Temperature-dependent interfacial interactions and time-varying diffusion behaviors of gas in heterogeneous porous media

Transient gas transport in heterogeneous porous media subjected to thermal perturbation is a fundamental challenge in fluid dynamics. In this study, we investigated the thermal-driven evolution of pore topology and gas migration kinetics using coal as a representative multi-scale porous matrix. Isothermal adsorption and desorption experiments were conducted across various temperature gradients to quantify temperature-dependent gas–solid interfacial interactions, initial mass transfer rates, and volumetric release capacities. Both exponential and time-varying diffusion models were employed to characterize the non-isothermal gas diffusion kinetics. The results indicate that thermal perturbation significantly alters the geometric fractal characteristics of the solid matrix, leading to expanded pore volumes and increased topological complexity of the interfacial surfaces. Thermodynamically, elevated temperatures suppress the gas adsorption capacity while amplifying both the kinetic release rate and the intrinsic gas diffusion coefficient. Based on these fundamental mechanisms, an explicit mathematical expression for the time-varying dynamic diffusion coefficient during the initial transient stage of thermal perturbation is proposed. This work advances the fundamental understanding of non-isothermal gas transport mechanisms in complex porous networks, providing theoretical constraints for predicting fluid behavior under varying thermal boundary conditions.