Analytical model for multicomponent wall film evaporation with non-unity Lewis number

Abstract

Analytical expressions for the external heat flux from ambient to the wallfilm liquid-vapor interface and the phase change rates at the interface are derived from first principles using the governing equations. This is done in two models. The first assumes the unity Lewis number condition and the second, relaxes the unity Lewis number assumption with a simplifying assumption for the specific heat to obtain an analytical expression. A correction factor is obtained from these two models, which is used to derive the final expression. The model was coded into a computer program and applied to simulate transient evaporation of liquid wallfilms placed on the bottom wall of a square channel. Normal evaporation and flash boiling conditions were considered for various liquid composition of the wallfilms, including single component light (n-heptane, iso-octane) and heavy (tetradecane) alkanes and a multicomponent case of 50% n-heptane 50% iso-octane. Computation results for all these cases are presented and the phase change behavior simulated is discussed.