New constitutive relations for filtered two‐fluid models (TFM) of gas‐particle flows are obtained by systematically filtering results generated through highly resolved simulations of a kinetic theory‐based TFM. It was found in our earlier studies that the residual correlations appearing in the filtered TFM equations depended principally on the filter size and filtered particle volume fraction. Closer inspection of a large amount of computational data gathered in this study reveals an additional, systematic dependence of the correction to the drag coefficient on the filtered slip velocity, which serves as a marker for the extent of subfilter‐scale inhomogeneity. Furthermore, the residual correlations for the momentum fluxes in the gas and particle phases arising from the subfilter‐scale fluctuations are found to be modeled nicely using constitutive relations of the form used in large‐eddy simulations of single‐phase turbulent flows. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3265–3275, 2013

The accuracy of fluidized-bed CFD predictions using the two-fluid model can be improved significantly, even when using coarse grids, by replacing the microscopic kinetic-theory-based closures with coarsegrained constitutive models. These coarse-grained constitutive relationships, called filtered models, account for the unresolved gas-particle structures (clusters and bubbles) via sub-grid corrections.Following the previous 2-D approaches of Igci et al.

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Recebido em 8/3/07; aceito em 11/7/07; publicado na web em 19/12/07Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the preexponential factor and the activation energy. Coal samples of 10 mg and 775 μm mean size were used in synthetic air atmospheres (21 % O 2 ). Heating rates from 10 to 50 o C/min were applied until the temperature reached 850 o C, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol.