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Based on the porous medium model, a threedimensional double Utube heat exchanger heat transfer model considering groundwater seepage was established, and the effects of seepage velocity and tube flow velocity on the temperature field of the heat exchanger were investigated by numerical simulation method. Moreover, the comparison of heat transfer performance was completed for the round tube (the crosssectional aspect ratio =1) with the flatoval tube ( is 0.54, 0.44, 0.34, respectively). The results show that increasing the seepage velocity and the tube flow velocity can increase the heat transfer capacity of the tube. When decreases, the heat transfer capacity increases more in the inlet tube than the outlet tube, and more in the vertically arranged tube than the horizontally arranged one. Reducing the aspect ratio of the tube crosssection can reduce the thermal resistance of the borehole and improve the heat exchange capacity of the tube, but it will also make the pressure drop of the tube increase, and the thermal shortcircuit loss is increase. When v=1.50×105 m/s, u=1.3 m/s, compared to the round tube, the heat exchange capacity of the flatoval tube with (=0.34 increases by 11.4%, the thermal resistance of the borehole decreases by 20.52%, and the pressure drop increases by 24.32%.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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