Numerical Simulation Of Vertical Buried Tubes And An Experimental Study

Ground source heat pump has a lot of advantages, such as high efficiency, energysaving, environmental protection and running stability. It is a typical application ofbuilding energy saving. Ground source heat pump is widely used in heating andcooling in the field of domestic construction. Buried tube heat exchanger is the corecomponent of the ground source heat pump, and its running state directly affects theheat transfer performance of the ground source heat pump system.Some natural factors including the thermal properties of soil, the initialtemperature of the formation and groundwater seepage velocity will influence theground heat exchanger performance, and some engineering factors such as the inlettemperature of flow and the inlet velocity of flow will also bring some effects on theperformance of heat exchange. This paper uses the Comsol to build atwo-dimensional model for the heat exchanging in the steady state between the singleU tube and soil based on the summary of the models about the buried pipe heatexchanger, each influencing factors of heat exchanging corresponds to six referencevalues, and each reference values was calculated by the Comsol. This paper conductsa single factor regression analysis, and obtains the regression equation of the heatexchange quantity per unit borehole depth and outlet water temperature concerningeach parameters with the the help of Spss. The conclusion indicates that the heatexchange quantity per unit borehole depth and outlet water temperature show alogarithm relationship with the inlet velocity of flow and are linear to otherinfluencing factors. The thermal conductivity of soil (λ) has the largest influence onthe heat exchange performance, and regression equation between the thermalproperties of soil (λ) and the heat exchange quantity per unit borehole depth (ql) is ql=0.8242λ+3.297, on the country, the specific heat capacity of soil has a minimal impacton the heat exchange performance and regression equation between the specific heatcapacity of soil (Cp) and the heat exchange quantity per unit borehole depth(ql) is ql=0.0041Cp+6.2327. When the groundwater seepage velocity is1×10-6m/s, the heatexchange quantity per unit borehole depth is68%larger than that under no flow condition. The seepage velocity increasing, the heat transfer performanceimprovement is more significant.In this paper, in order to find out the relationship between the heat transferperformance and hydrogeological conditions, experiments about heat exchanging inthe steady state between the single U tube and soil were conducted under threeconditions (dry sand, saturated sand and groundwater flow), and the size of theground source heat pump experiment rig with sand box which we used is3m×2.5m×1m. The experimental results show that under the groundwater flowcondition, the range of temperature is the maximum and is about2℃, the temperaturefiled will shift to the lower reaches along the flow direction, and the offset distance isabout94cm. Under the condition of dry sand, the difference in temperature is theminimum and is about0.3℃, and the distribution of temperature field is symmetricaland the thermal influencing radius is50cm. The difference in temperature is1.2℃under the condition of saturated sand, and the distribution of temperature field also issymmetrical. At the same time, the three-dimensional numerical simulation of heatexchanging was carried out under two conditions (dry sand, groundwater flow) basedon the same size of the experiment rig. The simulation can be verified accuratelythrough the comparison between the simulation data and experimental data.