Patent Publication Number: US-11384996-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 PCT/JP2017/037384, filed on Oct. 16, 2017, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a heat exchanger and a refrigeration cycle apparatus, particularly, a fin and tube type heat exchanger and a refrigeration cycle apparatus including the fin and tube type heat exchanger. 
     BACKGROUND 
     Conventionally, there has been known a fin and tube type heat exchanger including: a plurality of plate-like fins arranged at a predetermined fin pitch interval; and a plurality of heat transfer tubes extending through the fins along a direction in which the plurality of fins are arranged. 
     In the fin and tube type heat exchanger, the plurality of heat transfer tubes are inserted in openings provided in the plurality of fins, such as through holes or notches. Accordingly, the plurality of heat transfer tubes extend through the fins. An end portion of each heat transfer tube is connected to a distribution tube or a header. Accordingly, a target heat exchanging fluid such as water or refrigerant flows in each heat transfer tube, and heat is exchanged between the target heat exchanging fluid and a heat exchanging fluid such as air flowing between the plurality of fins. 
     A conventional fin and tube type heat exchanger has been known in which each heat transfer tube has a flat cross sectional shape perpendicular to the extending direction of the heat transfer tube. With the heat transfer tube having such a flat cross sectional shape, separation of airflow can be reduced and airflow resistance can be smaller than that in a heat transfer tube having a circular cross sectional shape. Hence, the heat transfer tubes having such flat cross sectional shapes can be mounted in high density. A heat exchanger in which the heat transfer tubes each having a flat cross sectional shape are mounted in high density has an improved balance between heat transfer performance and airflow performance. 
     On the other hand, when the heat exchanger is operated as an evaporator in an environment in which an outdoor air temperature is, for example, below a freezing point, a water content in the heat exchanging fluid is condensed around the heat transfer tubes to result in frost. Such frost is melted into water droplets by a defrosting operation; however, the water droplets need to be appropriately discharged from around the heat transfer tubes in order to prevent accumulation and freezing of the water droplets around the heat transfer tubes. 
     In order to reduce a defrosting time by appropriately discharging water droplets from around heat transfer tubes, Japanese Patent Laying-Open No. 10-62086 discloses a fin and tube type heat exchanger in which a clearance for flow of water is formed between a lower surface of a heat transfer tube having a flat shape and an insertion hole in which the heat transfer tube is inserted. 
     PATENT LITERATURE 
     
         
         PTL 1: Japanese Patent Laying-Open No. 10-62086 
       
    
     However, in the conventional fin and tube type heat exchanger, a portion between adjacent heat transfer tubes cannot be sufficiently prevented from being blocked by frost, disadvantageously. 
     In the fin and tube type heat exchanger, the absolute humidity of the heat exchanging fluid flowing between the adjacent heat transfer tubes becomes smaller from a windward side to a leeward side in a flow direction. A temperature boundary layer formed between the adjacent heat transfer tubes becomes thicker from the windward side to the leeward side. Hence, in the conventional fin and tube type heat exchanger described in Japanese Patent Laying-Open No. 10-62086, frost is more likely to be formed at the windward side at which the absolute humidity of the heat exchanging fluid is large and the temperature boundary layer is thin, than at the leeward side at which the absolute humidity of the heat exchanging fluid is small and the temperature boundary layer is thick. 
     Particularly, when the heat transfer tubes are mounted in high density, a flow path for the heat exchanging fluid between the adjacent heat transfer tubes is likely to be blocked by frost grown at the windward side, disadvantageously. When the flow path for the heat exchanging fluid is blocked by frost, performance of the refrigeration cycle apparatus during a heating operation is decreased. 
     SUMMARY 
     A main object of the present invention is to provide a heat exchanger and a refrigeration cycle apparatus to effectively suppress a flow path for a heat exchanging fluid from being blocked by frost as compared with a conventional fin and tube type heat exchanger. 
     A heat exchanger according to the present invention includes: a plate-like fin having one end and an other end in a first direction; and a first heat transfer tube and a second heat transfer tube that each extend through the fin and that are adjacent to each other in a second direction crossing the first direction. An outer shape of each of the first heat transfer tube and the second heat transfer tube in a cross section perpendicular to an extending direction of each of the first heat transfer tube and the second heat transfer tube is a flat shape having a long side direction and a short side direction. A first end portion of the first heat transfer tube located at the one end side is disposed at one side in the second direction relative to a second end portion of the first heat transfer tube located at the other end side. A third end portion of the second heat transfer tube located at the one end side is disposed at the one side in the second direction relative to a fourth end portion of the second heat transfer tube located at the other end side. A portion to which the fin and at least one of the first heat transfer tube and the second heat transfer tube are connected, and at least one clearance portion that separates between the fin and the at least one of the first heat transfer tube and the second heat transfer tube are disposed between the fin and the at least one of the first heat transfer tube and the second heat transfer tube. The at least one clearance portion is disposed at the one end side in the first direction relative to an imaginary center line that passes through a center of the first heat transfer tube in the long side direction and that extends along the short side direction. 
     According to the present invention, by the clearance portion disposed to overlap with the first imaginary line, the temperature of the fin located on the first imaginary line during an operation as an evaporator is suppressed from being decreased as compared with a conventional heat exchanger. Hence, according to the present invention, there can be provided a heat exchanger and a refrigeration cycle apparatus to effectively suppress a flow path for a heat exchanging fluid from being blocked by frost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an exemplary refrigerant circuit of a refrigeration cycle apparatus according to a first embodiment. 
         FIG. 2  is a perspective view showing an exemplary heat exchanger shown in  FIG. 1 . 
         FIG. 3  is a partial cross sectional view of the heat exchanger shown in  FIG. 2 . 
         FIG. 4  is a partial cross sectional view of the heat exchanger shown in  FIG. 2 . 
         FIG. 5  is a partial cross sectional view when seen from a line segment V-V in  FIG. 4 . 
         FIG. 6  is a partial cross sectional view showing a heat flux distribution of the heat exchanger shown in  FIG. 3 . 
         FIG. 7  is a partial cross sectional view showing a heat flux distribution of a comparative example. 
         FIG. 8  is a partial cross sectional view of a heat exchanger according to a second embodiment. 
         FIG. 9  is a partial cross sectional view of a heat exchanger according to a third embodiment. 
         FIG. 10  is a partial cross sectional view of a heat exchanger according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes embodiments of the present invention with reference to figures. It should be noted that in the below-described figures, the same or corresponding portions are given the same reference characters and are not described repeatedly. 
     First Embodiment 
     &lt;Configuration of Refrigeration Cycle Apparatus&gt; 
     With reference to  FIG. 1 , a refrigeration cycle apparatus  1  according to a first embodiment will be described. As shown in  FIG. 1 , refrigeration cycle apparatus  1  includes a compressor  2 , an indoor heat exchanger  3 , an indoor fan  4 , a throttle device  5 , an outdoor heat exchanger  10 , an outdoor fan  6 , and a four-way valve  7 . For example, compressor  2 , outdoor heat exchanger  10 , throttle device  5 , and four-way valve  7  are provided in an outdoor unit, and indoor heat exchanger  3  is provided in an indoor unit. 
