Abstract
The approach developed by Nguyen et al. (1975) for predicting bubble behaviour in beds of Geldart's (1973) Group B particles has been modified to enable application to beds of larger scale. The model predicts that the size and spatial distribution of bubbles at any level above the distibutor is dependent on the bed depth above that level. Davidson and Harrison's (1963) expression for bubble rise velocity in freely-bubbling beds fortuitously gives a good estimate for the overall mean velocity of interacting and coalescing bubbles.