Patent Publication Number: US-2007119581-A1

Title: Heat exchanger tube

Description:
TECHNICAL FIELD  
      The present invention relates to heat exchanger tubes in which a medium flowing through their passages conducts heat exchange with heat conducted to the tubes.  
     BACKGROUND ART  
      A heat exchanger such as a radiator, an evaporator or the like used for a refrigerating cycle is known that it is configured by alternately stacking flat heat exchanger tubes and corrugated radiating fins to form a core and connecting ends of the tubes to tanks. A refrigerant is taken into the heat exchanger from one of the tanks, flowed through the heat exchanger tubes while performing heat exchange with heat conducted to the core, and discharged out of the other of the tanks. Such a heat exchanger is produced by assembling the component members such as heat exchanger tubes, fins, tanks and the like into one body and brazing the assembled body in a furnace.  
      The heat exchanger tubes of the heat exchanger of the above type are also disclosed in the following Patent Documents 1 through 33. The heat exchanger tubes have the corrugated inner fins disposed within the tube body portion which configures the outer shell of the flow passages where the medium flows, so that the heat exchange efficiency of the medium can be improved. And, it is possible to improve the compression strength of the tubes by brazing the inner fins to the inner surface of the tube body portion. 
      Patent Document 1: Japanese Patent Laid-Open Publication No. Sho 60-114698     Patent Document 2: Japanese Utility Model Laid-Open Publication No. Sho 61 8783     Patent Document 3: Japanese Patent Laid-Open Publication No. Sho 61-66091     Patent Document 4: Japanese Utility Model Laid-Open Publication No. Sho 62-8576     Patent Document 5: Japanese Utility Model Laid-Open Publication No. Sho 62 142440     Patent Document 6: Japanese Utility Model Laid-Open Publication No. Sho 63 134273     Patent Document 7: Japanese Utility Model Laid-Open Publication No. Sho 63 150721     Patent Document 8: Japanese Utility Model Laid-Open Publication No. Sho 63 159667     Patent Document 9: Japanese Utility Model Laid-Open Publication No. Sho  63-179472       Patent Document 10: Japanese Utility Model Laid-Open Publication No. Hei 1-8071     Patent Document 11: Japanese Patent Laid-Open Publication No. 4-198692     Patent Document 12: Japanese Patent Laid-Open Publication No. Hei 5-1893     Patent Document 13: Japanese Patent Laid-Open Publication No. Hei 5-113297     Patent Document 14: Japanese Patent Laid-Open Publication No. Hei 5 169246     Patent Document 15: Japanese Patent Laid-Open Publication No. Hei 6-74607     Patent Document i6: Japanese Patent Laid-Open Publication No. Hei 6-129734     Patent Document 17: Japanese Patent Laid-Open Publication No. Hei 7-32133     Patent Document 18: Japanese Patent Laid-Open Publication No. Hei 7-265985     Patent Document 19: Japanese Patent Laid-Open Publication No. Hei 8 170888     Patent Document 20: Japanese Patent Laid-Open Publication No. Hei 8 271167     Patent Document 21: Japanese Patent Laid-Open Publication No. Hei 9 206980     Patent Document 22: Japanese Patent Laid-Open Publication No. Hei 10 197180     Patent Document 23: Japanese Patent Laid-Open Publication No. Hei 10-300382     Patent Document 24: Japanese Patent Laid-Open Publication No. Hei 11 101586     Patent Document 25: Japanese Patent Laid-Open Publication No. Hei 11-248383     Patent Document 26: Japanese Patent Laid-Open Publication No. Hei 11-257886     Patent Document 27: Japanese Patent Laid-Open Publication No. Hei 11 264675     Patent Document 28: Japanese Patent Laid-Open Publication No. 2000-97589     Patent Document 29: Japanese Patent Laid-Open Publication No. 2000 105089     Patent Document 30: Japanese Patent Laid-Open Publication No. 2001-38439     Patent Document 31: Japanese Patent Laid-Open Publication No. 2001 107082     Patent Document 32: Japanese Patent Laid-Open Publication No. 2001 221588     Patent Document 33: Japanese Patent Laid-Open Publication No. 2002-350083    

      In recent years, the heat exchanger tubes tend to be made compact and precise in order to improve the performance of the heat exchanger. To improve the performance and the productivity, setting of sizes of individual components, arrangement of a brazing material and the like are becoming more and more significant conditions.  
