A cluster structure-dependent drag coefficient model applied to risers

Cluster structures affect macroscopic hydrodynamic behavior in gas–solid risers. The moment and energy balances for the dense phase and dilute phase are presented by the multi-scale resolution approach to investigate the dependence of drag coefficient on structure parameters. The modified model of cluster structure-dependent (CSD) drag coefficient is proposed on the basis of the minimization of energy dissipation by heterogeneous drag (MEDHD). Unlike previous works on CSD drag coefficient model, the modified CSD drag model takes wall friction into account. The closure for the drag coefficient depends not only on flow behavior of gas and particles but also on the wall friction. The structure-dependent drag coefficients calculated from the approach of the minimization of energy dissipation by drag force are then incorporated into the two-fluid model to simulate the behavior of gas–solid flow in a riser. The distributions of concentration and velocity of particles are predicted. Simulated results are in agreement with experimental data published in the literature. The effect of the wall friction on flow behavior of particles is analyzed.

A modified cluster structure-dependent drag coefficient (modified CSD drag) model for considering the presence of clusters is presented. Both modified CSD drag model A and model B give the equivalent cluster diameter increase with the increase of solid concentrations.Figure optionsDownload as PowerPoint slideHighlights
► A cluster structure-dependent drag model with wall friction (modified CSD drag) is proposed.
► A gas-solids two-fluid model is proposed with modified CSD drag model.
► Simulations are in agreement with experiments.
► A comparison between modified CSD drag model and Ergun/Wen and Yu model is performed.