     Compressor  2 , indoor heat exchanger  3 , throttle device  5 , outdoor heat exchanger  10 , and four-way valve  7  constitute a refrigerant circuit in which refrigerant can circulate. In refrigeration cycle apparatus  1 , a refrigeration cycle is performed in which the refrigerant circulates with a phase change in the refrigerant circuit. 
     Compressor  2  compresses the refrigerant. Compressor  2  is a rotary compressor, a scroll compressor, a screw compressor, a reciprocating compressor, or the like, for example. 
     Indoor heat exchanger  3  functions as a condenser during a heating operation, and functions as an evaporator during a cooling operation. Indoor heat exchanger  3  is a fin and tube type heat exchanger, a micro channel heat exchanger, a shell and tube type heat exchanger, a heat pipe type heat exchanger, a double-tube type heat exchanger, a plate heat exchanger, or the like, for example. 
     Throttle device  5  expands and decompresses the refrigerant. Throttle device  5  is an electrically powered expansion valve or the like that can adjust a flow rate of the refrigerant, for example. It should be noted that examples of throttle device  5  may include not only the electrically powered expansion valve but also a mechanical expansion valve employing a diaphragm for a pressure receiving portion, a capillary tube, or the like. 
     Outdoor heat exchanger  10  functions as an evaporator during the heating operation, and functions as a condenser during the cooling operation. Outdoor heat exchanger  10  is a fin and tube type heat exchanger. Details of outdoor heat exchanger  10  will be described later. 
     Four-way valve  7  can switch a flow path for the refrigerant in refrigeration cycle apparatus  1 . During the heating operation, four-way valve  7  is switched to connect a discharge port of compressor  2  to indoor heat exchanger  3 , and connect a suction port of compressor  2  to outdoor heat exchanger  10 . Moreover, during the cooling operation and a dehumidification operation, four-way valve  7  is switched to connect the discharge port of compressor  2  to outdoor heat exchanger  10  and connect the suction port of compressor  2  to indoor heat exchanger  3 . 
     Indoor fan  4  is attached to indoor heat exchanger  3  and supplies indoor air to indoor heat exchanger  3  as a heat exchanging fluid. Outdoor fan  6  is attached to outdoor heat exchanger  10  and supplies outdoor air to outdoor heat exchanger  10 . 
     &lt;Configuration of Heat Exchanger&gt; 
     Next, heat exchanger  10  will be described with reference to  FIG. 2  and  FIG. 3 . 
     It should be noted that in the description below, for ease of description, the x direction represents a direction in which a short side of each of a plurality of fins  30  included in heat exchanger  10  extends, the y direction represents a direction in which each of a plurality of heat transfer tubes  20  included in heat exchanger  10  extends, and the z direction (second direction) represents a direction in which a long side of each of the plurality of fins  30  included in heat exchanger  10  extends and in which the plurality of heat transfer tubes  20  are arranged and disposed to be separated from each other. In refrigeration cycle apparatus  1 , heat exchanger  10  is disposed such that the x direction is along the flow direction of the heat exchanging fluid supplied from outdoor fan  6  shown in  FIG. 1  and such that the z direction is along a gravity direction. 
     As shown in  FIG. 2 , heat exchanger  10  is a heat exchanger having a two-column structure, for example. Heat exchanger  10  includes: a first heat exchanger  11  disposed at a windward side in the x direction; and a second heat exchanger  12  disposed at a leeward side in the x direction. Each of first heat exchanger  11  and second heat exchanger  12  is configured as a fin and tube type heat exchanger. Each of first heat exchanger  11  and second heat exchanger  12  includes: a plurality of heat transfer tubes disposed to be separated from each other in the gravity direction; and a plurality of fins through which each of the plurality of heat transfer tubes extends. It should be noted that depending on a heat exchange load imposed on heat exchanger  10 , heat exchanger  10  may be configured as a heat exchanger having a one-column structure, i.e., having one of first heat exchanger  11  and second heat exchanger  12 . 
     As shown in  FIG. 2 , one end of each heat transfer tube of first heat exchanger  11  is connected to first header portion  13 . One end of each heat transfer tube of second heat exchanger  12  is connected to second header portion  14 . The other end of the heat transfer tube of first heat exchanger  11  and the other end of the heat transfer tube of second heat exchanger  12  are connected to an inter-column connection member  15 . 
     First header portion  13  is provided to distribute externally supplied refrigerant to each of the heat transfer tubes of first heat exchanger  11 . Second header portion  14  is provided to distribute externally supplied refrigerant to each of the heat transfer tubes of second heat exchanger  12 . Accordingly, heat exchanger  10  has a refrigerant flow path in which first header portion  13 , each heat transfer tube of first heat exchanger  11 , inter-column connection member  15 , each heat transfer tube of second heat exchanger  12 , and second header portion  14  are connected in this order. 
     First heat exchanger  11  and second heat exchanger  12  have equivalent configurations, for example. In the description below, the configuration of first heat exchanger  11  will be described on behalf of first heat exchanger  11  and second heat exchanger  12 . 
     As shown in  FIG. 3  and  FIG. 4 , first heat exchanger  11  includes the plurality of heat transfer tubes  20  and the plurality of fins  30 . Each of the plurality of heat transfer tubes  20  extends along the y direction. The plurality of heat transfer tubes  20  include a first heat transfer tube  20   a  and a second heat transfer tube  20   b  that are adjacent to each other in the z direction. First heat transfer tube  20   a  is disposed below second heat transfer tube  20   b.    
     Each of the plurality of fins  30  is provided in a plate-like form. Each of the plurality of fins  30  has a surface that is perpendicular to the y direction and that has a rectangular outer shape, for example. When seen in the y direction, the short side of fin  30  is along the x direction, and the long side of fin  30  is along the z direction. Fin  30  has one end  30   a  and an other end  30   b  in the x direction. One end  30   a  is disposed at the windward side in the flow direction of the heat exchanging fluid, and other end  30   b  is disposed at the leeward side in the flow direction of the heat exchanging fluid. The plurality of fins  30  are provided with: through holes through which respective ones of the plurality of heat transfer tubes  20  extend; and clearance portions  41   a ,  41   b  continuous to the through holes (details will be described later). It should be noted that first heat transfer tube  20   a  and second heat transfer tube  20   b  shown in  FIG. 3  are any two heat transfer tubes that are adjacent to each other in the gravity direction among the plurality of heat transfer tubes  20  in first heat exchanger  11 . Fin  30  shown in  FIG. 3  is any one fin of the plurality of fins  30  in first heat exchanger  11 . 
     As shown in  FIG. 3 , the outer shape of each of first heat transfer tube  20   a  and second heat transfer tube  20   b  in the cross section perpendicular to the y direction is a flat shape having a long side direction and a short side direction orthogonal to the long side direction. Each of first heat transfer tube  20   a  and second heat transfer tube  20   b  has an upper flat surface and a lower flat surface disposed to be separated from each other in the short side direction. The upper flat surfaces and lower flat surfaces of first heat transfer tube  20   a  and second heat transfer tube  20   b  are disposed in parallel, for example. Each of first heat transfer tube  20   a  and second heat transfer tube  20   b  further has a first surface and a second surface, the first surface connecting the upper flat surface to the lower flat surface at the windward side, the second surface connecting the upper flat surface to the lower flat surface at the leeward side. In each of first heat transfer tube  20   a  and second heat transfer tube  20   b , a plurality of flow paths for refrigerant to flow are disposed side by side in the long side direction of the flat shape, for example. 
