Wall effects on space averaged two-fluid model equations for simulations of gas–solid flows in risers

For the study of gas–solid flows in a circulating fluidized bed (CFB) riser, the model based on the Eulerian description of phases is widely used. Such a description requires the usage of a fine mesh and a short time step in the numerical simulations. Due to the constraint of long calculation times with fine meshes, it becomes practical to simulate the gas–solid flow in a CFB riser with coarse meshes. This work is the continuation of formulating the subgrid-scale models for the space averaged two-fluid model equations which can be used in coarse mesh simulations of gas–solid flows in risers. In this study, the vertical component of the drag force and the convective term are analyzed and their dependence on the averaging size and solid volume fraction with the distance from the wall is presented.

► Two-fluid model was used for numerical simulation of gas–solid flow in a riser with Geldart group B particles. ► Space averaging applied over the gas–solid drag and the convective term to analyze the subgrid-scale modeling. ► Wall effects were studied for subgrid-scale models. ► Subgrid-scale models showed dependence on distance from the wall, averaging size and solid volume fraction. ► Results obtained for Geldart group B particles clearly differ from those presented in the literature for Geldart group A particles.