PARTICLE FLOW PATTERNS IN A MECHANICALLY STIRRED 2-DIMENSIONAL CYLINDRICAL

In evaluation of the surface-to-bed heat transfer coefficient in the agitated bed of dryers, the overall mixing patterns and individual particle movements, especially in the immediate vicinity of the heated surface, play an important role. This study examines such mixing patterns in a two-dimensional horizontal vessel containing various granular materials agitated by paddle-type blades. Flow regime maps outlining the optimum range of operation for good solids mixing and the torque required to stir the bed are presented for the above. The effects of rotational speed, number of blades, particle size and shape, bi-dispersity of particles, bed hold-up, particle surface stickiness and wall-to-blade clearance are discussed. For the first time, the effect of blade perforations on the torque required to stir the bed have been presented. It was observed that the mechanisms of surface-to-bed heat transfer are different for spherical free-flowing and non-spherical and/or cohesive particles. Possible implications of the above results in the dryer design are discussed. © 1990.