Comprehensive assessment of the accuracy of CFD-DEM simulations of bubbling fluidized beds

Abstract

The present study aims to validate CFD–DEM (Discrete Element Method) simulations of bubbling fluidized beds comprehensively, based on the small scale “challenge” problem recently released by NETL (https://mfix.netl.doe.gov/). Both the averaged and fluctuated values of an extensive list of properties are evaluated, including the pressure drop, the bubble size and rise velocity, and the particle velocity. Five common gas-solid drag models are compared, while the contact model is fixed. The predictions are generally in good agreement with the experiments covering fluidization gas velocities from 2umf to 4umf (minimum fluidization velocity), but an overprediction is observed for the particle velocity fluctuations and time-averaged horizontal particle velocity. The properties which are accurately predicted include: the mean and fluctuation frequency of the bed pressure drop, umf, and the time-averaged vertical particle velocity. The predictions of the bubble size and rise velocity agree generally with the correlations in literature. The predictions of the fluctuations of the vertical and horizontal particle velocities, and the particle granular temperature, are somewhat larger than the experiments. The time-averaged horizontal particle velocity is also overpredicted, especially for conditions at 2umf and 3umf. The disagreement between the simulations and experiments cannot be fully removed by selecting the different drag models investigated in this article.