Patent Publication Number: US-2022214085-A1

Title: Evaporator and refrigeration cycle apparatus including the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to an evaporator of a refrigeration cycle apparatus in which a non-azeotropic refrigerant mixture is enclosed. 
     BACKGROUND 
     As an evaporator of a refrigeration cycle apparatus, there is an evaporator in a form in which a plurality of heat transfer tubes are unevenly distributed more on either one of the windward side and the leeward side of the center of a heat transfer fin. For example, the evaporator described in PTL 1 (WO2017/183180) is a stack-type heat exchanger in which elongated holes each having a longitudinal diameter extending in the width direction of a fin are provided at a predetermined interval in a direction orthogonal to the width direction and the thickness direction of the fin and in which a flat pipe is inserted into each of the elongated holes. 
     SUMMARY 
     An evaporator according to one or more embodiments is an evaporator of a refrigeration cycle apparatus in which a non-azeotropic refrigerant mixture is enclosed, the evaporator including a plurality of fins and a plurality of heat transfer tubes. The plurality of fins are arranged at a predetermined interval in a plate thickness direction (a fin direction). The plurality of heat transfer tubes extend through the plurality of fins in the plate thickness direction. In the evaporator, a first heat exchange section is formed. In the first heat exchange section, when the plurality of heat transfer tubes are viewed as a heat-transfer-tube group in the plate thickness direction of the fins, a distribution center of the heat-transfer-tube group in an airflow direction is positioned on the leeward side of the center of the fins in the airflow direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an air conditioning apparatus as a refrigeration apparatus according to one or more embodiments of the present disclosure. 
         FIG. 2  is a schematic front view of an indoor heat exchanger. 
         FIG. 3  is an external perspective view of an outdoor heat exchanger. 
         FIG. 4  is a P-H diagram of a non-azeotropic refrigerant mixture. 
         FIG. 5A  is a perspective view of a first heat exchange section of an outdoor heat exchanger according to first embodiments. 
         FIG. 5B  is a perspective view of a second heat exchange section of the outdoor heat exchanger according to the first embodiments. 
         FIG. 6A  is a schematic perspective view of an outdoor heat exchanger that uses both the first heat exchange section and the second heat exchange section. 
         FIG. 6B  is a schematic perspective view of a different outdoor heat exchanger that uses both the first heat exchange section and the second heat exchange section. 
         FIG. 7A  is a perspective view of a first heat exchange section of an outdoor heat exchanger according to second embodiments. 
         FIG. 7B  is a perspective view of a second heat exchange section of the outdoor heat exchanger according to the second embodiments. 
         FIG. 7C  is a perspective view of a third heat exchange section of an outdoor heat exchanger according to a modification of the second embodiments. 
         FIG. 8A  is a perspective view of a first heat exchange section of an outdoor heat exchanger according to third embodiments. 
         FIG. 8B  is a perspective view of a second heat exchange section of the outdoor heat exchanger according to the third embodiments. 
         FIG. 8C  is a perspective view of a third heat exchange section of an outdoor heat exchanger according to a modification of the third embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiments 
     (1) Configuration of Air Conditioning Apparatus  1   
       FIG. 1  is a schematic diagram of an air conditioning apparatus  1  according to one or more embodiments of the present disclosure. In  FIG. 1 , the air conditioning apparatus  1  is a refrigeration apparatus that performs cooling operation and heating operation by a vapor compression refrigeration cycle. 
     A refrigerant circuit  10  of the air conditioning apparatus  1  is constituted by an outdoor unit  2  and an indoor unit  4  that are connected to each other via a liquid-refrigerant connection pipe  5  and a gas-refrigerant connection pipe  6 . 
     A refrigerant enclosed in the refrigerant circuit  10  is a non-azeotropic refrigerant mixture. The non-azeotropic refrigerant mixture includes any of a HFC (hydrofluorocarbon) refrigerant, a HFO (hydrofluoroolefin) refrigerant, CF3I (trifluoroiodomethane), and a natural refrigerant. 
     (1-1) Indoor Unit  4   
     The indoor unit  4  is installed indoors and constitutes part of the refrigerant circuit  10 . The indoor unit  4  includes an indoor heat exchanger  41 , an indoor fan  42 , and an indoor-side control unit  44 . 
     (1-1-1) Indoor Heat Exchanger  41   
     The indoor heat exchanger  41  functions as an evaporator for the refrigerant during cooling operation and cools indoor air. In addition, the indoor heat exchanger  41  functions as a radiator for the refrigerant during heating operation and heats indoor air. The refrigerant inlet side of the indoor heat exchanger  41  during cooling operation is connected to the liquid-refrigerant connection pipe  5 , and the refrigerant outlet side thereof is connected to the gas-refrigerant connection pipe  6 . 
       FIG. 2  is a front view of the indoor heat exchanger  41 . In  FIG. 2 , the indoor heat exchanger  41  is a cross-fin-type heat exchanger. The indoor heat exchanger has a heat transfer fin  412  and a heat transfer tube  411 . 
