Patent Publication Number: US-2016245560-A1

Title: Tube fitting, heat exchanger, and air-conditioning apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a tube fitting, a heat exchanger, and an air-conditioning apparatus. 
     BACKGROUND ART 
     Tube fittings thus far developed include a type having a through portion formed therethrough, to a first end portion of which a flat tube is connected and to a second end portion of which a tube different in cross-sectional shape from the flat tube, for example a round tube, is connected. The flat tube includes a plurality of flow paths aligned in the direction of the major axis (see, for example, Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-142454 (Paragraph [0009], FIG. 1, FIG. 2) 
     SUMMARY OF INVENTION 
     Technical Problem 
     In such conventional tube fittings, a fluid flowing through the tube different in cross-sectional shape from the flat tube may be subjected to inertial force acting in a direction parallel to the major axis of the flat tube, in which case the balance among the flows of fluid flowing into each of the flow paths formed in the flat tube may fluctuate. In particular, when the fluid flowing through the tube different in cross-sectional shape from the flat tube is refrigerant in a two-phase gas-liquid, the fluctuation of the balance becomes more prominent. However, in such tube fittings, the central axis of the first end portion to which the flat tube is connected and the central axis of the second end portion, to which the tube different in cross-sectional shape from the flat tube is connected, coincide with each other, and therefore there is no way to cope with the fluctuation of the balance among the flows of fluid flowing into each of the flow paths formed in the flat tube. In other words, with the conventional tube fitting the balance among the flows of fluid flowing into the plurality of flow paths in the flat tube is unable to be optimized. 
     The present invention has been accomplished in view of the foregoing problem, and provides a tube fitting capable of optimizing the balance among the flows of fluid flowing into the plurality of flow paths in the flat tube. The present invention also provides a heat exchanger including the mentioned tube fitting. Further, the present invention provides an air-conditioning apparatus including the mentioned heat exchanger. 
     Solution to Problem 
     In an aspect, the present invention provides a tube fitting that includes a through portion to a first end portion of which a flat tube is connected and to a second end portion of which another tube different in cross-sectional shape from the flat tube is connected, in which the central axis of the first end portion and the central axis of the second end portion are deviated from each other. 
     Advantageous Effects of Invention 
     With the tube fitting according to the present invention, even when a fluid flowing through the tube different in cross-sectional shape from the flat tube is subjected to inertial force acting in a direction parallel to the major axis of the flat tube, the balance among the flows of fluid flowing into each of the flow paths formed in the flat tube can be optimized, since the central axis of the first end portion of the through portion and the central axis of the second end portion of the through portion are deviated from each other. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a heat exchanger according to Embodiment 1. 
         FIG. 2  is an exploded perspective view of a stacked header of the heat exchanger according to Embodiment 1. 
         FIG. 3  is a perspective view of a cylindrical header of the heat exchanger according to Embodiment 1. 
         FIG. 4  is a schematic drawing illustrating connection between a heat exchange unit and a branch/junction section of the heat exchanger according to Embodiment 1. 
         FIG. 5  is another schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 1. 
         FIG. 6  is a schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to a variation of Embodiment 1. 
         FIG. 7  is a schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to another variation of Embodiment 1. 
         FIG. 8  is a schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to still another variation of Embodiment 1. 
         FIG. 9  is a schematic drawing showing a configuration of a windward concentric tube fitting and a leeward concentric tube fitting of the heat exchanger according to Embodiment 1. 
         FIG. 10  is a schematic drawing showing a configuration of a windward concentric tube fitting and a leeward concentric tube fitting of the heat exchanger according to a comparative example. 
         FIG. 11  is a schematic drawing showing a configuration of a windward eccentric tube fitting and a leeward eccentric tube fitting of the heat exchanger according to Embodiment 1. 
         FIG. 12  is a block diagram showing a configuration of an air-conditioning apparatus including the heat exchanger according to Embodiment 1. 
         FIG. 13  is another block diagram showing the configuration of the air-conditioning apparatus including the heat exchanger according to Embodiment 1. 
         FIG. 14  is a schematic drawing illustrating liquid distribution of refrigerant flowing into a leeward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as evaporator. 
         FIG. 15  is a graph illustrating the liquid distribution of the refrigerant flowing into the leeward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as evaporator. 
         FIG. 16  is a schematic drawing illustrating gas distribution of refrigerant flowing into a windward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as condenser. 
         FIG. 17  is a graph illustrating the gas distribution of the refrigerant flowing into the windward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as condenser. 
         FIG. 18  is a perspective view of a heat exchanger according to Embodiment 2. 
         FIG. 19  is a schematic drawing illustrating connection between a heat exchange unit and a branch/junction section of the heat exchanger according to Embodiment 2. 
         FIG. 20  is another schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 2. 
         FIG. 21  is a schematic drawing illustrating connection between the heat exchange unit and the branch/junction section of the heat exchanger according to a variation of Embodiment 2. 
         FIG. 22  is a block diagram showing a configuration of an air-conditioning apparatus including the heat exchanger according to Embodiment 2. 
         FIG. 23  is another block diagram showing the configuration of the air-conditioning apparatus including the heat exchanger according to Embodiment 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, a tube fitting according to the present invention will be described with reference to the drawings. 
     Configurations and operations described hereunder are merely exemplary, and the configurations and operations of the tube fitting according to the present invention are not limited to the description given hereunder. In the drawings, the same or similar constituents will be given the same reference numeral, or may be cited without the numeral. Minor details of the configuration may be simplified or omitted, as the case may be. Descriptions of the same or similar configurations may be simplified or omitted, as the case may be. 
     Although the tube fitting according to the present invention is employed in a heat exchanger in the following description, the tube fitting according to the present invention may be incorporated in an apparatus other than the heat exchanger. Although the heat exchanger including the tube fitting according to the present invention is employed in an air-conditioning apparatus in the following description, the heat exchanger may be incorporated in another refrigeration cycle apparatus having a refrigerant circuit. Further, although the heat exchanger including the tube fitting according to the present invention is exemplified by an outdoor heat exchanger of the air-conditioning apparatus in the description given hereunder, the heat exchanger may be an indoor heat exchanger of the air-conditioning apparatus. In addition, although the air-conditioning apparatus cited hereunder is configured to be switched between a heating operation and a cooling operation, the air-conditioning apparatus may be configured to perform only either of the heating operation and the cooling operation. 
