Numerical study of evaporation assisted hybrid cooling for thermal powerplant application

This paper describes a numerical study of the effect of evaporative cooling on forced convective heat transfer in a system experiencing combined heat and mass transport. A multi-dimensional mathematical model has been developed to conduct simulations over a range of operating parameters to acquire insight into the dual mode cooling where convective heat transfer is augmented by evaporative heat and mass transfer process. The system being modeled consists of a thin liquid water film that undergoes evaporation as a result of being exposed to a prescribed heat flux and laminar convective flow condition. Predictions from the simulations indicate that in comparison to pure forced convection cooling, under convective-evaporative hybrid cooling conditions the overall heat transfer coefficient is increased by a factor of similar to 4 to 5, where evaporation alone contributes to 80 - 90% of the overall performance. A critical Reynolds number has been found beyond which no significant enhancement in the overall heat transfer is observed. Numerical results also identify a critical film thickness beyond which the thermal inertia across the liquid film becomes dominant and starts to suppress the overall heat transfer process. System size requirements and water consumption of hybrid cooling for power plant applications are compared with conventional water, and air- cooled systems and was found to be significantly lower.