Patent Publication Number: US-2023139313-A1

Title: Use of composition as refrigerant in compressor, compressor, and refrigeration cycle apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2021/025308, filed on Jul. 5, 2021, which claims priority under 35 U.S.C. 119(a) to Patent Application No. 2020-115910, filed in Japan on Jul. 3, 2020, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the use of a composition as a refrigerant in a compressor, the compressor, and a refrigeration cycle apparatus. 
     BACKGROUND ART 
     Conventionally, hydrofluoroolefins (HFO refrigerants) having lower global warming potential (hereinafter also simply referred to as GWP) than HFC refrigerants have attracted attention for refrigeration apparatuses. For example, 1,2-difluoroethylene (HFO-1132) is considered as a refrigerant with low GWP in Patent Literature 1 (Japanese Patent Laid-Open No. 2019-196312). 
     SUMMARY 
     The use of a composition as a refrigerant in a compressor according to a first aspect is the use of a composition as a refrigerant in a compressor in which the flow rate of the refrigerant flowing through a discharge pipe of the compressor under a predetermined high-pressure condition is greater than or equal to 1 m/s. The composition includes one or more compounds selected from the group consisting of ethylene-based fluoroolefins, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,3,3,3-tetrafluoropropene (HFO-1234ze). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram of a refrigeration cycle apparatus. 
         FIG.  2    is a block configuration diagram of the refrigeration cycle apparatus. 
         FIG.  3    is a side cross-sectional view illustrating a schematic configuration of a compressor. 
         FIG.  4    is a plan cross-sectional view illustrating a region around a cylinder chamber of the compressor. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a compressor, a refrigeration cycle apparatus, and the use of a composition as a refrigerant in such a compressor or an apparatus will be specifically described with reference to examples. However, the following description is not intended to limit the present disclosure. 
     (1) Refrigeration Cycle Apparatus  1   
     A refrigeration cycle apparatus  1  is an apparatus for performing vapor-compression refrigeration cycles to process a heat load of a target space. For example, the refrigeration cycle apparatus  1  is an air-conditioning apparatus for conditioning air in a target space. 
       FIG.  1    is a schematic configuration diagram of the refrigeration cycle apparatus.  FIG.  2    is a block configuration diagram of the refrigeration cycle apparatus. 
     The refrigeration cycle apparatus  1  mainly includes an outdoor unit  20 ; an indoor unit  30 ; a liquid-side refrigerant communication pipe  6  and a gas-side refrigerant communication pipe  5  each connecting the outdoor unit  20  and the indoor unit  30 ; a remote controller (not illustrated); and a controller  7  that controls the operation of the refrigeration cycle apparatus  1 . 
     In the refrigeration cycle apparatus  1 , refrigeration cycles are performed such that a refrigerant enclosed in a refrigerant circuit  10  is compressed, and is then cooled or condensed, and is then decompressed, and is then heated or evaporated, and is then compressed again. In the present embodiment, the refrigerant circuit  10  is filled with a refrigerant for performing vapor-compression refrigeration cycles. 
     (2) Refrigerant 
     Examples of the refrigerant filling the refrigerant circuit  10  include one or more compounds selected from the group consisting of ethylene-based fluoroolefins, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,3,3,3-tetrafluoropropene (HFO-1234ze). Note that regarding the burning velocity defined by the ISO 817, 1,3,3,3-tetrafluoropropene (HFO-1234ze) with a burning velocity of 1.2 cm/s is more preferable than 2,3,3,3-tetrafluoropropene (HFO-1234yf) with a burning velocity of 1.5 cm/s. Regarding the LFL (Lower Flammability Limit) defined by the ISO 817, 1,3,3,3-tetrafluoropropene (HFO-1234ze) with a LFL of 65000 vol.ppm or 6.5% is more preferable than 2,3,3,3-tetrafluoropropene (HFO-1234yf) with a LFL of 62000 vol.ppm or 6.2%. In particular, the refrigerant may include one or more compounds selected from the group consisting of 1,2-difluoroethylene (HFO-1132), 1,1-difluoroethylene (HFO-1132a), 1,1,2-trifluoroethylene (HFO-1123), monofluoroethylene (HFO-1141), and perhaloolefins. Above all, the refrigerant preferably include 1,2-difluoroethylene (HFO-1132) and/or 1,1,2-trifluoroethylene (HFO-1123). 
