Calculation of drag force on an object settling in gas-solid fluidized beds

Gas-solid fluidized beds can be used for dry beneficiation of minerals. Estimation of the drag force on separated materials is important for the design and operation of separators. Previous research was based on the empirical correlation or on the hypothesis that fluidized beds behave as a Newtonian fluid. However, much experimental evidence showed that the hypothesis of Newtonian fluid was suspect. The drag forces on spheres passing through fluidized beds were calculated using the Bingham fluid model. The plastic viscosity and yield stress of afluidized bed can be obtained by measurement of the terminal settling velocity of spheres. The relationship between drag coefficient (C-D), sphere size (d(o)), settling velocity (u(t)), bed bulk density (rho(b)), plastic viscosity (mu), and yield stress (tau(0)) is expressed as C-D = 24/Re-m(1 + 0.15 Re-m(0.687)), Re-m = d(o)u(t)rho(b)/mu + tau(0)d(o)/3u(t). The calculated results agree well with the experimental data.