SLIP FLOW IN LONG, SINGLE CAPILLARIES: PART II. STEADY-STATE FLOW AND SPECULAR REFLECTION

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Abstract
The steady-state slip flow of the rare gases (He, Ne, Ar, Kr, and Xe) and of propane, CO2, and SO2 has been studied at different temperatures in long, single glass capillaries. The results give values of viscosity which are in agreement with literature values when Ar is used as a calibrating gas. The results can be expressed as a linear plot of the non-dimensional permeability ratio K/K0 against reciprocal Knudsen number; the intercept on the K/K0 axis is a. The value of this intercept depends on both gas and temperature being higher for light gases and high temperatures than for more condensable gases and low temperatures. The parameter a is therefore replaced by ((2 – β)/β)a1 where (1 – β) is the so-called specular reflection coefficient and a1 is a constant. The factors affecting (1 – β) have been discussed. It is suggested that contributions to (1 – β) will arise both from elastically and from inelastically scattered molecules, and the magnitude of these contributions is assessed in terms of the properties of the gas and the surface. The expression finally obtained is compared with experimental values of (1 – β).