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Partic. vol. 43 pp. 123-136 (April 2019)
doi: 10.1016/j.partic.2018.04.003

Simultaneous effects of mesh refinement, grid configuration and wall boundary condition on prediction of pressure gradients and velocity profiles of microparticles in a conical fluidized bed

Alireza Bahramian*

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bahramian@aut.ac.ir

Highlights

    • Pressure gradients and velocity fields of microparticles were studied in a conical vessel. • Numerical analysis was performed to predict the bed fluidization characteristics. • A CFD model was presented to study the mesh sensitivity to size and shape. • Simultaneous effects of mesh configuration and wall boundary conditions were studied. • Computational grids and the effects of mesh refinement were analyzed.

Abstract

The reliability and accuracy of numerical results of microparticle fluidization in a conical bed, affected simultaneously by mesh refinement, the grid configuration and the wall boundary condition (BC), are analyzed. Specifically, pressure gradients and velocity profiles of titania powder are studied for a conical bed. The Gidaspow drag correlation and different wall BCs are considered using a Eulerian–Eulerian two-fluid model. Predictions of the pressure fluctuation, power spectra of the corresponding pressure fluctuations, bed pressure drop, minimum fluidization velocity, axial solid velocity, bed expansion ratio, and particle size distribution are compared with experimental data. Mesh sensitivity analysis using hexahedral and tetrahedral cells with a uniform mesh and near-wall mesh refinement is conducted to investigate the effects of mesh configurations in estimating particle flow patterns. Simulations show that significant savings in terms of computational time are realized by choosing a uniform mesh while the hexahedral structure, the near-wall mesh refinement, and the free-slip BC give the closest fit to the experimental data.

Graphical abstract

Keywords

Conical fluidized bed; Mesh configuration; Grid refinement; Velocity field; Pressure gradient