     Embodiment 1 
     The heat exchanger according to Embodiment 1 will be described. 
     &lt;Configuration of Heat Exchanger&gt; 
     Hereunder, a configuration of the heat exchanger according to Embodiment 1 will be described. 
     (General Configuration of Heat Exchanger) 
     Hereunder, a general configuration of the heat exchanger according to Embodiment 1 will be described. 
       FIG. 1  is a perspective view of the heat exchanger according to Embodiment 1. 
     As shown in  FIG. 1 , the heat exchanger  1  includes a heat exchange unit  2  and a branch/junction section  3 . 
     The heat exchange unit  2  includes a windward heat exchange unit  21  located windward in the flow direction of air passing through the heat exchange unit  2  (blank arrow in  FIG. 1 ), and a leeward heat exchange unit  31  located leeward in the air flow direction. The windward heat exchange unit  21  includes a plurality of windward heat transfer tubes  22 , and a plurality of windward fins  23  respectively joined to the windward heat transfer tubes  22 , for example by brazing. The leeward heat exchange unit  31  includes a plurality of leeward heat transfer tubes  32 , and a plurality of leeward fins  33  respectively joined to the leeward heat transfer tubes  32 , for example by brazing. The heat exchange unit  2  may be constituted of two rows, namely a row of the windward heat exchange unit  21  and a row of the leeward heat exchange unit  31 , or three or more rows. 
     The windward heat transfer tubes  22  and the leeward heat transfer tubes  32  are flat tubes, each including a plurality of flow paths aligned in the direction of the major axis. Each of the plurality of windward heat transfer tubes  22  and the plurality of leeward heat transfer tubes  32  is bent in a hair-pin shape between a first end portion and a second end portion, so as to form a turnback section  22   a ,  32   a . The windward heat transfer tubes  22  and the leeward heat transfer tubes  32  are arranged in a plurality of columns stacked in a direction intersecting the flow of air passing through the heat exchange unit  2  (blank arrow in  FIG. 1 ). The first end portion and the second end portion of each of the windward heat transfer tubes  22  and the leeward heat transfer tubes  32  are aligned so as to oppose the branch/junction section  3 . 
     The branch/junction section  3  includes a stacked header  51  and a cylindrical header  61 . The stacked header  51  and the cylindrical header  61  are aligned in the flow direction of air passing through the heat exchange unit  2  (blank arrow in  FIG. 1 ). A non-illustrated refrigerant tube is connected to the stacked header  51 , via a joint tube  52 . A non-illustrated refrigerant tube is also connected to the cylindrical header  61 , via a joint tube  62 . The joint tube  52  and the joint tube  62  are, for example, round tubes. 
     The stacked header  51  includes therein a branch/junction flow path  51   a , and is connected to the windward heat exchange unit  21 . When the heat exchange unit  2  acts as evaporator, the branch/junction flow path  51   a  serves as branch flow path for distributing the refrigerant received through the non-illustrated refrigerant tube to the plurality of windward heat transfer tubes  22  in the windward heat exchange unit  21 . When the heat exchange unit  2  acts as condenser, the branch/junction flow path  51   a  serves as junction flow path for merging the refrigerant received from each of the windward heat transfer tubes  22  in the windward heat exchange unit  21  and passing the merged flow to the non-illustrated refrigerant tube. The stacked header  51  corresponds to the “header located on a windward side” in the present invention. 
     The cylindrical header  61  includes therein a branch/junction flow path  61   a , and is connected to the leeward heat exchange unit  31 . When the heat exchange unit  2  acts as condenser, the branch/junction flow path  61   a  serves as branch flow path for distributing the refrigerant received through the non-illustrated refrigerant tube to the plurality of leeward heat transfer tubes  32  in the leeward heat exchange unit  31 . When the heat exchange unit  2  acts as evaporator, the branch/junction flow path  61   a  serves as junction flow path for merging the refrigerant received from each of the leeward heat transfer tubes  32  in the leeward heat exchange unit  31  and passing the merged flow to the non-illustrated refrigerant tube. The cylindrical header  61  corresponds to the “header located on a leeward side” in the present invention. 
     (Configuration of Stacked Header) 
     Hereunder, a configuration of the stacked header of the heat exchanger according to Embodiment 1 will be described. 
       FIG. 2  is an exploded perspective view of the stacked header of the heat exchanger according to Embodiment 1. Arrows in  FIG. 2  indicate the flow of the refrigerant realized when the branch/junction flow path  51   a  of the stacked header  51  serves as branch flow path. 
     As shown in  FIG. 2 , the stacked header  51  includes a first plate member  53  including a flow path segment  53   a , a plurality of second plate members  54 _ 1  to  54 _ 3  respectively including flow path segments  54   a _ 1  to  54   a _ 3 , and a third plate member  55  including a plurality of flow path segments  55   a , the first, second, and third plate members being stacked via clad members  56 _ 1  to  56 _ 4  each including one or more flow path segments  56   a , sequentially interposed between the plate members. A braze material is applied to one or both surfaces of the clad members  56 _ 1  to  56 _ 4 . In the description given hereunder, the first plate member  53 , the plurality of second plate members  54 _ 1  to  54 _ 3 , the third plate member  55 , and the plurality of clad members  56 _ 1  to  56 _ 4  may be collectively referred to as “plate member”. 
     The flow path segments  53   a ,  55   a ,  56   a  are circular through holes. Each of the flow path segments  54   a _ 1  to  54   a _ 3  is a linear through slot in which a first end portion and a second end portion are located at different heights in the gravity direction (for example, Z-shape or S-shape). The non-illustrated refrigerant tube is connected to the flow path segment  53   a , via the joint tube  52 . The windward heat transfer tubes  22  are respectively connected to the flow path segments  55   a , via a joint tube  57 . The joint tube  57  is, for example, a round tube or an elliptical tube. 
