Initial density dependence of gas viscosity

Abstract

The gas viscosity depends on pressure or density and was expressed as a sum of the viscosity which arose from the effect of molecular association and that which was caused from the effect of transfer of the momentum by the molecular collision. The initial density dependence of gas viscosity, α'=η_0^-1(∂η/∂p)_p→0, was obtained from the experimental viscosity values and was compared with the theoretically calculated α'-values, where η is viscosity of gas; p density; and η_0 the viscosity extrapolated to zero density. For a nonpolar gas, the experimental α'-values were obtained from the viscosity data of eleven kinds of gases. The effect of molecular association on the gas viscosity was slight, and the contribution from collisional transfer was correlated by use of T^*, where T^*=T/ek^-1; T is absolute temperature; e the potential parameter; and k the Boltzman constant. The improved α'-values were in better agreement with the experimental ones than the original theoretical ones. For a polar gas, the experimental α'-values were obtained from the viscosity data of NH_3, SO_2, H_2O and three hydrocarbon halides. The effect of molecular association on the gas viscosity was extremely larger than that of a nonpolar gas. The theoretically calculated α'-values were correlated by use of the polarity parameter, δ. The improved α'-values were in good agreement with the experimental ones except H_2O.