A study of soil thermal conductivity measurement based on the actively heated distributed temperature sensing cable
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摘要:
主动加热型分布式温度感测技术（AH-DTS）可通过植入土体中的光缆实现不同层位土体导热系数的分布式连续测量，但AH-DTS光缆导热系数测量方法的准确性和敏感性有待进一步研究。通过室内试验，对比了碳纤维加热感测光缆（CFHC）和铜网加热感测光缆（CMHC）的热响应过程，通过数值模拟验证了光缆结构对导热系数测量结果的影响。研究结果表明：（1）CFHC和CMHC的热响应过程可通过微分法分为光缆内部传热、纤-土过渡以及土体稳定传热3个阶段，光缆结构差异导致传热速率不同，使得CFHC导热系数测量初始时刻比CMHC提前100 s；（2）光缆尺寸与比热容差异下CFHC的升温值更高，相同测温精度CFHC的导热系数测量结果较CMHC更加稳定准确；（3）增大加热功率或延长加热时间均会提高CFHC和CMHC测量土体导热系数的准确性。研究成果为该技术的进一步完善和推广提供了重要依据。
Abstract:The actively heated distributed temperature sensing technology (AH-DTS) can realize distributed continuous measurement of the soil thermal conductivity in different layers through optical cables implanted in the soil. However, the accuracy and sensitivity of soil thermal conductivity measurement by AH-DTS method need to be further studied. Through designing indoor tests with the loess, the aim of this study is to compare the thermal response process and the soil thermal conductivity measured by carbon fiber heated cable (CFHC) and copper-mesh heated cable (CMHC) under different heating strategies. The numerical simulation is used to furtherly verify the influence of the optical cable structure on the thermal conductivity measurement results. The results show that the thermal response process of CFHC and CMHC can be divided into three stages: Internal heat transfer of optical cable, fiber-soil transition and stable heat transfer of soil. The difference in optical cable structure will lead to different heat transfer rates, which makes the initial time of thermal conductivity measurement of CFHC 100 s earlier than that of CMHC. The temperature rise value of CFHC is higher under the difference of optical cable size and specific heat capacity. The thermal conductivity measurement result of CFHC is more stable and accurate than CMHC under the same DTS temperature measurement accuracy. Increasing the heating power or increasing the heating time will improve the accuracy of the soil thermal conductivity measurement by CFHC and CMHC. The research results provide an important basis for further improvement and promotion of this technology.
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表 1 黄土的基本物理参数
Table 1. Basic physical parameters of the test soil
参数 原位含水率 塑限 液限 塑性指数 测量值 20.29% 17% 27% 10 
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表 2 不同加热功率Q下CMHC的ΔT-lnt曲线拟合结果
Table 2. ΔT-lnt fitted results of CMHC under different heating power
Q
/（W·m−1）k R2 λ
/（W·m−1·K−1）相对误差
/（W·m−1·K−1）5 0.4012 0.9741 0.9917 −0.2523 10 0.6690 0.9775 1.1895 −0.0545 15 1.0092 0.9827 1.1828 −0.0612 20 1.3598 0.9939 1.1704 −0.0736 25 1.6210 0.9987 1.2273 −0.0167
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