High-power Stirling-type pulse tube cryocooler: Observation and reduction of regenerator temperature-inhomogeneities

A single stage Stirling-type pulse tube cryocooler driven by a 10 kW-class linear compressor was built and tested. During operation an azimuthal temperature inhomogeneity around the circumference of the regenerator was observed indicating a significant parasitic streaming in the regenerator. The nature of this streaming was examined and a numerical model based on the Sage software was created to understand its origin. It turns out that there is a critical operating condition where a self-preserving streaming starts to circulate in the regenerator. This critical condition is found to depend on the temperature gradient in the regenerator, the amount of mass flow and on the transverse thermal conductivity of the regenerator material. To overcome the negative effect of circulating streaming, the transverse heat conductance in the regenerator was increased by use of sandwich type fillings, where a part of the original stainless screens was replaced by materials with higher thermal conductance. Using these type regenerator fillings, the losses from streaming were significantly reduced and the refrigeration temperature was lowered to 34.5 K. Cooling powers of 50 W at 45 K and 200 W at 70 K are available with electric input powers of 6.3 kW and 8.6 kW, respectively.