Spontaneous combustion in coal mine goafs is one of the main risks during mining. The effectiveness of existing coal spontaneous combustion prevention technologies is influenced by fluid flow resistance loss in goaf porous media. This study proposes a sphere-cylinder assembly (SCA) as a fundamental unit for investigating flow loss in goaf porous media. The Hagen–Poiseuille equation, combined with the capillary model and the theory of average hydraulic radius, was used to derive expressions for viscous and inertial pressure losses, leading to the development of the SCA pressure drop prediction model (S-C model). An experimental setup was constructed to study the flow characteristics of porous media and validate the S-C model. Results indicate that the S-C model's prediction errors are mostly below 20%, outperforming the Ergun equation. Flow states within the porous media were delineated based on pressure drop and Reynolds number relationships, establishing ranges for Darcy flow, transition flow, and non-Darcy flow. Analysis of the friction factor f and Reynolds number Re further confirmed the accuracy of the flow state classification. The empirical f formula showed significant errors at high Reynolds numbers, highlighting the limitations of empirical approaches. Research results provide an important reference for calculating specific parameters in the implementation of coal spontaneous combustion prevention and control technologies.
Chen et al. (Wed,) studied this question.