Porosity Distribution in Monodisperse and Polydisperse Fixed Beds and Its Impact on the Fluid Flow
This work is devoted to the numerical study of the porosity distribution and gas flow within randomly-packed fixed beds comprising polydisperse spherical particles with Rosin-Rammler particle size distribution in a cylindrical container. The fixed bed is numerically generated using gravity-forced sedimentation modeled utilizing the Discrete Element Method. The radial porosity distribution of monodisperse fixed beds was validated against published experimental data and good agreement was achieved. The diameter ratio of smallest to largest particle was varied from 1:2 to 1:5 and then 1:10. The simulation revealed overall porosities of 0.38 for the monodisperse bed and 0.345 and 0.33, for polydisperse beds with ratios of 1:2 and 1:10, respectively. In the second part, the fluid flow within the generated fixed beds was examined using a numerical solution to the incompressible Navier-Stokes equations in the Brinkman-Forcheimer formulation. An analysis of the results showed that in the case of a monodisperse fixed bed and low Reynolds numbers (Re) the pressure drop predicted numerically is close to the values calculated using Ergun’s relation. The increase in Re leads to the deviation between the numerical and analytical predictions. This effect is because of channeling due to the sinusoidal distribution of the void fraction close to the wall.
Keywords: Discrete element methode, Fixed bed, Fluid flow, Numerical analysis, Porous media