Experimental comparison of thermal and solute dispersion under one‐dimensional water flow in saturated soils

Abstract

Thermal dispersion, which is similar to solute dispersion, results mainly from microscopic differences in pore‐scale water velocities in porous media. In this study, heat and Cl− were used as tracers to perform a systematic and quantitative comparison of the characteristics of coupled heat and solute dispersion through three types of saturated packed media (a sand, silt loam and sandy clay loam soil). An inverse model was used to calculate the thermal dispersion coefficient (Dh) and solute dispersion coefficient (Ds) by fitting a heat and solute transport model to the measured temperature and solute breakthrough curves obtained using the thermo–time domain reflectometry (thermo–TDR) technique under the same experimental conditions. Results showed that Ds and Dh were both described by a power function of water flux. Most importantly, heat and solute dispersivities had the same dimensions of length , the magnitudes of which were maintained almost unchanged with water flux densities and depended considerably on soil texture. Fine‐textured soil had a greater dispersivity than did coarse‐textured soil, and solute dispersivity was 220% greater than heat dispersivity in sandy clay loam, about 92% greater in silt loam soil and 36% greater in sand. We suggest that the magnitude and dimension of heat dispersion were essentially comparable to those of solute dispersion, which provides a better understanding of the relation between heat and solute dispersion. It has also been shown to be advantageous in practice for using heat dispersion to quantify easily solute dispersion approximately (or vice versa).Highlights Thermal and solute dispersion coefficients were power functions of water fluxes. Heat and solute dispersivities had the same length and order of magnitude. Thermal dispersion was experimentally comparable to solute dispersion. Solute dispersion may be predicted quantitatively by heat dispersion values (or vice versa).