Abstract:
A heat exchanger which, while having excellent heat exchanging performance, has a structure easy to produce, is of low cost, and has high quality and reliability. The heat exchanger has first base plates ( 26 ), in each of which first slits ( 30 ) and second slits ( 40 ) are provided in substantially parallel to each other, and has second base plates ( 28 ), in each of which third slits ( 50 ) with substantially the same shape as a first slit ( 30 ) are provided. The length in the longitudinal direction of a second base plate ( 28 ) is set to be less than the length of a second slit ( 40 ). The first base plates ( 26 ) and the second base plates ( 28 ) are layered over each other such that the first slits ( 30 ) provided in the first base plates ( 26 ) and the third slits ( 50 ) provided in the second base plates ( 28 ) are communicated. Flow paths ( 60 ) outside tubes are constructed by the first slits ( 30 ) provided in the first base plates ( 26 ) and the third base plates ( 50 ) provided in the second base plates ( 28 ). Flow paths ( 70 ) inside the tubes are constructed by the second slits ( 40 ) provided in the first base plates ( 26 ) and the second base plates ( 28 ). Since a heat exchanging section formed only by tubes can be constructed by the base plates with the slits, the heat exchanger can be easily produced. Further, the heat exchanger can be provided at low cost.

Description:
RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2005/007062 filed on Apr. 12, 2005, which in turn claims the benefit of Japanese Application No. 2004-118621 filed on Apr. 14, 2004, and Japanese Application No. 2005-035624 filed on Feb. 14, 2005, the disclosures of which Applications are incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to a heat exchanger for a cooling system, a heat radiation system, and a heating system, and more particularly to a heat exchanger of liquid and gas used in a system such as an information device requiring compactness. 
     BACKGROUND ART 
     Conventionally, a heat exchanger formed of tubes and fins is generally used. For aiming at compactness, recently, the tube diameter and tube pitch have been decreased, and the tube density has been increased. For example, a heat exchanging section is formed of extremely thin tubes of which outer diameter is about 0.5 mm. 
       FIG. 27  is a front view of a conventional heat exchanger disclosed in Japanese Patent Unexamined Publication No. 2001-116481. In the conventional heat exchanger, inlet tank  31  and outlet tank  32  are faced to each other at a predetermined interval as shown in  FIG. 27 . Core section  34  is formed between inlet tank  31  and outlet tank  32 , and, in core section  34 , a plurality of tubes  33  with annular cross section are disposed and external fluid flows outside tubes  33 . 
     Tubes  33  are arranged in a square grid shape, the outer diameter of tubes  33  is set between 0.2 mm and 0.8 mm inclusive, and the value derived by dividing the pitch between adjacent tubes  33  by the outer diameter is set between 0.5 and 3.5 inclusive. Thus, the heat exchange amount per working power can be significantly increased. 
     The specific elements and manufacturing method of the conventional heat exchanger are not described. In a generally considered method, however, many thin tubes  33  are prepared, inlet tank  31  and outlet tank  32  of which specific surfaces previously have many small circular holes are prepared, the opposite ends of tubes  33  are inserted into the circular holes in inlet tank  31  and outlet tank  32 , and the inserted parts of tubes  33  are bonded to inlet tank  31  and outlet tank  32  by welding or the like. However, for manufacturing the thin circular tubes, a precise processing device is required, and hence the heat exchanger becomes expensive. Further, small circular holes into which tubes  33  are inserted must be disposed in inlet tank  31  and outlet tank  32  at a predetermined fine pitch, and hence it is difficult to perform a process of inserting and bonding tubes  33  to inlet tank  31  and outlet tank  32 . Therefore, even when the heat exchanging performance of such a heat exchanger is high, the heat exchanger is extremely expensive, the reliability against the leak of the used fluid is not sufficient, and hence problems remain. 
     The present invention addresses the conventional problems, and provides a heat exchanger that keeps extremely high heat exchanging performance, has an easy-to-manufacture structure, is inexpensive, and has high reliability. 
     SUMMARY OF THE INVENTION 
     In a heat exchanger of the present invention, a plurality of substrates that have a plurality of long plates arranged substantially in parallel, slits disposed between the long plates, and recesses disposed longitudinally continuously in one-side main surfaces of some long plates are stacked. The long plates of adjacent substrates are interconnected to form tubes. The recesses form tube internal flow channels, and the slits form tube external flow channels. Thus, the heat exchanging section including only tubes can be formed on the substrates. 
