with their recess portions  6   a ,  6   b  opposed to each other to join the opposed peripheral ridges  3 ,  3  of the plates  2 ,  2  to each other end-to-end, the opposed central ridges  4 ,  4  thereof to each other end-to-end and each of the opposed pairs of channel dividing rides  5 ,  5  to each other end-to-end and to thereby form a flat tube  12  having a U-shaped refrigerant channel  8  inside thereof, with parallel divided refrigerant passageways  7  formed in the inside the flat tube  12  (see FIG. 7 of the first embodiment).  
     [0121] A required number of flat tubes  12  are arranged side by side. Spectacle-shaped upper and lower header members  51 ,  52 , each comprising a pair of front and rear refrigerant passing tube portions  53 ,  53  or  54 ,  54  and a connecting portion  55  or  56  therebetween, are interposed respectively between the upper ends of each pair of adjacent flat tubes and between the lower ends thereof, the tube portions  53  or  54  being in communication with the corresponding through holes  10  of the opposed plates  2 .  
     [0122] As shown in detail in FIG. 14, of the pairs of front and rear through holes  10 ,  10  formed in the upper and lower ends of the plate  2 , the pair of front and rear through holes  10   a ,  10   a  in the upper end of the plate  2  are each in the form of a circle which is elongated horizontally. In corresponding relation with these holes, the front and rear tube portions  53 ,  53  of the upper header member  51  provided between the upper ends of the flat tubes  12 ,  12  have a circular cross section which is similarly elongated horizontally. On the other hand, the pair of front and rear through holes  10   b ,  10   b  in the lower end of the plate  2  are each in the form of a circle which is elongated as inclined forwardly downward or rearwardly downward. In corresponding relation with these holes, the front and rear tube portions  54 ,  54  of the lower header member  52  provided between the lower ends of the flat tubes  12 ,  12  have a circular cross section which is similarly elongated as inclined forwardly downward or rearwardly downward.  
     [0123] With reference to FIGS. 16 and 17, opposite end faces of the tube portions  53 ,  53  and  54 ,  54  of the upper and lower header members  51 ,  52  are joined to flat surfaces on the other sides of the plates of the flat tubes  12 ,  12  which surfaces are opposed to the end faces, whereby upper and lower headers  57 ,  58  are formed in communication respectively with the upper ends and lower ends of the flat tubes  12 ,  12 .  
     [0124] Between the upper and lower headers  57 ,  58 , a corrugated louver fin  24  for effecting heat exchange with air is interposed between each pair of adjacent flat tubes  12 ,  12 . The fin  24  is joined at opposite side edges thereof to the other sides, i.e., the flat surfaces of the plates  2 ,  2  of the flat tubes  12 ,  12 .  
     [0125] Of the upper and lower header members  51 ,  52  between the adjacent flat tubes  12 ,  12  in the evaporator  1  of the third embodiment, the lower header member  52  has passages  59 ,  59  formed at opposite sides of the intermediate connecting portion  56  for interconnecting the front and rear tube portions  54 ,  54  of the header member  52 .  
     [0126] With the evaporator  1  of the third embodiment described, the refrigerant is introduced from an inlet through hole  18  in an inlet-outlet pipe connecting block  27  into the front tube portion  53  of each upper header member  51  providing the front upper header  57 , from which the refrigerant flows into the front upper end of refrigerant channel  8  of each flat tube  12 , further flows down the straight divided refrigerant passageways  7  to reach the front lower end of the channel  8 , from which the refrigerant temporarily flows into the front tube portion  54  of the lower header member  52  providing the front lower header  58 , then passes through the interconnecting passages  59 ,  59  in the lower header member  52  and flows into the rear tube portion  54  providing the rear lower header  58 . Subsequently, the refrigerant flows into the rear lower end of the refrigerant channel  8  of the flat tube  12 , further ascends the straight divided refrigerant passageways  7  to reach the rear upper end of the channel  8 , passes through the rear tube portion  53  of the upper header member  51  providing the rear upper header  57  and flows out of an outlet through hole  28  in the block  27 .  
