Numerical investigation into the low-pressure detection sensor performance of hydrogen gas with variable soft sphere molecular model

Abstract

Direct Simulation Monte Carlo (DSMC) method is used to simulate the hydrogen detection process with Microscale In-Plane Knudsen Radiometric Actuator (MIKRA). The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures that its results are compared with variable soft sphere (VSS) in literature. On the right side of the shuttle arm, the influence of molecular model (VSS and VHS) on the simulation results is small. And the temperature ratio, heat transfer ratio and pressure ratio are highly close to 1. But on the left side of the shuttle arm, the differences are significant resulting from molecular models. Especially, for the heat transfer on the left side of the shuttle arm, heat transfer ratio of VHS model to VSS model is maximally about 4.3. The influence of gas pressures and hydrogen concentrations on the detection performance of MIKRA is also discussed. The decrease of hydrogen concentration and the increase of gas pressure cause the center of the main vortex to move towards the heater arm, and the influence of the gas pressure is more significant. On the other hand, Knudsen force increases with the increase of the hydrogen concentration and its peak value is obtained in a higher gas pressure. For example, the peak value of Knudsen force can be attained for the gas pressure of about 387 Pa in the pure hydrogen domain while in the pure nitrogen domain, the gas pressure of about 260 Pa. Simultaneously, the relation of the linear dependence of Knudsen force on the hydrogen concentration is proposed to detect hydrogen concentration in N2–H2 mixtures.