     In the heat exchanger of the present invention, substrates and other substrates are alternately stacked. The former substrates have a plurality of long plates arranged substantially in parallel and slits disposed between the long plates. The latter substrates have a plurality of long plates arranged substantially in parallel, slits disposed between the long plates, and recesses disposed longitudinally continuously in one-side main surfaces of long plates. Thus, about half the total number of substrates requires only simple drilling, so that the structure and manufacturing process of the heat exchanger are simplified. 
     In the heat exchanger of the present invention, holding plates for holding the long plates at their both ends and long holes formed inside the holding plates are disposed on the substrates. The ends of the recesses formed in one-side main surfaces of some long plates communicate with the long holes, and the long holes in adjacent substrates are interconnected, thereby forming branch flow channels. The tube internal flow channels formed of the recesses are connected to the branch flow channels. The substrate where the branch flow channels and tubes are integrated can be thus formed. 
     In the heat exchanger of the present invention, by setting the thickness of some long plates to be smaller than that of the holding plates, a clearance is formed between the tubes also in the stacking direction of the substrates, and tube external flow channels are formed also between the substrates. Thus, the heat transfer area outside the tubes can be increased, the tube external flow channels can be widened, and flow resistance of the tube external fluid can be suppressed. 
     In the heat exchanger of the present invention, the fluid in the tube external flow channels is made to flow in the plane direction of the substrates. Therefore, the boundaries between the stacked substrates do not disturb the flow of the tube external fluid. 
     In the heat exchanger of the present invention, lids for covering the long holes are disposed at both ends of the stacked substrates, and a part of each lid has an inflow tube or an outflow tube. Thus, a part forming a branch flow channel can be used also as the inflow tube or the outflow tube. 
     In the heat exchanger of the present invention, the substrates are made of resin. The heat exchanger can be thus lightened. 
     The heat exchanger of the present invention is manufactured by bonding and stacking the substrates by welding. 
     The substrates are easily bonded to each other without clogging the tube internal flow channels and the tube external flow channels. 
     In the present invention, the heat exchanging section formed of only tubes can be formed of substrates, so that the heat exchanger can be manufactured using extremely inexpensive components. 
     In the heat exchanger of the present invention, the branch flow channels can be formed of substrates integrally with the tubes, so that the connection between the tubes and branch flow channels is not required, the process can be further simplified, and the reliability against the leak of liquid and fluid can be improved. 
     In the heat exchanger of the present invention, a plurality of first substrates and second substrates are stacked. Each first substrate has a plurality of first slits and second slits substantially in parallel. Each second substrate has third slits with substantially the same shape as that of the first slits at substantially the same positions as the projection positions of the first slits, and is shorter than the longitudinal length of the second slits. The first slits and the third slits form tube external flow channels, and the second slits and the second substrates form tube internal flow channels. 
     Thus, the heat exchanging section formed of only tubes can be formed of substrates having slits, so that the heat exchanger can be relatively easily manufactured. 
     In the heat exchanger of the present invention, a plurality of first substrates are stacked between second substrates. 
     Thus, the cross section of the tube internal flow channels can be easily varied by changing the number of stacked first substrates. 
     In the heat exchanger of the present invention, the tube internal flow channels are enlarged in the substrate stacking direction on an inflow side of external fluid. 
     Thus, on the inflow side of the external fluid, on which the temperature difference between the external fluid and internal fluid is large and the amount of heat exchange is large, much internal fluid can be made to flow, and efficient heat exchange is allowed. Therefore, the heat exchanger can be further decreased. 
     In the heat exchanger of the present invention, the inlet and outlet of the tube internal flow channels are extended in the direction of the tube external flow channels. Thus, the opening area of the inlet and outlet of the internal fluid can be increased, the resistance in tube can be reduced, and the flow rate of the internal fluid can be increased. The performance of the heat exchanger can be therefore increased, and hence the heat exchanger can be downsized. 
     In the manufacturing method of the heat exchanger of the present invention, at least either the first substrates or second substrates are processed by pressing. Thus, the substrates can be manufactured easily and inexpensively. 
     In the manufacturing method of the heat exchanger of the present invention, at least either the first substrates or second substrates are processed by etching. Thus, even when the interval between the first slit and second slit is shortened, and the wall thickness of the tube internal flow channel is reduced, stress is not applied in manufacturing the slits. The heat exchanger can be therefore, easily manufactured. 
     In the manufacturing method of the heat exchanger of the present invention, the substrates are bonded together by thermal welding. Thus, the substrates can be easily bonded together without using solder material, the tube internal flow channels are not clogged, and the quality and reliability of the heat exchanger are improved. 