     [0127] With the evaporator  1  of the third embodiment, the front and rear tube portions  54 ,  54  of the lower header member  52  between the lower ends of the flat tubes  12 ,  12  have a circular cross section which is elongated as inclined forwardly downward or rearwardly downward so as to cause the water produced upon condensation on the outer surface of the evaporator  1  during due to be drained smoothly.  
     [0128] Although not shown, the evaporator  1  of the third embodiment may also be modified like the modification of FIG. 8, by forming a plurality of cutouts  15  in the channel dividing ridges  5  on each plate so that the adjacent divided refrigerant passageways  7 ,  7  inside the flat tube  12  communicate with each other through the cutouts  15 .  
     [0129] Of the upper and lower header members  51 ,  52  provided between the adjacent flat tubes  12 ,  12  at their upper ends and lower ends in the evaporator  1  of the third embodiment, the upper header member  51  may have passages  59 ,  59  formed at opposite sides of the intermediate connecting portion  55  for interconnecting the front and rear tube portions  53 ,  53  of the header member  51 , in converse relation with the illustrated case so as to cause the refrigerant to flow in the opposite direction to the illustrated case.  
     [0130] The evaporator  1  of the third embodiment otherwise has the same construction as the first embodiment described, so that like parts are designated by like reference numerals throughout the drawings concerned.  
     [0131]FIGS. 18 and 19 show a second modification of channel dividing ridges  5  on the plate  2  for use in the evaporator according to the first embodiment of the invention, i.e., channel dividing ridges  5   a ,  5   b  formed in the refrigerant channel recess  6  of each plate  2 , which differ from the channel dividing U-shaped ridges  5  shown in FIGS. 2, 3 and  5  showing the first embodiment in configuration and arrangement. Another difference is that the ridges  5   a ,  5   b  on each plate  2  have top ends joined to the flat bottom wall of the plate  2  opposed thereto and providing the refrigerant channel recess  6  thereof.  
     [0132] With reference to FIGS. 18 and 19, each plate  2  of the evaporator  1  has on one side thereof a peripheral ridge  3  along the periphery thereof and a central ridge  4  at the center of the width of the plate and extending downward from the upper end of the plate to a position where a return channel can be formed. More specifically, each pair of plates  2   a ,  2   b  have formed in a refrigerant channel recess  6  thereof a multiplicity of front and rear channel dividing ridges  5   a ,  5   b  having a height twice the depth of the channel recess  6 . These ridges  5   a ,  5   b  are so provided as to form independent parallel U-shaped divided refrigerant passageways  7  in a U-shaped refrigerant channel  8  of a flat tube  12  when the pair of plates  2   a ,  2   b  are fitted together.  
     [0133] With reference to FIG. 18, these ridges  5   a ,  5   b  each comprise a straight portion  5   a   1  or  5   b   1  positioned in the front or rear straight channel recess portion  6   a  or  6   b  of the refrigerant channel recess  6  and a quarter circular-arc portion  5   a   2  or  5   b   2  extending from the straight portion and positioned in the return portion  6   c  of the recess  6 . The ridges  5   a ,  5   b  correspond to exactly half of a U-shape in configuration.  
     [0134] When the pair of plates  2   a ,  2   b  are fitted together with the recesses  6 ,  6  opposed to each other, the straight portions  5   a   1 ,  5   b   1  and quarter circular-arcs  5   a   2 ,  5   b   2  of these ridges  5   a ,  5   b  are alternately arranged at a predetermined spacing.  
