CFD study of the minimum bubbling velocity of Geldart A particles in gas-fluidized beds

The minimum bubbling velocity, which demarcates the homogeneous and heterogeneous fluidization regimes, plays a pivotal role in gas fluidization of Geldart A particles. We systematically study the effect of gas and particle properties on the minimum bubbling velocity of Geldart A particles in gas-fluidized beds using both Eulerian–Eulerian and Eulerian–Lagrangian models. We find that the minimum bubbling velocities as obtained from the simulations are in reasonable agreement with the well-known experimental correlation of Abrahamsen and Geldart (Powder Technology, 1980, 26: 35–46). To our best knowledge, this is the first time that the minimum bubbling velocity is correctly predicted by Eulerian–Eulerian models, without using an artificial ad-hoc modification of the gas–solid interaction force. Furthermore, we have performed a systematic investigation into the effect of the specific method that is used for determining minimum bubbling velocity. Our simulations show that the minimum bubbling velocity that would be obtained from the simulated bed contraction is larger than the one obtained from visual observation, which in its turn exceeds the one obtained from sudden change of standard deviation of pressure drop. We find that the abrupt change of the granular temperature with increasing superficial gas velocity may be a more suitable indicator for identifying the onset of heterogeneous fluidization.