SIMPLIFIED SCALING RELATIONSHIPS FOR FLUIDIZED-BEDS

Simplifications to the full set of scaling parameters for dynamic similarity of fluidized beds, Glicksman, Chemical Engineering Science, 39 (1984) 373, were explored. A new set of simplified scaling laws includes the Froude number based on column height, the solid to gas density ratio, the ratio of superficial to minimum fluidization velocity, bed geometric ratios, and particle sphericity and size distribution. When the gas to particle drag is represented by either the Ergun equation or a single particle drag equation, the new simplified laws hold exactly in both the viscous dominated and gas inertia dominated limits. For intermediate conditions, the gas to particle drag is well approximated in models based on the simplified scaling laws. The simplified scaling laws allow very small models to be constructed which properly simulate the hydrodynamics of a full size reactor or combustor. Experimental confirmation of the new simplified scaling laws and the viscous limit scaling parameters, where equality of the density ratio is omitted, were carried out in circulating fluidized beds. Within the viscous limit, the solid to gas density ratio is an important modeling parameter when the slugging regime is approached. In general, the solid to gas density must be matched to achieve good similarity. Using the new simplified scaling laws, good agreement was observed even when the length scale of the air fluidized model was as small as 1/16 that of an atmospheric combustor.