     [0135] With the pair of plates  2   a ,  2   b  fitted together, the opposed central ridges  4 ,  4  are butted against and joined to each other, with the peripheral ridges  3 ,  3  similarly joined to each other, and the straight portions  5   a   1 ,  5   b   1  and the quarter circular-arcs  5   a   2 ,  5   b   2  of the channel dividing ridges  5   a ,  5   b  on each of the plates  2   a ,  2   b  are joined at their top ends to the bottom wall flat surface of the other plate  2   a  or  2   b  opposed thereto and providing the channel recess  6 , whereby a flat tube  12  is formed with a U-shaped refrigerant channel  8  formed therein. In the channel  8  of the flat tube  12 , the front channel dividing ridges  5   a  on the plate  2   a  of the pair  2   a ,  2   b  are joined in a U-form to the rear ridges  5   b  on the other plate  2   b , providing divided parallel U-shaped refrigerant passageways  7 . The divided passageways  7  in the return portion are in the form of semicircular arcs.  
     [0136] The return channel recess portion  6   c  of the U-shaped channel recess  6  is provided at the corners on front and rear sides with short circular-arc ridges  9   a ,  9   b  to ensure improved heat exchange performance of this portion. These circular-arc ridges  9   a ,  9   b  are so arranged as to be positioned alternately at a predetermined spacing when the pair of plates  2   a ,  2   b  are fitted together with the recesses  6 ,  6  thereof opposed to each other.  
     [0137] The above modification is the same as the first embodiment otherwise; for example, each plate  2  is made by forging or cutting. Throughout the drawings concerned, therefore, like parts are designated by like reference numerals.  
     [0138] With the evaporator  1  described above, the front and rear channel dividing ridges  5   a ,  5   b  on the pair of plates  2   a ,  2   b  comprise straight portions  5   a   1 ,  5   b   1  and quarter circular-arc portions  5   a   2 ,  5   b   2  and are shaped to correspond to exactly half of a U-shape. These ridges  5   a ,  5   b  are so arranged that when the pair of plates  2   a ,  2   b  are fitted together with the recesses  6 ,  6  opposed to each other, the ridges  5   a ,  5   b  are positioned alternately at a predetermined spacing. Accordingly, the number of dividing ridges  5   a ,  5   b  to be made as by forging or cutting can be diminished, while the ridges  5   a ,  5   b  on the plates  2   a ,  2   b  can be spaced apart by an increased interval and can be shaped to have exactly half of the U-shape, hence the advantage that the plates  2   a ,  2   b  are easy to produce.  
     [0139]FIGS. 20 and 21 show a third modification of channel dividing ridge  5  on the plate  2  for use in the evaporator  1  according to the first embodiment of the invention. The modification differs from the first embodiment in that two kinds of plates  2   a ,  2   b  have channel dividing U-shaped ridges  5   a ,  5   b  which are different in arrangement in refrigerant channel recesses  6 ,  6 , and that the ridges  5   a ,  5   b  on the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surface of the recesses  6  of the plates  2   b ,  2   a  opposed thereto.  
     [0140] With reference to the same drawings, the channel dividing U-shaped ridges  5   a ,  5   b  having a height twice the depth of recesses  6 ,  6  are provided in the U-shaped recesses  6 ,  6  of the pair of plates  2   a ,  2   b  so as to be alternately positioned at a predetermined spacing when these plates  2   a ,  2   b  are fitted together face-to-face.  
     [0141] With these plates  2   a ,  2   b  fitted together face-to-face, the opposed central ridges  4 ,  4 , as well as the opposed plate peripheral ridges  3 ,  3 , are butted against and joined to each other, and the channel dividing U-shaped ridges  5   a ,  5   b  on the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surfaces of the recesses  6 ,  6  of the plates  2   b ,  2   a  opposed thereto, whereby a flat tube  12  is formed which has parallel U-shaped refrigerant passageways  7  divided by the ridges  5   a ,  5   b  and provided in the U-shaped refrigerant channel  8 .  
     [0142] In the front and rear corners of the refrigerant return channel recess portions  6   c  of the U-shaped refrigerant channel recesses  6 ,  6 , short circular-arc ridges  9   a ,  9   b  are provided for these portions to exhibit improved heat exchange performance. These front and rear short circular-arc ridges  9   a ,  9   b  are alternately positioned at a predetermined spacing when the pair of plates  2   a ,  2   b  are fitted together face-to-face.  