     Herein, examples of ethylene-based fluoroolefins include 1,2-difluoroethylene (HFO-1132), 1,1-difluoroethylene (HFO-1132a), 1,1,2-trifluoroethylene (HFO-1123), monofluoroethylene (HFO-1141), and perhaloolefins. Examples of perhaloolefins include chlorotrifluoroethylene (CFO-1113) and tetrafluoroethylene (FO-1114). 
     Note that the refrigerant circuit  10  is also filled with refrigerator oil together with the aforementioned refrigerant. 
     (3) Outdoor Unit  20   
     The outdoor unit  20  is connected to the indoor unit  30  via the liquid-side refrigerant communication pipe  6  and the gas-side refrigerant communication pipe  5 , and consists part of the refrigerant circuit  10 . The outdoor unit  20  mainly includes a compressor  21 , a four-way switching valve  22 , an outdoor heat exchanger  23 , an outdoor expansion valve  24 , an outdoor fan  25 , a receiver  41 , a gas-side shut-off valve  28 , and a liquid-side shut-off valve  29 . 
     The compressor  21  is a device that compresses a low-pressure refrigerant in a refrigeration cycle up to a high pressure. Herein, the compressor  21  may be a hermetic compressor in which a rotary-type or scroll-type positive-displacement compression element is rotationally driven by a compressor motor. In the present embodiment, a rotary compressor is used. The compressor motor is used to change the volume, and its operating frequency can be controlled with an inverter. 
     The four-way switching valve  22  switches a flow channel of the refrigerant circuit  10 . Specifically, the four-way switching valve  22  can switch between a state in which the discharge side of the compressor  21  and the outdoor heat exchanger  23  are connected and the suction side of the compressor  21  and the gas-side shut-off valve  28  are connected and a state in which the discharge side of the compressor  21  and the gas-side shut-off valve  28  are connected and the suction side of the compressor  21  and the outdoor heat exchanger  23  are connected. 
     The outdoor heat exchanger  23  is a heat exchanger that functions as a radiator or a condenser for a high-pressure refrigerant in a refrigeration cycle during the cooling operation, and functions as an evaporator for a low-pressure refrigerant in a refrigeration cycle during the heating operation. 
     The outdoor expansion valve  24  is provided between the liquid-side outlet of the outdoor heat exchanger  23  and the liquid-side shut-off valve  29  in the refrigerant circuit  10 . The outdoor expansion valve  24  is a motor-operated expansion valve with an adjustable opening degree. 
     The outdoor fan  25  produces an air flow for causing outdoor air to be sucked into the outdoor unit  20 , and causing the sucked air to exchange heat with a refrigerant in the outdoor heat exchanger  23 , and then causing the air to be discharged to the outside. The outdoor fan  25  is rotationally driven by an outdoor fan motor. 
     The receiver  41  is a refrigerant container that is provided between the suction side of the compressor  21  and one of connection ports of the four-way switching valve  22 , and that can store an excess refrigerant in the refrigerant circuit  10  as a liquid refrigerant. 
     The liquid-side shut-off valve  29  is a manual valve disposed at a portion of the outdoor unit  20  connected to the liquid-side refrigerant communication pipe  6 . 
     The gas-side shut-off valve  28  is a manual valve disposed at a portion of the outdoor unit  20  connected to the gas-side refrigerant communication pipe  5 . 
