Experimental and numerical study of coupled flow and heat transport

Abstract

The greater difference between day and night temperatures in arid and semi-arid areas influences water movement and heat transport in the vadose zone, and further influences the water and heat fluxes between the water table and the atmosphere. An evaporator and lysimeter, designed by the authors, and combined numerical simulation technology were used to study water movement and heat transport in the vadose zone, and the evaporation of phreatic water under the influence of surface temperature for different groundwater depths. The differences between water movement of the vadose zone and phreatic water evaporation calculated by isothermal and anisothermal models were also compared. The results of experiment and numerical simulations show that the surface temperature has a great influence on both water movement and heat transport in the vadose zone, as well as on evaporation intensity and the evaporation depth of phreatic water when the surface temperature is more than 25°C. The influential depth for the soil water content of vadose zone and the temperature of unsaturated and saturated zones is about 70 cm, but the greatest change is in the top 35 cm. The limited evaporation depth of phreatic water was about 70 cm for the experimental medium (silt/fine sand). The evaporation intensity of phreatic water was found to be maximum for a groundwater level of 20–40 cm (about 0·096 cm/h for silt/fine sand). The error of more than 8% was due to water movement of the vadose zone and the evaporation intensity of phreatic water calculated using an isothermal model. A coupled water and heat model was used to simulate water movement of the vadose zone and the exchange flux between the water table and atmosphere for surface temperatures higher than 25°C. For surface temperature below 25°C, the results of the isothermal and anisothermal models were coherent. There is thus no need to consider the influence of surface temperature on water movement of the vadose zone or the flux between the water table and the atmosphere.