Measurements of viscosity, velocity slip coefficients, and tangential momentum accommodation coefficients using a modified spinning rotor gauge

A selection of experimental viscosity and slip measurements are reported fo r He and Ar. The measured values have been made with a modified spinning ro tor gauge (SRG-2; MKS Instruments, Inc.) where the sphere is coaxially rota ted in the cylindrical tube housing. All of the experiments were conducted in the slip regime in accordance with the theory previously developed [S. K . Loyalka, J. Vac. Sci. Technol. A 14, 2940 (1996)]. The theoretical result s from this previous article allow one to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation co efficient from the experimentally obtained angular retardation data for eac h gas without a need for calibration of the system against a known gas visc osity. Since the existing manufactured SRGs mount horizontally with the rot or angular momentum vector oriented vertically, the required SRG modificati ons were necessarily limited to the interior of the mounting tube. Here, an insert was developed for the mounting tube in which was bored a short, ver tically oriented, cylindrical hole in which the rotor could turn coaxially. Measurements made with this modified version of the SRG are compared with previous experimental results and a discussion of the errors associated wit h both wall and end effects is included. (C) 2001 American Vacuum Society.