Patent Publication Number: US-2022212278-A1

Title: Heat exchanger, heat pump device, and method of manufacturing heat exchanger

Description:
TECHNICAL FIELD 
     The present disclosure relates to a heat exchanger, a heat pump device, and a method of manufacturing the heat exchanger. 
     BACKGROUND 
     A refrigerant cycle apparatus such as an air conditioner conventionally includes a heat exchanger provided with a heat transfer tube allowing a refrigerant to flow therein and connected to a header. 
     An exemplary heat exchanger described in Patent Literature 1 (WO 2015/004719 A) includes a header constituted by a plurality of laminated plate-shaped members. The header includes bare materials provided with no brazing filler material, and clad materials having front and rear surfaces each provided with the brazing filler material, and the bare materials and the clad materials are laminated alternately and are joined by brazing. 
     Patent Literature 
     Patent Literature 1: WO 2015/004719 A 
     When the plurality of members mentioned above is joined by brazing, a brazing filler material positioned far from a heat source for provision of heat is less likely to melt in comparison to a brazing filler material positioned close to the heat source, to possibly cause defective brazing. 
     SUMMARY 
     In one or more embodiments, a heat exchanger inhibits defective brazing of a header constituted by a plurality of members, a heat pump device, and a method of manufacturing the heat exchanger. 
     A heat exchanger according to one or more embodiments includes a header, and a plurality of heat transfer tubes connected to the header. The header has a plurality of members including a first member, a second member, and a third member to be brazed. A brazing layer between the second member and the third member has a melt rate, at a predetermined temperature, being larger than a melt rate, at the predetermined temperature, of at least one of a brazing layer between the first member and the second member and a brazing layer between the first member and the third member. 
     There may be provided either one or both of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     The predetermined temperature should not be limited and, for example, may be a temperature at which a melt is generated at both a brazing layer between the second member and the third member and the brazing layer between the first member and the second member, may be a temperature at which a melt is generated at both the brazing layer between the second member and the third member and the brazing layer between the first member and the third member, or may be a temperature at which a melt is generated at all the brazing layer between the second member and the third member, the brazing layer between the first member and the second member, and the brazing layer between the first member and the third member. The temperature may be, for example, 580° C. or more, or 590° C. or more. The predetermined temperature has an upper limit that should not be limited, and the upper limit may be 660° C. or less and can be 630° C. or less. An ambient temperature in a furnace should not be limited, and may be exemplarily 1000° C. or more and 1300° C. or less. 
     Though not limited, the heat exchanger may be constructed such that the header has a vertical or horizontal longitudinal direction. 
     The heat exchanger can achieve an excellent joining state of brazing between the second member and the third member, even in a case where the brazing layer between the second member and the third member is lower in temperature during brazing than at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     A heat exchanger according to one or more embodiments includes a header, and a plurality of heat transfer tubes connected to the header. The header has a plurality of members including a first member, a second member, and a third member to be brazed. The brazing layer between the second member and the third member has a silicon content larger than a silicon content of at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     The brazing layer between the second member and the third member preferably contains a silicon alloy larger in silicon content than a silicon alloy in at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     The predetermined temperature should not be limited and, for example, may be a temperature at which a melt is generated at both a brazing layer between the second member and the third member and the brazing layer between the first member and the second member, may be a temperature at which a melt is generated at both the brazing layer between the second member and the third member and the brazing layer between the first member and the third member, or may be a temperature at which a melt is generated at all the brazing layer between the second member and the third member, the brazing layer between the first member and the second member, and the brazing layer between the first member and the third member. The temperature may be, for example, 580° C. or more, or 590° C. or more. The predetermined temperature has an upper limit that should not be limited, and the upper limit may be 660° C. or less and can be 630° C. or less. Ambient temperature in a furnace should not be limited, and may be exemplarily 1000° C. or more and 1300° C. or less. 
     The heat exchanger can achieve an excellent joining state of brazing between the second member and the third member, even in a case where the brazing layer between the second member and the third member is lower in temperature during brazing than at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     In one or more embodiments of the heat exchanger, the brazing layer between the second member and the third member has a melt rate, at predetermined temperature, being larger than a melt rate at the predetermined temperature of at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. The heat exchanger can achieve an excellent joining state of brazing between the second member and the third member, even in a case where the brazing layer between the second member and the third member is lower in temperature during brazing than at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     In one or more embodiments of the heat exchanger, the brazing layer between the second member and the third member is disposed inside at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     In one or more embodiments of the heat exchanger, the brazing layer between the second member and the third member is disposed inside at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. The heat exchanger thus achieves an excellent joining state of brazing between the second member and the third member even in a case where the brazing layer between the second member and the third member receives less heat, during brazing, than at least one of the brazing layer between the first member and the second member and the brazing layer between the first member and the third member. 
     In one or more embodiments of the heat exchanger, the first member has a first portion having a plate shape. The first portion has a plurality of first openings into which the heat transfer tubes are inserted. The third member is a plate-shaped member having a plurality of second openings into which the heat transfer tubes are inserted. The first portion and the third member are laminated in a thickness direction. 
     The heat exchanger achieves joining by brazing of the inserted heat transfer tubes in the first openings in the first portion of the first member. The first member and the third member are laminated in the thickness direction to secure a total thickness for improvement in strength of the header. This configuration allows the first member to be thinned while securing strength of the header, for less friction between circumferential surfaces of the heat transfer tubes and the first openings upon insertion of the heat transfer tubes. 
     In one or more embodiments of the heat exchanger, in a view in an extending direction of the heat transfer tubes, each of the first openings has an outline positioned inside an outline of a corresponding one of the second openings. 
     In the heat exchanger, any excessive brazing filler material around ends of the heat transfer tubes during brazing can be shifted into regions outside the heat transfer tubes and inside the second openings of the third member. This inhibits the brazing filler material from blocking flow paths in the heat transfer tubes. 
     In one or more embodiments of the heat exchanger, each of the first member, the second member, and the third member contains aluminum or an aluminum alloy. 
     In one or more embodiments of the heat exchanger, each of the first member, the second member, and the third member has a thickness equal to or less than 3 mm. 
     Each of the first member, the second member, and the third member has a thickness equal to or less than 3 mm in the heat exchanger, and each of the members can thus be easily formed into a specific shape. 
     In one or more embodiments, a heat pump device is equipped with the heat exchanger according to any of the above-described embodiments. 
     In one or more embodiments, a method of manufacturing a heat exchanger including a header and a plurality of heat transfer tubes connected to the header involves laminating and brazing. The header includes a first member, a second member, and a third member. The first member has a clad layer. The third member has a clad layer. The laminating involves laminating the first member, the second member, and the third member with positioning the clad layer of the first member on the second member side and positioning the clad layer of the third member on the second member side. The brazing involves heating the first member, the second member, and the third member to braze the first member and the second member as well as braze the second member and the third member. The clad layer of the third member has a melt rate at predetermined temperature larger than a melt rate at the predetermined temperature of the clad layer of the first member. 
     The second member may optionally be provided with a clad layer in addition to the first member and the third member. 
     The predetermined temperature should not be limited. For example, it may be a temperature at which a melt is generated at both the clad layer of the first member and the clad layer of the third member, and may be, for example, 580° C. or more, or 590° C. or more. The predetermined temperature has an upper limit that should not be limited, and the upper limit may be 660° C. or less and can be 630° C. or less. Ambient temperature in a furnace should not be limited, and may be exemplarily 1000° C. or more and 1300° C. or less. 
     The method of manufacturing the heat exchanger can provide the heat exchanger in an excellent joining state of brazing between the second member and the third member even in a case where the clad layer of the third member is lower in temperature than the clad layer of the first member during brazing by heating the first member, the second member, and the third member. 
     In one or more embodiments, a method of manufacturing a heat exchanger including a header and a plurality of heat transfer tubes connected to the header involves laminating and brazing. The header includes a fifth member, a sixth member, and a seventh member. The seventh member has a first clad layer and a second clad layer. The laminating involves laminating the fifth member, the sixth member, and the seventh member with positioning the first clad layer on the fifth member side and positioning the second clad layer on the sixth member side. The brazing involves heating the fifth member, the sixth member, and the seventh member to braze the fifth member and the seventh member as well as braze the sixth member and the seventh member with the second clad layer being interposed therebetween. The second clad layer has a melt rate at predetermined temperature larger than a melt rate at the predetermined temperature of the first clad layer. 
     The fifth or sixth member may optionally be provided with a clad layer in addition to the seventh member. 
