Experiments on the Effects of Pulse Tube Geometry on PTR Performance

Abstract

Commercial and defense-related demand for reliable, low cost cryocoolers continues to drive the development of pulse tube cryogenic refrigerators. While related to the Stirling cryocooler, the Pulse Tube Refrigerator (PTR) has the distinct advantage over the Stirling of having no moving parts in the expander, yielding the potential for great improvement in the areas of reliability, cost, and vibration minimization. Though the fundamental science of pulse tube refrigeration is well understood, more accurate analytic and numerical modeling tools are needed to facilitate the development of different and higher efficiency PTRs. At the present time, one of the primary areas of uncertainty in pulse tube cryocooler modeling is the calculation of the refrigeration losses due to dissipative mechanisms occurring within the pulse tube itself. The purpose of the experiments described herein is to provide insight into how the volume and aspect ratio of the pulse tube influence both the performance of the PTR and the magnitude of the pulse tube losses. To accomplish that task, a modular PTR was designed such that the pulse tube component could be changed independently of the other components in the system (compressor, heat exchangers, etc.). This facilitated a series of parametric tests on distinct PTRs where the only design variables were those related to the geometry of the pulse tube component. The PTR performance was shown to be relatively insensitive to aspect ratio and sensitive to volume over the range of pulse tubes tested.