     The flow path segment  56   a  of the clad member  56 _ 1  is formed so as to oppose the flow path segment  53   a . The flow path segments  56   a  of the clad member  56 _ 4  are formed so as to oppose the respective flow path segments  55   a . The first end portion and the second end portion of the flow path segments  54   a _ 1  to  54   a _ 3  are located so as to oppose the flow path segment  56   a  of one of the clad members  56 _ 2  to  56 _ 4  stacked on the side of the windward heat exchange unit  21 . A section of each of the flow path segments  54   a _ 1  to  54   a _ 3  between the first end portion and the second end portion is located so as to oppose the flow path segment  56   a  of one of the dad member  56 _ 1  to  56 _ 3  stacked on the opposite side of the windward heat exchange unit  21 . 
     When the plate members are stacked together, the flow path segments  53   a ,  54   a _ 1  to  54   a _ 3 ,  55   a ,  56   a  are allowed to communicate with each other, so as to form the branch/junction flow path  51   a . The branch/junction flow path  51   a  serves as branch flow path when the refrigerant flows in the direction of the arrows in  FIG. 2 , and serves as junction flow path when the refrigerant flows in the direction opposite to the arrows. 
     When the branch/junction flow path  51   a  serves as branch flow path, the refrigerant which has entered the flow path segment  53   a  through the joint tube  52  flows into the section between the first end portion and the second end portion of the flow path segment  54   a _ 1  through the flow path segment  56   a , thereby colliding with the surface of the clad member  56 _ 2  and being branched in two directions. The refrigerant thus branched flows out through the first end portion and the second end portion of the flow path segment  54   a _ 1  and flows into the section between the first end portion and the second end portion of the flow path segment  54   a _ 2  through the flow path segments  56   a , thereby colliding with the surface of the clad member  56 _ 3  and being branched in two directions. The refrigerant thus branched flows out through the first end portion and the second end portion of the flow path segment  54   a _ 2  and flows into the section between the first end portion and the second end portion of the flow path segment  54   a _ 3  through the flow path segments  56   a , thereby colliding with the surface of the clad member  56 _ 4  and being branched in two directions. The refrigerant branched as above flows out through the first end portion and the second end portion of the flow path segment  54   a _ 3 , and flows into each of the joint tubes  57  through the corresponding flow path segment  56   a  and the flow path segment  55   a.    
     When the branch/junction flow path  51   a  serves as junction flow path, the refrigerant which has entered the flow path segment  55   a  through the joint tube  57  passes through the flow path segment  56   a  and flows into the first end portion and the second end portion of the flow path segment  54   a _ 3 , and then into the flow path segment  56   a  communicating with the section between the first end portion and the second end portion of the flow path segment  54   a _ 3 , thus to be merged together. The refrigerant thus merged flows into the first end portion and the second end portion of the flow path segment  54   a _ 2 , and then into the flow path segment  56   a  communicating with the section between the first end portion and the second end portion of the flow path segment  54   a _ 2 , thus to be merged together. The refrigerant thus merged flows into the first end portion and the second end portion of the flow path segment  54   a _ 1 , and then into the flow path segment  56   a  communicating with the section between the first end portion and the second end portion of the flow path segment  54   a _ 1 , thus to be merged together. The refrigerant merged as above flows into the joint tube  52  through the flow path segment  53   a.    
     Here, the first plate member  53 , the second plate members  54 _ 1  to  54 _ 3 , and the third plate member  55  may be directly stacked on each other without the clad members  56 _ 1  to  56 _ 4  being interposed. When the clad members  56 _ 1  to  56 _ 4  are interposed, the flow path segments  56   a  serve as a refrigerant isolation flow path, and assures the isolation of the refrigerant flows passing through the flow path segments  53   a ,  54   a _ 1  to  54   a _ 3 , and  55   a . Alternatively, each of the first plate member  53 , the second plate member  54 _ 1  to  54 _ 3 , and the third plate member  55  may be coupled with the corresponding clad member  56 _ 1  to  56 _ 4 , and such plate members may be directly stacked on each other. 
     (Configuration of Cylindrical Header) 
     Hereunder, a configuration of the cylindrical header of the heat exchanger according to Embodiment 1 will be described. 
       FIG. 3  is a perspective view of the cylindrical header of the heat exchanger according to Embodiment 1. Arrows in  FIG. 3  indicate the flow of the refrigerant realized when the branch/junction flow path  61   a  of the cylindrical header  61  serves as junction flow path. 
     As shown in  FIG. 3 , the cylindrical header  61  includes a cylindrical portion  63  having the both end portions closed, and aligned such that the axial direction is parallel to the gravity direction. Here, it is not mandatory that the axial direction of the cylindrical portion  63  is parallel to the gravity direction. Arranging the cylindrical header  61  so as to make the axial direction of the cylindrical portion  63  parallel to the longitudinal direction of the stacked header  51  allows reduction of the footprint of the branch/junction section  3 . Here, the cylindrical portion  63  may be an oval tube having an elliptical cross-section. 
     The non-illustrated refrigerant tube is connected to the sidewall of the cylindrical portion  63 , via the joint tube  62 . To the sidewall of the cylindrical portion  63 , also a plurality of joint tubes  64 , respectively connected to the leeward heat transfer tubes  32 , are connected. The joint tube  64  is, for example, a round tube or an elliptical tube. The cylindrical portion  63  includes therein the branch/junction flow path  61   a . The branch/junction flow path  61   a  serves as junction flow path when the refrigerant flows in the direction of the arrows in  FIG. 3 , and serves as branch flow path when the refrigerant flows in the direction opposite to the arrows. 
     When the branch/junction flow path  61   a  serves as junction flow path, the refrigerant which has entered the plurality of joint tubes  64  flows through inside the cylindrical portion  63  and then flows into the joint tube  62 , thus to be merged. When the branch/junction flow path  61   a  serves as branch flow path, the refrigerant flowing in through the joint tube  62  passes through inside the cylindrical portion  63  and then flows into each of the joint tubes  64 , thus to be branched. 
     It is preferable that a circumferential position of the cylindrical portion  63  where the joint tube  62  is connected and circumferential positions where the joint tubes  64  are connected are not opposed across the center of the cylindrical portion  63 . Such a configuration facilitates the refrigerant to evenly flow into the plurality of joint tubes  64 , when the branch/junction flow path  61   a  serves as branch flow path. 
     (Connection Between Heat Exchange Unit and Branch/Junction Section) 
     Hereunder, connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 1 will be described. 
       FIG. 4  and  FIG. 5  are schematic drawings illustrating the connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 1.  FIG. 5  is a cross-sectional view taken along a line A-A in  FIG. 4 . 