     In the description below, for ease of description, a windward side end portion  21   a  (first end portion) represents an end portion of first heat transfer tube  20   a  located at the windward side (the one end  30   a  side of fin  30 ), and a leeward side end portion  22   a  (second end portion) represents an end portion of first heat transfer tube  20   a  located at the leeward side (the other end  30   b  side of fin  30 ). A first boundary portion  25   a  represents a boundary portion between the upper flat surface and first surface of first heat transfer tube  20   a , and a second boundary portion  26   a  represents a boundary portion between the lower flat surface and first surface of first heat transfer tube  20   a . A windward side end portion  21   b  (third end portion) represents an end portion of second heat transfer tube  20   b  located at the windward side, and a leeward side end portion  22   b  (fourth end portion) represents an end portion of second heat transfer tube  20   b  located at the leeward side. A third boundary portion  25   b  represents a boundary portion between the upper flat surface and first surface of second heat transfer tube  20   b , and a fourth boundary portion  26   b  represents a boundary portion between the lower flat surface and first surface of second heat transfer tube  20   b.    
     As shown in  FIG. 3  and  FIG. 4 , windward side end portion  21   a  is disposed at the upper side relative to leeward side end portion  22   a . Windward side end portion  21   b  is disposed at the upper side relative to leeward side end portion  22   b . In other words, each of first heat transfer tube  20   a  and second heat transfer tube  20   b  is inclined downward in the gravity direction from the windward side to the leeward side in the flowing direction. From a different viewpoint, it can be said that a distance (seen as L 11 ) in the z direction between windward side end portion  21   a  of first heat transfer tube  20   a  and leeward side end portions  22   b  of second heat transfer tube  20   b  is shorter than a distance (seen as L 12 ) in the z direction between leeward side end portion  22   a  of first heat transfer tube  20   a  and windward side end portion  21   b  of second heat transfer tube  20   b.    
     As shown in  FIG. 3  and  FIG. 4 , in the cross section perpendicular to the y direction, each long side direction of first heat transfer tube  20   a  and second heat transfer tube  20   b  is disposed to form a smaller angle with respect to the x direction than an angle formed with respect to the z direction. In the cross section perpendicular to the y direction, each short side direction of first heat transfer tube  20   a  and second heat transfer tube  20   b  is disposed to form a larger angle with respect to the x direction than an angle formed with respect to the z direction. In the cross section perpendicular to the y direction, each long side direction of first heat transfer tube  20   a  and second heat transfer tube  20   b  forms an angle of less than or equal to 20° with respect to the x direction, for example. 
     As shown in  FIG. 3  and  FIG. 4 , windward side end portion  21   a  and windward side end portion  21   b  are disposed to overlap in the z direction. First boundary portion  25   a  and second boundary portion  26   a  are disposed to overlap in the short side direction. Third boundary portion  25   b  and fourth boundary portion  26   b  are disposed to overlap in the short side direction. Leeward side end portion  22   a  and leeward side end portion  22   b  are disposed to overlap in the z direction. First boundary portion  25   a  and third boundary portion  25   b  are disposed to overlap in the z direction. 
     As shown in  FIG. 3 ,  FIG. 4 , and  FIG. 5 , first heat transfer tube  20   a  and second heat transfer tube  20   b  extend through each of of the plurality of fins  30 . The plurality of fins  30  are disposed to be separated from each other at a predetermined interval FP (see  FIG. 5 ) in the y direction. 
     As shown in  FIG. 3 , a first imaginary line segment  1   a  is defined to represent an imaginary line segment that extends along the short side direction, that passes through first boundary portion  25   a  and second boundary portion  26   a , and that is located between first heat transfer tube  20   a  and second heat transfer tube  20   b . An imaginary center line L 2   a  is defined to represent an imaginary line that extends along the short side direction and that passes through the center of first heat transfer tube  20   a  in the long side direction. A second imaginary line segment L 1   b  is defined to represent an imaginary line segment that extends along the short side direction, that passes through third boundary portion  25   b  and fourth boundary portion  26   b , and that is located between third heat transfer tube  20   c  and second heat transfer tube  20   b . Further, an imaginary line L 3  is defined to represent an imaginary line that passes through the center between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the short side direction and that extends along the long side direction. An imaginary line L 4   b  is defined to represent an imaginary line obtained by extending the lower flat surface of second heat transfer tube  20   b . An imaginary line L 5   a  is defined to represent an imaginary line obtained by extending the upper flat surface of first heat transfer tube  20   a . An imaginary line L 5   b  is defined to represent an imaginary line obtained by extending the upper flat surface of second heat transfer tube  20   b . An imaginary line L 7  is defined to represent an imaginary line that connects windward side end portion  21   a  to windward side end portion  21   b . An imaginary line L 8  is defined to represent an imaginary line that connects leeward side end portion  22   a  to leeward side end portion  22   b.    
     As shown in  FIG. 4 , an airflow path region RP is defined to represent a region which is located between first heat transfer tube  20   a  and second heat transfer tube  20   b  and in which the heat exchanging fluid flows along fin  30 . In the y direction, airflow path region RP is disposed between imaginary line L 7  that connects windward side end portion  21   a  to windward side end portion  21   b  and imaginary line L 8  that connects leeward side end portion  22   a  to leeward side end portion  22   b . A windward region RW is defined to represent a region that is disposed at the windward side relative to airflow path region RP, i.e., at the windward side relative to imaginary line L 7  and that is continuous to airflow path region RP. A leeward region RL is defined to represent a region that is disposed at the leeward side relative to airflow path region RP, i.e., at the leeward side relative to imaginary line L 8  and that is continuous to airflow path region RP. A second airflow path region RP 2  is defined to represent a region which is disposed between second heat transfer tube  20   b  and third heat transfer tube  20   c  and in which the heat exchanging fluid flows. Airflow path region RP and second airflow path region RP 2  are disposed with second heat transfer tube  20   b  being interposed therebetween. 
     As shown in  FIG. 4 , in airflow path region RP, a first region R 1  is defined to represent a region in which first heat transfer tube  20   a  and second heat transfer tube  20   b  are connected in the shortest distance. First region R 1  is a region disposed on fin  30  between imaginary line L 5   a  obtained by extending the upper flat surface of first heat transfer tube  20   a  and imaginary line L 4   b  obtained by extending the lower flat surface of second heat transfer tube  20   b  in the z direction, and between first imaginary line segment L 1   a  and third imaginary line L 6   b  in the flow direction. First region R 1  has a rectangular shape. Further, in airflow path region RP, a second region R 2  is defined to represent a region disposed between first region R 1  and windward region RW, and a third region R 3  is defined to represent a region disposed between first region R 1  and leeward region RL. 
