Abstract Heat transfer model is important for the design of coaxial borehole heat exchanger (CBHE). However, the existing models have some disadvantages, such as costing too much computation time, ignoring the geothermal gradient and concerning the borehole heat capacity as a whole. In this paper, a semi-analytical model is developed by considering the geothermal gradient and the heat capacities of different parts of the borehole: 1D radial heat transfer in the grout and the soil is analyzed based on an analytical solution; temperature distributions of the internal fluid and the annular fluid are calculated numerically. To verify the feasibility of the proposed model, it is compared with another model and experimental data, and it is compared with OGS simulation data of a deep CBHE. Compared with another model, the fluid temperature distributions calculated by the proposed model match better with experimental data especially at the early time of heat injection. The fluid temperature distributions calculated by the proposed model match well with OGS simulation data except during the early several days, noting that the OGS simulation data are not accurate at the early time. The results show that the proposed model is feasible and efficient.

中文翻译：

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同轴埋管换热器传热的半解析模型

摘要 传热模型对于同轴埋管换热器（CBHE）的设计具有重要意义。然而，现有模型存在计算时间过长、忽略地温梯度、将井眼热容作为一个整体考虑等缺点。在本文中，通过考虑地温梯度和钻孔不同部位的热容量，建立了一个半解析模型：基于解析解分析灌浆和土壤中的一维径向传热；数值计算了内部流体和环形流体的温度分布。为了验证所提出模型的可行性，将其与另一个模型和实验数据进行了比较，并与一个深层CBHE的OGS模拟数据进行了比较。与另一款车型相比，所提出的模型计算的流体温度分布与实验数据更好地匹配，尤其是在热注入的早期。所提出的模型计算出的流体温度分布与 OGS 模拟数据很好地匹配，除了早期的几天，注意到 OGS 模拟数据在早期并不准确。结果表明，所提出的模型是可行且高效的。