Viscosity of argon and of argon-ammonia mixtures under pressures

Abstract

The viscosity of argon and of four argon-ammonia gaseous mixtures was measured using an oscillating disk viscometer at temperatures, 25, 50, 75, and 100℃; for argon, at the pressure range up to about 120×10^5 Pa; and for argon-ammonia mixtures, up to around the saturated vapor pressure of ammonia at each temperature. The accuracy of the measurements was estimated to be within ±0.3%. The gas viscosity values of dilute binary mixtures were calculated by applying a correction factor, which was set up by use of critical compressibility factors. The calculated values were in better agreement with the experimental ones than those calculated by original Chapman-Enskog's method. The initial density dependence of the viscosity, η_0^-1(∂η/∂p)_p→0, of argon-ammonia mixtures was obtained from the experimental values, and the effects of the concentration of nonpolar gases and of temperature on the initial density dependence were compared with those in the case of the nitrogen-ammonia system and of the hydrogen-ammonia system, where η is viscosity of gas, p density, and η_0 the viscosity extrapolated to zero density. It was concluded from the comparison that molecular association of polar gases was hindered by the presence of nonpotar molecules and by a rise in temperature, and that the larger the molecular weight of a nonpolar gas was, the more strongly the nonpolar molecules hindered moecular association of polar substances. By taking into account the mole fraction of nonpolar gases, the initial density dependence of the viscosity could be correlated with the temperature reduced by the critical temperature of the mixtures, and a similar tendency was observed regardless of the system.