     In the manufacturing method of the heat exchanger of the present invention, the substrates are bonded together by ultrasonic bonding. 
     Thus, the material of only the bonding part melts. Therefore, a problem of clogging of the tube internal flow channels by the melting material can be avoided, and hence the reliability of the heat exchanger is further improved. 
     In the manufacturing method of the heat exchanger of the present invention, the substrates are bonded together by diffusion bonding. 
     Thus, the material does not melt. Therefore, the tube internal flow channels are not clogged, and hence the reliability of the heat exchanger is further improved. 
     The heat exchanger of the present invention has an easy-to-manufacture structure, and hence can be provided inexpensively. 
     The manufacturing method of the heat exchanger of the present invention can provide a heat exchanger that is easy-to-manufacture and has high quality and reliability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a heat exchanger in accordance with exemplary embodiment 1 of the present invention. 
         FIG. 2  is a sectional view of the heat exchanger in the direction orthogonal to the tube axis in accordance with exemplary embodiment 1. 
         FIG. 3  is a sectional view of the heat exchanger in the tube axis direction in accordance with exemplary embodiment 1. 
         FIG. 4  is a front view of a substrate forming the heat exchanger in accordance with exemplary embodiment 1. 
         FIG. 5  is a sectional view of the substrate of the heat exchanger in accordance with exemplary embodiment 1. 
         FIG. 6  is a front view of another substrate forming the heat exchanger in accordance with exemplary embodiment 1. 
         FIG. 7  is a sectional view of the substrate of the heat exchanger in accordance with exemplary embodiment 1. 
         FIG. 8  is a sectional view of another heat exchanger in the direction orthogonal to the tube axis in accordance with exemplary embodiment 1. 
         FIG. 9  is a sectional view of yet another heat exchanger in the direction orthogonal to the tube axis in accordance with exemplary embodiment 1. 
         FIG. 10  is a sectional view of still another heat exchanger in the direction orthogonal to the tube axis in accordance with exemplary embodiment 1. 
         FIG. 11  is a perspective view of a heat exchanging section in accordance with exemplary embodiment 2 of the present invention. 
         FIG. 12  is a front view of a first substrate in accordance with exemplary embodiment 2. 
         FIG. 13  is a front view of a second substrate in accordance with exemplary embodiment 2. 
         FIG. 14  is a front view of a heat exchanger in accordance with exemplary embodiment 2. 
         FIG. 15  is a side view of the heat exchanger in accordance with exemplary embodiment 2. 
         FIG. 16  is a sectional view taken in the line A-A of  FIG. 14  in accordance with exemplary embodiment 2. 
         FIG. 17  is a sectional view taken in the line B-B of  FIG. 14  in accordance with exemplary embodiment 2. 
         FIG. 18  is a sectional view taken in the line C-C of  FIG. 15  of the heat exchanger in accordance with exemplary embodiment 2. 
         FIG. 19  is a perspective view of a heat exchanging section in accordance with exemplary embodiment 3 of the present invention. 
         FIG. 20  is a front view of a first substrate in accordance with exemplary embodiment 3. 
         FIG. 21  is a front view of a second substrate in accordance with exemplary embodiment 3. 
         FIG. 22  is a front view of a heat exchanger in accordance with exemplary embodiment 3. 
         FIG. 23  is a side view of the heat exchanger in accordance with exemplary embodiment 3. 
         FIG. 24  is a sectional view taken in the line D-D of  FIG. 22  in accordance with exemplary embodiment 3. 
         FIG. 25  is a sectional view taken in the line E-E of  FIG. 22  in accordance with exemplary embodiment 3. 
         FIG. 26  is a sectional view taken in the line F-F of  FIG. 23  in accordance with exemplary embodiment 3. 
         FIG. 27  is a front view of a conventional heat exchanger. 