     The heat transfer fin  412  is a thin aluminum flat plate. The heat transfer fin  412  has a plurality of through holes. The heat transfer tube  411  has a straight tube  411   a  inserted into the through holes of the heat transfer fin  412 , and U-shaped tubes  411   b  and  411   c  that couple end portions of mutually adjacent straight tubes  411   a  to each other. 
     The straight tube  411   a  is in close contact with the heat transfer fin  412  by being subjected to tube expansion processing after inserted into the through holes of the heat transfer fin  412 . The straight tube  411   a  and the first U-shaped tube  411   b  are formed integrally with each other. The second U-shaped tube  411   c  is coupled to an end portion of the straight tube  411   a  by welding, brazing, or the like after the straight tube  411   a  is inserted into the through holes of the heat transfer fin  412  and subjected to tube expansion processing. 
     (1-1-2) Indoor Fan  42   
     The indoor fan  42  takes indoor air into the indoor unit  4 , causes the indoor air to exchange heat with the refrigerant in the indoor heat exchanger  41 , and then supplies the air to the inside of a room. As the indoor fan  42 , a centrifugal fan, a multi-blade fan, or the like is employed. The indoor fan  42  is driven by an indoor fan motor  43 . 
     (1-1-3) Indoor-Side Control Unit  44   
     The indoor-side control unit  44  controls operation of each portion that constitutes the indoor unit  4 . The indoor-side control unit  44  has a microcomputer and a memory that are for controlling the indoor unit  4 . 
     The indoor-side control unit  44  transmits and receives a control signal and the like to and from a remote controller (not illustrated). In addition, the indoor-side control unit  44  transmits and receives a control signal and the like to and from an outdoor-side control unit  38  of the outdoor unit  2  via a transmission line  8   a.    
     (1-2) Outdoor Unit  2   
     The outdoor unit  2  is installed outdoors and constitutes part of the refrigerant circuit  10 . The outdoor unit  2  includes a compressor  21 , a four-way switching valve  22 , an outdoor heat exchanger  23 , an expansion valve  26 , a liquid-side shutoff valve  27 , and a gas-side shutoff valve  28 . 
     (1-2-1) Compressor  21   
     The compressor  21  is a device that compresses a low-pressure refrigerant of the refrigeration cycle. The compressor  21  drives and rotates a positive-displacement compression element (not illustrated) of a rotary type, a scroll type, or the like by a compressor motor  21   a.    
     A suction pipe  31  is connected to the suction side of the compressor  21 , and a discharge pipe  32  is connected to the discharge side thereof. The suction pipe  31  is a refrigerant pipe that connects the suction side of the compressor  21  and the four-way switching valve  22  to each other. The discharge pipe  32  is a refrigerant pipe that connects the discharge side of the compressor  21  and the four-way switching valve  22  to each other. 
     An accumulator  29  is connected to the suction pipe  31 . The accumulator  29  separates a flowed-in refrigerant into a liquid refrigerant and a gas refrigerant and causes only the gas refrigerant to flow to the suction side of the compressor  21 . 
     (1-2-2) Four-Way Switching Valve  22   
     The four-way switching valve  22  switches the direction of the flow of the refrigerant in the refrigerant circuit  10 . During cooling operation, the four-way switching valve  22  causes the outdoor heat exchanger  23  to function as a radiator for the refrigerant and causes the indoor heat exchanger  41  to function as an evaporator for the refrigerant. 
     During cooling operation, the four-way switching valve  22  connects the discharge pipe  32  of the compressor  21  and a first gas refrigerant pipe  33  of the outdoor heat exchanger  23  to each other and connects the suction pipe  31  of the compressor  21  and a second gas refrigerant pipe  34  to each other (refer to the solid lines of the four-way switching valve  22  in  FIG. 1 ). 
     During heating operation, the four-way switching valve  22  is switched to a heating cycle state in which the outdoor heat exchanger  23  functions as an evaporator for the refrigerant and in which the indoor heat exchanger  41  functions as a radiator for the refrigerant. 
     During heating operation, the four-way switching valve  22  connects the discharge pipe  32  of the compressor  21  and the second gas refrigerant pipe  34  to each other and connects the suction pipe  31  of the compressor  21  and the first gas refrigerant pipe  33  of the outdoor heat exchanger  23  to each other (refer to the broken lines of the four-way switching valve  22  in  FIG. 1 ). 
     Here, the first gas refrigerant pipe  33  is a refrigerant pipe that connects the four-way switching valve  22  and the refrigerant inlet of the outdoor heat exchanger  23  during cooling operation to each other. The second gas refrigerant pipe  34  is a refrigerant pipe that connects the four-way switching valve  22  and the gas-side shutoff valve  28  to each other. 
     (1-2-3) Outdoor Heat Exchanger  23   
     The outdoor heat exchanger  23  functions as a radiator for the refrigerant during cooling operation. In addition, the outdoor heat exchanger  23  functions as an evaporator for the refrigerant during heating operation. One end of a liquid refrigerant pipe  35  is connected to the refrigerant outlet of the outdoor heat exchanger  23  during cooling operation. The other end of the liquid refrigerant pipe  35  is connected to the expansion valve  26 . 