      The present invention has been made in view of the above circumstances and an object of the invention is to provide heat exchanger tubes which are configured more reasonably based on the current production technology.  
     DISCLOSURE OF THE INVENTION  
      The invention recited in claim  1  of the present application is a heat exchanger tube comprising: a tube body portion constituting an outer shell of flow passages for flowing a medium, and corrugated inner fins for dividing the flow passages, wherein tops of the inner fins are flat tubes brazed to the inner surface of the tube body portion and in which the medium performs heat exchange with heat conducted to the tubes, wherein a brazing material which is required for brazing the tops of the inner fins and the inner surface of the tube body portion is not clad to a first material constituting the tube body portion but clad to a second material constituting the inner fins.  
      The invention recited in claim  2  of the present application is the heat exchanger tube according to claim  1 , wherein a thickness of a clad layer of the brazing material in the second material is 5 to 10% in ratio with respect to the thickness of the second material.  
      The invention recited in claim  3  of the present application is the heat exchanger tube according to claim  1  or  2 , wherein the second material has a thickness of 0.1 mm or less.  
      The invention recited in claim  4  of the present application is the heat exchanger tube according to claim  3 , wherein the second material has a thickness of 0.05 to 0.07 mm.  
      The invention recited in claim  5  of the present application is the heat exchanger tube according to any one of claims  1  through  4 , wherein the first material has a thickness of 0.25 mm or less.  
      The invention recited in claim  6  of the present application is the heat exchanger tube according to claim  5 , wherein the first material has a thickness of 0.18 to 0.24 mm.  
      The invention recited in claim  7  of the present application is the heat exchanger tube according to any one of claims  1  through  6 , wherein the tube has a thickness of 1.2 mm or less.  
      The invention recited in claim  8  of the present application is the heat exchanger tube according to claim  7 , wherein the tube has a thickness of 0.8 to 1.2 mm.  
      The invention recited in claim  9  of the present application is the heat exchanger tube according to any one of claims  1  through  8 , wherein the tube has a width of 16 mm or less.  
      The invention recited in claim  10  of the present application is the heat exchanger tube according to claim  9 , wherein the tube has a width of 12 to 16 mm.  
      The invention recited in claim  11  of the present application is the heat exchanger tube according to any one of claims  1  through  10 , wherein the flow passages divided by the inner fins have an equivalent diameter of 0.559 mm or less.  
      The invention recited in claim  12  of the present application is the heat exchanger tube according to claim  11 , wherein the flow passages divided by the inner fins have an equivalent diameter of 0.254 mm to 0.559 mm.  
      The invention recited in claim  13  of the present application is the heat exchanger tube according to any one of claims  1  through  12 , wherein the tops of the inner fins have a pitch of 1.0 mm or less.  
      The invention recited in claim  14  of the present application is the heat exchanger tube according to any one of claims  1  through  13 , wherein an Al—Zn alloy layer is formed on the surface of the first material which becomes an outer shell of the tube.  
      The invention recited in claim  15  of the present application is the heat exchanger tube according to any one of claims  1  through  14 , wherein the tops of the inner fins are flat.  
      The invention recited in claim  16  of the present application is the heat exchanger tube according to any one of claims  1  through  15 , wherein ends of the second material in its breadth direction are brazed with the first material by the brazing material which is clad to the second material.  
      The invention recited in claim  17  of the present application is the heat exchanger tube according to claim  16 , wherein both ends of the first material in its breadth direction are engaged and brazed with an end of the second material in its breadth direction sandwiched at one end of the tube in its breadth direction so as not to separate from each other.  
