(139e) Flow of Granular Materials in a Bladed Mixer: Effect of Particle and Process Parameters on Impeller Torque

Impeller torque is an important parameter that is measured to indicate the status of a system and to control the progress of processes such as mixing and granulation in the pharmaceutical industry. In this study, experiments were performed using monodisperse, spherical glass beads flowing in a cylindrical bladed mixer agitated by an impeller. Experimental measurements of the torque that the impeller blades exerted on the granular bed were made using a data acquisition and recording device. Computational simulations of spheres flowing in a four-bladed mixer were also carried out by means of the discrete element method (DEM). The effects of various material properties and impeller blade design configurations on the torque were investigated as a function of the impeller blade rotational speed. It was demonstrated that the time-averaged torque values exerted on the granular system were dependent on the particle size and friction coefficient, the fill height of the glass beads above the blades, and the moisture content in the system. It was also shown that average torque depended upon the number of impeller blades, their design configuration, and their position in the granular bed. It was also found that the experimentally measured impeller torque was largely different in the cases of shallow and deep bed granular systems. A scale-up relationship for the deep granular bed was also developed. It was proposed that time-averaged torque in deep bed granular systems scaled with the square of the normalized height of the material above the blades.