Viscosity Measurements on Water Vapor and Their Evaluation

Abstract

Results of new high-precision measurements of the viscosity of water vapor at low densities are reported. The measurements were performed using an all-quartz oscillating-disk viscometer with small gaps. Ten isochoric series were carried out at temperatures between (298 and 438) K and at densities from (0.001 to 0.013) mol·L- 1. The uncertainty is estimated to be ± 0.2 % at ambient temperature increasing up to ± 0.3 % at higher temperatures. Isothermal values were analyzed with a density series for the viscosity in which only a linear contribution is considered. Values for the viscosity of the saturated vapor were also obtained at low temperatures. The new results and reliable data sets from literature are used to represent the viscosity of water vapor at moderately low densities. The second viscosity virial coefficient was modeled by means of the Rainwater−Friend theory. An individual correlation according to the extended theorem of corresponding states was necessary to describe the zero-density viscosity...