      The invention recited in claim  18  of the present application is the heat exchanger tube according to any one of claims  1  through  17 , wherein the portion between the tops of the inner fins is not perpendicular with respect to the central axis of the tube in its breadth direction.  
      The invention recited in claim  19  of the present application is the heat exchanger tube according to any one of claims  1  through  18 , wherein the tube is a constituting member of the heat exchanger, and the heat exchanger is produced by assembling the tubes and other constituting members into one body and brazing the assembled body in a furnace, and the brazing material clad to the second material melts when brazed in the furnace earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages thereby to prevent the flow passages from being clogged.  
      The invention recited in claim  20  of the present application is the heat exchanger tube according to claim  19 , wherein the brazing material clad to the second material has a melting point lower than that of the brazing material which melts from the other constituting members and penetrates into the flow passages.  
      The invention recited in claim  21  of the present application is the heat exchanger tube according to claim  19 , wherein the brazing material clad to the second material melts earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages because the tube has a thermal resistance lower than that of the other constituting members.  
      The invention recited in claim  22  of the present application is the heat exchanger tube according to any one of claims  19  through  21 , wherein among plural flow passages divided by the inner fins, an equivalent diameter of the flow passage, which is positioned at the lowest position when brazing in the furnace, or individual equivalent diameters of the flow passage positioned at the lowest position and flow passages positioned nearby when brazing in the furnace are larger than a whole average of the equivalent diameters of the plural flow passages divided by the inner fins.  
      The invention recited in claim  23  of the present application is a heat exchanger tube comprising: a tube body portion constituting an outer shell of flow passages for flowing a medium, and corrugated inner fins for dividing the flow passages, wherein the tops of the inner fins are flat tube brazed to the inner surface of the tube body portion and in which the medium performs heat exchange with heat conducted to the tube, wherein the tube has a thickness of 1.2 mm or less, the tube has a width of 16 mm or less, a first material constituting the tube body portion has a thickness of 0.25 mm or less, a second material constituting the inner fins has a thickness of 0.10 mm or less, and the flow passages divided by the inner fins have an equivalent diameter of 0.559 mm or less.  
      The invention recited in claim  24  of the present application is the heat exchanger tube according to claim  23 , wherein the second material has a thickness of 0.05 to 0.07 mm.  
      The invention recited in claim  25  of the present application is the heat exchanger tube according to claim  23  or  24 , wherein the first material has a thickness of 0.18 to 0.24 mm.  
      The invention recited in claim  26  of the present application is the heat exchanger tube according to any one of claims  23  through  25 , wherein the tube has a thickness of 0.8 to 1.2 mm.  
      The invention recited in claim  27  of the present application is the heat exchanger tube according to any one of claims  23  through  26 , wherein the tube has a width of 12 to 16 mm.  
      The invention recited in claim  28  of the present application is the heat exchanger tube according to any one of claims  23  through  27 , wherein the flow passages divided by the inner fins have an equivalent diameter of 0.254 mm to 0.559 mm.  
      The invention recited in claim  29  of the present application is the heat exchanger tube according to any one of claims  23  through  28 , wherein the tops of the inner fins have a pitch of 1.0 mm or less.  
      The invention recited in claim  30  of the present application is the heat exchanger tube according to any one of claims  23  through  29 , wherein an Al-Zn alloy layer is formed on the surface of the first material which becomes an outer shell of the tube.  
      The invention recited in claim  31  of the present application is the heat exchanger tube according to any one of claims  23  through  30 , wherein the tops of the inner fins are flat.  
      The invention recited in claim  32  of the present application is the heat exchanger tube according to any one of claims  23  through  31 , wherein ends of the second material in its breadth direction are brazed to the first material.  
      The invention recited in claim  33  of the present application is the heat exchanger tube according to claim  32 , wherein both ends of the first material in its breadth direction are engaged and brazed with an end of the second material in its breadth direction sandwiched at one end of the tube in its breadth direction so as not to separate from each other.  
