Experimental and numerical study of free-falling streams of particles impacting an inclined surface

Abstract

This paper presents a detailed experimental and numerical analysis of free-falling particle streams impacting a 45° inclined surface of differing materials. The particles used in this study were glass spheres with average diameters of 136 and 342 µm and a density of 2500 kg/m3. The three mass flow rates considered are 50, 150, and 250 grams per minute (gpm). The effect of wall material on the collision process was also analysed. Special attention was paid to the influence of wall roughness. Therefore, a plate of stainless steel with polished surface, an aluminium sheet, and a Perspex plate with similar properties to those of the rest of the wall sections were used. The experimental data were used to improve and validate a wall collision model in the frame of the Lagrangian approach. A new drag force formula that includes the effects of particle concentration as well as particle Reynolds number was implemented into commercially available codes from CFX4-4 package. It was found that the improved CFD model better predicted the experimental measurements for the particle rebound properties. The rough-wall model in these results showed greater effect on smaller particles than on larger particles. The results also showed that the improved CFD model predicted the velocity changes slightly better than the standard model, and this was confirmed by both the quantitative velocity comparisons and the qualitative concentration plots. Finally, the inclusion of the particle-particle collision was shown to be the dominant factor in providing the dispersion of the particles post collision. Without a sufficient particle-particle collision model, the standard model showed all particles behaving virtually identical, with the main particle stream continuing after the collision process.