A model for predicting soil evaporation rate with consideration of evaporation surface descent

Water evaporation is a major process of energy and material exchange between soil and atmosphere, which is a direct cause of numerous geotechnical and environmental engineering issues. In this work, after the energy supply and water vapor transfer conditions in the evaporation process being analyzed, the characteristics that the evaporation surface constantly moves down during the evaporation process were considered, a modified model for predicting soil water evaporation rate was established by introducing the relative humidity at the evaporation surface and soil heat flux. Based on these, a large-scale environmental chamber evaporation test system was developed. The evaporation tests were conducted on aeolian sands under constant groundwater level and given atmospheric conditions. Experimental results show that the sensible heat flux within ± 50 mm of the soil surface is up to about 20 times greater than that outside this area, indicating that the exchanges of heat and moisture during the evaporation process are strongly concentrated in the region within a range of ± 50 mm from the soil surface in the environmental chamber. As evaporation progresses, position of the lowest temperature in soil moves downward from the soil surface, confirming the downward movement of the evaporation surface. Moreover, the influence of soil thermal flux on moisture evaporation transforms from a promoting to a suppressing effect. Compared to that in the existing models, the changes in energy and moisture supply during the evaporation process could be more comprehensive reproduced in the proposed model. Accordingly, the predicted results of the modified model significantly agreed with the experimental data.