Flow of granular materials in a bladed mixer: Effect of particle properties and process parameters on impeller torque and power consumption

The torque and power needed to drive an impeller are important quantities that can indicate flow behavior and can be used to control processes, especially mixing and granulation in the pharmaceutical industry. In this study, experiments were conducted on monodisperse spherical glass beads flowing in a cylindrical bladed mixer agitated by an impeller. The impeller torque was measured using a rotating platform and a data recording device, and the power draw for the motor driving the impeller was measured using a power meter. The effect of various impeller blade designs and material properties on the torque and power were investigated as a function of the impeller blade rotation rate. It was found that the torque exerted on a granular bed and the power consumption were a strong function of the impeller blade configuration, the position of the blades in a deep granular bed, the fill height of the glass beads, and the size and friction coefficient of the particles. It was observed that the time-averaged torque and power consumption for different particle sizes qualitatively scaled with particle diameter. A scale-up relationship for a deep granular bed was developed: the time-averaged torque and average adjusted power consumption scaled with square of the material fill height.