Dynamic Analysis of a Free Piston Stirling Refrigerator

Abstract

Small free-piston type Stirling refrigerators are widely used for the cooling of cryogenic infra-red sensors. In this study, a dynamic analysis of a small free-piston type Stirling refrigerator is performed with an isothermal thermodynamic model to understand the characteristics of the refrigerator. In the free-piston type Stirling refrigerator, the pressure wave, which is generated by the dual opposed pistons of the compressor, is the driving force of the displacer. The cooling capacity in the displacer's expansion space is generated by the motion of the displacer and the pressure wave. Therefore, the dynamic characteristics of the linear compressor's pistons and displacer have a strong effect on the thermodynamic performance of the refrigerator. In this study, the electric equations describing the motor's force generation and the equations of motion for the linear compressor's pistons and displacer were simultaneously solved using a 4 th-order Runge-Kutta method. The pressure drop through the displacer, which contains the regenera-tor, was included as the driving force of the displacer. The analysis was performed for an example refrigerator, with the key operating variables treated parametrically; these variables included the operating frequency of the linear compressor, the charge pressure of the refrigerator, and the supplied electric voltage to the linear compressor.