Graduate Thesis Or Dissertation
 

Evaporation synergy in a bi-textured soil system

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  • Evaporation synergy is the phenomenon in which two porous medium textures that share a common vertical boundary experience a higher cumulative evaporation than either homogeneous texture can produce. Studies that have been conducted to date address this phenomenon in relatively fine and coarse sands but not in finer textured soils where viscous forces play a major role. The purpose of this study was to determine which of the 66 combinations of soil textures would exhibit evaporation synergy and develop a conceptual model of the conditions necessary for synergy. The numerical modeler HYDRUS was used to investigate all soil texture combinations and generate evaporation rates and cumulative evaporation amounts for each system. In addition, two combinations of soils were selected as laboratory experiments based on the HYDRUS predictions: one that exhibited synergy (Loamy Sand & Silt Loam) and one that did not (Loamy Sand & Sandy Clay). The laboratory data supported the HYDRUS predictions for evaporation synergy and non-synergy. The conditions necessary for evaporation synergy were developed from the numerical and physical models’ predictions and results. The two textures must experience different air-entry values to create lateral and vertical pressure gradients, the fine must possess a high enough hydraulic conductivity to allow water to move to its surface before it reaches its own air-entry value and possess the capillarity to maintain liquid film flow to its surface, and the viscous forces within the coarse must be low enough for water to be pulled from itself to the fine. It was also determined that the evaporation rate of a bi-texture decreases as a series of constant-rate steps until the fine enters S2 evaporation and is associated with a stepwise recession of the drying front in the coarse media. The duration of each step appears to be associated with the lateral distance from which water can be extracted within the coarse media.
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