     As shown in  FIG. 3 , first imaginary line segment L 1   a  is an imaginary line segment that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance and that is drawn at the most windward side in the x direction. In other words, first imaginary line segment L 1   a  is drawn at the most windward side on first region R 1 , and constitutes one side of first region R 1 . Second imaginary line segment L 1   b  is an imaginary line segment that connects, in the shortest distance, between second heat transfer tube  20   b  and third heat transfer tube  20   c  disposed above second heat transfer tube  20   b  and adjacent to second heat transfer tube  20   b . Second imaginary line segment L 1   b  is an imaginary line segment drawn at the most windward side in the x direction. Imaginary center line L 2   a  is an imaginary line that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance and that is drawn at the leeward side relative to first imaginary line segment L 1   a . Imaginary center line L 2   a  passes through the leeward side relative to the center of first region R 1  in the long side direction. Each of the imaginary lines that connect between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance, such as first imaginary line segment L 1   a  and imaginary center line L 2   a , is drawn on first region R 1 . 
     As shown in  FIG. 3 , in airflow path region RP, clearance portion  41   a  that separates between first heat transfer tube  20   a  and fin  30  is disposed at the windward side relative to imaginary center line L 2   a . Clearance portion  41   a  is disposed not to overlap with imaginary center line L 2   a . Clearance portion  41   a  is formed as a through hole extending through fin  30  in the y direction, for example. Clearance portion  41   a  may have any configuration as long as a heat path between first heat transfer tube  20   a  and fin  30  facing clearance portion  41   a  can be made longer than a heat path between first heat transfer tube  20   a  and fin  30  not facing clearance portion  41   a . For example, clearance portion  41   a  may be configured as a portion depressed with respect to a plane perpendicular to the y direction in fin  30 . 
     As shown in  FIG. 3 , clearance portion  41   b  is disposed at the windward side relative to imaginary center line L 2   b  of second heat transfer tube  20   b , for example. Clearance portion  41   b  is disposed not to overlap with imaginary center line L 2   b  of second heat transfer tube  20   b , for example. 
     As shown in  FIG. 3 , clearance portion  41   a  is disposed to overlap with first imaginary line segment L 1   a , for example. Clearance portion  41   a  faces a portion of each of the upper flat surface and first surface of first heat transfer tube  20   a , for example. When seen in the y direction, clearance portion  41   a  is disposed to span first region R 1  and second region R 2 , for example. That is, clearance portion  41   a  faces a portion of the upper flat surface of first heat transfer tube  20   a  located at the most windward side. It should be noted that when seen in the y direction, clearance portion  41   a  may be disposed to span first region R 1 , second region R 2 , and windward region RW, for example. 
     Although clearance portion  41   a  may have any planar shape when seen in the y direction, clearance portion  41   a  has a sector shape centering on a portion of first heat transfer tube  20   a  located on first imaginary line segment L 1   a , i.e., first boundary portion  25   a  as shown in  FIG. 3 , for example. The width of clearance portion  41   a  in the short side direction is the widest on first imaginary line segment L a, for example. The width of clearance portion  41   a  in the long side direction is the widest on imaginary line L 5   a , for example. In other words, the widest portion of clearance portion  41   a  in the long side direction is a portion of clearance portion  41   a  facing first heat transfer tube  20   a , for example. The width of clearance portion  41   a  in the short side direction becomes gradually narrower as clearance portion  41   a  is further away from first imaginary line segment L 1   a  in the long side direction, for example. The width of clearance portion  41   a  in the long side direction becomes gradually narrower as clearance portion  41   a  is further away from first heat transfer tube  20   a  in the short side direction, for example. 
     As shown in  FIG. 3 , since clearance portion  41   a  is disposed, a width W 1  of fin  30  on first imaginary line segment L 1   a  is shorter than width W 2  of fin  30  on any imaginary line that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance without clearance portion  41   a  being interposed therebetween in first region R 1 , such as imaginary center line L 2   a.    
     As shown in  FIG. 3 , width W 1  of fin  30  on first imaginary line segment L 1   a  is shorter than the width of fin  30  on any imaginary line that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance in first region R 1 , such as an imaginary line that is located at the leeward side relative to first imaginary line segment L 1   a  and that is drawn to overlap with clearance portion  41   a.    
     As shown in  FIG. 3 , when seen in the y direction, the maximum width of clearance portion  41   a  is less than the width of first heat transfer tube  20   a  in the short side direction, for example. The length, in the long side direction, of a portion of the upper flat surface of first heat transfer tube  20   a  that faces clearance portion  41   a  is shorter than the length, in the long side direction, of a portion thereof that is located at the leeward side relative to the foregoing portion and that faces fin  30 , for example. 
     As shown in  FIG. 3 , in second airflow path region RP 2 , clearance portion  41   b  that separates between second heat transfer tube  20   b  and fin  30  is disposed to overlap with second imaginary line segment L 1   b . Clearance portion  41   b  has the same configuration as that of clearance portion  41   a . From a different viewpoint, it can be said that second heat transfer tube  20   b  has the same configuration as that of first heat transfer tube  20   a  with regard to a relation with third heat transfer tube  20   c . Two adjacent heat transfer tubes in the gravity direction among the plurality of heat transfer tubes of first heat exchanger  11  have the same configurations as those of first heat transfer tube  20   a  and second heat transfer tube  20   b . In first heat exchanger  11  shown in  FIG. 3  and  FIG. 4 , the number of clearance portions disposed in one fin  30  is equal to the number of heat transfer tubes. 
     In each of the plurality of fins  30 , clearance portions  41   a ,  41   b  such as those shown in  FIG. 3  are disposed when fin  30  is seen in a plan view. Clearance portion  41   a  of one fin  30  is disposed to overlap with a clearance portion  41   a  of another fin  30  in the y direction. In other words, respective ones of the plurality of clearance portions disposed in one fin  30  are disposed to overlap with respective ones of the clearance portions disposed in the other fin  30  in the y direction. That is, in first heat exchanger  11 , a plurality of groups of clearance portions are provided to be separated from each other in the z direction with each of the groups being constituted of a plurality of clearance portions disposed to overlap in the y direction. 
     As shown in  FIG. 5 , each of first heat transfer tube  20   a  and second heat transfer tube  20   b  is joined to fin  30  via a brazing material  33 , except for a region facing clearance portion  41   a  or clearance portion  41   b . Fin  30  has fin collar portions  32  provided around the through holes of fin  30  in which first heat transfer tube  20   a  and second heat transfer tube  20   b  are inserted. Each of fin collar portions  32  has a structure obtained by bending fin  30  with respect to a main plate portion  31  thereof having a surface perpendicular to the y direction. Fin collar portions  32  are also provided at regions facing clearance portions  41   a ,  41   b . Fin collar portions  32  not facing clearance portions  41   a ,  41   b  are in contact with first heat transfer tube  20   a  and second heat transfer tube  20   b , and a fillet is formed therebetween by brazing material  33 . Accordingly, first heat transfer tube  20   a  and second heat transfer tube  20   b  are joined to fin  30  by way of the metal. A close contact area (joining area) between fin  30  and each of first heat transfer tube  20   a  and second heat transfer tube  20   b  is provided to be wide by way of the metal joining with brazing material  33 , whereby excellent heat transfer can be attained therebetween. That is, heat transfer from first heat transfer tube  20   a  to fin  30  located on the above-described imaginary line (for example, imaginary center line L 2   a ) that is located at the leeward side relative to first imaginary line segment L 1   a  and that does not overlap with clearance portion  41   a  is performed efficiently in the shortest path. 