     The outdoor heat exchanger  23  will be described in detail in the section “(3) Detailed Structure of Outdoor Heat Exchanger  23 ”. 
     (1-2-4) Expansion Valve  26   
     The expansion valve  26  is an electric expansion valve. During cooling operation, the expansion valve  26  decompresses a high-pressure refrigerant that is sent from the outdoor heat exchanger  23  to a low pressure. During heating operation, the expansion valve  26  decompresses a high-pressure refrigerant that is sent from the indoor heat exchanger  41  to a low pressure. 
     (1-2-5) Liquid-Side Shutoff Valve  27  and Gas-Side Shutoff Valve  28   
     The liquid-side shutoff valve  27  is connected to the liquid-refrigerant connection pipe  5 . The gas-side shutoff valve  28  is connected the gas-refrigerant connection pipe  6 . The liquid-side shutoff valve  27  is positioned downstream the expansion valve  26  in a refrigerant circulation direction during cooling operation. The gas-side shutoff valve  28  is positioned upstream the four-way switching valve  22  in a refrigerant circulation direction during cooling operation. 
     (1-2-6) Outdoor Fan 
     The outdoor unit  2  includes an outdoor fan  36 . The outdoor fan  36  takes outdoor air into the outdoor unit  2 , causes the outdoor air to exchange heat with the refrigerant in the outdoor heat exchanger  23 , and then discharges the air to the outside. As the outdoor fan  36 , a propeller fan or the like is employed. The outdoor fan  36  is driven by an outdoor-fan motor  37 . 
     (1-2-7) Outdoor-Side Control Unit  38   
     The outdoor-side control unit  38  controls operation of each portion that constitutes the outdoor unit  2 . The outdoor-side control unit  38  has a microcomputer and a memory that are for controlling the outdoor unit  2 . 
     The outdoor-side control unit  38  transmits and receives a control signal and the like to and from the indoor-side control unit  44  of the indoor unit  4  via the transmission line  8   a.    
     (1-3) Refrigerant Connection Pipes  5  and  6   
     The connection pipes  5  and  6  are refrigerant pipes that are constructed at a local site during installation of the air conditioning apparatus  1  in an installation location at a building or the like. As each of the connection pipes  5  and  6 , a pipe having an appropriate length and an appropriate diameter is employed in accordance with installation conditions such as an installation location, a combination of the outdoor unit  2  and the indoor unit  4 , and the like. 
     (2) Basic Operation of Air Conditioning Apparatus 
     Next, a basic operation of the air conditioning apparatus  1  will be described with reference to  FIG. 1 . The air conditioning apparatus  1  is capable of performing cooling operation and heating operation as basic operation. 
     (2-1) Cooling Operation 
     During cooling operation, the four-way switching valve  22  is switched to a cooling cycle state (the state indicated by the solid lines in  FIG. 1 ). In the refrigerant circuit  10 , a low-pressure gas refrigerant of the refrigeration cycle is sucked by the compressor  21  and discharged after compressed. 
     The high-pressure gas refrigerant discharged from the compressor  21  is sent to the outdoor heat exchanger  23  via the four-way switching valve  22 . 
     In the outdoor heat exchanger  23  that functions as a radiator, the high-pressure gas refrigerant sent to the outdoor heat exchanger  23  radiates heat by exchanging heat with outdoor air supplied from the outdoor fan  36 , and becomes a high-pressure liquid refrigerant. The high-pressure liquid refrigerant is sent to the expansion valve  26 . 
     The high-pressure liquid refrigerant sent to the expansion valve  26  is decompressed to a low pressure of the refrigeration cycle by the expansion valve  26  and becomes a low-pressure gas-liquid two-phase refrigerant. The low-pressure gas-liquid two-phase refrigerant decompressed in the expansion valve  26  is sent to the indoor heat exchanger  41  via the liquid-side shutoff valve  27  and the liquid-refrigerant connection pipe  5 . 
     The low-pressure gas-liquid two-phase refrigerant sent to the indoor heat exchanger  41  evaporates in the indoor heat exchanger  41  by exchanging heat with indoor air supplied from the indoor fan  42 . Consequently, the indoor air is cooled. Then, the cooled air is supplied to the inside of a room, thereby cooling the inside of the room. 
     The low-pressure gas refrigerant that has evaporated in the indoor heat exchanger  41  is sucked again by the compressor  21  via the gas-refrigerant connection pipe  6 , the gas-side shutoff valve  28 , and the four-way switching valve  22 . 
     (2-2) Heating Operation 
     During heating operation, the four-way switching valve  22  is switched to the heating cycle state (the state indicated by the broken lines in  FIG. 1 ). In the refrigerant circuit  10 , a low-pressure gas refrigerant of the refrigeration cycle is sucked by the compressor  21  and discharged after compressed. 
