地热浅埋孔回填材料中砂粒结构对导热系数的影响

地热浅埋孔回填材料的导热系数是影响地埋管换热器取热性能的关键因素之一。目前以一定配比的砂粒骨料与水泥、粘土、石英等的混合材料最常见，而材料中颗粒的结构形态是影响回填材料导热系数的关键因素之一。本文以回填材料中砂粒骨料为研究对象，从结构特征出发，探究内部颗粒级配及磨圆度对回填材料导热系数的影响。利用所开发的基于孔隙率的二维导热系数计算模型及三维热阻模型，定量研究不同固相导热系数、不同颗粒物粒级配及不同棱角磨圆度下，材料导热系数的变化规律。结果表明，在颗粒级配和磨圆度不变的情况下，材料整体的导热系数随固相导热系数的增加而增加。同一材料不同尺寸粒径间的差别较大时更易获得更高的整体有效导热系数，且粒径不同所造成的回填材料有效导热系数差别会随着固体导热系数的增大而变得更为显著。而磨圆度不同所造成的有效导热系数差异会随固体导热系数的增大而变得更为显著。颗粒磨圆度很高（球体）或很低（锥体）时，同样固相导热系数下材料的有效导热系数较小。本研究所得理论结果可以为回填材料的优选配置提供依据，有助于提高地埋管换热器的取热效率及地热能利用效率。

Influence of Grain Structure on the Thermal Conductivity of Geothermal Shallow Borehole Backfill Materials

The thermal conductivity of backfill material is a key factor affecting the performance of shallow borehole heat exchangers. The mixture of cement, clay and quartz with a certain ratio is commonly used. The structural morphology affects the thermal conductivity of backfill materials. In this study, the effects of gradation and psephicity on the thermal conductivity of the backfill material were explored. Using the proposed two-dimensional model based on porosity and three-dimensional thermal resistance model, the material thermal conductivities under different matrix materials, gradation and psephicity were quantitatively investigated. The results showed that when the gradation and psephicity are unchanged, the overall thermal conductivity increases with the increase of solid phase thermal conductivity. When there are large differences among particle sizes, it is easier to obtain higher effective thermal conductivity. The difference of effective thermal conductivity caused by different particle sizes is more significant with the increase of the thermal conductivity of solid matrix. The influence of psephicity will become more significant with the increase of solid matrix thermal conductivity. When the psephicity is very large (sphere) or small (cone), the thermal conductivity will become smaller under the same solid phase. The theoretical conclusions of the present study provide guidance for the application of backfill materials and efficient utilization of geothermal energy.