Experimental Verification of a Thermodynamic Model for a Pulse Tube Cryocooler

Abstract

In a recently submitted article¹ a thermodynamic model is described which provides an explanation for the performance of a GM type pulse tube cycle, permits optimization of cooling power for a given pulse tube system through the control of valve timing, and allows the design of pulse tubes to achieve the optimized coefficient of performance for specific cooling capacities. The cooling capacity is shown to be correlated with the net work done by the cold end control volume over one cycle. This paper presents an experimental verification of that model for two different scenarios, optimizing cooling power for a given pulse tube system and optimizing COP for a given compressor. The influence of the important parameters, including two intermediate pressures, the timing of the isobaric processes, and the size of the pulse tube on the refrigeration performance are intensively investigated. In addition, the results define a minimum necessary compressor capacity based on the pulse tube size and cycle frequency. Performance is characterized by the cooldown time, the minimum cold end temperature, and the cooling capacity at 60 K. The model predictions are compared both with experimental results obtained from systems driven by a GM compressor with an electrical input power of 1 kW, and with those reported for the Active Buffer system of Zhu².