The unsteady state flow of ammonia gas has been investigated to determine its viscosity at elevated pressures and moderate temperatures. This was accomplished in an experimental unit of the transpiration type which was calibrated with nitrogen, for which viscosity data at high pressures were available in the literature. To obtain the viscosity at the operating conditions the basic differential equation for the unsteady state flow caused by the experimental procedure was developed and solved with an IBM-650 digital computer.
Experimental runs were conducted for pressures ranging from 250 to 5,000 lb./sq. in. and temperatures from 100° to 200°C. This information has been used to establish the viscosity of ammonia at these dense phase conditions for which no viscosities had been previously reported. These values were used to develop a unique correlation between the residual viscosity and the density. This correlation then enabled the determination of ammonia's viscosity at the critical point μc = 2,395×10−5 centipoises.
The Enskog viscosity equation has been used with the values resulting from this study and PVT data for ammonia to develop a relationship for the probability of nearness. This relationship enables viscosities to be calculated for densities up to 0.450 g./cc. which are in close agreement with the experimental values.