Experiment Study On Water, Vapor, And Heat Transport In The Unsaturated Sandbox

Coupled water, water vapor, and heat transport in unsaturated soil has enjoyed intensive focus in hydrology and soil physics. This research plays an important role in identifying water and energy exchange process between land surface and atmosphere in arid and semiarid areas.The coupling of the water and heat transfer equations is mainly resulting from the water vapor movement, therefore, naturally, this area research has focused on each water vapor transport mechanisms in the unsaturated soil. Domestic and foreign scholars have done a lot of research on the water vapor diffusion and yet, pay relatively little attention to the research of water vapor convection and dispersion.Based on the soil physical parameters experiment and calibration experiment of temperature effect of the soil moisture monitoring equipment EasyAG50, this dissertation conducts sandbox experiment under three different conditions, using fine sand which is collected from the Badain Jaran Desert. Meanwhile, according to the experiment results, this dissertation preliminary probes into the impact of each water vapor transport mechanisms on the changes in soil moisture content.Through sandbox experiment under airtight and constant temperature conditions, the author concludes that the effect of liquid water transport on changes in soil moisture content could be ignored when using air-dry desert fine sand in this sandbox experiment.Through sandbox experiment under airtight and fluctuant temperature conditions, the author concludes that the change in soil moisture content under fluctuant temperature condition mainly results from the temperature effect of the equipment EasyAG50 itself, the water vapor diffusion plays a minor role at this stage; and that when the soil temperature gradually stabilizes, the change in soil moisture content chiefly arises from the water vapor diffusion but not the equipment temperature effect. Through sandbox experiment under ventilated and fluctuant temperature conditions, the author concludes that under the actual average air flow rate 0.011cm/s conditions, the contribution rates of water vapor convection and equipment temperature effect on changes in soil moisture content are 191.2% and 28.6% respectively, while the contribution rates of water vapor diffusion and dispersion on changes in soil moisture content are -25.5% and -94.1% respectively. This indicates that under such conditions, water vapor convection is the most important factors to the change in soil moisture content, but not the well-known water vapor diffusion.