     The predetermined temperature should not be limited. For example, it may be a temperature at which a melt is generated at both the first clad layer and the second clad layer, and may be, for example, 580° C. or more, or 590° C. or more. The predetermined temperature has an upper limit that should not be limited, and the upper limit may be 660° C. or less and can be 630° C. or less. Ambient temperature in a furnace should not be limited, and may be exemplarily 1000° C. or more and 1300° C. or less. 
     The method of manufacturing the heat exchanger can provide the heat exchanger in an excellent joining state of brazing between the sixth member and the seventh member even in a case where the second clad layer is lower in temperature than the first clad layer during brazing by heating the fifth member, the sixth member, and the seventh member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of an air conditioner. 
         FIG. 2  is a schematic perspective view of an outdoor heat exchanger. 
         FIG. 3  is a partial enlarged view of a heat exchange unit included in the outdoor heat exchanger. 
         FIG. 4  is a schematic view depicting attachment states of heat transfer fins to flat tubes in the heat exchange unit. 
         FIG. 5  is an explanatory view depicting how a refrigerant flows in the outdoor heat exchanger functioning as a refrigerant evaporator. 
         FIG. 6  is an outer appearance configuration diagram in a side view, depicting how a main gas refrigerant pipe connecting portion is connected to a gas header. 
         FIG. 7  is a planar sectional view of the gas header. 
         FIG. 8  is a planar sectional view depicting how the main gas refrigerant pipe connecting portion and a flat tube are connected to the gas header. 
         FIG. 9  is a schematic view from behind, of a first member. 
         FIG. 10  is a schematic view from behind, of a third member. 
         FIG. 11  is a schematic view from behind, of a second member. 
         FIG. 12  is an outer appearance perspective view of the second member. 
         FIG. 13  is a schematic view from behind, of a fourth member. 
         FIG. 14  is a projection view depicting positional relationship of openings in a case where the first member is viewed from behind. 
         FIG. 15  is an exploded planar sectional view of clad layers in members of the gas header. 
         FIG. 16  is a planar sectional view depicting how the main gas refrigerant pipe connecting portion and a flat tube are connected to the gas header in a modification example A. 
         FIG. 17  is a projection view depicting positional relationship of openings in a case where the second member is viewed from behind in the modification example A. 
         FIG. 18  is a planar sectional view of the gas header in a modification example B. 
         FIG. 19  is a schematic exploded perspective view of a header in a modification example C. 
     
    
    
     DETAILED DESCRIPTION 
     Description will be made hereinafter to an air conditioner according to one or more embodiments, including a heat exchanger of the present disclosure. 
     (1) Configuration of Air Conditioner 
     An air conditioner  1  will be described with reference to drawings. 
       FIG. 1  is a schematic configuration diagram of the air conditioner  1  including, as an outdoor heat exchanger  11 , a heat exchanger according to one or more embodiments of the present disclosure. 
     The air conditioner  1  (exemplifying a heat pump device) is configured to achieve a vapor compression refrigeration cycle to cool and heat an air conditioning target space. Examples of the air conditioning target space include a space in a building such as an office building, a commercial facility, or a residence. The air conditioner merely exemplifies a refrigerant cycle apparatus. The heat exchanger according to the present disclosure may be included in a different refrigerant cycle apparatus such as a refrigerator, a freezer, a hot-water supplier, or a floor heater. 
     As depicted in  FIG. 1 , the air conditioner  1  principally includes an outdoor unit  2 , an indoor unit  9 , a liquid-refrigerant connection pipe  4 , a gas-refrigerant connection pipe  5 , and a control unit  3  configured to control devices constituting the outdoor unit  2  and the indoor unit  9 . The liquid-refrigerant connection pipe  4  and the gas-refrigerant connection pipe  5  are refrigerant connection pipes connecting the outdoor unit  2  and the indoor unit  9 . The outdoor unit  2  and the indoor unit  9  are connected via the liquid-refrigerant connection pipe  4  and the gas-refrigerant connection pipe  5  to constitute a refrigerant circuit  6  in the air conditioner  1 . 
     The air conditioner  1  depicted in  FIG. 1  includes one indoor unit  9 . The air conditioner  1  may alternatively include a plurality of indoor units  9  connected parallelly to the outdoor unit  2  by the liquid-refrigerant connection pipe  4  and the gas-refrigerant connection pipe  5 . The air conditioner  1  may still alternatively include a plurality of outdoor units  2 . Still alternatively, the air conditioner  1  may be of an integral type including the outdoor unit  2  and the indoor unit  9  that are formed integrally with each other. 
     (1-1) Outdoor Unit 
     The outdoor unit  2  is disposed outside the air conditioning target space, such as on a roof of a building or adjacent to a wall surface of a building. 
     The outdoor unit  2  principally includes an accumulator  7 , a compressor  8 , a four-way switching valve  10 , the outdoor heat exchanger  11 , an expansion mechanism  12 , a liquid-side shutoff valve  13 , a gas-side shutoff valve  14 , and an outdoor fan  16  (see  FIG. 1 ). 
     The outdoor unit  2  principally includes, as a refrigerant pie connecting various devices constituting the refrigerant circuit  6 , a suction pipe  17 , a discharge pipe  18 , a first gas refrigerant pipe  19 , a liquid refrigerant pipe  20 , and a second gas refrigerant pipe  21  (see  FIG. 1 ). The suction pipe  17  connects the four-way switching valve  10  and a suction side of the compressor  8 . The suction pipe  17  is provided with the accumulator  7 . The discharge pipe  18  connects a discharge side of the compressor  8  and the four-way switching valve  10 . The first gas refrigerant pipe  19  connects the four-way switching valve  10  and a gas side of the outdoor heat exchanger  11 . The liquid refrigerant pipe  20  connects a liquid side of the outdoor heat exchanger  11  and the liquid-side shutoff valve  13 . The liquid refrigerant pipe  20  is provided with the expansion mechanism  12 . The second gas refrigerant pipe  21  connects the four-way switching valve  10  and the gas-side shutoff valve  14 . 
     The compressor  8  is configured to suck a low-pressure refrigerant in the refrigeration cycle from the suction pipe  17 , compresses the refrigerant by means of a compression mechanism (not depicted), and discharge the compressed refrigerant to the discharge pipe  18 . 
     The four-way switching valve  10  is a mechanism configured to switch a refrigerant flow direction to change a state of the refrigerant circuit  6  between a cooling operation state and a heating operation state. While the refrigerant circuit  6  is in the cooling operation state, the outdoor heat exchanger  11  functions as a refrigerant radiator (condenser) and an indoor heat exchanger  91  functions as a refrigerant evaporator. While the refrigerant circuit  6  is in the heating operation state, the outdoor heat exchanger  11  functions as a refrigerant evaporator and the indoor heat exchanger  91  functions as a refrigerant condenser. When the four-way switching valve  10  brings the state of the refrigerant circuit  6  into the cooling operation state, the four-way switching valve  10  causes the suction pipe  17  to communicate with the second gas refrigerant pipe  21  and causes the discharge pipe  18  to communicate with the first gas refrigerant pipe  19  (see solid lines in the four-way switching valve  10  in  FIG. 1 ). When the four-way switching valve  10  brings the state of the refrigerant circuit  6  into the heating operation state, the four-way switching valve  10  causes the suction pipe  17  to communicate with the first gas refrigerant pipe  19  and causes the discharge pipe  18  to communicate with the second gas refrigerant pipe  21  (see broken lines in the four-way switching valve  10  in  FIG. 1 ). 
     The outdoor heat exchanger  11  (exemplifying a heat exchanger) is configured to cause heat exchange between a refrigerant flowing inside and air (heat source air) at an installation site of the outdoor unit  2 . The outdoor heat exchanger  11  will be described in detail later. 
     The expansion mechanism  12  is disposed between the outdoor heat exchanger  11  and the indoor heat exchanger  91  on the refrigerant circuit  6 . The expansion mechanism  12  according to one or more embodiments is disposed on the liquid refrigerant pipe  20  between the outdoor heat exchanger  11  and the liquid-side shutoff valve  13 . The expansion mechanism  12  is provided at the outdoor unit  2  in the air conditioner  1  according to one or more embodiments. The expansion mechanism  12  may alternatively be provided at the indoor unit  9  to be described later. The expansion mechanism  12  is configured to adjust pressure and a flow rate of a refrigerant flowing in the liquid refrigerant pipe  20 . The expansion mechanism  12  according to one or more embodiments is an electronic expansion valve having a variable opening degree. Alternatively, the expansion mechanism  12  may be a temperature sensitive cylinder expansion valve or a capillary tube. 
     The accumulator  7  is a vessel having a gas-liquid separation function of separating a received refrigerant into a gas refrigerant and a liquid refrigerant. The accumulator  7  is also a vessel having a function of reserving an excessive refrigerant generated due to operation load change or the like. 
