Study on 4K-GM Refrigerator : Effects of Specific Heat of Regenerator Material on Refrigeration Capacity

In this paper we describe the analysis of the effects of the specific heat of a regenerator material on the refrigeration capacity of a 4K-GM (Gifford-McMahon) refrigerator. The findings revealed by the analysis are given below. When the specific heat of the regenerator material is changed from 1.5 J/(K・cm^3) to 0.01 J/(K・cm^3), the no-load temperature is changed from 2.11 K to 26.9 K. The lowest temperature that can be theoretically attained in this refrigerator is the temperature around the λ point of helium. It is sufficient for the regenerator material to provide a specific heat of 0.8 J/(K・cm^3). The refrigeration capacity is found to be superior over a wider temperature range when the specific heat distribution is uniform than when it has a peak. When different kinds of regenerator materials are stacked, the material stacked at the cold part of the regenerator may have a low specific heat at high temperatures, but the material stacked at the hot part of the regenerator should have a high specific heat at low temperatures.