Parametric study of a free-piston Stirling cryocooler capable of providing 350 W cooling power at 80 K

Abstract

High cooling capacity free-piston Stirling cryocooler (FPSC) has been considered a promising candidate for high temperature superconducting and gas liquefaction applications, which require a cost effective and highly reliable cryocooler capable of providing large cooling power (several hundred watts to several kW) at liquid nitrogen temperature. This paper introduced an advance in a FPSC capable of providing 350 W cooling power at liquid nitrogen temperature. To reveal the relationship between operating parameters and cooling performance, the integrated impact of mean pressure and working frequency on acoustic impedance, acoustic field as well as exergy loss of cooler is studied numerically. The numerical results indicate that for the current design, by tuning the mean pressure and working frequency, an optimal operating scenario of the refurbished FPSC could be obtained, which leads to a higher thermal efficiency. Based on the optimization, a series of experiments were carried out on the improved experimental setup. A cooling power of 350 W at 80 K was obtained with an input electric power of 3.57 kW and the corresponding overall relative Carnot efficiency reached up to 26.8%. Compared with previous reports, the performance has been greatly improved by 25.2%. In addition, a special attention is paid to the heat transfer at the ambient heat exchanger due to the large detected local solid-gas temperature difference in the previous work. Comparisons of two different types of ambient heat exchanger in calculations and experiments indicate that an even better performance could further be expected by employing a shell-tube type heat exchanger with 1 mm inner diameter and a porosity around 0.16.