Effect of expander shape on cooling characteristics of model pulse tube refrigerator (2nd Report)

Pulse tube cryocoolers do not have moving parts in the cold section, and they have high reliability. The expander in cryocoolers typically has an inverted U or coaxial shape because this attains a wider absorber area, lower height, and compactness. However, the performance of a Stirling-type pulse tube cryocooler is inferior to that of a Stirling refrigerator. Cooling characteristics of the pulse tube cryocooler greatly depend on the shape of the expander. In this study, an inertance type refrigerator, which uses atmospheric air for the working gas, was developed to examine the effect of the expander shape. This refrigerator model with changeable expander operated with a Stirling cycle, and it was composed of a reciprocating compressor, after-cooler, regenerator, absorber, pulse tube, hot-end, and inertance tube with reservoir. The following expander shapes were tested: in-line, L, L-L, and coaxial shape. The effect of the expander shapes on cooling capacity was examined experimentally and numerically using the model pulse tube refrigerator. Also, analysis using CFD was carried out. The results of experiments showed that the L-shaped expander had the highest performance and the coaxial expander had the lowest performance.