UNSTEADY-STATE EVAPORATION IN WEIGHTLESSNESS

The problem of phase transition is one of the key problems in modern s cience and technology. Evaporation of liquids and condensed gases in a multi-component atmosphere usually takes place under non-equilibrium conditions in the presence of heat fluxes. Phase equilibrium and trans itions in the absence of heat fluxes are investigated thoroughly nowad ays. The existing Hertz-Knudsen and Clausius-Clapeyron models describe phase coexisting curve and non-equilibrium states (deviations from th is curve) in the absence of heat fluxes. The present paper deals with investigations of non-equilibrium phase transitions in the presence of heat, mass and momentum fluxes through the phase interface. The model is based on mass, momentum and energy fluxes conservation equations o n phase interface. The problem of unsteady state evaporation of conden sed gas in multicomponent atmosphere is solved under the assumption th at parameters of the interface are located within phase coexisting hyp erspace in the phase space of parameters. A selfsimilar solution of th e unsteady problem is obtained providing the possibility to follow tem perature and concentration of species profiles' evolution in time. The mass rate of evaporation as a function of time is determined. For val idation of the mathematical model, experiments on unsteady evaporation of liquefied oxygen were carried out. The dynamics of temperature, de nsity and concentration profiles near the phase interface were investi gated experimentally. Comparisons show good qualitative and quantitati ve agreement of theoretical and experimental results. A unique approac h is worked out to solve problems of non-equilibrium phase transitions in the presence of heat fluxes. (C) 1997 Elsevier Science Ltd.