Drag coefficient and settling velocity of fine particles with varying surface wettability

Abstract

The surface wettability of micron particles affects many engineering applications, such as forth flotation and dust removing. The settling velocities of glass beads with diameters in the range 15–100 μm and varying surface wettability were obtained using a high-speed dynamic system. The results showed that the surface wettability of the particle surface has a significant effect on the terminal settling velocity (VT) when the particle dimensionless diameter (d∗ = (∆g/v2)1/3d) is less than two. As the contact angles increase, the VT increases and the drag coefficient (CD) decreases. The classical Stokes model does not reflect this change; consequently, a modified Stokes model that considers surface wettability is proposed. Experimental results indicate that the average relative error of the proposed model is 3.10% for the modified settling velocity formula, and 3.06% for modified drag coefficient formula. Both modified formulas were validated using the experimental data of spherical aluminum oxide (Al2O3) particles.