      The invention recited in claim  34  of the present application is the heat exchanger tube according to any one of claims  23  through  33 , wherein the portion between the tops of the inner fins is not perpendicular with respect to the central axis of the tube in its breadth direction.  
      The invention recited in claim  35  of the present application is the heat exchanger tube according to any one of claims  23  through  34 , wherein the tube is a constituting member of the heat exchanger, and the heat exchanger is produced by assembling the tubes and other constituting members into one body and brazing the assembled body in a furnace, the brazing material which is required for brazing the tops of the inner fins and the inner surface of the tube body portion is disposed within the flow passages, and the brazing material disposed within the flow passages melts when brazed in the furnace earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages thereby to prevent the flow passages from being clogged.  
      The invention recited in claim  36  of the present application is the heat exchanger tube according to claim  35 , wherein the brazing material disposed within the flow passages has a melting point lower than that of the brazing material which melts from the other constituting members and penetrates into the flow passages.  
      The invention recited in claim  37  of the present application is the heat exchanger tube according to claim  35 , wherein the brazing material disposed within the flow passages melts earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages because the tube has a thermal resistance which is lower than that of the other constituting members.  
      The invention recited in claim  38  of the present application is the heat exchanger tube according to any one of claims  35  through  37 , wherein among plural flow passages divided by the inner fins, an equivalent diameter of the flow passage, which is positioned at the lowest position when brazing in the furnace, or individual equivalent diameters of the flow passages positioned at the lowest position and flow passages positioned nearby when brazing in the furnace are larger than a whole average of the equivalent diameters of the plural flow passages divided by the inner fins.  
      The invention recited in claim  39  of the present application is a heat exchanger tube comprising: a tube body portion constituting an outer shell of flow passages for flowing a medium, and a flow passage dividing body for dividing the flow passages the flow passage dividing body being a tube brazed to the inner surface of the tube body portion, and the medium performing heat exchange with heat conducted to the tube, wherein the tube is a constituting member of a heat exchanger, and the heat exchanger is produced by assembling the tube and other constituting members into one body and brazing the assembled body in a furnace, a brazing material which is required for brazing the flow passage dividing body and the inner surface of the tube body portion is disposed within the flow passages, and the brazing material disposed within the flow passages melts when brazed in the furnace earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages thereby to prevent the flow passages from being clogged.  
      The invention recited in claim  40  of the present application is the heat exchanger tube according to claim  39 , wherein the flow passage dividing body is a corrugated inner fins, and the tops of the inner fins are brazed to the inner surface of the tube body portion.  
      The invention recited in claim  41  of the present application is the heat exchanger tube according to claim  39 , wherein the flow passage dividing body is beads obtained by shaping a material constituting the tube body portion, and the tops of the beads are brazed to the inner surface of the tube body portion.  
      The invention recited in claim  42  of the present application is the heat exchanger tube according to any one of claims  39  through  41 , wherein the brazing material disposed within the flow passages has a melting point lower than that of the brazing material which melts from the other constituting members and penetrates into the flow passages.  
      The invention recited in claim  43  of the present application is the heat exchanger tube according to any one of claims  39  through  41 , wherein the brazing material disposed within the flow passages melts earlier than the brazing material which melts from the other constituting members and penetrates into the flow passages because the tube has a thermal resistance which is lower than that of the other constituting members.  
      The invention recited in claim  44  of the present application is the heat exchanger tube according to any one of claims  39  through  43 , wherein the flow passages divided by the flow passage dividing body have an equivalent diameter of 0.559 mm or less.  
      The invention recited in claim  45  of the present application is the heat exchanger tube according to claim  44 , wherein the flow passages divided by the flow passage dividing body have an equivalent diameter of 0.254 mm to 0.559 mm.  
