竖直U型地埋管传热性能数值模拟

Numerical simulation on heat transfer behavior of a ground vertical U-shaped tube

对土壤源热泵系统在制冷季中垂直U型地埋管的传热性能进行数值模拟,揭示U型管入口水温、入口流速和回填材料导热系数对地埋管传热性能的影响规律.计算结果表明：在30～60°C的入口温度范围内,当雷诺数从3 000提高到11 000时,会使地埋管热流量增大10～23W,但会导致流体进出口温差降低0.2～1.34°C,在工程应用中流体进口流速要控制在一定范围内.水的入口温度和雷诺数分别为45°C和7 000时,回填材料导热系数从0.5 W/m·K增大至2.5 W/m·K,U型地埋管的热流量增大了将近2倍,也就是说在工程应用中,如果在回填土中掺混一定比例的保水材料将会增强埋管换热,并防止埋管长期运行时由于土壤本身保水性差使得土壤板结从而导致埋管失效.模拟结果与实验数据进行对比吻合较好.

Heat transfer behavior of a ground vertical U-shaped tube in ground source heat pump system in the cool supply season is evaluated based on numerical simulation.The influences of the inlet temperature and flow velocity of the water in the tube,and thermal conductivity of the backfill materials on the heat transfer characteristics are highlighted.Within an inlet temperature range of 30-60°C,as Reynolds number from 3 000 up to 1 1000,the heat flux of the tube is increased by about 10-23 W,while the temperature drops are decreased by 0.2-1.34°C,which suggest that the flow velocity of the water should be limited in further engineering application.At inlet temperatures of 45°C and Reynolds number of 7 000,the heat flux is increased by about2 times with increasing the thermal conductivity of the backfill materials from 0.5to 2.5W/（m·K）,which indicate that the heat transfer would be enhanced and that the tube is prevented from invalidation by adding some water retaining agent into the backfill materials.The calculation results are well agreeable with experimental data.