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Three physically realistic collisional parameters, the friction coefficient and the normal and tangential restitution coefficients, are used to characterize the rough particle collisions. The corresponding kinetic theory model and boundary conditions are incorporated into a two-fluid model to investigate the influence of these collisional parameters on the numerical simulation of a gas–solid bubbling fluidized bed. The simulated results reveal that coefficients of friction and normal restitution play important roles in the formation of heterogeneous structures in the bubbling bed, but their inherent effects on particle motion and bed expansion are quite different. In addition, the time-averaged gas–solid flow fields for different friction coefficients vary significantly, but those for different normal restitution coefficients exhibit very similar patterns. To achieve a better agreement with the experimental data, adjusting the friction coefficient is more effective than refining the normal restitution coefficient. The tangential restitution coefficient has relatively weak but non-monotonic effects on particle motion and bed expansion, and the flow fields for different tangential coefficients remain almost the same. Distinct effects of particle–particle and particle–wall collisions are also studied. For the overall fluidization behavior in a small-scale bubbling bed, the most crucial parameter is the friction coefficient for particle–wall collisions, followed by the normal restitution coefficient of particle–particle collision. [ABSTRACT FROM AUTHOR]

Abstract: Kinetic theory of granular flow is extended for rough particles. Both the translational and rotational granular temperatures are introduced to characterize the random fluctuations of particles. Sliding and sticking mechanisms are distinguished in the binary collision model with the friction coefficient and coefficients of normal and tangential restitution. Collision integrals are performed to produce new expressions of the constitutive relations for rough particles. Flat wall boundary conditions for rough particles are proposed according to the particle–wall collisions. The present model is incorporated in Euler–Euler simulations of a bubbling gas–solid fluidized bed. The computed bed expansion dynamics and flow patterns are validated with experimental measurements and Euler–Lagrange simulations. The ratio of rotational to translational granular temperatures is found to be influenced by the particle volume fraction and the fluidization velocity. Comparison among the present model, the original smooth particle model and another rough particle model is also carried out. [Copyright &y& Elsevier]

Abstract: A numerical study based on a gas–solid two-fluid model using body-fitted coordinates to predict the immersed tube erosion rate in a bubbling fluidized bed has been conducted. Computations have been performed at various s/D ratios (ratio of the spacing between two tube centers to the diameter of the tubes) for a bed into which one, two, three or four immersed tubes were inserted. A monolayer kinetic energy dissipation model is implemented to simulate the erosion on the surfaces of the immersed tubes at the body-fitted coordinates. The effect of the s/D ratios on the erosion rate in the bubbling fluidized bed is investigated. A granular temperature distribution provides an indication of the regions on the immersed tubes that could be susceptible to fluctuation intensity of the solid phase. Wake properties influenced the erosion rate remarkably. Calculated erosion rates on the surfaces of the immersed tubes were in good agreement with previous experimental and numerical findings. [Copyright &y& Elsevier]

In this work, a hard sphere particle method for non-spherical particles is applied to study particle behaviors in a bubbling fluidized bed. The influence of the non-spherical particle method and the restitution coefficient are examined. The particle behaviors, including the overall fluidization state (distributions of particle translational and rotational velocities, void fraction, etc.), bubble and particle fluctuations (particle and bubble granular temperatures), are studied. Specific variation rules which are difficult to measure experimentally are presented. As the bubble boundaries in the non-spherical particle system are not as clear as in the spherical case, there is a stronger fluctuation movement of bubbles, which also dominates the particle turbulent movement. The absolute values of particle translational and rotational velocities increase when the restitution coefficient decreases. And it affects the periodic fluctuation characteristics of gas-solid interactions. The variation rules for bubbles and particles as a function of the restitution coefficient are different. [ABSTRACT FROM AUTHOR]