Miniature pulse tube cooler with linear compressor

Abstract

Pulse tube coolers operate without any moving solid parts inside the cold finger. This feature promises higher reliability, lower vibrations, and lower production cost, when compared to conventional Stirling coolers. We have designed and constructed a miniature-size pulse tube cooler for potential future replacement of Stirling coolers. To allow for easy access to the cold platform, a U-shaped configuration of pulse tube (diameter 4.5 mm, length 60 mm) and regenerator has been chosen. The pressure oscillation of the helium working fluid in the system is generated by means of a commercial linear compressor (AIM, model SL100) operated at a frequency of 50 Hz. A combination of capillary and buffer volume and a second-inlet capillary, which are connected to the warm end of the pulse tube, serve to adjust the phase shift between pressure and mass flow oscillation in the cooler. A maximum cooling power of about 0.3 W at 80 K and a slope of the load line of 40 mW/K have been achieved so far at a compressor input power of 90 W and a heat rejection temperature of about 330 K. The overall COP of 0.3% at 80 K is still appreciably lower than that of comparable Stirling coolers, which is related to enhanced regenerator losses and DC gas-flow in the pulse tube cold head. The experimental data are compared to a linear network model for the pulse tube cold head.