Patent Publication Number: US-10760824-B2

Title: Heat exchanger and refrigeration cycle apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application No. PCT/JP2015/085362, filed on Dec. 17, 2015, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a heat exchanger and a refrigeration cycle apparatus. 
     BACKGROUND 
     Conventionally, there has been known a heat exchanger including a pair of upper and lower headers horizontally facing each other, a plurality of flat heat transfer tubes communicatively connected to these headers such that the plurality of flat heat transfer tubes are in parallel with each other at a regular interval, and a corrugated fin interposed into a gap between the flat heat transfer tubes in close contact therewith. In the heat exchanger, refrigerant serving as a heat exchange medium flows in the plurality of flat heat transfer tubes simultaneously in parallel. 
     When heating operation is performed in a cold climate using such a heat exchanger as a heat pump-type outdoor unit for air conditioning for both cooling and heating, frost forms on surfaces of the fin and the heat transfer tubes, and heat exchange efficiency is decreased. 
     As a measure against such frost formation, Japanese Patent Laying-Open No. 9-280754 (PTD 1) discloses a heat exchanger including a corrugated fin disposed to protrude on windward side from flat heat transfer tubes, and louvers formed only in a leeward portion. 
     PATENT LITERATURE 
     PTD 1: Japanese Patent Laying-Open No. 9-280754 However, in the heat exchanger described in PTD 1, since the fin protrudes on the windward side relative to refrigerant flow paths (flat tubes), frost formation on the fin located on the windward side can be suppressed, but efficiency of defrosting frost on the fin is poor. 
     SUMMARY 
     The present invention has been made to solve the aforementioned problem. A main object of the present invention is to provide a heat exchanger which can suppress frost formation on a fin and has a high defrosting efficiency. 
     A heat exchanger in accordance with the present invention includes: a plurality of first heat transfer tubes disposed at intervals in a first direction and having respective first ends and respective second ends; a plurality of second heat transfer tubes disposed at a distance from the plurality of first heat transfer tubes to face the plurality of first heat transfer tubes in a second direction crossing the first direction, located on leeward side relative to the plurality of first heat transfer tubes, and having respective third ends and respective fourth ends; a plurality of fins connecting the first heat transfer tubes adjacent to each other and connecting the second heat transfer tubes adjacent to each other; a first distribution unit connecting the first ends of the plurality of first heat transfer tubes and the third ends of the plurality of second heat transfer tubes; and a second distribution unit connecting the second ends of the plurality of first heat transfer tubes and the fourth ends of the plurality of second heat transfer tubes. The first distribution unit includes a flow rate control unit configured to be capable of switching between a first state and a second state. In the first state, refrigerant flows in the plurality of first heat transfer tubes and the plurality of second heat transfer tubes. In the second state, in only the plurality of first heat transfer tubes, a flow rate of the refrigerant is smaller than a flow rate of the refrigerant in the first state. 
     According to the present invention, a heat exchanger which can suppress frost formation on a fin and has a high defrosting efficiency can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a heat exchanger and a refrigeration cycle apparatus in accordance with a first embodiment. 
         FIG. 2  is a schematic view showing the heat exchanger in accordance with the first embodiment. 
         FIG. 3  is a partially enlarged view of the heat exchanger shown in  FIG. 2 . 
         FIG. 4  is a cross sectional view for illustrating a fin of the heat exchanger shown in  FIG. 3 . 
         FIG. 5( a )  is a plan view showing one fin and two first and second heat transfer tubes respectively adjacent to each other with the fin being sandwiched therebetween, in the heat exchanger shown in  FIG. 3 .  FIG. 5( b )  is a graph showing distribution of temperature of a surface of the fin shown in  FIG. 5( a )  and distribution of temperature of air passing over the surface at the time of heating operation.  FIG. 5( c )  is a graph showing distribution of the amount of heat exchange between the fin and the air on the fin shown in  FIG. 5( a )  at the time of heating operation. 
         FIG. 6  is a plan view showing a heat exchange state at the time of defrosting operation in the heat exchanger shown in  FIG. 5( a ) . 
         FIG. 7  is an end view in a line segment VII-VII in  FIG. 6 . 
         FIG. 8  is an end view in a line segment VIII-VIII in  FIG. 6 . 
         FIG. 9  is a view showing a heat exchanger and a refrigeration cycle apparatus in accordance with a second embodiment. 
         FIG. 10  is a view showing a heat exchanger and a refrigeration cycle apparatus in accordance with a third embodiment. 
         FIG. 11  is a partially enlarged view showing a variation of the heat exchangers in accordance with the first to third embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that, in the drawings below, identical or corresponding parts will be designated by the same reference numerals, and the description thereof will not be repeated. 
     First Embodiment 
     &lt;Refrigeration Cycle Apparatus&gt; 
     First, a refrigeration cycle apparatus  200  in accordance with a first embodiment will be described with reference to  FIG. 1 . Refrigeration cycle apparatus  200  includes an outdoor heat exchanger  100 , a compressor  3 , a four-way valve  4 , an indoor heat exchanger  5 , an expansion valve  6 , an outdoor fan  7 , and an indoor fan  8 . Outdoor heat exchanger  100 , compressor  3 , four-way valve  4 , indoor heat exchanger  5 , and expansion valve  6  are connected with one another to constitute a refrigerant circuit through which refrigerant circulates. 
