磁性蓄冷材を使用した小型冷凍機 ４Ｋ‐ＧＭ冷凍機における吸排気バルブの最適化

Abstract

The influence of intake/exhaust valve timing on performance of a 4K Gifford-McMahon (GM) cryocooler has been investigated for the optimization of intake and exhaust valves. The 4K-GM cryocooler employed for the present study was a standard two-stage type with a rotary valve for intake/exhaust. The second stage regenerator in the cryocooler had both lead spheres and spherical magnetic regenerator material, ErNi0·9Co0·1, with the latter arranged at the colder end. The experimental results described in this paper show that a reasonably early valve open timing not only produced much greater cooling capacities on both stages, but also was advantageous in terms of cycle speed, no load temperature and input power to the compressor. Under the optimum conditions, the cooling capacities, above 1.10W at 4.2K as well as close to 40W at 40K, were obtained with an input electric power of about 7kW. This paper discusses the results of cooling capacity with P-V diagrams, and indicates that the reduction in pressure drop at the intake and exhaust valves is important for a 4K-GM cryocooler.