      The invention recited in claim  46  of the present application is the heat exchanger tube according to any one of claims  39  through  45 , wherein among plural flow passages divided by the flow passage dividing body, an equivalent diameter of the flow passages, which is positioned at the lowest position when brazing in the furnace, or individual equivalent diameters of the flow passage positioned at the lowest position and flow passages positioned near by when brazing in the furnace are larger than a whole average of the equivalent diameters of the plural flow passages divided by the inner fins. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an explanatory diagram showing a heat exchanger according to an embodiment of the present invention (First embodiment).  
       FIG. 2  is an explanatory diagram and an enlarged view of an essential portion showing sections of a heat-exchanger tube, before brazing thereof, according to the embodiment of the present invention (First embodiment).  
       FIG. 3  is an explanatory diagram showing a section of a second material according to the embodiment of the present invention (First embodiment).  
       FIG. 4  is an enlarged diagram of an essential portion showing a section of a heat-exchanger tube, before brazing thereof, according to an embodiment of the present invention (Second embodiment).  
       FIG. 5  is an enlarged diagram of an essential portion showing a section of a heat-exchanger tube, before brazing thereof, according to an embodiment of the present invention (Third embodiment).  
       FIG. 6  is an enlarged diagram of an essential portion showing a section of a heat-exchanger tube, before brazing thereof, according to the embodiment of the present invention (Third embodiment).  
       FIG. 7  is an enlarged diagram of an essential portion showing a section of a heat-exchanger tube, before brazing thereof, according to the embodiment of the present invention (Third embodiment).  
       FIG. 8  is an explanatory diagram showing a section of a heat-exchanger tube, before brazing thereof, according to an embodiment of the present invention (Fourth embodiment). 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      A first embodiment of the invention will be described below with reference to  FIG. 1  through  FIG. 3 .  
      A heat exchanger  1  shown in  FIG. 1  is a radiator for a refrigerating cycle for in-car air conditioning mounted on an automobile. This heat exchanger  1  comprises a core  10  which is formed by alternately stacking heat exchanger tubes  100  and radiating fins  20 , and a pair of tanks  30  with which both ends of the individual heat exchanger tubes  100  in their longitudinal direction are in communicative connection.  
      Reinforcing members  40  each is disposed on upper and lower sides of the core  10 , and both ends of the individual reinforcing members  40  in their longitudinal direction are supported by the tanks  30 .  
      An inlet  31  and an outlet  32  for a medium (namely, a refrigerant which circulates through the refrigerating cycle) are disposed at the required portions of the tanks  30 , so that the medium which has entered through the inlet  31  flows through the heat exchanger tubes  100  while performing heat exchange with heat conducted to the core  10  and flows out through the outlet  32 .  
      Constituting members of the heat exchanger  1 , such as the fins  20 , the tanks  30 , the inlet  31 , the outlet  32 , the side plates  40  and the heat exchanger tubes  100  are formed of an aluminum or aluminum alloy member. They are assembled into one body by means of a jig, and the assembled body undergoes a heat treatment in a furnace to be brazed into one body. To braze in the furnace, a brazing material and flux are disposed on the required portions of the individual members.  
      The heat exchanger tube  100  of this embodiment shown in  FIG. 2  has a tube body portion  200  which forms the outer shell of flow passages  101  for flowing the medium and corrugated inner fins  300  for dividing the flow passages  101  and the tops of the inner fins  300  are flat and brazed to the inner surface of the tube body portion  200 .  
      This heat exchanger tube  100  has a thickness t tube  of 1.2 mm or less. It is desirable that the heat exchanger tube  100  has a thickness t tube  of 0.8 to 1.2 mm. And, the heat exchanger tube  100  has a width w tube  of 16 mm or less. It is desirable that the heat exchanger tube  100  has a width w tube  of 12 to 16 mm. Besides, the individual flow passages  101  divided by the inner fins  200  each having an equivalent diameter of 0.559 mm or less. It is desirable that the flow passage  101  has an equivalent diameter of 0.254 mm to 0.559 mm.  
      An equation to obtain the equivalent diameter de is de=4×(flow passage sectional area)/(overall length of wet edge of flow passage cross section). The medium performs heat exchange with heat conducted to the heat exchanger tubes  100 .  
      The tube body portion  200  is formed by roll forming a first material of an aluminum or aluminum alloy strip. Both ends  201  of the first material in its breadth direction are mutually engaged and brazed at one end  102  of the heat exchanger tube  100  in its breadth direction so that they are not separated from each other. And, the other end  103  of the heat exchanger tube  100  in its breadth direction is a portion where substantially a center of the first material is bent.  
      The inner fins  300  are formed by roll forming a second material of an aluminum or aluminum alloy strip. Pitch P between the tops of the inner fins is 1.0 mm or less. The inner fins  300  are inserted between the first materials in an appropriate stage of the roll forming of the tube body portion  200  and disposed within the tube body portion  200 .  
      In this embodiment, the brazing material, which is required for brazing the tops  310  of the inner fins  300 , which are a flow passage dividing body to the inner surface of the tube body portion  200 , is not clad to the first material which forms the tube body portion  200  but to the second material which forms the inner fins  300 .  
      Specifically, in a case where the tops  310  of the inner fins  300  and the inner surface of the tube body portion  200  are brazed, at least one of the first material and the second material is clad with the brazing material, and the structure of cladding only the second material with the brazing material is adopted in this embodiment. The reason for this is to suppress the use of brazing material to a minimum required quantity. Its concept will be described below.  
      First, the brazing material containing silicon is indispensable for brazing but becomes a cause of eroding the core material after brazing. Therefore, it is desirable that the brazing material is suppressed to a quantity as small as possible. And, a material clad with the brazing material is produced by stacking and rolling the core material and the brazing material at a prescribed ratio, so that the thickness of the clad layer of the brazing material has a lower limit with respect to the thickness of the material. According to the present technology, the lower limit of the thickness of the clad layer is about 5% with respect to the thickness of the material.  
      Besides, where thickness t 1  of the first material and thickness t 2  of the second material are compared, the thickness t 2  of the second material can be made thinner to some extent in view of the structure of the heat exchanger tube  100 . As a result, only the second material is desirably clad with the brazing material to determine the brazing material to a small quantity.  
      Meanwhile, the ends  201  of the first material are brazed with the brazing material, which penetrates from the tanks  30  by capillary action, by brazing in the furnace described above. According to this configuration, the quantity of the brazing material to be used can be reduced, and the depth of a silicon diffusion layer of the first material can be decreased, so that the thickness of the first material can be made thinner.  
      For improvement of support strength of the inner fins  300  to the tube body portion  200  and durability of the inner fins  300 , the ends  301  of the second material in its breadth direction are brazed to the first material with the brazing material which is clad to the second material. Brazing of the ends  301  of the second material to the first material prevents the ends  301  of the second material from being fluctuated by the flowing medium, and the durability of the heat exchanger tubes  100  and the stability of the medium flow can be improved surely.  
      The thickness t 1  of the first material is 0.25 mm or less. It is desirable that the thickness t 1  of the first material is 0.18 to 0.24 mm. And, an Al—Zn alloy layer is disposed as a sacrifice layer for improving corrosion resistance of the heat exchanger tubes  100  on the surface of the first material which becomes the outer shell of the heat exchanger tube  100 .  
      Meanwhile, the second material is formed by disposing a clad layer  300   b  of the brazing material on both surfaces of a core material  300   a  as shown in  FIG. 3 , and its thickness t 2  is 0.1 mm or less. It is desirable that the thickness t 2  of the second material is 0.05 to 0.07 mm. And, the thickness of the clad layer  300   b  of the brazing material in the second material is 5 to 10% in ratio with respect to the thickness t 2  of the second material.  
      In this embodiment, the tops  310  of the inner fins  300  are flat, so that sufficient brazing areas are secured between the tops  310  of the inner fins  300  and the inner surface of the tube body portion  200 .  
