| 地下换热管土结构冻胀变形模拟 |
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| 引用本文： | 白莉,王有镗,高青,江彦,李兆强.地下换热管土结构冻胀变形模拟[J].农业工程学报,2016,32(18):118-124. |
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| 作者姓名： | 白莉 王有镗 高青 江彦 李兆强 |
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| 作者单位： | 1. 吉林建筑大学市政与环境工程学院,长春,130118;2. 山东理工大学建筑工程学院,淄博,255049;3. 吉林大学热能工程系,长春,130025;4. 吉林医药食品工程有限公司,长春,130021 |
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| 基金项目： | 国家自然科学基金资助项目（51376080）；山东省优秀中青年科学家科研奖励基金项目（BS2014SF013） |
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| 摘 要： | 以地源热泵技术在农业节能领域中的应用为研究背景，针对地下换热管土结构冻胀变形问题开展数值模拟研究，基于孔隙增长率函数、冻土本构方程、含水量方程和相变传热理论建立数值模型，并结合试验验证该模型的有效性。利用模型对冻胀过程中岩土应力和管体变形特性进行分析，并考察管体降温速率（0.1、0.2、0.3℃/h）对上述2方面的影响。结果表明，岩土冻胀应力和管体变形程度均随冻结范围增大而增大，当冻结直径达到365 mm时，进水管流通面积减小约3.5%，出水管流通面积减小可超过4%，可见出水管的变形更为明显；冻结范围基本一致的情况下，换热管体缓慢降温可导致较大的岩土冻胀应力和出水管变形。
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| 关 键 词： | 热泵系统 管体 变形 管土结构 冻胀 岩土应力 |
| 收稿时间： | 2016/3/14 0:00:00 |
| 修稿时间： | 2016/6/10 0:00:00 |
Simulation on underground pipe-soil heat exchange structure deformation due to frost heave |
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| Bai Li,Wang Youtang,Gao Qing,Jiang Yan and Li Zhaoqiang.Simulation on underground pipe-soil heat exchange structure deformation due to frost heave[J].Transactions of the Chinese Society of Agricultural Engineering,2016,32(18):118-124. |
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| Authors: | Bai Li Wang Youtang Gao Qing Jiang Yan and Li Zhaoqiang |
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| Institution: | 1. School of Municipal and Environmental Engineering, Jilin Jianzhu University, Changchun 130118, China,2. School of Architectural Engineering, Shandong University of Technology, Zibo 255049, China,3. Department of Thermal Engineering, Jilin University, Changchun 130025, China,3. Department of Thermal Engineering, Jilin University, Changchun 130025, China and 4. Jilin Medicine and Food Engineering Co., Ltd, Changchun 130021, China |
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| Abstract: | Abstract: The research background of this paper is the ground source heat pump (GSHP) technology applied in the field of agriculture energy conservation. The typical application is the GSHP used in greenhouse. However, the operating temperature of ground heat exchange pipe usually sustains below 0°C, when the GSHP runs during the winter night in cold regions. The sustaining low temperature can lead to pore water freeze and volume expansion in soil, which is called frost heave. In this paper, numerical simulation study was conducted to investigate the deformation of pipe-soil heat exchange structure due to frost heave. The numerical model, on the basis of porosity rate function, frozen soil constitutive equation, water content equation and phase change heat transfer theory, was built on the simulation platform ABAQUS and thermal-mechanical coupled subroutine compiled in Fortran. The semicircle soil computational domain and U-pipe were adopted in 2-D geometrical model. Based on the assumptions of this model, its application was restricted to: 1) The initial soil is homogeneous and saturated; 2) The difference of soils inside and outside borehole is neglected; 3) The internal and external pressure of the pipe is uniform; 4) The heat transfer takes place by conduction only; 5) The operational mode of pipe is cooling or constant temperature. This numerical model was verified by frost heave experiment, and the verification included mainly soil freezing temperature field and pipe deformation strain. The result of verification showed that the temperature of center point in the freezing area had a maximum absolute error of 0.6°C, the freezing radius had a maximum relative error of 9.1%, and the pipe strains had a maximum relative error of 16.4%. This numerical model could be applied for the study of pipe-soil structure frost heave and deformation. By means of this model, the characteristics of soil stress and pipe deformation during soil frost heave were analyzed. The results showed that elliptical deformation appeared in the pipe cross-sections under the frost heave force, which manifested as the decreasing diameter in X-axis and the increasing diameter in Y-axis. The soil stress and pipes'' elliptical deformation increased with the extension of freezing area, under 1°C temperature difference between outlet and inlet pipe, the deformation of outlet pipe was greater than inlet pipe. Meanwhile, the deformation caused the pipe cross-sections'' circulating area gradual decrease, and the decrease rate showed linear increase with the extension of freezing area. Moreover, the influence of different pipe cooling rate (0.1°C/h, 0.2°C/h, 0.3°C/h) were also investigated. For almost the same freezing range, the lower cooling rate of heat exchange pipe could lead to larger soil stress and pipe deformation. It can be found from the simulation, when the soil freezing diameter increased to 365 mm, the circulating area decrease rates of inlet pipe were about 3.5% in the 3 different cooling rate, and the circulating area decrease rates of outlet pipe were 4.6%, 4% and 3.8%, respectively, in cooling rate of 0.1°C/h, 0.2°C/h and 0.3°C/h. By contrast, the cooling rate showed almost no influence on the inlet pipe deformation, but an obvious influence on the outlet pipe deformation. In order to reduce the impact on the pipe cross-sections for the same heat exchange, it is reasonable to adopt a rapid cooling mode. |
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| Keywords: | heat pump systems pipe deformation pipe-soil structure frost heave soil stress |
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