Verification and validation of a coarse grain model of the DEM in a bubbling fluidized bed Mikio Sakai a,⇑ , Minami Abe b , Yusuke Shigeto b , Shin Mizutani b , Hiroyuki Takahashi c , Axelle Viré d,e , James R. Percival d , Jiansheng Xiang d , Christopher C. Pain d a Resilience Engineering Research Center, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan b Department of Systems Innovation, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan c Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan d Applied Modeling and Computation Group, Department of Earth Science and Engineering, Imperial College London, Prince Consort Road, London SW7 2BP, UK e Faculty of Aerospace Engineering, Delft University of Technology, 2629 HS Delft, The Netherlands highlights  The coarse grain model was verified in two-dimensional fluidized beds so far.  In this study, the coarse grain model is verified and validated in a 3D fluidized bed.  Macroscopic behavior agreed between the original system and the coarse grain model.  Adequacy of the coarse grain model is shown through this study.  The coarse grain model fabricates application of the DEM in industrial scale system. graphical abstract article info Article history: Received 7 October 2013 Received in revised form 19 December 2013 Accepted 11 January 2014 Available online 18 January 2014 Keywords: Discrete element method Coarse grain model Scaling law Fluidized beds DEM–CFD method Gas–solid flow abstract Dense granular flows are encountered in various engineering fields. The discrete element method (DEM) is used extensively for the numerical simulation of these flow types. Improvements in computer specifi- cations have made it possible to apply the DEM in various systems. Although the DEM is well-established, it has a fatal problem. The problem is that the number of calculated particles is substantially restricted when the simulation needs to be finished within practical time using a single personal computer. On the other hand, many industries require application of the DEM to large scale systems on a single per- sonal computer. We therefore developed the DEM coarse grain model in our previous studies. In the coarse grain model, a group of original particles is simulated using a large-sized particle termed a coarse grain particle, where the total energy is modeled to agree between the coarse grain and original particles. The coarse grain model therefore makes it feasible to perform large scale DEM simulations by using a smaller number of particles than the actual number. The coarse grain model thus far has been verified in two-dimensional fluidized beds. In this study, adequacy of the coarse grain model is verified and val- idated in a three-dimensional fluidized bed, where scaling ratio is low and high respectively. Conse- quently, the coarse grain model is shown to simulate the macroscopic behavior of solid particles in three-dimensional dense gas–solid flows. Ó 2014 Elsevier B.V. All rights reserved. 1385-8947/$ - see front matter Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2014.01.029 ⇑ Corresponding author. Tel./fax: +81 3 5841 6977. E-mail address: mikio_sakai@n.t.u-tokyo.ac.jp (M. Sakai). Chemical Engineering Journal 244 (2014) 33–43 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej