Multi-dimensional digital core simulation based research on heat transfer characteristics of multiphase fluids

The study of heat transfer in coal and rock masses is crucial for thermal storage engineering and geothermal utilization in abandoned mines. Nevertheless, previous research on heat transfer in this field has frequently neglected the interconnection between the flow and heat transfer of heat-working substances (HWS) within three-dimensional microcracks. To reveal the above mechanism, first, the multi-factor influence mechanism of coal and rock heat conduction was analyzed based on the gray system theory. Subsequently, meshes of the matrix and fractures were reconstructed using the digital core simulation technology based on scanning electron microscopy and computed tomography. Finally, a multi-dimensional and multi-scale coal conjugate heat transfer model was built. The results indicate that the heat flux of heat transfer in coal and rock in the heat inflow direction is 3.03–6.44 times as high as that in the direction perpendicular to the heat inflow direction. As the heat transfer of HWS continues, the influence of coal and rock composition diminishes, and the development degree of fractures becomes the major factor affecting heat transfer. Furthermore, alterations in phase state will result in modifications to the conjugated heat transfer mechanism. This study can provide guidance for HWS selection in abandoned mines.