基于DTS的土体分布式导热系数测试方法

土体导热系数的确定对地源热泵的优化设计起着至关重要的作用。为了获得更精细的土体导热系数,在常规热响应试验的基础上,引入分布式光纤测温系统(DTS),对换热孔的温度进行分布式测量,得到孔内竖直方向岩土初始地温分布和在热响应试验过程中换热孔温度分布及其随时间的变化情况,通过与热电阻温度传感器的对比,验证了DTS测温的准确性。在线热源传热模型的基础上,建立了以换热孔为线热源的传热模型。分别进行了双U型管和单U型管恒热流热响应测试,根据DTS监测的温度分布及其变化,得到了土体导热系数随深度的分布。与综合导热系数相比,分布式导热系数不仅精度满足要求,而且可以更精细地反映土体导热系数分布的不均匀性,对于地源热泵的优化设计和换热能力的评价具有重要的意义。

Testing Method of Distributed Thermal Conductivity of Soil Based on DTS

The determination of soil thermal conductivity plays an important role in the design of the ground source heat pump system (GSHP).In order to obtain more detailed thermal conductivity of soil,the fibre optic distributed temperature sensor (DTS) was introduced on the basis of conventional thermal response test (TRT).The distributed temperature of the heat ex-changer hole was measured and the initial soil temperature distribution in the vertical direction of the borehole was obtained.Meanwhile,the temperature distribution of the borehole and its variation with time was achieved during the TRT.The accuracy of the DTS was verified by comparison with the thermal resistance temperature sensor.Based on the line heat source model,the heat transfer model with heat ex-changer hole as heat source was established.The double U-tube and single U-tube constant heat flow thermal response test were carried out respectively.Based on the measured temperature distribution and its variation,the soil thermal conductivity at different depth was obtained.Compared with the complex thermal conductivity,the distributed thermal conductivity not only satisfied the precision requirement,but also can reflect the in-homogeneity of the soil thermal conductivity distribution finely,which is of great significance for the optimization design of the ground source heat pump and the evaluation of the heat exchange capacity.