(404b) The Effect of Cohesion on Particle Flow and Heat Transfer in a Rotary Drum

There is a wide range of granular materials used in daily items like building materials, chemicals, pharmaceuticals, and food. Sand, sugar, corn, wheat, salt, peanuts, flour, cereal, fertilizers, wood chips, catalysts, and pills are just a few examples. Rotary drums are the most common equipment used for the thermal treatment of solids and are used for both free-flowing and cohesive materials. A better understanding of heat transfer in rotary drums can improve the quality of products as well as save energy and materials. For good product quality, it is often necessary to raise the temperature of the particles uniformly. In general, materials may be cohesive due to their inherent nature or may be cohesive due to the presence of water or other binding agents. Studies have been done on the mixing of cohesive materials in rotary drums. However, to the best of the authors’ knowledge there are no studies concentrating on heat transfer of cohesive materials in the rotary drums.

Understanding the relationship between cohesive particle properties and rotary drum operating conditions on the heating time is important for predicting processing time in real-world applications. In this work simulations using the discrete element method (DEM) and the 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. It is based on the pull-off force due to the surface energy of particles and the van-der-Waal 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.

The angle of repose can indicate the cohesiveness of the granular material, referring to the Carr classification of flowability. 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, thermal conductivity and coefficient of friction. Generally, increasing particle-to-particle cohesion increases the thermal time as particles form low density clumps which leads to lower rates of heat transfer. Generally increasing particle-to-drum cohesion decreases the thermal time as particles stick to the drum wall; however, this may be undesirable due to the non-uniformity of the heating. At higher fill, the effect of wall cohesion is less important since there is a lower fraction of particles at the wall but at low fill, wall cohesion dominates the heat transfer effects.