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Single And Multiphase Mixing In Partially Filled Stirred Vessels, Shilan Motamedvaziri

Dissertations

In many industrial applications, mixing vessels have a liquid height-to-tank diameter ratio, H/T, equal to, or larger than 1. However, there are many instances where this ratio is lower than 1, as in all those cases in which the vessel is either emptied or filled. Even when H/T<1, sufficient agitation must still be provided in order to attain the desired process objectives. When the impeller submergence is reduced as a result of lowering the liquid level, the fluid dynamics of even a single-phase stirred liquid can become quite complex, with different regimes possibly existing depending on the geometric characteristics of the system (such as impeller clearance, liquid height, or liquid submergence above the impeller). The objectives of this work were to study in detail the hydrodynamic changes that occur when H/T is decreased, and to determine the minimum liquid levels and the critical impeller submergence for different impeller off-bottom distances, impeller diameters and agitation speeds where adequate mixing process can still be achieved, both in a single liquid phase and in solid-liquid suspensions.

Flat-bottomed, baffled vessels (5L, 12L, 20L and 170L) equipped with a single disk turbine (DT) of four different sizes placed at five different impeller off-bottom clearances were used here to study the system's hydrodynamics and related mixing phenomena. A number of experimental tools were used to analyze the systems under investigation, including: …