Influence on Blend Times

The above-described effect is caused by the power needed for suspending the particles not being available for keeping up the continuous flow. As this flow is slowed down, the blend time consecutively increases. As it has been found in experimental investigations [15], micrombdng processes are not influenced as long as the solids content in the vessel does not increase above x. = 0.05. 

If similarity theory is applied correctly, the dimensionless numbers and characteristics that are determined are independent of the scale. This makes it possible, by using appropriate scale-up rules, to specify the operating parameters for industrial-scale systems from the results of tests carried out on models. Computational fluid dynamics (CFD) can be used to visualize the impeller system at its full scale, thus contributing to solving scale-up problems. 

The cubic scale factor is used to convert the ratio of the power per unit volume from the industrial scale to the model scale. Each of the straight lines results from a combination of the power equation with different scale-up criteria. Taking the 

In a similar way, all the other straight lines can be determined by combining the power equation with other elements such as the Froude number (Procn d2), the Nusselt equation (a a oc the Reynolds number (Re oc nd ), and so on. 

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As soon as solids appear in the stirred vessel, they have a significant influence on blend time. The correlations known from one-phase operation lose their validity in the presence of a solid phase [14]. In Figure 13.13, the influence of solids concentration is visualized when dealing with solids concentrations larger than Xs = 0.1. Results are presented for both cases, one-phase and two-phase media. As... 

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