DEM-CFD

In this study, particle fluidization behaviors in a RFB were numerically analyzed by using a DEM-CFD coupling model [3]. The particle motion was calculated by DEM, which calculates the motion of each particle by integrating the Newton s equations for individual particle step by step, allowing for the external forces acting on a particle. Equations of transitional and rotational motions for individual particles are as follows ... 

To understand the mechanisms of solids slug flows, a two-dimensional coupled DEM/CFD numerical model was built to simulate the motion of a pre-formed slug (ca. 0.3 m long) in a 1 m long horizontal 50 mm bore pipe as shown in Fig. 1. The pipe was initially filled with a layer of particles, approximately 15 mm thick at the bottom. (The thickness of this stationary layer was determined based on experience from previous experiments and computer test runs). 

Fig. 2. Solids slug flow and deposition - DEM/CFD simulation (time interval between each picture 0.2 s and total time 1.0 s).

Fig. 6. Gas velocity profile in pipe cross section — DEM/CFD simulation (at 0.4 s).

The DEM-CFD method has been implemented for the modeling of some industrial processes such as complex processes, gas cyclones (for separating particles from fluids), and powder flow and dispersion. 

Figure 7.36 shows DEM-CFD simulation of a complex process flow in a circulating fluidized bed by Chu and Yu [77]. The system consists of a fluidization vessel... 

FIGURE 7.36 (See color insert.) DEM-CFD simulation of particle size distribution (particles are colored by size) in circulating fluidized bed. (Reprinted from Powder Technol, 179, Chu, K.W. and Yu, A.B., Numerical simulation of complex particle-fluid flows, 104-114, Copyright 2008, with permission from Elsevier.)... 

Discrete particle modeling (DPM) is an advanced computational technique for particulate systems (in this case, fluidized beds) that has already been presented in Chapter 7 of Volume 3, Modem Drying TechnoU. DPM combines continuous (Eulerian) CFD for the gas phase with a discrete (Lagrangian) consideration of the particle phase by means of a discrete element method (DEM), and is therefore often also denoted as DEM-CFD. Its appHcation enables the resolution of not only interactions between the gas and the particle phase, but also of particle-particle and particle-wall interactions, in the sense of a four-way coupling (compare also with Chapter 5 in Volume 1, Modem Drying Technology). 

Fries L, Antonyuk S, Heinrich S, Palzer S DEM-CFD modehng of a fluidized bed spray granulator, Chem Eng Sci 66 2340-2355, 2011. 

Li L, Remmelgas J, van Wachem BGM, et al Residence time distributions of different size particles in the spray zone of a Wurster fluid bed studied using DEM-CFD, Powder Technol 280 124-134, 2015b. 

Di Maio PP, Di Renzo A, Trevisan D Comparison of heat transfer models in DEM-CFD simulations of fluidized beds with an immersed probe. Powder Technol 193 257—265, 2009. 

So far, some researchers have analyzed particle fluidization behaviors in a RFB, however, they have not well studied yet, since particle fluidization behaviors are very complicated. In this study, fundamental particle fluidization behaviors of Geldart s group B particle in a RFB were numerically analyzed by using a Discrete Element Method (DEM)- Computational Fluid Dynamics (CFD) coupling model [3]. First of all, visualization of particle fluidization behaviors in a RFB was conducted. Relationship between bed pressure drop and gas velocity was also investigated by the numerical simulation. In addition, fluctuations of bed pressure drop and particle mixing behaviors of radial direction were numerically analyzed. 

Keywords Pneumatic conveying Slug flow Solids deposition CFD model DEM simulation... 

In recent years, DEM has been used in combination with computational fluid dynamics (CFD) aiming at investigating particulate behavior in fluid phase. For a two-phase particle-fluid system, the solid motion and fluid mechanics are solved through the application of Newton s equations of motion for the discrete particles and Navier-Stokes equations for the continuum fluid [2]. 

As stated by Zhu et al. [3], the major applications of this method are in particle fluidization, pneumatic conveying, and process studies for which examples are provided later. DEM coupled with CFD has been used widely for analyzing particulate behavior in fluid systems such as gas fluidization with noncohesive [74,75] and cohesive particles [76], pneumatic conveying [77], and particle dispersion in liquids [78-80] and gases [81,82]. 

Washino, K. Tan, H.S. Hounslow, M.J. Salman, A.D. (2013) A new capillary force model implemented in micro-scale CFD-DEM coupling for wet granulation. Chemical... 

Kloss, C. Goniva, C. Hager, A. Amberger, S. Pirker, S. (2012) Models, algorithms and validation for opensource DEM and CFD-DEM. Progress in Computational Fluid Dynamics 12, 140-152. 

Besides the Eulerian—Eulerian approaches (say, TFM and SFM) discussed above, various Eulerian—Lagrangian approaches have been proposed and developed rapidly in recent years, say, CFD-DEM (Tsuji et al, 1993 Xu... 

Rong, D., and M. Horio, DEM simulation of char combustion in a fluidized bed. Second International Conference on CFD in the Minerals and Process Industries, 1999... 

We hope to have shown that the SD implementation can be used for hydrodynamics for any appropriate DEM simulation, be it restructuring aggregates or aggregate sedimentation behavior, but the fuUy-resolved CFD methods are always required for validating the simulations. The free-draining approximation should not be considered as a vahd comparison for colloidal aggregates in shear flow as it neglects many-particle effects [35]. 

An overall modeling strategy must include a model of the two-phase flow of the particles in the miU currently a combined CFD-DEM is the best and most advanced choice. In order to make DEM truly predictive, intrinsic material properties such as Young s modulus and visco-plastic deformation... 

The FB process is simulated using a DPM. This model couples the DEM (Cundall and Strack, 1979), which describes the motion and interactions of every individual particle by equations of motion, and the CFD, which calculates the process gas dynamics in the apparatus by volume-averaged Navier-Stokes equations. The interactions between particles, particles and apparatus walls as well as between particles and gas are described. 

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