Comparisons of Eulerian-Eulerian and CFD-DEM simulations of mixing behaviors in bubbling fluidized beds

Abstract

The Eulerian-Eulerian model and CFD-DEM have been applied extensively to investigate various aspects of fluidized bed systems. However, there have been very limited studies to date on comparisons of predictions made using these two fundamentally different approaches. To address this gap in the existing literature, both approaches were applied to perform simulations of solids mixing behaviors in gas fluidized beds with various inlet gas velocities. It was observed in both modeling approaches that bubbling had a significant influence on solids mixing behaviors. Higher gas velocities gave rise to larger and more plentiful bubbles throughout the bed which led to higher rates of mixing. All beds were observed to be well-mixed after 10s of fluidization. Both modeling approaches predicted similar fluidization behaviors and bubbling phenomena, while there were slight discrepancies in the solids volume fraction profiles possibly due to innate differences in the models and parameters used. When the amount of solids was increased by two times, deeper and more extensive bubbling was observed at all gas velocities due to the larger initial bed height. However, owing to the greater amount of solids, a longer fluidization time was needed to achieve the same extent of mixing. At low gas velocity, the rate of solids mixing predicted by CFD-DEM was higher than that by the Eulerian-Eulerian model. At high gas velocities, good agreement in extents of mixing at different instants of time during the fluidization processes between the two modeling approaches was achieved. However, a vigorous initial bed expansion process predicted by CFD-DEM was not observed in the Eulerian-Eulerian simulations and this might be another manifestation of the fundamental differences between the two modeling approaches.