A numerical simulation analysis of the effect of the interface drag function on cluster evolution in a CFB riser gas-solid flow

Abstract

-The dynamics of formation, dissipation and breaking of coherent structures in the riser gas-solid flow of a circulating fluidized bed (CFB) are evaluated by numerical simulation. The simulation is performed using the MICEFLOW code, which includes IIT's two-fluid hydrodynamic model B. The methodology for cluster characterization is used from Sharma et al. and is based on determination of four characteristics, average lifetime, average volumetric fraction of solid, existence time fraction and frequency of occurrence. Clusters are identified applying a criterion for the time average value of the volumetric solid fraction. A qualitative analysis of the influence of different drag function correlations on the hydrodynamics of the flow, including the evolution of coherent structures, is performed. The simulation predictions are also compared to experimental results. The results indicate that the choice of a correlation for drag function should be quite judicious. Finally it is shown that the mean clustering criteria of Sharma et al. should be modified to take into account other factors that influence cluster dynamics.

A new relation of drag force for high Stokes number monodisperse spheres by direct numerical simulation

“…It is usually the primary force to suspend and transport the particles and have significant influence on the results. For example Benyahia [9], Gomez and Milioli [10], Heynderickx et al [11] and Wang et al [12] compared solid-volume-fraction variations in the riser of circulating fluidized bed and observed that the drag laws based on empirical relations give more homogenous structures as compared to experiments. Du et al [13] compared voidage profiles, particle velocity profiles and solid flow patterns in spouted beds and observed different results by different drag relations.…”

Momentum Exchange in Solid–Fluid System Modeling with the Eulerian Multiphase Model

“…Similar to other models, in case of particles nonspherical in shape, the coefficient of sphericity / s can be introduced. [3,18] The issue of sphericity coefficient is discussed later in the article. An interesting expanded mathematical model, based on the Ergun equation, is described in Béttega et al [19] The Richardson-Zaki drag model (1954) has the form of: [6] b fs ¼…”

“…The resistance of the surrounding is determined most frequently from the Schiller-Neumann formula: [3,4,13,14,16,20] C D ¼ where Re s is the local Reynolds number:…”

“…In some studies, [3,4] because of nonspherical shape of the granulate particles, the diameter d s is modified by introducing the so-called coefficient of sphericity / s (for spheres / s ¼ 1). In such cases the coefficient of momentum exchange will be described as follows: [3,4] …”

“…Gomez and Milioli [3] -comparative studies (also concerning a CFB system) using the models by Luo, Ergun, Wen-Yu, Gidaspow and Di Felice. Hjertager, Solberg and Hansen [4] -studies applying the models by Ergun, Wen-Yu, and Gibilaro.…”