Keywords: modelling, computational fluid dynamics, discrete element modelling, fluidization, coupled CFD-DEM.

Fluidization is a process in which a gas or liquid is blown upward and evenly through a bed of solid particles with sufficient force to cause the particles to rise up and move around inside their container. The most common reason for fluidizing a bed is to obtain vigorous agitation of the solid particles in contact with the fluid, leading to excellent contact of the solid particles and the fluid as well as with the solid and the wall. Good mixing of the solid which avoids the presence of local hot or cold points in the reactors is required. For these reasons fluidized bed units are used in a variety of industries such as oil, petrochemicals, minerals, pharmaceuticals and food processing. Accurate models which provide detailed information on the key phenomena occurring in the bed are necessary to properly design and operate fluidized beds at the desired conditions.

The aim of the work described in this paper is to simulate the behaviour of a fluidized bed in order to achieve optimization of this energy costly process. The approach adopted is based on a coupling of discrete element modelling (DEM) of the behaviour of granular media and a finite element modelling of fluid flow (CFD). The codes used in this research are the Salome platform and code_Saturne a general purpose computational fluid dynamics software which is produced by EDF of France. In the first step the drag force is calculated in three-dimensional fluid flow over one sphere with different sizes (diameters 0.5, 1 and 2 mm) which is held fixed in the passage of the fluid stream, for different types of meshing (moderate and fine). The interaction between the fluid and each particle is translated through a drag force, and the effect of local concentration of particles on the fluid flow is modelled as a function of porosity. Several models for estimating the local porosity were studied. The experimental results allowed us to identify for the model the value of the parameters modelled by comparing the heights of fluidized beds as a function of fluid velocity. The study focuses on two column diameters and different heights of beds to demonstrate the efficiency of the approach.

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