Numerical simulation of coal surface contact angle based on roughness

Coal dust is one of the seven disasters in coal mine. It affects the health of workers and causes coal dust explosion. The wetting effect of coal has a great influence on dust removal. Studies have shown that the wetting effect of coal is related to the wettability, surface roughness and surfactants of coal. In order to effectively solve the problem of coal dust under the mines, which selects hydrophilic Hami lignite, hydrophobic Anyang coking coal and weakly hydrophilic anthracite of Zhaogu No.2 mine as the research objects. The mean square roughness of the three coal samples were measured by the optical contact angle morphology combined instrument, the intrinsic contact angles of the three coal samples were measured, the two-dimensional physical model was constructed by COMSOL numerical software, the simulation conditions were set, the simulation parameters were adjusted, the experimental and simulation values were analyzed and compared, the feasibility of COMSOL numerical simulation was verified, and the influence of coal surface roughness on coal surface contact angle was studied. The results show that the droplet spreading process, the droplet spreading velocity and the droplet spreading shape of numerical simulation are similar to those of experiment, but the simulated contact angle is larger than that of experiment. With the increase of coal surface roughness, the contact angle of lignite decreases from 60.7° to 50.9°, the variation range is about 10°, the contact angle of coking coal increases from 96.5° to 112.7°, the variation range is about 16°, and the contact angle of anthracite decreases from 89.7° to 78.3°, and the variation range is about 11°. The simulated and experimental values of contact angle of three kinds of coal samples with the same surfactant have the same change trend, but the simulated value is larger than the experimental value. It is feasible to study the influence of coal surface roughness on coal surface contact angle by numerical simulation. The wetting of coal surface affected by roughness conforms to Wenzel model. The existence of surfactant does not change the variation of contact angle with surface roughness of three coal samples.