EFFECT OF BUBBLE COALESCENCE ON ENTRAINMENT IN GAS-FLUIDIZED BEDS

An entrainment flux model for freely bubbling gas-solid fluidized beds was described. The model was based on particle trajectories in the fr eeboard with consideration of interactions between the dense and lean phases. These interactions include a bubble eruption mechanism, namely , single and coalescence bubble eruptions, bubble induced gas puff vel ocity, and particle ejection mechanism. It was shown that the average particle velocity and entrainment profiles revealed a two-level decay trend. This could be attributed to different bubble eruption mechanism s; for single bubble eruptions where both the initial gas puff and eje cted particle velocities were low, the first decay would form at lower freeboard height. The second decay trend at higher freeboard height w ould be formed by the higher gas puff and particle velocities due to t he double-bubble coalescence eruption. However, the overall profile co uld be considered as an exponential decay with a slightly faster decay than Wen and Chen, AIChE J., 28 (1982) 117, suggested. A simple exper imental set-up was used to confirm the two-level entrainment decay tre nd. The results obtained showed similar trends to the predictions from the model.