A Test of Coupled Soil Heat and Water Transfer Prediction under Transient Boundary Temperatures

Abstract

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.

Development and Application of the Heat Pulse Method for Soil Physical Measurements

“…The HP‐SHB method has been applied to measure subsurface evaporation in the laboratory (Deol et al, ; Trautz et al, ), at bare soil sites (Deol et al, ; Heitman, Horton, Ren, et al, ; Heitman, Horton, Sauer, et al, ; Y. Wang et al, ; Xiao et al, ), and vegetated fields (Xiao et al, ). This method provides an alternative and complementing approach for long‐term measurement of evaporation, especially in vegetated sites where root water uptake alters soil water distribution (Agam et al, ), and the existence of vegetation changes the micro‐climate (e.g., decrease in temperature and increase in humidity; Holland et al, ) through wind speed reduction (Cammalleri et al, ; Heilman et al, ) and shading (Colaizzi et al, ; Ham & Kluitenberg, ; Horton, ; Horton et al, ; Pieri, ).…”

“…Steady‐state methods (e.g., guarded hot plate, heat flux meter, and divided bar method) require thermal insulation to minimize edge or end effects, and a relatively long time is required to attain thermal equilibrium (Woodside & Messmer, ). For partially saturated soil, this method can alter the thermal properties being measured (Bristow, White, et al, ; Farouki, ; Moench & Evans, ), because heat transport in unsaturated soil is usually accompanied by appreciable moisture migration induced by the temperature gradient, evaporation or distillation of water vapor (de Vries, ; de Vries & Peck, ; Farouki, ; Heitman, Horton, Ren et al, ; Moench & Evans, ; Nassar & Horton, , , ; Nassar et al, , ). In addition, it can also dry the soil adjacent to the heat source (Moench & Evans, ).…”

Evaporation from soils under thermal boundary conditions: Experimental and modeling investigation to compare equilibrium‐ and nonequilibrium‐based approaches

“…Neglecting gas phase resistance and assuming that the water vapor in air is always at equilibrium are common assumptions in the current literature on modeling evaporation from bare soils [e.g., Philips and de Vries , 1957; Milly et al , 1982; Bear et al , 1991; Cahill and Parlange , 1998; Saito et al , 2006; Bittelli et al , 2008; Heitman et al , 2008; Sakai et al , 2009]. In this case, is removed, and and are combined to yield …”

“…The study of phase change in unsaturated soils is often evaluated based on the assumption of equilibrium applied at the scale of the representative elementary volume (REV) [ Philips and de Vries , 1957; Milly , 1982; Bear et al , 1991; Cahill and Parlange , 1998; Saito et al , 2006; Bittelli et al , 2008; Heitman et al , 2008; Sakai et al , 2009]. This traditional equilibrium‐based approach, which is commonly used in soil hydrology, assumes that water vapor concentration in air is always in equilibrium with liquid water, i.e., vaporization occurs instantaneously (hereinafter, referred to as the equilibrium approach).…”

Philip-s Semi-Analytical Solution on Water Infiltration into Unsaturated Soil based on Van Genuchten Equation

“…1 In soil physics, water flow model is based on Richards' equation. It has been extended by other researchers to model water flow in temperature gradient environment [7]. Also, the water vapor and energy transfers are modeled simultaneously with water flow.…”