Characterization of a Knudsen force based vacuum sensor for N2[sbnd]H2O gas mixtures

Abstract

Radiometric phenomena can arise in gas flows in which the local molecular mean free path is in the same order as the temperature gradient length scale. The forces exerted on immersed bodies by such rarefied flows are known as Knudsen (or thermophoretic) forces and can play a major role in nonisothermal microflows. In this work, the direct simulation Monte Carlo (DSMC) method is used to numerically characterize the force and thermal mechanisms on a second generation Microscale In-Plane Knudsen Radiometric Actuator (MIKRA) designed for gas pressure and composition sensing. First, a brief verification analysis of the present DSMC solver in reproducing the thermal conductivity for the gas species of interest – nitrogen and water vapor – is carried out. The geometric impact of the gap between MIKRA beams is then investigated for pure N2 environments. In addition, the beam heat transfer coefficients for N2H2O binary mixtures are extracted from the DSMC data and a dimensionless correlation is proposed for predicting the corresponding Knudsen forces. These results are intended to assist in the operation and design of the MIKRA device.