Influence Of Underground Seepage On Heat Transfer Characteristics Of Buried Pipe Groups

Geothermal energy as a renewable energy has significant environmental protection benefits,and the application of ground source heat pump systems is increasing under the support of the "dual carbon policy".Due to the large climatic differences in some regions,uneven heating and cooling may occur in the heat exchange area after the system runs for a period of time,which affects the operating efficiency of the ground source heat pump system.The underground seepage can weaken the accumulation of cooling or heat in the soil and help the soil temperature recovery.Therefore,the underground seepage should be considered when analyzing the buried pipe group model.Firstly,this thesis establishes the continuity equation and energy equation of underground seepage,improves the ILS model and the FLS model,and uses the superposition principle to establish the layered seepage heat transfer model of the double U-shaped buried pipe group.Through the geothermal response test and core sampling,the thermophysical parameters of different soil qualities and the initial temperature of the soil in a certain engineering project are determined.Secondly,the ANSYS software is used to simulate the two heat transfer models of the buried pipe group,and the correctness of the models is verified by the measured values.Set up temperature monitoring points in the horizontal direction of the heat exchange area,and analyze the differences of each soil temperature monitoring point in different soil qualities under the pure thermal conductivity model and the layered seepage model of the buried pipe group.Afterwards,the axial soil temperature drop of the buried pipe group in different models and different soil qualities,and the variation law of the soil temperature drop value within the thermal action range were studied.Through the numerical modeling results,the heat transfer per unit well depth of the buried pipes under different models,and the variation of the temperature difference between the inlet and outlet of the corner wells,side wells and middle wells with time in different soil types are calculated.The results show that,compared with the pure thermal conductivity model,the higher the seepage velocity within a certain range,the greater the horizontal and axial soil temperature,the range of heat action,the heat transfer per unit well depth,and the inlet and outlet water temperature difference of corner well,side well and middle well in the pure thermal conductivity model.In this project,when underground seepage velocity is 1.4e-5 m/ s,the heat transfer effect of buried pipe group is most significantly improved.Finally,the calculation parameters of buried pipes in the two models were optimized,and the horizontal value and response value were determined by analyzing the influencing factors of heat transfer of buried pipes,and several experimental schemes were designed by taguchi method.The relationship between the response value and the three influencing factors is determined through the experimental results,and the Delta value of each factor and the contribution to the response value are obtained.After calculating the average S/N ratio,a set of calculation parameter optimization data of the buried pipe group is obtained,that is,when the thermal conductivity of the backfill material is 2.2W/(m·K),the buried depth of the buried pipe is 120 m,and the distance between the buried pipes is 5.5m,the unit well depth heat transfer ratio of corner well increases by 16.47%,side well by 17.36%,and middle well by 18.37% on average before optimization.Compared with the original project,the unit well depth heat transfer of buried pipe is further improved.