(118d) Validation of Cfd Model for Fluidised Bed over Broad Ranges of Operating

Numerical simulation of the hydrodynamic features in a bubbling fluidized over a broad range of operating conditions has been validated by experimental measurement. The two-fluid model code, MFIX Ver. 2005-1, employing the constitutive relation of kinetic theory, was used to simulate the fluidized bed hydrodynamics. Experiments were conducted in a cold conventional gas-solid bubbling column of 15 cm diameter. Particles in the size range of 125 ? 1800 mm (belonging to Geldart group A/B, B and D) where fluidised over a broad range of gas velocity. Electrical Capacitance tomography (ECT) was used to record the cross-sectional particle-gas distribution for the duration of 50 seconds operation. These measurements where then used to estimate the bubble characteristics. Qualitatively, the model gives satisfactory result for group B and D particles, while unsatisfactory prediction were observed for the smaller particles. The Phenomenon of high homogeneity predicted by the model, especially for the particle size 125 mm, does not match with the clear bubbles boundary observed with the ECT. The accuracy of the quantitative bubble characteristics (velocity, frequency, volumetric flow rate) is very sensitive to the particle size and the predictions are significantly poor. These finding are in support of the recent growing concern about the validity of classic kinetic constitutive relation in capturing the mechanism of particle-particle interactions mechanism in bubbling fluidized bed.