Hybrid Two-Fluid DEM Simulation of Gas-Solid Fluidized Beds

Abstract

Simulations of gas-solid fluidized beds have been performed using a hybrid simulation method, which couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) continuum equations for the gas phase. The coupling between the two phases is modeled using an interphase momentum transfer term. The results of the hybrid TF-DEM simulations are compared to experimental data and TF model simulations. It is found that the TF-DEM simulation is capable of predicting general fluidized bed dynamics, i.e., pressure drop across the bed and bed expansion, which are in agreement with experimental measurements and TF model predictions. Multiparticle contacts and large contact forces distribute in the regions away from bubbles, as demonstrated from the TF-DEM simulation results. The TF-DEM model demonstrates the capability to capture more heterogeneous structural information of the fluidized beds than the TF model alone. The implications to the solid phase constitutive closures for TF models are discussed. However, the TF-DEM simulations depend on the form of the interphase momentum transfer model, which can be computed in terms of averaged or instantaneous particle quantities. Various forms of the interphase momentum transfer model are examined, and simulation results from these models are compared.

Realistic representation of grain shapes in CFD–DEM simulations of sediment transport with a bonded-sphere approach

“…To resolve the collision between the sediment particles, the contact force between sediment particles is computed with a linear spring-dashpot model (Cundall and Strack, 1979). The time step to resolve the particle collision is less than 1/50 the contact time to avoid particle inter-penetration (Sun et al, 2007). The algorithm in Fig.…”

Study of sedimentation of non-cohesive particles via CFD–DEM simulations

“…The micro-particle contact force can be converted to the effective stress by Eq. (28). This can help to enlarge the application of CFD-DEM model in more and more practical civil engineering projects.…”

“…The particle time step (DEM time step) should be large enough to avoid the particle interpenetration, yet not so large as to induce too much calculation consumption, which typically set as the value of /50 [28]. Quantity represents the particle contact time, and its value depends on , , and the masses of two contacted particles.…”

“…A linear spring-dashpot model is utilized to simulate the particle-particle and particle-wall collision during the settling. The normal and tangential interaction forces , and , between two contacted particles i and j is [28]:…”

“…The tangential force , between two particles grows according to a tangential spring and dash-pot model until , / , = and is then held at , = , until the particles lose contact. The total force f i and torque T i acting on particle i is [28]:…”