Influence of gas axial conduction enhancement factor on the oscillating flow behavior of an inertance pulse tube cryocooler

Abstract

Most one-dimensional simulation models developed so far to estimate the theoretical performance of pulse tube cryocoolers ignore the effect of heat loss arising out of thermal dispersion in porous media and turbulent conduction in pipes. In this paper one-dimensional numerical simulation of an inertance type pulse tube cryocooler has been carried out to illustrate the effect of thermal dispersion and turbulent conduction on the oscillating gas flow and heat transfer behavior. The study has been conducted under three conditions: simulation of cryocooler without considering gas axial heat conduction effects, simulation of cryocooler with gas axial heat conduction but neglecting the influence of thermal dispersion and turbulent conduction, and simulation of the cryocooler with gas axial heat conduction including the influence of thermal dispersion and turbulent conduction. The effect of thermal dispersion and turbulent conduction in the gas phase has been expressed in terms of an axial-conduction-enhancement-factor in the gas energy equation. It is revealed that the inclusion of axial-conduction enhancement factor in the porous media and tubes of the pulse tube cryocooler creates a positive phase shift in all oscillating physical quantities. This phase change causes an adverse effect on the cooling mechanism of the pulse tube cryocooler. It is found that, the coefficient of performance decreases by 8.6% and the minimum cooling temperature increases by 6.67% when the axial-conduction enhancement factor is included in the one-dimensional simulation model.