Particle-Cluster Formation and Vorticity in Gas-Solid Flows

Abstract

Fluidized beds are widely used in industry for combustion, gasification, catalytic cracking and several other purposes. Pneumatic conveying of air is popularly used in industry to transport materials such as pulverized coal through pipelines. A common observation in gas-solid flow dynamics in both of the above systems is the formation of high concentration regions of particles; known as clusters in fluidized beds and rope like structures in pipe bends and ducts. Both the clustering and roping phenomenon were clearly observed in some experiments and in simulations of both fluidized beds and gas-solid flows in pipe bends. It has been found from these simulations that there is a strong correlation between vorticity and concentration. The high particle concentration regions are bounded by vortices of clockwise and counter clockwise direction of roughly the same order of magnitude and there is very low vorticity at the high concentration regions. The goal of this study is to find the cause and effect relation between the gas vorticity and the high particle concentration regions; in particular whether the gas vorticity causes particle agglomeration into clusters or vice-versa. Numerical study has been performed on a vertical pipe by creating a vortex field. In this regard, very large eddy simulations with Lagrangian Discrete Phase model have been performed using Ansys FLUENT and MFIX software packages. The influence of particles on the vorticity has been studied. Influence of several factors such as particle size, injection velocity etc. have also been studied. Correlations among turbulent kinetic energy, vorticity, and particle clustering and/or roping are illustrated.