     The liquid-side shutoff valve  13  is provided at a connecting portion between the liquid refrigerant pipe  20  and the liquid-refrigerant connection pipe  4 . The gas-side shutoff valve  14  is provided at a connecting portion between the second gas refrigerant pipe  21  and the gas-refrigerant connection pipe  5 . The liquid-side shutoff valve  13  and the gas-side shutoff valve  14  are opened while the air conditioner  1  is in operation. 
     The outdoor fan  16  is configured to suck outside heat source air into a casing (not depicted) of the outdoor unit  2  and supply the outdoor heat exchanger  11  with the heat source air, and to discharge air having exchanged heat with a refrigerant in the outdoor heat exchanger  11  from the casing of the outdoor unit  2 . Examples of the outdoor fan  16  include a propeller fan. 
     (1-2) Indoor Unit 
     The indoor unit  9  is disposed in the air conditioning target space. The indoor unit  9  is, for example, of a ceiling embedded type. Alternatively, the indoor unit may be of a ceiling pendant type, a wall mounted type, or a floor-standing type. The indoor unit  9  may alternatively be disposed outside the air conditioning target space. For example, the indoor unit  9  may be installed in an attic space, a machine chamber, or a garage. In such a case, there is disposed an air passage for supply, from the indoor unit  9  to the air conditioning target space, of air having exchanged heat with a refrigerant in the indoor heat exchanger  91 . Examples of the air passage include a duct. 
     The indoor unit  9  principally includes the indoor heat exchanger  91  and an indoor fan  92  (see  FIG. 1 ). 
     The indoor heat exchanger  91  causes heat exchange between a refrigerant flowing in the indoor heat exchanger  91  and air in the air conditioning target space. The indoor heat exchanger  91  should not be limited in terms of its type, and is exemplarily a fin-and-tube heat exchanger including a plurality of heat transfer tubes and a plurality of fins (not depicted). The indoor heat exchanger  91  has a first end connected to the liquid-refrigerant connection pipe  4  via a refrigerant pipe. The indoor heat exchanger  91  has a second end connected to the gas-refrigerant connection pipe  5  via a refrigerant pipe. 
     The indoor fan  92  is a mechanism configured to suck air in the air conditioning target space into a casing (not depicted) of the indoor unit  9  and supply the indoor heat exchanger  91  with the air, and to blow, into the air conditioning target space, air having exchanged heat with a refrigerant in the indoor heat exchanger  91 . Examples of the indoor fan  92  include a turbo fan. The indoor fan  92  should not be limited to the turbo fan but may be appropriately selected in terms of its type. 
     (1-3) Control Unit 
     The control unit  3  is a functional unit configured to control operation of various devices constituting the air conditioner  1 . 
     The control unit  3  is exemplarily constituted such that an outdoor control unit (not depicted) of the outdoor unit  2  and an indoor control unit (not depicted) of the indoor unit  9  are communicably connected via a transmission line (not depicted). Each of the outdoor control unit and the indoor control unit exemplarily includes a microcomputer, and a memory or the like storing various programs for control of the air conditioner  1  and executed by the microcomputer.  FIG. 1  depicts, for convenience, the control unit  3  distant from the outdoor unit  2  and the indoor unit  9 . 
     The control unit  3  has a function that does not need to be implemented by cooperation of the outdoor control unit and the indoor control unit. For example, the function of the control unit  3  may be implemented by one of the outdoor control unit and the indoor control unit, or may be implemented partially or entirely by a control device (not depicted) different from the outdoor control unit and the indoor control unit. 
     As depicted in  FIG. 1 , the control unit  3  is electrically connected to various devices of the outdoor unit  2  and the indoor unit  9 , including the compressor  8 , the four-way switching valve  10 , the expansion mechanism  12 , the outdoor fan  16 , and the indoor fan  92 . The control unit  3  is also electrically connected to various sensors (not depicted) provided at the outdoor unit  2  and the indoor unit  9 . The control unit  3  is configured to be communicable with a remote controller (not depicted) that is operated by a user of the air conditioner  1 . 
     The control unit  3  operates and stops the air conditioner  1 , and controls operation of the various devices constituting the air conditioner  1 , in accordance with measurement signals from the various sensors, a command received from the remote controller (not depicted), and the like. 
     (2) Configuration of Outdoor Heat Exchanger 
     The outdoor heat exchanger  11  will be described in terms of its configuration with reference to the drawings. 
       FIG. 2  is a schematic perspective view of the outdoor heat exchanger  11 .  FIG. 3  is a partial enlarged view of a heat exchange unit  27  to be described later, in the outdoor heat exchanger  11 .  FIG. 4  is a schematic view depicting attachment states of fins  29  to be described later, to flat tubes  28  in the heat exchange unit  27 .  FIG. 5  is a schematic configuration diagram of the outdoor heat exchanger  11 .  FIG. 5  includes arrows in the heat exchange unit  27 , indicating refrigerant flows during heating operation (when the outdoor heat exchanger  11  functions as an evaporator). 
     The following description may include expressions such as “up”, “down”, “left”, “right”, “front (before)”, and “rear (behind)”, for indication of directions and positions. These expressions follow directions of arrows included in  FIG. 2 , unless otherwise specified. These expressions describing the directions and the positions are adopted for convenience of description. Unless otherwise specified, such expressions will not limit directions and positions of the entire outdoor heat exchanger  11  and various constituents of the outdoor heat exchanger  11  to the directions and the positions being described. 
     The outdoor heat exchanger  11  is configured to cause heat exchange between a refrigerant flowing inside and air. 
     The outdoor heat exchanger  11  principally includes a flow divider  22 , a flat tube group  28 G including a plurality of flat tubes  28 , a plurality of fins  29 , and a liquid header  40  and a gas header  70  (exemplifying headers) (see  FIG. 4  and  FIG. 5 ). Each one of the flow divider  22 , the flat tubes  28 , the fins  29 , the liquid header  40 , and the gas header  70  is made of aluminum or an aluminum alloy. 
     As to be described later, the flat tubes  28  and the fins  29  fixing the flat tubes  28  constitute the heat exchange unit  27  (see  FIG. 2  and  FIG. 3 ). The outdoor heat exchanger  11  includes rather the heat exchange unit  27  in a single row than the plurality of flat tubes  28  aligned in an air flow direction. When air flows in air ducts constituted by the flat tubes  28  and the fins  29  of the heat exchange unit  27 , the outdoor heat exchanger  11  causes heat exchange between a refrigerant flowing in the flat tubes  28  and the air flowing in the air ducts. The heat exchange unit  27  is divided into a first heat exchange portion  27   a , a second heat exchange portion  27   b , a third heat exchange portion  27   c , a fourth heat exchange portion  27   d , and a fifth heat exchange portion  27   e , which are aligned vertically (see  FIG. 2 ). 
     (2-1) Flow Divider 
     The flow divider  22  is a mechanism configured to distribute a refrigerant. The flow divider  22  is also a mechanism configured to merge refrigerants. The flow divider  22  is connected with the liquid refrigerant pipe  20 . The flow divider  22  includes a plurality of branching pipes  22   a  to  22   e . The flow divider  22  has a function of distributing, into the plurality of branching pipes  22   a  to  22   e , a refrigerant flowing into the flow divider  22  from the liquid refrigerant pipe  20 , and guiding the refrigerant into a plurality of spaces provided in the liquid header  40 . The flow divider  22  further has a function of merging refrigerants flowing from the liquid header  40  through the branching pipes  22   a  to  22   e  and guiding the refrigerants to the liquid refrigerant pipe  20 . 
     (2-2) Flat Tube Group 
     The flat tube group  28 G exemplifies a heat transfer tube group. The flat tube group  28 G includes, as a plurality of heat transfer tubes, the plurality of flat tubes  28  (exemplifying heat transfer tubes). As depicted in  FIG. 3 , the flat tubes  28  are flat heat transfer tubes each having upper and lower flat surfaces  28   a  functioning as heat transfer surfaces. As in  FIG. 3 , each of the flat tubes  28  is provided with a plurality of refrigerant passages  28   b  allowing refrigerants to flow. Examples of the flat tubes  28  include a flat porous tube provided with a large number of refrigerant passages  28   b  each having a small sectional area of a passage allowing a refrigerant to flow. The plurality of refrigerant passages  28   b  according to one or more embodiments are aligned in the air flow direction. The flat tube  28  has a section vertical to the refrigerant passages  28   b  and having a maximum width that may be 70% or more, or 85% or more, of an outer diameter of a main gas refrigerant pipe connecting portion  19   a.    
