AVS 47th International Symposium
    Vacuum Technology Thursday Sessions
       Session VT-ThA

Paper VT-ThA7
Study of Thermal Transpiration of Capacitance Diaphragm Gauge by DSMC Method

Thursday, October 5, 2000, 4:00 pm, Room 201

Session: Pressure and Flow Measurements
Presenter: M. Hirata, Electrotechnical Laboratory, Japan
Authors: M. Hirata, Electrotechnical Laboratory, Japan
S. Nishizawa, Electrotechnical Laboratory, Japan
K. Watanabe, CRC Corporation, Japan
Correspondent: Click to Email
Capacitance diaphragm gauge (CDG) is one of the most important vacuum gauges in low and middle vacuum ranges. Sensor head of a high precision CDG is kept for 45°C in order to minimize zero drift from room temperature fluctuation. The difference of temperature between the sensor head and the vacuum chamber gives a non-linear sensitivity of the gauge depending on the pressure less than 130 Pa 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. Empirical equation is widely used to explain the effect.@footnote 1@ In this study, by using a direct simulation Monte Carlo (DSMC) method @footnote 2@, pressure distribution in the connecting tube of the gauge was obtained under the pressure range from molecular flow regime to viscous flow regime (10@super -2@ - 10@super 2@ Pa) with taking account of temperature distribution along the connecting tube. Furthermore, the pressure dependence of sensitivity of CDG for several gases was derived from the pressure difference between the hot and cold ends. It was in good agreement with the pressure dependence of sensitivity obtained by static expansion system experimentally. The pressure distribution inside the connecting tube explains the mechanism of thermal transpiration phenomenon. This method can be also applied for complicated real system. @FootnoteText@ @footnote 1@ T.Takaishi and Y.Sensui, Trans.Faraday Soc. 59, 2503(1963). @footnote 2@ G.A.Bird, "Molecular Gas Dynamics and the Direct Simulation of Gas Flows", Clarendon, Oxford (1994).