     Outdoor heat exchanger  100  includes a heat exchanger main body unit  1  and an LEV (linear electronic expansion valve)  2  serving as a flow rate control unit (details thereof will be described later). Outdoor heat exchanger  100  is a heat exchanger disposed outside a space (room) in which air temperature is controlled by heating or cooling operation in refrigeration cycle apparatus  200 . Outdoor heat exchanger  100  is disposed outside the room to perform heat exchange between the refrigerant and outdoor air. Indoor heat exchanger  5  is disposed inside the room to perform heat exchange between the refrigerant and indoor air. Outdoor heat exchanger  100  and indoor heat exchanger  5  are connected on one side via compressor  3  and four-way valve  4 , and are also connected on the other side via expansion valve  6 . 
     Compressor  3  has a suction side and a discharge side which are connected with four-way valve  4 . Four-way valve  4  is provided to be capable of switching between refrigerant flow paths at the time of cooling operation and defrosting operation and at the time of heating operation. In  FIG. 1 , a solid line and arrows F 1  indicate a refrigerant flow path at the time of heating operation, and a broken line and arrows F 2  indicate a refrigerant flow path at the time of cooling operation and defrosting operation. Four-way valve  4  is provided to be capable of causing the refrigerant (having high temperature and high pressure) discharged from compressor  3  to flow out to indoor heat exchanger  5  at the time of heating operation. Four-way valve  4  is provided to be capable of causing the refrigerant having high temperature and high pressure discharged from compressor  3  to flow out to outdoor heat exchanger  100  at the time of cooling operation and defrosting operation. Expansion valve  6  expands the refrigerant flowing from indoor heat exchanger  5  to outdoor heat exchanger  100  at the time of heating operation. Expansion valve  6  expands the refrigerant flowing from outdoor heat exchanger  100  to indoor heat exchanger  5  at the time of cooling operation and defrosting operation. Fan  7  is provided to be capable of blowing air to outdoor heat exchanger  100  along a second direction B described later. Fan  8  is provided to be capable of blowing air to indoor heat exchanger  5 . 
     &lt;Outdoor Heat Exchanger&gt; 
     Next, outdoor heat exchanger  100  will be described with reference to  FIGS. 1 and 2 . Outdoor heat exchanger  100  includes heat exchanger main body unit  1 , a first distribution unit  20  having LEV  2 , and a second distribution unit  24 ,  25 ,  26 . Heat exchanger main body unit  1  includes a plurality of first heat transfer tubes  11 , a plurality of second heat transfer tubes  12 , and a plurality of fins  13  (details thereof will be described later). The plurality of first heat transfer tubes  11  are disposed at intervals in a first direction A. The plurality of first heat transfer tubes  11  have respective first ends and respective second ends located opposite to the respective first ends. The plurality of second heat transfer tubes  12  are disposed at intervals in first direction A. The plurality of second heat transfer tubes  12  are disposed at a distance from first heat transfer tubes  11  to face first heat transfer tubes  11  in second direction B crossing first direction A. The plurality of second heat transfer tubes  12  are located on leeward side relative to the plurality of first heat transfer tubes  11 . The plurality of second heat transfer tubes  12  have respective third ends and respective fourth ends located opposite to the respective third ends. The first ends and the third ends are one ends in a third direction C (for example, a vertical direction) crossing first direction A and second direction B, and are lower ends of the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12 , for example. The second ends and the fourth ends are the other ends in third direction C, and are upper ends of the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12 , for example. 
     As shown in  FIG. 2 , first distribution unit  20  connects the first ends of the plurality of first heat transfer tubes  11  and the third ends of the plurality of second heat transfer tubes  12 . First distribution unit  20  includes a first distributor  21 , a second distributor  22 , and an inlet and outlet portion  23 . 
     As shown in  FIG. 2 , first distributor  21  is connected with the first ends of the plurality of first heat transfer tubes  11 . First distributor  21  is provided to extend along first direction A. The plurality of first heat transfer tubes  11  are connected to first distributor  21  such that the plurality of first heat transfer tubes  11  are in parallel with one another, and first distributor  21  is provided to be capable of distributing the refrigerant to the plurality of first heat transfer tubes  11 . 
     As shown in  FIG. 2 , second distributor  22  is connected with the third ends of the plurality of second heat transfer tubes  12 . Second distributor  22  is provided to extend along first direction A. The plurality of second heat transfer tubes  12  are connected to second distributor  22  such that the plurality of second heat transfer tubes  12  are in parallel with one another, and second distributor  22  is provided to be capable of distributing the refrigerant to the plurality of second heat transfer tubes  12 . 
     Inlet and outlet portion  23  is located between a first connection portion and a second connection portion, the first connection portion being between first distributor  21  and the plurality of first heat transfer tubes  11 , the second connection portion being between second distributor  22  and the plurality of second heat transfer tubes  12 , and is provided to allow the refrigerant to flow in and out between first distributor  21  and second distributor  22 . 
     At the time of heating operation, first distribution unit  20  acts as a bifurcating tube which distributes the refrigerant flowing through refrigeration cycle apparatus  200  into first distributor  21  and second distributor  22  in outdoor heat exchanger  100 , and also acts as a distributor which distributes the refrigerant distributed into first distributor  21  and second distributor  22  to the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12 , respectively. 
