Abstract Based on the finite line source (FLS) model, A heat transfer model considering both multilayer soil and multiple Borehole Heat Exchangers (BHEs) is proposed. The accuracy of the model is verified by experiments. The model is used to study the effect of thermal physical properties of multilayer geological media on the overall thermal efficiency of multiple BHEs. The dimensionless regional thermal efficiency (E) is introduced as an evaluation index of heat transfer characteristics of multiple BHEs. Under a certain geological structure, the heat transfer efficiency of multiple BHEs in homogeneous soils and multilayer soils were compared with the analytical model. The results show that the E of the multilayer multiple BHEs model is less than that of the homogeneous multiple BHEs model, with the maximum difference being 11.43% in 2,000 h. With these thermal properties and soil layer structure, the rate at which E decrease for the multilayer model is a factor of 4 higher than that for the homogeneous model. In the soil layer where the thermal interaction is the most intense, the unit Heat Transfer Rate (HTR) decreased by 25.3%. At a fixed spacing, the thermal diffusivity is the key to determining the degree of thermal interaction. Under the 4 × 4 BHEs layout, the dynamic performance loss increases by about 4% for every 1 × 10−7 m2/s increase in soil thermal diffusivity. When the multiple BHEs are in a multilayer geological media with a large difference in thermal properties (especially thermal diffusivity), a comprehensive multilayer analysis is needed to obtain the thermal efficiency of the overall multiple BHE area accurately. The multilayer multiple finite line source model can be used during the engineering design stages of a BHE field to predict the regional thermal efficiency with borehole spacing and the number of boreholes.

中文翻译：

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多层岩土介质中多埋管换热器的热性能分析

摘要 基于有限线源（FLS）模型，提出了一种同时考虑多层土壤和多个钻孔换热器（BHE）的传热模型。通过实验验证了模型的准确性。该模型用于研究多层地质介质的热物理特性对多个BHEs整体热效率的影响。引入无量纲区域热效率（E）作为多管换热器传热特性的评价指标。在一定的地质结构下，将多个BHEs在均质土壤和多层土壤中的传热效率与解析模型进行了比较。结果表明，多层多重BHEs模型的E值小于均质多重BHEs模型，2000 h最大差异为11.43%。有了这些热特性和土层结构，多层模型的 E 减小速率比均质模型高 4 倍。在热相互作用最强烈的土层，单位传热率（HTR）下降了25.3%。在固定间距下，热扩散率是确定热相互作用程度的关键。在 4 × 4 BHEs 布局下，土壤热扩散率每增加 1 × 10−7 m2/s，动态性能损失增加约 4%。当多个 BHE 处于热性质（尤其是热扩散率）差异较大的多层地质介质中时，需要进行综合的多层分析，以准确获得整体多个 BHE 区域的热效率。