     The outdoor unit  20  includes an outdoor unit controller  27  that controls the operation of each portion forming the outdoor unit  20 . The outdoor unit controller  27  has a microcomputer including a CPU and a memory, for example. The outdoor unit controller  27  is connected to an indoor unit controller  34  of each indoor unit  30  via a communication line, and transmits and receives control signals, for example. 
     The outdoor unit  20  is provided with a discharge pressure sensor  61 , a discharge temperature sensor  62 , a suction pressure sensor  63 , a suction temperature sensor  64 , an outdoor heat exchange temperature sensor  65 , and an outdoor air temperature sensor  66 , for example. Each of such sensors is electrically connected to the outdoor unit controller  27 , and transmits a detection signal to the outdoor unit controller  27 . The discharge pressure sensor  61  detects the pressure of a refrigerant flowing through a discharge pipe that connects the discharge side of the compressor  21  and one of the connection ports of the four-way switching valve  22 . The discharge temperature sensor  62  detects the temperature of the refrigerant flowing through the discharge pipe. The suction pressure sensor  63  detects the pressure of a refrigerant flowing through a suction pipe that connects the suction side of the compressor  21  and the receiver  41 . The suction temperature sensor  64  detects the temperature of the refrigerant flowing through the suction pipe. The outdoor heat exchange temperature sensor  65  detects the temperature of a refrigerant flowing through the liquid-side outlet of the outdoor heat exchanger  23  on the side opposite to the side connecting to the four-way switching valve  22 . The outdoor air temperature sensor  66  detects the temperature of outdoor air before it passes through the outdoor heat exchanger  23 . 
     (4) Indoor Unit  30   
     The indoor unit  30  is disposed on an indoor wall surface or ceiling as a target space, for example. The indoor unit  30  is connected to the outdoor unit  20  via the liquid-side refrigerant communication pipe  6  and the gas-side refrigerant communication pipe  5 , and consists part of the refrigerant circuit  10 . 
     The indoor unit  30  includes an indoor heat exchanger  31  and an indoor fan  32 . 
     The indoor heat exchanger  31  is connected on its liquid side to the liquid-side refrigerant communication pipe  6 , and is connected on its gas side to the gas-side refrigerant communication pipe  5 . The indoor heat exchanger  31  is a heat exchanger that functions as an evaporator for a low-pressure refrigerant in a refrigeration cycle during the cooling operation, and functions as a condenser for a high-pressure refrigerant in a refrigeration cycle during the heating operation. 
     The indoor fan  32  produces an air flow for causing indoor air to be sucked into the indoor unit  30 , and causing the sucked air to exchange heat with a refrigerant in the indoor heat exchanger  31 , and then causing the air to be discharged to the outside. The indoor fan  32  is rotationally driven by an indoor fan motor. 
     The indoor unit  30  includes the indoor unit controller  34  that controls the operation of each unit forming the indoor unit  30 . The indoor unit controller  34  includes a microcomputer including a CPU and a memory, for example. The indoor unit controller  34  is connected to the outdoor unit controller  27  via the communication line, and transmits and receives control signals, for example. 
     The indoor unit  30  is provided with an indoor liquid-side heat exchange temperature sensor  71  and an indoor air temperature sensor  72 , for example. Each of such sensors is electrically connected to the indoor unit controller  34 , and transmits a detection signal to the indoor unit controller  34 . The indoor liquid-side heat exchange temperature sensor  71  detects the temperature of a refrigerant flowing through the liquid-refrigerant-side outlet of the indoor heat exchanger  31 . The indoor air temperature sensor  72  detects the temperature of indoor air before it passes through the indoor heat exchanger  31 . 
     (5) Controller  7   
     In the refrigeration cycle apparatus  1 , the outdoor unit controller  27  and the indoor unit controller  34  are connected via the communication line, thus consisting the controller  7  that controls the operation of the refrigeration cycle apparatus  1 . 
