(421b) The Effect of Wall Friction and Baffles on Particle Flow and Heat Transfer in a Rotary Drum

Rotary drums are a common equipment used in several industries such as in catalysts, pharmaceutical, chemical, and the food industry. They are used for thermal treatment for a wide range of materials. Better understanding of particle flow and heat transfer can greatly improve the product quality and reduce wasted energy and materials. It is necessary to uniformly increase the material temperature for good product quality. Typically, rotary drums are made of steel, but can be made of cast iron or ceramic, each having significantly different textures and surface roughness. Surface roughness can have a significant effect on heat transfer and temperature uniformity on the material. Studies have been done on mixing of materials in rotary drums. However, to the best of the authors’ knowledge there are no studies focusing on heat transfer based on equipment surface roughness in a rotary drum.

Understanding the relationship of equipment surface roughness on heating time is important for predicting processing time in real-world applications. In this work, simulations using the discrete element method (DEM) and the Hertz-Mindlin contact model were conducted to better understand the effect of surface roughness (coefficient of static friction) on heat transfer for non-cohesive particles. The model accounts for particle-to-wall and particle-to-particle interactions. The coefficient of static friction between particle and wall and the number of baffles in the rotary drum were investigated. We found that static friction has a significant effect on thermal time and temperature uniformity. Depending on the static friction tested, two flow regimes were exhibited: Slipping and rolling regime. At low static frictions, thermal time is high and temperature uniformity is poor, while increasing static friction, decreases thermal time and improves temperature uniformity. Particle tracking and total kinetic energy of the particles were investigated to further understand the effect of static friction on heat transfer and flow patterns. Baffles were added in the simulations to investigate their effect on heat transfer for different values of static friction. We found that adding baffles for low static friction cases greatly improves heat transfer and temperature uniformity, but consequently increases the total kinetic energy of the particles, which can lead to attrition. This work provides quantitative findings on how equipment design affects heat transfer and temperature uniformity in a rotary drum.