Dense Gas-Solid Two-Phase Flow Simulation With Rough Spheres

Not only the nonlinear coupling between gas and solid but also the dissipation between particle-particle collisions are included in dense gas-solid flow. Thus dense gas-solid flow shows strong spatial and temporal characteristics of the non-uniform flow structure. The kinetic theory of granular flow provides particle phase fluid transport equations and constitutive equations with particle microscopic motion and collision behavior. The theory is widely used in numerical simulation of dense gas-solid two-phase flow cooperated to Euler-Euler two-fluid flow model. The common model used in numerical simulation of dense gas-solid flow assumes that particles are smooth and frictionless, which only consider momentum transfer and energy dissipation caused by normal collisions between particles. However, actual particles surface is rough, which leads to momentum and energy contributions from normal and tangential collision. Therefore, the research on kinetic theory of rough spheres numerical simulation has significance and practical value.The kinetic theory of rough sphere in this article has the following characteristics:1. Using Coulomb friction coefficient, the normal and tangential elasticity coefficient of restitution to describe the behavior of binary collisions between particles, including particle-particle and particle-wall collision.2. Using translational and rotational temperature to describe the characteristics of particle pulse, and the corresponding transport equations are solved simultaneously.The results obtained by our works are compared with the experimental data and the Lagrangian method for proving the relevant validation of rough spheres model in studying bubbling fluidized bed flow characteristics. The simulation got bed expansion ratio, particle volume fraction and velocity vector in kinetic theory of rough spheres, which is agreed with Euler-Lagrangian model proposed by Goldschmidt. The study found that the ratio between the particle rotation temperature and the translational temperature is affected by particle concentration and fluidization velocity.The rough spheres model is used to study the effects of different coefficients (normal restitution coefficient, friction coefficient and tangential restitution coefficient) for the gas-solid flow characteristics in bubbling fluidized bed. The tangential restitution coefficient affect the gas-solid flow structure is minimal, while friction coefficient and tangential restitution coefficient impact the dynamic characteristics a lot. The method to increase the friction coefficient has greater pulse amplitude with a small average bed height compared to reduce the normal restitution coefficient. However, the change of normal restitution coefficient will not affect the basic form of average gas-solid flow, there is no strong influence caused by friction coefficient.Macro-momentum transfer between particles and wall is obtained by considering particles translational and rotational movement. The qualitative and quantitative analysis are used in numerical simulation of Couette flow and bubbling fluidized bed with specularity coefficient. The studies have shown that coefficient of friction influence a lot on simulation results.