Model for drag forces in the crevice of piston gauges in the viscous-flow and molecular-flow regimes
نویسندگان
چکیده
A model for drag forces in the crevice of pneumatic piston gauges is presented. The model uses an interpolation function for momentum transfer between the piston and the cylinder mediated by the gas flowing in the crevice. The interpolation function bridges the gap between the molecular-flow and viscous-flow regimes, and is then used to develop an expression for the effective area of a piston gauge. The deviations of the effective area of this model from the viscous-flow results are derived for both floating-piston and floating-cylinder designs. Model results are compared with published measurements of the effective area of several piston gauges in which relative changes as large as 30 10–6 (30 ppm) were observed when different pressurizing gases were used.
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