Experimental study of the flow of granular media through a horizontal screw feeder system

Abstract

A significant fraction of the materials handled in the chemical, food-processing, and pharmaceutical industries are particulate in nature. Screw feeder systems are often employed in such scenarios to achieve their bulk transport. Several studies have attempted to characterize the overall flow behavior of granular material in screw feeder systems by linking the flow rate with rotational speed and the design parameters of the screw. However, a detailed description of the flow mechanics of granular material in the screw feeder systems is lacking. This thesis describes a detailed experimental study of the flow of dry (cohesionless) granular materials in different helical screws of the different pitch-to-barrel-diameter ratios in the horizontal screw feeder system. We measured stress profiles at different axial positions on the barrel surface, flow rate, and detailed kinematics using the particle tracking velocimetry (PTV) technique for every helical screw. The qualitative behavior of local stress variation with time, measured at different axial positions, on the barrel’s surface remains the same in comparison to the previous study by our group, which relied on the discrete element method (DEM). Stress values decrease from inlet to outlet in every helical screw, which was not observed previously because of the assumptions of a completely filled and fully developed system. The fill level of granular material also decreases from the inlet to the outlet. Combining these results allows us to illustrate gravity’s vital role in reducing the fill level of the granular material in the screw feeder systems, which has been overlooked in previous investigations. Furthermore, the particle tracking velocimetry technique also highlights the crucial dependence of flow mechanics on the pitch-to-barrel-diameter ratio of the helical screw. We observed a similar trend in experimentally obtained flow rate variation with a pitch-to-barrel-diameter ratio of the helical screw compared to the analytical model and DEM simulations obtained from a previous study. We also performed the DEM simulations, where we simulated the entire system by combining the inlet hopper and screw feeder geometry without employing periodic boundary conditions (allowing the system to vary along the axial direction). These DEM simulations confirmed that the fill level decreases along the axial direction in the presence of gravity. We have also performed sensitivity analysis on the coefficient of friction of the screw and barrel surface to see its effect on the flow rate. We observed an increase in flow rate with an increase in the barrel surface’s coefficient of friction and a decrease in flow rate with an increase in the screw surface’s coefficient of friction.