Effects of Heterogeneous Nucleation of Water Vapor in Nozzles

Abstract

Condensation initiated by heterogeneous nucleation, which is surface dependent, is examined experimentally for the case of rapid nozzle expansions of water vapor. In contrast to previous de Laval nozzle steam experiments for vapor condensation initiated by homogeneous nucleation, the present results are for flows seeded with inorganic smoke and metallic ions. The influence of heterogeneous seeding materials on the condensation process is readily observable by comparison of seeded and unseeded experiments which are otherwise identical. Quantitative results for temperature and other properties, as well as condensation rates, follow based on pressure distribution. The results indicate that the prolonged isentropic expansion of a seeded flow gives a substantial decrease in entropy production for 1/10 micron and below particle sizes determined by electron microscopy. An attempt is made at determining the relative influence of ions and smokes. The competitive nature between heterogeneous and homogeneous processes is clearly evident.