Heat Transfer Proformance Theory Research On U-Tube Heat Exchangers For Ground Source Heat Pump System

With the energy and environmental issues are now increasingly the world's widespread concerns, ground-source heat pump system are also more and more people's attention because of its significant energy saving and environmental benefits. At present the application on the ground-source heat pump technology research focus on heat exchangers in ground-coupled heat pump system for the thermal and heat transfer characteristics research. However, our research on the ground-source heat pump system is still in the initial stage, and not yet mature design and operation of the lessons learned. Thus, the improvements based on several existing traditional heat transfer model heat exchanger have a very important significance. This paper focus on the heat transfer mechanism of the U-tube vertical geothermal heat exchangers in the closed ground-source heat pump system to study, improve and perfect the underground heat transfer model, and compare with existing heat transfer model, thus establish more accurate heat transfer model for vertical U-tube geothermal heat exchangers in order to provide some reference on the future theoretical research and engineering design practice.The paper aim at the phenomenon of stratification on thermal properties of soil parameters in the depth direction, and combine the traditional cylindrical heat source model and the V.C.Mei model of heat transfer to improve, and then use the conservation of energy equation and the heat transfer equation establish the new cylindrical source of heat transfer model for the ground-source heat pump heat exchanger. The new model make up the traditional heat transfer model generally agreed that the soil is the same nature, and thermal parameters is constant, so compared with heat transfer process the amended transfer model is more realistic. In the solving process for two-dimensional partial differential equation along the radial and axial direction, the paper simplify properly the boundary conditions and initial conditions, and use the Laplace transform, Bessel functions, and non-dimensional analysis methods of mathematical physics find out the soil temperature distribution around the U-tube heat exchanger and fluid temperature distribution when soil layer along the depth direction. By comparing with two engineering examples of the experimental data the theoretical solution of this paper's heat transfer model is better coincide with the actual situation than the traditional lines and cylindrical heat source model, and it also verify the correctness of this model. The paper analyzes the impact of various parameters in new heat transfer model for the effects of heat transfer, finally come to some conclusions and recommendations.