Analytical model for a pulse tube cryocooler bellows phase shifter and experimental results

Abstract

Losses within a pulse tube cryocooler (PTC) are dominated by regenerator losses that scale directly with the magnitude of the mass flow rate within the regenerator. Therefore, in order to maximize PTC performance it is necessary to minimize the ratio of the mass flow rate in the regenerator to the acoustic power. This is accomplished by controlling the phase between the mass flow and the pressure with a phase shifting device installed at the warm end of the pulse tube. The most common device, the inertance tube, has significant disadvantages including limited achievable phase angles and large mass and volume. Also, once installed the inertance tube is not tunable. It has been proposed that the inertance tube be replaced with a hybrid mechanical/electrical phase shifting system. The damping for this system is provided by an eddy current damper and can be controlled via an applied external magnetic field that provides active real-time phase control. This paper presents an analytical model of a bellows phase shifting mechanism for a PTC. The model is used to determine properties of the phase shifting mechanism (volume, mass, spring constant, damping force, etc.) based on typical PTC operating conditions. Initial experimental results are also presented.