An EMMS-based multi-fluid model (EFM) for heterogeneous gas–solid riser flows: Part II. An alternative formulation from dominant mechanisms

The gas–solid flow in circulating fluidized bed risers is characterized by the existence of two-phase structure with particle-rich dense phase and gas-rich dilute phase, but in traditional coarse grid simulation using two-fluid models, the constitutive laws are based on the assumption of structural homogeneity inside computational cells, which seems to be inaccurate for riser flows. One way out is to carry out coarse grid simulation with proper meso-scale or sub-grid scale models considering the effect of heterogeneous structures on the constitutive laws. In this study, we propose an EMMS-based two-fluid model (EFM), which features: (i) the particle-rich dense phase and the gas-rich dilute phase representing the physical realizations of particle-dominated and gas-dominated mechanisms are defined as the two interpenetrating continua; (ii) the interactions between heterogeneous gas–solid flow are decomposed into the interactions within three homogeneous sub-systems according to the concept of EMMS model, that is, dilute-phase, dense-phase and inter-phase; (iii) the constitutive laws are determined by the EMMS model featuring a stability condition. It was shown that the hydrodynamics of a riser predicted by EFM are in a good agreement with experimental data, indicating the feasibility of EFM for describing the hydrodynamics of heterogeneous gas–solid flow in risers.

► An EMMS-based two-fluid model is established and demonstrated.
► The particle-rich dense phase and gas-rich dilute phase are treated as two interpenetrating continua.
► The governing equations are derived directly according to structural characteristics.
► A fluid corresponds to the physical realization of a dominant mechanism.
► The heterogeneous gas–solid flows are decomposed into three homogeneous sub-systems.