Semi-empirical boundary conditions for strong evaporation of a polyatomic gas

Abstract

Semi-empirical procedure of obtaining the boundary conditions for strong evaporation of a polyatomic gas from a plane surface is proposed. The procedure is based on specifying the dependencies of specific momentum and enthalpy of the flow from the gas flow rate. The latter are derived from the analysis of the available data concerning the evaporation of polyatomic and monatomic gases. The procedure predicts the exactly sonic terminal velocity of the flow and leads to some corrections of existing boundary conditions in transonic region. Thus, for j = 2 and sonic flow the corrections for pressure, temperature and fraction of back-scattered molecules are about 0.7%, -3% and -8%.