Numerical and experimental investigations on coiled resonance tube of a duplex Stirling cryocooler

Abstract

Duplex Stirling cryocooler is promising in mitigating methane emission due to its environmentally-friendly working gas, high thermal efficiency and high adaptivity to varying methane concentration. In this work, a coiled resonance tube is introduced to supplant the conventional straight tube in a resonance tube coupled duplex free-piston Stirling cryocooler (RT-DFPSC) to reduce footprint and elevate power density. At first, an experimental setup was built employing resistance-compliance acoustic load to produce the analogical acoustic field. It was observed from experiments that on a coiled resonance tube, an acoustic power transfer efficiency of 35% was obtained. Based on the experiments, a three-dimensional computational fluid dynamics (CFD) model was subsequently developed to pinpoint the loss mechanism. Due to the interaction of centrifugal, viscous and inertial force, there are two secondary flow vortices in the cross-section of the coiled resonance tube during the reversing flow, accounting for the primary loss. Furthermore, the acoustic loss of the coiled resonance tube increases with the decrease of the coiled diameter, while the spiral pitch has minimal effect on the acoustic and flow field. Typically, the acoustic loss of a coiled resonance tube with a diameter of 0.8 m increases by approximately 9% compared to that of a straight tube. Finally, a one-dimensional equivalent model of the coiled resonance tube was established and integrated into a one-dimensional system-level model. Compared to the straight RT-DFPSC, a system with a coiled tube resonance tube demonstrates a cooling capacity and overall exergy efficiency reduction by 465.2 W and 2.4%, respectively.