Heat and mass transfer during ethanol evaporation on the walls of a flat channel at forced convection of humid air

Abstract

• The process of joint heat and mass transfer during the flow of moist air in a flat channel at ethanol evaporation on the walls was studied. A similarity in distributions of velocity, temperature, and component concentration profiles has been found. • The contribution of the heat flux components to the total energy exchange on an adiabatic wall has been determined. It was found that with an increase in the moisture content, the contribution of the convective component decreases. • Condensation of steam intensifies the process of ethanol evaporation, as a result of which the mass flows of water and ethanol vapors increase with increasing inlet air humidity. • The use of ethanol as an evaporative agent allows obtaining of the high values of the air cooling parameter, including those at high humidityφ in → 100%. The results of numerical investigation of heat and mass transfer in the laminar flow of humid air in a plane-parallel channel with adiabatic walls from the surface of which ethanol is evaporated are presented. The main attention is paid to studying the influence of air humidity at the inlet in the entire range of its change from absolutely dry to fully saturated state ( φ = 0 ÷ 100 % ) on the heat and mass transfer intensity and cooling efficiency. It has been established that ethanol evaporation and steam condensation occur simultaneously on the channel walls. The relationship between the components of the heat and diffusion flows on the wall is determined depending on the initial air humidity. An increase in the humidity of steam at the channel inlet is accompanied by an increase in the gas temperature at the outlet of the evaporation cell and, accordingly, deterioration in the cooling efficiency. Nevertheless, even when a steam-air mixture in the saturation state ( φ = 100 % ) with ethanol as an evaporation agent is fed to the cell inlet, the efficiency of such a cell remains high and approximately equal to the theoretical limit of water evaporation into dry air.