Thermoacoustic heat pumping effect in a Gifford-McMahon refrigerator

The heat exchange process between the working helium gas and the regenerator materials in a Gifford-McMahon refrigerator is studied from the viewpoint of thermoacoustic phenomena, by measuring the cooling power as a function of the phase angle between pressure and displacement oscillations of the working gas. It is found that the optimum phase angle maximizing the cooling power dramatically increases when the operating temperature decreases below 20 K. This behavior represents the progress of the irreversible heat exchange process due to the reduction of the thermal diffusivity of helium gas. (C) 2002 American Institute of Physics.