     [0143] The above modification is the same as the first embodiment otherwise; for example, each plate  2  is made by forging or cutting. Throughout the drawings concerned, therefore, like parts are designated by like reference numerals.  
     [0144] With the evaporator  1  wherein the two kinds of plates  2   a ,  2   b  are used, the channel dividing U-shaped ridges  5   a ,  5   b  on the two plates  2   a ,  2   b  are so arranged that when these plates  2   a ,  2   b  are fitted together face-to-face, the ridges  5   a ,  5   b  are positioned alternately at a predetermined spacing. Accordingly, the number of dividing ridges  5   a ,  5   b  to be made as by forging or cutting can be smaller, while the ridges  5   a ,  5   b  on the plates  2   a ,  2   b  can be spaced apart by an increased interval, hence the advantage that the plates  2   a ,  2   b  are easy to produce.  
     [0145]FIGS. 22 and 23 show a fourth modification of channel dividing ridge  5  on the plate  2  for use in the evaporator  1  according to the first embodiment of the invention. The modification differs from the first embodiment in that a multiplicity of channel dividing ridges  5  are provided only in the rear half of the refrigerant channel recess  6  of each plate  2 , with no ridges  5  whatever provided in the front half of the recess  6  and with the front half made flat-surfaced, in that the ridges  5  are shaped to have exactly half of a U-shape, and in that the ridges  5  on each plate  2  have their top ends joined to the bottom wall flat surface of the recess  6  of the other plate  6  opposed thereto.  
     [0146] With reference to the same drawings, each plate  2  of the evaporator  1  has a peripheral ridge  3  provided on one side of the plate along a periphery thereof and a central ridge  4  provided on the same side of the plate at the center of the width thereof and extending downward from an upper end of the plate to a position where a return channel can be formed. A multiplicity of channel dividing ridges  5   b  having a height twice the depth of the recess  6  are provided in the rear half of the refrigerant channel recess  6  of each plate  2 , with no ridges  5  whatever provided in the front half of the recess  6  and with the front half made flat-surfaced.  
     [0147] Stated more specifically with reference to FIG. 22, the channel dividing ridges  5   b  provided in the rear half of the refrigerant channel recess  6  of each plate  2  each comprise a straight portion  5   b   1  formed in a rear straight channel recess portion  6   b  and a quarter circular-arc portion  5   b   2  extending from the straight portion and provided in a return portion  6   c  of the recess  6 , the ridges  5   b  being shaped to have exactly half of a U-shape.  
     [0148] With a pair of plates  2   a ,  2   b  fitted together face-to-face, the opposed central ridges  4 ,  4 , as well as the opposed plate peripheral ridges  3 ,  3 , are butted against and joined to each other, and the channel dividing U-shaped ridges  5 ,  5  on the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surfaces of the refrigerant channel recesses  6 ,  6  of the plates  2   b ,  2   a  opposed thereto, whereby a flat tube  12  is formed which has a U-shaped refrigerant channel  8 . The front ridges  5   a  on one plate  2   a  of the two  2   a ,  2   b  are made continuous with the rear ridges  5   b  on the other plate  2   b , whereby parallel U-shaped divided refrigerant passageways  7  are formed in the U-shaped refrigerant channel  8  of the flat tube  12 . The passageways  7  have semicircular-arc return portions.  
     [0149] Short circular-arc ridges  9  are provided on the rear corner portion of the return channel recess portion  6   c  of the recess  6  for this portion to exhibit improved heat exchange performance.  
     [0150] The above modification is the same as the first embodiment otherwise; for example, each plate  2  is made by forging or cutting. Throughout the drawings concerned, therefore, like parts are designated by like reference numerals.  
     [0151] With the evaporator  1 , the channel dividing ridges  5  on each plate  2  each comprise a straight portion  5   b   1  and a quarter circular-arc portion  5   b   2  extending therefrom and are shaped to have exactly half of a U-shape, while the front half of the recess  6  of each plate  2  has a flat surface provided with no channel dividing ridges  5 . Accordingly, the ridges  5  to be formed on the plate  2  as by forging or cutting can be half, hence the advantage that the plates  2   a ,  2   b  are easy to make.  
