Investigation of Transient Thermo‐Fluid‐Mass Coupling in a Hydrogen Knudsen Compressor Under Different Thermal Non Equilibrium Processes

Frequent heat source drift and environmental disturbances maintain hydrogen compressors in a state of thermal non-equilibrium, where transient interactions between thermal transpiration and Poiseuille flows significantly influence stability and safety. A comprehensive understanding of how time-dependent temperature patterns modulate coupled behavior remains lacking. This study addresses this gap by solving the slip-boundary Navier–Stokes equations to examine transient thermo-fluidic-mass coupling for six periodic temperature waveforms, including rectangular, segmented, square, Gaussian pulse, triangular, and sinusoidal. The results demonstrate that the heating rate predominantly determines the intensity of forward Poiseuille flow, while cooling rate and plateau duration exert minimal influence. Thermal transpiration flow, through mass redistribution, indirectly governs the formation and reversal of pressure gradients, thereby coupling temperature and pressure fields. Both transpiration intensity and the resulting reverse Poiseuille flow increase with prolonged high-temperature residence time; extending the plateau from 0.1 to 0.5 seconds more than doubles their peak values. Among the six waveforms, the square wave produces the highest peaks for all three flow components due to its maximum heating and cooling rates and the longest high-temperature hold. These findings elucidate the distinct modulation of flow responses by waveform structures and offer theoretical support for stability assessment and thermal management optimization.