      In other words, brazing strength and reliability of brazing are improved surely by configuring as described above. And, friction between the tube body portion  200  and the inner fins  300  is increased because the tops  310  of the inner fins  300  are flat. Thus, there is also an advantage that when the heat exchanger tube  100  is cut to a prescribed length before brazing, displacement of the inner fins  300  can be prevented. Width W flat  of the flat portions of the tops  310  is 2.5 to 0.5 when the thickness t 2  of the material is 1.  
      Besides, a portion between the tops  310  and  310  of the inner fins  300  becomes non-perpendicular to a central axis L of the heat exchanger tube  100  in its breadth direction. Specifically, an intersection angle θ between the portion between the tops  310  and  310  of the inner fins  300  and the central axis L in the breadth direction is 65 to 85°. In a case where the intersection angle θ is perpendicular and the heat exchanger tubes  100  is cut to a prescribed length before brazing, the inner fins  300  are largely deformed when a cutting blade is moved in parallel to the central axis L in the breadth direction. But, such a disadvantage is avoided in this embodiment by setting the intersection angle θ to a favorable value.  
      In this embodiment, where the brazing is effected in the furnace, the brazing material which is clad to the second material melts earlier than the brazing material, which melts from the other constituting members such as the tanks  30  constituting the heat exchanger  1  and penetrates into the flow passages  101 , thereby to prevent the flow passages  101  from being clogged. If the interior of the heat exchanger tube  100  is dry when the brazing material penetrates into the flow passages  101  from outside, the penetrated brazing material stays locally within the flow passages  101  because of an influence of its surface tension and the like, and the flow passages  101  are clogged. The brazing material which is clad to the second material has a melting point lower than that of the brazing material which melts from the surfaces of the tanks  30  and penetrates into the flow passages  101 . Otherwise, the brazing material which is clad to the second material melts earlier than the brazing material which melts from the surface of the tanks  30  and penetrates into the flow passages  101  because a thermal resistance of the heat exchanger tubes  100  is smaller than that of the tanks  30 .  
      Besides, to prevent the flow passages  101  from being clogged, among the plural flow passages  101  divided by the inner fins  300 , the equivalent diameter of the flow passage  101 , which is positioned at the lowest position when brazing in the furnace, or the individual equivalent diameters of the flow passage  101  which is positioned at the lowest position and the flow passages  101  which are positioned nearby when brazing in the furnace are desirably determined to be larger than a whole average of the equivalent diameters of the plural flow passages  101  which are divided by the inner fins  300 .  
      It is because the melted brazing material tends to move in a direction of gravitational force, so that the flow passage  101  which is positioned at the lowest position when brazing in the furnace and the flow passages  101  which are positioned nearby tend to have a large amount of the penetrated brazing material in comparison with the other flow passages  101 .  
      In this embodiment, the heat exchanger  1  is brazed in the furnace with the core  10  laid on its side, so that the equivalent diameter of the flow passage  101  which is positioned at one end  102  of the heat exchanger tube  100  in its breadth direction is determined larger, and if necessary, the equivalent diameter of the flow passage  101  positioned near the pertinent flow passage  101  is also determined to be large. Otherwise, the equivalent diameter of the flow passage  101  which is positioned at the other end  103  of the heat exchanger tube  100  in its breadth direction is determined to be large, and if necessary, the equivalent diameter of the flow passage  101  which is positioned near the pertinent flow passage  101  is also determined to be large.  
      Where the equivalent diameter of the flow passage  101  which is positioned near the flow passage  101  which is positioned at one end  102  or the other end  103  is determined to be large, a pitch P of the tops at the required portions of the inner fins  300  is determined to be larger than a pitch P of the tops at the other portion.  
      Besides, when the equivalent diameter of the flow passage  101  at the one end  102  and the equivalent diameter of the flow passage  101  at the other end  103  are determined to be large, either end may be positioned on the lower side, so that it is also possible to secure generality in terms of brazing posture.  