     As shown in  FIG. 4  and  FIG. 5 , a windward concentric tube fitting  41 A is joined to the first end portion  22   b  of the windward heat transfer tube  22 . A windward eccentric tube fitting  41 B is joined to the second end portion  22   c  of the windward heat transfer tube  22 . A leeward concentric tube fitting  42 A is joined to the second end portion  32   c  of the leeward heat transfer tube  32 . A leeward eccentric tube fitting  42 B is joined to the first end portion  32   b  of the leeward heat transfer tube  32 . 
     The joint tube  57  of the stacked header  51  is connected to the windward concentric tube fitting  41 A. To the leeward concentric tube fitting  42 A, the joint tube  64  of the cylindrical header  61  is connected. The windward eccentric tube fitting  41 B and the leeward eccentric tube fitting  42 B are connected to each other via a row joint tube  43 . The row joint tube  43  is, for example, a round tube or an elliptical tube, bent in an arcuate shape. 
       FIG. 6  is a schematic drawing illustrating the connection between the heat exchange unit and the branch/junction section of the heat exchanger according to a variation of Embodiment 1. Here,  FIG. 6  is a cross-sectional view from a position corresponding to the line A-A in  FIG. 4 . 
     The windward heat transfer tubes  22  and the leeward heat transfer tubes  32  may be arranged such that, when viewed from a lateral position of the heat exchanger  1 , the first end portion  22   b  and the second end portion  22   c  of the windward heat transfer tube  22  and the first end portion  32   b  and the second end portion  32   c  of the leeward heat transfer tube  32  are formed in a staggered manner as shown in  FIG. 5 , or form a checker patter as shown in  FIG. 6 . 
       FIG. 7  and  FIG. 8  are schematic drawings illustrating the connection between the heat exchange unit and the branch/junction section of the heat exchanger according to another variation of Embodiment 1. Here,  FIG. 7  and  FIG. 8  are cross-sectional views from a position corresponding to the line A-A in  FIG. 4 . 
     As shown in  FIG. 7  and  FIG. 8 , the second end portion  22   c  of the windward heat transfer tube  22  and the first end portion  22   b  of the windward heat transfer tube  22  of the adjacent column may be connected to each other via a windward column joint tube  44  and the windward concentric tube fitting  41 A, and the second end portion  32   c  of the leeward heat transfer tube  32  and the first end portion  32   b  of the leeward heat transfer tube  32  of the adjacent column may be connected via a leeward column joint tube  45  and the leeward concentric tube fitting  42 A. The windward column joint tube  44  and the leeward column joint tube  45  are, for example, round tubes or elliptical tubes bent in an arcuate shape. 
     In addition, instead of bending the section between the first end portion and the second end portion of the windward heat transfer tube  22  and the leeward heat transfer tube  32  in the hair-pin shape, to form the turnback sections  22   a ,  32   a , the first end portion of the windward heat transfer tube  22  and the first end portion of the adjacent windward heat transfer tube  22  may be connected via the windward column joint tube  44  and the windward concentric tube fitting  41 A, and the first end portion of the leeward heat transfer tube  32  and the first end portion of the adjacent leeward heat transfer tube  32  may be connected via the leeward column joint tube  45  and the leeward concentric tube fitting  42 A, so as to allow the refrigerant to turn the flow direction. 
     (Detailed Configuration of Windward Concentric Tube Fitting and Leeward Concentric Tube Fitting) 
     Hereunder, the detailed configuration of the windward concentric tube fitting and the leeward concentric tube fitting of the heat exchanger according to Embodiment 1 will be described. 
       FIG. 9  is a schematic drawing showing the configuration of the windward concentric tube fitting and the leeward concentric tube fitting of the heat exchanger according to Embodiment 1.  FIG. 9  includes a front cross-sectional view of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A, a side cross-sectional view thereof, and an upper plan view and a bottom view thereof. In  FIG. 9 , further, the tubes respectively connected to a first end portion  72  and a second end portion  73  of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A are indicated by broken lines. As shown in  FIG. 9 , round tubes are employed as joint tube  57  of the stacked header  51  and joint tube  64  of the cylindrical header  61 . 
     As shown in  FIG. 9 , the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A each include a through portion  71 . The first end portion  72  of the through portion  71  has a cross-sectional shape that matches the cross-sectional shape of the windward heat transfer tube  22  or the leeward heat transfer tube  32 . The second end portion  73  of the through portion  71  has a cross-sectional shape that matches the cross-sectional shape of the joint tube  57  of the stacked header  51  or the joint tube  64  of the cylindrical header  61 . The central axis of the first end portion  72  and the central axis of the second end portion  73  coincide with each other. 
     In the front view of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A, the inner diameter D 1  of the second end portion  73  is smaller than or equal to the inner diameter W 1  of the first end portion  72  taken along the major axis. In the side view of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A, the inner diameter D 2  of the second end portion  73  is larger than or equal to the inner diameter W 2  of the first end portion  72  taken along the minor axis. Accordingly, the inner diameter D (D 1 , D 2 ) of the cross-section of the second end portion  73  with respect to the entire circumference thereof may be expressed as W 2 ≦D≦W 1 . In addition, the flow path cross-sectional area (d 1   2 ×π/4) of the joint tube  57  of the stacked header  51  and the joint tube  64  of the cylindrical header  61  is larger than the flow path cross-sectional area (w 1 ×w 2 ×number of flow paths) of the windward heat transfer tube  22  and the leeward heat transfer tube  32 . Here, when the joint tube  57  of the stacked header  51  and the joint tube  64  of the cylindrical header  61  are elliptical tubes, D 1  may be either larger or smaller than D 2 . 
     The foregoing configuration not only enables reduction in size of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A by making D 1  smaller, but also suppresses pressure loss of the refrigerant flowing through the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A by increasing D 2  so as to allow a tube having a larger flow path cross-sectional area to be connected. In addition, the configuration that can be expressed as W 2 ≦D≦W 1  contributes to improving the degree of freedom in bending work of the joint tube  57  of the stacked header  51  and the joint tube  64  of the cylindrical header  61 . 
       FIG. 10  is a schematic drawing showing a configuration of the windward concentric tube fitting and the leeward concentric tube fitting of the heat exchanger according to a comparative example.  FIG. 10  is a front cross-sectional view of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A. In  FIG. 10 , the tubes respectively connected to the first end portion  72  and the second end portion  73  of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A are indicated by broken lines. 
