(571h) Heat Transfer in a Rotary Drum: Effect of Equipment Design

Rotary calciners and dryers are a common equipment used in a number of industries such as in pharmaceutical, catalysts, food industry, and chemical industry. Calciners and dryers are common equipment used for thermal treatment for several materials. Understanding heat transfer and particle flow can reduce wasted energy and materials and significantly improve the product quality. For good product quality, it is a necessity to uniformly increase the material temperature. Typically, rotary drums are made of steel, but can be made of ceramic or cast iron, each having a different surface roughness and texture. 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 calciners and dryers. 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 study, simulations using the discrete element method (DEM) and the Hertz-Mindlin contact model were used to better understand the effect of the coefficient of static friction (surface roughness) on heat transfer for non-cohesive particles. The model accounts for particle-to-particle and particle-to-wall interactions. The surface roughness between particle and wall and the number of baffles in the rotary drum were studied. We saw that static friction has a large 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. Total kinetic energy of the particles and particle tracking were investigated to further understand the effect of surface roughness on flow patterns and heat transfer. 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.