Geometry solid-liquid mixing

What is the minimum agitator speed to suspend the solids In stirred tanks, there is always an impeller speed below which settling solids will tend to accumulate on the bottom of the vessel. This speed is different for different types of impellers and for identical impellers located at different clearances from the bottom of the vessel. It also depends on the properties of the solid and liquid phases. The minimum speed may be estimated for certain impeller and tank geometries using the Zwietering correlation. It is advisable, however, to determine this value experimentally for processes where solid-liquid mixing is deemed critical. See Section 10-2.2 for details. 

The Doppler technique measures the frequency shift of scattered waves with respect to incident sound waves. The technique, therefore, requires the presence of scatterers in the flow that is being monitored. The scatterers could be turbulent eddies or vortex shedding for liquid single-phase flows, and solid particles for solid/fluid mixed-phase flows. The basic geometry of a Doppler... 

The hydrodynamic parameters that are required for stirred tank design and analysis include phase holdups (gas, liquid, and solid) volumetric gas-liquid mass-transfer coefficient liquid-solid mass-transfer coefficient liquid, gas, and solid mixing and heat-transfer coefficients. The hydrodynamics are driven primarily by the stirrer power input and the stirrer geometry/type, and not by the gas flow. Hence, additional parameters include the power input of the stirrer and the pumping flow rate of the stirrer. 

The first necessary condition [6.21] to be taken into account in all particularization cases is the use of general mixing parameters (factors related to the geometry of agitation, the properties of liquid media, the type of agitators and rotation speed) as well as the use of the specific factors of the studied application. For example, in the case of suspended solid dissolution, we can consider the mass transfer coefficient for dissolving suspended solids, the mean dimension of the suspended solid particles, and the diffusion coefficient of the dissolved species in the liquid. 

The solid in liquid-fluidized bed systems, as distinct from most fluidized with gas, is generally suspended uniformly. Liquid flow, with reasonable column geometry, can be uniformly mixed radially with minimal backmixing. Even in a column of constant diameter, the particles tend to classify according to size (largest at the bottom). Plug flow can be further enhanced by having a substantial tapered section in the bottom. 

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