     The through portion  71  includes a shape transition section  74  located between the first end portion  72  and the second end portion  73 . Through the shape transition section  74 , the cross-sectional shape of the inner circumferential surface of the first end portion  72  is gradually translated into the cross-sectional shape of the inner circumferential surface of the second end portion  73 . When the shape transition section  74  is not provided in the through portion  71 , in other words when the first end portion  72  and the second end portion  73  directly communicate with each other as shown in  FIG. 10 , a vortex flow is generated at corner portions of the first end portion  72 , which incurs pressure loss of the refrigerant flowing through the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A. However, forming the shape transition section  74  in the region between the first end portion  72  and the second end portion  73  of the through portion  71  suppresses such a phenomenon. 
     Further, the joint tube  57  of the stacked header  51  and the joint tube  64  of the cylindrical header  61  are inserted to the boundary between the second end portion  73  and the shape transition section  74 , when joined to the tube fitting  41 A,  42 A. In other words, the region in the inner circumferential surface of the second end portion  73  where the outer circumferential surface of the joint tube  57  of the stacked header  51  or the joint tube  64  of the cylindrical header  61  is joined is closely adjacent to the shape transition section  74 . Therefore, the refrigerant flowing in through the joint tube  57  of the stacked header  51  or the joint tube  64  of the cylindrical header  61  can flow into the windward heat transfer tube  22  or the leeward heat transfer tube  32  without passing over a stepped portion, thereby being more effectively exempted from suffering pressure loss. Further, the second end portion  73  can be formed in a reduced axial length, which leads to reduction in size of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A. 
     (Detailed Configuration of Windward Eccentric Tube Fitting and Leeward Eccentric Tube Fitting) 
     Hereunder, the detailed configuration of the windward eccentric tube fitting and the leeward eccentric tube fitting of the heat exchanger according to Embodiment 1. 
       FIG. 11  is a schematic drawing showing the configuration of the windward eccentric tube fitting and the leeward eccentric tube fitting of the heat exchanger according to Embodiment 1.  FIG. 11  includes a front cross-sectional view of the windward eccentric tube fitting  41 B and the leeward eccentric tube fitting  42 B, and associated components. 
     The windward eccentric tube fitting  41 B and the leeward eccentric tube fitting  42 B basically have the same configuration as that of the windward concentric tube fitting  41 A and the leeward concentric tube fitting  42 A, however are different therefrom in that the central axis of the first end portion  72  and the central axis of the second end portion  73  are deviated from each other, as shown in  FIG. 11 . The eccentricity Z may be expressed as 0&lt;Z&lt;W 3 /2, where W 3  represents the outer diameter taken along the major axis of the windward heat transfer tube  22  and the leeward heat exchanger  32   
     The central axes are deviated such that the distance between the central axis of the second end portion  73  of the through portion  71  of the windward eccentric tube fitting  41 B and the central axis of the leeward heat transfer tube  32  becomes shorter than the distance between the central axis of the first end portion  72  of the through portion  71  of the windward eccentric tube fitting  41 B and the central axis of the leeward heat transfer tube  32 . Likewise, the central axes are deviated such that the distance between the central axis of the second end portion  73  of the through portion  71  of the leeward eccentric tube fitting  42 B and the central axis of the windward heat transfer tube  22  becomes shorter than the distance between the central axis of the first end portion  72  of the through portion  71  of the leeward eccentric tube fitting  42 B and the central axis of the windward heat transfer tube  22 . 
     &lt;Configuration of Air-Conditioning Apparatus Including Heat Exchanger&gt; 
     Hereunder, a configuration of an air-conditioning apparatus that includes the heat exchanger according to Embodiment 1 will be described. 
       FIG. 12  and  FIG. 13  are block diagrams showing the configuration of the air-conditioning apparatus including the heat exchanger according to Embodiment 1.  FIG. 12  represents the case where the air-conditioning apparatus  91  performs a heating operation.  FIG. 13  represents the case where the air-conditioning apparatus  91  performs a cooling operation. 
     As shown in  FIG. 12  and  FIG. 13 , the air-conditioning apparatus  91  includes a compressor  92 , a four-way valve  93 , an outdoor heat exchanger (heat source-side heat exchanger)  94 , an expansion device  95 , an indoor heat exchanger (load-side heat exchanger)  96 , an outdoor fan (heat source-side fan)  97 , an indoor fan (load-side fan)  98 , and a controller  99 . The compressor  92 , the four-way valve  93 , the outdoor heat exchanger  94 , the expansion device  95 , and the indoor heat exchanger  96  are connected via a refrigerant pipe, so as to form a refrigerant circuit. The four-way valve  93  may be another type of flow switching device. 
     The outdoor heat exchanger  94  corresponds to the heat exchanger  1 . In the heat exchanger  1 , the stacked header  51  is located on the windward side and the cylindrical header  61  is located on the leeward side, in the airflow generated when the outdoor fan  97  is driven. The outdoor fan  97  may be provided either windward or leeward of the heat exchanger  1 . 
     To the controller  99 , for example the compressor  92 , the four-way valve  93 , the expansion device  95 , the outdoor fan  97 , the indoor fan  98 , and various sensors are connected. The controller  99  switches the flow path in the four-way valve  93 , thereby switching between the heating operation and the cooling operation. 
     &lt;Operation of Heat Exchanger and Air-Conditioning Apparatus&gt; 
     Hereunder, an operation of the heat exchanger according to Embodiment 1 and the air-conditioning apparatus including the heat exchanger will be described. 
     (Operation of Heat Exchanger and Air-Conditioning Apparatus in Heating Operation) 
     Referring to  FIG. 12 , the flow of the refrigerant in the heating operation will be described hereunder. 
     The high-pressure and high-temperature gas refrigerant discharged from the compressor  92  flows into the indoor heat exchanger  96  through the four-way valve  93 , and is condensed through heat exchange with air supplied by the indoor fan  98 , thereby heating the indoor air. The condensed refrigerant turns into high-pressure subcooled liquid refrigerant and flows out of the indoor heat exchanger  96 , and then turns into low-pressure two-phase gas-liquid refrigerant in the expansion device  95 . The low-pressure two-phase gas-liquid refrigerant flows into the outdoor heat exchanger  94 , and is evaporated through heat exchange with air supplied by the outdoor fan  97 . The evaporated refrigerant turns into low-pressure superheated gas refrigerant and flows out of the outdoor heat exchanger  94 , and is then sucked into the compressor  92  through the four-way valve  93 . Thus, the outdoor heat exchanger  94  acts as evaporator in the heating operation. 