     As depicted in  FIG. 5 , the outdoor heat exchanger  11  includes the flat tubes  28  that extend horizontally between the liquid header  40  and the gas header  70  and are aligned vertically to form a plurality of columns. In one or more embodiments, each of the flat tubes  28  extending between the liquid header  40  and the gas header  70  is bent at two portions, such that the heat exchange unit  27  constituted by the flat tubes  28  has a substantially U shape in a planar view (see  FIG. 2 ). The flat tubes  28  extend in an anteroposterior direction (exemplifying a first direction) at portions connected to the gas header  70 , and extend in the anteroposterior direction at portions connected to the liquid header  40 . The plurality of flat tubes  28  according to one or more embodiments is disposed to be constantly spaced apart in the vertical direction. 
     (2-3) Fin 
     The plurality of fins  29  are members provided for increasing a heat transfer area of the outdoor heat exchanger  11 . The fins  29  are plate-shaped member extending along the columns of the flat tubes  28 . The outdoor heat exchanger  11  is used in a state where the plurality of flat tubes  28  extending horizontally is aligned vertically. The fins  29  extend vertically in a state where the outdoor heat exchanger  11  is installed in the outdoor unit  2 . 
     The fins  29  are provided with a plurality of cut-away parts  29   a  extending in a direction of inserting the flat tubes  28  as depicted in  FIG. 4 , to receive the plurality of flat tubes  28 . The cut-away parts  29   a  extend in an extending direction of the fins  29 , and in a direction perpendicular to a thickness direction of the fins  29 . The cut-away parts  29   a  provided at the fins  29  extend horizontally in the state where the outdoor heat exchanger  11  is installed in the outdoor unit  2 . The cut-away parts  29   a  of the fins  29  substantially match an outline of the section of the flat tube  28 . The cut-away parts  29   a  are provided at the fins  29  so as to be spaced apart correspondingly to spaces of the aligned flat tubes  28 . In the outdoor heat exchanger  11 , the plurality of fins  29  is aligned in an extending direction of the flat tubes  28 . When the flat tubes  28  are inserted correspondingly to the plurality of  29   a  of the plurality of fins  29 , spaces between the flat tubes  28  adjacent to each other are divided into a plurality of air ducts allowing air to flow. 
     The fins  29  have connective portions  29   b  connected vertically and positioned upstream or downstream of the flat tubes  28  in the air flow direction. The connective portions  29   b  of the fins  29  are positioned upstream of the flat tubes  28  in one or more embodiments. 
     (2-4) Gas Header and Liquid Header 
     The liquid header  40  and the gas header  70  are hollow members. 
     As depicted in  FIG. 5 , the liquid header  40  is connected with first ends of the flat tubes  28 , and the gas header  70  is connected with second ends of the flat tubes  28 . The outdoor heat exchanger  11  is disposed in the casing (not depicted) of the outdoor unit  2  such that the liquid header  40  and the gas header  70  having substantially columnar shapes have axial directions substantially matching the vertical direction. The heat exchange unit  27  of the outdoor heat exchanger  11  according to one or more embodiments has the U shape in a planar view as depicted in  FIG. 2 . The liquid header  40  is disposed adjacent to a front left corner of the casing (not depicted) of the outdoor unit  2  (see  FIG. 2 ). The gas header  70  is disposed adjacent to a front right corner of the casing (not depicted) of the outdoor unit  2  (see  FIG. 2 ). 
     (2-4-1) Liquid Header 
     The liquid header  40  has a longitudinal direction matching the vertical direction. 
     The liquid header  40  has a liquid side internal space  23  divided into a plurality of sub spaces  23   a  to  23   e  by a plurality of partition plates  24  (see  FIG. 5 ). 
     The plurality of sub spaces  23   a  to  23   e  is aligned vertically. The sub spaces  23   a  to  23   e  are partitioned by the partition plates  24  so as not to be communicable with each other in the liquid side internal space  23  of the liquid header  40 . 
     The sub spaces  23   a  to  23   e  are connected, one by one, with the branching pipes  22   a  to  22   e  included in the flow divider  22 . During cooling operation, refrigerants reaching the sub spaces  23   a  to  23   e  flow in the branching pipes  22   a  to  22   e  to be merged at the flow divider  22 . During heating operation, refrigerants divided by the flow divider  22  are supplied to the sub spaces  23   a  to  23   e.    
     (2-4-2) Gas Header 
     The gas header  70  has a longitudinal direction matching the vertical direction (exemplifying a second direction). 
     The gas header  70  has a single internal space. The gas header  70  has a gas side internal space  25  provided with no partition plates partitioning vertically aligned spaces as in the liquid header  40 . 
     The gas header  70  is connected with the main gas refrigerant pipe connecting portion  19   a  and a branch gas refrigerant pipe connecting portion  19   b  constituting ends adjacent to the gas header  70 , of the first gas refrigerant pipe  19  (see  FIG. 5 ). Though not limited, the outer diameter of the main gas refrigerant pipe connecting portion  19   a  may be, for example, three times or more or five times or more, of an outer diameter of the branch gas refrigerant pipe connecting portion  19   b.    
     The main gas refrigerant pipe connecting portion  19   a  has a first end connected to the gas header  70  so as to communicate with the gas side internal space  25  at an intermediate position in a height direction of the gas header  70 . 
     The branch gas refrigerant pipe connecting portion  19   b  has a first end connected to the gas header  70  so as to communicate with the gas side internal space  25  at a position adjacent to a lower end in the height direction of the gas header  70 . The branch gas refrigerant pipe connecting portion  19   b  has a second end connected to the main gas refrigerant pipe connecting portion  19   a . The branch gas refrigerant pipe connecting portion  19   b  is smaller in inner diameter than the main gas refrigerant pipe connecting portion  19   a  and connected to the gas header  70  below the main gas refrigerant pipe connecting portion  19   a , to allow refrigerating machine oil reserved adjacent to the lower end of the gas header  70  to flow into the main gas refrigerant pipe connecting portion  19   a  and return to the compressor  8 . 
     (3) Refrigerant Flow in Outdoor Heat Exchanger 
     When the air conditioner  1  executes heating operation and the outdoor heat exchanger  11  functions as a refrigerant evaporator, a refrigerant in a gas-liquid two-phase state flowing from the liquid refrigerant pipe  20  and reaching the flow divider  22  flows through the branching pipes  22   a  to  22   e  and flows into the sub spaces  23   a  to  23   e  constituting the liquid side internal space  23  of the liquid header  40 . Specifically, the refrigerant flowing in the branching pipe  22   a  flows into the sub space  23   a , the refrigerant flowing in the branching pipe  22   b  flows into the sub space  23   b , the refrigerant flowing in the branching pipe  22   c  flows into the sub space  23   c , the refrigerant flowing in the branching pipe  22   d  flows into the sub space  23   d , and the refrigerant flowing in the branching pipe  22   e  flows into the sub space  23   e , respectively. The refrigerants flowing into the sub spaces  23   a  to  23   e  of the liquid side internal space  23  flow in the flat tubes  28  connected to the sub spaces  23   a  to  23   e . The refrigerants flowing in the flat tubes  28  exchange heat with air to be evaporated and become gas-phase refrigerants, and flow into the gas side internal space  25  of the gas header  70  to be merged. 
     When the air conditioner  1  executes cooling operation or frost operation, the refrigerant flows in the refrigerant circuit  6  oppositely to the case of heating operation. Specifically, a gas-phase refrigerant having high temperature flows into the gas side internal space  25  of the gas header  70  through the main gas refrigerant pipe connecting portion  19   a  and the branch gas refrigerant pipe connecting portion  19   b  of the first gas refrigerant pipe  19 . The refrigerant flowing into the gas side internal space  25  of the gas header  70  are distributed to flow into the flat tubes  28 . Refrigerants flowing into the flat tubes  28  passes through the flat tubes  28  and flows into the sub spaces  23   a  to  23   e  of the liquid side internal space  23  of the liquid header  40 . The refrigerants flowing into the sub spaces  23   a  to  23   e  of the liquid side internal space  23  are merged by the flow divider  22  to be flow out to the liquid refrigerant pipe  20 . 
     (4) Details of Gas Header 
       FIG. 6  is an outer appearance configuration diagram in a side view, depicting how the main gas refrigerant pipe connecting portion  19   a  is connected to the gas header  70 .  FIG. 7  is a planar sectional view of the gas header  70 .  FIG. 8  is a planar sectional view depicting how the main gas refrigerant pipe connecting portion  19   a  and the flat tube  28  are connected to the gas header  70 . 
