Development of a 25 K Pulse Tube Refrigerator for Future HTS-Series Products in Power Engineering

Abstract

Demands are made on refrigerators for future HTS‐series products like generators, motors, transformers, which are only partly fulfilled by commercially available refrigerators. Based on the experiences with HTS‐prototypes, pulse tube refrigerators (PTRs) are considered to have the highest potential to fulfill the identified requirements. Siemens have therefore started the development of a high‐performance PTR together with TransMIT Giessen. Design target is a PTR with a cooling power of 80 W near 25 K based on an oil‐free CFIC — linear compressor with a power input of 2 × 5 kW. The initial tests on the first single‐stage laboratory version of this PTR with stainless steel mesh regenerator revealed high regenerator losses from circulating mass flow that manifests itself in form of an azimuthal temperature asymmetry in the regenerator. The circulating flow can be greatly reduced by increasing the transverse heat conductance of the matrix by use of stacks of different materials. So far, the minimum no‐load temperature of the PTR is 35 K and a cooling power of 75 W is available at 50 K with a compressor efficiency of about 80 %. Further optimization of the regenerator matrix appears to be possible.