Performance modelling of aqueous alcoholic mixtures based heat pipes

Abstract

An analytical model that predicts the thermal performance of a heat pipe has been presented here. Results are shown in terms of the total thermal resistance that constitutes evaporator and condenser convective resistances. Some alcohol-water mixtures exhibit a gradient in surface tension with respect to concentration and temperature difference in the fluid that leads to the flow of the fluid towards the heated surface. To examine the effect of this phenomenon, the working fluids considered in this work were methanol-water and 2-propanol-water mixtures. For the evaporator heat transfer coefficient, a theoretical model that accounts for the mass diffusion of the volatile component within the fluid was validated and used. Condenser side heat transfer coefficient was predicted using a film condensation correlation, with an aligned pin fin array providing the necessary cooling on the external condenser side. It is observed that the total heat pipe thermal resistance increases with an increase in mass fraction of methanol at both values of input heat flux, 1×105 W/m2 and 2×105 W/m2. For 2-propanol-water, a maximum in heat pipe thermal resistance is observed at a mass fraction of 0.3, while very low mass fractions of 2-propanol result in minimum heat pipe thermal resistance at both input heat fluxes.