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.

Finite Analytic Method for Solving the Unsaturated Flow Equation

“…A laboratory‐scale surface evaporation–vadose zone–groundwater system, comprising an evaporation simulator, a lysimeter column, and a Mariotte bottle (Fig. 6), was designed (Wang et al, 2011b). It creates an evaporation environment above the surface of the lysimeter column by the evaporation simulator.…”

“…It creates an evaporation environment above the surface of the lysimeter column by the evaporation simulator. Details of the experimental set‐up can be found in Wang et al (2011b).…”

“…Moisture movement in the vadose zone has long been a concern regarding groundwater recharge, evaporation, pollution, and the ecological effects induced by groundwater (Youngs, 1995; Keese et al, 2005; Abit et al, 2008; Shokri et al, 2009; Wang et al, 2011a, 2011b, 2013). Usually the moisture movement in the unsaturated zone is described by Richards' equation (Haverkamp et al, 1977).…”

Estimation of ground heat flux from soil temperature over a bare soil

“…Accurate determination of ground soil heat flux, G 0 , is required to evaluate surface energy balance (de Silans et al 1997;Heusinkveld et al 2004;Roxy et al 2014), to estimate soil evaporation (Kampf et al 2005;Heitman et al 2010;Yao et al 2013), and to describe water and vapor transformation processes in vadose zone (Yamanaka et al 1997;Saito et al 2006;Bittelli et al 2008;Wang et al 2011aWang et al , 2011bZhang et al 2015). However, measurement of G 0 has still been a challenging task for researchers till now.…”

Editorial: Make models work for water science and engineering

“…Wang et al (2011) contribute to the progress on numerical modelling of water movement in the vadose zone influenced by temperature from four aspects: the mechanisms and effective factors in the movement of water and heat in the vadose zone under surface evaporation conditions; the mechanisms of phreatic water evaporation at different groundwater levels under evaporation conditions; phreatic water evaporation intensity and limited depth of evaporation of groundwater driven by surface temperature; and the differences between an isothermal model and a coupled water and heat model when used to analyse water movement in the vadose zone.…”