       FIG. 9  is a schematic view from behind, of a first member  71 .  FIG. 10  is a schematic view from behind, of a third member  73 .  FIG. 11  is a schematic view from behind, of a second member  72 .  FIG. 13  is a schematic view from behind, of a fourth member  74 .  FIG. 14  is a projection view depicting positional relationship of openings in a case where the first member  71  is viewed from behind. 
       FIG. 15  is a planar sectional view of clad layers in the first member  71 , the third member  73 , and the fourth member  74  constituting the gas header  70 . 
     The gas header  70  includes the first member  71 , the second member  72 , the third member  73 , the fourth member  74 , as well as a top lid member and a bottom lid member (not depicted). The gas header  70  is constituted such that the first member  71 , the second member  72 , the third member  73 , the fourth member  74 , the top lid member, and the bottom lid member are joined by brazing. 
     The gas header  70  has an outline in a planar view, which has a substantially quadrilateral shape provided with one side connected with the flat tubes  28 . 
     (4-1) First Member 
     The first member  71  principally constitutes a periphery of the outline of the gas header  70 , along with the fourth member  74  to be described later. 
     The first member  71  has a clad layer C 1  containing a brazing filler material and provided on a surface (outer surface) constituting a circumference of the gas header  70 , of a core material made of aluminum or an aluminum alloy. The first member  71  has a clad layer C 2  (exemplifying a brazing layer between the first member and the second member, or exemplifying a brazing layer between the first member and the third member) containing a brazing filler material and provided on a surface (inner surface) opposite to the surface constituting the circumference of the gas header  70 , of the core material made of aluminum or an aluminum alloy. Though not limited, an exemplary member (the same applies hereinafter) provided with a clad layer may be manufactured while joining a plate-shaped clad layer to a core material by means of hot rolling. The first member  71  according to one or more embodiments can be formed through bending, at a pleat line in a longitudinal direction of the gas header  70 , a single sheet metal obtained by rolling or the like. In this case, the first member  71  has a first thickness that is uniform across portions. The first thickness is preferably less than the maximum thickness of the second member  72  or a thickness of the fourth member  74 , and may be equal in thickness to the third member  73 . The first thickness can be exemplarily set to 1.0 mm or more and 2.0 mm or less, and is preferably 1.5 mm. 
     The clad layer C 1  constitutes the outer surface of the gas header  70 , and thus contains the brazing filler material as well as a sacrificial anodic material having corrosion resistance. Examples of the sacrificial anodic material include zinc or an alloy containing zinc. The clad layer C 1  contains silicon having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. The clad layer C 1  contains an Al—Si alloy having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. Examples of the clad layer C 1  include an alloy having A4N43 as an alloy number prescribed by the Japanese Industrial Standards for aluminum. 
     The clad layer C 2  constitutes the inner surface of the gas header  70 , and thus needs no corrosion resistance. The clad layer C 2  contains silicon having a content that may be equal to or different from the content of the clad layer C 1 , and can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. The clad layer C 2  contains an Al—Si alloy having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. Examples of the clad layer C 2  include an alloy having A4343 as an alloy number prescribed by the Japanese Industrial Standards for aluminum. 
     The first member  71  includes a flat tube connection plate  71   a , a first outer wall  71   b , a second outer wall  71   c , a first claw  71   d , and a second claw  71   e.    
     The flat tube connection plate  71   a  (exemplifying a first portion) is a flat plate portion expanding vertically and transversely. The flat tube connection plate  71   a  is provided with a plurality of flat tube connection openings  71   x  (exemplifying openings) aligned vertically. The flat tube connection openings  71   x  penetrate the flat tube connection plate  71   a  in its thickness direction. In a state where the flat tubes  28  are inserted to the flat tube connection openings  71   x  such that first ends of the flat tubes  28  completely pass therethrough, the flat tubes  28  are joined by brazing. In such a state where the flat tubes  28  are joined by brazing, an entire inner circumferential surface of each of the flat tube connection openings  71   x  is in contact with an entire outer circumferential surface of a corresponding one of the flat tubes  28 . The first thickness of the first member  71  including the flat tube connection plate  71   a  is set relatively small such as about 1.0 mm or more and 2.0 mm or less, and the inner circumferential surfaces of the flat tube connection openings  71   x  can thus have small length in a thickness direction. When the flat tubes  28  are inserted to the flat tube connection openings  71   x  prior to joining by brazing, the inner circumferential surface of each of the flat tube connection openings  71   x  and the outer circumferential surface of the corresponding one of the flat tubes  28  generate less friction for facilitated insertion. 
     The first outer wall  71   b  is a planar portion extending forward from a front surface of a left (inside the outdoor unit  2  and the liquid header  40  side) end of the flat tube connection plate  71   a  along a first inner wall  72   b  to be described later. 
     The second outer wall  71   c  is a planar portion extending forward from a front surface of a right (outside the outdoor unit  2  and far from the liquid header  40 ) end of the flat tube connection plate  71   a  along a second inner wall  72   c  to be described later. 
     The first claw  71   d  extends rightward from a front end of the first outer wall  71   b . The second claw  71   e  extends leftward from a front end of the second outer wall  71   c.    
     The first claw  71   d  and the second claw  71   e  extend along and beyond the first outer wall  71   b  and the second outer wall  71   c , respectively, before the second member  72 , the third member  73 , and the fourth member  74  are disposed inside the first member  71  in a planar view. In a state where the second member  72 , the third member  73 , and the fourth member  74  are disposed inside the first member  71  in a planar view, the first claw  71   d  and the second claw  71   e  are bent to be closer to each other such that the first member  71  caulks the second member  72 , the third member  73 , and the fourth member  74  so as to be fixed to each other. Brazing is executed in a furnace or the like in this state to join the members by brazing for complete fixation. 
     (4-2) Third Member 
     The third member  73  is a flat plate portion laminated to be in contact with a surface connected with the first gas refrigerant pipe  19 , of the flat tube connection plate  71   a  of the first member  71  and expanding vertically and transversely. The third member  73  is similar in transverse length to a portion excluding the both ends of the flat tube connection plate  71   a  of the first member  71 . 
     The third member  73  does not include any portion constituting the circumference of the gas header  70 , but constitutes an internal portion of the gas header  70  and is positioned inside the first member  71 . 
     The third member  73  has a clad layer C 3  (exemplifying a brazing layer between the second member and the third member) containing a brazing filler material and provided on a surface (the second member  72  side surface) opposite to a surface facing the flat tube connection plate  71   a  of the first member  71 , of a core material made of aluminum or an aluminum alloy. 
     The third member  73  has uniform third thickness. The third thickness is preferably less than the maximum thickness of the second member  72  or the thickness of the fourth member  74 , and may be equal in thickness to the first member  71 . The third thickness can be exemplarily se to 1.0 mm or more and 2.0 mm or less, and is preferably 1.5 mm. 
     The clad layer C 3  contains silicon having a content that can be exemplarily set to 9.0 percent by weight or more and 11.0 percent by weight or less. The clad layer C 3  contains an Al—Si alloy having a content that can be exemplarily set to 9.0 percent by weight or more and 11.0 percent by weight or less. Examples of the clad layer C 3  include an alloy having A4045 as an alloy number prescribed by the Japanese Industrial Standards for aluminum. 
     Though not limited, the third member  73  may not be provided with any clad layer on the surface opposite to the surface provided with the clad layer C 3 , and may be preferably provided with a flux layer for removal of a surface oxide film. 
     The third member  73  includes an inner plate  73   a  and a plurality of internal openings  73   x.    
     The inner plate  73   a  has a flat plate shape expanding vertically and transversely. 
     The plurality of internal openings  73   x  (exemplifying second openings) is aligned vertically and penetrates the inner plate  73   a  in its thickness direction. 
     The internal openings  73   x  of the third member  73  are larger than the flat tube connection openings  71   x  provided in the flat tube connection plate  71   a  of the first member  71 . In the state where the third member  73  is laminated on the flat tube connection plate  71   a  of the first member  71 , the internal openings  73   x  in the third member  73  have outer edges positioned outside outer edges of the flat tube connection openings  71   x  provided in the flat tube connection plate  71   a  of the first member  71  in a lamination direction of members, more specifically, in the anteroposterior direction. This configuration inhibits the brazing filler material from shifting due to a capillary phenomenon during joining by brazing and blocking the refrigerant passages  28   b  of each of the flat tubes  28 . In view of this, the outer edges of the internal openings  73   x  of the third member  73  have upper and lower portions that may be distant by 2 mm or more from upper and lower portions of the outer edges of the flat tube connection openings  71   x  of the flat tube connection plate  71   a , and are preferably distant by 3 mm or more. 
     The clad layer C 3  of the third member  73  is positioned inside the clad layer C 2  of the first member  71  in the gas header  70 . 
