Temperature dynamics during nonisothermal evaporation from drying porous surfaces



[1] The partitioning of incoming shortwave radiative energy on evaporative surfaces determines mass and energy exchange with the atmosphere, and influences measurements of various climatic and hydrologic processes. We quantified the coupling between an evaporative flux from a drying porous surface and the corresponding surface temperature dynamics. The analytical approach employs a pore-scale diffusion model for the evaporative flux from a unit cell (representing the porous surface) based on Schlünder's (1988) model. The evaporation flux from the unit cell's pore was linked with other components of the surface energy balance through heat exchange across the pore's solid walls. Model predictions for evaporative flux and associated mean thermal fields during the drying of porous surfaces were in good agreement with experimental results. The model was used to predict the so-called soil evaporation transfer coefficient (ha), yielding good agreement with measurements. Analysis shows that commonly assumed interfacial isothermal conditions (where surface and air temperatures are similar) may yield 15–40% overestimation in evaporation rates relative to nonisothermal conditions (where evaporation rates affect surface temperature). Theoretical results indicate that when shortwave radiation is significant, an evaporating porous surface may gradually warm up as it dries resulting in enhancement of evaporation rates and energy partitioning. The analytical model addresses the long standing challenge of nonlinear evaporative fluxes from drying surfaces while providing predictions for surface energy partitioning over evaporating surfaces.