     The high-pressure gas refrigerant discharged from the compressor  21  is sent to the indoor heat exchanger  41  via the four-way switching valve  22 , the gas-side shutoff valve  28 , and the gas-refrigerant connection pipe  6 . 
     The high-pressure gas refrigerant sent to the indoor heat exchanger  41  radiates heat in the indoor heat exchanger  41  by exchanging heat with indoor air supplied from the indoor fan  42 , and becomes a high-pressure liquid refrigerant. Consequently, the indoor air is heated. Then, the heated air is supplied to the inside of a room, thereby heating the inside of the room. 
     The high-pressure liquid refrigerant that has radiated heat in the indoor heat exchanger  41  is sent to the expansion valve  26  via the liquid-refrigerant connection pipe  5  and the liquid-side shutoff valve  27 . 
     The high-pressure liquid refrigerant sent to the expansion valve  26  is decompressed to a low pressure of the refrigeration cycle by the expansion valve  26  and becomes a low-pressure gas-liquid two-phase refrigerant. The low-pressure gas-liquid two-phase refrigerant decompressed in the expansion valve  26  is sent to the outdoor heat exchanger  23 . 
     The low-pressure gas-liquid two-phase refrigerant sent to the outdoor heat exchanger  23  evaporates in the outdoor heat exchanger  23  by exchanging heat with outdoor air supplied from the outdoor fan  36 , and becomes a low-pressure gas refrigerant. 
     The low-pressure refrigerant that has evaporated in the outdoor heat exchanger  23  is sucked again by the compressor  21  through the four-way switching valve  22 . 
     (3) Detailed Description of Outdoor Heat Exchanger  23   
     (3-1) Structure 
       FIG. 3  is an external perspective view of the outdoor heat exchanger  23 . In  FIG. 3 , the outdoor heat exchanger  23  is a stack-type heat exchanger. The outdoor heat exchanger  23  includes a plurality of flat pipes  231  and a plurality of heat transfer fins  232 . 
     (3-1-1) Flat Pipes  231   
     Each flat pipe  231  is a multi-hole pipe. The flat pipe  231  is formed of aluminum or an aluminum alloy and has a flat portion  231   a  that serves as a heat transfer surface, and a plurality of internal flow paths  231   b  in which the refrigerant flows. 
     The flat pipes  231  are arrayed in a plurality of stages to be stacked with a gap (ventilation space) therebetween in a state in which respective flat portions  231   a  are directed upward/downward. 
     (3-1-2) Heat Transfer Fins  232   
     Each heat transfer fin  232  is a fin made of aluminum or an aluminum alloy. The heat transfer fin  232  is disposed in a ventilation space between the flat pipes  231  that are vertically adjacent to each other and is in contact with the flat portions  231   a  of the flat pipes  231 . 
     The heat transfer fin  232  has cutouts  232   c  (refer to  FIG. 5A  and  FIG. 5B ) into which the flat pipes  231  are inserted. After the flat pipes  231  are inserted into the cutouts  232   c  of the heat transfer fins  232 , the heat transfer fins  232  and the flat portions  231   a  of the flat pipes  231  are joined to each other by brazing or the like. 
     (3-1-3) Headers  233   a  and  233   b    
     The headers  233   a  and  233   b  are coupled to both ends of the flat pipes  231  arrayed in the plurality of stages in the up-down direction. The headers  233   a  and  233   b  have a function of supporting the flat pipes  231 , a function of guiding the refrigerant to the internal flow paths of the flat pipes  231 , and a function of gathering the refrigerant that has flowed out from the internal flow paths. 
     When the outdoor heat exchanger  23  functions as an evaporator for the refrigerant, the refrigerant flows into the first header  233   a . The refrigerant that has flowed into the first header  233   a  is distributed to the internal flow paths of the flat pipes  231  of the stages substantially evenly and flows toward the second header  233   b . The refrigerant that flows in the internal flow paths of the flat pipes  231  of the stages absorbs heat via the heat transfer fins  232  from an air flow that flows in the ventilation spaces. The refrigerant that has flowed in the internal flow paths of the flat pipes  231  of the stages gathers at the second header  233   b  and flows out from the second header  233   b.    
     When the outdoor heat exchanger  23  functions as a radiator for the refrigerant, the refrigerant flows into the second header  233   b . The refrigerant that has flowed into the second header  233   b  is distributed to the internal flow paths of the flat pipes  231  of the stages substantially evenly and flows toward the first header  233   a . The refrigerant that flows in the internal flow paths of the flat pipes  231  of the stages radiates heat via the heat transfer fins  232  into an air flow that flows in the ventilation spaces. The refrigerant that has flowed in the internal flow paths of the flat pipes  231  of the stages gathers at the first header  233   a  and flows out from the first header  233   a.    
     (3-2) Suppression of Frost 
       FIG. 4  is a P-H diagram of a non-azeotropic refrigerant mixture. In  FIG. 4 , the refrigerant temperature increases toward the evaporator outlet. Since the composition of the non-azeotropic refrigerant mixture is different between a liquid phase and a gas phase, a “temperature gradient” in which an evaporation start temperature and an evaporation end temperature in the evaporator are different is present. Due to the temperature gradient, the temperature at the inlet easily decreases in the evaporator, which easily causes frost during heating operation. 
