Transient heat transfer model of a three-dimensional spiral heat source in an energy pile
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摘要: 將螺旋埋管等效為三維螺旋線熱源，考慮螺旋埋管能源樁的傳熱過程，運用格林函數和第一型曲線進行積分，推導給出了考慮時間、空間位置、埋管參數和巖土體熱物理性質4參數的螺旋埋管能源樁的溫度場解析解，建立高精度三維螺旋埋管能源樁的傳熱模型。并通過在數值模擬軟件中建立螺旋埋管能源樁三維模型，依據邊界條件，求解得出三維螺旋埋管能源樁溫度場數值解。對比結果表明：所建立的能源樁三維螺旋線熱源模型具有很高的解析精度。最后，基于解析模型討論了螺旋埋管能源樁換熱溫度場的空間分布和時間效應。Abstract: An energy pile is a new type of ground source heat pump system. A heat exchanger is casted into the concrete pile foundation of a building structure for the purpose of heating or cooling the building through heat exchange between the pile foundation and surrounding soil. An energy pile can be developed rapidly because of its high heat transfer efficiency and stable structure and because it requires no additional drilling requirements. In the long-term operation, energy piles have to bear both the overlying and thermal loads caused by changes in the temperature field. Thus, accurately evaluating the temperature field of an energy pile and its surrounding soil is one of the key problems in the design and application of energy piles. To improve the heat transfer efficiency of energy piles, U-type, W-type, spiral type, and similar types of coils have been developed to be casted into the energy pile. Results of thermal efficiency analysis show that the spiral type coil has the best heating and cooling performance and was nearly 150% more thermally efficient than the double U-type coil. Thus, a spiral coil is selected as the main coils’ form in the current practical application. However, due to the complex heat exchange structure of the spiral pipe, the present analytical model had to be simplified to accurately characterize the temperature field characteristics of a spiral pipe casted in an energy pile. In this paper, the spiral pipe was regarded as a three-dimensional spiral heat source. Considering the existing heat transfer model, an analytical solution of the temperature field was obtained by integrating green’s function and the first curve function; then, the high-precision, three-dimensional (3-D) heat transfer model of the spiral pipe was established considering the time, space, buried pipe parameters, and thermal property of host soil. In addition, a 3-D model of a spiral pipe casted in an energy pile was created in the numerical simulation software COMSOL; after simulation, the numerical solution of the temperature field was obtained. The contrastive results showed that the built 3-D spiral heat source model has high analytical accuracy. Finally, based on the analytical model, the spatial distribution and time effect of a spiral pipe casted in an energy pile were discussed.
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Key words:
- energy pile /
- spiral pipe /
- heat transfer model /
- temperature field /
- analytical solution
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圖 7 數值解與解析解對比圖。（a）數值模擬結果；（a）解析解結果
Figure 7. Comparison between the numerical and analytical solutions: (a) numerical result; (b) analytical result
中文字幕在线观看表 1 數值模型參數
Table 1. Parameters of numerical simulation
Description Parameters Values Description Parameters Values Heat conductivity kiso/(W·m?1·K?1) 1.3 Burial depth Hspi/m 3 Thermal capacity Cp/(J·kg?1·K?1) 840 Helical pitch bspi/dm 3 Soil density rho/ (kg·m?3) 1460 Helical diameter rspi/dm 1 Calculated length Liso/m 4 Initial temperature Tcomp1/K 288.15 Calculated depth Hiso/m 4 Dirichlet temperature T0/ K 288.15 Calculated width Wiso/m 4 Heat consumption Ql/ W 20 Neumann boundary P0/ W 5 
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參考文獻
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