Thermal-hydro Model And Applications In Buried Pipes In Groud Source Heat Pump System

Ground source heat pump system (GSHP) is most commonly used to extract geothermalenergy from shallow soil for indoor heating/cooling. At present, the design of theunderground heat exchanger mainly focuses on borehole pipes heat exchanger, whileenergy foundations such as energy piles and energy diaphragm walls are temporarilyrare, also considered in some certain cases. As the heat transfer proceeding of a heatexchanger is a very complicated thermal-hydro coupled problem, it is difficult to obtaina direct analytical solution. While for numerical simulation, it takes too muchcomputing resource to reproduce this proceeding as the simulation of the fluid part willbe very tedious if the solid element is used. To solve this problem, an ANSYS modelapplying the line element called FLUID116is established by Xianlei Zong to simplifythe heat transfer between fluid and soil. In this thesis, a further study on thermal-hydroproblem is made to gain a better understanding of the heat transfer proceeding.In this thesis, the analytical solution of the1D T-H model under Cauchy’s boundarycondition has been deprived in this thesis, which is used to validate the line element(FLUID116) in ANSYS model. A good coincidence has been found between theanalytical results and numerical results of FLUID116. Besides, a comparison betweennumerical models using solid elements (COMSOL) and line elements (ANSYS) is alsomade in this thesis and the ANSYS model is proved to be of good efficiency.The author participated in the in-situ test of thermal-hydro-mechanics coupled problem(based on an energy pile) in the Science and Technology Exhibition Hall in JiangningDistrict, Nanjing Province. An ANSYS model is established to simulate thethermal-hydro part of this test, and a good coincidence has been found between thenumerical results and the test data.In the last part of the thesis, a study of how different parameters will affect the heattransfer of buried pipes is made by applying the ANSYS model, such as thermalparameters of soil, distance of buried pipes and the connection mode of buried pipes. Also a supplement of groundwater part is made to the ANSYS model to extend theconcept of thermal-hydro model. And by doing this, now it is possible for the AYNSYSmodel to handle the heat transfer problem in porous media, which means the new modelcan handle the heat transfer problem caused by groundwater flow as well as the heattransfer between fluid and soil. By using this new model, some preliminary results havebeen found in the thesis. In this thesis, the comparison among this new model,COMSOL model and Ogata&Banks solution is made to verify the feasibility of thisnew model, based on the heat transfer problem in porous media under the thermalinsulated condition. A preliminary conclusion can be made that the efficiency of theheat transfer of borehole pipes can be very sensitive to the velocity of ground waterflow if the velocity is just in some certain range. If the velocity is very small, the heattransfer is seldom influenced by groundwater flow. However, if the velocity increases to5E-5m/s, the heat transfer will rapidly increase as the velocity increases, and thisphenomenon will disappear when the velocity reaches a level of5E-3m/s.