     In the outdoor heat exchanger  94 , the refrigerant flows into the branch/junction flow path  51   a  of the stacked header  51  thus to be branched, and flows into the windward heat transfer tube  22  of the windward heat exchange unit  21 , through the windward concentric tube fitting  41 A. The refrigerant which has entered the windward heat transfer tube  22  sequentially passes through the windward eccentric tube fitting  41 B, the row joint tube  43 , and the leeward eccentric tube fitting  42 B, and flows into the leeward heat transfer tube  32  of the leeward heat exchange unit  31 . The refrigerant which has entered the leeward heat transfer tube  32  passes through the leeward concentric tube fitting  42 A and flows into the branch/junction flow path  61   a  of the cylindrical header  61 , thus to be merged. 
     (Operation of Heat Exchanger and Air-Conditioning Apparatus in Cooling Operation) 
     Referring to  FIG. 13 , the flow of the refrigerant in the cooling operation will be described hereunder. 
     The high-pressure and high-temperature gas refrigerant discharged from the compressor  92  flows into the outdoor heat exchanger  94  through the four-way valve  93 , and is condensed through heat exchange with air supplied by the outdoor fan  97 . The condensed refrigerant turns into high-pressure subcooled liquid refrigerant or low-quality refrigerant, and flows out of the outdoor heat exchanger  94  and then turns into low-pressure two-phase gas-liquid refrigerant in the expansion device  95 . The low-pressure two-phase gas-liquid refrigerant flows into the indoor heat exchanger  96 , and is evaporated through heat exchange with air supplied by the indoor fan  98 , thereby cooling the indoor air. The evaporated refrigerant turns into low-pressure superheated gas refrigerant and flows out of the indoor heat exchanger  96 , and is then sucked into the compressor  92  through the four-way valve  93 . Thus, the outdoor heat exchanger  94  acts as condenser in the cooling operation. 
     In the outdoor heat exchanger  94 , the refrigerant flows into the branch/junction flow path  61   a  of the cylindrical header  61  thus to be branched, and flows into the leeward heat transfer tube  32  of the leeward heat exchange unit  31 , through the leeward concentric tube fitting  42 A. The refrigerant which has entered the leeward heat transfer tube  32  sequentially passes through the leeward eccentric tube fitting  42 B, the row joint tube  43 , and the windward eccentric tube fitting  41 B, and flows into the windward heat transfer tube  22  of the windward heat exchange unit  21 . The refrigerant which has entered the windward heat transfer tube  22  passes through the windward concentric tube fitting  41 A and flows into the branch/junction flow path  51   a  of the stacked header  51 , thus to be merged. 
     &lt;Effects of Heat Exchanger&gt; 
     Hereunder, the effects of the heat exchanger according to Embodiment 1 will be described. 
     In the heat exchanger  1 , the central axis of the first end portion  72  and the central axis of the second end portion  73  are deviated from each other, in the windward eccentric tube fitting  41 B and the leeward eccentric tube fitting  42 B. Therefore, the balance among the flows of flows of the fluid flowing into the windward heat transfer tube  22  and the leeward heat transfer tube  32  can be optimized. 
       FIG. 14  and  FIG. 15  are a schematic drawing and a graph respectively, illustrating liquid distribution of the refrigerant flowing into the leeward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as evaporator. In  FIG. 14 , the flow direction of the refrigerant is indicated by solid arrows. 
     When the heat exchange unit  2  acts as evaporator, the refrigerant flows parallel to the airflow generated by driving the outdoor fan  97  as shown in  FIG. 14  and  FIG. 15 , in other words flows from the windward heat transfer tube  22  to the leeward heat transfer tube  32 , and then flows into the leeward eccentric tube fitting  42 B through the row joint tube  43  in the two-phase gas-liquid state. The two-phase gas-liquid refrigerant flowing through the row joint tube  43  is subjected to centrifugal force, so that a high-density portion of the refrigerant flows along the outer side and a low-density portion of the refrigerant flows along the inner side. In the leeward eccentric tube fitting  42 B, therefore, if the eccentricity Z between the central axis of the first end portion  72  and the central axis of the second end portion  73  were 0, a larger portion of the liquid refrigerant flowing into the leeward eccentric tube fitting  42 B would flow toward a point L in the leeward heat transfer tube  32 , than a portion flowing toward a point S. 
     In the heat exchanger  1 , in contrast, the eccentricity Z between the central axis of the first end portion  72  and the central axis of the second end portion  73  is larger than 0 in the leeward eccentric tube fitting  42 B, and therefore a major portion of the liquid refrigerant flowing into the leeward eccentric tube fitting  42 B flows toward the point S in the leeward heat transfer tube  32 . When the heat exchanger  1  acts as evaporator, the thermal load (heat exchange amount) of the airflow generated by driving the outdoor fan  97  is larger on the windward side, and therefore distributing the liquid refrigerant to the flow path openings of the flat tube such that a major portion thereof flows toward the point S of the leeward heat transfer tube  32 , in other words into the flow path on the windward side, allows the liquid refrigerant to be more efficiently evaporated, thereby improving the heat exchange efficiency. Further, the row joint tube  43  can be formed with a smaller curvature radius so as to increase the capacity of the heat exchange unit  2 , and therefore the heat exchange efficiency can be further improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
       FIG. 16  and  FIG. 17  are a schematic drawing and a graph respectively, illustrating gas distribution of the refrigerant flowing into the windward heat transfer tube, realized when the heat exchanger according to Embodiment 1 acts as condenser. In  FIG. 16 , the flow direction of the refrigerant is indicated by solid arrows. 
