Quasi-equilibrium evaporation characteristics of oxygen in the liquid–vapor interfacial region

Abstract

Evaporation is a ubiquitous non-equilibrium phenomenon which plays a vital role in both micro and macro phase transition systems. Leading evaporation theories, such as the kinetic gas theory and the statistical rate theory, rely on the interfacial temperature data to predict the mass flux. Compared to water and other room temperature fluids, the interfacial temperature measurement for cryogenic fluids were seldom reported, which means the evaporation calculations at cryogenic temperatures have to use regular correlations or coefficients developed from non-cryogenic fluids. In the present study, a visualized and controlled evaporation system was designed and fabricated. Liquid oxygen was used as the testing fluid since it is the common oxidant of the cryogenic propellants. The temperature distributions in the interfacial regions of steady-state evaporating liquid oxygen were obtained at a set of mass flux and pressure. Temperature discontinuities up to 0.79 K were observed across the liquid–vapor interface of evaporating oxygen. It was found that the liquid was overheated. The measurement implied that the examined evaporation theories lose their accuracy in predicting mass flux rate and temperature jump at cryogenic temperatures by deviations on several orders of magnitude. A modified expression for the evaporation coefficient was provided which shows higher accuracy than early expressions especially in atmospheric pressure regions.