CFD Simulation of Orifice Pulse Tube Refrigerator

Abstract

A commercial Computational fluid dynamics (CFD) software package Fluent 6.1 is used to model the oscillating flow inside a pulse tube cryocooler. In this paper analysis of orifice type pulse tube refrigerator (OPTR) systems operating under a variety of thermal boundary conditions are modeled at different frequencies. The compressor used is having dual opposed piston arrangement. The simulations are done at different frequencies with helium as working fluid. The simulated OPTR consists of a compressor (dual opposed piston), a transfer line, an after cooler, a regenerator, a pulse tube, a pair of heat exchangers for cold and hot end, an orifice valve and a reservoir. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary conditions are a cyclically moving piston wall at one end of the tube and constant temperature or heat flux boundaries at the external walls of the hot end and cold end heat exchangers. The experimental method to evaluate the optimum parameters of OPTR is difficult. On the other hand, developing a computer code for CFD analysis is equally complex. The objectives of the present investigation are to ascertain the suitability of CFD based commercial package, Fluent and also to examine the performance for the effect of compressor frequency on the orifice type pulse tube refrigerator (OPTR). The results confirm that CFD based Fluent simulations are capable of elucidating complex periodic processes in OPTRs. As a result, the performance analysis also shows that an optimum frequency always exists corresponding to the minimum cold end temperature for same operating boundary conditions. Results show that at high frequency the secondary-flow recirculation occur at the vicinity of component-to-component junctions to reduce the heat pumping effect from low temperature heat exchanger (HX) to high temperature HX. On the contrary, at low frequency, the low pumping rate affects to achieve the minimum temperature. Hence the system performance is best achieved at an optimum frequency.