Study On The Performance Of Single U-shaped Vertical Borehole Heat Exchanger Effected By Groundwater Seepage Velocity In Different Soils

At the present stage in China, the population and building density are huge, the consumption and requirement of resources are now increasing rapidly, and the energy supply is more and more serious. So many industries have started to pay attention to building energy-saving. The ground source heat pump is a system not only energy-saving, environmentally friendly but also meets requirements for sustainable development. It brings an opportunity to solve two problems of environmental pollution and energy crisis problems encountered in the development of our country, and therefore the prospects of ground source heat pump technology in China will be very clear and bright.In applied research of the ground source heat pump, it involves a variety of parameters related to conditions, which include shallow geological conditions. The geotechnical properties act as a decisive role during the operation of the ground source heat pump. The dynamics factor of groundwater flow is a very important factor in the theoretical study and practical application of ground source heat pump. The current researchers believe that groundwater flow factor is one of the central factors for accurately ground source heat pump system design.Firstly, the working principle, composition and classification, system features and the current situation of ground source heat pump have been described in detail in this paper. And then the heat foundation and ground heat exchanger heat transfer theories have been analyzed. At last, the process of heat exchanger heat transfer mathematical model and percolation models were discussed, which regard the soil as a saturated porous media. The preprocessor GAMBIT have been used to establish fluid within the tube model, vertical U-tube model, and the thermal coupling seepage physical model of the surrounding soil. And the numerical simulation and post-processing have been done by FLUENT software.In this paper, the summer conditions in the absence of no groundwater flow is studied, the vertical U-tube is respectively buried in five different kinds of soil (namely dense sand, light sand, silty clay, pebbles (Huanggang rocks), sand). Then, simulations and data analysis are made for different flow velocity (100m/y,200m/y,300m/y,400m/y,500m/y,600m/y,700m/y,800m/y,900m/y,1000m/y).At last, the soil temperature field around the U-shaped heat exchanger and the temperature difference between the inlet and outlet pipe were analyzed.The results show that, in the absence of groundwater flow, the soil temperature field around buried pipes will extent offset along the flow direction, and the effect of heat transfer of the U-shaped pipe heat exchanger is significantly better than without groundwater flow. The optimum flow velocity are given by comparing the simulation results under each type of soil. The optimum flow velocity of dense sand, light sand, silty clay, pebbles (Huanggang rock, etc.) and sandstone are respectively500m/y,600m/y,800m/y,300m/y and300m/y. The temperature difference between imports and exports of the U-type heat exchanger is maximum under the optimum flow velocity. And the temperature differences between imports and exports of sandstone and egg rock are influenced by the flow velocity and the curvature changes significantly. While the curve of temperature differences between imports and exports of sandstone, dense sand and silty clay soil are gentle and less influenced by the flow velocity. These results have a guiding role for U-shaped ground-source heat pump heat exchanger engineering designing.