Development of Stirling-type pulse tube coolers driven by commercial linear compressors

Abstract

After an introductory section on pulse tube cryocoolers (PTC) this paper reports the state of development of some medium-size PTCs for potential future replacement of commercial Stirling cold fingers. The coolers were designed for operation with the AIM SL200 compressor (nominal input power: 100 W) and Leybold Polar SC7 compressor (nominal input power: 200 W), respectively. Adjustment of phase shift between pressure and mass flow oscillation is accomplished by means of inertance tubes in combination with a reservoir and a second-inlet flow impedance that are attached to the warm end of the pulse tube. Two coolers with U-shaped and one with linear arrangement of regenerator and pulse tube have been built and optimized. Up to now, the smaller U-shaped PTC driven by the AIM compressor at 100 W input power reached a no-load temperature of 45 K, and a cooling capacity of 2.85 W at 80 K is achieved, corresponding to a coefficient of performance of COP = 2.85 %. For the two larger PTCs driven by the Leybold compressor at 200 W of input, the obtained no-load temperature and cooling power at 80 K are 38 K and 6 W for the U-shaped cooler and 44 K and 8.1 W for the linear cooler, corresponding to COPs of 3 % and 4 % at 80 K, respectively. Measurements of the refrigeration temperature as function of the cold head orientation with respect to gravity revealed a small convection-induced temperature variation of several percent. The minimum temperature is achieved with the pulse tube cold end facing downwards.