One-dimensional Heat-moisture Coupled Transfer Model And Experimental Study Of Unsaturated Soils

As a natural and non-polluting renewable energy source,soil has been widely concerned about energy use,such as ground-source heat pumps,geothermal storage and utilization,etc.And because of its porous,multi-phase complex structure,it has important research significance in many fields,such as underground transportation of thermal pipelines,irrigation and water conservancy,nuclear industry and geothermal industry,etc.This article first reviewed and analyzed the development history and achievements of research at home and abroad,since the beginning of the 20 th century,people began to study the heat and moisture transfer of soils and other porous media,at this stage,they continuously explored and corrected their operating mechanism and mathematical model.However,the complexity and microcosmic nature of the study have not yet reached a conclusion in this regard,the internal operating mechanism is not clear,especially with respect to targeted experimental analysis.Therefore,this paper analyzes several mathematical models that have matured in the development process based on previous research results,and based on the research and development trends and optimization,finally adopts a more reasonable three-field model,hotwater-force three-field coupling,this model is developed based on the coupling of heat and moisture two fields.A one-dimensional experimental platform for unsaturated soil heat and moisture transfer was set up,the heat and moisture transfer laws for 11 conditions were studied for different initial moisture content and different temperature gradients,the experimental results are analyzed,and simulations are performed according to the mathematical model to verify the experimental results.According to the difference of initial moisture content,the experimental conditions in this article can be divided into 4 groups,namely 9.2%,13.5%,16.5% and 22.8% with higher water content.Under the same initial moisture content,different temperature gradients were set and the heat and moisture transfer law was studied according to the gradient from low temperature to high temperature.The soil temperature gradually increases with time,but the growth rate shows an exponential decline with the distance from the heat source,the size of the index coefficient determines the degree of temperature increase with distance.In the humidity field,peaks occur and the peaks continue to increase.Since the soil moisture migrates to the far heat source during this process,this peak is also constantly shifted back,but the rate slows down as the moisture migration rate slows.After that,the influence of different initial moisture content on the temperature and humidity field was analyzed,it was found that the higher the initial moisture content,the greater the temperature increase and the earlier the humidity peak appeared.Finally,based on the mathematical model of heat-moisture coupled transfer,the program was programmed on the MATLAB platform and the simulation was performed,the results were compared with the experimental values,and the error was within a small range,which proved the accuracy of the model.Based on this model,the effect of soil saturated hydraulic conductivity on water migration was studied.