In this study, the effects of impeller rotation speed, off-bottom clearance, blade angle, types of solid and liquid, etc., on the suspension pattern of sedimentary particles and particle rise height in liquid were investigated with a hemispherical vessel without baffles under low particle concentration. The transition conditions of suspension pattern between regimes I and II, and regimes II and III, were observed visually, and their non-dimensional equations were expressed with an acceptable correlation by varying the above operation factors a great deal. Here, regime I is stagnation of particles on a vessel bottom, II is partial suspension, and III is complete suspension in liquid. The non-dimensional equation of the maximum particle rise height was also successfully obtained. The combination of the non-dimensional equations of transition and maximum particle rise height permitted us to determine the adequate solid/liquid mixing operation conditions without collision of particles with device parts.
The solid/liquid mass transfer rate of particles stagnation on vessel bottom and partial suspension in liquid was insufficiently known compared with that of completely suspended condition. In this study, the effect of suspension regime of sedimentary particles on the solid/liquid mass transfer rate in a mechanically stirred vessel without baffles was investigated. The solid/liquid mass transfer rate increased slightly with the increasing rotation speed at the stagnation regime; its rapid enhancement was found at the partially suspended regime, and the increasing rate became slow again at the complete suspension. Nondimensional equations for solid/ liquid mass transfer rate of stagnation and completely suspended conditions were obtained with a good correlation. On the other hand, the suspended particle ratio under the partial suspension condition was estimated by the mass transfer rate of stagnation and completely suspended regimes and followed an S curve against the normalized rotation speed.
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