      As described above, the heat exchanger tube  100  of this embodiment is configured very rationally and can be used favorably as a component part of the heat exchanger  1 . Setting of the values of the individual portions of the heat exchanger tubes  100  was obtained by studying the performance of the heat exchanger tubes  100  based on the current manufacturing technology.  
      It should be noted that the structure of this embodiment can be changed in its design appropriately without departing from the technical scope recited in the appended claims and is not limited to the illustrated one.  
      Then, a second embodiment of the invention will be described with reference to  FIG. 4 .  
      As shown in  FIG. 4 , the heat exchanger tube  100  of this embodiment has both ends  201  of the first material in its breadth direction mutually engaged and brazed at one end  102  of the heat exchanger tube  100  in its breadth direction so that they are not separated from each other. And, the other end  301  of the second material is brazed with the end  201  of the first material. The other basic structure is same with that of the above-described embodiment.  
      Thus, the end  301  of the second material may be brazed to the end  201  of the first material.  
      A third embodiment of the present invention will be described with reference to  FIG. 5  through  FIG. 7 .  
      As shown in  FIG. 5 , the heat exchanger tube  100  of this embodiment has both ends  201  of the first material in its breadth direction mutually engaged and brazed at one end  102  of the heat exchanger tube  100  in its breadth direction with the end  301  of the second material in its breadth direction sandwiched so that they are not separated from each other.  
      The end  201  of the first material and the end  301  of the second material are brazed with the brazing material which is clad to the second material and the brazing material which penetrates from the tanks  30 .  
      A shape of the end  201  of the first material and a shape of the end  301  of the second material can be determined appropriately as shown in, for example,  FIG. 6  and  FIG. 7 , and are not limited to a particular shape. The other basic structure is same with that of the above-described embodiment.  
      Thus, the end  301  of the second material may be configured to sandwich the end  201  of the first material. According to this embodiment, the ends  201  of the first material can be mutually brazed with the brazing material which is clad to the second material. In a case where the ends  201  of the first material in its breadth direction are mutually brazed with only the brazing material which penetrates from the tanks  30 , there is a case that the brazing material does not spread sufficiently if the heat exchanger tube  100  is relatively long, and defective brazing may be caused. In this connection, such a defect can be avoided by this embodiment, and the brazing of the ends  201  of the first material in its breadth direction can be improved surely in its reliability.  
      And, the end  301  of the second material in its breadth direction is sandwiched between both ends  201  of the first material in its breadth direction, so that the inner fins  300  can be positioned accurately within the heat exchanger tube  100 . Especially, the size of the flow passage  101  at one end  102  and the other end  103  of the heat exchanger tube  100  can also be controlled accurately. And, a decrease in resistance to pressure due to displacement of the inner fins  300  can also be prevented.  
      Then, a fourth embodiment of the present invention will be described with reference to  FIG. 8 .  
      As shown in  FIG. 8 , in the heat exchanger tube  100  of this embodiment, beads  202  which are formed by shaping the required portions of the first material are disposed as a flow passage dividing body for dividing the flow passages  101 . The tops of the beads  202  are brazed to the inner surface of tube body portion  200 .  
      The brazing material which is required for brazing the tube body portion  200  with the tops of the beads  202 , and the brazing material which is required for brazing the both ends  201  of the first material, are clad to one surface of the first material which becomes the inside of the flow passages. When brazing in the furnace, the brazing material which is clad to the first material melts earlier than the brazing material which penetrates from outside into the flow passages  101 , so that the flow passages  101  are prevented from being clogged. And the other basic structure is same with that of the above-described embodiment.  
      Thus, the beads can also be disposed as the flow passage dividing body. In such a case, the brazing material is clad to the first material, and to braze in the furnace, it is configured so that the brazing material melts earlier than the brazing material, which melts from the other constituting members constituting the heat exchanger, and penetrates into the flow passages  101 .  
     INDUSTRIAL APPLICABILITY  
      The heat exchanger tubes of the present invention can be used as constituting members of, for example, a vehicle-mounted heat exchanger.