Experiments on Condensation of Water Vapor by Homogeneous Nucleation in Nozzles

Abstract

Condensation of water vapor in a highly supersaturated state was studied with steady flow of moist air in supersonic nozzles of different temperature gradients. With measured centerline static pressures, known initial conditions, and known nozzle geometry, the equations of motion could be solved. From these results heat addition to the flow owing to condensation could be determined. By estimating latent heats, condensate mass fractions and condensation rates have been found. It was inferred that at temperatures from 200 to 220°K the condensate was ice. Classical steady-state nucleation theories in conjunction with a droplet growth law were applied to solutions of the condensation integral equation. It was found that on this basis the onset of measurable condensation cannot be predicted from first principles. In a qualitative manner, however, the observations could be correlated with the theory. A contributing factor to the failure of nucleation theory is the lack of knowledge of material properties at the low temperatures in question. In conclusion, new work based on the findings of the conditions at the onset of condensation is suggested.