为解决能源桩传热分析中一般将桩土视为相同介质而引起误差的问题,建立一种可考虑桩体与土体之间热物性差异的U型埋管能源桩非稳态传热模型,将其与线热源模型进行对比,验证该模型的准确性。在此基础上,通过级数展开得到近似简化的能源桩热响应半径表达式。最后,对单位桩长换热量、桩体的热扩散系数、桩径以及土体类型进行分析,利用“储热比”评价上述参数对能源桩传热过程的影响。结果表明：该模型较线热源模型可更精准地描述能源桩传热过程,可有效避免传热初期低估桩壁过余温度以及传热稳定期高估桩体温度的问题;在典型的能源桩运行周期内,所提出的热响应半径计算方法误差在0.1 ℃以内,符合工程要求;能源桩传热过程中,土体的储热比随桩体热容、桩土间热扩散系数相对差异的减小而增大;桩壁过余温度及土体储热比均随桩径的增大而减小,随着传热时间的增加,不同桩径对应的桩壁过余温度差逐渐加大,土体储热比差值逐渐减小;相同换热功率作用下能源桩桩壁过余温度的变化率几乎不随传热时间增长而变化;传热90 d后,桩径对能源桩传热过程中能量传递分布影响不大。
Abstract
In order to solve the problem of error caused by treating pile and soil as the same medium in heat transfer analysis of energy pile, an unsteady heat transfer model of U-shaped buried pipe energy pile is established, which can consider the thermophysical properties difference between pile and soil. The accuracy of the model is verified by comparing with the linear heat source model. On this basis, the approximate simplified expression of thermal response radius of energy pile is obtained by series expansion. Finally, the heat exchange per unit pile length, the thermal diffusion coefficient, pile diameter and the soil type are analyzed, and the "heat storage ratio" is used to evaluate the influence of the above parameters on the heat transfer process of the energy pile. The results show that： compared with the linear heat source model, the model can describe the heat transfer process of energy pile more accurately, which can effectively avoid the problems of underestimating the excess temperature of pile wall in the initial stage of heat transfer and overestimating the pile temperature in the stable stage of heat transfer; in the typical operation cycle of energy pile, the error of the calculation method of thermal response radius proposed in this study is within 0.1 ℃, which meets the engineering requirements; during the heat transfer process of energy pile, the heat storage ratio of soil increases with the decrease of the heat capacity of pile and the relative difference of thermal diffusion coefficient between pile and soil; the excess temperature of pile wall and the heat storage ratio of soil decrease with the increase of pile diameter; with the increase of heat transfer time, the excess temperature difference of pile wall corresponding to different pile diameter increases gradually, and the difference of heat storage ratio of soil decreases gradually; under the same heat transfer power, the change rate of excess temperature of energy pile wall hardly changes with the increase of heat transfer time; after 90 days of heat transfer, the pile diameter has little effect on the distribution of energy transfer.
关键词
地源热泵 /
传热模型 /
热物理特性 /
热响应半径 /
能源桩
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基金
国家自然科学基金（52068004; 51978179; 51768006）; 广西重点研发项目（AC20238002）
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