考虑颗粒形貌的干砂热传导特性研究

Thermal conduction behaviors of dry sands considering effects of particle shape

为揭示颗粒形貌对干砂热导率的影响规律,通过砂颗粒形貌测量和室内热探针试验,研究不同天然河砂的二维颗粒形貌统计分布特征以及颗粒形貌特征参数与热导率的相关关系,同时从细观尺度探讨砂颗粒接触传热的内在机制。结果表明:天然河砂颗粒圆度和球度值的统计分布具有正态分布特征,期望值可作为定量表征颗粒形貌的参数;干砂热导率随孔隙率增加而减小,在半对数坐标中两者具有良好的线性关系,直线斜率与“平均形貌因子”Am呈线性减小关系;相同孔隙率下,浑圆颗粒的干砂热导率值较大,不同干砂间热导率值的差异随孔隙率的增加而逐渐减小;提出的热导率计算新模型综合考虑了颗粒形貌和矿物组分的影响,相比于传统Côté和Konrad模型,具有更好的适用性和先进性;颗粒形貌对干燥状态下无黏性土热传导特性的作用受多因素综合影响,与应力环境、颗粒刚度等密切相关。

The aim of this study is to reveal the influences of particle shape of dry sands on their thermal conductivity.A series of particle shape determination and thermal probe experiments are conducted to investigate the statistical distribution characteristics of two-dimensional particle morphology for various natural river sands and the relationship between particle shape parameters and thermal conductivity.The internal mechanisms of contact thermal conduction among sand particles are also discussed in mesoscale.The results indicate that both the roundness and the sphericity of natural sand exhibit normal distribution features in statistics,and their expected values are the proper parameters for quantitatively characterizing the particle morphology.The thermal conductivity displays a linearly decreasing trend with an increasing porosity in the semi-logarithmic coordinates,with the slope of the line linearly decreasing with the increase of the average shape factor Am.At a given porosity,round particles possess higher thermal conductivity,and the higher porosity leads to the less significant discrepancy in the thermal conductivity of different dry sands.The proposed model is excellent in applicability and advanced as compared to the Côtéand Konrad model.The effects of particle shape on the thermal conductivity for dry and non-cohesive soils are comprehensively affected by multiple factors,which are dependent on the factors including stress condition and particle stiffness.