Simulation Research On Thermal Process Of Deep U-pipe Geothermal Heat Exchanger

Extracting groundwater and ground source heat pump are main geothermalutilizations nowadays. Each has advantage and disadvantage. Deep U-pipe geothermalwell can realize “taking hot without water”, don’t destroy underground water and takemore quantity of heat. A mathematical and physical model on heat transfer for deep U-pipe geothermal well located in Xi’an was established in this thesis. The model has beenverified with calculation result and the practical data of straight well, the result indicatethat the calculated value of outlet water temperature has a relative error of7.77%. Thisshows that model is reasonable and reliable.Heated effect in120days has been calculated in various velocity, pipe diameter,horizontal pipe length, geothermal gradient. Calculation results indicate that undercondition of the same pipe diameter, flow velocity decrease with outlet watertemperature increasing, but the quality of heat reached maximum when velocity is0.75~1.0m/s. While the pipe diameter is0.1538m, the length of horizontal pipe extended1000meters, the outlet water temperature increased3.3℃. When horizontal pipe lengthis1000meters, the best parameters are that pipe diameter is0.1538m, flow velocity is0.75m/s, the maximum quantity of heat is0.8488MW. Under the best condition, whengeothermal gradient increased1℃/hm, the quantity of heat increased by0.515MW.When temperature gradient is10℃/hm, the average quantity of heat can reach4.45MW,it will meet the heating demand of about89000m2.The geothermal restore model has been established. The temperature recovery of rock has been calculated for240days with different geothermal gradient. Calculationresults show: under all geothermal gradients, recovery rate is higher than92%at pipewall. Recovery speed is fast at the beginning, and then becomes slower.