     (4-3) Second Member 
     The second member  72  is disposed between the flat tube connection plate  71   a  of the first member  71  and the main gas refrigerant pipe connecting portion  19   a  in the anteroposterior direction. The second member  72  has a substantially U shape in a planar view. 
     Inside the second member  72 , more specifically, in a space surrounded with the second member  72 , the third member  73 , and the ends of the flat tubes  28 , the gas side internal space  25  is provided. 
     The maximum thickness of the second member  72  is preferably more than the thickness of the first member  71 . The maximum thickness of the second member  72  may be preferably 4.0 mm or less and may be more preferably 3.0 mm in view of facilitated pressing and punching. 
     Though not limited, the second member  72  is preferably obtained through extrusion molding in an extrusion direction matching the longitudinal direction of the gas header  70 . Extrusion molding facilitates provision of portions varied in thickness. A thick sheet metal is relatively expensive. Provision of the thick second member  72  through extrusion direction leads to cost reduction. The second member  72  according to one or more embodiments, which is obtained through extrusion direction, is not provided with any clad layer containing a brazing filler material. 
     The second member  72  includes the first inner wall  72   b , the second inner wall  72   c , a coupling portion  72   a , a first projection  72   d , a second projection  72   e , a first edge  72   f , and a second edge  72   g.    
     The coupling portion  72   a  is a plate-shaped portion facing a main gas refrigerant pipe connecting portion  19   a  side surface, of the third member  73 , and expanding vertically and transversely. The coupling portion  72   a  is positioned in the main gas refrigerant pipe connecting portion  19   a  side of the gas header  70 . The coupling portion  72   a  is provided with an internal gas pipe connection opening  72   x  connected with an end of the main gas refrigerant pipe connecting portion  19   a  and penetrating the coupling portion  72   a  in its thickness direction. The coupling portion  72   a  is further provided with an opening (not depicted) connected with an end of the branch gas refrigerant pipe connecting portion  19   b  and penetrating the coupling portion  72   a  in the thickness direction. 
     The first inner wall  72   b  is a planar portion extending backward toward the extending flat tubes  28 , from a left (inside the outdoor unit  2  and the liquid header  40  side) end of the coupling portion  72   a . The first inner wall  72   b  has a left surface in surface contact with a right surface of the first outer wall  71   b  of the first member  71 . 
     The second inner wall  72   c  is a planar portion extending backward toward the extending flat tubes  28 , from a right (outside the outdoor unit  2  and far from the liquid header  40 ) end of the coupling portion  72   a . The second inner wall  72   c  has a right surface in surface contact with a left surface of the second outer wall  71   c  of the first member  71 . 
     The first inner wall  72   b  and the second inner wall  72   c  face each other. Specifically, a front end of the first inner wall  72   b  and a front end of the second inner wall  72   c  also face each other. 
     The coupling portion  72   a , the first inner wall  72   b , and the second inner wall  72   c  are thicker than the first member  71 , and may be thicker by 1.5 times or more and are preferably thicker by 2 times or more. 
     Though not limited, the first inner wall  72   b  and the second inner wall  72   c  have length in an extending direction (anteroposterior direction) of the flat tubes  28 , which may be larger by three times or more and is preferably larger by five times or more than length of the coupling portion  72   a  in the extending direction (anteroposterior direction) of the flat tubes  28 . 
     The coupling portion  72   a  couples the first inner wall  72   b  and the second inner wall  72   c . Specifically, the coupling portion  72   a  couples the front end (the main gas refrigerant pipe connecting portion  19   a  side end) of the first inner wall  72   b  and the front end (the main gas refrigerant pipe connecting portion  19   a  side end) of the second inner wall  72   c . The coupling portion  72   a  extends transversely (exemplifying a third direction that is preferably perpendicular to both the first direction and the second direction, and the first direction, the second direction, and the third direction are more preferably perpendicular to one another) in a planar view of the gas header  70 . 
     The second member  72  can increase the gas side internal space  25  by simply extending the first inner wall  72   b  and the second inner wall  72   c  without adding any other member. This configuration allows a gas refrigerant to be unlikely to have pressure loss while passing through the gas side internal space  25 . Although the first inner wall  72   b  and the second inner wall  72   c  extend in the extending direction of the flat tubes  28  for increasing the gas side internal space  25 , the first inner wall  72   b  and the second inner wall  72   c  are coupled via the coupling portion  72   a  to integrate the coupling portion  72   a , the first inner wall  72   b , and the second inner wall  72   c . This configuration can improve strength of the second member  72  and improve compressive strength of the gas header  70 . 
     The first edge  72   f  is provided behind (the flat tubes  28  side) the first inner wall  72   b . The first edge  72   f  has a left surface provided flush with the left surface of the first inner wall  72   b , and is in surface contact with the right surface of the first outer wall  71   b  of the first member  71 . The first edge  72   f  has a rear end in contact with a front surface of the third member  73 . The first edge  72   f  has a thickness (transverse width) less than thickness (transverse width) of the first inner wall  72   b . The first edge  72   f  and the front surface of the third member  73  are in contact with each other at a position displaced leftward from the flat tubes  28  and displaced leftward from left ends of the internal openings  73   x  of the third member  73 . 
     The second edge  72   g  is provided behind (the flat tubes  28  side) the second inner wall  72   c . The second edge  72   g  has a right surface provided flush with the right surface of the second inner wall  72   c , and is in surface contact with the left surface of the second outer wall  71   c  of the first member  71 . The second edge  72   g  has a rear end in contact with the front surface of the third member  73 . The second edge  72   g  has a thickness (transverse width) less than a thickness (transverse width) of the second inner wall  72   c . The second edge  72   g  and the front surface of the third member  73  are in contact with each other at a position displaced rightward from the flat tubes  28  and displaced rightward from right ends of the internal openings  73   x  of the third member  73 . 
     In a planar view, the first edge  72   f  and the second edge  72   g  are distant from each other by length that is larger than width of the flat tubes  28 , is larger than width of the flat tube connection openings  71   x  of the first member  71 , and is larger than width of the internal openings  73   x  of the third member  73 . Each of the first edge  72   f  and the second edge  72   g  extends from an upper end to a lower end of the gas header  70 . 
     The first projection  72   d  extends rightward (toward the second inner wall  72   c ) from a portion in front of the first edge  72   f  at a rear end of the first inner wall  72   b . The first projection  72   d  extends from the upper end to the lower end of the gas header  70 . The first projection  72   d  has a right end displaced rightward from the left ends of the internal openings  73   x  of the third member  73  and displaced rightward from left ends of the flat tubes  28 . The first projection  72   d  is positioned closer to the flat tubes  28  than an anteroposterior center of the second member  72 . 
     The second projection  72   e  extends leftward (toward the first inner wall  72   b ) from a portion in front of the second edge  72   g  at a rear end of the second inner wall  72   c . The second projection  72   e  extends from the upper end to the lower end of the gas header  70 . The second projection  72   e  has a left end displaced leftward from the right ends of the internal openings  73   x  of the third member  73  and displaced leftward from right ends of the flat tubes  28 . The second projection  72   e  is positioned closer to the flat tubes  28  than the anteroposterior center of the second member  72 . 
     The first projection  72   d  and the second projection  72   e  have a minimum distance (transverse distance) smaller than the maximum width on the section vertical to the refrigerant passages  28   b  of each of the flat tubes  28 . When the flat tubes  28  are inserted to the gas header  70 , the first projection  72   d  and the second projection  72   e  can thus set how deep the flat tubes  28  are inserted. This configuration inhibits reduction of the gas side internal space  25  due to excessive insertion of the flat tubes  28 . Furthermore, the first projection  72   d  and the second projection  72   e  can align the ends of the plurality of flat tubes  28  in the gas header  70 . 
     (4-4) Fourth Member 
     The fourth member  74  is a flat plate portion laminated to be in contact with a front surface of the coupling portion  72   a  of the second member  72  and expanding vertically and transversely. The fourth member  74  is similar in transverse length to the third member  73 , and is similar in transverse length to the portion excluding the both ends of the flat tube connection plate  71   a  of the first member  71 . 
     The fourth member  74  is provided with a clad layer C 4  having a surface (outer surface) constituting the circumference of the gas header  70  and containing a brazing filler material. The fourth member  74  has a clad layer C 5  containing a brazing filler material and provided on a surface (inner surface) opposite to a surface constituting the circumference of the gas header  70 , of a core material made of aluminum or an aluminum alloy. 
     The fourth member  74  has a uniform fourth thickness. The fourth thickness is preferably more than the first thickness and the third thickness, and may be equal in thickness to the first member  71 . The fourth thickness is preferably 4.0 mm or less in view of facilitated pressing and punching, is preferably 2.0 mm or more in view of improvement in compressive strength, and may be more preferably 3.0 mm. 
