Numerical simulation of thermal transpiration of capacitance diaphragm gauge

The Capacitance diaphragm gauge (CDG) is one of the most important vacuum gauges in low and middle vacuum ranges. The difference of temperature between the sensor head and the vacuum chamber gives a non-linear sensitivity of the gauge depending on the pressure due to thermal transpiration effect. Change in the sensitivity of about 4% between molecular flow regime and viscous flow regime is significant for metrological use of the gauge. In this study, by using a 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 with taking account of temperature distribution along the connecting tube. It was in good agreement with the pressure dependence of sensitivity obtained by static expansion system experimentally. Furthermore, influence of gas-surface interaction on the thermal transpiration was also discussed.