     On the other hand, fin collar portions  32  facing clearance portions  41   a ,  41   b  are disposed to be separated from first heat transfer tube  20   a  and second heat transfer tube  20   b . They are not joined via brazing material  33 . That is, no brazing material  33  is provided in clearance portion  41   a  between first heat transfer tube  20   a  and fin collar portion  32  on first imaginary line segment L 1   a . In clearance portion  41   a , portions of the upper flat surface and first surface of first heat transfer tube  20   a  are exposed. Hence, heat transfer from first heat transfer tube  20   a  to fin  30  located on first imaginary line segment L 1   a  via the shortest path is inhibited by clearance portion  41   a.    
     Clearance portions  41   a ,  41   b  can be formed by any method, but are formed simultaneously with the forming of fin collar portions  32 , for example. Moreover, clearance portions  41   a ,  41   b  can be used as regions in which bar-like brazing materials are disposed, when joining first heat transfer tube  20   a  and second heat transfer tube  20   b  to the plurality of fins  30 . The bar-like brazing materials are prepared to correspond to the number of the clearance portions disposed on one fin  30 , for example. The length of each bar-like brazing material in the extending direction is equal to the length of first heat exchanger  11  in the y direction, for example. Each bar-like brazing material is provided to be insertable in a group of clearance portions disposed to be continuous in the y direction. After the bar-like brazing material is inserted in the group of clearance portions, the bar-like brazing material is heated and melted to be permeated into a portion located between heat transfer tube  20  and fin  30  and disposed to be continuous to each clearance portion, i.e., into fin collar portion  32 . Then, the brazing material is cooled to be solidified, whereby heat transfer tube  20  and fin  30  are joined firmly as shown in  FIG. 5 . 
     &lt;Operations of Air Conditioner and Outdoor Heat Exchanger&gt; 
     Next, operations of refrigeration cycle apparatus  1  and outdoor heat exchanger  10  will be described. Refrigeration cycle apparatus  1  is provided to perform the cooling operation, the heating operation, and the defrosting operation. In refrigeration cycle apparatus  1 , each of the cooling operation and the defrosting operation, and the heating operation are switched by switching the refrigerant circuit by four-way valve  7 . It should be noted that in  FIG. 1 , a broken line arrow represents a flow direction of the refrigerant during the cooling operation and the defrosting operation, and a solid line arrow represents a flow direction of the refrigerant during the heating operation. 
     During the cooling operation of refrigeration cycle apparatus  1 , a refrigerant circuit is formed in which compressor  2 , outdoor heat exchanger  10 , throttle device  5 , and indoor heat exchanger  3  are connected in this order. High-temperature and high-pressure single-phase gas refrigerant discharged from compressor  2  flows, via four-way valve  7 , into outdoor heat exchanger  10  functioning as a condenser. In outdoor heat exchanger  10 , heat exchange is performed between the high-temperature high-pressure gas refrigerant thus having flowed thereinto and air supplied by outdoor fan  6 , whereby the high-temperature high-pressure gas refrigerant is condensed into single-phase high-pressure liquid refrigerant. The high-pressure liquid refrigerant sent out from outdoor heat exchanger  10  is formed, by throttle device  5 , into two-phase state refrigerant including low-pressure gas refrigerant and liquid refrigerant. The two-phase state refrigerant flows into indoor heat exchanger  3  functioning as an evaporator. In indoor heat exchanger  3 , heat exchange is performed between the two-phase state refrigerant thus having flowed thereinto and air supplied by indoor fan  4 , whereby the liquid refrigerant of the two-phase state refrigerant is evaporated into single-phase low-pressure gas refrigerant. With this heat exchange, inside of a room is cooled. The low-pressure gas refrigerant sent out from indoor heat exchanger  3  flows into compressor  2  via four-way valve  7 , is compressed into high-temperature high-pressure gas refrigerant, and is discharged again from compressor  2 . Thereafter, this cycle is repeated. 
     During the heating operation of refrigeration cycle apparatus  1 , a refrigerant circuit is formed in which compressor  2 , indoor heat exchanger  3 , throttle device  5 , and outdoor heat exchanger  10  are connected in this order. High-temperature and high-pressure single-phase gas refrigerant discharged from compressor  2  flows, via four-way valve  7 , into indoor heat exchanger  3  functioning as a condenser. In indoor heat exchanger  3 , heat exchange is performed between the high-temperature high-pressure gas refrigerant thus having flowed thereinto and air supplied by indoor fan  4 , whereby the high-temperature high-pressure gas refrigerant is condensed into single-phase high-pressure liquid refrigerant. With this heat exchange, inside of a room is heated. The high-pressure liquid refrigerant sent out from indoor heat exchanger  3  is formed, by throttle device  5 , into two-phase state refrigerant including low-pressure gas refrigerant and liquid refrigerant. The two-phase state refrigerant flows into outdoor heat exchanger  10  functioning as an evaporator. In outdoor heat exchanger  10 , heat exchange is performed between the two-phase state refrigerant thus having flowed thereinto and air supplied by outdoor fan  6 , whereby the liquid refrigerant of the two-phase state refrigerant is evaporated into single-phase low-pressure gas refrigerant. 
     The low-pressure gas refrigerant sent out from outdoor heat exchanger  10  flows into compressor  2  via four-way valve  7 , is compressed into high-temperature high-pressure gas refrigerant, and is discharged again from compressor  2 . Thereafter, this cycle is repeated. 
     During the heating operation, a water content included in outdoor air is condensed by outdoor heat exchanger  10  functioning as an evaporator, whereby condensed water is generated on surfaces of the plurality of heat transfer tubes  20  and the plurality of plate-like fins  30 . The condensed water falls down via the surfaces of heat transfer tubes  20  and fins  30 , and is discharged to below the evaporator as drain water. Here, each of the plurality of heat transfer tubes  20  is inclined downward in the gravity direction from the windward side to the leeward side in the flow direction. Hence, the condensed water having reached the surfaces of heat transfer tubes  20  are efficiently discharged from outdoor heat exchanger  10 . Furthermore, outdoor heat exchanger  10  has a high frost formation resistance (details will be described later). 
     However, part of the condensed water may become frost and the frost may be adhered to outdoor heat exchanger  10 . The frost adhered to outdoor heat exchanger  10  inhibits heat exchange between the refrigerant and the outdoor air, with the result that the heating efficiency of refrigeration cycle apparatus  1  is decreased. Hence, refrigeration cycle apparatus  1  is provided to perform the defrosting operation for melting the frost adhered to outdoor heat exchanger  10 . 
     During the defrosting operation of refrigeration cycle apparatus  1 , the same refrigerant circuit as that during the cooling operation is formed. The refrigerant compressed in compressor  2  is sent to outdoor heat exchanger  10  to heat and melt the frost adhered to outdoor heat exchanger  10 . Accordingly, the frost adhered to outdoor heat exchanger  10  during the heating operation is melted into water by the defrosting operation. The melt water is effectively discharged from outdoor heat exchanger  10 . It should be noted that during the defrosting operation, indoor fan  4  and outdoor fan  6  are made non-operational, for example. 
