Model Experiment And Numerical Simulation Of One-dimensional Horizontal Migration To Soil Thermal Seepage

Ground-source heat pump systems have received widespread attention due to the good characteristics of geothermal energy saving and environmental protection.However,due to the uncertainty of the heat transfer performance of the buried pipe,it has hindered the design of the ground source heat pump system.Among them,groundwater seepage is closely related to the heat transfer performance of buried tube heat exchangers.The groundwater in Guangxi is widely distributed,and karst fissures develop,resulting in a large groundwater seepage velocity.Aiming at this situation,this paper selects medium sand from Guilin as the research object,and uses 3D printing technology to develop a one-dimensional horizontal soil thermal infiltration coupling experimental platform,and discusses the soil under the combined action of temperature field and horizontal flow field Heat transfer efficiency.Based on this indoor model experiment,the multiphysics simulation software COMSOL Multiphysics was used to model and compare the results.The actual physical model was analyzed and corrected.Then,the numerical model established was used to simulate soils such as gravel,silt,silty clay and clay.Research results show:1.The self-developed one-dimensional model experimental platform can effectively simulate soil heat transfer under the action of groundwater seepage.One-dimensional horizontal seepage can reduce the maximum temperature in the experimental soil column and the final temperature difference between the hot and cold ends,that is,alleviate the heat accumulation in the soil.When seepage flows in the direction of heat transfer（forward seepage）,the greater the seepage speed,the higher the heat transfer efficiency;at lower seepage speeds,the temperature in the soil column of the experiment shows a trend of rapid change after time;When the seepage velocity is high,the final temperature changes at a constant rate over time.When the percolation acts in the direction of heat transfer（reverse percolation）,the influence range of the heat source is reduced,that is,the heat transfer is hindered.2.The experimental study of medium sand as a typical seepage soil was calibrated by the three-dimensional physical model established by COMSOL Multiphysics software.The results show that the maximum relative error in the distribution of the temperature field is12%during forward seepage and 6%during reverse seepage.The maximum relative error of sensor changes is based on the T1 sensor,which is 6%for forward seepage and 4%for reverse seepage.Since the accuracy requirements are met,the model can be used to carry out numerical simulation studies on other types of soils.3.Through simulation research on the heat transfer laws of gravel,silt,silty clay and clay,it is concluded that when seepage velocity u≤1×10^-5m/s,the effect of forward seepage on soil heat transfer is less than reverse seepage In the case of seepage velocity u≥5×10^-5m/s,the temperature field formed by forward seepage and reverse seepage tends to the horizontal line,but the temperature transmitted by forward seepage is higher than that during reverse seepage.At isoosmotic velocity(u=2×10^-5m/s),the heat transfer efficiency of different soils is:gravel>silt>silty clay>clay.The temperature change recorded by each temperature sensor will reach a fixed equilibrium value one by one along the seepage direction over time.The sequence of this thermal equilibrium between the four types of soil is:clay≥silty clay>silk=gravel.