(77e) Development of Collisional Dissipation Rate Models for Non-Spherical Particles Using the Discrete Element Method

Authors: 
Buettner, K. E., University of Florida
Guo, Y., Zhejiang University
Curtis, J. S., UC Davis
Two-fluid simulations based on Computational Fluid Dynamics (CFD) have the ability to simulate large domains of granular flows. Unfortunately, the accuracy of these granular flow simulations is hampered due to the models available, which tend to assume that the particles are spherical. Introducing models that take particle shape into account offers the ability to improve the accuracy, making two-fluid simulations more viable for process design. This work presents a method that utilizes the Discrete Element Method (DEM) simulations to create a collisional dissipation rate model for non-spherical particle systems.

Homogeneous Cooling System (HCS) simulations of frictionless particles at a wide range of solid volume fractions (from 0.025 to 0.6, nearly the packing limit) are performed to measure the collisional dissipation rate, i.e. the rate of granular temperature decrease with time. Two types of particle models are used in the simulations: the glued-sphere particle, which is formed by rigidly connecting a string of spheres in a straight line, and the true cylindrical particle, which has the shape of true cylinder. Unlike the frictionless spheres, the frictionless, non-spherical particles can rotate after collisions, inducing the rotational granular temperature. Equal partition of rotational and translational granular temperatures is observed for the elongated particles with the particle aspect ratio equal or greater than 2. Larger dissipation rates are obtained for the non-spherical particles compared to the spherical particles. The dissipation rate increases as the particle aspect ratio increases. Most importantly, it is found that the collisional dissipation rate for non-spherical particles can be expressed as a function of the dissipation rate for spherical particles. This finding may allow a simple modification of the granular kinetic theory to account for the effect of particle shape. Overall, the HCS simulation using the DEM provides an effective approach for the development of the dissipation rate models for the particle systems of complex shapes.