     &lt;Function and Effect&gt; 
     Next, with reference to  FIG. 6  and  FIG. 7 , the following describes function and effect of heat exchanger  10  based on a comparison with a comparative example.  FIG. 6  is a partial enlarged view showing the configuration of heat exchanger  10  and a heat flux distribution representing an amount of exchanged heat per unit area on fin  30 .  FIG. 7  is a partial enlarged view showing a configuration of the comparative example and a heat flux distribution representing an amount of exchanged heat per unit area on a fin  130 . Each of annular point lines shown in  FIG. 6  and  FIG. 7  indicates a heat flux contour line representing the amount of exchanged heat per unit area on the fin. It should be noted that since there is generally a correlation between heat transfer and mass transfer, it is considered that the heat flux has a correlation with an amount of mass transfer per unit area, i.e., mass flux indicating a local frost formation amount. 
     The heat exchanger of the comparative example shown in  FIG. 7  is different from heat exchanger  10  in terms of the configuration of the clearance portion. In the comparative example, a clearance portion  140   a  that separates between a first heat transfer tube  120   a  and fin  30  is disposed to face an airflow path region between first heat transfer tube  120   a  and a second heat transfer tube  120   b . Clearance portion  140   a  is disposed at the leeward side relative to imaginary center line L 2   a  that passes through the center of first heat transfer tube  120   a  in the long side direction and that extends along the short side direction. Clearance portion  140   a  is provided as part of a discharge path for condensed water. 
     When the heat exchanger of the comparative example is operated as an evaporator, the temperature of the refrigerant serving as a target heat exchanging fluid is lower than the temperature of the air serving as a heat exchanging fluid. Therefore, the surface temperature of heat transfer tube  120   a  in which the refrigerant flows is lower than the surface temperature of fin  130  in the airflow path region through which the air flows. Since heat transfer between heat transfer tube  120   a  and fin  130  is performed from fin  130  to heat transfer tube  120   a , the surface temperature of fin  130  indicates a distribution according to a distance between fin  130  and heat transfer tube  120   a . Moreover, when flowing from the windward side to the leeward side via heat transfer tube  130  in which the refrigerant serving as a target heat exchanging fluid flows, the air is cooled and the water content in the air is condensed. Hence, the temperature and absolute humidity of the air supplied to the windward side in the fin and tube type heat exchanger is higher than the temperature and absolute humidity of the air passing at the leeward side. 
     By taking the above surface temperature distribution and the temperature and humidity distribution of the air into consideration, a heat flux (mass flux) distribution shown in  FIG. 7  is found. In the comparative example shown in  FIG. 7 , first heat transfer tube  120   a  and fin  130  located at the windward side relative to imaginary center line L 2   a  are connected in the shortest distance. Therefore, in the region located at the windward side relative to imaginary center line L 2   a , the heat flux contour line is disposed more densely and more widely from one of first heat transfer tube  120   a  and second heat transfer tube  120   b  to the other than that in the region located at the leeward side relative to imaginary center line L 2   a . Therefore, in the comparative example, a temperature difference between fin  130  and the air in the whole of the region located at the windward side relative to imaginary center line L 2   a  and including imaginary line L 3  becomes large to such an extent that frost is formed. 
     Particularly, on imaginary line L 3 , the temperature difference between fin  130  and the air is the maximum on first imaginary line segment L 1   a , i.e., the temperature difference therebetween is the maximum on an intersection between first imaginary line segment L 1   a  and imaginary line L 3 . This is due to the following reason: fin  130  on the intersection is connected to first heat transfer tube  120   a  and second heat transfer tube  120   b  in the shortest distance and is therefore sufficiently cooled, whereas air having a comparatively high temperature is supplied onto the intersection to result in a large temperature difference between fin  130  and the air on the intersection. 
     Hence, in the comparative example, frost is likely to be formed also on imaginary line L 3 , with the result that airflow path region RP is likely to be blocked by the frost. Clearance portion  140   a  cannot sufficiently suppress such blocking. This makes it difficult for the heat exchanger of the comparative example to exhibit sufficient evaporation performance during the heating operation, thus resulting in decreased performance (heating performance) at the indoor unit side. 
     On the other hand, as shown in  FIG. 6 , heat exchanger  10  includes: plate-like fin  30 ; and first heat transfer tube  20   a  and second heat transfer tube  20   b  that each extend through fin  30  and that are adjacent to each other in the gravity direction. In the cross section perpendicular to the first direction in which first heat transfer tube  20   a  and second heat transfer tube  20   b  extend, the outer shape of each of first heat transfer tube  20   a  and second heat transfer tube  20   b  is a flat shape. First heat transfer tube  20   a  is disposed below second heat transfer tube  20   b . The portion to which fin  30  and first heat transfer tube  20   a  are connected, and clearance portion  41   a  that separates between fin  30  and first heat transfer tube  20   a  are disposed between first heat transfer tube  20   a  and fin  30 . Clearance portion  41   a  is disposed at the windward side in the flowing direction relative to imaginary center line L 2   a  that passes through the center of first heat transfer tube  20   a  in the long side direction and that extends along the short side direction. 
     In heat exchanger  10  shown in  FIG. 6 , portions of first heat transfer tube  20   a  and fin  30  located at the windward side relative to imaginary center line L 2   a  are connected to each other with clearance portion  41   a  being interposed therebetween, and the other portions thereof are connected directly to each other without clearance portion  41   a  being interposed therebetween. Therefore, a heat path between first heat transfer tube  20   a  and fin  30  connected to each other with clearance portion  41   a  being interposed therebetween becomes longer than a heat path between first heat transfer tube  20   a  and fin  30  connected directly to each other without clearance portion  41   a  being interposed therebetween. As a result, the heat flux contour line shown in  FIG. 6  is depressed toward the first heat transfer tube  20   a  side at a region of fin  30  overlapping, in the short side direction, with clearance portion  41   a  disposed at the windward side relative to imaginary center line L 2   a . That is, according to heat exchanger  10 , the temperature of fin  30  located at the windward side relative to imaginary center line L 2   a  during its operation as an evaporator, particularly, the temperature of fin  30  overlapping with clearance portion  41   a  in the short side direction and located on imaginary line L 3  can be higher than that in the comparative example. Accordingly, in heat exchanger  10 , frost formation in airflow path region RP, particularly, frost formation on imaginary line L 3  can be suppressed as compared with the comparative example. Hence, airflow path region RP can be suppressed from being blocked by the frost. As a result, heat exchanger  10  can exhibit sufficient evaporation performance during the heating operation, whereby performance (heating performance) at the indoor unit side can be suppressed from being decreased. 
     Further, in clearance portion  41   a  of heat exchanger  10 , portions of the upper flat surface and first surface of first heat transfer tube  20   a  are exposed. Accordingly, according to heat exchanger  10 , during its operation as an evaporator, frost can be intensively generated on the surfaces of first heat transfer tube  20   a  exposed in clearance portion  41   a , whereby the flow path for the heat exchanging fluid can be suppressed more effectively from being blocked by frost. 