     In first distribution unit  20 , LEV  2  is provided between inlet and outlet portion  23  and the first connection portion between first distributor  21  and the plurality of first heat transfer tubes  11 . LEV  2  is provided to be capable of controlling a flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11 . LEV  2  is connected with a control device (not shown), and is provided such that its degree of opening can be changed by a control signal from the control device. 
     Second distribution unit  24 ,  25 ,  26  connects the second ends of the plurality of first heat transfer tubes  11  and the fourth ends of the plurality of second heat transfer tubes  12 . Second distribution unit  24 ,  25 ,  26  includes a third distributor  24 , a fourth distributor  25 , and an inlet and outlet portion  26 . First distribution unit  20  and second distribution unit  24 ,  25 ,  26  are provided to face each other with heat exchanger main body unit  1  being sandwiched therebetween in direction C. In refrigeration cycle apparatus  200 , first distribution unit  20  is disposed below in the vertical direction relative to second distribution unit  24 ,  25 ,  26 . 
     Third distributor  24  is connected with the second ends of the plurality of first heat transfer tubes  11 . Third distributor  24  is provided to extend along first direction A. The plurality of first heat transfer tubes  11  are connected to third distributor  24  such that the plurality of first heat transfer tubes  11  are in parallel with one another, and third distributor  24  is provided to be capable of distributing the refrigerant to the plurality of first heat transfer tubes  11 . 
     Fourth distributor  25  is connected with the fourth ends of the plurality of second heat transfer tubes  12 . Fourth distributor  25  is provided to extend along first direction A. The plurality of second heat transfer tubes  12  are connected to fourth distributor  25  such that the plurality of second heat transfer tubes  12  are in parallel with one another, and fourth distributor  25  is provided to be capable of distributing the refrigerant to the plurality of second heat transfer tubes  12 . 
     Inlet and outlet portion  26  is located between a connection portion between third distributor  24  and the plurality of first heat transfer tubes  11 , and a connection portion between fourth distributor  25  and the plurality of second heat transfer tubes  12 , and is provided to allow the refrigerant to flow in and out between third distributor  24  and fourth distributor  25 . 
     At the time of cooling operation and defrosting operation, second distribution unit  24 ,  25 ,  26  acts as a bifurcating tube which distributes the refrigerant flowing through refrigeration cycle apparatus  200  into third distributor  24  and fourth distributor  25  in outdoor heat exchanger  100 , and also acts as a distributor which distributes the refrigerant distributed into third distributor  24  and fourth distributor  25  to the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12 , respectively. 
     Next, heat exchanger main body unit  1  will be described with reference to  FIG. 3 . As described above, heat exchanger main body unit  1  includes the plurality of first heat transfer tubes  11 , the plurality of second heat transfer tubes  12 , and the plurality of fins  13 . The plurality of first heat transfer tubes  11  are provided such that two first heat transfer tubes  11  adjacent to each other in first direction A face each other with one fin  13  being sandwiched therebetween. The plurality of second heat transfer tubes  12  are provided such that two second heat transfer tubes  12  adjacent to each other in first direction A face each other with one fin  13  being sandwiched therebetween in first direction A. Each first heat transfer tube  11  and each second heat transfer tube  12  are disposed at a distance from each other along second direction B crossing first direction A. In refrigeration cycle apparatus  200 , the plurality of first heat transfer tubes  11  are located on windward side relative to the plurality of second heat transfer tubes  12 . 
     The plurality of first heat transfer tubes  11  each have the same structure, for example. The plurality of second heat transfer tubes  12  each have the same structure, for example. The plurality of fins  13  each have the same structure, for example. First heat transfer tubes  11  and second heat transfer tubes  12  are formed to extend along direction C. First heat transfer tubes  11  and second heat transfer tubes  12  are provided to have flat outer shapes when fins  13  are viewed in plan view (outer shapes of cross sections orthogonal to direction C). In first direction A, a width of first heat transfer tube  11  is equal to a width of second heat transfer tube  12 . In second direction B, a width of first heat transfer tube  11  is narrower than a width of second heat transfer tube  12 . In second direction B, the width of first heat transfer tube  11  is less than or equal to half of a width of fin  13 , and the width of second heat transfer tube  12  is more than or equal to half of the width of fin  13 . Fin  13  is constituted as a corrugated fin formed of a thin plate made of metal or the like having a wavelike shape, for example. 
     As shown in  FIG. 3 , side ends  11 A of first heat transfer tubes  11  located outside in second direction B and side ends  13 A of fins  13  located outside in second direction B are provided to lie in the same plane in first direction A, for example. Side ends  12 B of second heat transfer tubes  12  located outside in second direction B and side ends  13 B of fins  13  located outside in second direction B are provided to lie in the same plane in first direction A, for example. Side ends  12 A of second heat transfer tubes  12 , which are located opposite to side ends  12 B in second direction B and face first heat transfer tubes  11  with a distance therebetween, are provided to be located on the side ends  13 A side of fins  13  relative to the center of fins  13  in second direction B. 
     As shown in  FIG. 3 , a plurality of through holes  14  extending from the first ends to the second ends are formed in the plurality of first heat transfer tubes  11 . A plurality of through holes  15  extending from the third ends to the fourth ends are formed in the plurality of second heat transfer tubes  12 . Through holes  14  include two through holes  14   a  and  14   b , for example. Through holes  15  include six through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f , for example. 
