Computational Fluid Dynamics Modeling Methodologies

This chapter provides a comprehensive review of the computational fluid dynamics (CFD) modeling approaches for gas-solid flows including a variety of drag models, turbulence models, and chemical kinetic models as well as the commercial and open-source software available for simulation. Two-fluid model considers the solid phase as a continuum, while CFD-discrete element method (DEM) approach calculates the force acting on individual particles. The two methods have the advantages of high computational efficiency and accuracy, respectively. The momentum transfer between the gas and solid phases is important especially in fluidized bed reactors. Different types of commonly used drag models are introduced including the Wen and Yu drag model, Ergun drag model, Gidaspow drag model, Syamlal and O’Brien drag model, and sub-grid model. To describe the turbulence characteristics of gas flow, two-equation standard k-ε and SST k-ω turbulence models as well as the one-equation Spalart-Allmaras (SA) and Wray-Agarwal (WA) turbulence models are described. In addition, three types of kinetic models commonly used for prediction of gas-solid reaction in numerical simulation are described; these are shrinking core model, changing grain size model, and nucleation and nuclei growth model. Over the years, several powerful numerical simulation tools have been developed for simulation of the complex multiphase gas-solid flows and to analyze their flow field and reaction characteristics; these include ANSYS Fluent, Barracuda, MFiX, OpenFOAM, etc., which can simulate both the Eulerian two-fluid model as well as the Lagrangian CFD-DEM to provide valuable guidance for the design and optimization of CLC reactors.