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摘要该文旨在分析基于钻孔埋管换热器的热响应测试(thermal response tests, TRT)测试用于桩基埋管换热器时的通用性与局限性。首先选用不同的分析模型进行温度响应的计算与比较,并选用包含流体对流换热的有限元模型(FEM),模拟了不同桩径、不同埋管形式以及不同加热功率的能源桩TRT。计算表明:用于钻孔埋管的TRT测试同样适用于能源桩,但随着桩径的增大,测试所需的最短时间变长;桩内埋管数量的增加和加热功率的提高也不能缩短测试时间。通过模拟北京CFG(cement fly-ash gravel)桩的TRT测试,有限元模型得到了验证。该试验表明:能源桩TRT测试的加热功率不宜过大。对直径大于400 mm的能源桩,TRT测试时长>100 h,测试条件不易保证,建议采用原位钻孔取样后实验室测试的方法获取岩土热物性参数。
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| 关键词 ：地源热泵(GSHP),能源桩,热响应测试(TRT),传热模型,测试时长 |
Abstract：Thermal response tests (TRT) are used to investigate the thermal properties of the ground for dimensioning borehole heat exchangers. This study analyzes the versatility and limitations of TRT in energy piles. Several analytical solutions are presented for the temperature response of the borehole system with a finite element model (FEM) used to study the effect of convection for different pile diameters, different types of pipes and different heating powers. The results show that the TRT tests can be used in energy piles but the minimum duration of the tests increases with increasing pile diameter, while the types of pipes and the heating power have no effects. The accuracy of the FEM model was verified by simulations of Beijing TRT tests on CFG (cement fly-ash gravel) piles with the results indicating that the high heating power is not appropriate. TRT tests may take hundreds of hours for large diameter piles (larger than 400 mm); thus, lab tests for the thermal parameters are suggested using undisturbed borehole samples.
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| Key words：ground source heat pumps (GSHP)energy pilesthermal response test (TRT)heat transfer modeltest duration |
| 收稿日期: 2014-03-20 出版日期: 2015-05-15 |
| 基金资助:清华-MIT-剑桥三校低碳大学联盟基金资助项目(300907001) |
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| 不同热源解析模型的温度响应计算 |
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| TRT测试的有限元模型示意图 |
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| 桩基埋管截面示意图 |
 | 算例 | 几何参数 | | l/m | d/mm | D/mm | dout/mm | din/mm | | 1 | 30 | 150 | 120 | 25 | 20 | | 2 | 30 | 600 | 400 | 25 | 20 | | 3 | 30 | 800 | 600 | 25 | 20 |
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| 桩基埋管几何参数 |
参数 | 热导率/(W·m-1·K-1) | 密度/(kg·m-3) | 热容/(kJ·kg-1·K-1) | 流量/(m3·h-1) | 加热功率/(W·m-1) | | λs | λc | ρs | ρc | cs | cc | Q | q | | 取值 | 2.0 | 1.5 | 2 000 | 2 400 | 1.0 | 0.96 | 0.6 | 70 |
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| 桩基埋管换热数值模拟参数取值 |
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| 不同桩径的能源桩TRT测试进出口平均水温模拟结果 |
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| 埋管布置示意图 |
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| 不同埋管形式的能源桩TRT测试模拟结果 |
| 时间/h | 计算综合热导率/(W·m-1·K-1) | | 1U埋管 | 2U埋管 | 3U埋管 | | 起 | 止 | 3D FEM | 2D FEM | ILS | 3D FEM | 2D FEM | ILS | 3D FEM | 2D FEM | ILS | | 10 | 48 | 2.69 | 3.80 | 3.19 | 3.10 | 3.80 | 3.19 | 3.16 | 3.80 | 3.19 | | 120 | 240 | 2.08 | 2.14 | 2.13 | 2.17 | 2.14 | 2.13 | 2.10 | 2.14 | 2.13 | | 222 | 322 | 2.06 | 2.08 | 2.08 | 2.11 | 2.08 | 2.08 | 2.06 | 2.08 | 2.08 | | 222 | 422 | 2.06 | 2.07 | 2.07 | 2.10 | 2.07 | 2.07 | 2.07 | 2.07 | 2.07 |
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| 不同埋管形式的桩基TRT测试取不同时段计算的综合热导率 |
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| 不同加热功率的能源桩TRT测试模拟结果 |
| 时间/h | 计算综合热导率/(W·m-1·K-1) | | 起 | 止 | q=
70 W·m-1 | q=
117 W·m-1 | q=
210 W·m-1 | | 48 | 222 | 2.18 | 2.18 | 2.18 | | 222 | 422 | 2.07 | 2.07 | 2.07 |
