Effect of Clustering on Gas−Solid Drag in Dilute Two-Phase Flow

Abstract

When coarse-grid calculations in two-phase flow are performed, mesoscale fluctuations, such as clusters, cannot be explicitly captured. Their impact on macroscale fluctuations, however, has to be taken into account by the introduction of an appropriate closure model. A new closure model to describe gas-solid drag is introduced. The effect of particle clustering on the interphase momentum-transfer coefficient is taken into account by introducing the concept of effective drag. Clustering results in a decreasing value of the interphase momentum-transfer coefficient because the contribution of particles in the cluster is considered to be negligible in dilute phase flow. For solids fractions greater than 1%, clustering phenomena become increasingly important, resulting in an important decrease of the interphase momentum-transfer coefficient. Calculation results for a riser reactor, both neglecting and including the effects of clustering on the gassolid drag, are presented and validated with experimental data. With the effective-drag model, the solids fraction profiles in a riser reactor are predicted more accurately.

Effect of Particle Clusters on Carrier Flow Turbulence: A Direct Numerical Simulation Study

“…The variation of R is statistically identical to R ( f ) 22 , it is not shown here. The Reynolds stress becomes anisotropic inside the fixed bed and significant redistribution of Reynolds stress is observed for both uniform and clustered particle configurations.…”

“…While current CFD simulations of gas-solid flow are capable of reproducing the core-annulus flow in risers [9,47,48], there is still considerable uncertainty regarding models for gas-particle interaction. Phenomenological models of cluster drag have been proposed to explicitly account for the formation of clusters [22,30,41,67], but these may not be predictive for general flows because they lack information about the microscale flow physics. Also to the best of our knowledge, the interaction between fluid-phase velocity fluctuations and particle clusters has not been modeled.…”

Verification of filtered two‐fluid models for gas‐particle flows in risers

“…[14][15][16] Researchers have approached this problem of treating unresolved structures through various approximate schemes. O'Brien and Syamlal, 17 Boemer et al, 18 and Heynderickx et al 19 noted the need to correct the drag coefficient to account for the consequence of clustering and proposed corrections for the very dilute limit. Some authors have used an apparent cluster size in an effective drag coefficient closure as a tuning parameter; 20 others have deduced corrections to the drag coefficient using an Energy Minimization MultiScale (EMMS) approach.…”

Filtered two‐fluid models for fluidized gas‐particle suspensions

“…O'Brien and Syamlal, 33 Boemer et al 34 and Heynderickx et al 35 pointed out the need to correct the drag coefficient to account for the consequence of clustering, and proposed a correction for the very dilute limit. Some authors have used an apparent cluster size in an effective drag coefficient closure as a tuning parameter, 36 others have deduced corrections to the drag coefficient using an energy minimization multiscale approach.…”