     As shown in  FIG. 3 , through holes  14   a  and  14   b  and through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  have an equal width in first direction A, for example. The plurality of through holes  14   a  and  14   b  and through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  have an equal width in second direction B, for example. Through holes  14   a  and  14   b  are disposed to be spaced from each other in second direction B. Through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  are disposed to be spaced from one another in second direction B. Cross sections orthogonal to direction C of through holes  14   a  and  14   b  and through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  may have any shape, and for example, have a rectangular shape. The plurality of through holes  14   a  and  14   b  are each connected with first distributor  21  and third distributor  24 , and are provided such that the refrigerant can flow therethrough. The plurality of through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  are each connected with second distributor  22  and fourth distributor  25 , and are provided such that the refrigerant can flow therethrough. 
     As shown in  FIG. 3 , a total sum S 1  of areas of the cross sections orthogonal to direction C of the plurality of through holes  14   a  and  14   b  formed inside the plurality of first heat transfer tubes  11  is less than or equal to a total sum S 2  of areas of the cross sections orthogonal to direction C of the plurality of through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  formed inside the plurality of second heat transfer tubes  12 . A total sum W 1  of the widths in second direction B of the plurality of through holes  14   a  and  14   b  formed inside the plurality of first heat transfer tubes  11  is less than or equal to a total sum W 2  of the widths in second direction B of the plurality of through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  formed inside the plurality of second heat transfer tubes  12 . 
     As shown in  FIG. 3 , the sum of the areas of the cross sections orthogonal to direction C of through holes  14   a  and  14   b  formed inside two first heat transfer tubes  11  facing each other with one fin  13  being sandwiched therebetween is less than or equal to the sum of the areas of the cross sections orthogonal to direction C of through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  formed inside two second heat transfer tubes  12  provided at a distance from two first heat transfer tubes  11 , respectively, in second direction B. The sum of the widths in second direction B of through holes  14   a  and  14   b  formed inside two first heat transfer tubes  11  facing each other with one fin  13  being sandwiched therebetween is less than or equal to the sum of the widths in second direction B of through holes  15   a ,  15   b ,  15   c ,  15   d ,  15   e , and  15   f  formed inside two second heat transfer tubes  12  provided at a distance from two first heat transfer tubes  11 , respectively, in second direction B. Preferably, two first heat transfer tubes  11  and two second heat transfer tubes  12  facing each other with each fin  13  being sandwiched therebetween are provided such that they each satisfy the relations described above. 
     As shown in  FIG. 3 , fin  13  is connected with both first heat transfer tubes  11  and second heat transfer tubes  12 . Fin  13  is fixed to first heat transfer tubes  11  and second heat transfer tubes  12  by brazing, for example. A plurality of louvers  16  are formed in a portion of fin  13  located between portions connected with first heat transfer tubes  11  and between portions connected with second heat transfer tubes  12 . The plurality of louvers  16  are formed, for example, to extend along first direction A, and are formed to be spaced from one another in second direction B. Referring to  FIGS. 3 and 4 , louvers  16  are provided such that, for example, those located on the side end  13 A side relative to the center in second direction B and those located on the side end  13 B side relative to the center in second direction B are line-symmetric. 
     &lt;Operation of Refrigeration Cycle Apparatus&gt; 
     Next, operation of refrigeration cycle apparatus  200  and outdoor heat exchanger  100  will be described with reference to  FIG. 1 . First, operation of refrigeration cycle apparatus  200  and outdoor heat exchanger  100  at the time of heating operation will be described. At the time of heating operation, refrigeration cycle apparatus  200  constitutes the refrigerant flow path indicated by the solid line and arrows F 1  in  FIG. 1 . The refrigerant in a gas-liquid two-phase state condensed by indoor heat exchanger  5  and expanded by expansion valve  6  is supplied to first distribution unit  20  of outdoor heat exchanger  100 . In outdoor heat exchanger  100 , a refrigerant flow path extending from first distribution unit  20  to second distribution unit  24 ,  25 ,  26  through heat exchanger main body unit  1  is formed. 
     On this occasion, LEV  2  is completely closed to close between first distributor  21  and inlet and outlet portion  23 . Accordingly, at the time of heating operation, a flow of the refrigerant passing through first distributor  21 , the plurality of first heat transfer tubes  11 , and third distributor  24  in outdoor heat exchanger  100  is closed by LEV  2 . By means of LEV  2 , only a refrigerant flow path passing through second distributor  22 , the plurality of second heat transfer tubes  12 , and fourth distributor  25  is formed in outdoor heat exchanger  100  at the time of heating operation. Thereby, in heat exchanger main body unit  1 , the refrigerant flowing through through holes  15  in second heat transfer tubes  12  exchanges heat with the outdoor air blown by fan  7  from the first heat transfer tubes  11  side toward the second heat transfer tubes  12  side, via second heat transfer tubes  12  and fins  13 . 
