Compressor-Specific Design of a Single Stage Pulse Tube Refrigerator

Abstract

A single stage active valve pulse tube refrigerator has been designed to operate at 30 K and provide a nominal cooling power in excess of 30 watts. This report details the various considerations comprising the system design, focusing on the limitations imposed by the reciprocating-type compressor commonly used for GM-style pulse tube refrigerators. We describe a design method for GM-style pulse tubes to maximize the pulse tube cooling power that can be produced from a compressor of fixed capacity. The method provides a physical understanding of the various influencing factors, and is illustrated using the specifications for the Cryomech CP640 compressor, which draws a maximum electrical power of 5.5 kW. The design process begins by defining mass flow and compressor work as a function of the discharge and suction pressures, thereby producing a compressor performance map. The compressor map in turn provides a framework from which the pulse tube system geometry can be optimized for maximum cooling power. Various real constraints, such as pressure drop through the valves and regenerator, laminar boundary layer along the pulse tube walls, and conduction losses are included in the design process and are shown to significantly impact the optimized result.