     [0152]FIG. 24 shows a pair of plates for use in the evaporator  1  of the first embodiment of the invention, with one of the plates replaced by a flat plate.  
     [0153] With reference to the drawing, the ridged plate  2  of the first embodiment, i.e., the plate  2   b  comprises, as will be apparent from FIG. 2, a peripheral ridge  3  provided on one side of the plate along a periphery thereof and a central ridge  4  provided on the same side of the plate at the center of the width thereof and extending downward from the upper end of the plate to a position where a refrigerant return channel can be formed. Formed in the plate internally of the peripheral ridge  3  is a U-shaped refrigerant channel recess  6  comprising front and rear straight refrigerant channel recess portions  6   a ,  6   b  positioned on opposite sides of the central ridge  4  and a refrigerant return channel recess portion  6   c  positioned under the central ridge. The plate has a plurality of channel diving U-shaped ridges  5  formed inside the channel recess  6  and extending over the approximate entire length thereof. The plate  2   b  is provided in the widthwise midportion of its upper end with a notch  14  which is U-shaped when seen from the front. The central ridge  4  is joined at its upper end to the peripheral ridge  3  at the lower end of this notch  14 . The channel recess  6  of the plate  2   b  has one of refrigerant inlet-outlet through holes  10 ,  10  formed at one end thereof and the other through hole  10  formed at the other end thereof.  
     [0154] The flat plate  2   a , on the other hand, has no U-shaped recess nor any channel dividing U-shaped ridge but has a flat surface and the same contour as the ridge plate  2   b . The plate  2   a  is provided at the widthwise midportion of its upper end with a notch which is U-shaped when seen from the front. The flat plate  2   a  further has refrigerant inlet-outlet through holes formed in its upper end at front and rear sides thereof (not shown).  
     [0155] Such flat plates  2   a  and ridged plates  2   b  are provided in pairs, with each pair of plates fitted together face-to-face. The peripheral ridge  3  on the ridged plate  2   b  has its top end joined to the flat surface of the peripheral edge portion of the flat plate  2   a , with the top end of the central ridge  4  joined to the flat surface of the central portion of the flat plate  2   a , and with the top ends of the ridges  5  joined to the corresponding flat surface portions of the flat plate  2   a , whereby a flat tube  12  is formed which has a U-shaped refrigerant channel  8 , with a plurality of divided refrigerant passageways  7  formed in the channel  8 .  
     [0156] The evaporator  1  comprising flat plates  2   a  described is the same as the first embodiment otherwise; for example, the ridged plate  2   b  is made as by forging or cutting. Throughout the drawings concerned, therefore, like parts are designated by like reference numerals.  
     [0157] The evaporator  1  comprises ridged plates  2   b  having a peripheral ridge  3 , central ridge  4  and channel dividing ridges  5 , and flat plates  2   a -having the same contour as the plate  2   b . This serves to halve the number of ridged plates  2   b  used which are prepared as by forging or cutting, consequently entailing the advantage of making the evaporator  1  easy to fabricate.  
     [0158] The evaporator  1  can be modified as will be described below which is the second embodiment of the invention shown in FIGS. 11 and 12 and wherein a pair of front and rear header members  41 ,  42  used are each in the form of a pipe of rectangular cross section.  