     Referring to  FIG. 5( a )  and  FIG. 5( b ) , at the time of heating operation, a partial region R 1  of fin  13  sandwiched between second heat transfer tubes  12  adjacent to each other is cooled down by the refrigerant flowing through through holes  15  in second heat transfer tubes  12 , to a temperature which is nearly equal to the temperature of the refrigerant. Accordingly, in the partial region, a surface temperature of fin  13  exhibits a uniform temperature distribution. It should be noted that the partial region of fin  13  is a region located between a portion aligned with side ends  12 A located on the first heat transfer tubes  11  side (windward side) of second heat transfer tubes  12  in first direction A (see  FIG. 3 ) and a portion aligned with side ends  12 B in first direction A. On the other hand, in another region of fin  13  sandwiched between first heat transfer tubes  11  adjacent to each other and located on the first heat transfer tubes  11  side (windward side) relative to the partial region, the refrigerant does not flow through through holes  14  in first heat transfer tubes  11 , and the other region is apart from second heat transfer tubes  12  through which the refrigerant flows, when compared with the partial region. Accordingly, in the other region, the surface temperature of fin  13  exhibits temperature distribution according to the distance from second heat transfer tubes  12 . That is, the surface temperature of fin  13  exhibits temperature distribution in which the surface temperature is highest at side end  13 A of fin  13  located farthest from side ends  12 A of second heat transfer tubes  12 , and gradually decreases toward a position aligned with side ends  12 A of second heat transfer tubes  12  in first direction A. 
     Referring to  FIG. 5( b ) , at the time of heating operation, temperature of air passing over a surface of fin  13  which exhibits temperature distribution as described above is higher than the surface temperature of fin  13 , and exhibits temperature distribution in which the temperature of the air gradually decreases from the side end  13 A side (windward side) toward the side end  13 B side (leeward side) of fin  13 . It should be noted that, in  FIG. 5( b ) , the axis of ordinates represents the temperature of the surface of fin  13  or the air passing over the surface, and the axis of abscissas represents the position on the surface of fin  13  (distance from side end  13 A of fin  13  (side ends  11 A of first heat transfer tubes  11 ) in second direction B (see  FIG. 3 )). In  FIG. 5( c ) , the axis of ordinates represents the amount of heat exchange between the refrigerant and the air via fin  13 , and the axis of abscissas represents the position on the surface of fin  13  (distance from side end  13 A of fin  13  (side ends  11 A of first heat transfer tubes  11 ) in second direction B (see  FIG. 3 )). 
     Since the surface temperature of fin  13  and the temperature of the air passing over the surface of fin  13  exhibit the temperature distributions shown in  FIG. 5( b ) , the amount of heat exchange between the refrigerant and the outside air via fin  13  exhibits a substantially uniform distribution from side end  13 A to side end  13 B of fin  13 , as shown in  FIG. 5( c ) . Thereby, at the time of heating operation, the amount of frost formation on fin  13  can be substantially uniformized from side end  13 A to side end  13 B of fin  13 , as shown in  FIG. 4 . 
     Next, operation of refrigeration cycle apparatus  200  and outdoor heat exchanger  100  at the time of defrosting operation (at the time of cooling operation) will be described. At the time of cooling operation and defrosting operation, refrigeration cycle apparatus  200  constitutes the refrigerant flow path indicated by the broken line and arrows F 2  in  FIG. 1 . The refrigerant in a gas single-phase state evaporated by indoor heat exchanger  5  and compressed by compressor  3  is supplied to second distribution unit  24 ,  25 ,  26  of outdoor heat exchanger  100 . In outdoor heat exchanger  100 , a refrigerant flow path extending from second distribution unit  24 ,  25 ,  26  to first distribution unit  20  through heat exchanger main body unit  1  is formed. 
     On this occasion, LEV  2  is completely opened. Accordingly, at the time of defrosting operation (at the time of cooling operation), a refrigerant flow path passing through third distributor  24 , the plurality of first heat transfer tubes  11 , and first distributor  21 , and a refrigerant flow path passing through fourth distributor  25 , the plurality of second heat transfer tubes  12 , and second distributor  22  are simultaneously formed in outdoor heat exchanger  100 . Referring to  FIG. 6 , fin  13  is provided such that side end  13 A and side end  13 B in second direction B are respectively aligned with side ends  11 A of first heat transfer tubes  11  and side ends  12 B of second heat transfer tubes  12  in first direction A. Accordingly, at the time of defrosting operation, heat of the refrigerant flowing through through holes  14  in first heat transfer tubes  11  and through holes  15  in second heat transfer tubes  12  is also effectively transferred to the vicinity of side end  13 A and side end  13 B of fin  13 . That is, at the time of defrosting operation, the heat of the refrigerant flowing through through holes  14  in first heat transfer tubes  11  and through holes  15  in second heat transfer tubes  12  is effectively transferred to an entire region R 2  of fin  13 . 
     Further, a partial region of fin  13  located on the side end  13 A side relative to the center in second direction B is in contact with neither first heat transfer tubes  11  nor second heat transfer tubes  12 . However, the partial region is sandwiched between a region adjacent to through holes  14   b  in the first heat transfer tubes  11  and a region adjacent to through holes  15   a  in second heat transfer tubes  12 , in second direction B. Accordingly, at the time of defrosting operation, the heat of the refrigerant flowing through through holes  14  in first heat transfer tubes  11  and through holes  15  in second heat transfer tubes  12  is also effectively transferred to the partial region of fin  13  which is not in contact with first heat transfer tubes  11  and second heat transfer tubes  12 . 