     The controller  7  mainly includes a CPU (central processing unit) and a memory, such as ROM and RAM. Note that various processes and control performed by the controller  7  are implemented as the portions, which are included in the outdoor unit controller  27  and/or the indoor unit controller  34 , function in an integrated manner. 
     (6) Operation Modes 
     The refrigeration cycle apparatus  1  can execute at least a cooling operation mode and a heating operation mode. 
     The controller  7  determines whether the instruction indicates the cooling operation mode or the heating operation mode, based on an instruction received from the remote controller or the like, and executes the mode. 
     In the cooling operation mode, the operating frequency of the compressor  21  is controlled to control the volume so that the evaporating temperature of the refrigerant in the refrigerant circuit  10  reaches a target evaporating temperature, for example. 
     The gaseous refrigerant discharged from the compressor  21  is condensed in the outdoor heat exchanger  23  via the four-way switching valve  22 . The refrigerant that has flowed through the outdoor heat exchanger  23  is decompressed while passing through the outdoor expansion valve  24 . 
     The refrigerant decompressed in the outdoor expansion valve  24  flows through the liquid-side refrigerant communication pipe  6  via the liquid-side shut-off valve  29 , and is then sent to the indoor unit  30 . After that, the refrigerant evaporates in the indoor heat exchanger  31 , and then flows into the gas-side refrigerant communication pipe  5 . The refrigerant that has flowed through the gas-side refrigerant communication pipe  5  is sucked into the compressor  21  again via the gas-side shut-off valve  28 , the four-way switching valve  22 , and the receiver  41 . 
     In the heating operation mode, the operating frequency of the compressor  21  is controlled to control the volume so that the condensation temperature of the refrigerant in the refrigerant circuit  10  reaches a target condensation temperature, for example. 
     The gaseous refrigerant discharged from the compressor  21  flows through the four-way switching valve  22  and the gas-side refrigerant communication pipe  5 , and then flows into the gas-side end of the indoor heat exchanger  31  of the indoor unit  30  so that the refrigerant is condensed or is allowed to radiate heat in the indoor heat exchanger  31 . The refrigerant, which has been condensed or has been allowed to radiate heat in the indoor heat exchanger  31 , flows through the liquid-side refrigerant communication pipe  6 , and then flows into the outdoor unit  20 . 
     The refrigerant that has passed through the liquid-side shut-off valve  29  of the outdoor unit  20  is decompressed in the outdoor expansion valve  24 . The refrigerant that has been decompressed in the outdoor expansion valve  24  evaporates in the outdoor heat exchanger  23 , and is sucked into the compressor  21  again via the four-way switching valve  22  and the receiver  41 . 
     (7) Detailed Configuration of Compressor  21   
     The compressor  21  of the present embodiment is a one-cylinder rotary compressor as illustrated in  FIG.  3   , and is a rotary compressor including a casing  81  as well as a drive mechanism  82  and a compression mechanism  88  disposed in the casing  81 . In the compressor  21 , the compression mechanism  88  is disposed below the drive mechanism  82  in the casing  81 . 
     (7-1) Drive Mechanism 
     The drive mechanism  82  is housed in the upper part of the internal space of the casing  81 , and drives the compression mechanism  88 . The drive mechanism  82  includes a motor  83  as a drive source, and a crankshaft  84  as a drive shaft attached to the motor  83 . 
     The motor  83  is a motor for rotationally driving the crankshaft  84 , and mainly includes a rotor  85  and a stator  86 . The rotor  85  has the crankshaft  84  fit-inserted in its internal space, and rotates together with the crankshaft  84 . The rotor  85  includes laminated electromagnetic steel plates and a magnet embedded in a rotor body. The stator  86  is disposed radially outward of the rotor  85  with a predetermined space from the rotor  85 . The stator  86  is disposed while being divided into a plurality of sections at predetermined intervals in the circumferential direction. That is, the stator  86  includes a plurality of sections provided in the circumferential direction each including laminated electromagnetic steel plates and a coil  86   a  wound around a stator body  86   c  having teeth  86   b.  In the motor  83 , the rotor  85  is caused to rotate together with the crankshaft  84  with an electromagnetic force that is generated in the stator  86  as a current is passed through the coil  86   a.  The coil  86   a  of the stator  86  is supplied with power via a wire (not illustrated) connected to a terminal portion  98  provided at the upper end of the casing  81 . 
