(573c) DEM Simulations for Predicting Radial Mixing and Axial Moving of Sweet Sorghum Stalk Particles in a Rotary Drum Bioreactor

A soft rod-shaped discrete particle model was used to simulate transverse mixing and axial transfer of sweet sorghum particles in a rotary drum bioreactor. In this paper, a suitable discrete particle model and contact model was found by studying the properties of sweet sorghum particles. The three dimensional simulations based on Discrete Element Method (DEM) were qualitatively and quantitatively sustained by mixing experiments using image analysis techniques. In order to describe extent of mixing of irregular sweet sorghum particles, a new ‘separation index’ was used in this work. It was found that the simulations predicted the mixing behavior well under the conditions mentioned in this paper. Mixing rate of sweet sorghum particles increased with the decrease of filling degree and the increase of rotate speed in certain range in a rotary drum bioreactor. Baffles with certain length and numbers enhanced mixing. With this soft rod-shaped discrete particle model, DEM simulations also predicted mean residence time of particles in a long rotary drum bioreactor. Soft rod-shaped discrete particle model and linear cohesion contact model were considered as effective tools for studying mixing of other solid substrate particles, not only sweet sorghum particles.