Pore-scale study of thermal fields during evaporation from drying porous surfaces

Abstract

The drying of a porous surface and subsequent pore emptying resemble a sequence of drainage whereby pores are invaded according to their respective capillary size (large pores are invaded first). The emptying of pores modifies both the local evaporative fluxes and surface thermal fields adjacent to invaded pores. These local adjustments could result in a gradual decrease in evaporation rate and a potential increase in surface temperature thereby altering energy partitioning over the drying surface as described by the Pore-scale Coupled Energy Balance (PCEB) model of Aminzadeh and Or (2014). This study aims to observe and quantify these dynamic pore-scale mass and energy interactions to test key assumptions in the basis of the PCEB model and gain new insights into these important processes. We used a novel experimental system consisting of individual and clustered evaporating pores drilled into rough glass surfaces. Thermal fields around individual evaporating pores and their interactions were observed using highly resolved infrared imager under different radiative fluxes. Thermal observations and direct measurements of evaporative fluxes were in good agreement with predictions by the PCEB model. Drying of a glass beads surface was captured by optical and thermal imaging to provide links between pore emptying sequence and surface thermal adjustments. The results highlight the upscalability of pore-based representation of surface drying and the predictability of energy partitioning over drying porous surfaces.