     Further, first heat transfer tube  20   a  and second heat transfer tube  20   b  are inclined such that leeward side end portions  22   a .  22   b  are located at the lower side relative to windward side end portions  21   a .  21   b  in the z direction. Accordingly, according to heat exchanger  10 , for example, even when no air is supplied from outdoor fan  6  shown in  FIG. 1  during the defrosting operation, water droplets adhered on the surfaces of first heat transfer tube  20   a  and second heat transfer tube  20   b  flow out to the leeward side due to gravity, and are discharged via the leeward region. 
     Accordingly, heat exchanger  10  has a high water discharging characteristic. 
     In heat exchanger  10 , clearance portion  41   a  is disposed to overlap with the first imaginary line segment that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance and that is drawn at the most windward side in the flowing direction. 
     Therefore, fin  30  and first boundary portion  25   a  of first heat transfer tube  20   a  located on first imaginary line segment L 1   a  are connected with clearance portion  41   a  being interposed therebetween, and are therefore not connected to each other in the shortest distance. That is, heat transfer from first heat transfer tube  20   a  to fin  30  located on first imaginary line segment L 1   a  is inhibited from being performed via the shortest path, by clearance portion  41   a  disposed to overlap with first imaginary line segment L 1   a . Accordingly, according to heat exchanger  10 , the temperature of fin  30  located on first imaginary line segment L 1   a  during its operation as an evaporator, such as the temperature of fin  30  located on the intersection between first imaginary line segment L 1   a  and imaginary line L 3 , can be higher than that in the comparative example. As a result, in heat exchanger  10 , as compared with the comparative example, the flow path for the heat exchanging fluid can be suppressed effectively from being blocked by frost. 
     In heat exchanger  10 , the width of fin  30  on first imaginary line segment L 1   a  is shorter than the width of fin  30  on imaginary center line L 2   a  that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance and that passes through the center of first heat transfer tube  20   a . Fin  30  facing airflow path region RP and located at least on imaginary center line L 2   a  is connected to first heat transfer tube  20   a  in the shortest distance. Accordingly, heat can be efficiently exchanged with first heat transfer tube  20   a . That is, according to heat exchanger  10 , sufficient heat exchanging performance can be secured while effectively suppressing the flow path for the heat exchanging fluid from being blocked by frost during its operation as an evaporator as compared with the conventional heat exchanger. 
     In heat exchanger  10 , the width of clearance portion  41   a  in the direction along first imaginary line segment L 1   a  is the maximum on first imaginary line segment L 1   a.    
     In this way, heat exchange between fin  30  and first heat transfer tube  20   a  on the region not overlapping with first imaginary line segment L a is not greatly inhibited by clearance portion  41   a . Therefore, according to heat exchanger  10 , sufficient heat exchanging performance can be secured while effectively suppressing the flow path for the heat exchanging fluid from being blocked by frost during its operation as an evaporator as compared with the conventional heat exchanger. 
     Each of first heat transfer tube  20   a  and second heat transfer tube  20   b  of heat exchanger  10  has: the upper flat surface and lower flat surface disposed in parallel to be separated from each other in the short side direction in the cross section; and the first surface and second surface, the first surface connecting the upper flat surface to the lower flat surface at the windward side, the second surface connecting the upper flat surface to the lower flat surface at the leeward side in the flowing direction. First imaginary line segment L 1   a  passes through first boundary portion  25   a  between the upper flat surface and first surface of first heat transfer tube  20   a . Clearance portion  41   a  faces the upper flat surface and first surface of first heat transfer tube  20   a.    
     In this way, in a method for manufacturing heat exchanger  10 , when clearance portion  41   a  is used as an insertion portion for the bar-like brazing material, the melted brazing material can be spread widely via the upper flat surface and can be spread widely via the first surface. As a result, a fillet can be uniformly formed using brazing material  33  around first heat transfer tube  20   a.    
     Refrigeration cycle apparatus  1  includes: heat exchanger  10 ; and fan  6  configured to blow the heat exchanging fluid to heat exchanger  10 . In such a refrigeration cycle apparatus  1 , when heat exchanger  10  is used as an evaporator, heat exchanger  10  can exhibit high evaporation performance as described above. Hence, higher heating performance can be exhibited than that in a refrigeration cycle apparatus including the heat exchanger of the comparative example. 
     From a viewpoint that does not take into consideration a manner in which heat exchanger  10  is disposed within refrigeration cycle apparatus  1 , it can be said that the first end portion (windward side end portion  21   a ) of first heat transfer tube  20   a  located at the one end  30   a  side of fin  30  in the x direction is disposed at the one side in the z direction relative to the second end portion (leeward side end portion  22   a ) of first heat transfer tube  20   a  located at the other end  30   b  side of fin  30  in the x direction. The third end portion (windward side end portion  21   b ) of second heat transfer tube  20   b  located at the one end  30   a  side in the x direction is disposed at the one side in the z direction relative to the fourth end portion (leeward side end portion  22   b ) located at the other end  30   b  side of fin  30  in the x direction. The distance in the z direction between the first end portion (windward side end portion  21   a ) of first heat transfer tube  20   a  and the fourth end portion (leeward side end portion  22   b ) of second heat transfer tube  20   b  is shorter than the distance in the z direction between the second end portion (leeward side end portion  22   a ) of first heat transfer tube  20   a  and the third end portion (windward side end portion  21   b ) of second heat transfer tube  20   b . In the x direction, clearance portion  41   a  is disposed at the one end  30   a  side relative to imaginary center line L 2   a  that passes through the center of first heat transfer tube  20   a  in the long side direction and that extends along the short side direction. 
     As described above, heat exchanger  10  serving as an outdoor heat exchanger in refrigeration cycle apparatus  1  is disposed such that: the x direction is along the direction of flow of the heat exchanging fluid caused by outdoor fan  6 ; one end  30   a  of fin  30  in the x direction is disposed at the windward side of the heat exchanging fluid, and the z direction is along the gravity direction. Accordingly, the first end portion of first heat transfer tube  20   a  and the third end portion of second heat transfer tube  20   b  are disposed at the windward side and serve as windward side end portions  21   a ,  21   b , and the second end portion of first heat transfer tube  20   a  and the fourth end portion of second heat transfer tube  20   b  are disposed at the leeward side, and serve as leeward side end portions  22   a ,  22   b . Further, first heat transfer tube  20   a  is disposed below second heat transfer tube  20   b.    
     Second Embodiment 
     As shown in  FIG. 8 , a heat exchanger  10 A according to a second embodiment includes basically the same configuration as that of heat exchanger  10  according to the first embodiment, but is different therefrom in that a clearance portion  42   b  provided to face airflow path region RP faces the lower flat surface of second heat transfer tube  20   b.    
     Clearance portion  42   b  faces only the lower flat surface of the surfaces of second heat transfer tube  20   b , for example. Clearance portion  42   b  does not face the first surface of second heat transfer tube  20   b , for example. Although clearance portion  42   b  may have any planar shape when seen in the y direction, clearance portion  42   b  has a sector shape centering on a portion of second heat transfer tube  20   b  located on first imaginary line segment L 1   a  as shown in  FIG. 8 , for example. Clearance portion  42   b  is provided in line symmetry with respect to first imaginary line segment L 1   a  in the long side direction, for example. 
