Stirred tank baffles

As in boundary-layer flows, smaller reference floe diameters are found with gas sparging than with the same average power input in a baffled stirred tank 127] or [44,45]. This can be explained if it is assumed that the floes come into close contact with the gas phase and find their way into the zones of higher stress. 

The presented results for systematic studies on hydrodynamic stress in shake flasks, baffled stirred tanks, reactors in which boundary layer flow predominates (e.g. stirred tank with a smooth disc or unbaffled stirred tank), viscosi-... 

A study carried out at the Lawrence Radiation Laboratory of the University of California by Vanderveen (Vl) strongly suggests another type of interaction model see also Vermeulen (V5). Vanderveen measured the drop size at different distances from the impeller of a baffled, stirred tank reactor in which two immiscible liquid phases were contacted, and found that a very substantial increase in drop size occurs at remote distances. The increase, which was attributed to coalescence, appeared to be dependent on the physical properties of the phase system. 

As iB well known, in baffled, stirred tank reactors there is a strong circulation pattern, as shown in Fig. 22. The dispersed drops will move with this... 

Jenne, M. and Reuss, M. (1999), A critical assessment on the use of k-e turbulence model for simulation of the turbulent liquid flow induced by a Rushton turbine in baffled stirred tank reactor, Chem. Eng. ScL, 54, 3921-3941. 

In experiments [141, 566] in three baffled stirred tanks with turbine stirrers (V = 1 20 100 1), the position of the feed point for the add and the stirrer power were varied. The micro-mixing was determined according to the ViUermaux s method. The results in Fig. 1.26 show a fairly weak dependence of the degree of micromixing a upon thepower per unit mass e ... 

Calderbank [64] determined a by physical means at low Reynolds numbers in two baffled stirred tanks with turbine stirrers (V = 5 and 100 1), utilizing 10 different liquids and found... 

Ranade and Van den Akker [74] introduced the snapshot method for simulating flows in baffled stirred tanks. The snapshot method has many similarities with the traditional IBC method but differs in that the effect of the impeller rotation is approximately modeled mechanistically and not deduced from empirical data analysis solely. The snapshot method thus represents an early attempt to improve on the main limitation associated with the IBC method. 

Ranade and Van den Akker [74], for example, used the snapshot method for simulating gas-liquid flows in baffled stirred tanks using a time after volume averaged two-fluid model for incompressible flows (as described in sect 3.3). These multiphase simulations also predicted the near-impeller flows with fair accuracy. Most important, the cavities due to the accumulation of gas in the low-pressure region behind the impeller blades were detected. 

In un-baffled stirred tanks, a vortex formation occurs at Reynolds larger than 300. This phenomenon should be avoided by working in laminar regime, or by using baffles in turbulent mixing (Re > lO" ). Because Np = Kp the following relation is obtained ... 

The problems encountered will be discussed with reference to a fully-baffled stirred tank operating under fully turbulent conditions, i.e. Re > 10. Under these conditions the Newton number, Ne, also called the power number, is constant so that the expression for power consumption P is... 

Experiment c. Experiments were done in a baffled stirred-tank system with a 35 cm diameter tank. We expect that Eq. (17-37al will be valid, except the coefficient 0.04433 has to be adjusted. The stirrer was operated at 900 rpm The inlet solution was 0.005 wt frac sodium chloride. The measured wt frac were Xp = 0.0001287, and x u = 0.006218. 

In preparation for carrying out a hydrolysis reaction, a 1-molar aqueous solution of KOH at lOOdC is to be produced using a baffled stirred tank. The vessel has a diameter of 4 m with 0.3-m-long impeller blades d and a volume of approximately 50 m. The required amount of potassium hydroxide is 2500 kg (p = 2000 kg/m ) and its saturated concentration 900 kg/m. In addition, we set the number of revolutions N at 1 S . Other data are as follows ... 

Fignre 5-lfl shows the outline of a simple baffled stirred tank containing a Rushton turbine on a centrally mounted shaft. The tank has diameter T. The impeller has diameter D and is located a distance C off the bottom of the tank. These symbols are used throughout the chapter. 

---