     The clad layer C 4  constitutes the outer surface of the gas header  70 , and thus contains the brazing filler material as well as a sacrificial anodic material having corrosion resistance. Examples of the sacrificial anodic material include zinc or an alloy containing zinc. The clad layer C 4  contains silicon having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. The clad layer C 4  contains an Al—Si alloy having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. Examples of the clad layer C 4  include an alloy having A4N43 as an alloy number prescribed by the Japanese Industrial Standards for aluminum. 
     The clad layer C 5  constitutes the inner surface of the gas header  70 , and thus needs no corrosion resistance. The clad layer C 5  contains silicon having a content that may be equal to or different from the content of the clad layer C 4 , and can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. The clad layer C 5  contains an Al—Si alloy having a content that can be exemplarily set to 6.8 percent by weight or more and 8.2 percent by weight or less. Examples of the clad layer C 5  include an alloy having A4343 as an alloy number prescribed by the Japanese Industrial Standards for aluminum. 
     The fourth member  74  is a plate-shaped member and can thus be easily provided on the surface with a clad layer containing a brazing filler material. Even in a case where the second member  72  is not provided with any clad layer containing a brazing filler material as in an exemplary case where the second member  72  is obtained through extrusion, the second member  72  can be joined by brazing to any other member with use of the brazing filler material provided on the fourth member  74 . 
     The fourth member  74  includes an outer plate  74   a  and an external gas pipe connection opening  74   x.    
     The outer plate  74   a  has a flat plate shape expanding vertically and transversely. 
     The external gas pipe connection opening  74   x  is connected with the end of the main gas refrigerant pipe connecting portion  19   a  and penetrates the outer plate  74   a  in its thickness direction. 
     The outer plate  74   a  is further provided, in a lower portion, with an opening (not depicted) connected with the end of the branch gas refrigerant pipe connecting portion  19   b  and penetrating the outer plate  74   a  in the thickness direction. 
     The main gas refrigerant pipe connecting portion  19   a  and the branch gas refrigerant pipe connecting portion  19   b  thus communicate with an inner surface of the flat tube connection plate  71   a  of the first member  71  via the external gas pipe connection opening  74   x , the internal gas pipe connection opening  72   x , and the gas side internal space  25  interposed between the first inner wall  72   b  and the second inner wall  72   c.    
     The fourth member  74  has a front surface caulked while being in contact with the first claw  71   d  and the second claw  71   e  of the first member  71 . 
     (4-5) Brazing 
     The outdoor heat exchanger  11  is heated in a furnace to be brazed in a state where the plurality of flat tubes  28 , the flow divider  22 , the first gas refrigerant pipe  19 , and the like are temporarily assembled to the liquid header  40  and the gas header  70 . 
     When the gas header  70  is temporarily assembled, a portion of the clad layer C 2  provided on the flat tube connection plate  71   a  of the first member  71  is made in contact with a portion of the third member  73  where the clad layer C 3  is not provided, and portions of the clad layer C 2  provided inside the first outer wall  71   b  and the second outer wall  71   c  of the first member  71  are made in contact with the first inner wall  72   b  and the second inner wall  72   c  of the second member  72 . The clad layer C 3  of the third member  73  is made in contact with rear surfaces of the first edge  72   f  and the second edge  72   g  of the second member  72 . The fourth member  74  has a portion provided with the clad layer C 5 , the portion being made in contact with the front surface of the coupling portion  72   a  of the second member  72 , and has both left and right ends of a portion provided with the clad layer C 4 , the ends being caulked by the first claw  71   d  and the second claw  71   e  to be made in contact with rear surfaces of the first claw  71   d  and the second claw  71   e.    
     The outdoor heat exchanger  11  thus temporarily assembled is heated in a furnace to melt the clad layers C 1  to C 5  to braze the first member  71 , the second member  72 , the third member  73 , and the fourth member  74  each other. The outdoor heat exchanger  11  placed in a furnace has ambient temperature being exemplarily 1000° C. or more and 1300° C. or less. 
     (5) Characteristics of One or More Embodiments 
     (5-1) 
     In the gas header  70  of the outdoor heat exchanger  11  according to one or more embodiments, the clad layer C 3  on the third member  73  positioned inside the first member  71  is larger in silicon content than the clad layer C 1  and the clad layer C 2  on the first member  71  positioned at the circumference. 
     When the members constituting the gas header  70  are brazed in a furnace or the like, even if the third member  73  at an inner position is not higher in temperature than the first member  71  at an outer position, the brazing filler material contained in the clad layer C 3  on the third member  73  can generate more melt in comparison to a case where the clad layer C 3  on the third member  73  is equal in silicon content to the clad layer C 1  and the clad layer C 2  on the first member  71 . 
     This configuration achieves excellent joining by brazing of a member positioned inside the gas header  70 . This configuration also achieves an excellent joining state of brazing with use of a clad layer positioned inside the gas header  70 . 
     Specifically, when the gas side internal space  25  of the gas header  70  is increased to have a larger capacity, an inner member and an inner clad layer may have more difficulty in receiving heat during heating for brazing becomes evident. Even in such a case, joining by brazing can be excellently achieved with an increase in a melt rate by increasing silicon content of the member and the inner clad layer that have more difficulty in receiving heat. 
     (5-2) 
     When the flat tubes which are flat heat transfer tubes are inserted to a conventional gas header having a cylindrical shape, the flat tubes need to be inserted deeply to the gas header such that the entire ends of the flat tubes are positioned inside the gas header having the cylindrical shape. In the gas header having the cylindrical shape, the ends of the flat tubes are accordingly provided thereabove and therebelow with useless spaces allowing a refrigerant to be reserved. Such a tendency is more significant as the flat tubes have larger width. 
     In contrast, in the gas header  70  of the outdoor heat exchanger  11  according to one or more embodiments, the flat tube connection plate  71   a  of the first member  71  and the third member  73  have the plate shapes. Furthermore, the flat tubes  28  are inserted vertically to the flat tube connection plate  71   a  of the first member  71  and the third member  73 . The first outer wall  71   b  and the second outer wall  71   c  extend vertically from both the left and right ends of the flat tube connection plate  71   a  of the first member  71 , and the first inner wall  72   b  and the second inner wall  72   c  of the second member  72  are joined vertically to both the left and right ends of the third member  73 . 
     The gas header  70  of the outdoor heat exchanger  11  according to one or more embodiments can thus decrease the useless spaces allowing a refrigerant to be reserved, around the ends of the flat tubes  28 . This achieves reduction in pressure loss of a gas refrigerant flowing in the gas header  70 . 
     (5-3) 
     In the gas header  70  of the outdoor heat exchanger  11  according to one or more embodiments, the first member  71  including the flat tube connection plate  71   a  is relatively thinned. When the flat tubes  28  are inserted to the flat tube connection openings  71   x  prior to joining by brazing, the inner circumferential surface of each of the flat tube connection openings  71   x  and the outer circumferential surface of the corresponding one of the flat tubes  28  generate less friction for facilitated insertion. 
     Even when the first member  71  including the flat tube connection plate  71   a  is relatively thinned, the flat tube connection plate  71   a  further has the third member  73  laminated in the thickness direction. This configuration can thus improve compressive strength of the gas header  70  at the portion connected with the flat tubes  28 . 
     Furthermore, the outer edges of the internal openings  73   x  of the third member  73  are positioned outside the outer edges of the flat tube connection openings  71   x  provided in the flat tube connection plate  71   a  of the first member  71 . Even when the brazing filler material interposed between the flat tube connection openings  71   x  of the flat tube connection plate  71   a  and the flat tubes  28  leaks toward the ends of the flat tubes  28  during brazing, the brazing filler material having leaked is sent outside the flat tubes  28 , into spaces in the internal openings  73   x  of the third member  73 . This inhibits the refrigerant passages  28   b  of each of the flat tubes  28  from being filled with the brazing filler material. 
     (5-4) 
     In the gas header  70  of the outdoor heat exchanger  11  according to one or more embodiments, the first projection  72   d  and the second projection  72   e  of the second member  72  have the minimum distance (transverse distance) smaller than the maximum width on the section vertical to the refrigerant passages  28   b  of each of the flat tubes  28 . This configuration can thus set how deep the flat tubes  28  are inserted to the gas header  70 . 
     The first projection  72   d  and the second projection  72   e  that define how deep the flat tubes  28  are inserted are both positioned closer to the flat tubes  28  than the anteroposterior center of the second member  72 . This makes it possible to sufficiently increase the gas side internal space  25 . 
