Two Phase Flow Behaviour in the Freeboard of a Gas Fluidized Bed

Abstract

The axial and lateral velocity distributions of the gas-phase and the particulate-phase in the freeboard of a two-dimensional fluidized bed were measured. A Laser Doppler Velocimeter (LDV) was used. A Laser fluorescence technique was developed to enable velocity discrimination between the two-phases. The gas-phase experiments revealed a fast decay of gas, local mean and r.m.s. velocity profiles with freeboard height. The lateral gas velocity distribution, close to the bed surface, showed a maximum at the column centre. The location of the maximum velocity shifted towards the column wall at higher freeboard levels. The axial particle velocity measurements indicated a two-staged decay of the velocity profile with height. Two simple models were developed to predict local gas velocity values with freeboard height and to predict the transport disengagement height (TDH). The results are in good agreement with data obtained from the experiments.