Stirred Rushton Turbine impellers

Culture and bioconversion. The precultured cells were recovered by centrifugation at 4 °C and the cell pellet was inoculated into a 3 L fermenter (stirred tank with two Rushton turbine impellers and four baffles) containing 1.0 L of supplemented M9 medium. 

The cylindrical mixing tank simulated in this study has an ellipsoidal bottom with four equally spaced, wall-mounted baffles extending from the vessel bottom to the free surface, stirred by two centrally located six-blade Rushton turbine impellers. The tank diameter measured 0.138 m, and the baffle width was 0.008 m. The impeller diameter was 0.046 m (PIT=2) for both impellers. The distance between the impellers was 0.061 m. The bottom impeller center was positioned at a distance C=T/3 off the tank bottom. The liquid level was equal to the tank diameter, Z/7 =1.3. 

Fig. 8. This is a snapshot of a spatial particle distribution. The plane shown is the horizontal cross-section just below the disc of a Rushton turbine in a flat-bottomed stirred tank. The impeller revolves in the counter clockwise direction. Particle size is some 0.468mm Re = 1.5- - x 105 volume fraction amounts to 3.6% number of particles tracked in the simulation just over 6.7 million. Reproduced with permission from Derksen (2003).

An aerated stirred-tank fermenter equipped with a standard Rushton turbine of the following dimensions contains a liquid with density p = 1010kgm and viscosity n = 9.8 X 10 Pa s. The tank diameter D is 0.90 m, liquid depth Hl = 0.90 m, impeller diameter d = 0.30 m. The oxygen diffusivity in the liquid Dl is 2.10 X 10 5 cm- s T Estimate the stirrer power required and the volumetric mass transfer coefficient of oxygen (use Equation 7.36b), when air is supplied from the tank bottom at a rate of 0.60 m min at a rotational stirrer speed of 120 rpm, that is 2.0 s T... 

Fig. 7.16. Simulating the effect of a Rushton turbine on the flow one practice is to impose empirical profiles for the physical quantities like Vr, vg, k and e on the vertical control surface bounding the impeller-swept region in a stirred vessel [10].

The overall mixing pattern in a stirred tank is a function of the impeller type, and the phase ratios. Figs 2 shows mixing patterns derived from particle tracking techniques for (Fig. 2a) a pitched blade turbine and (Fig 2b) a Rushton turbine in the same vessel (100 mm diameter), with the same impeller diameter and rotation speed. It is evident that the overall patterns are very different. These patterns are in fact very time averaged and the actual trace of the "flow follower" particle indicates signifrcant randomness and chaos in... 

From systematic simulations of tracer experiments in a stirred vessel equipped with a Rushton turbine, a height/tank diameter ratio = 1.0, an im-peller/tank diameter ratio = 0.3125, and an impeller clearance/height of liquid ratio = 0.31 the following correlation was obtained ... 

FIGURE 7A.3 Some commonly used impellers for two-/three-phase stirred reactors, (a) Standard six-blade Rushton turbine, (b) Six-blade 45° pitched turbine, (c) Lightnin A315 . (d) SC ABA 6SRGT. (Reproduced from Middleton 2000 with permission from Elsevier. 1992.)... 

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. 

Imperfect stirred tank 0.652 for 6280 L, Rushton turbine with N = 24.4 rpm, feed at impeller discharge... 

Figure 20-6 Effect of yield stress on suspension motion in a stirred tank. Cm = 0.02 FBK suspension. The vessel is 30 cm in diameter with the suspension height set at 30 cm. A D = 10 cm diameter Rushton turbine was located 10 cm from the vessel floor. Impeller speeds are N = (a) 4, (b) 7, and (c) 14 rps. The red dye shows regions of suspension motion. In image (a) the cavan has not reached the vessel wall. See insert for a color representation of this figure.

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