The Study On Influence Of Ground Heat Exchanger Under Groundwater Advection Conditions

As an energy saving and environment friendly air conditioning technology, the ground source heat pump(GSHP) is becoming more and more popular in many countries and regions, and which has the greatest developmental future. The heat transfer performance of ground heat exchanger is affected by a lot of factors, where ground heat exchanger is one of the key research content of GSHP. In recent years, a lot of researches have been done not only in the practical application of ground source heat pump system, but also in experimental test and numerical calculation. While almost all the design tool for ground heat exchanger are based on principles of heat conduction, ignoring the flow of groundwater, which may induce the deviations from actual needs in designing heat exchanger.In view of the above, the heat transfer performance of ground heat exchanger under the flow of groundwater are implemented in this paper, based on the theory of heat and mass transfer in porous media, and the numerical model of ground heat exchanger under different depths and directions of the groundwater flow is built.At first, on the basis of actual engineering exploration geological conditions and the 3D simulation put forward on by the predecessors, establishing the model of vertical double U-tube heat exchanger under coupled thermal conduction, by thermal response test obtaining boundary conditions, initial conditions and the calculate time of numerical model, and simulates in Fluent. According to the results of numerical calculating, analyzing the effect on the ground heat exchanger under different flow velocity and porosity, and analysis the numerical solution and test values, concludes that the model of coupled thermal conduction and advection under certain groundwater flow conditions is in conformity with the actual dates of thermal response, it proves that the numerical simulation model and method can be used in practical project, and also obtained the flow velocity and porosity of the thermal response test area.Then, based on the vertical double U-tube heat exchanger under coupled thermal conduction model as the original model, establishing the model of ground heat exchanger under different depths of the groundwater flow, analyzing changes in heat transfer performance caused by the location of the groundwater flow. The result of the analysis indicates that where there is groundwater flow, the temperature field of soil offset, and the inlet water temperature drop significantly greater than no seepage zone temperature drop, outlet water temperature drop almost equal to no seepage zone temperature drop. With respect to the case of no groundwater flow, groundwater flow are located in the upper, middle, lower heat exchange rose by 5.8%, 4.9%, 2.6%, that is when the groundwater flow are located in the upper place, it can be seen that is most useful for ground heat exchanger operation, and indirectly validated the layer heat transfer theory.At last, based on the model of vertical double U-tube heat exchanger under coupled thermal conduction as the original model, establishing the ground heat exchanger under different directions of the groundwater flow model, analyzing changes in heat transfer performance caused by the direction of the groundwater flow. The results found that the greater the flow rate, the more heat transfer between the media and soil, regardless of the direction of groundwater flow, and the inlet temperature drop is always greater than the outlet temperature drop. But when the groundwater flow direction come from inlet pipe at upstream, outlet pipe at downstream, and outlet pipe at upstream, inlet pipe at downstream, and is perpendicular to the horizontal axis of inlet/outlet pipe the inlet tube heat exchange gradually decreased, the outlet tube heat exchange gradually increased, at the meantime, the value of heat transfer coefficient increases, that is when the groundwater direction is outlet pipe at upstream, inlet pipe at downstream, it can be seen that is most useful for ground heat exchanger operation.