Gas flow measurement by means of orifices and Venturi tubes

Abstract

Numerous applications of vacuum technology require the measurement of gas throughput, as e.g. generation of calibration pressures, testing of vacuum pumps, thin film coating, and semiconductor manufacturing. Since primary methods for measuring gas flow are rather inconvenient, we have explored the gas flow measurement by means of orifices and Venturi tubes. These devices act as converters which transform a throughput to a difference pressure which can be conveniently measured. A thin orifice in the molecular flow regime and a Venturi tube in the viscous flow regime are almost fundamental converters whose characteristics can be calculated from first principles. Furthermore, these devices have high inherent stability. Thin orifices and Venturi tubes have been built and their characteristics for different gases were measured by fundamental methods. By varying diameter and inlet pressure, a wide flow range from 10 -7 to 10 5 mbar s -1 is covered. The experimental data are compared to calculated values and the characteristics are discussed.