Effect of multifractal characteristics of pore structure in coal adsorbed by low pressure gas on thermal conductivity and thermal diffusion

Abstract

Thermal conductivity and thermal diffusivity are critical physical properties influencing safe mining operations, geothermal field studies, and underground coal gasification technologies. This study investigates the pore structure and multifractal characteristics of coal with varying metamorphic degrees in southwest China using low-pressure N₂ and CO₂ adsorption techniques. The thermal conductivity and diffusivity of coal samples were measured using the transient plane source method. Furthermore, we analyzed the relationship between multifractal parameters and the thermal properties of coal. Our results indicate a weak correlation between industrial parameters and the thermal properties of coal. We found that the pore volume and specific surface area of intermediate pores in coal are positively correlated with thermal conductivity and negatively correlated with thermal diffusivity. Both thermal conductivity and diffusivity increase with the pore volume and specific surface area. Multifractal self-similarity analysis reveals that coal samples exhibit strong multifractal characteristics, with micropores displaying stronger multifractal features than intermediate pores. The distribution of pores in coal primarily influences thermal conductivity and diffusivity, whereas the structure and complexity of the pores themselves have a negligible effect compared to pore uniformity.