Experimental study on the effect of aftercooler configuration on the performance of pulse tube cryocoolers

Abstract

An aftercooler for a pulse tube cryocooler (PTC) was experimentally investigated. The aftercooler is the heat exchanger on the high-temperature side and one of the main components of a PTC. Three types of aftercoolers were studied: a mesh type with complex flow channels, a square hole type and a circular hole type with uniform flow channels. The mesh type has high heat transfer characteristics but also a large viscous loss, while the latter two types have low heat transfer but also small viscous loss due to their uniform flow channels. In this study, one mesh type and two circular hole type aftercoolers were constructed, and their heat transfer characteristics in steady flow, and the cooling performance of the PTC were experimentally evaluated. In the steady flow experiments, the mesh type aftercooler showed higher heat-transfer performance than the circular hole type aftercoolers. Next, an oscillatory flow experiment was conducted by installing the aftercoolers into a PTC. The PTC with the circular multi-hole type aftercoolers showed better cooling performance than the PTC with the mesh type aftercooler, contrary to the results of the steady flow experiment. To investigate the reason for this difference, we evaluated the power loss in the aftercooler and measured the temperature distribution along it in oscillatory flow experiments, and found that the mesh type aftercooler showed characteristics different from those of the other aftercoolers. Based on these results and the relationship between the flow channel radius and the thermal boundary layer thickness, the issues with the mesh type aftercooler were clarified and necessary information for an improved design was developed.