Research On The Characteristics Of Pipe-group Heat Exchanger Under Coupled Thermal Conduction And Groundwater Advection

With the speeding up of the modernization process, traditional fossil energy consumption is growing rapidly, in all sectors of energy consumption, the amount of building energy consumption is rising year by year in our country, currently accounts for27.45%of total energy consumption. Soil source heat pump through the soil energy storage, realize the use of cold/heat during summer and winter seasons, has the characteristics of high efficiency and energy saving. The key technology of soil source heat pump is the matching of underground buried pipe heat transfer characteristics and heat pump unit performance. The performance of the pipe-group heat exchanger directly affects the reliability of the system, energy saving and efficiency. Much of the research about the pipe-group heat exchanger did not consider for the influence of the moisture migration of groundwater, the only research is mostly based on the analysis for the set of the working conditions, the research result that is too poor to guiding engineering design and system optimization operation. Aiming at this problem, this paper mainly studies the heat transfer effect of groundwater seepage and dynamic load about the pipe-group heat exchanger. This paper is mainly from the following several aspects.Firstly, the heat transfer process of the pipe-group heat exchanger is analyzed, including the heat transfer of the tube fluid and the soil, the heat conduction and heat convection of the pipe flow and tube wall, the heat conduction of tube wall and the backfill materials of borehole, the heat conduction of the inside of the backfill material, the heat conduction of the wall and the soil. On this basis, the influence of groundwater seepage underground on the pipe-group heat exchanger is analyzed, then the heat transfer mathematical model considering of groundwater seepage is built, meshing and boundary conditions are set accordingly to the experimental data in literature was selected, the model was verified and corrected.Secondly, the paper uses the heat transfer mathematical model of the pipe-group heat exchanger that had been verified, the main influencing factors (including the thermal and physical properties of the soil, backfill material, inlet water temperature of tubes buried tube, fluid velocity and tube arrangement, etc) to the pipe-group heat exchanger was researched under the condition of constant temperature. On this basis, the added software UDF in the FLUENT is used to link the building dynamic load characteristic and the pipe-group heat exchanger system. The dynamic load are analyzed, regardless of the effect of the heat transfer characteristics about groundwater seepage, the influence of the uneven load for the soil temperature field about buried pipe heat exchanger is studied.Finally, the action of load characteristic on dynamic construction under is researched, consider the annual change of soil temperature field around the buried tube on different seepage velocity, the influence of groundwater seepage for taking from heat in summer and the exhausting heat in winter from soil is analyzed respectively, the improve effect of the problem about heat balance of soil on the groundwater seepage caused by uneven building cooling and heat load was researched quantitatively. The influence of groundwater seepage for the use of solar energy seasonal heat storage to improve soil thermal equilibrium problems is analyzed, the influence of the groundwater seepage on seasonal heat storage effect is studied, that part of the analysis results can provide the reference to determine soil source heat pump system design and operation control method for the future.