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Numerical Study on the Flow Behavior of Near Wall Cluster in the Circulating Fluidized Bed

The flow behavior of near wall cluster has an important effect on the heat transfer and attrition of the circulating fluidized beds (CFBs). In this paper, the gas-solid two-phase flow in the riser of CFBs was simulated by means of Large Eddy Simulation (LES) and the direct simulation Monte Carlo (DSMC) method. A extended cluster identification method was used to investigate the cluster properties. The distributions of time-averaged solid concentration and velocity of cluster near the wall region were analyzed. Simulated results showed that the descent velocity of near wall clusters appears to keep constant. The solid concentration of near wall cluster decreases along the height of riser. The simulated results have a reasonable agreement with the previous experimental data. In this study the locally averaged Navier-Stokes equations of gas phase and Lagrangian type particle motion equations were simultaneously solved. The mutual interaction between gas phase and particles was taken into account. Gas turbulence is modeled by means of LES method. Particle collision is modeled by means of the DSMC method. The variations of the time-averaged descent velocity and solid concentration of the near cluster along the height of riser were analyzed. At the same time, the variation of them as a function of cross- sectional averaged solid concentration was studied too.