     As shown in  FIG. 8 , since clearance portion  42   b  is disposed, width W 3  of fin  30  on first imaginary line segment L 1   a  is shorter than width W 2  of fin  30  on any imaginary line that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance without clearance portion  42   b  being interposed therebetween in first region R 1 , such as imaginary center line L 2   a.    
     A clearance portion  42   a  facing the lower flat surface of first heat transfer tube  20   a  includes the same configuration as that of clearance portion  42   b . Clearance portion  42   a  is disposed at the windward side relative to an imaginary center line of another heat transfer tube (not shown) disposed adjacent to first heat transfer tube  20   a  at a lower position in the gravity direction, and is disposed to overlap with a first imaginary line in the other heat transfer tube. Clearance portion  42   a  is disposed at the windward side relative to imaginary center line L 2   a  of first heat transfer tube  20   a , for example. Clearance portion  42   a  is disposed to overlap with imaginary center line L 2   b  of second heat transfer tube  20   b , for example. 
     According to such a heat exchanger  10 A, clearance portion  42   b  is disposed at the windward side relative to imaginary center line L 2   a  in airflow path region RP, and is also disposed to overlap with first imaginary line segment L 1   a . Hence, the same effect as that of heat exchanger  10  can be exhibited. That is, in heat exchanger  10 A, as compared with the comparative example shown in  FIG. 7 , the flow path for the heat exchanging fluid can be suppressed effectively from being blocked by frost. 
     Third Embodiment 
     As shown in  FIG. 9 , a heat exchanger  10 B according to a third embodiment includes basically the same configuration as those of heat exchanger  10  according to the first embodiment and heat exchanger  10 A according to the second embodiment, but is different therefrom in that a clearance portion  43   b  provided to face airflow path region RP is not disposed to overlap with first imaginary line segment L 1   a  and is disposed at the windward side relative to first imaginary line segment L 1   a.    
     Clearance portion  43   b  is disposed to overlap with second imaginary line segment L 1   b , for example. Clearance portion  43   b  faces the lower flat surface of second heat transfer tube  20   b  and the first surface of second heat transfer tube  20   b , for example. Although clearance portion  43   b  may have any planar shape when seen in the y direction, clearance portion  43   b  has a sector shape centering on a portion of second heat transfer tube  20   b  located on first imaginary line segment L 1   a , i.e., fourth boundary portion  26   b  as shown in  FIG. 9 , for example. 
     A clearance portion  43   a  facing the lower flat surface of first heat transfer tube  20   a  includes the same configuration as that of clearance portion  43   b . Clearance portion  43   a  is disposed at the windward side relative to a first imaginary center line of another heat transfer tube (not shown) disposed adjacent to first heat transfer tube  20   a  at a lower position in the gravity direction, and is disposed to overlap with a first imaginary line segment L 1   a  of first heat transfer tube  20   a.    
     According to such a heat exchanger  10 B, clearance portion  43   b  is disposed at the windward side relative to imaginary center line L 2   a  in airflow path region RP, and is also disposed to overlap with first imaginary line segment L 1   a . Hence, the same effect as that of heat exchanger  10  can be exhibited. That is, in heat exchanger  10 B, as compared with the comparative example shown in  FIG. 7 , the flow path for the heat exchanging fluid can be suppressed effectively from being blocked by frost. 
     Fourth Embodiment 
     As shown in  FIG. 10 , a heat exchanger  10 C according to a fourth embodiment includes basically the same configuration as that of heat exchanger  10  according to the first embodiment, but is different therefrom in that a plurality of clearance portions (a first clearance portion  44   a  and a second clearance portion  45   b ) are disposed in one airflow path region RP. 
     The plurality of clearance portions include: first clearance portion  44   a  that faces the upper flat surface of first heat transfer tube  20   a ; and second clearance portion  45   b  that is disposed to be separated from first clearance portion  44   a  in the short side direction and that faces the lower flat surface of second heat transfer tube  20   b.    
     First clearance portion  44   a  includes the same configuration as that of clearance portion  41   a  shown in  FIG. 3 . Second clearance portion  45   b  includes the same configuration as that of clearance portion  42   b  shown in  FIG. 8 . First clearance portion  44   a  and second clearance portion  45   b  are disposed to be separated from each other in the short side direction. First clearance portion  44   a  and second clearance portion  45   b  are disposed to overlap with first imaginary line segment L 1   a.    
     As shown in  FIG. 10 , since clearance portion  41   a  is disposed, width W 4  of fin  30  on first imaginary line segment L 1   a  is shorter than width W 2  of fin  30  on any imaginary line that connects between first heat transfer tube  20   a  and second heat transfer tube  20   b  in the shortest distance without first clearance portion  44   a  and second clearance portion  45   b  being interposed therebetween in first region R 1 , such as imaginary center line L 2   a . Width W 4  is shorter than width W 1  in heat exchanger  10  shown in  FIG. 3  by the width of second clearance portion  45   b  in the short side direction. 
     Moreover, width W 4  is shorter than width W 3  in heat exchanger  10  shown in  FIG. 8  by the width of first clearance portion  44   a  in the short side direction. Fin  30  on the intersection between first imaginary line segment L 1   a  and imaginary line L 3  is connected to first heat transfer tube  20   a  with first clearance portion  44   a  being interposed therebetween, and is connected to second heat transfer tube  20   b  with second clearance portion  45   b  being interposed therebetween. 
     In another airflow path region adjacent to airflow path region RP with first heat transfer tube  20   a  being interposed therebetween, a second clearance portion  45   a  facing the lower flat surface of first heat transfer tube  20   a  is disposed. As shown in  FIG. 10 , first clearance portion  44   a  facing the upper flat surface of first heat transfer tube  20   a  and second clearance portion  45   a  facing the lower flat surface of first heat transfer tube  20   a  are disposed not to overlap with each other in the short side direction, for example. It should be noted that respective portions of first clearance portion  44   a  and second clearance portion  45   a  may be disposed to overlap with each other in the short side direction. 
     Clearance portion  44   b  includes the same configuration as that of clearance portion  41   b  shown in  FIG. 3 . Clearance portion  45   a  includes the same configuration as that of clearance portion  42   a  shown in  FIG. 8 . 
     According to such a heat exchanger  10 C, since first clearance portions  44   a ,  44   b  including the same configurations as those of clearance portions  41   a ,  41   b  of heat exchanger  10  and clearance portions  45   a ,  45   b  including the same configurations as those of clearance portions  42   a ,  42   b  of heat exchanger  10 A are provided, the same effects as those of heat exchanger  10  and heat exchanger  10 A can be exhibited. 
     Further, according to heat exchanger  10 C, fin  30  on the intersection between first imaginary line segment L 1   a  and imaginary line L 3  is connected to first heat transfer tube  20   a  with first clearance portion  44   a  being interposed therebetween, and is connected to second heat transfer tube  20   b  with second clearance portion  45   b  being interposed therebetween. Accordingly, according to heat exchanger  10 C, frost can be suppressed from being adhered to fin  30  on the intersection as compared with heat exchangers  10 ,  10 A, whereby the flow path for the heat exchanging fluid can be suppressed more effectively from being blocked by frost. 
     Although the embodiments of the present invention have been illustrated as described above, the above-described embodiments can be modified in various manners. 
     Moreover, the scope of the present invention is not limited to the above-described embodiments. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.