Numerical simulation of thermal transpiration in Capacitance diaphragm gauge

The Capacitance diaphragm gauge 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 due to thermal transpiration effect. This sensitivity depends not only on pressure but also gas species. It is supposed that under the same condition of gas-surface interaction, the sensitivity should be normalized by mean free path independently of gas species. However, the sensitivity normalized by mean free path also depends on gas species. In this study, by using DSMC method, the influence of gas-surface interaction on thermal transpiration was analyzed. In case of random reflection model, the sensitivity has non-linearity and depends on mean free path. On the other hand, in case of a perfectly elastic reflection model, the sensitivity is constant regardless mean free path. In case of complex reflection that is composed of random and elastic reflections, as increasing the elastic reflection component, the sensitivity decreases from that of random reflection to elastic reflection.