Abstract: Different modelling approaches have been developed to study the complex physics associated with multiphase flows. These models can simulate typical gas–solid multiphase flows at different scales with different levels of details. Based on how the solid phase is handled, two different classes of models can be distinguished: Eulerian–Lagrangian (E–L) models and Eulerian–Eulerian (E–E) models. This chapter focuses on the two most widely used models for gas–solid flows: the EE two‐fluid model (E–E TFM) and the E–L computational fluid dynamics discrete particle method (EL‐CFD‐DPM). In both TFM and CFD–DPM, closure models are needed for the gas–solid interactions for momentum and energy equations. In CFD simulations, it is critical to define the proper computational domain and then supply corresponding boundary conditions. Usually, the computational domain for a fluidized‐bed reactor is simplified as much as possible to reduce the computational cost.