     
    
    
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           3  Tube 
           4  Tube internal flow channel 
           5  Tube external flow channel 
           6  Branch flow channel 
           7  Inflow tube 
           8  Outflow tube 
           9  Long plate 
           10  Long plate 
           11  Long hole 
           12  Long hole 
           13  Lid 
           14  Lid 
           15  Substrate 
           16  Substrate 
           17  Recess 
           18  Slit 
           19  Holding plate 
           20  Slit 
           21  Holding plate 
           22  Space 
           26  First substrate 
           28  Second substrate 
           30  First slit 
           31  Inlet tank 
           32  Outlet tank 
           33  Tube 
           34  Core section 
           40  Second slit 
           50  Third slit 
           60  Tube external flow channel 
           70  Tube internal flow channel 
           80  Inlet header 
           90  Outlet header 
           126  First substrate 
           128  Second substrate 
           130  First slit 
           140  Second slit 
           150  Third slit 
           160  Tube external flow channel 
           170  Tube internal flow channel 
           171  Inlet of tube internal flow channel 
           172  Outlet of tube internal flow channel 
       
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Exemplary Embodiment 
       FIG. 1  is a front view of a heat exchanger in accordance with exemplary embodiment 1 of the present invention.  FIG. 2  is a sectional view of a heat exchanging section in the direction orthogonal to the tube axis in the heat exchanger.  FIG. 3  is a sectional view of the heat exchanging section in the tube axis direction in the heat exchanger. 
     In  FIG. 1  through  FIG. 3 , the heat exchanger has heat exchanging section  1 , and header sections  2  disposed at opposite ends of heat exchanging section  1 . Heat exchanging section  1  has tubes  3  arranged in a grid shape, tube internal flow channels  4 , and tube external flow channels  5 . Header sections  2  include branch flow channels  6 , inflow tube  7 , and outflow tube  8 . Tube internal flow channels  4  are connected to branch flow channels  6 . Each tube  3  has a substantially square cross section, and has band-like long plate  9  and long plate  10  having U-shaped cross section. Each branch flow channel  6  is formed by continuously interconnecting long holes  11  and  12 . Flat lid  13  is disposed at one end of branch flow channel  6 , and lid  14  having inflow tube  7  or outflow tube  8  is disposed at the other end of branch flow channel  6 . This heat exchanger has two kinds of resin-made substrates  15  and  16 . 
       FIG. 4  is a front view of substrate  15 ,  FIG. 5  is a sectional view of substrate  15 ,  FIG. 6  is a front view of substrate  16 , and  FIG. 7  is a sectional view of substrate  16 . 
     In  FIG. 4  through  FIG. 7 , recesses  17  are continuously disposed in the longitudinal direction of one main surface of substrate  15 . Substrate  15  is formed of a plurality of long plates  10  arranged in parallel, slits  18  disposed between long plates  10 , holding plates  19  for holding both longitudinal ends of long plates  10 , and long holes  11  disposed inside holding plates  19 . Ends of recesses  17  communicate with long holes  11 . Substrate  16  is formed of a plurality of flat long plates  9  arranged in parallel, slits  20  disposed between long plates  9 , holding plates  21  for holding both longitudinal ends of long plates  9 , and long holes  12  disposed inside holding plates  21 . Long plates  9  are made thinner than holding plates  21 , and space  22  is formed in one-side main surfaces of long plates  9 . Substrates  15  and substrates  16  are alternately stacked and welded to form a heat exchanger. Recesses  17  define tube internal flow channels  4 , slits  18 , slits  20  and spaces  22  define tube external flow channels  5 , and long holes  11  and  12  define branch flow channels  6 . 
     In the heat exchanger having this structure, liquid flowing from inflow tube  7  is branched by branch flow channel  6 , flows in tube internal flow channels  4 , merges in branch flow channel  6 , and flows out of outflow tube  8 . Air current flows in tube external flow channels  5  in the plane direction of substrates  15  and substrates  16 . The liquid and air current are heat-exchanged via tubes  3  in heat exchanging section  1 . At this time, substrates  15  and substrates  16  are finely processed, tubes  3  are narrowed, and pitch between tubes  3  can be easily reduced, so that the extremely compact heat exchanger can be easily formed. 
     In the heat exchanger of embodiment 1, substrates  15  and substrates  16  are alternately stacked. Each substrate  16  has slits  20  between a plurality of long plates  9  arranged in parallel. Each substrate  15  has slits  18  disposed between a plurality of long plates  10  arranged in parallel, and recesses  17  continuously disposed in the longitudinal direction of one-side main surfaces of long plates  10 . Long plates  10  and  9  of adjacent substrates  15  and  16  are interconnected to form tubes  3 , recesses  17  define tube internal flow channels  4 , and slits  18  and  20  define tube external flow channels  5 . Thus, heat exchanging section  1  formed of only tubes  3  can be constituted by substrates  15  and  16 , and can be manufactured using inexpensive components. 
     Substrate  16  has slits  20  disposed between the plurality of long plates  9  arranged in parallel, so that substrate  16  requires only simple drilling. Therefore, the heat exchanger can be manufactured in a simple process. 