     (6) MODIFICATION EXAMPLES 
     (6-1) Modification Example A 
     The embodiments described above exemplify the case where the coupling portion  72   a  couples the end of the first inner wall  72   b  and the end of the second inner wall  72   c  in the second member  72  included in the gas header  70  of the outdoor heat exchanger  11 . 
     The second member included in the gas header  70  of the outdoor heat exchanger  11  may alternatively be replaced with a second member  172  depicted in  FIG. 16  and  FIG. 17 .  FIG. 16  is a planar sectional view depicting how the main gas refrigerant pipe connecting portion  19   a  and the flat tube  28  are connected to the gas header  70 .  FIG. 17  is a projection view depicting positional relationship of openings in a case where the second member  172  is viewed from behind. 
     The second member  172  includes a coupling portion  172   a  in place of the coupling portion  72   a  of the second member  72  according to the above-described embodiments. The coupling portion  172   a  couples a portion between the both ends in the anteroposterior direction (the extending direction of the flat tubes  28 ) of the first inner wall  72   b  and a portion between the both ends in the anteroposterior direction (the extending direction of the flat tubes  28 ) of the second inner wall  72   c . The coupling portion  172   a  couples the portions other than the ends, of the first inner wall  72   b  and the second inner wall  72   c  to achieve improvement in structural strength of the second member  172 . 
     The coupling portion  172   a  is a plate-shaped portion expanding vertically and transversely. The coupling portion  172   a  has a plurality of internal gas pipe connection openings  172   x  aligned vertically. The internal gas pipe connection openings  172   x  are provided correspondingly to the flat tubes  28 . The internal gas pipe connection openings  172   x  are larger in vertical size than the flat tubes  28  and the flat tube connection openings  71   x  of the first member  71 , but are smaller in size in a width direction (transverse direction) than the flat tubes  28  and the flat tube connection openings  71   x  of the first member  71 . This configuration can thus set how deep the flat tubes  28  are inserted. The internal gas pipe connection openings  172   x  have edges that can set how deep the flat tubes  28  are inserted, and there is thus no need to provide the first projection  72   d  or the second projection  72   e  of the second member  72  according to the above-described embodiments. 
     (6-2) Modification Example B 
     The above-described embodiments exemplify the case where the gas header  70  includes the third member  73  and the fourth member  74 . 
     As exemplarily depicted in  FIG. 18 , the gas header  70  may alternatively exclude at least one of the third member  73  and the fourth member  74  according to the above-described embodiments. 
     In this case, the flat tube connection plate  71   a  of the first member  71  is made thicker to secure compressive strength. 
     (6-3) Modification Example C 
     The above-described embodiments exemplify the case where the clad layer C 3  on the third member  73  positioned inside the gas header  70  is larger in silicon content than the clad layer C 1  and the clad layer C 2  on the first member  71  positioned outside the gas header  70 . 
     Alternatively, at least one of the gas header and the liquid header in the heat exchanger may be replaced with, for example, a header  270  obtained through joining by brazing members as depicted in  FIG. 19 . 
     The header  270  includes a first outer member  271 , a first inner member  272 , a second inner member  273 , a third inner member  274 , and a second outer member  275 . 
     All of the first outer member  271 , the first inner member  272 , the second inner member  273 , the third inner member  274 , and the second outer member  275  are plate-shaped members. The first outer member  271 , the first inner member  272 , the second inner member  273 , the third inner member  274 , and the second outer member  275  are aligned in the mentioned order and are joined to each other by brazing. 
     The first outer member  271  (exemplifying a first member or exemplifying a fifth member) has a plurality of heat transfer tube connection openings  271   x  connected with a plurality of heat transfer tubes such as the flat tubes  28  described in the above-described embodiments. The heat transfer tube connection openings  271   x  penetrate in the thickness direction. The plurality of heat transfer tube connection openings  271   x  is aligned in a longitudinal direction of the first outer member  271 . 
     The first inner member  272  (exemplifying a third member or exemplifying a seventh member) is joined by brazing to the first outer member  271 . The first inner member  272  has a first internal opening  272   x  to be communicable with the plurality of heat transfer tube connection openings  271   x.    
     The second inner member  273  (exemplifying a second member or exemplifying a sixth member) has a first surface joined by brazing to the first inner member  272  and a second surface joined by brazing to the third inner member  274 . The second inner member  273  has a second internal opening  273   x  similar in size to the first internal opening  272   x  of the first inner member  272 . 
     The third inner member  274  (exemplifying the third member or exemplifying the seventh member) is joined by brazing to the second outer member  275 . The third inner member  274  has a third internal opening  274   x  similar in size to the second internal opening  273   x  of the second inner member  273 . 
     The second outer member  275  (exemplifying the first member or exemplifying the fifth member) has an external refrigerant pipe connection opening  275   x  connected with the main gas refrigerant pipe connecting portion  19   a  or the like described in the above-described embodiments or a refrigerant pipe as a liquid refrigerant pipe. The external refrigerant pipe connection opening  275   x  penetrates in the thickness direction. The external refrigerant pipe connection opening  275   x  communicates with the third internal opening  274   x  of the third inner member  274 . 
     In the configuration described above, a clad layer is provided on each surface of at least both surfaces of the first inner member  272  and both surfaces of the third inner member  274 . Specifically, a clad layer C 6  (exemplifying a brazing layer between the first member and the second member, exemplifying a brazing layer between the first member and the third member, or exemplifying a first clad layer) is provided on the first outer member  271  side surface of the first inner member  272 . A clad layer C 7  (exemplifying a brazing layer between the second member and the third member, or exemplifying a second clad layer) is provided on the second inner member  273  side surface of the first inner member  272 . A clad layer C 8  (exemplifying the brazing layer between the first member and the second member, exemplifying the brazing layer between the first member and the third member, or exemplifying the first clad layer) is provided on the second outer member  275  side surface of the third inner member  274 . A clad layer C 9  (exemplifying the brazing layer between the second member and the third member, or exemplifying the second clad layer) is provided on the second inner member  273  side surface of the third inner member  274 . 
     Each of the clad layers C 6  to C 9  contains silicon, and contains an Al—Si alloy or the like. The clad layer C 7  is larger in silicon content than the clad layer C 6 . The clad layer C 9  is larger in silicon content than the clad layer C 8 . 
     In the configuration described above, it is difficult for the second inner member  273  to receive heat in a case of joining by brazing while the first outer member  271 , the first inner member  272 , the second inner member  273 , the third inner member  274 , and the second outer member  275  are laminated and a heat source is disposed at least one of the first outer member  271  side and the second outer member  275  side. However, the clad layer C 7  is larger in silicon content than the clad layer C 6  and the clad layer C 9  is larger in silicon content than the clad layer C 8 . Thus, the clad layer C 7  and the clad layer C 9  far from the heat source can also achieve an increase in a melt rate for excellent joining by brazing. 
     (6-4) Modification Example D 
     The above-described embodiments and the modification examples exemplify the case where, in two clad layers joining members, the clad layer far from the heat source is larger in silicon content than the clad layer close to the heat source to achieve an increase in a melt rate for excellent joining by brazing. 
     Alternatively, there may be provided three or more clad layers joining members varied in distance from the heat source and the clad layers are aligned such that a clad layer further from the heat source has a larger silicon content, to achieve an increase in the melt rate for excellent joining by brazing. 
     Although the present disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure should be limited only by the attached claims. 
     REFERENCE SIGNS LIST 
       1 : air conditioner (heat pump device) 
       11 : outdoor heat exchanger (heat exchanger) 
       28 : flat tube (heat transfer tube) 
       70 : gas header (header) 
       71 : first member 
       71   a : flat tube connection plate (first portion) 
       71   x : flat tube connection opening (opening) 
       72 : second member 
       73 : third member 
       73   x : internal opening (second opening) 
     C 1 : clad layer 
     C 2 : clad layer (brazing layer between first member and second member, brazing layer between first member and third member, or clad layer of first member) 
     C 3 : clad layer (brazing layer between second member and third member, or clad layer of third member) 
     C 6 : clad layer (brazing layer between first member and second member, brazing layer between first member and third member, or first clad layer) 
     C 7 : clad layer (brazing layer between second member and third member, or second clad layer) 
     C 8 : clad layer (brazing layer between first member and second member, brazing layer between first member and third member, or first clad layer) 
     C 9 : clad layer (brazing layer between second member and third member, or second clad layer) 
       270 : header 
       271 : first outer member (first member or fifth member) 
       272 : first inner member (third member or seventh member) 
       273 : second inner member (second member or sixth member) 
       274 : third inner member (third member or seventh member) 
       275 : second outer member (first member or fifth member) 
       271   x : heat transfer tube connection opening (opening)