Study of a 72 Hz high-capacity pulse tube cryocooler for space applications

Abstract

Most infrared detectors work at low temperature, which enhances their detection sensitivity and visual field. Nowadays, the cryocoolers commonly used in space detectors are Stirling and pulse tube cryocoolers (PTCs). Compared with the Stirling cryocoolers, PTCs have no moving parts in the cold finger, resulting in low vibration and long lifetimes, and after decades of development, some PTCs already have comparable efficiencies to Stirling models. Thus, PTCs have been considered as ideal substitutes for Stirling cryocoolers in the future. In recent years, with the rapid progress of aerospace applications, the structure and the function of infrared detectors have become more complicated, requiring a higher cooling capacity. However, increasing cooling power always increases of the PTC’s weight, whereas many special aerospace applications have strict size and weight restrictions. As a result, miniaturization of high-capacity PTCs is required urgently in space applications. According to the Radebaugh’s research, increasing the operation frequency of PTCs can be an efficient way to minimize their size and mass because a high operating frequency can increase the energy density. Thus, many researchers and institutions at home and abroad have focused on the study of miniaturized PTCs, but most of the work is carried out on the PTCs used in space with cooling capacities under 5 W. Although some studies have been conducted on high-capacity miniature PTCs in China, none are designed for space applications. Thus, there is an urgent demand for miniaturized PTCs with cooling power above 10 W at 80 K. To minimize the sizes and weights of PTCs, the influences of the length of the regenerators, the charging pressure, and the regenerator matrix upon the operating frequency are presented. The results show that decreasing the volume of the regenerator, increasing the charge pressure, and decreasing the hydraulic diameter of the matrix are beneficial for promoting PTC efficiency with high operating frequency. On the basis of this optimization, 35-mm and 45-mm-length regenerators are designed and manufactured. Some systematic experiments are carried out using the newly designed PTCs. The experimental results also demonstrate that the length of the regenerator, charge pressure, and hydraulic diameter of the matrix significantly impact the efficiency of PTCs with high operating frequencies. Finally, a 72-Hz high-capacity coaxial-pulse-tube cryocooler is obtained with a cooling capacity of 12 W at 80 K and an input electrical power of 250 W. It achieves around 13.2% of the Carnot efficiency at 80 K, which is high compared with the same kind of PTCs. Benefiting from our mature techniques in space-PTC design, this PTC is easy to transform into an engineering model with little difference in efficiency. The success of the design of a 72-Hz PTC cold finger solves the critical problem of ministration and can provide some theoretical and experimental guidance for the design of miniaturized PTCs for space applications.