Computational Studies on the Effects of Non-Linear Temperature Functions in Thermal Creep Membranes of Radiantly Driven Knudsen Compressors

Employing rarefied gas phenomenon of thermal creep (also known as thermal transpiration), Knudsen Compressor is a micro/meso-scale gas compressor/pump without moving parts. Driven by a temperature difference, gas molecules moved from the cold side of the thermal creep channel, which has a size less than the molecular mean free path, to the hot side of the channel. To utilize its low thermal conductivity and nanometer range size pores, carbon opacified aerogel membranes, treated as a bundle of thermal creep channels, were used in prior experimental studies of radiantly driven Knudsen Compressors. By absorbing the radiation energy, a temperature gradient will develop inside of a carbon opacified aerogel membrane to drive thermal creep flows. Analytical studies of the radiation energy absorbed by a carbon opacified aerogel membrane were performed and the resulting non-linear temperature distribution function within the carbon opacified aerogel thermal creep membrane was identified previously. This paper presents DSMC (Direct Simulation Monte Carlo) simulation studies that incorporate the previously reported non-linear temperature distribution function to investigate the performance of the radiantly driven Knudsen Compressor with a carbon opacified aerogel membrane. Cases with different connector temperatures for a closed system Knudsen Compressor were studied to observe the maximum pressure differences. Comparison of results indicates that radiantly driven Knudsen Compressor with a carbon opacified aerogel membrane could achieve a larger pressure gradient than what is predicted by the theoretical model reported by Muntz et al.