Numerical and experimental study of partly tapered pulse tube in a pulse tube cryocooler

Abstract

• A pulse tube partly tapered at the ambient end is proposed. • Simulations show that partly tapered pulse tube is better than that of a straight pulse tube with ambient flow straightener. • Experiments show that partly tapered pulse tube can eliminate the need for an ambient flow straightener. • Flow straightener is necessary in a straight pulse tube. For a pulse tube cryocooler, the expansion efficiency of the pulse tube is important and is strongly related to the flow inside. Conventionally, flow straighteners are used at both ends of the empty pulse tube to ensure a uniform flow. This approach complicates the system and also becomes a source of flow losses. In this paper, a partly tapered pulse tube that has a tapered section at the ambient end is used to replace the flow straightener. Its performance was compared with that of a conventional straight pulse tube without or with flow straightener at the ambient end numerically and experimentally. Simulation results show that the flow straightener is necessary in the straight pulse tube due to the influence of jet-driven streaming in the location where abrupt cross-sectional area change occurs. The partly tapered pulse tube can effectively eliminate the need for flow straightener. The expansion efficiency is the highest (about 94%) for the partly tapered pulse tube, while an efficiency of 88% is obtained with the straight pulse tube with a flow straightener. Experiments have been conducted; the cooling power of the straight pulse tube without flow straightener, the straight pulse tube with flow straightener, and the partly tapered pulse tube is 3.9, 28, and 29 W, respectively. The cooling power of the straight pulse tube with flow straightener and that of the partly tapered pulse tube are almost the same, which indicates that the partly tapered pulse tube can effectively eliminate the need for an ambient flow straightener.