Material mixing is an important unit operation in industrial processes. Most of the previous research focused on the analysis of the mixing and segregation mechanism of the mixer materials and the optimal design of the mixer. Most of the research methods used were numerical simulation and analysis at a smaller scale, but the scale-up rules of the mixer and its performance prediction has received little attention and still remains a challenge. In this work, we conducted a similarity study on the mixer scale up, evaluated the material mixing performance indicators, and compared different mixer scale-up mechanisms. We use the GPU based DEM to study and scale up three different mixers: blade, drum and spiral mixers. The three mixers are scaled up based on the Froude number, and the scale-up relationship as a function of the scale up ratio and the Froude number is fitted to predict the mixing performance in terms of mixing index, mixing rate, blade torque and energy consumption. Studies have confirmed that maintaining similar kinematics during mixer scale-up does not result in mixers with similar mixing performance. We further evaluated the mixing time and energy consumption required to mix the same mass of material in mixers of different sizes and found that the mixing time increased as the mixer size increased. However, compared with large-volume mixers, small-volume mixers consume more power per unit mass of material. We also proposed the scale-up mechanism of the material mixing process and explained the reasons why the mixing effect becomes worse and the mixing rate becomes slower during the scale-up process of the mixer. The study provides a reliable basis for the design and selection of mixers.
 

Granular materials; Discrete element method; Rotating drum; Segregation rate; Scale-up