     The crankshaft  84  is fit-inserted in the rotor  85 , and rotates about the rotation axis. As illustrated in  FIG.  4   , a crankpin  84   a,  which is an eccentric portion of the crankshaft  84 , is inserted through a roller  89   a  (which is described below) of a piston  89  of the compression mechanism  88 , and fits in the roller  89   a  in a state where it can transmit torque from the rotor  85 . The crankshaft  84  rotates with the rotation of the rotor  85 , and eccentrically rotates the crankpin  84   a,  thus causing the roller  89   a  of the piston  89  of the compression mechanism  88  to revolve. That is, the crankshaft  84  has a function of transmitting a drive force of the motor  83  to the compression mechanism  88 . 
     (7-2) Compression Mechanism 
     The compression mechanism  88  is housed in the lower part of the casing  81 . The compression mechanism  88  compresses a refrigerant sucked thereinto via a suction pipe  99 . The compression mechanism  88  is a rotary compression mechanism, and mainly includes a front head  91 , a cylinder  92 , the piston  89 , and a rear head  93 . A refrigerant compressed in a compression chamber S 1  of the compression mechanism  88  is discharged to a space in which the motor  83  is disposed and the lower end of a discharge pipe  95  is located from a front-head discharge hole  91   c  formed in the front head  91  via a muffler space S 2  surrounded by the front head  91  and a muffler  94 . 
     (7-2-1) Cylinder 
     The cylinder  92  is a metal cast member. The cylinder  92  includes a cylindrical central portion  92   a,  a first extension portion  92   b  extending radially outward from the central portion  92   a  to one side, and a second extension portion  92   c  extending from the central portion  92   a  to a side opposite to the first extension portion  92   b.  The first extension portion  92   b  has formed therein a suction hole  92   e  for sucking a low-pressure refrigerant in a refrigeration cycle. A cylindrical space on the inner side of an inner peripheral face  92   a   1  of the central portion  92   a  corresponds to a cylinder chamber  92   d  into which a refrigerant sucked through the suction hole  92   e  flows. The suction hole  92   e  extends from the cylinder chamber  92   d  to an outer peripheral face of the first extension portion  92   b,  and is open at the outer peripheral face of the first extension portion  92   b.  The suction hole  92   e  has inserted therein the tip end portion of the suction pipe  99 . In addition, the cylinder chamber  92   d  houses the piston  89  for compressing a refrigerant that has flowed into the cylinder chamber  92   d,  for example. 
     The cylinder chamber  92   d,  which is formed by the cylindrical central portion  92   a  of the cylinder  92 , has at its lower end a first end that is open, and has at its upper end a second end that is open. The first end that is the lower end of the central portion  92   a  is closed by the rear head  93  described below. The second end that is the upper end of the central portion  92   a  is closed by the front head  91  described below. 
     The cylinder  92  has formed therein a blade oscillation space  92   f  in which a bushing  89   c  and a blade  89   b  described below are disposed. The blade oscillation space  92   f  is formed across a region from the central portion  92   a  to the first extension portion  92   b,  and the blade  89   b  of the piston  89  is oscillatably supported on the cylinder  92  via the bushing  89   c.  The blade oscillation space  92   f  is formed to extend toward the outer periphery side from the cylinder chamber  92   d  around the suction hole  92   e  as seen in plan view. 
