A theory describing both vapor and liquid phases of moisture transfers in porous materials is developed. The two equations included extend previous work, which only considered moisture and temperature gradients, by also including solute concentration effects. The new equations include six diffusivities to be considered in describing vapor and liquid movement in soil. Three liquid diffusivities are for liquid‐phase flow associated with water content, temperature, and solute concentration, and three vapor diffusivities are for vaporphase flow. Steady‐state heat and mass transfer laboratory experiments were performed by using moist salinized and solute‐free closed soil columns. From observations of water content, temperature, and solute distributions, five of the diffusivities (vapor diffusivities due to temperature, water, and solute concentration and liquid diffusivities due to temperature and solute concentration) are determined. The isothermal liquid diffusivity as a function of soil water content is determined in a separate experiment. In general, the liquid diffusivities are larger than the vapor diffusivities for the experimental conditions considered. For the soil conditions investigated, the water fluxes due to the solute gradients are nearly equal to the water fluxes due to the temperature gradients within salinized soil columns, but the water fluxes resulting from gradients in soil water content are small in comparison. To test the validity of the theory, two different approaches are used. The first approach involves using water diffusivities of moist solute‐free soil along with the new theory to predict steady‐state water distributions within moist salinized soil for comparison with observations. The predicted values of soil water content are in good agreement with the observed values. The second approach is to predict steady‐state soil water distributions within the moist salinized soil column while neglecting the solute effects on soil water movement. The predictions using this approach are markedly different from the experimental observations.

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Water evaporation and solute transport were studied in open soil columns. The study included two different soil materials — Clarinda clay (fine, montmorillonitic, mesic, sloping Typic Argiaquoll) and Fayette silty clay loam (fine‐silty, mixed, mesic Typic Hapludalf) — and three conditions. Two conditions were noncompacted solute‐free and salinized noncompacted soil columns of both Clarinda and Fayette soils, and one condition was compacted salinized soil columns of Clarinda soil only. The initial soil water contents were 0.271 and 0.181 m3 m−3 for noncompacted Clarinda and Fayette soils, respectively. The initial soil water content of compacted Clarinda was 0.393 m3 m−3 The initial KCl concentrations were 1.11 and 0.92 mol kg−1 of soil solution for Clarinda and Fayette soils, respectively. Measured ratios of evaporation loss from the noncompacted salinized soil columns to the amount of water evaporated from noncompacted solute‐free soil columns increased with time from 0.78 to 0.89 for Clarinda and 0.90 to 0.95 for Fayette soils. Evaporation from noncompacted Clarinda soil increased with time from 0.73 to 0.77 of the evaporation from compacted Clarinda soil. A numerical model of heat, water, and solute transfer was used to predict distributions of temperature, water content, and solute concentration for a given evaporation rate. Efficiency of the model for reproducing the water content and solute concentration ranged from 94.5 to 61.1%. The predicted and observed solute concentrations increased with time in the upper 0.02 m of noncompacted soil. Also, the upper soil portion, the 0.05‐m layer, dried drastically. Both observations and predictions indicate complex interactions between heat, water, and chemicals near evaporating surfaces.

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Diffusion‐based coupled soil heat and water transfer theory includes capability to describe transient behavior. Unfortunately, laboratory tests of theory typically include a single initial water content distribution with a single set of boundary conditions, rather than providing a set of experimental conditions with a range of measurements for comparison with predictions. Agreement between theory and measurements can result from calibration, but this provides an incomplete test of theory. The objective of this work was to test diffusion‐based coupled heat and water transfer theory by comparing theory‐based predictions with measured transient temperature and water content distributions. Data from a single boundary condition were used for calibration of each of two soils, silt loam and sand. Subsequent testing was performed at additional boundary and initial conditions using measurements from the same soil. Results indicate that the theory can be calibrated for a single boundary condition with adjustment of soil saturated hydraulic conductivity and/or the vapor enhancement factor, which adjust the liquid and vapor fluxes, respectively. For silt loam, calibration reduced Root Mean Square Error (RMSE) by 67 and 18% for water content and temperature distributions, respectively. For sand, RMSE was reduced by 14 and 46% for water content and temperature, respectively. Using this calibration, there was agreement between calculated and measured distributions for additional boundary and initial conditions with RMSE ≤ 0.03 m3m−3 and 1.28°C for water content and temperature distributions, respectively. However, when the boundary temperature gradient was instantly reversed, noticeable differences occurred between measured and calculated patterns of heat and moisture redistribution. The theory described observations well when boundary temperature conditions were changed gradually, but results suggested a need for further development of coupled heat and water transfer theory combined with testing under transient conditions to make improvements in the description of transfer mechanisms.

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This paper presents observed soil moisture redistribution within unsaturated soil in response to imposed boundary temperatures. Both salinized and solute‐free soil conditions are studied. Two different uniform initial soil water contents and solute concentrations are used for the salinized soil columns. Likewise, two different uniform initial soil water contents are used for solute‐free soil columns. High and low boundary temperatures are similar for all of the soil columns. Thus, the experiments are designed to directly observe the impacts of thermal, soil matric, and osmotic gradients on redistribution of soil water. In all cases, appreciable amounts of water move in the direction of decreasing temperature within the soil columns. This is not a general rule of soil water movement, but a result of the uniform initial water content, the presence of solute, and the imposed boundary temperatures under salinized soil, or the initial water content and the imposed boundary temperatures under solute‐free soil. For both solute‐free and salinized soils, the net amount of transported water to achieve steady‐state conditions is greater for low initial water content than for high initial water content. Therefore, the steady‐state variations in the soil moisture content increased by decreasing the initial moisture content. When the same initial water content is used for both salinized and solute‐free soils, the net water transported to achieve steady‐state conditions is greater for the solute‐free soil than for salinized soil. These observations indicate clearly that solute concentration affects soil water transport with unsaturated, nonisothermal conditions.