       FIG. 5A  is a perspective view of a first heat exchange section  23   a  of the outdoor heat exchanger  23  according to one or more embodiments. In  FIG. 5A , the opening side of the cutouts  232   c  is positioned on the leeward side in the airflow direction in the first heat exchange section  23   a.    
       FIG. 5B  is a perspective view of a second heat exchange section  23   b  of the outdoor heat exchanger  23  according to one or more embodiments. In  FIG. 5B , the opening side of the cutouts  232   c  is positioned on the windward side in the airflow direction. 
     Since the openings of the cutouts  232   c  are positioned on the windward side in the airflow direction in the second heat exchange section  23   b  illustrated in  FIG. 5B , a difference between an air temperature and a heat-exchanger surface temperature is large, and thus has a feature of improving heat exchange performance but easily causing frost. 
     Meanwhile, since the openings of the cutouts  232   c  are positioned on the leeward side in the airflow direction in the first heat exchange section  23   a  illustrated in  FIG. 5A , a difference between an air temperature and a heat-exchanger surface temperature is small compared with the second heat exchange section  23   b . Frost is thus suppressed. 
     Therefore, in one or more embodiments, the first heat exchange section  23   a  is formed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator. 
     (3-3) Improvement of Heat Exchange Performance 
     As described above, compared with the second heat exchange section  23   b , a difference between an air temperature and a heat-exchanger surface temperature is small in the first heat exchange section  23   a . The heat exchange performance is thus degraded. Therefore, constituting the entirety of the outdoor heat exchanger  23  by the first heat exchange section  23   a  may not be preferable for performance. 
     Thus, in one or more embodiments, both the first heat exchange section  23   a  and the second heat exchange section  23   b  are used to improve heat exchange performance while suppressing frost. 
       FIG. 6A  is a schematic perspective view of the outdoor heat exchanger  23  that uses both the first heat exchange section  23   a  and the second heat exchange section  23   b .  FIG. 6B  is a schematic perspective view of a different outdoor heat exchanger  23 ′ that uses both a first heat exchange section  23   a ′ and a second heat exchange section  23   b′.    
     In  FIG. 6A , when the outdoor heat exchanger  23  functions as an evaporator for the refrigerant, the refrigerant that has flowed into the first header  233   a  is distributed to the internal flow paths  231   b  of the flat pipes  231  of the stages substantially evenly and flows toward the second header  233   b . The temperature of the non-azeotropic refrigerant mixture at the evaporator inlet easily decreases, which easily causes frost. Therefore, a certain section from the first header  233   a  toward the second header  233   b  is constituted by the first heat exchange section  23   a  to suppress frost. 
     Meanwhile, the temperature of the non-azeotropic refrigerant mixture increases toward the evaporator outlet. Thus, to improve heat exchange performance, a part between the first heat exchange section  23   a  and the second header  233   b  is constituted by the second heat exchange section  23   b.    
     It is possible by thus disposing the first heat exchange section  23   a  on the evaporator inlet side and the second heat exchange section  23   b  on the evaporator outlet side to improve heat exchange performance while suppressing frost. 
     In  FIG. 6B , when the outdoor heat exchanger  23 ′ functions as an evaporator for the refrigerant, the refrigerant that has flowed into the lower stage of the first header  233   a ′ is distributed to internal flow paths  231   b ′ of the flat pipes  231  of the stages of the lower stage substantially evenly and flows toward the second header  233   b′.    
     The refrigerant that has reached the lower stage of the second header  233   b ′ gathers temporarily and flows into the upper stage of the second header  233   b ′ via a curved pipe  234 . Thereafter, the refrigerant is distributed to the internal flow paths  231   b  of the flat pipes  231  of the stages of the upper stage substantially evenly and flows toward the second header  233   b′.    
     The temperature of the non-azeotropic refrigerant mixture at the evaporator inlet easily decreases, which easily causes frost. Therefore, a section from the lower stage of the first header  233   a ′ toward the lower stage of the second header  233   b ′ is constituted by the first heat exchange section  23   a ′ to suppress frost. 
     Meanwhile, the temperature of the non-azeotropic refrigerant mixture increases toward the evaporator outlet. Thus, to improve heat exchange performance, a section from the upper stage of the first header  233   b ′ toward the upper stage of the first header  233   a ′ is constituted by the second heat exchange section  23   b′.    
     It is possible by thus disposing the first heat exchange section  23   a ′ on the evaporator inlet side and the second heat exchange section  23   b ′ on the evaporator outlet side to improve heat exchange performance while suppressing frost. 
     (4) Features 
     (4-1) 
     In the first heat exchange section  23   a  of the outdoor heat exchanger  23 , the opening side of the cutouts  232   c  of the heat transfer fins  232  is positioned on the leeward side in the airflow direction. By disposing the first heat exchange section  23   a  on the side of the inlet for the non-azeotropic refrigerant mixture, it is possible to improve frost proof performance (capacity of suppressing frost) when the outdoor heat exchanger  23  functions as an evaporator. 