     When the heat exchange unit  2  acts as condenser, the refrigerant flows against the airflow generated by driving the outdoor fan  97  as shown in  FIG. 16  and  FIG. 17 , in other words the refrigerant flows from the leeward heat transfer tube  32  to the windward heat transfer tube  22 , and then flows into the windward eccentric tube fitting  41 B through the row joint tube  43  in the two-phase gas-liquid state. The two-phase gas-liquid refrigerant flowing through the row joint tube  43  is subjected to centrifugal force, so that a high-density portion of the refrigerant flows along the outer side and a low-density portion of the refrigerant flows along the inner side. In the windward eccentric tube fitting  41 B, therefore, if the eccentricity Z between the central axis of the first end portion  72  and the central axis of the second end portion  73  were 0, a larger portion of the liquid refrigerant flowing into the windward eccentric tube fitting  41 B would flow toward a point L in the windward heat transfer tube  22 , than a portion flowing toward a point S. 
     In the heat exchanger  1 , in contrast, the eccentricity Z between the central axis of the first end portion  72  and the central axis of the second end portion  73  is larger than 0 in the windward eccentric tube fitting  41 B, and therefore a major portion of the gas refrigerant flowing into the windward eccentric tube fitting  41 B flows toward the point L in the windward heat transfer tube  22 , since a major portion of liquid refrigerant flows toward the point S. When the heat exchanger  1  acts as condenser, the thermal load (heat exchange amount) of the airflow generated by driving the outdoor fan  97  is larger on the windward side, and therefore distributing the gas refrigerant to the flow path openings of the flat tube such that a major portion thereof flows toward the point L of the windward heat transfer tube  22 , in other words into the flow path on the windward side, allows the gas refrigerant to be more efficiently condensed, thereby improving the heat exchange efficiency. Further, the row joint tube  43  can be formed with a smaller curvature radius and the capacity of the heat exchange unit  2  can be increased, and therefore the heat exchange efficiency can be further improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
     Further, in the windward concentric tube fitting  41 A, the leeward concentric tube fitting  42 A, the windward eccentric tube fitting  41 B, and the leeward eccentric tube fitting  42 B of the heat exchanger  1 , since the inner diameter D (D 1 , D 2 ) of the cross-section of the second end portion  73  with respect to the entire circumference thereof is set to W 2 &lt;D&lt;W 1 , where WI represents the inner diameter of the first end portion  72  taken along the major axis and W 2  represents the inner diameter thereof taken along the minor axis, reduction in size and reduction in pressure loss can both be realized. Accordingly, the spacing between the heat exchange unit  2  and the branch/junction section  3  can be narrowed so as to increase the capacity of the heat exchange unit  2 , and therefore the heat exchange efficiency can be improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
     Still further, in the windward concentric tube fitting  41 A, the leeward concentric tube fitting  42 A, the windward eccentric tube fitting  41 B, and the leeward eccentric tube fitting  42 B of the heat exchanger  1 , the shape transition section  74  is provided in the region between the first end portion  72  and the second end portion  73  of the through portion  71 , and the region in the inner circumferential surface of the second end portion  73  where the outer circumferential surface of the joint tube  57  of the stacked header  51 , the joint tube  64  of the cylindrical header  61 , or the row joint tube  43  is joined is closely adjacent to the shape transition section  74 , and therefore reduction in size and reduction in pressure loss can both be realized. Accordingly, the spacing between the heat exchange unit  2  and the branch/junction section  3  can be narrowed so as to increase the capacity of the heat exchange unit  2 , and therefore the heat exchange efficiency can be improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
     Embodiment 2 
     Hereafter, a heat exchanger according to Embodiment 2 will be described. 
     The description of the aspects same as or similar to those of Embodiment 1 will be simplified or omitted, as the case may be. 
     &lt;Configuration of Heat Exchanger&gt; 
     Hereunder, a configuration of the heat exchanger according to Embodiment 2 will be described. 
     (General Configuration of Heat Exchanger) 
     Hereunder, a general configuration of the heat exchanger according to Embodiment 2 will be described. 
       FIG. 18  is a perspective view of the heat exchanger according to Embodiment 2. 
     As shown in  FIG. 18 , the heat exchange unit  2  only includes the windward heat exchange unit  21 . The windward heat transfer tubes  22  are arranged in a plurality of columns in a direction intersecting the flow direction of air passing through the heat exchange unit  2  (blank arrow in  FIG. 18 ). Each of the windward heat transfer tubes  22  is bent in a hair-pin shape between the first end portion and the second end portion, so as to form a turnback section  22   a . The first end portion and the second end portion of each of the windward heat transfer tubes  22  are aligned so as to oppose the stacked header  51 . 
     The stacked header  51  includes therein a branch/junction flow path  51   a , and is connected to the windward heat exchange unit  21 . When the heat exchange unit  2  acts as evaporator, the branch/junction flow path  51   a  serves as branch flow path for distributing the refrigerant received through a non-illustrated refrigerant tube to the plurality of windward heat transfer tubes  22  in the windward heat exchange unit  21 . When the heat exchange unit  2  acts as condenser, the branch/junction flow path  51   a  serves as junction flow path for merging the refrigerant received from each of the windward heat transfer tubes  22  in the windward heat exchange unit  21  and passing the merged flow to the non-illustrated refrigerant tube. 
     The cylindrical header  61  includes therein a branch/junction flow path  61   a , and is connected to the windward heat exchange unit  21 . When the heat exchange unit  2  acts as condenser, the branch/unction flow path  61   a  serves as branch flow path for distributing the refrigerant received through a non-illustrated refrigerant tube to the plurality of windward heat transfer tubes  22  in the windward heat exchange unit  21 . When the heat exchange unit  2  acts as evaporator, the branch/junction flow path  61   a  serves as junction flow path for merging the refrigerant received from each of the windward heat transfer tubes  22  in the windward heat exchange unit  21  and passing the merged flow to the non-illustrated refrigerant tube. 
     (Connection Between Heat Exchange Unit and Branch/Junction Section) 
     Hereunder, connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 2 will be described. 
       FIG. 19  and  FIG. 20  are schematic drawings illustrating the connection between the heat exchange unit and the branch/junction section of the heat exchanger according to Embodiment 2.  FIG. 20  is a cross-sectional view taken along a line B-B in  FIG. 19 . 
     As shown in  FIG. 19  and  FIG. 20 , each of the windward concentric tube fittings  41 A is joined to the first end portion  22   b  or the second end portion  22   c  of the windward heat transfer tube  22 . The joint tube  57  of the stacked header  51  is connected to the windward concentric tube fitting  41 A joined to the first end portion  22   b  of the windward heat transfer tube  22 . The joint tube  64  of the cylindrical header  61  is connected to the windward concentric tube fitting  41 A joined to the second end portion  22   c  of the windward heat transfer tube  22 . 