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| 3D FEM中不同加热功率计算的综合热导率 |
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| 北京CFG桩埋管位置图 |
| 深度 | 各土层
土样
描述 | 热物参数 | | m | 密度 | 热容 | 热导率 | | g·cm-3 | J·kg-1·K-1 | W·m-1·K-1 | | 0~1.3 | 素填土层 | 2.00 | 2.00 | 1.50 | | 1.3~3.9 | 砂质粉土 | 1.93 | 1.21 | 1.67 | | 3.9~4.4 | 粉质粘土 | 1.92 | 1.37 | 1.58 | | 4.4~6.3 | 砂质粉土 | 1.97 | 1.21 | 1.67 | | 6.3~14.2 | 卵石 | 2.50 | 0.78 | 2.20 | | 14.2~16.3 | 粉质粘土 | 2.04 | 1.37 | 1.58 | | 16.3~18.1 | 砂质粉土 | 2.03 | 1.17 | 1.64 | | 18.1~20.0 | 卵石 | 2.50 | 0.78 | 2.20 |
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| 原状土样热物参数测定结果 |
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| 北京CFG桩TRT测试模拟结果(直角坐标) |
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| 北京CFG桩TRT测试模拟结果(对数坐标) |
| 时间/h | 数据
来源 | 计算综合热导率/(W·m-1·K-1) | | 起 | 止 | q=
97 W·m-1 | q=
120 W·m-1 | q=
194 W·m-1 | | 77 | 96 | 3D
FEM | 1.72 | 1.72 | 1.72 | | 试验 | 1.08 | 1.88 | 4.67 | | 77 | 120 | 3D
FEM | 1.57 | 1.57 | 1.57 | | 试验 | — | 1.71 | 8.86 |
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| 北京CFG桩TRT测试的热导率计算 |
| [1] | Brandl H. Energy foundations and other thermo-active ground structures[J]. Géotechnique, 2006, 56(2): 81-122. |
| [2] | Gao J, Zhang X, Liu J, et al.Numerical and experimental assessment of thermal performance of vertical energy piles: An application[J]. Applied Energy, 2008, 85(10): 901-910. |
| [3] | 桂树强, 程晓辉. 能源桩换热过程中结构响应原位试验研究[J]. 岩土工程学报, 2014, 36(6): 1087-1094. GUI Shuqiang, CHENG Xiaohui. In-situ test for structural responses of energy pile to heat exchanging process[J]. Chinese Journal of Geotechnical Engineering, 2014, 36(6): 1087-1094. (in Chinese) |
| [4] | National House-Building Council (NHBC). Efficient Design of Piled Foundations for Low Rise Housing: Design Guide [M]. Watford, UK: IHS BRE Press, 2010. |
| [5] | Ground Source Heat Pump Association (GSHPA). Thermal Pile Design, Installation & Materials Standards[M]. Milton Keynes, UK: National Energy Centre, 2013. |
| [6] | American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). 2011 ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning Applications[M]. Atlanta, USA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2011. |
| [7] | Loveridge F, Powrie W. Temperature response functions (G-functions) for single pile heat exchangers[J]. Energy, 2013, 57, 554-564. |
| [8] | Man Y, Yang H, Diao N, et al.A new model and analytical solutions for borehole and pile ground heat exchangers[J]. International Journal of Heat and Mass Transfer, 2010, 53(13): 2593-2601. |
| [9] | Carslaw H S, Jaeger J C. Conduction of Heat in Solids [M]. Oxford, UK: Clarendon Press, 1947. |
| [10] | Eskilson P. Thermal Analysis of Heat Extraction Boreholes [D]. Lund, Sweden: Lund University, 1987. |
| [11] | Gehlin S E A, Hellström G. Comparison of four models for thermal response test evaluation[J]. ASHRAE Transactions, 2003, 109(1): 131-142. |
| [12] | Thompson III W H. Numerical Analysis of Thermal Behavior and Fluid Flow in Geothermal Energy Piles [D]. Blacksburg, USA: Virginia Polytechnic Institute and State University, 2013. |
| [13] | Loveridge F, Powrie W. Pile heat exchangers: Thermal behaviour and interactions[J]. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 2013, 166(2): 178-196. |
| [14] | You S, Cheng X, Guo H, et al.In-situ experimental study of heat exchange capacity of CFG pile geothermal exchangers[J]. Energy and Buildings, 2014, 79: 23-31. |
),李翔宇,程晓辉