     (7-2-2) Front Head 
     As illustrated in  FIG.  3   , the front head  91  includes a front-head disc portion  91   b  that closes the opening at the second end, which is the upper end, of the cylinder  92 , and an upper bearing portion  91   a  extending upward from the peripheral edge of the front-head opening in the center of the front-head disc portion  91   b.  The upper bearing portion  91   a  is cylindrical and functions as a bearing for the crankshaft  84 . 
     The front-head disc portion  91   b  has formed therein the front-head discharge hole  91   c  at a plane position illustrated in  FIG.  4   . A refrigerant, which has been compressed in the compression chamber S 1  having a variable volume in the cylinder chamber  92   d  of the cylinder  92 , is intermittently discharged through the front-head discharge hole  91   c.  The front-head disc portion  91   b  is provided with a discharge valve that opens or closes the outlet of the front-head discharge hole  91   c.  When pressure in the compression chamber S 1  has become higher than pressure in the muffler space S 2 , the discharge valve is opened due to the pressure difference, thereby causing the refrigerant to be discharged to the muffler space S 2  through the front-head discharge hole  91   c.    
     (7-2-3) Muffler 
     As illustrated in  FIG.  3   , the muffler  94  is attached to the top face of the peripheral edge portion of the front-head disc portion  91   b  of the front head  91 . The muffler  94  forms the muffler space S 2  together with the top face of the front-head disc portion  91   b  and the outer peripheral face of the upper bearing portion  91   a,  and attempts to reduce noise generated along with the discharge of a refrigerant. The muffler space S 2  and the compression chamber S 1  communicate with each other via the front-head discharge hole  91   c  when the discharge valve is open as described above. 
     The muffler  94  has formed therein a central muffler opening (not illustrated) for passing the upper bearing portion  91   a,  and a muffler discharge hole (not illustrated) through which a refrigerant is flowed from the muffler space S 2  to a housing space for the motor  83  above the muffler space S 2 . 
     Note that the muffler space S 2 , the housing space for the motor  83 , the space where the discharge pipe  95  is located above the motor  83 , and a space where lubricating oil accumulates below the compression mechanism  88 , for example, are all continuous, and form a high-pressure space with equal pressure. 
     (7-2-4) Rear Head 
     The rear head  93  includes a rear-head disc portion  93   b  that closes the opening at the first end, which is the lower end, of the cylinder  92 , and a lower bearing portion  93   a  as a bearing extending downward from the peripheral edge portion of the opening in the center of the rear-head disc portion  93   b.  The front-head disc portion  91   b,  the rear-head disc portion  93   b,  and the central portion  92   a  of the cylinder  92  form the cylinder chamber  92   d  as illustrated in FIG.  4 . The upper bearing portion  91   a  and the lower bearing portion  93   a  are cylindrical boss portions, and axially support the crankshaft  84 . 
     (7-2-5) Piston 
     The piston  89  is disposed in the cylinder chamber  92   d,  and is attached to the crankpin  84   a  that is the eccentric portion of the crankshaft  84 . The piston  89  is a member integrating the roller  89   a  and the blade  89   b.  The blade  89   b  of the piston  89  is disposed in the blade oscillation space  92   f  formed in the cylinder  92 , and is oscillatably supported on the cylinder  92  via the bushing  89   c  as described above. The blade  89   b  is slidable on the bushing  89   c,  and oscillates and also repeatedly moves away from the crankshaft  84  and closer to the crankshaft  84  during operation. 
     As illustrated in  FIG.  4   , the roller  89   a  and the blade  89   b  of the piston  89  form the compression chamber S 1 , which has a volume variable with the revolution of the piston  89 , such that the roller  89   a  and the blade  89   b  of the piston  89  partition the cylinder chamber  92   d . The compression chamber S 1  is a space surrounded by the inner peripheral face  92   a   1  of the central portion  92   a  of the cylinder  92 , the top face of the rear-head disc portion  93   b,  the bottom face of the front-head disc portion  91   b,  and the piston  89 . The volume of the compression chamber S 1  changes with the revolution of the piston  89  so that a low-pressure refrigerant sucked thereinto through the suction hole  92   e  is compressed to become a high-pressure refrigerant, and is then discharged to the muffler space S 2  through the front-head discharge hole  91   c.    