     Referring to  FIGS. 7 and 8 , frost melted by the defrosting operation described above turns into water W and is drained and removed from outdoor heat exchanger  100 . Outdoor heat exchanger  100  has two drain paths for defrosted frost. One drain path is a drain path directed from above to below in the vertical direction through the surface of fin  13  and louvers  16 . Another drain path is a drain path directed from above to below in the vertical direction through side ends  11 A,  11 B,  12 A,  12 B in second direction B of first heat transfer tubes  11  and second heat transfer tubes  12 . 
     Function and Effect 
     Next, the function and effect of outdoor heat exchanger  100  and refrigeration cycle apparatus  200  will be described. Outdoor heat exchanger  100  includes: the plurality of first heat transfer tubes  11  disposed at intervals in first direction A; the plurality of second heat transfer tubes  12  disposed at a distance from the plurality of first heat transfer tubes  11  to face the plurality of first heat transfer tubes  11  in second direction B crossing first direction A, and located on leeward side relative to the plurality of first heat transfer tubes  11 ; the plurality of fins  13  connecting first heat transfer tubes  11  adjacent to each other and connecting second heat transfer tubes  12  adjacent to each other; first distribution unit  20  connecting the first ends of the plurality of first heat transfer tubes  11  and the third ends of the plurality of second heat transfer tubes  12 ; and second distribution unit  24 ,  25 ,  26  connecting the second ends of the plurality of first heat transfer tubes  11  and the fourth ends of the plurality of second heat transfer tubes  12 . First distribution unit  20  includes LEV  2  for controlling the flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11 . 
     A conventional outdoor heat exchanger is provided such that only two heat transfer tubes are disposed to face each other with one corrugated fin being sandwiched therebetween, and both ends of each heat transfer tube are aligned with both ends of the fin in a flow direction of air. Accordingly, at the time of heating operation, a surface temperature of the entire fin is cooled down by refrigerant to a constant temperature, and a temperature difference between temperature of the air and the surface temperature of the fin increases toward windward side. As a result, in the conventional outdoor heat exchanger, the amount of heat exchange between the refrigerant and the air via the fin increases on the windward side when compared with leeward side, and the amount of frost formation increases in particular on the windward side. Further, in such a conventional outdoor heat exchanger, since the amount of frost formation increases in particular on the windward side, the speed of melting frost at the time of defrosting operation decreases on the windward side when compared with the leeward side. As a result, the conventional outdoor heat exchanger has a poor energy efficiency at the time of defrosting operation. Furthermore, in the heat exchanger described in PTD 1, it is not possible to efficiently defrost frost on the corrugated fin located on the windward side. 
     In contrast, in outdoor heat exchanger  100 , at the time of heating operation of refrigeration cycle apparatus  200 , a state in which the refrigerant flows in only the plurality of second heat transfer tubes  12  without flowing in the plurality of first heat transfer tubes  11  can be realized by LEV  2 . Thereby, at the time of heating operation, the amount of heat exchange between the refrigerant and the outside air via fin  13  exhibits a substantially uniform distribution from side end  13 A to side end  13 B of fin  13  (see  FIG. 5( c ) ). As a result, frost formation on fin  13  on the windward side can be suppressed, and the amount of frost formation on fin  13  can be substantially uniformized from side end  13 A to side end  13 B of fin  13 . 
     Further, in outdoor heat exchanger  100 , at the time of defrosting operation and cooling operation of refrigeration cycle apparatus  200 , a state in which the refrigerant flows in both first heat transfer tubes  11  and second heat transfer tubes  12  can be realized. As a result, at the time of defrosting operation, the heat of the refrigerant flowing through first heat transfer tubes  11  and second heat transfer tubes  12  can be effectively transferred to frost substantially uniformly forming on fin  13  from the windward side to the leeward side at the time of heating operation described above, via entire fin  13 . Accordingly, in outdoor heat exchanger  100 , the speed of melting frost is equal on the windward side and on the leeward side, and thus outdoor heat exchanger  100  has a high defrosting efficiency. Further, outdoor heat exchanger  100  has a high heat exchange efficiency at the time of cooling operation. 
     In addition, the conventional outdoor heat exchanger described above has a poor drain efficiency due to a limited drain path for frost melted by defrosting operation. For example, in the conventional heat exchanger provided such that only two heat transfer tubes are disposed to face each other with one corrugated fin being sandwiched therebetween, and both ends of each heat transfer tube are aligned with both ends of the fin in the flow direction of the air, only a drain path directed from above to below in the vertical direction through folded portions of the fin and louvers is formed in a region other than ends on the windward side and on the leeward side. Further, since the region is sandwiched between the two heat transfer tubes, water is likely to stagnate at connection portions between the fin and the heat transfer tubes included in the drain path. In addition, in the heat exchanger described in PTD 1, two drain paths are formed in the corrugated fin protruding on the windward side relative to the heat transfer tubes. That is, there are formed a drain path directed from above to below in the vertical direction through louvers, and a drain path directed from above to below in the vertical direction through a surface of the fin. However, the two drain paths are both formed on the fin, and water is likely to stagnate therein. 
