NEW FLOW BEHAVIOR OF GASES AND VAPORS IN VACUUM AT VERY LOW FLOW-RATES

An investigation of flow of gases and vapors in vacuum through a path of very small cross-sectional area, namely that of a high vacuum gas leak valve, reveals the existence of a new flow behavior which is well behaved. The characteristics are different from that of the molecular flow or that of the sonic flow through a small aperture. The unambiguous nature of the flow has been observed by three independent flow measurement techniques. The conductance is found to decrease with the pressure upstream and depends on the geometry and specie. The effect of the residence time of the gas molecules during the collisions with the wall of the conducting path has been attributed as a possible mechanism to explain the observed flow phenomenon. The flow behavior has also been studied for two isotopic water vapors. Based on the defined characteristics of the flow, an application technique is proposed for finding the partial pressures of the component vapor and gases in a low-vacuum system by making the measurements in a coupled high vacuum system using a quadrupole mass analyzer. The applicability and sensitivity of the technique are demonstrated by an example measurement of the compositions of hydrogen and oxygen gas mixture.