A pulse tube refrigerator below 2 K

Abstract

Up to now, all pulse tube refrigerators operating at the liquid helium temperature range use 4 He as the working¯uid. However, the lambda transition of 4 He is a barrier for reaching temperatures below 2 K. Theoretical analysis in this paper shows that, using 3 He, the temperature limit is below 2 K, and the eciency of a 4 K pulse tube refrigerator can be improved signi®cantly. A threestage pulse tube refrigerator is constructed. A compressor with input power of 4 kW and a rotary valve are used to generate the pressure oscillations. With 4 He, a minimum average temperature of 2.19 K was reached. Replacing 4 He by 3 He, at the same valve settings and operating parameters, the minimum average temperature goes down to 1.87 K and the cooling power at 4.2 K is enhanced about 60%. After ®ne tuning of the valves, a minimum average temperature of 1.78 K was obtained. This is the lowest temperature achieved by mechanical refrigerators. Ó

Performance of cryogenic regenerator with 3He as working fluid

“…Regenerative cryocoolers are seen as a solution satisfying these demands. In the last 40 years, most cryocoolers used in scientific studies and even commercial products employ working substances of 4 He [1][2][3]. 4 He is an excellent refrigerant and easily available in the market.…”

“…Its thermophysical properties including equation of state are well known. However, due to a small thermal expansion coefficient, the cooling capacity of 4 He regenerative cryocoolers diminishes quickly at liquid helium temperatures close to the lambda transition line of this fluid. The lowest non-load cooling temperatures achieved by commercial regenerative cryocoolers are of order 2.3 K, while the cooling power at 4.2 K can reach 1-1.5 W. Much of the research on cryocoolers has focused on such issues as 1) improving heat transfer at the cold end, 2) modifying the structures, *Corresponding author (email: huangyh@sjtu.edu.cn) and 3) adjusting the phase shifter.…”

“…The stable isotope 3 He exhibits advantages with better integrated features in density, specific heat, enthalpy, thermal conductivity and viscosity for regenerative cryocoolers, which have been verified by preliminary experimental investigations. de Waele et al [4] were the first to introduce 3 He in a three-stage pulse tube cryocooler and succeed in attaining 1.87 K at the cold end of the last stage. Satoh and Numazawa [5] then achieved a cooling temperature of 1.47 K using 3 He as working fluid in a G-M cryocooler with a new regenerative material.…”

“…Jiang et al [6] further lowered the cooling temperature down to 1.27 K in a separated-type two-stage pulse tube cryocooler. They also compared experimental results obtained by substituting 3 He for 4 He. More recently, a four-stage pulse tube cryocooler developed by Nast et al [7] at Lockheed-Martin using 3 He in the last stage, reached a temperature of 3.8 K with an input power of 300 W and a frequency of 31 Hz.…”

“…In collaboration with our group, Radebaugh et al [8,9] from NIST developed a new version of the regenerator modeling code-REGEN3.3, which incorporates the thermophysical properties of both 4 He and 3 He. Preliminary calculations of high frequency cryocoolers with 3 He and 4 He have been conducted to investigate how geometry and materials, among other aspects, affect the performance of the regenerator working at 4 K at the cold end and 20 K at the hot end.…”