Evaluating EMMS model for simulating high solid flux risers

Gas-solid flows in high solid flux risers exhibit dynamic formation of clusters of solid particles. This work attempts to understand and investigate the influence of formation of such clusters on effective drag between gas and solid phases using the energy minimization multi scale (EMMS) model. Unlike previous works on EMMS, the model is investigated outside the CFD domain and predictions were compared with the experimental data for risers and downers. The predicted drag coefficient from the EMMS approach was evaluated for its sensitivity with respect to model parameters. Though overall picture postulated in EMMS looks promising, the critical examination of EMMS for simulating gas solid flows reveal some limitations of the EMMS model. The minimum energy consumption was obtained at lowest possible of cluster voidage, arbitrarily assumed in the model simulation. The cluster voidage significantly affected the predicted drag coefficient. Possible ways to minimize or eliminate some of the limitations were also discussed. The results presented in this work will provide a useful basis for further improvements in the EMMS framework and for further work on gas-solid flows.