Evaluation of Cu and Pb particles with different sizes as regenerator materials in the Gifford-McMahon-Cycle refrigerator

The time-averaged enthalpy flow 〈Ḣ〉 into the second-stage expansion space was evaluated by analyzing the measured pressure in the second-stage expansion space and temperature in the tube connecting the regenerator and the expansion space. Pb and Cu particles with diameters ranging from 0.2 to 1.0mm were chosen as the second-stage regenerator materials. 〈Ḣ〉 was calculated as a function of operating temperature for all these regenerator materials. It was found that the magnitude of 〈Ḣ〉 always increases with decreasing operating temperature, and that 〈Ḣ〉 strongly depends on both the specific heat and the diameter of the particles. We clearly show how 〈Ḣ〉 depends on these two parameters by analyzing the temperature profile in the second-stage regenerator. Heat loss 〈Q̇_loss〉 was also evaluated by taking the energy balance in the second-stage expansion space into account.