     (4-2) 
     In addition, by disposing the first heat exchange section  23   a  on the side of the inlet for the non-azeotropic refrigerant mixture and disposing the second heat exchange section  23   b , in which the openings of the cutouts  232   c  are positioned on the windward side in the airflow direction, on the side of the outlet, it is possible to improve heat exchange performance while suppressing frost. 
     (4-3) 
     The first heat exchange section  23   a  and the second heat exchange section  23   b  are integral with each other. 
     (5) Modification 
     With the first heat exchange section  23   a  being disposed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator and the second heat exchange section  23   b  being disposed on the outlet side, a third heat exchange section  23   c  may be disposed between the first heat exchange section  23   a  and the second heat exchange section  23   b.    
     In the third heat exchange section  23   c , the distribution center (i.e., center of distribution) of the flat pipes  231  in the width direction coincides with the center of the heat transfer fins  232  in the airflow direction. 
     The technical significance of this modification is that it is possible to try a combination of the heat exchange sections suitable for a refrigerant temperature in the outdoor heat exchanger  23  that functions as an evaporator. As a result, it is possible to improve heat exchange performance while suppressing frost. 
     The first heat exchange section  23   a  may be integral with at least either one of the second heat exchange section  23   b  and the third heat exchange section  23   c.    
     Second Embodiments 
     In one or more embodiments, a stack-type heat exchanger in which the flat pipes  231  are inserted into the cutouts  232   c  provided in the heat transfer fins  232  is employed as the outdoor heat exchanger  23 . 
     In one or more embodiments, a stack-type heat exchanger in which flat pipes extend through elongated holes provided in heat transfer fins is employed as the outdoor heat exchanger  23 . 
     (1) Suppression of Frost 
       FIG. 7A  is a perspective view of a first heat exchange section  123   a  of the outdoor heat exchanger  23  according to one or more embodiments. In the first heat exchange section  123   a  in  FIG. 7A , a distance from the windward-side end of a flat pipe  231 M positioned on the most windward side in the airflow direction to the windward-side end of a heat transfer fin  232 M is a first dimension D 1 . 
       FIG. 7B  is a perspective view of a second heat exchange section  123   b  of the outdoor heat exchanger  23  according to embodiments. In the second heat exchange section  123   b  in  FIG. 7B , a distance from the windward-side end of the flat pipe  231 M positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 M is a second dimension D 2  smaller than the first dimension D 1 . 
     Since the distance (second dimension D 2 ) from the windward-side end of the flat pipe  231 M positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 M in the second heat exchange section  123   b  illustrated in  FIG. 7B  is smaller than the distance (first dimension D 1 ) in the first heat exchange section  123   a , a difference between an air temperature and a heat-exchanger surface temperature is large. The second heat exchange section  123   b  thus has a feature of improving heat exchange performance but easily causing frost. 
     Meanwhile, since the distance from the windward-side end of the flat pipe  231 M positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 M in the first heat exchange section  123   a  illustrated in  FIG. 7A  is larger than the distance (second dimension D 2 ) in the second heat exchange section  123   b , a difference between an air temperature and a heat-exchanger surface temperature is small, compared with the second heat exchange section  123   b , which suppresses frost. 
     Therefore, in one or more embodiments, the first heat exchange section  123   a  is formed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator. 
     (2) Improvement of Heat Exchange Performance 
     As described above, compared with the second heat exchange section  123   b , a difference between an air temperature and a heat-exchanger surface temperature is small in the first heat exchange section  123   a . The heat exchange performance is thus degraded. Therefore, constituting the entirety of the outdoor heat exchanger  23  by the first heat exchange section  123   a  may not be preferable for performance. 
     Thus, in one or more embodiments, both the first heat exchange section  123   a  and the second heat exchange section  123   b  are used, as in the first embodiments, to improve heat exchange performance while suppressing frost.  FIG. 6A  and  FIG. 6B  are also applied to the second embodiments by replacing the first heat exchange section  23   a  of the first embodiments with the “first heat exchange section  123   a ” and replacing the second heat exchange section  23   b  of the first embodiments with the “second heat exchange section  123   b”.    
     In  FIG. 6A , when the outdoor heat exchanger  23  functions as an evaporator for the refrigerant, the refrigerant that has flowed into the first header  233   a  is distributed to the internal flow paths of the flat pipes of the stages substantially evenly and flows toward the second header  233   b . The temperature of the non-azeotropic refrigerant mixture at the evaporator inlet easily decreases, which easily causes frost. Therefore, a certain section from the first header  233   a  toward the second header  233   b  is constituted by the first heat exchange section  123   a  to suppress frost. 
     Meanwhile, the temperature of the non-azeotropic refrigerant mixture increases toward the evaporator outlet. Thus, to improve heat exchange performance, a part between the first heat exchange section  123   a  and the second header  233   b  is constituted by the second heat exchange section  123   b.    