     Substrate  15  has also holding plates  19  that hold long plates  10  at both longitudinal ends of long plates  10 , and long holes  11  disposed inside holding plates  19 . Substrate  16  has holding plates  21  that hold long plates  9  at both ends of long plates  9 , and long holes  12  disposed inside holding plates  21 . The extended parts of recesses  17  of substrate  15  communicate with long holes  11 , long holes  11  and  12  in adjacent substrates  15  and  16  are interconnected to form branch flow channels  6 . Tube internal flow channels  4  defined by recesses  17  are connected to branch flow channels  6 . Branch flow channels  6  can be formed of substrates  15  and  16  integrally with tubes  3 , so that the connection between the tubes and branch flow channels is not required, the process is further simplified, and the reliability against the leak of liquid and fluid can be improved. 
     Long plates  9  are made thinner than holding plates  21 , and space  22  is formed on one main surface of each long plate  9 . Thus, clearances between tubes  3  are disposed also in the stacking direction of substrates  15  and  16 , tube external flow channels  5  are disposed between substrates  15  and  16 , so that the heat transfer area outside the tubes can be increased, the tube external flow channels can be widened, and flow resistance of the tube external fluid can be suppressed. 
     The fluid in tube external flow channels  5  is made to flow in the plane direction of substrates  15  and  16 , and the boundaries between stacked substrates  15  and  16  do not disturb the flow of the tube external fluid. Therefore, the flow resistance of the tube external fluid can be further suppressed, and adhesion of dust or the like can be prevented. 
     In the heat exchanger of the present invention, lids  13  and  14  for covering long holes  11  and  12  are disposed at opposite ends of stacked substrates  15  and  16 , and inflow tube  7  or outflow tube  8  is disposed in lids  14 . In this structure, a part of branch flow channels  6  can be used as inflow tube  7  or outflow tube  8 , so that the number of components of the heat exchanger can be reduced and the heat exchanger can be manufactured more inexpensively. 
     Since both of substrates  15  and  16  are made of resin, the heat exchanger can be lightened. 
     In this manufacturing method, substrates  15  and  16  are bonded and stacked by welding, so that bonding of substrates  15  and  16  can be easily performed without clogging tube internal flow channels  4  and tube external flow channels  5 . 
     The cross section shape of tubes  3  is a substantial square in the heat exchanger of embodiment 1; however, the cross section shape of tubes  3  may be another shape, for example, a substantial octagon shown in  FIG. 8  or a substantial circle shown in  FIG. 9 . 
     In the heat exchanger of embodiment 1, clearances between tubes  3  are disposed in the stacking state by alternately stacking substrates  15  and  16 , and air current is made to flow in the plane direction of substrates  15  and  16 . However, even when substrates  15  are continuously stacked to bring tubes  3  into contact with each other as shown in  FIG. 10 , for example, and air current is made to flow in the direction perpendicular to the plane of substrates  15 , similar advantage can be obtained. 
     Second Exemplary Embodiment 
       FIG. 11  is a perspective view of a heat exchanging section in accordance with exemplary embodiment 2 of the present invention. 
       FIG. 12  is a front view of a first substrate in accordance with exemplary embodiment 2.  FIG. 13  is a front view of a second substrate in accordance with exemplary embodiment 2. The heat exchanging section is formed by alternately stacking first substrates  26  and second substrates  28 . A plurality of first slits  30  and a plurality of second slits  40  are alternately arranged substantially in parallel on each first substrate  26 . Third slits  50  having the same shape as that of first slits  30  are disposed on each second substrate  28  at the same positions as the projection positions of first slits  30 . 
     First slits  30  and third slits  50  overlap each other on the projection plane and communicate with each other, thereby forming tube external flow channels  60 . The longitudinal size of third slits  50  disposed on second substrate  28  is shorter than that of second slits  40 . Both longitudinal ends of second slits  40  are extended out of both ends of second substrates  28 . Parts of second slits  40  except for the longitudinal both ends are sandwiched between second substrates  28  to form tube internal flow channels  70 , and the longitudinal both ends of second slits  40  define inlets and outlets of tube internal flow channels  70 . First substrates  26  and second substrates  28  are alternately stacked in embodiment 2. When a plurality of first substrates  26  are disposed between second substrates  28 , however, the cross section of tube internal flow channels  70  can be increased. 