     (7-3) Operation 
     In the foregoing compressor  21 , the volume of the compression chamber S 1  changes with the movement of the piston  89  of the compression mechanism  88  that revolves with the eccentric rotation of the crankpin  84   a.  Specifically, first, while the piston  89  starts revolving, a low-pressure refrigerant is sucked into the compression chamber S 1  through the suction hole  92   e.  The volume of the compression chamber S 1  facing the suction hole  92   e  gradually increases while it sucks the refrigerant. When the piston  89  further revolves, the communication state between the compression chamber S 1  and the suction hole  92   e  is canceled so that the refrigerant starts to be compressed in the compression chamber S 1 . After that, the volume of the compression chamber S 1  that communicates with the front-head discharge hole  91   c  becomes significantly small, and the pressure of the refrigerant therein increases. After that, as the piston  89  further revolves, the refrigerant with the increased pressure pushes and opens the discharge valve through the front-head discharge hole  91   c,  and thus is discharged to the muffler space S 2 . The refrigerant introduced into the muffler space S 2  is discharged to a space above the muffler space S 2  through the muffler discharge hole of the muffler  94 . The refrigerant discharged to the outside of the muffler space S 2  passes through a space between the rotor  85  and the stator  86  of the motor  83  to cool the motor  83 , and is then discharged from the discharge pipe  95 . 
     (8) Control of Compressor 
     During operation in the cooling operation mode and operation in the heating operation mode, for example, the controller  7  controls the operating frequency of the compressor  21  to control its volume so as to attain a predetermined target evaporating temperature and a predetermined target condensation temperature, respectively, as target values. 
     Herein, even when a disproportionation reaction of a refrigerant has occurred inside the compressor  21  or in the discharge pipe  95 , the controller  7  controls the compressor so as to suppress the propagation of the disproportionation reaction to a portion beyond the discharge pipe  95  in the refrigerant circuit  10 . 
     During the control, the controller  7  controls the operating frequency so that the flow rate of a gaseous refrigerant flowing through the discharge pipe  95  of the compressor  21  becomes greater than or equal to 1 m/s when the compressor  21  has entered an operation state in which its discharge pressure is greater than or equal to 1 MPa. Herein, the controller  7  performs control of increasing the operating frequency in the aforementioned volume control if necessary for allowing the flow rate of a gaseous refrigerant flowing through the discharge pipe  95  to become greater than or equal to 1 m/s. 
     Herein, the controller  7  can use the pressure of the refrigerant detected by the discharge pressure sensor  61  as the discharge pressure of the compressor  21 . In addition, the controller  7  can determine the flow rate of the gaseous refrigerant flowing through the discharge pipe  95  of the compressor  21  by determining the circulation volume, which is the volume flow rate of the refrigerant, based on a known relational expression using the pressure of the refrigerant detected by the suction pressure sensor  63 , the temperature of the refrigerant detected by the suction temperature sensor  64 , and a predetermined piston displacement and volumetric efficiency of the compressor  21 , and dividing the determined circulation volume of the refrigerant by the diameter of the discharge pipe  95 . 
     (9) Feature of Embodiment 
     In the refrigeration cycle apparatus  1  of the present embodiment, a refrigerant that may undergo a disproportionation reaction is used. Such a disproportionation reaction of the refrigerant occurs with a certain probability under an environment where predetermined high-temperature conditions, high-pressure conditions, and ignition energy conditions are satisfied. Then, the disproportionation reaction may propagate to surrounding regions from the portion where the disproportionation reaction has occurred. 
