Heat transfer in an inclined rotary drum: scale up and effect of material and process parameters
Creators: name: Ardalani, Elaheh
Publisher: name: No Publisher Supplied
Year: 2023

description: Granular materials and powders often require thermal treatment in the food, mineral, pharmaceutical and chemical industries. Rotating drums (kilns) are common devices for the thermal treatment of particulate systems. Developing a better understanding of heat transfer in rotary drums can improve the quality of the product as well as save on energy and material costs. For good product quality, it is often necessary to raise the temperature of the particles uniformly. Although studies have demonstrated the effectiveness and importance of baffles/flights in decreasing the heating time and improving the final product uniformity, many questions about the use of baffles still remain. Understanding the relationship between particle properties and rotary drum operating conditions on the heating time is important for predicting processing time in real-world applications. In this dissertation, cohesionless (dry) and cohesive (wet) solid particulate flows in a rotary drum will be studied using a computational approach to obtain better understanding of the flow behaviors and mixing kinetics. Some of the significant particle properties and process parameters will be varied to investigate their effects on the efficiency of heat transfer and flow behaviors. Additionally, scaling-up of rotary drum systems with baffles will be accomplished to examine the impact the aforementioned factors on the heat transfer and flow behaviors at the larger, industrially relevant scale.First, simulations using the discrete element method (DEM) were carried out as a means of better understanding the role of baffles in regulating heat transfer. The operating conditions were altered by adjusting the following variables: particle fill level, drum size, baffle size, number of baffles, and the speed of rotation. Furthermore, the effect of material parameters was investigated by varying the size and thermal conductivity of the particles. The results demonstrate how fill level as well as the number and size of baffles play an important role in the heat transfer process. Significant improvements were noted by increasing the number and size of the baffles. Secondly, the impact of particle properties along with varying some process parameters on temperature distribution in a rotary drum with baffles has been investigated. In addition, scaling-up of rotary drum with baffles to develop a model capable of capturing the essential physics of continuous powder flow and drying has been examined. Another primary objective of this part was to develop science-based methodologies to optimize and scale-up unit operations. Lastly, in order to understand how powder cohesion regulates the heat transfer of granular materials in rotary drums, a series of simulations using the discrete element method (DEM) and the Johnson–Kendall–Roberts (JKR) cohesion contact model were carried out as a means of better understanding the effect of cohesion on heat transfer. The model takes particle-to-particle and particle-to-wall interactions into account and is based on the pull-off force due to the surface energy of particles and the van der Waals force curve regularization. The operating conditions were altered by adjusting the following variables: particle fill level and speed of rotation. Furthermore, the effect of material parameters was investigated by varying the surface energy, size, and thermal conductivity of the particles. In order to calibrate the effective surface energy of the different DEM models running in the rotary drum, an angle of repose (AOR) funnel experiment was simulated. The results demonstrate the effect of particle cohesion on the rate of heat transfer as a function of fill level and thermal conductivity.