     [0159] Like the modification shown in FIGS. 18 and 19, the first of modifications has a multiplicity of channel diving ridges  5   a ,  5   b  formed in the channel recess  6  of each plate  2 , comprising straight portions  5   a   1 ,  5   b   1  and quarter circular-arc portions  5   a   2 ,  5   b   2  extending therefrom, and having exactly half of a U-shape and a height twice the depth of the recess  6 . When a pair of plates  2   a ,  2   b  are fitted together face-to-face, a flat tube  12  is formed wherein the ridges  5   a ,  5   b  form independent parallel U-shaped divided refrigerant passageways  7  in a U-shaped refrigerant channel  8 . The ridges  5   a ,  5   b  of each plate  2  have their top ends joined to the bottom wall flat surface of the recess  6  of the other plate  2  opposed to the ridges. Like the modification shown in FIGS. 20 and 21, two kinds of plates  2   a ,  2   b  can be used in the second modification to be described below. The plates  2   a ,  2   b  have channel dividing U-shaped ridges  5   a ,  5   b  which are different in arrangement in refrigerant channel recesses  6 ,  6 , and have a height twice the depth of the recesses  6 ,  6 . In this case, the ridges  5   a ,  5   b  on each of the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surface of the recesses  6  the other of these plates  2   b ,  2   a  opposed thereto.  
     [0160] As is the case with the embodiment shown in FIGS. 22 and 23, usable in a third modification are plates  2  which have a multiplicity of channel dividing ridges  5  formed only in the rear half of the refrigerant channel recess  6 . The front half of the recess  6  has no ridges whatever and is flat-surfaced. In this case, the ridges  5  on each plate  2  have their top ends joined to the bottom wall flat surface of the recess  6  of the other plate  2  opposed thereto.  
     [0161] As is the case with the flat tube shown in FIG. 24, usable in a fourth modification in combination with a ridged plate  2   b  which is the plate  2  of the second embodiment of FIG. 12 is a flat plate  2   a  having the same contour as the plate  2   b . In this case, the peripheral ridge  3  on the ridged plate  2   b  has its top end joined to the flat surface of the peripheral edge portion of the flat plate  2   a , with the top end of the central ridge  4  joined to the flat surface of the central portion of the flat plate  2   a  and with the top ends of the channel dividing ridges  5  joined to the corresponding flat surface portions of the flat plate  2   a , whereby a flat tube  12  is provided wherein a plurality of U-shaped divided refrigerant passageways  7  are formed in a refrigerant channel  8 .  
     [0162] Although not shown, the evaporator  1  of the third embodiment of the invention wherein the upper and lower headers  57 ,  58  are provided may comprise the pair of front and rear header members  41 ,  42  each in the form of a rectangular pipe and shown in FIGS. 11 and 12, in place of the spectacle-shaped upper and lower header members  51 ,  52  shown in FIGS. 16 and 17.  
     [0163] The evaporator thus modified will be referred to a fourth embodiment of the invention. The evaporator  1  according to the fourth embodiment of the invention will be described using reference numerals of FIGS. 11 and 12. Each of plates  2  in pairs has straight side edge ridges  33 ,  33  provided on one side of the plate along opposite side edges thereof and a central ridge  34  provided on the same side of the plate at the center of the width thereof and having bifurcated upper and lower ends  34   a ,  34   a , the ridges being formed by forging or cutting, each plate  2  having front and rear straight channel recess portions  36   a ,  36   a  formed inwardly of the side edge ridges on opposite sides of the central ridge  34 , each plate  2  having a flat surface on the other side thereof, each of the pairs of plates being fitted together with their front and rear channel recess portions  36   a ,  36   b  opposed to each other to join the opposed straight side edge ridges  33 ,  33  to each other end-to-end and the opposed central ridges  34 ,  34  including the bifurcated upper and lower ends  34   a ,  34   a  to each other end-to-end and to thereby form a flat tube  32  having bifurcated open upper and lower ends and front and rear straight fluid channels  38 ,  38  inside thereof, an upper and a lower pair of front and rear header members  41 ,  42  being each in the form of a pipe having a rectangular cross section, each of the header members  41 ,  42  having slits  44 ,  44  formed in an upper wall  47  or a lower wall thereof  43  and arranged at a predetermined spacing, a plurality of flat tubes  32  being arranged in parallel by inserting the bifurcated upper or lower ends thereof into the respective slits  44 ,  44  in the header members  41 ,  42  to join the flat tubes to the header members and to provide an upper and a lower pair of front and rear headers in communication with the bifurcated upper and lower ends of the flat tubes  32  respectively. At this time, the rear wall  46  and the front wall  45  of the respective juxtaposed front and rear header members  41 ,  42  are fitted as joined together into U-shaped notches  37 ,  37  in the upper ends of the opposed plates  2 ,  2  of each flat tube  32 .  