       FIG. 21  is a schematic drawing illustrating the connection between the heat exchange unit and the branch/junction section of the heat exchanger according to a variation of Embodiment 2. Here,  FIG. 21  is a cross-sectional view from a position corresponding to the line B-B in  FIG. 19 . 
     As shown in  FIG. 21 , the second end portion  22   c  of the windward heat transfer tube  22  and the first end portion  22   b  of the windward heat transfer tube  22  of the adjacent column may be connected to each other via the windward column joint tube  44  and the windward concentric tube fitting  41 A. 
     &lt;Operation of Heat Exchanger and Air-Conditioning Apparatus&gt; 
     Hereunder, an operation of the heat exchanger according to Embodiment 2 and the air-conditioning apparatus including the heat exchanger will be described. 
     (Operation of Heat Exchanger and Air-Conditioning Apparatus in Heating Operation) 
       FIG. 22  is a block diagram showing the configuration of the air-conditioning apparatus including the heat exchanger according to Embodiment 2.  FIG. 22  represents the case where the air-conditioning apparatus  91  performs a heating operation. 
     Referring to  FIG. 22 , the flow of the refrigerant in the heating operation will be described hereunder. 
     In the outdoor heat exchanger  94 , the refrigerant flows into the branch/junction flow path  51   a  of the stacked header  51  thus to be branched, and flows into the windward heat transfer tube  22  of the windward heat exchange unit  21 , through the windward concentric tube fitting  41 A. The refrigerant which has entered the windward heat transfer tube  22  passes through the windward concentric tube fitting  41 A and flows into the branch/junction flow path  61   a  of the cylindrical header  61 , thus to be merged. 
     (Operation of Heat Exchanger and Air-Conditioning Apparatus in Cooling Operation) 
       FIG. 23  is a block diagram showing the configuration of the air-conditioning apparatus including the heat exchanger according to Embodiment 2.  FIG. 23  represents the case where the air-conditioning apparatus  91  performs a cooling operation. 
     Referring to  FIG. 23 , the flow of the refrigerant in the cooling operation will be described hereunder. 
     In the outdoor heat exchanger  94 , the refrigerant flows into the branch/junction flow path  61   a  of the cylindrical header  61  thus to be branched, and flows into the windward heat transfer tube  22  of the windward heat exchange unit  21 , through the windward concentric tube fitting  41 A. The refrigerant which has entered the windward heat transfer tube  22  passes through the windward concentric tube fitting  41 A and flows into the branch/junction flow path  51   a  of the stacked header  51 , thus to be merged. 
     &lt;Effects of Heat Exchanger&gt; 
     Hereunder, the effects of the heat exchanger according to Embodiment 2 will be described. 
     In the windward concentric tube fitting  41 A of the heat exchanger  1 , as in the heat exchanger  1  according to Embodiment 1, the inner diameter D (D 1 , D 2 ) of the cross-section of the second end portion  73  with respect to the entire circumference thereof is set to W 2 ≦D≦W 1 , where WI represents the inner diameter of the first end portion  72  taken along the major axis and W 2  represents the inner diameter thereof taken along the minor axis, and therefore reduction in size and reduction in pressure loss can both be realized. Accordingly, the spacing between the heat exchange unit  2  and the branch/junction section  3  can be narrowed so as to increase the capacity of the heat exchange unit  2 , and consequently the heat exchange efficiency can be improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
     Further, in the windward concentric tube fitting  41 A of the heat exchanger  1 , as in the heat exchanger  1  according to Embodiment 1, the shape transition section  74  is provided in the region between the first end portion  72  and the second end portion  73  of the through portion  71 , and the region in the inner circumferential surface of the second end portion  73  where the outer circumferential surface of the joint tube  57  of the stacked header  51  or the joint tube  64  of the cylindrical header  61  is joined is closely adjacent to the shape transition section  74 , and therefore reduction in size and reduction in pressure loss can both be realized. Accordingly, the spacing between the heat exchange unit  2  and the branch/junction section  3  can be narrowed so as to increase the capacity of the heat exchange unit  2 , and therefore the heat exchange efficiency can be improved. The improvement in heat exchange efficiency leads to improved operation efficiency of the refrigeration cycle, thereby upgrading the energy saving performance. Further, the footprint of the heat exchanger  1  can be reduced without compromising the performance level of the refrigeration cycle. 
     Although Embodiment 1 and Embodiment 2 have been described as above, the present invention is in no way limited to the foregoing Embodiments. For example, the whole or a part of Embodiments may be combined as desired. 
     REFERENCE SIGNS LIST 
       1 : heat exchanger,  2 : heat exchange unit,  3 : branch/junction section,  21 : windward heat exchange unit,  22 : windward heat transfer tube,  22   a : turnback section,  22   b : the first end portion,  22   c : the second end portion,  23 : windward fin,  31 : leeward heat exchange unit,  32 : leeward heat transfer tube,  32   a : turnback section,  32   b : the first end portion,  32   c : the second end portion,  33 : leeward fin,  41 A: windward concentric tube fitting,  41 B: windward eccentric tube fitting,  42 A: leeward concentric tube fitting,  42 B: leeward eccentric tube fitting,  43 : row joint tube  44 : windward column joint tube  45 : leeward column joint tube,  51 : stacked header,  51   a : branch/junction flow path,  52 ,  57 : joint tube,  53 : first plate member,  54 _ 1  to  54 _ 3 : second plate member,  55 : third plate member,  56 _ 1  to  56 _ 4 : clad member,  53   a ,  54   a _ 1  to  54   a _ 3 ,  55   a ,  56   a : flow path segment,  61 : cylindrical header,  61   a : branch/junction flow path,  62 ,  64 : joint tube,  63 : cylindrical portion,  71 : through portion,  72 : first end portion,  73 : second end portion,  74 : shape transition section,  91 : air-conditioning apparatus,  92 : compressor,  93 : four-way valve,  94 : outdoor heat exchanger,  95 : expansion device,  96 : indoor heat exchanger,  97 : outdoor fan,  98 : indoor fan,  99 : controller