Research On Heat Transfer Between Surface, Vadose-zone And Shallow Groundwater In The Mu Us Desert

The Mu Us desert also called Erdos desert is one of the four large deserts in China. It’s about 42.2 thousand km2, located in the border region of Shaanxi, Ningxia and Inner Mongolia. The temperature difference between day and night in this region is generally more than 30 ℃. This region belongs to semi-arid areas, the annual rainfall less than 400 mm. The industries about energy, petroleum and chemical have developed rapidly in recent years, it raises the economic benefit, but it also increase the pressure of fragile ecological environment of this region.The heat transfer in soil will cause a change on temperature, which indirectly impact on moisture movement, microbial activity in soil, the root system absorbing nutrients and moisture and the germination of seeds. Most research focuses on the heat transfer on the surface of soil, in this paper the research focus on the heat transfer between surface, vadose zone and shallow buried groundwater. This research is guided by the soil water dynamics theory, the in situ and laboratory experiments was conducted, and simulation technique was applied. The influences of surface temperature and groundwater temperature were considered simultaneously. The heat transfer between unsaturated zone and atmosphere and heat transfer between saturated zone and unsaturated zone have been researched. For the sustainable development of regional groundwater and ecological environment, the results has theoretical and practical significance.An in situ experiment field was selected in the Mu Us desert to monitor the temperature, moisture content of soil and the water table. The Saturated permeability coefficient of soil was measured in the field, the heat conductivity, specific heat capacity, heat diffusivity and other hydraulic parameter of soil was determinate in the laboratory.Base on the experiment data, the heat conducted in surface layer of soil and heat conducted on free water surface which represent the heat conducted between shallow groundwater and unsaturated zone was calculated respectively. The heat conducted in the surface layer was obviously affected by the air temperature. The heat was conducted into soil at high air temperature and conducted out at a low air temperature through the surface layer. Contrarily, the heat conducted out of the research boundary at high air temperature and conducted in at a low air temperature through the free water surface. The factors influence the heat transfer in soil have been analyzed, it’s found that the other approaches of heat transfer can not be neglected besides heat conduct.In order to further study the combined effect of heat conduction and heat convection on heat transfer in soil, the process of heat transfer in soil was simulated by computer program VS2 DH with the monitor data from August 21, 2013 to November 11, 2013. In this period, the heat was released from the model area by heat dispersion and heat conduction. Simultaneously, the heat was flowed into the model area by heat convection. Consequently, the heat was reduced from model area under the combined effect of heat dispersion, heat conduction and heat convection in this period, except some time heat was increased with water table rising. The simulation result is consist with the heat storage change from August 21 to November 11 that deduced by the temperature change of soil, and that verify the reliability of the results.