Determination of the friction coefficient of coal particles by discrete element simulation and experimentation

Abstract The friction coefficient of coal is the main factor influencing the results of discrete element simulation. In this study, the friction coefficient of coal was determined using a self-made testing instrument for measuring the static friction coefficient and an automatic cylinder lifting device on the basis of discrete element simulation, image processing, and orthogonal testing. The correlations between the angle of repose of coal particles, the rolling friction coefficient between coal particles, and the rolling friction coefficient between the coal particles and stainless steel were evaluated by linear regression analysis. Results indicated that the dependent variable (angle of repose of coal particles) was linearly correlated to the two independent variables (rolling friction factor between the coal particles, as well as the rolling friction factor between the coal and the stainless steel). The angle of repose of the coal particles was largely affected by the rolling friction coefficient between the coal particles but not by the rolling friction coefficient between the coal particle and stainless steel. Moreover, the static friction coefficient between the coal particles was 0.53, and that between the coal particle and the stainless steel was 0.38. The rolling friction coefficient between the coal particles was 0.048, and that between the coal particles and the stainless steel was 0.03. These friction coefficients were used to simulate the bottomless cylinder test of the coal particles. The angle of repose in the simulation test was 30.77°, whereas that in the real test was 31.47°; the relative error was 2.22%. Therefore, no significant difference in the results was indicated between the simulation test and the real test, verifying the effectiveness of the method used to determine friction coefficients. The aforementioned technique can be applied to determine the friction coefficient of lump coal particles.