Experimental And Simulation Study Of Heat And Moisture Transfer For High-Temperature Heat Storage Of Soils

Soil heat storage at high temperature,as an efficient and practical way of solar energy cross-season storage technology,has been paid more and more attention.Soil heat storage technology at high temperature in China is still in its infancy.The key to popularize and develop this technology is to study the characteristics and mechanism of soil heat and moisture transfer under the action of high temperature gradient.This paper first carried out experiments and model studies on soil thermal conductivity of different types and different initial water content,and constructed a calculation model of soil thermal conductivity related to soil saturation.Then,the soil heat and moisture transfer under the conditions of low temperature（35℃）,medium temperature（53℃）and high temperature（65℃）were studied experimentally with medium sand.Then,the heat and moisture transfer of soil under the condition of high temperature heat storage was simulated by using Hydrus-1D software.The main conclusions are as follows:（1）The thermal conductivity of unsaturated sandy soil,sandy loam,loam clay and silt clay was studied when the moisture content was 0%,3%,5%,8%,10%,13%,15%,18%and 20%,respectively.The results show that the thermal conductivity of soil increases non-linearly with the increase of moisture content,soil type is the main factor affecting thermal conductivity at low water content,porosity mainly affects the thermal conductivity at dry state,and soil composition mainly affects the thermal conductivity at high moisture content.（2）A thermal conductivity model was built based on soil type,soil saturation,porosity and quartz.Eight kinds of experimental values were used to calibrate the model parameters of the thermal conductivity model,and then 51 kinds of Canada and China in the literature of different types of measured soil thermal conductivity values were used to validate the model.The results show that the RMSE,PBIAS and NES values range from 0.038 to 0.18,-0.262 to 0.079 and 0.758 to 0.996,respectively,which are better than the current commonly used thermal conductivity models,indicating that the model has a wider application range and higher accuracy.（3）According to the soil heat and moisture transfer experiments under high,medium and low temperatures studied by one-dimensional soil column experimental equipment,the temperature variation trend of each measuring point in soil column at high,medium and low temperatures is the same,that is,with the increase of heat storage time,the temperature of each measuring point in soil column shows a general trend of rapid increase at first and then tends to stabilize;Under the condition of the same distance from the heat storage end,the higher the soil heat storage temperature,the greater the temperature gradient between the measured points.Near the heat storage end,the soil moisture content will appear a peak,and the peak value increases first and then decreases with the increase of heat storage temperature.When the soil moisture content reaches stability,it is lower than the initial soil moisture content.（4）Under the condition of high temperature thermal storage heat transfer numerical simulation studies show that the soil moisture content is less than 0.1 m³ m^-3,heat accumulation near the end of soil moisture content reduce continuously and fast,would have been to the residual water content of soil,soil moisture content in the thermal storage in the late soil temperature decline phenomenon,directly affect the storage of the soil thermal efficiency.When the initial moisture content is 0.15～0.2m³m^-3,the soil can store the highest heat.The higher the temperature of heat storage,the higher the temperature the soil can reach,and the more heat the soil near the heat storage end loses in the process of heat storage.