     In contrast, in outdoor heat exchanger  100 , at least three drain paths are formed. That is, there are formed a drain path directed from above to below in the vertical direction through louvers  16  in fin  13 , a drain path directed from above to below in the vertical direction through side ends  11 A of first heat transfer tubes  11  and side ends  12 B of second heat transfer tubes  12 , and a drain path directed from above to below in the vertical direction through side ends  11 B of first heat transfer tubes  11  and side ends  12 A of second heat transfer tubes  12 . Since the drain paths directed from above to below in the vertical direction through side ends  11 A,  11 B,  12 A,  12 B in second direction B of first heat transfer tubes  11  and second heat transfer tubes  12  have a distance shorter than that of a drain path formed on fin  13 , and water is less likely to stagnate therein, the drain paths can drain much water in a short time. As a result, outdoor heat exchanger  100  has defrosting efficiency higher than that of the conventional heat exchanger described above. Further, outdoor heat exchanger  100  can shorten time required for defrosting when compared with the conventional heat exchanger described above. Accordingly, in outdoor heat exchanger  100 , even when heating operation is resumed after defrosting operation, water stagnating on the fin without being drained at the time of defrosting operation can be suppressed from turning into frost again, and heat exchange efficiency after heating operation is resumed can be increased when compared with the conventional heat exchanger described above. 
     Refrigeration cycle apparatus  200  includes outdoor heat exchanger  100 , and fan  7  configured to blow gas to outdoor heat exchanger  100  along second direction B. In refrigeration cycle apparatus  200 , outdoor heat exchanger  100  is disposed such that first heat transfer tubes  11  are located on the windward side in a flow direction of the air produced by fan  7 , and second heat transfer tubes  12  are located on the leeward side. Accordingly, since refrigeration cycle apparatus  200  includes outdoor heat exchanger  100  which suppresses frost formation at the time of heating operation as described above, refrigeration cycle apparatus  200  has a high heat exchange efficiency at the time of heating operation. Further, since refrigeration cycle apparatus  200  includes outdoor heat exchanger  100  having a high defrosting efficiency as described above, refrigeration cycle apparatus  200  can shorten time for defrosting operation, and has a high heat exchange efficiency after heating operation is resumed. 
     Second Embodiment 
     Next, an outdoor heat exchanger  101  and a refrigeration cycle apparatus  201  in accordance with a second embodiment will be described with reference to  FIG. 9 . Although outdoor heat exchanger  101  in accordance with the second embodiment has basically the same configuration as that of outdoor heat exchanger  100  (see  FIG. 1 ) in accordance with the first embodiment, outdoor heat exchanger  101  is different from outdoor heat exchanger  100  in that the flow rate control unit is not an LEV but a solenoid valve  9 . Although refrigeration cycle apparatus  201  in accordance with the second embodiment has basically the same configuration as that of refrigeration cycle apparatus  200  (see  FIG. 1 ) in accordance with the first embodiment, refrigeration cycle apparatus  201  is different from refrigeration cycle apparatus  200  in that refrigeration cycle apparatus  201  includes outdoor heat exchanger  101  instead of outdoor heat exchanger  100  (see  FIG. 1 ). 
     Also with such a configuration, solenoid valve  9  is provided to be capable of controlling the flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11 . Accordingly, in outdoor heat exchanger  101 , at the time of heating operation of refrigeration cycle apparatus  201 , the state in which the refrigerant flows in only the plurality of second heat transfer tubes  12  without flowing in the plurality of first heat transfer tubes  11  can be realized by solenoid valve  9 . As a result, outdoor heat exchanger  101  can produce the same effect as that of outdoor heat exchanger  100 . Further, refrigeration cycle apparatus  201  can produce the same effect as that of refrigeration cycle apparatus  200 . 
     Further, solenoid valve  9  can control the flow rate of the refrigerant flowing in first heat transfer tubes  11  by turning on/off an electric signal (opening/closing solenoid valve  9 ). That is, solenoid valve  9  can be controlled by a control device having a structure simpler than that of the control device required to control the degree of opening of LEV  2  of outdoor heat exchanger  100  in accordance with the first embodiment. Accordingly, the manufacturing cost of outdoor heat exchanger  101  is lower than that of outdoor heat exchanger  100 . 
     Third Embodiment 
     Next, an outdoor heat exchanger  102  and a refrigeration cycle apparatus  202  in accordance with a third embodiment will be described with reference to  FIG. 10 . Although outdoor heat exchanger  102  in accordance with the third embodiment has basically the same configuration as that of outdoor heat exchanger  100  (see  FIG. 1 ) in accordance with the first embodiment, outdoor heat exchanger  102  is different from outdoor heat exchanger  100  in that the flow rate control unit is not an LEV but a check valve  10 . Although refrigeration cycle apparatus  202  in accordance with the third embodiment has basically the same configuration as that of refrigeration cycle apparatus  200  (see  FIG. 1 ) in accordance with the first embodiment, refrigeration cycle apparatus  202  is different from refrigeration cycle apparatus  200  in that refrigeration cycle apparatus  202  includes outdoor heat exchanger  102  instead of outdoor heat exchanger  100  (see  FIG. 1 ). 
     Also with such a configuration, check valve  10  is provided to be capable of controlling the flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11 . Accordingly, in outdoor heat exchanger  102 , at the time of heating operation of refrigeration cycle apparatus  202 , the state in which the refrigerant flows in only the plurality of second heat transfer tubes  12  without flowing in the plurality of first heat transfer tubes  11  can be realized by check valve  10 . As a result, outdoor heat exchanger  102  can produce the same effect as that of outdoor heat exchanger  100 . Further, refrigeration cycle apparatus  202  can produce the same effect as that of refrigeration cycle apparatus  200 . 
