BEHAVIOUR OF FREELY BUBBLING FLUIDISED BEDS

This paper considers two aspects of the behaviour of freely bubbling fluidised beds: 1. The rising velocity of bubbles in a fluidised bed has been found to be greater for a swarm of bubbles than for a bubble in isolation. This appears to be caused primarily by the acceleration of overtaking bubbles during the coalescence process. The influence of bubble-induced solids motion on bubble rising velocities is also considered and the theory which is developed is in reasonable agreement with experiment. 2. Direct experimental evidence indicates that the recent analysis of Lockett, Davidson, and Harrison comes closer to predicting the division of gas between the two phases of a fluidised bed than the earlier theory of Toomey and Johnstone. Nevertheless, bubble throughflow velocities appear to be greater than predicted by the available theories, and it is shown that at least part of the discrepancy between theory and experiment can be accounted for by considering the effects of modifications in bubble shape and high local concentrations of bubbles. © 1969.