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Condensation of ethanol by homogeneous nucleation of liquid droplets has been studied in a supersonic nozzle. Continuous static pressure measurements on the nozzle centerline and light scattering measurements permit the condensation process to be resolved in detail for comparison with theory. Nucleation rates found in the present work are in general agreement with previous results obtained in diffusion and expansion cloud chambers. It is seen that the predictions of the classical theory of homogeneous nucleation or that of the statistical mechanical theory with the assumptions of Dunning roughly agree with the experimental results. Various terms entering different versions of nucleation theory are given quantitatively. The pressure variations in the flow found beyond the onset point of condensation are used to study droplet growth processes. It is shown that a simple kinetic growth law with a constant mass condensation coefficient describes the condensation process well.

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.

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