     [0164] Described below are modifications of the evaporator  1  of the third embodiment of the invention wherein the upper and lower headers  57 ,  58  are provided by the spectacle-shaped upper and lower header members  51 ,  52  and the evaporator  1  of the fourth embodiment of the invention wherein the upper and lower headers are provided by pairs of front and rear header members  41 ,  42  in the form of rectangular pipes.  
     [0165] Like the embodiment shown in FIGS. 18 and 19, usable for a first modification are plates  2 ,  2   a ,  2   b  each having formed in respective front and rear refrigerant channel recess portions  6   a ,  6   b  thereof many front and rear channel dividing ridges  5   a ,  5   b  having a height twice the depth of the recess portions  6   a ,  6   b . These ridges  5   a ,  5   b  are so provided as to form parallel divided independent refrigerant passageways  7  in a refrigerant channel  8  in a flat tube  12  when each of pairs of plates  2   a ,  2   b  are fitted together face-to-face. In this case, the channel dividing ridges  5   a ,  5   b  of each of the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surface of recess portions  6   a ,  6   b  of the other plate  2   a  or  2   b  opposed thereto.  
     [0166] Like the embodiment shown in FIGS. 20 and 21, two kinds of plates  2   a ,  2   b  are usable for a second modification. These plates  2   a ,  2   b  are different in the arrangement of straight channel dividing ridges  5   a ,  5   b  which are provided in refrigerant channel recesses  6 ,  6  and which have a height twice the depth of the recesses  6 ,  6 . In this case, the straight channel dividing ridges  5   a ,  5   b  on each of the plates  2   a ,  2   b  have their top ends joined to the bottom wall flat surface of recess portion of the other plate  2   a  or  2   b  opposed thereto.  
     [0167] As is the case with the embodiment shown in FIGS. 22 and 23, usable in a third modification are plates  2  which have a multiplicity of channel dividing straight ridges  5  formed only in the rear half of the refrigerant channel recess  6 . The front half of the recess  6  has no ridges whatever and is flat-surfaced. In this case, the straight ridges  5  on one plate  2  have their top ends joined to the bottom wall flat surface of the recess  6  of the other plate  2  opposed thereto.  
     [0168] As in the case of the flat tube shown in FIG. 24, usable in a fourth modification in combination with a ridged plate  2   b  is a flat plate  2   a  having the same contour as the plate  2   b . In this case, the side edge ridges  3 ,  33  on the ridged plate  2   b  have their top ends joined to the flat surface of the side edge portions of the flat plate  2   a , with the top end of the central ridge  4 ,  34  joined to the flat surface of the central portion of the flat plate  2   a  and with the top ends of the channel dividing straight ridges  5  joined to the corresponding flat surface portions of the flat plate  2   a , whereby a flat tube  12 ,  32  is provided which has front and rear straight refrigerant channel  8 ,  38  formed in the tube and a plurality of divided refrigerant passageways  7  formed in the refrigerant channel  8 ,  38 .  
     [0169] Although the heat exchanger  1  of the present invention has been described with reference to embodiments for use as evaporators for motor vehicle air conditioners, the present invention can be applied also to heat changers for use in motor vehicles or in industries, such as evaporators, condensers, oil coolers, intercoolers, heater cores, etc.  
     [0170] In the case where the heat exchanger  1  of the invention is to be used, for example, as a heater heat exchanger for heating systems, efficient heat exchange is available since the entire width of the channel for the fluid is equal to the contact width of the radiator fin  24 . Furthermore, the internal fluid can be passed in a counterflow relation with air. This results in an increased temperature efficiency to achieve higher heat exchanger effectiveness and realize a compacted device.