     It is possible by thus disposing the first heat exchange section  123   a  on the evaporator inlet side and the second heat exchange section  123   b  on the evaporator outlet side to improve heat exchange performance while suppressing frost. 
     (3) Features of Second Embodiments 
     (3-1) 
     The temperature of the non-azeotropic refrigerant mixture increases from the inlet toward the outlet of the evaporator. Thus, a high priority on frost proof performance (capacity of suppressing frost) on the inlet side and a high priority on heat exchange performance on the outlet side may be put. 
     Therefore, it is possible to try a combination suitable for a refrigerant temperature in the evaporator, the combination being such that the first heat exchange section  123   a  is disposed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator and the second heat exchange section  123   b  is disposed on the outlet side. 
     (3-2) 
     The first heat exchange section  123   a  and the second heat exchange section  123   b  are integral with each other. 
     (4) Modification 
     With the first heat exchange section  123   a  being disposed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator and the second heat exchange section  123   b  being disposed on the outlet side, a third heat exchange section may be disposed between the first heat exchange section  123   a  and the second heat exchange section  123   b.    
       FIG. 7C  is a perspective view of a third heat exchange section  123   c  of the outdoor heat exchanger  23  according to a modification of one or more embodiments. In the third heat exchange section  123   c  in  FIG. 7C , a distance (a first distance) D 3  from the windward-side end of the flat pipe  231 M positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 M and a distance (a second distance) from the leeward-side end of the flat pipe  231 M positioned on the most leeward side in the airflow direction to the leeward-side end of the heat transfer fin  232 M are equal to each other. 
     The technical significance of this modification is that it is possible to try a combination of the heat exchange sections suitable for a refrigerant temperature in the outdoor heat exchanger  23  that functions as an evaporator. As a result, it is possible to improve heat exchange performance while suppressing frost. 
     The first heat exchange section  123   a  may be integral with at least either one of the second heat exchange section  123   b  and the third heat exchange section  123   c.    
     Third Embodiments 
     In the first embodiments and the second embodiments, a stack-type heat exchanger is employed as the outdoor heat exchanger  23 . In one or more embodiments, a cross-fin-type heat exchanger is employed as the outdoor heat exchanger  23 . 
     (1) Suppression of Frost 
       FIG. 8A  is a perspective view of a first heat exchange section  223   a  of the outdoor heat exchanger  23  according to one or more embodiments. In the first heat exchange section  223   a  in  FIG. 8A , when a plurality of heat transfer tubes  231 N are viewed as a heat-transfer-tube group in the plate thickness direction of a heat transfer fin  232 N, the distribution center of the heat-transfer-tube group in the airflow direction is positioned on the leeward side of the center of the heat transfer fin  232 N in the airflow direction. 
       FIG. 8B  is a perspective view of a second heat exchange section  223   b  of the outdoor heat exchanger  23  according to one or more embodiments. In the second heat exchange section  223   b  in  FIG. 8B , the distribution center of the heat-transfer-tube group in the airflow direction is positioned on the windward side of the center of the heat transfer fin  232 N in the airflow direction. 
     Since the distribution center of the heat-transfer-tube group is positioned on the windward side of the center of the heat transfer fin  232 N in the airflow direction, a distance from the windward-side end of the heat transfer tube  231 N positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 N is smaller in the second heat exchange section  223   b  illustrated in  FIG. 8B  than the distance in the first heat exchange section  223   a . As a result, a difference between an air temperature and a heat-exchanger surface temperature is large. The second heat exchange section  223   b  thus has a feature of improving heat exchange performance but easily causing frost. 
     Meanwhile, since the distribution center of the heat-transfer-tube group in the airflow direction is positioned on the leeward side of the center of the heat transfer fin  232 N in the airflow direction, a distance from the windward-side end of the heat transfer tube  231 N positioned on the most windward side in the airflow direction to the windward-side end of the heat transfer fin  232 N is larger in the first heat exchange section  223   a  illustrated in  FIG. 8A  than the distance in the second heat exchange section  223   b . As a result, compared with the second heat exchange section  223   b , a difference between an air temperature and a heat-exchanger surface temperature is small, which suppresses frost. 
     Therefore, in one or more embodiments, the first heat exchange section  223   a  is formed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator. 
     (2) Improvement of Heat Exchange Performance 
     As described above, compared with the second heat exchange section  223   b , a difference between an air temperature and a heat-exchanger surface temperature is small in the first heat exchange section  223   a . The heat exchange performance is thus degraded. Therefore, constituting the entirety of the outdoor heat exchanger  23  by the first heat exchange section  223   a  may not be preferable for performance. 
     Thus, in one or more embodiments, both the first heat exchange section  223   a  and the second heat exchange section  223   b  are used, as in the first embodiments and the second embodiments, to improve heat exchange performance while suppressing frost.  FIG. 6A  and  FIG. 6B  are also applied to the third embodiments by replacing the first heat exchange section  23   a  of the first embodiments with the “first heat exchange section  223   a ” and replacing the second heat exchange section  23   b  of the first embodiments with the “second heat exchange section  223   b”.    