     When first substrates  26  are bonded to second substrates  28  by thermal welding, solder material is not required, the bonding can be performed by melting material, and hence a problem of leak of the solder material into tube internal flow channels  70  does not arise. Therefore, tube internal flow channels  70  can be prevented from being clogged. Especially, when ultrasonic bonding is employed, only the bonded part can be heated, and hence the quality and service life of the heat exchanger can be improved. When diffusion bonding is employed, the heating and pressurizing can be simultaneously applied until a temperature at which the material does not melt is obtained. Thus, atoms are diffused (mutually diffused), and the bonding can be performed by atom binding. In other words, when the bonding is performed by diffusion bonding, the melting of the material can be prevented, the clogging of tube internal flow channels  70  can be prevented, and hence the reliability of the heat exchanger is further improved. 
     When at least either first substrates  26  or second substrates  28  are molded by pressing, many substrates are molded relatively easily and hence the heat exchanger can be manufactured inexpensively. The interval between first slits  30  defining the walls of tube internal flow channels  70  and second slits  40  is made larger than the thickness of first substrates  26 . Thus, a problem of twist of the walls of tube internal flow channels  70  by stress during pressing can be avoided, so that the production yield improves. Therefore, the heat exchanger can be manufactured inexpensively. When first substrates  26  and second substrates  28  are molded by etching, stress during molding of the slits can be eliminated or moderated, and hence a problem of twist of the walls of tube internal flow channels  70  can be avoided. Therefore, even when the walls of tube internal flow channels  70  are narrowed, the heat exchanger can be manufactured easily and inexpensively. 
       FIG. 14  is a front view of the heat exchanger in accordance with exemplary embodiment 2.  FIG. 15  is a side view of the heat exchanger in accordance with exemplary embodiment 2.  FIG. 16  is a sectional view taken in the line A-A of  FIG. 14 .  FIG. 17  is a sectional view taken in the line B-B of  FIG. 14 .  FIG. 18  is a sectional view taken in the line C-C of  FIG. 15 . Inlet header  80  and outlet header  90  of internal fluid are typically mounted to the opposite ends of the heat exchanging section. Inlet header  80  and outlet header  90  may be interchanged. 
     Operations of the heat exchanger having such a structure are described hereinafter. The internal fluid flowing from inlet header  80  is branched, flows in tube internal flow channels  70 , and flows out of outlet header  90 . External fluid flows in tube external flow channels  60  in the plane direction of first substrates  26  and second substrates  28 . Heat is exchanged between the internal fluid and the external fluid in the heat exchanging section. The width of second slits  40  formed in first substrates  26  is made fine, and the interval between first slits  30  and second slits  40  is reduced, thereby narrowing the tubes. The pitch between tubes can be easily reduced by reducing the widths of first slits  30  and third slits  50 , so that an extremely compact heat exchanger can be easily formed. 
     The heat exchanger of embodiment 2 has first substrates  26  where the plurality of first slits  30  and the plurality of second slits  40  are alternately arranged substantially in parallel, as discussed above. A plurality of second substrates  28  are stacked which have third slits  50  having substantially the same shape as that of first slits  30  at substantially the same positions as the projection positions of first slits  30  and are shorter than the longitudinal length of second slits  40 . First slits  30  and third slits  50  form tube external flow channels  60 . Second slits  40  and second substrates  28  between which second slits  40  are sandwiched form tube internal flow channels  70 . In the heat exchanger of the present invention, a heat exchanging section that is conventionally formed of only tubes is formed of substrates having slits. This structure can be manufactured relatively easily, and the heat exchanger can be provided inexpensively. 
     In embodiment 2, at least either first substrates  26  or second substrates  28  can be manufactured by pressing, so that many substrates are easily and inexpensively manufactured and hence the heat exchanger can be provided inexpensively. 
     When first substrates  26  are bonded to second substrates  28  by thermal welding, solder material is not required and the bonding can be performed by melting material. Therefore, a problem of leak of the solder material into tube internal flow channels  70  does not arise, and hence tube internal flow channels  70  can be prevented from being clogged. Especially, when ultrasonic bonding is used, only the bonded part can be heated, and hence the quality and reliability of the heat exchanger can be improved. When diffusion bonding is employed, the heating and pressurizing can be simultaneously applied until a temperature at which the material does not melt is obtained. Thus, atoms are diffused (mutually diffused), and the bonding can be attained by atom binding. When the bonding is performed by diffusion bonding, the melting of the material is prevented, the clogging of tube internal flow channels  70  can be prevented, the reliability of the heat exchanger is further improved, the production yield is improved, and the heat exchanger can be provided inexpensively. 
