The Analysis Of Influence Factors Of The Coaxial Tube Borehole Heat Exchanger Baced On CFD

Compared to a conventional building HVAC system,the ground source heat pump(GSHP)system is more effient and environmentally friendly.Because it use the soil as the source of heat and cold,and the soil resource is rich.This form of HVAC system is very economical and environmentally friendly,if the ground source heat pump system can be used effectively,then it will make a certain contribution to alleviating energy shortages.As the initial stage of the ground source heat pump design,the design of the buried pipe is particularly important.Whether the design is reasonable relates to the quality of the ground source heat pump.Vertically buried pipes can be divided into U-shaped pipes and coaxial bushings depending on the form.Since U-tubes are common in the market,the researches and applications of coaxial tube are less than U-tube,so the paper will study on the heat transfer of coaxial tube.In this paper,the three-dimensional numerical model of casing buried pipe is first established by fluent software,and grid independence test is performed on it.The summer standard conditions and winter standard conditions are simulated respectively.It was found that the heat transfer efficiency in summer conditions is better than the winter conditions.The effects of different factors on the heat transfer rate of coaxial tube are studied in the paper,those factors include inlet and outlet water flow rates and temperatures,inlet and outlet modes,thermal properties of soil and backfill materials and internal and external pipe materials of the coaxial tube.Among them,in the situation of different influent water mode,the distribution of temperature along the inner and outer tubes varies greatly;Inner tube materials have a greater influence on thermal short-circuit phenomena;the soil layering model of the casing pipe is proposed for the first time in this paper,and compared with the homogeneous model of the soil,it is found that the homogeneous model of the soil can replace the layered model to simplify the study.The analysis of the above phenomena leads to some conclusions.These conclusions can provide certain reference value for the design and application of coaxial tube in practical projects.