Study On Medium-Deep Geothermal Heat Extraction System And Heat Transfer Model

Under the constraints of energy structure adjustment and environmental pollution,new energy sources such as geothermal energy have become development strategies of national energy.Geothermal energy has great potential for development as a renewable energy source.It has abundant reserves,high energy quality,and clean and environmental protection.Based on this,this paper aims at the highly efficient development and utilization of geothermal energy,explores the flow-heat transfer process of underground rock and soil,analyzes the flow-heat transfer phenomenon in the seepage field of porous media,and focuses coaxial borehole heat exchanger at mid-deep geothermal system.The heat transfer efficiency and heat transfer characteristics of the coaxial heat exchanger in the mid-deep geothermal energy recovery system are studied.Firstly,the geothermal wells in the middle and deep layers are surveyed,and the stratum data are obtained according to the drilling cuttings,and the basic parameters of the thermal properties of the geotechnical soil are obtained.The distribution,characteristics and yield of the heat storage are then described.It is proposed that the heat capacity of the heat reservoir is used to reflect the heat capacity of the heat storage.According to the geotechnical skeleton model,the equivalent thermal conductivity and the equivalent thermal diffusion coefficient are proposed.The thermal properties of the rock,such as thermal conductivity,specific heat capacity and thermal diffusivity,are given,and secondly,the distribution and void characteristics of groundwater are introduced,and finally,the geothermal well structure,drilling and well-forming technology and geometrical dimensions of the project background are introduced.Secondly,the coaxial borehole heat exchanger and the mid-deep geothermal heat recovery system are introduced.The experimental research on the mid-deep geothermal resource heating system is carried out to obtain the temperature field and temperature gradient of the heat storage.The geothermal energy reaches 80.7? at 2000 meters.The average geothermal gradient is greater than 3.5?/hm,and the heat transfer potential and heat recovery capacity of the heat storage are known through heat transfer test.In the test,the heat exchange test power can reach 280 kW,and the heat recovery rate is about0.724?/h.Finally,the heat transfer process of the concentric tube heat exchanger and its surrounding rock formation is analyzed.The proper assumptions were made for the heat transfer process,and then the second-order parabolic partial differential heat transfer model of the concentric tube heat exchanger and its surrounding rock formation was established.The finite difference method is used to numerically calculate the model.By analyzing and comparing the model calculation results under different discrete results in the time space calculation domain,the average error is only 1.843?,and the established mathematical physics model is found to have high precision.