     In response, the inventors used 1,2-difluoroethylene (HFO-1132) as the refrigerant, and prepared a predetermined flow channel connecting to an ignition source to conduct a test of observing a view in which a disproportionation reaction generated in the ignition source propagates, using a super slow camera while changing the flow rate of the refrigerant. The test results demonstrate that the propagation of the disproportionation reaction can be suppressed more when the flow rate of the refrigerant is greater than or equal to 1 m/s than when the flow rate of the refrigerant is less than 1 m/s, and also demonstrate that the effects of suppressing the propagation of the disproportionation reaction are more excellent when the flow rate of the refrigerant is even greater. 
     The compressor  21  for which the refrigerant of the present embodiment is used, and the refrigeration cycle apparatus  1  including such a compressor  21  are configured such that the flow rate of a refrigerant flowing through the discharge pipe  95  of the compressor  21  under predetermined high-pressure conditions becomes greater than or equal to 1 m/s. Accordingly, even when an unstable refrigerant is used in the compressor  21  and the refrigeration cycle apparatus  1  of the present embodiment, and such a refrigerant undergoes a disproportionation reaction inside the compressor  21  or in the discharge pipe  95 , it is possible to suppress the propagation of the disproportionation reaction in the discharge pipe  95 . 
     (10) Other Embodiments 
     (10-1) Another Embodiment A 
     The foregoing embodiment has exemplarily illustrated a case where the operating frequency is controlled such that the flow rate of a gaseous refrigerant flowing through the discharge pipe  95  becomes greater than or equal to 1 m/s when the compressor  21  has entered an operation state in which its discharge pressure is greater than or equal to 1 MPa. 
     In contrast, it is also possible to control the operating frequency such that the flow rate of a gaseous refrigerant flowing through the discharge pipe  95  becomes greater than or equal to 1 m/s when the compressor  21  has entered an operation state in which its discharge pressure is greater than or equal to 3 MPa or greater than or equal to 5 MPa, which is more likely to cause a disproportionation reaction. 
     (10-2) Another Embodiment B 
     The foregoing embodiment has exemplarily illustrated a case where the flow rate of a refrigerant flowing through the discharge pipe  95  of the compressor  21  becomes greater than or equal to 1 m/s so that the propagation of a disproportionation reaction is suppressed. 
     In contrast, the flow rate to be controlled is not limited to 1 m/s. For example, the flow rate of a refrigerant flowing through the discharge pipe  95  of the compressor  21  may become greater than or equal to 3 m/s, or greater than or equal to 5 m/s, or further, greater than or equal to 10 m/s. In this manner, the higher the flow rate of a refrigerant flowing through the discharge pipe  95  of the compressor  21 , the more effectively the propagation of a disproportionation reaction can be suppressed. 
     (10-3) Another Embodiment C 
     The foregoing embodiment has exemplarily illustrated a case where a rotary compressor is used as the compressor  21 . 
     In contrast, a compressor for suppressing the propagation of a disproportionation reaction by increasing the flow rate through the discharge pipe  95  is not limited to a rotary compressor, and may be a known scroll compressor or swing compressor. 
     (10-4) Others 
     Note that the compressor may be a compressor in which the flow rate of a refrigerant flowing through a discharge pipe under a predetermined high-pressure condition is greater than or equal to 5 m/s, or greater than or equal to 10 m/s. The higher the flow rate of the refrigerant flowing through the discharge pipe, the more effectively the propagation of disproportionation can be suppressed. 
     Note that 1,2-difluoroethylene may be trans-1,2-difluoroethylene [(E)-HFO-1132], cis-1,2-difluoroethylene [(Z)-HFO-1132], or a mixture of them. 
     (Supplement) 
     Although the embodiments of the present disclosure have been described above, it is to be understood that various changes to the forms or details are possible without departing from the spirit or scope of the present disclosure recited in the claims. 
     REFERENCE SIGNS LIST 
     
         
           1  Refrigeration cycle apparatus 
           10  Refrigerant circuit 
           21  Compressor 
           95  Discharge pipe 
       
    
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Patent Laid-Open No. 2019-196312