Article

Allgemeing�ltige Aussage zur Mindest-R�hrerdrehzahl beim Suspendieren

Chemie Ingenieur Technik (Impact Factor: 0.66). 01/1985; 57(8):692-693. DOI: 10.1002/cite.330570811

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    ABSTRACT: Complete suspension of fine-grained particles is achieved at mean circulation velocities of the fluid exceeding the settling velocities of the particles by several orders of magnitude. It is therefore argued that boundary layer effects are significant. In this paper, through an analysis of the boundary layer flow in an agitated vessel two theoretical criteria for the required minimum stirrer angular velocities are derived. The evaluation of own experiments proves the significance of one of them for Archimedes numbers Ar ≲ 40, i.e. for particles completely immersed in the viscous sublayer. For higher Archimedes numbers, i.e. for particles protruding into the buffer layer and into the turbulent near wall layer, criteria based on the boundary layer flow turn out not to be suitable.
    No preview · Article · Dec 1987 · Chemical Engineering Science
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    ABSTRACT: A criterion for the prediction of minimum stirrer rotation speeds is derived for the suspension of coarse-grained particles (Archimedes numbers ≳ 40). Minimum stirrer rotation speeds can be predicted by the evaluation of two diagrams for the drag of fluidized particles as a function of the concentration and for the pressure-head volumetric flow rate characteristics of an agitated vessel. The reliable prediction of required minimum stirrer angular velocities is discussed in the light of the results derived in this paper and in Part I of this series.
    No preview · Article · Dec 1987 · Chemical Engineering Science
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    ABSTRACT: Suspension of solids in stirred tanks – Comparison of different calculations. The suspension of solids in stirred tanks has been the subject of various investigations over the last three decades. Though many equations for the calculation of the critical impeller suspension speed were derived and published during this period of time no conclusive descriptions have been achieved. As a consequence, serious problems arose concerning the scaling-up of the mixer, since the various equations led to completely different designs. Over the last few years new physical models have been developed to improve on this point. These models aimed to reach a better description by considering the fluid-dynamic process more accurately. This survey presents the actual state of investigation by systematically comparing the results of the latest models. Careful consideration of the experimental conditions gave fairly consistent results. The decisive problem of the scale-up procedure, however, remains unsolved.
    No preview · Article · Nov 1988 · Chemie Ingenieur Technik
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