CFD-DEM simulation of Small-Scale Challenge Problem 1 with EMMS bubble-based structure-dependent drag coefficient

In this study, the energy minimization multi-scale (EMMS)/Bubbling model is coupled with the computational fluid dynamics/discrete element method (CFD-DEM) model via a structure-dependent drag coefficient to simulate the National Energy Technology Laboratory (NETL) small-scale challenge problem using the open-source multiphase flow code MFIX. The numerical predictions are compared against particle velocity measurements obtained from high-speed particle image velocimetry (HSPIV) and differential pressure measurements. The drag-reduction effect of the EMMS bubble-based drag coefficient is observed to significantly improve predictions of the horizontal particle velocity and granular temperature when compared to several other drag coefficients tested; however, the vertical particle velocity and pressure fluctuation characteristic predictions are degraded. The drag-reduction effect is characterized by a reduction in the sizes of slugs or voids, as identified through spectral decomposition of the pressure fluctuations. Overall, this study shows great promise in employing drag coefficients, developed via multi-scale approaches (such as the EMMS paradigm), in CFD-DEM models. (C) 2020 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.