Viscosity of hydrogen and of hydrogen-ammonia mixtures under pressures

Abstract

The viscosity of gaseous hydrogen and of gaseous hydrogen-ammonia mixtures of four different ratios was measured using an oscillating disk-type viscometer at temperatures of 25, 50, 75, and 100℃, and in the pressure range up to about 120×10^5 Pa for hydrogen and up to the vicinity of the sacurated vapor pressure of ammonia for hydrogen-ammonia mixtures. The accuracy of the measurements is estimated to be within ±0.3%. In the calculation of the gas viscosity of dilute binary mixtures based on Chapman-Enskog's theory, a modification of the combination rule using the critical compressibility factor was presented. The calculated viscosity values obtained by applying the critical compressibility factor were in better agreement with the experimental ones than the original Chapman-Enskog's theoretical ones. The initial density dependence of the viscosity of hydrogen-ammonia mixtures, i.e., η_0^-1(∂η/∂p)_p→0, increased with an increase in temperature and in the mole fraction of hydrogen as in the case of the nitrogen-ammonia system, where η is the viscosity of a gas, η_0 is the viscosity extrapolated to zero density, and p is density, Further, it may be concluded that the nonpolar molecules of larger molecular weight disturb more strongly the dimerization of polar molecules than those of smaller molecular weight.