A MODEL FOR THE DISTRIBUTION OF VOIDAGE AROUND BUBBLES IN A FLUIDIZED-BED

A physical model is suggested to explain the occurrence of a shell of varying porosity around a gaseous bubble rising in a fluidized bed. Ac cording to the model, this phenomenon is a direct consequence of the n ecessity to maintain the balance of forces acting on solid particles i n the vicinity of the bubble. Both volume forces due to gravity, drag and inertia and surface forces caused by the particulate pressure are shown to be essential. The agreement between model predictions and exp erimental data is good apart from some difference in the particle conc entration at the edge of the bubble void. Requirements of the mass, mo mentum and energy conservation at this edge regarded as a surface of d iscontinuity result in conclusions concerning the particle flux throug h the bubble surface and the solid concentration inside the bubble.