Thermo-evaporative fluxes from heterogeneous porous surfaces resolved by infrared thermography

Abstract

Variations in evaporative fluxes from heterogeneous wet terrestrial surfaces may induce a distinct and spatially variable thermal signature detectable by modern infrared thermography (IRT) methods. Combining measured temperature distribution for an evaporative surface with surface energy balance offers a means for extraction of spatial and temporal distributions of evaporative flux as a function of surface temperature. Recent advances in IRT technology offer spatially resolved thermal images at unprecedented sensitivity for in situ estimation of surface evaporation flux distribution currently unobservable by other methods. We studied evaporation patterns from surfaces of initially saturated sand columns containing sharp vertical textural contrasts (fine-sand inclusion in coarse-sand background) to evaluate the performance of the proposed method. We examined several algorithms for model validation. Spatial and temporal IRT data are numerically inverted to obtain evaporation flux values that are compared with rates of mass loss from direct weighing of the samples. Analytical solutions of some special cases are also compared with the experimental data. We introduce a convenient approximation based on mean surface temperatures of similar textural regions to resolve spatial evaporative fluxes. Estimates are in good agreement with experimental results. Our results also confirm the occurrence of lateral capillary flows from coarse to fine sand in the presence of sharp heterogeneity during evaporation. The proposed method could under certain conditions be used to convert highly resolved temperature fields to deduce drying patterns of interest in various fields from hydrology to food processing and other engineering applications. Copyright 2010 by the American Geophysical Union.