Experiment and radial multi-scale dynamic apparent diffusion model of gas in cylindrical coal core

In order to improve the accuracy of measuring gas content in long borehole, experiments of gas desorption flow in radial direction of ?准50 mm × 100 mm cylindrical coal and 1-3 mm granular coal were carried out. The experimental results show that the constant coefficient diffusion model can not describe the whole process of gas flow in radial direction accurately. The experimental value is larger than the theoretical value before 90 min and smaller than the theoretical value after 90 min. This phenomenon is caused by the multi-scale pore structure of coal. Furthermore, a new model of gas radial multi-scale dynamic apparent diffusion coefficient of cylindrical coal core is proposed. The calculation shows that the new radial dynamic apparent diffusion model can accurately describe the gas apparent diffusion in the cylindrical coal core. In the same time, the radial desorption ratio of cylindrical coal is much smaller than that of granular coal and the loss is smaller. Therefore, the cylindrical coal core has more advantages than the granular coal when the gas content is measured for a long time.