     The heat exchanger where the plurality of first slits  30  and the plurality of second slits  40  are alternately arranged has been described in embodiment 2. Thus, tube external flow channels  60  and tube internal flow channel  70  are alternately arranged, so that heat exchanging efficiency is further improved and the whole region of the substrates can be efficiently used. However, the present invention is not limited to this embodiment. For example, a plurality of second slits  40  may be disposed between first slits  30 , or a plurality of first slits  30  may be disposed between second slits  40 . 
     As one design example, the region of a plurality of first slits  30  may be separated from the region of a plurality of second slits  40 . 
     The shape of the heat exchanging section is not limited to the slit shape. Instead of first slits  30  and second slits  40 , any slit shape expected to have the same advantage may be employed. 
     First slits  30  and second slits  40  are preferably arranged substantially in parallel from the viewpoints of the space factor or heat exchanging efficiency in forming the flow channels. However, arranging the slits substantially in parallel is not necessarily required, and the arrangement may be modified appropriately in response to design issues, a processing device, or an employed processing method of the heat exchanger. 
     Third Exemplary Embodiment 
       FIG. 19  is a perspective view of a heat exchanging section in accordance with exemplary embodiment 3 of the present invention. The heat exchanging section is formed by stacking first substrates  126  and second substrates  128  so that first substrates  126  are sandwiched between second substrates  128 . First slits  130  and third slits  150  form tube external flow channels  160  similarly to embodiment 2. Second slits  140  and second substrates  128  form tube internal flow channels  170 . Three first substrates  126  are stacked between second substrates  128  on the inflow side of the external fluid, two first substrates  126  are stacked between them in the intermediate part, and one first substrate  126  is disposed between them on the outflow side thereof. Thus, tube internal flow channels  170  are enlarged in the substrate stacking direction on the inflow side of the external fluid. 
     Three rows of first substrates  126  are disposed in the flow direction of the external fluid in embodiment 3; however, the number of rows is not limited to three, but a plurality of rows may be disposed. The number of stacked first substrates  126  is changed to increase the length of tube internal flow channels  170  in the substrate stacking direction in embodiment 3; however, the thickness of stacked first substrates  126  may be changed to increase the length in the substrate stacking direction. 
       FIG. 20  is a front view of first substrate  126  in accordance with exemplary embodiment 3.  FIG. 21  is a front view of second substrate  128 . First substrate  126  has a plurality of first slits  130  and second slits  140  substantially in parallel. Inlet  171  and outlet  172  of the tube internal flow channel of each second slit  140  are extended in the direction of tube external flow channel  160 . Second substrate  128  has third slits  150  with the same shape as that of first slits  130  at the same positions as the projection positions of first slits  130 . 
     When first substrates  126  are bonded to second substrates  128  by thermal welding, solder material is not required and the bonding can be performed by melting material. The solder material does not leak into tube internal flow channels  170 , and hence tube internal flow channels  170  can be prevented from being clogged. Especially, when ultrasonic bonding is employed, only the bonded part can be heated, and hence the quality and reliability of the heat exchanger are improved. When diffusion bonding is employed, by applying the heating and pressurizing simultaneously until a temperature at which the material does not melt is obtained, atoms are diffused (mutually diffused), and the bonding can be attained by atom binding. When the diffusion bonding is employed, the melting of the material can be prevented, the clogging of tube internal flow channels  170  can be prevented, and hence the reliability of the whole heat exchanger is further improved. 
     When first substrates  126  and second substrates  128  are molded by pressing, many substrates can be molded relatively easily and hence the heat exchanger can be manufactured inexpensively. The interval between first slits  130  defining walls of tube internal flow channels  170  and second slits  140  is made larger than the thickness of first substrates  126 . Thus, twist of the walls of tube internal flow channels  170  by stress during pressing can be suppressed, so that the quality and the production yield of the heat exchanger improve. Therefore, the heat exchanger can be manufactured inexpensively. When at least either first substrates  126  or second substrates  128  are molded by etching, a problem of twist of the walls of tube internal flow channels  170  can be avoided. Therefore, even when the walls of tube internal flow channels  170  are narrowed, the heat exchanger can be manufactured easily and inexpensively. 
       FIG. 22  is a front view of the heat exchanger in accordance with exemplary embodiment 3.  FIG. 23  is a side view of the heat exchanger in accordance with exemplary embodiment 3.  FIG. 24  is a sectional view taken in the line D-D of  FIG. 22 .  FIG. 25  is a sectional view taken in the line E-E of  FIG. 22 .  FIG. 26  is a sectional view taken in the line F-F of  FIG. 23 . Inlet header  80  and outlet header  90  of internal fluid are typically mounted to the opposite ends of the heat exchanging section. Inlet header  80  and outlet header  90  may be interchanged. 
