Study Of Ground Tube Heat Transfer Model With Underground Water Conditions

Ground-source heat pumps are shallow geothermal energy devices that convert low-grade thermal energy to high-grade thermal energy through a small amount of high-grade energy(electric energy).In winter,the soil supplies heat to the building through the circulating water in the U-shaped underground pipe.In summer,the heat of the building is discharged into the soil under the effect of the circulating water to achieve the cooling effect.In the ground source heat pump system,the ground tube heat exchanger is an important component of heat exchange,so its reasonable and accurate design helps to improve the reliability of the system and reduce the initial cost of the project.However,the accuracy of the design of ground heat exchanger depends on the accurate acquisition of soil,and grout thermal parameters(thermal conductivity and heat capacity of soil,thermal conductivity and heat capacity of grout)and related parameters of seepage.In order to study the influence of these parameters on the heat transfer performance of the ground heat exchanger,a numerical analysis model for the heat transfer process of the ground heat exchanger under the condition of seepage was established to optimize the realization of the ground exchanger and the design of the heat exchanger.In the soil area outside the borehole of the buried pipe,the body-fitted grid was introduced to conduct the heat transfer calculation of the soil outside the buried pipe.In this thesis,the Poisson equation is used to mesh the soil area outside the buried pipe and the body mesh is orthogonalized by adjusting the Poisson equation source term.This thesis deduces and discretizes the convective diffusion equation on the body-fitted grid,and uses the porous media energy equation to establish an analytical model of the soil heat transfer process outside the buried pipe.In this thesis,the heat transfer process in the ground exchanger is simulated using the four-residue model in the borehole,and the heat transfer model of the ground exchanger is coupled with the external heat transfer model of the ground exchanger.The results of simulation analysis verified the established model and found that compared with the CFD model,the model built in this thesis has the advantages of high accuracy and short solution time.In this thesis,based on the three-dimension heat transfer model of buried pipe in the four-resistance model of borehole,combined with the simplex parameter optimization method,a new geotechnical thermal response test data processing method is proposed to obtain geophysical parameters.This method can quickly calculate the equivalent thermal conductivity and specific heat capacity of soil around a buried pipe.The comparison and analysis of the thermal response test data processing results with the conventional line-based heat source model verified the correctness and accuracy of the thermal response test data processing method based on the three-dimensional heat transfer model of the ground heat exchanger.It plays an extremely important role in the large-scale engineering practice of the ground source heat pump system.