Modeling of Coupled Heat and Mass Transfer for the Optimization of Evaporative Cooling Using a Porous Clay Plate

Abstract

This study investigates the complex mechanisms of coupled heat and mass transfer within a fired porous clay plate optimized for evaporative cooling in hot and dry climates. The primary objective was to model and experimentally validate the material's ability to lower air temperature through capillary evaporation. Local results highlight a pronounced leading-edge effect, where a maximum evaporation flux of 0.78 g/m² induces rapid cooling within the first few centimeters of the plate. Under nominal conditions of 40°C and 20% relative humidity (RH), the outlet air temperature drops significantly to 25.38°C, corresponding to a thermal gain of nearly 15°C. The theoretical validity of the model is confirmed by the perfect superposition of local Nusselt (Nu x ) and Sherwood (Sh x ) numbers, demonstrating the consistency of the Chilton-Colburn analogy. Parametric analysis reveals that system efficiency is highly dependent on residence time and hygrometric potential: a moderate air velocity of 1.5 m/s combined with low initial humidity (10%) optimizes the process, achieving a record cooling of 17.4°C. Despite some simplifying assumptions (adiabatic walls, uniform saturation), comparison with experimental data shows excellent agreement, with an average relative error of 6% to 7% and a root mean square error (RMSE) of approximately 2°C. The research demonstrates that fired clay, owing to its porous structure that promotes capillary transport, constitutes an efficient passive heat exchanger and a sustainable alternative to energy-intensive air conditioning systems.