Systematic Investigation of Transient Thermo-Fluid-Mass Coupling in a Hydrogen Knudsen Compressor Under Diverse Thermal Non-Equilibrium Waveforms.

Frequent heat-source drift and environmental disturbances keep hydrogen compressors in a state of thermal non-equilibrium, where transient interactions between thermal transpiration and Poiseuille flows significantly influence system stability and safety. The mechanisms by which time-dependent temperature patterns modulate this coupling remain insufficiently understood. This research addresses this knowledge gap by numerically solving slip-boundary Navier-Stokes equations for six periodic temperature waveforms: rectangular, segmented, square, Gaussian, triangular, and sinusoidal. The results indicate that the heating rate predominantly determines the intensity of forward Poiseuille flow, whereas cooling rate and plateau duration exert comparatively minor effects. Extending the high-temperature plateau from 0.1 to 0.5 s increases both thermal transpiration and backward Poiseuille peaks by more than 100 percent, while slower heating reduces forward Poiseuille peaks by up to 11 percent. Among the six waveforms, the square wave yields the highest peaks for all three flow components. These findings elucidate how waveform structures modulate transient flow responses and offer quantitative guidance for stability assessment and thermal management in hydrogen Knudsen compressors.