Multi-scale modeling of dense phase gas–particle flow

First, gas–particle flows are classified based on particle–particle interaction. Next, methods of numerical analysis of gas–particle flows are classified based on the concept of length scale. That is, the methods are classified into micro-, meso- and macro-scale approaches. The scale-based classification is applied to gas-phase and particulate phase, respectively. Most of existing models of multiphase flows are categorized into one of the combination of scale-based models for gas and particles. After the classification, description focuses on the discrete particle simulation which belongs to the micro-scale approach for the particle phase. The advantage of the particle–micro approach is to deal with particle–particle interaction in the rational way. To treat the particle-to-particle interaction mathematically, techniques named DEM (Distinct Element Method) and DSMC (Direct Simulation Monte Carlo) have been developed. DEM is a powerful means for the contact-dominated flows and DSMC method for the collision-dominated flows. Combining DEM or DSMC with CFD (computer fluid dynamics), applications of the discrete particle simulation have drastically expanded into many industrial flows because both particle-to-particle and particle-to-fluid interactions have significant effects on most industrial flows. Various examples of simulations are shown; such as dense phase pneumatic conveying, spouted bed, fast circulating fluidized bed and so on.