A new approach to jet phenomena. Gas entrainment and recirculation in a bidimensional spouted fluidized bed

Although literature studies report the fluctuating nature of jets escaping into a fluidized bed, up to now the models assumed steady and permanent jets. A new approach which accounts for the fluctuating nature of the jet is proposed. The experiments were carried out in a large 2-dimensional fluidized bed equipped with a ''V'' grid and a central jet. The gas jet velocity was kept around 100 m/s and the influence of the grid aeration on the gas mixing was investigated. A model was developed based on the concentration profiles of an inert tracer gas and the measurement with a light detector of the probability of jet presence. The model separates the bed in 2 zones: a zone in which the jet fluctuates (a point in this zone will alternately be in the jet and in the emulsion phase) and a zone in which the jet is never present. The model predicts the rate of gas entrainment into the jet and the rate of gas recirculation between the jet and the emulsion phase. When the grid aeration is close to the minimum fluidization velocity, the gas entrainment into the jet is limited by frictional resistance to the gas flow in the defluidized emulsion phase. For high gas aeration at the grid, the gas entrainment can reach 30% of the total gas introduced at the grid. The rate of gas recirculation between the jet and the emulsion phase is relatively low in all cases