Refrigeration System

Abstract

The low-side pressure of a refrigeration cycle and the refrigerant temperature at the exit of a gas cooler under reference operating conditions are employed as a reference low pressure and a reference refrigerant temperature, respectively, and the high-side pressure of the refrigeration cycle at which the COP of the refrigeration cycle reaches a maximum value under the reference operating conditions is employed as a reference high pressure. In this case, the volume v 2 of a first fluid chamber ( 72 ) in the expander ( 60 ) just after the closing off of fluid communication from its inlet channel and the volume v 3 of a second fluid chamber ( 82 ) in the expander ( 60 ) just before the provision of fluid communication with its outlet channel are set to v 2 =ρ 1 v 1 r/ρ 2 and v 3 =ρ 2 v 2 /ρ 3 , respectively, where ρ 1 is the density of saturated gas refrigerant at the reference low pressure, ρ 2 is the density of refrigerant at the reference high pressure and the reference refrigerant temperature, ρ 3 is the density of refrigerant adiabatically expanded from a condition of the reference high pressure and the reference refrigerant temperature into a condition of the reference low pressure, v 1 is the volume of the fluid chamber in the compressor just after the closing off of fluid communication from its suction channel, and r is the rotational speed ratio of the compressor to the expander.

1 . A refrigeration system including a refrigerant circuit ( 15 ) in which a compressor ( 50 ), a gas cooler ( 16 ), an expander ( 60 ) and an evaporator ( 17 ) are connected, the refrigeration system operating in a refrigeration cycle having a high-side refrigerant pressure equal to or above the critical pressure of the refrigerant by circulating the refrigerant through the refrigerant circuit ( 15 ), wherein
 the compressor ( 50 ) and the expander ( 60 ) are each composed of a displacement fluid machine whose fluid chamber is variable in volume and are connected one to the other with the rotational speed ratio of the one to the other fixed, and   the volume v 2  of the fluid chamber in the expander ( 60 ) just after the closing off of fluid communication from an inlet channel thereof is set to v 2 =ρ 1 v 1 r/ρ 2  and the volume v 3  of the fluid chamber in the expander ( 60 ) just before the provision of fluid communication with an outlet channel thereof is set to v 3 =ρ 2 v 2 /ρ 3 , where:   the low-side refrigerant pressure of the refrigeration cycle and the refrigerant temperature at the exit of the gas cooler ( 16 ) under reference operating conditions serving as a design standard are employed as a reference low pressure and a reference refrigerant temperature, respectively;   the high-side refrigerant pressure of the refrigeration cycle at which the coefficient of performance of the refrigeration cycle reaches a maximum value under the reference operating conditions is employed as a reference high pressure;   ρ 1  is the density of saturated gas refrigerant at the reference low pressure;   ρ 2  is the density of refrigerant at the reference high pressure and the reference refrigerant temperature;   ρ 3  is the density of refrigerant adiabatically expanded from a condition of the reference high pressure and the reference refrigerant temperature into a condition of the reference low pressure;   v 1  is the volume of the fluid chamber in the compressor ( 50 ) just after the closing off of fluid communication from a suction channel thereof; and   r is the rotational speed ratio of the compressor ( 50 ) to the expander ( 60 ).   
   
   
       2 . The refrigeration system of  claim 1 , wherein the refrigerant circuit ( 15 ) is provided with a receiver ( 18 ) between the exit side of the evaporator ( 17 ) and the suction side of the compressor ( 50 ). 
   
   
       3 . The refrigeration system of  claim 1 , wherein the refrigerant circuit ( 15 ) is provided with an internal heat exchanger ( 20 ) for providing heat exchange between refrigerant flowing from the gas cooler ( 16 ) towards the expander ( 60 ) and refrigerant flowing from the evaporator ( 17 ) towards the compressor ( 50 ).