Conjugate heat transfer characteristics of crushed coal rock mass under axial compression: Coupling numerical analysis based on CT reconstruction and FEM

Abstract

This study focuses on the heat transfer characteristics of crushed coal under axial compression in deep abandoned mines during geothermal extraction. By combining visualized experiments with CT image reconstruction, the study overcame the limitation in the simulation scale, increase the size of finite element model by tens of times. The transient conjugate heat transfer of multi-phase fluid flow process in real axial pressure crushed coal at macro scale is realized. The key findings are as follows: With regard to the thermal conductivity characteristics, the effective thermal conductivities of models filled with different fluids rise linearly with the increase in thermal conductivity of the matrix. As for conjugate heat transfer characteristics, dominant heat transfer paths significantly impact conjugate heat transfer during the non-steady-state phase. An increase in boundary velocity enhances heat extraction efficiency. However, when the boundary velocity increases to 0.001 m/s, the thermal breakthrough time decreases by 66.8 %. Additionally, an increase in the initial temperature difference enhances the heat extraction rate and thermal recovery rate. When gaseous CO₂ is used as the fluid, the temperature and conductive heat flux differences in the heat transfer model are mainly manifested as axial stratification. This research provides an important theoretical support for the development of digital core technology for heat transfer research.