     Operations of the heat exchanger having such a structure are described hereinafter. 
     The internal fluid flowing from inlet header  80  is branched, flows in tube internal flow channels  170  from inlets  171  of the tube internal flow channels, flows through outlets  172  thereof, and flows out of outlet header  90 . At this time, since inlets  171  and outlets  172  of the tube internal flow channels are extended, the flow channel resistance can be decreased and the circulation amount of the internal flow can be increased even at the same pump power. Therefore, the heat exchanging mount is increased and the heat exchanger can be downsized. The heat exchanger can be therefore provided inexpensively. External fluid flows in tube external flow channels  160  in the plane direction of first substrates  126  and second substrates  128 . Heat is exchanged between the internal fluid and the external fluid in the heat exchanging section. At this time, the number of stacked first substrates  126  is set larger to increase the length in the substrate stacking direction on the upstream side of the external fluid, on which temperature difference between the external fluid and the internal fluid is larger. Therefore, much internal fluid can be made to flow, the heat exchanging amount can be increased, and the heat exchanger can be downsized and provided inexpensively. 
     The heat exchanger of embodiment 3 includes first substrates  126  that have the plurality of first slits  130  and second slits  140  disposed substantially in parallel. Third slits  150  with substantially the same shape as that of first slits  130  are disposed at substantially the same positions as the projection positions of first slits  130 . The plurality of second substrates  128  shorter than second slits  140  are stacked. In this structure, first slits  130  and third slits  150  form tube external flow channels  160 , second slits  140  and second substrates  128  form tube internal flow channels  170 . This structure is relatively simple, so that the heat exchanger can be manufactured easily and inexpensively. 
     Since tube internal flow channels  170  are enlarged in the substrate stacking direction on the inflow side of the external fluid, the temperature difference between the external fluid and the internal fluid is large, much internal fluid can be made to flow on the inflow side of the external fluid having large heat exchanging amount. Therefore, the heat exchanging amount can be increased, and the heat exchanger can be further downsized and provided inexpensively. 
     Since the number of first substrates  126  stacked between second substrates  128  is changed to vary the length of tube internal flow channels  170  in the substrate stacking direction, the heat exchanger can be manufactured easily and inexpensively. 
     Since inlets  171  and outlets  172  of tube internal flow channels  170  are extended in the direction of tube external flow channels  160 , the opening areas of the inlet and outlet of the internal fluid can be increased. Thus, the tube internal resistance is decreased, the flow rate of the internal fluid is increased, hence the heat exchanging amount can be increased, and the heat exchanger can be downsized. 
     When at least either first substrates  126  or second substrates  128  are molded by pressing, many substrates can be molded relatively easily and hence the heat exchanger can be provided inexpensively. The interval between first slits  130  defining the walls of tube internal flow channels  170  and second slits  140  is made larger than the thickness of first substrates  126 . Thus, a problem of twist of the walls of tube internal flow channels  170  by stress during pressing can be avoided, so that the heat exchanger having high quality and high production yield can be provided inexpensively. When at least either first substrates  126  or second substrates  128  are molded by etching, a problem of twist of the walls of tube internal flow channels  170  can be avoided. Therefore, even when the walls of tube internal flow channels  170  are narrowed, the heat exchanger can be manufactured easily and inexpensively. 
     When first substrates  126  are bonded to second substrates  128  by thermal welding, solder material is not required and the bonding can be performed by melting material. A problem of leak of the solder material into tube internal flow channels  170  does not arise, and hence tube internal flow channels  170  can be prevented from being clogged. Especially, when ultrasonic bonding is employed, only the bonded part can be heated, and hence the quality and reliability of the heat exchanger are improved. When diffusion bonding is employed, by applying the heating and pressurizing simultaneously until a temperature at which the material does not melt is obtained, atoms are diffused (mutually diffused), and the bonding can be attained by atom binding. When the diffusion bonding is employed, the melting of the material is prevented, the clogging of tube internal flow channels  170  can be prevented, the quality and reliability of the heat exchanger are further improved, and the heat exchanger having a long service life can be manufactured inexpensively. 
     INDUSTRIAL APPLICABILITY 
     A heat exchanger of the present invention and its manufacturing method can be attained inexpensively while extremely high heat exchanging performance is kept. The heat exchanger can be applied to a refrigerator-freezer, an air conditioner, or an exhaust heat recovery apparatus. The industrial applicability thereof is high.