Influence of Valve Open Timing and Interval on Performance of 4K Gifford-McMahon Cycle Cryocooler

Abstract

The influence of intake/exhaust valve timing on performance of a 4 K Gifford-McMahon(GM) cycle cryocooler has been investigated. The 4 K GM cryocooler is one of the standard two-stage types with magnetic regenerator material, ErNi_0.9Co_0.1, in its second stage regenerator, and delivers more than 1 W cooling at 4.2 K. A reasonably early open timing of intake/exhaust valves not only brings about a cooling capacity above 1 W at 4.2 K on the second stage, but also produces a much larger cooling capacity at the first stage. Under the optimum conditions, 39.4 W cooling at 40 K on the first stage, as well as 1.18 W at 4.2 K on the second stage, was obtained with an input electric power of 7.05 kW. This paper discusses the results of cooling capacity with P-V diagrams, and indicates that the reduction in pressure drop at intake/exhaust valves is important for a 4 K GM cryocooler.