DSMC analysis of thermal transpiration of capacitance diaphragm gauge

The capacitance diaphragm gauge (CDG) is one of the most important vacuum gauges in low and medium vacuum ranges. CDG has a non-linear sensitivity below 100Pa because of the temperature difference between the sensor head and the vacuum chamber, which is called thermal transpiration. This sensitivity depends on gas species and pressure. In this study, by using a direct simulation Monte Carlo (DSMC) method, pressure distribution in the connecting tube of the gauge was obtained under the pressure range from molecular flow regime to viscous flow regime (10^-2-10²Pa) taking account of the temperature distribution along the connecting tube. Furthermore, the pressure dependence of the sensitivity of the CDG was derived from the pressure difference between the hot and cold ends, and found to be in good agreement with the pressure dependence of sensitivity obtained by an empirical equation. The influence of gas-surface interaction on the thermal transpiration was also analyzed.