A NEW FLUID DYNAMIC MODEL FOR THE CFD SIMULATIONS OF FLUIDIZED BEDS

A new Eulerian-Eulerian multidimensional model is proposed for the study of the dynamics of dense fluidized suspensions. The main distinctive feature of this new formulation of the equations of motion resides in the closure relationships adopted to express the fluid-particle interaction force. The force accounts for three contributions: buoyant force, drag force and elastic force. The buoyant force is related to the weight of the fluid displaced by the particles. The drag force is expressed as the product of the drag exerted on an unhindered particle, subject to the same volumetric flux of fluid, and a “corrective function ” dependent on both bed voidage and particle Reynolds number. The elastic force is related to spatial gradients in the bed voidage and is parallel to the drag force; the force can be regarded as the component of the drag which arises when the homogeneity of the suspension is lost at the macroscopic length scale. The model is used to study the fluidization dynamics of liquid-solid homogeneous beds and gas-solid bubbling beds with particles belonging to the Group B of the Geldart's classification (1). The results of the simulations are compared with experimental data mainly in terms of average bed height, average bed voidage and diameter of the rising bubbles