Effect of stirrer speed

As the stirer speed increases, not only the average droplet size is reduced, but also the droplet size distribution is markedly narrowed [125, 166]. This situation is graphically shown in Fig. 6.1. A bunching of the curves is realized, if, as in Fig. 6.2, the abscissas and the ordinates are standardized with the corresponding median value dsfl. 

If the results in Fig. 6.2 are plotted on double-logarithmic probability paper. Fig. 

a curve is obtained, which can be approximated by two straight lines, whereby that for dp/dso 1 is steeper than that for dp/dso 1- Chen and Middleman [73] obtained similar droplet size distributions for a 6-blade turbine stirrer and 14 different organic liquids in water, whereby, however, the value with = 0.001 to 0.005 was kept low. Judat found similar results for propeller and turbine stirrers for the cyclohexane/water system, see Fig. 6.4. 

2 With the median value dso standardized volume density distribution q3(dp/d5o) as a function of dp/dso for the 6-blade turbine impeller at different stirrer speeds and four different chlorohydrocarbons in water ( = 0.2) from [166] 

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Figure 5 Effect of stirrer speed during ethanolamine dehydrogenation over unpromoted skeletal copper under standard conditions for particles with different sizes.

Figure 8.6 The effect of stirrer speed on turnover frequency for the hydrogenation of benzene to cyclohexane. (Note that the turnover reaches its maximum at lower stirrer speed for the ionic liquid). , ionic liquid , water...

Experimental results for the effect of stirrer speed on the rate of filtration of a 10 per cent by mass suspension of clay are shown in Figure 7.4 taken from the work of Tiller and Cheng1 0, in which the filtrate volume collected per unit cross-section of filter is plotted against time, for several stirrer speeds. 

Fig. 9. Influence of hydrodynamic conditions and sulfite concentration on volumetric average rate of absorption tp (L2). (a and b) Cylindrical wetted wall effects of liquid flow rate, pH, sulfite concentration, (c) Stirred vessel, effect of stirrer speed, (d) Conic wetted wall, effect of liquid flow rate and pH.

Figure 6.2 Effect of stirrer speed on byproduct formation. (After Ref. 3.)...

Figure 6.3 Effects of stirrer speed and feed location on segregation index in a...

Figure 6.7 Effect of stirrer speed on the phase inversion boundary for cyclohexane and NPE surfactants (2 wt%)...

Effect of Stirrer Height—P igure 99, taken from data by Kammermeyer (1941), indicates the effect of stirrer height on the ratio Hu/H0. The data apply to a 19 percent suspension of calcium carbonate. The stirrer speed was adjusted to 2 rpm. From the curve shown in the... 

The true intrinsic kinetic measurements require (1) negligible heat and mass transfer resistances by the fluids external to the catalyst (2) negligible intraparticle heat and mass transfer resistances and (3) that all catalyst surface be exposed to the reacting species. The choice of the reactor among the ones described in this section depends upon the nature of the reaction system and the type of the required kinetic data. Generally, the best way to determine the conditions where the reaction is controlled by the intrinsic kinetics is to obtain rate per unit catalyst surface area as a function of the stirrer speed. When the reaction is kinetically controlled, the rate will be independent of the stirrer speed. The intraparticle diffusional effects and flow uniformity (item 3, above) are determined by measuring the rates for various particle sizes and the catalyst volume, respectively. If the reaction rate per unit surface area is independent of stirrer speed, particle size, and catalyst volume, the measurements can be considered to be controlled by intrinsic kinetics. It is possible... 

Solution As an approximation assume that the effect of agitator speed on kiOg is the same as shown in Fig. 10-7 for solution of oxygen in aqueous solutions. The power input P will be approximately proportional to the 2.5 power of the stirrer speed N. Then the ratio of (P/IOn to P/I tso will be as follows ... 

FIGURE CS11.1 The three-phase catalytic reactor (a) concentration profiles of gas and liquid phase components (b) effect of impeller speed on overall rate of reaction and (c) effect of particle size on overall rate of reaction at stirrer speeds higher than N. (From Patwardham, A. W. and Joshi, J. B., 1998.)... 

A gas/liquid reaction is carried out semi-batchwise in a stirred reactor. The reaction is first ord with respect to each of the reactants. The concentration of B, that originally was 1.00 gmol/1, is analysed every 5 minutes. One finds 0.563, 0.250, 0.125, 0.004 and 0.000 gmoI/1. What can be deduced from these data And what is Ae expected effect of an increase of stirrer speed ... 

It follows from x (Table II) and eqns (12,13) that is appreciably lowered by viscosity effects that occur during reaction. In practice this tendency is counteracted by both the interface temperature rise and free convection, driven by density and/or surface tension gradients. Both effects lower the extent of interface viscosity increase. Thus, a k is obtained which is independent of stirrer speed and lower than that for forced convection in the absence of interface viscosity effects as given in Figure 2. 

Effect of pressure on rate of reaction. Temperature, 25-26 °C hydrogen flow, 27.6 x 10-5 mole/sec catalyst weight, 0.976 g stirrer speed, 1500 rpm. 

The effect of temperature satisfies the Arrhenius relationship where the applicable range is relatively small because of low and high temperature effects. The effect of extreme pH values is related to the nature of enzymatic proteins as polyvalent acids and bases, with acid and basic groups (hydrophilic) concentrated on the outside of the protein. Finally, mechanical forces such as surface tension and shear can affect enzyme activity by disturbing the shape of the enzyme molecules. Since the shape of the active site of the enzyme is constructed to correspond to the shape of the substrate, small alteration in the structure can severely affect enzyme activity. Reactor s stirrer speed, flowrate, and foaming must be controlled to maintain the productivity of the enzyme. Consequently, during experimental investigations of the kinetics enzyme catalyzed reactions, temperature, shear, and pH are carefully controlled the last by use of buffered solutions. 

The parameter estimation is made in a stirred Lewis-type cell (Fig. 10.11) where, in the plateau region, chemical reaction prevails. With increasing stirring speed the initial mass transfer rates will increase as diffusional effects are diminished and a plateau is reached where mass transfer is independent of diffusion, as discussed elsewhere [31, 46]. A further increase in stirrer speed will disrupt the planar interface, leaving the operating area for determining the kinetics parameters. 

FIG. 19-35 Effect of aeration number and stirrer speed on the power number— N increases in order of Nx < N% < < N4. [Adapted from Baldi, Hydrodynamics... 

The importance of incorporating a rigorous treatmentT of the film heat and mass transfer processes is that interfacial conditions are determined whilst conversion and colour development are being predicted. Fig. 6(a) shows the predicted variation of interface temperature T with time for conditions corresponding to ] ig. 4(a)(variation in gas composition at N=400 rpm and G=2.3 mol s ). Substantial interface temperatures appear to accompany the absorption. For 9-8 SO, the initial temperature is 120°C above the bulk of 60°C. T then rails as complete conversion is approached. Even for 2.7 SO, the initial temperature increase is 25°C. A similar effect is observed in Fig. 6(b) with the highest T occurring for the lowest stirrer speed of 100 rpm. Absorption in the stirred cell is evidently quite exothermic. 

A correlation of k. has been derived in this work. It is found that this correlation agrees well with available literature evidence. Stirrer speed and power input have little effect on... 

In the representation of power characteristics, Ne(Re) curves for stirrers in Newtonian and non-Newtonian liquids under identical geometric conditions coincide if the Reynolds number has been formed by the effective viscosity iie((. According to the concept of Metzner and Otto [39], a direct proportionality between the stirrer speed, n, and the shear rate, y, exists ... 

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