The energy minimization multi-scale drag model for discrete particle method (EMMS/DP) is a heterogeneous drag model applicable for discrete particle simulations. Particles distribute heterogeneously in circulating fluidized bed (CFB) flows due to clustering effect. Discrete particle method can provide detailded particle distributon information including particle position and particle velocity, but need assume evenly gas distribution inside computational cells. The inconsistence between particle field resolution and gas flow field resolution can lead to deviation between simulation result and actual measurement for heterogeneous gas?solid flows. To solve this problem, EMMS theory is applied to resolve the flow field around particles by accounting for the existence of particle clusters. Subsequently the heterogeneous drag force as well as the heterogeneous index (HD) are calculated based on the decomposed flow field to close the the interphase interaction terms in gas and particle momentum equations. Since the online calculation of EMMS/DP drag is very time consuming in real simulations, a predifined gas?solid flow field is applied to generate the HD database. The generated HD database can be used directly in discrete particle simulations thereafter, but will not increase computation load significantly. The current work improves the generating method of predifiend gas?solid flow field by taking consideration of the inhomogensou particles distributtion. In this work, HD was correlated with solid concentration and slip velocity based on the generated HD database to account for the dynamic effects of meso-scale structures. A comparison between HD at particle sacle and HD at computational cell scale was illustrated. The improved EMMS/DP drag model coupling with the multi-phase particles in cell (MP-PIC) method was used to simulate the gas?solid two phase flows in two CFB risers to verify the model. The simulation results were in good agreement with the experimental data. The grid-independence and effect of the coarse grained model parameter for MP-PIC on simulation results were also studied.
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