     In  FIG. 6A , when the outdoor heat exchanger  23  functions as an evaporator for the refrigerant, the refrigerant that has flowed into the first header  233   a  is distributed to the heat transfer tubes of the stages substantially evenly and flows toward the second header  233   b . The temperature of the non-azeotropic refrigerant mixture at the evaporator inlet easily decreases, which easily causes frost. Therefore, a certain section from the first header  233   a  toward the second header  233   b  is constituted by the first heat exchange section  223   a  to suppress frost. 
     Meanwhile, the temperature of the non-azeotropic refrigerant mixture increases toward the evaporator outlet. Thus, to improve heat exchange performance, a part between the first heat exchange section  223   a  and the second header  233   b  is constituted by the second heat exchange section  223   b.    
     It is possible by thus disposing the first heat exchange section  223   a  on the evaporator inlet side and the second heat exchange section  223   b  on the evaporator outlet side to improve heat exchange performance while suppressing frost. 
     (3) Features of Third Embodiments 
     (3-1) 
     The temperature of the non-azeotropic refrigerant mixture increases from the inlet toward the outlet of the evaporator. Thus, a high priority on frost proof performance (capacity of suppressing frost) on the inlet side and a high priority on heat exchange performance on the outlet side may be put. 
     Therefore, it is possible to try a combination suitable for a refrigerant temperature in the evaporator, the combination being such that the first heat exchange section  223   a  is disposed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator and the second heat exchange section  223   b  is disposed on the outlet side. 
     (3-2) 
     The first heat exchange section  223   a  and the second heat exchange section  223   b  are integral with each other. 
     (4) Modification 
     With the first heat exchange section  223   a  being disposed on the inlet side of the outdoor heat exchanger  23  that functions as an evaporator and the second heat exchange section  223   b  being disposed on the outlet side, a third heat exchange section may be disposed between the first heat exchange section  223   a  and the second heat exchange section  223   b.    
       FIG. 8C  is a perspective view of a third heat exchange section  223   c  of the outdoor heat exchanger  23  according to a modification of one or more embodiments. In the third heat exchange section  223   c  in  FIG. 8C , the distribution center of the heat-transfer-tube group in the airflow direction coincides with the center of the fin in the airflow direction. 
     The technical significance of this modification is that it is possible to try a combination of the heat exchange sections suitable for a refrigerant temperature in the outdoor heat exchanger  23  that functions as an evaporator. As a result, it is possible to improve heat exchange performance while suppressing frost. 
     The first heat exchange section  223   a  may be integral with at least either one of the second heat exchange section  223   b  and the third heat exchange section  223   c.    
     &lt;Others&gt; 
     In each of the embodiments described above, the non-azeotropic refrigerant mixture is described to include any of a HFC refrigerant, a HFO refrigerant, CF3I, and a natural refrigerant. More specifically, a non-azeotropic refrigerant mixture corresponding to any of (A) to (G) below may be used. 
     (A) 
     A non-azeotropic refrigerant mixture that includes any of R32, R1132(E), R1234yf, R1234ze, CF3I, and CO2 
     (B) 
     A non-azeotropic refrigerant mixture that includes at least R1132(E), R32, and R1234yf 
     (C) 
     A non-azeotropic refrigerant mixture that includes at least R1132(E), R1123, and R1234yf 
     (D) 
     A non-azeotropic refrigerant mixture that includes at least R1132(E) and R1234yf 
     (E) 
     A non-azeotropic refrigerant mixture that includes at least R32, R1234yf, and at least one of R1132a and R1114 
     (F) 
     A non-azeotropic refrigerant mixture that includes at least R32, CO2, R125, R134a, and R1234yf 
     (G) 
     A non-azeotropic refrigerant mixture that includes at least R1132(Z) and R1234yf 
     Embodiments of the present disclosure have been described above; however, it should be understood that various changes in the forms and details are possible without departing from the gist and the scope of the present disclosure described in the claims. 
     The present disclosure is widely applicable to a refrigeration apparatus capable of performing cooling operation and heating operation. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the disclosure should be limited only by the attached claims. 
     REFERENCES SIGNS LIST 
     
         
         
           
               1  air conditioning apparatus (refrigeration apparatus) 
               23  outdoor heat exchanger (evaporator) 
               23   a  first heat exchange section 
               23   b  second heat exchange section 
               23   c  third heat exchange section 
               123   a  first heat exchange section 
               123   b  second heat exchange section 
               123   c  third heat exchange section 
               223   a  first heat exchange section 
               223   b  second heat exchange section 
               223   c  third heat exchange section 
               231  flat pipe (heat transfer tube) 
               231 M flat pipe (heat transfer tube) 
               231 N heat transfer tube 
               232  heat transfer fin 
               232   c  cutout 
               232 M heat transfer fin 
               232 N heat transfer fin 
           
         
       
    
     PATENT LITERATURE 
     
         
         PTL 1 
         WO2017/183180