NUCLEATION OF SUPERSATURATED VAPORS IN NOZZLES .1. H2O AND NH3

Measurements have been made of the results of homogeneous nucleation of NH3 and H2O vapors expanding in steady flow in a supersonic air nozzle. From the effect of the nucleation and growth of liquid from the vapor phase on the nozzle pressure distribution, the point of incidence of condensation is readily detected. Experimental results have been compared with the predictions of the classical nucleation rate equation and with the quantum-statistical treatment of Lothe and Pound. While H2O nucleation rates are in agreement with the classical equation, NH3 nucleation follows the very much higher rates (12 to 18 orders of magnitude) of the Lothe-Pound equation. A mass accommodation coefficient of 0.01 <ξ<0.1 for H2O was inferred from the experimental data.