     Further, check valve  10  can limit a flow direction of the refrigerant flowing in first heat transfer tubes  11  to only one direction without using a control signal, an electric signal, or the like. Specifically, check valve  10  closes a flow of the refrigerant directed from inlet and outlet portion  23  toward first heat transfer tubes  11  through first distributor  21  at the time of heating operation, and does not disturb a flow of the refrigerant directed from first heat transfer tubes  11  toward inlet and outlet portion  23  through first distributor  21  at the time of defrosting operation and cooling operation. Accordingly, the manufacturing cost of outdoor heat exchanger  102  is lower than those of outdoor heat exchanger  100  and outdoor heat exchanger  101 . Furthermore, since check valve  10  can be mounted in a smaller space when compared with LEV  2  or solenoid valve  9 , outdoor heat exchanger  102  can be downsized when compared with outdoor heat exchanger  100  and outdoor heat exchanger  101 . 
     It should be noted that, although side ends  11 A of first heat transfer tubes  11  and side ends  13 A of fins  13  are provided to lie in the same plane in first direction A as shown in  FIG. 3  in outdoor heat exchangers  100 ,  101 , and  102  in accordance with the first to third embodiments, the present invention is not limited thereto. Referring to  FIG. 11 , side end  13 A of fin  13  may protrude in second direction B relative to side ends  11 A of first heat transfer tubes  11 . The distance between side ends  11 A of first heat transfer tubes  11  and side end  13 A of fin  13  in second direction B may have any value as long as frost on side end  13 A can be melted by the heat of the refrigerant flowing through through holes  14  in first heat transfer tubes  11  at the time of defrosting operation, but it is more preferable that the distance is shorter. 
     Even in such heat exchanger main body unit  1 , the surface temperature of fin  13  at the time of heating operation exhibits temperature distribution in which the surface temperature is highest at side end  13 A of fin  13  located farthest from side ends  12 A of second heat transfer tubes  12 , and gradually decreases toward a position aligned with side ends  12 A of second heat transfer tubes  12  in first direction A. Further, the temperature of the air passing over the surface of fin  13  at the time of heating operation exhibits temperature distribution in which the temperature of the air gradually decreases from the side end  13 A side toward the side end  13 B side of fin  13 . Accordingly, the amount of frost formation on fin  13  at the time of heating operation can be substantially uniformized from side end  13 A to side end  13 B of fin  13 . 
     Further, at the time of defrosting operation, the heat of the refrigerant flowing through through holes  15  in second heat transfer tubes  12  is effectively transferred to the vicinity of side end  13 B of fin  13 . Furthermore, if the distance between side ends  11 A of first heat transfer tubes  11  and side end  13 A of fin  13  is short, the heat of the refrigerant flowing through through holes  14  in first heat transfer tubes  11  is effectively transferred to the vicinity of side end  13 A of fin  13 . As a result, an outdoor heat exchanger including heat exchanger main body unit  1  shown in  FIG. 11  can produce the same effect as those of outdoor heat exchangers  100 ,  101 , and  102  described above. 
     Further, although LEV  2 , solenoid valve  9 , or check valve  10  serving as the flow rate control unit is provided to be capable of switching between a state in which the refrigerant flows in the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12  (a first state) and a state in which the refrigerant flows in only the plurality of second heat transfer tubes  12  without flowing in the plurality of first heat transfer tubes  11  (a second state) in outdoor heat exchangers  100 ,  101 , and  102  in accordance with the first to third embodiments, the present invention is not limited thereto. The flow rate control unit only has to be provided to be capable of switching between the first state and a second state in which the flow rate of the refrigerant is smaller than that in the first state in only the plurality of first heat transfer tubes  11 . That is, the second state which can be realized by the flow rate control unit may be any state in which, when compared with the first state, the flow rate of the refrigerant flowing in the plurality of second heat transfer tubes  12  is not decreased, and only the flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11  is decreased. 
     For example, the flow rate control unit can switch between a first state in which the flow rate of the refrigerant flowing in first heat transfer tubes  11  is equal to the flow rate of the refrigerant flowing in second heat transfer tubes  12 , and a second state in which the flow rate of the refrigerant flowing in first heat transfer tubes  11  is relatively smaller than the flow rate of the refrigerant flowing in second heat transfer tubes  12 . Even in such an outdoor heat exchanger, the flow rate of the refrigerant flowing in first heat transfer tubes  11  at the time of heating operation can be decreased when compared with the conventional outdoor heat exchanger, and thus frost formation on fin  13  on the windward side can be suppressed, and defrosting efficiency can be increased. It should be noted that the state most suitable as the second state is the state in which the refrigerant flows in only the plurality of second heat transfer tubes  12  without flowing in the plurality of first heat transfer tubes  11 . Further, when the total flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11  and the plurality of second heat transfer tubes  12  is constant in the first state and the second state, the second state which can be realized by the flow rate control unit is a state in which, when compared with the first state, the flow rate of the refrigerant flowing in the plurality of first heat transfer tubes  11  is decreased, and the flow rate of the refrigerant flowing in the plurality of second heat transfer tubes  12  is increased. 
     It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention is advantageously applicable to a refrigeration cycle apparatus which performs heating operation in a cold climate, and a heat exchanger used for the refrigeration cycle apparatus.