ON THE RHEOLOGY OF THE DENSE PHASE OF A GAS-FLUIDIZED BED

Measurements of bubble rise velocities in two gas fluidised beds have been compared with numerical simulations of spherical bubble-wake regi ons rising through Newtonian liquids. The comparisons have been used t o elucidate the theological nature of the dense phase of gas fluidised beds. The investigation sheds new light upon results obtained in the past by other workers, who did not have the benefit of the powerful nu merical simulation techniques of today. It was found that the assumpti on of a Newtonian viscosity coefficient of 0.8 Pa s (values around thi s have often been suggested in the literature) yields bubble rise velo cities of the right order of magnitude. Nevertheless, the experimental ly determined variation in bubble rise velocity with size cannot be ex plained fully on basis of a Newtonian rheological model, but indicates shear-thickening behaviour of the dense phase. A discussion, also of the effect of bubble Reynolds number and wall effects upon the dense p hase flowpattern around rising bubbles, and comparison with other work is provided.