Two-stage expansion refrigerating device

Abstract

An object is to provide a two-stage expansion refrigerating device capable of performing control with low cost so that a pressure of a refrigerant which has flowed through a high-pressure-side expansion unit is an optimum pressure, the device comprises a control unit (a controller) which controls a compressor (a low-stage-side compression element and a high-stage-side compression element) and each expansion unit (a high-pressure-side expansion valve as a high-pressure-side expansion unit and a low-pressure-side expansion valve as a low-pressure-side expansion unit), and a temperature sensor (a temperature detection unit) which detects a temperature of the refrigerant which has flowed through the high-pressure-side expansion valve, and the controller estimates a pressure of the refrigerant which has flowed through the high-pressure-side expansion valve based on a temperature detected by the temperature sensor, and controls one of the high-pressure-side expansion valve and the low-pressure-side expansion valve based on the estimated pressure.

1 . A two-stage expansion refrigerating device which is provided with a refrigerant circuit including a compressor, a gas cooler, high-pressure-side expansion means, gas-liquid separation means, low-pressure-side expansion means and an evaporator and which returns a gas-phase refrigerant separated by the gas-liquid separation means to an intermediate-pressure section of the compressor and which allows a liquid-phase refrigerant to flow into the evaporator via the low-pressure-side expansion means, the device comprising:
 control means for controlling the compressor and each expansion means; and   temperature detection means for detecting a temperature of the refrigerant which has flowed through the high-pressure-side expansion means,   wherein the control means estimates a pressure P 2  of the refrigerant which has flowed through the high-pressure-side expansion means based on a temperature detected by the temperature detection means, and controls one of the high-pressure-side expansion means and the low-pressure-side expansion means based on the estimated pressure P 2 .   
   
   
       2 . The two-stage expansion refrigerating device according to  claim 1 , wherein the temperature detection means detects the temperature of the liquid-phase refrigerant separated by the gas-liquid separation means. 
   
   
       3 . The two-stage expansion refrigerating device according to  claim 1  or  2 , wherein the control means controls one of the high-pressure-side expansion means and the low-pressure-side expansion means based on the pressure P 2  and a pressure P 1  of the intermediate-pressure section of the compressor. 
   
   
       4 . The two-stage expansion refrigerating device according to  claim 1 ,  2  or  3 , wherein the control means controls one of the high-pressure-side expansion means and the low-pressure-side expansion means so that the pressure P 2  is lager than the pressure P 1 .