Research On Heat Transfer Characteristics Of Casing Ground Heat Exchanger With Medium And Deep Ground Source Heat Pump

The medium and deep ground source heat pump system is a new type of heat pump heating technology,which is of great significance for the realization of clean heating.The core of the heat pump system is the heat exchanger on the side of the heat exchanger.In order to ensure the stability of underground heat transfer,the casing structure is usually used.In this paper,the heat transfer characteristics of the interaction between the casing ground heat exchanger and the soil are studied systematically.The data of hydrogeology and soil temperature distribution in the experimental site are obtained through field exploration and arrangement,and the heating experiment scheme of heat source well casing ground heat exchanger and heat pump system is designed,and the field experiment is carried out.Through different experimental conditions of inlet temperature and flow,the heat transfer performance and the recovery time of soil temperature were explored.A heat transfer model suitable for medium and deep ground source heat pump system casing ground heat exchanger of medium and deep ground source heat pump system is established.The axial distribution of fluid temperature in the casing is derived,and the influence of velocity and internal and external tubing on the heat transfer of the casing ground heat exchanger is analyzed.The temperature rise of the wellbore of the 1200 meter heat source well is derived,and the temperature distribution of the wellbore at different depths is obtained,which is consistent with the experimental data.After verifying the reasonableness of various model hypothesis conditions,the numerical model of heat transfer inside and outside the heat source well is established on the basis of the heat transfer model of V.C.Mei,combined with the energy balance and heat conduction differential equation,and the numerical solution method is given and the numerical simulation is carried out.A brief heat transfer analysis is made for the simulation results.After neglecting the control equation of the tube wall,a simplified heat transfer model is established,which reduces the influence of the numerical error caused by the sudden change of the width of the meshing grid caused by the tube wall,and greatly speeds up the numerical calculation speed of the model.The influence parameters of heat transfer in casing ground heat exchanger are studied.The results show that increasing the depth of the heat source well can increase the heat exchange and save the area of the heat exchanger,but the cost of the drilling will increase sharply.The best depth of the heat source well should be selected in engineering.The tube of the tube heat exchanger should select the plastic pipe with poor thermal conductivity,so as to reduce the loss of heat flux short circuit.The pipe material should select the metal material with good thermal conductivity to enhance heat transfer with the surrounding soil heat source;the casing heat exchanger should select the appropriate outer tube diameter to improve the heat transfer effect;the shallow layer of the casing pipe should set the heat preservation measures;the temperature difference of the heat exchanger and the circulation flow influence the heat source well burying together.The heat pump unit can adjust the load change through the flow regulation measures.In the operation of the heat pump system,the heat exchanger circulates the low temperature inlet and the large flow operation,and the stability of the heat exchanger and the heat pump unit can be improved.The research work of this paper provides a theoretical reference for the medium and deep ground source heat pump system casing ground heat exchanger,and provides theoretical guidance and basis for the engineering practice.