The Numerical Simulation And Experimental Research Of U-Tube Borehole Heat Exchanger For Ground-Coupled Heat PUMP

Ground-coupled heat pump is a kind of highly efficient, energy saving, and environmentally-friendly form of air conditioning cold and heat source, as a renewable energy technology has broad prospects for development in China. However, the effect operating of ground-coupled depends on the heat transfer performance of the heat exchanger, and the change of soil temperature field has a great influence on the heat transfer performance of borehole heat exchanger. From the point of view of theoretical research and engineering practice, groundwater seepage has a great influence on the operation of ground-coupled heat pump. Therefore, it is necessary to study the groundwater seepage influence of soil temperature field around the ground heat exchanger, and improve the accuracy of borehole heat exchanger design.This paper briefly introduced the infinite line heat source model, finite line heat source model and moving infinite line heat source model that based on the line source, and had the analytical solution of soil excess temperature field, and MATLAB software was used to solve the analytic solution of the model expression to obtain the soil temperature distribution around borehole. Through comparative analysis of the differences between analytical solution based on different models, and analytical different seepage velocity influence on the soil excess temperature distribution, found that the seepage would make the soil excess temperature field a shift in the direction of seepage, shorten the soli excess temperature field to reach steady state.In order to simplify the model, many scholars simulate ground-coupled heat pump largely ignored the influencing factors of groundwater seepage. The article will regard the soil as saturated porous media and consideration of groundwater seepage, and U-tube borehole heat exchanger coupled heat transfer model is established, GAMBIT pre-treatment modeling software is adopted to establish the physical model, then using FLUENT software to simulate the heat transfer process of the buried pipe and the soil and the surrounding soil temperature field.Using of the ground heat exchanger miniature test bench to experimental study the heat transfer characteristic of borehole heat exchanger. By contrast whether thermal response test with groundwater seepage, get a number of valuable experimental data, found that groundwater flow will increase the general Geotechnical thermal conductivity in Geotechnical thermal response test, and increasing the heat transfer between borehole heat exchanger and the soil. When the seepage velocity is 0.02m/d to 0.1m/d, buried pipe heat transfer increased from 33.87% to 82.77%, and the faster groundwater seepage, the greater the heat exchange between buried pipe and the soil.