Fitting function and correlation.

The cell structure of three different densities of bituminous coal molecules was modeled and optimized by using Material Studio (MS) to reveal the mathematical relationship between the porosity and permeability of bituminous coal. The internal surface area was analyzed using the Connolly Surface module, and the specific surface area of the molecules was obtained by mass conversion; the grey processing method was used to evaluate the cell structure porosity, and the pore-permeability constitutive relationship of bituminous coal molecules was established by drawing on the Kozeny-Carman (KC) equation. The results show that the maximum value of 0.29 appears near the pore size of 2.01 Å; Porosity is the main factor affecting its permeability, and the permeability decreases with increasing porosity. The relationship between porosity and permeability was obtained by regression analysis as follows: K = 161 2.1/(1 + 12 2.1). This study provides a new method for the calculation of permeability of porous media.