Abstract
A new drag model, which is developed from the perspective of the particle size distribution (PSD), was proposed to improve the prediction accuracy for the simulation of flow behaviors in the downer. In this model, the actual control volume was divided into several sub-grids characterized by different characteristic particle sizes, and the total drag force was obtained by summing all the sub-grids drag forces. To obtain the slip velocity for each sub-grid separately, the widely-used Richardson-Zaki (R-Z) equation was introduced into each sub-grid. The simulation results showed that this model can more accurately predict the average solids holdup than other models, as well as the axial solids holdup distribution. Also, the axial pressure and pressure gradient distribution were given, and the unique flow pattern in the downer can be clearly captured. This model is expected to provide a new idea for the simulation of low solids holdup gas-solids system with a wide PSD.
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