Impeller discharge flow

The local aspects of liquid-liquid two-phase flow in RE has been the focus of CFD analysis by different research groups (123-126). In principle, all aspects concerning single-phase flow phenomena (residence time distribution, impeller discharge flow rate, etc.) can be tackled, even with complex geometries. However, the two-phase CFD is still a challenge, and the droplet interactions (breakup and coalescence) and mass transfer are not implemented in commercially available codes. Thus these issues constitute an open area for further research and development (127). 

The 45° PBT impeller has a larger value than the FBDT impeller, and this result is contrary to the case in which the tracer is injected into the impeller position described in Challenge 2.3. This difference is caused by the difference in the local mixing capacity at the region where the impeller discharge flow reaches. In other words, the change in the spatial distribution of the tracer concentration with time is significantly affected by the position of the tracer injection. 

After it is confirmed that the flow in the vessel has attained a steady state under a fixed Re, the velocity fluctuations are measured at the fixed impeller discharge flow region by using an electrode reaction velocity meter. The measured ESD is fitted by the new ESD defined by Eq. (4.7). 

Figure 4.5 ESD in impeller discharge flow region in a stirred vessel.

Const, impeller revolutional speed Const, circulation time Const, impeller discharge flow rate per unit vessel volume Fast reaction... 

Const, (power) dissipation energy per unit vessel volume Const, impeller discharge flow energy Turbulent dispersion Gas-liquid operation Reaction requiring microscale mixing... 

Const. Reynolds number Const, impeller discharge flow momentum Const, torque per unit discharge flow rate ... 

Figure 4.7 (a) Distributions of energy values of turbulent fluctuations (b) distributions of double correlation values of turbulent fluctuations in impeller discharge flow region in a stirred vessel. 

By analogy to hydraulics, this power input is also proportional to the product of the volumetric impeller discharge flow Q and a headiJC. Thus,... 

The aeration number (A a) is the ratio of gas flow rate to impeller discharge flow and is written as... 

Positioning of internal coils should be such that they are not placed in the discharge flow of the impeller. Since the impeller discharge flow is typically... 

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