Cooling Capacity Characteristics of Low Power Consumption （2 kW Class） 4 K-GM Cryocoolers

Abstract

From the COP （Coefficient of Performance） equation, there are two ways to improve the cooling efficiency of cryocoolers: （1） increasing the cooling capacity, and （2） decreasing the electrical input power. In recent years, we have focused on the possibility of method （2） for a 4 K-GM （Gifford-McMahon） cryocooler. In this paper, a 7 kW class compressor, which is commonly connected to a 4 K-GM cold head, was replaced with a low power consumption （2 kW class） compressor. The experiments achieved a measured cooling capacity of 0.95 W at 4.2 K with a cold head reciprocation speed of 36 rpm and a compressor electrical input of 1.9 kW. The calculated COP and the relative Carnot efficiency were 5.0×10-4 and 3.5 %, respectively. A low reciprocating speed was selected to secure sufficient expansion work in the second expansion space. This is an effective method to improve the cooling capacity at 4.2 K by a low power consumption compressor.