Optimum Design Charts for a Piston-Displacer Stirling Cryocooler

Abstract

Stirling cryocoolers are classified as two-piston and piston-displacer cryocoolers. The compression space is swept by one of the pistons in the two-piston cryocooler whereas it is swept by both, piston and displacer, in the piston-displacer cryocooler. An optimization of the principal design parameters for maximum refrigerating capacity of a two-piston Stirling cryocooler is due to an application of Schmidt analysis. Till to-day these design charts are considered to be the base line model for a preliminary design of the Stirling cryocoolers. However the present work indicates that the same cannot be used for piston-displacer cryocooler. Hence the design charts, for maximum refrigerating capacity considering the same Schmidt technique, are presented in this paper for a piston-displacer cryocooler. One of the major assumptions of the Schmidt technique is the perfect regeneration. An attempt is made to account the imperfect regeneration in this analysis by defining a more useful form of the regenerator effectiveness. The parametric study of the various design parameters, such as: swept volume ratio, angle of the phase shift between piston and displacer, temperature ratio and dead volume ratio; reveals that for imperfect regenerative cycle, the optimum design charts are possible to prepare not only for maximum refrigerating capacity but also for maximum coefficient of performance. After large computational work, the optimum design charts are presented for the maximum coefficient of performance and refrigerating capacity of a piston-displacer Stirling cryocooler.