(70bv) Estimation of the Hindered Settling Velocity of a Particle in Polydisperse Suspensions

The estimation of the hindered settling velocity of a particle in polydisperse suspensions is important to design powder process equipments. The velocity is affected with the particle-particle interaction and the interaction between particle and fluid flow induced by the settling particles. Then, the effects of particle concentration and particle size distribution on the behavior of a particle in hindered settling were investigated using a hybrid simulation with Discrete Element Method (DEM) and Direct Numerical Simulation (DNS). The simulation was carried out for the particles having uniform particle size and particle size distribution, and then particle velocity, fluid velocity, fluid drag force and particle collision force were calculated. Although the effect of collision force on hindered settling velocity was negligible in laminar flow region, fluid drag force and fluid velocity strongly affected the hindered settling velocity. By using these simulation results, the equation of hindered settling velocity was proposed, taking into consideration drag force and fluid velocity which vary with particle concentration and particle size distribution. The reliability of estimated particle velocity in hindered settling was confirmed by comparison with experimental values.