For stirred tanks

Figure 11 shows the reference floe diameter for viscometers as a function of shear stress and also the comparison with the results for stirred tanks. The stress was determined in the case of viscosimeters from Eq. (13) and impeller systems from Eqs. (2) and (4) using the maximum energy density according to Eq. (20). For r > 1 N/m (Ta > 2000), the disintegration performance produced by the flow in the viscosimeter with laminar flow of Taylor eddies is less than that in the turbulent flow of stirred tanks. Whereas in the stirred tank according to Eq. (4) and (16b) the particle diameter is inversely affected by the turbulent stress dp l/T, in viscosimeters it was found for r > 1.5 N/m, independently of the type (Searle or Couette), the dependency dp l/ pi (see Fig. 11). 

While in Fig. 16 selected results are plotted against the average energy density e = P/V9, in Fig. 17 all of the essential results for stirred tanks and bubble... 

For reactors with free turbulent flow without dominant boundary layer flows or gas/hquid interfaces (due to rising gas bubbles) such as stirred reactors with bafQes, all used model particle systems and also many biological systems produce similar results, and it may therefore be assumed that these results are also applicable to other particle systems. For stirred tanks in particular, the stress produced by impellers of various types can be predicted with the aid of a geometrical function (Eq. (20)) derived from the results of the measurements. Impellers with a large blade area in relation to the tank dimensions produce less shear, because of their uniform power input, in contrast to small and especially axial-flow impellers, such as propellers, and all kinds of inclined-blade impellers. 

For stirred tanks with hold-ups up to 0.35 the constant K = 0.024 ( 1For reciprocating-plate extraction columns K = 0.I8, while for pulsed perforated-plate columns AT = 0.18 Kirk-Othmer Encyclopedia of Technology, 1978-1984). 

Multiplying this value by a safety factor of 1.05 (the value for stirred tanks) we obtain V] = 1.23 m . For the vessel 2,... 

There are a variety of limiting forms of equation 8.0.3 that are appropriate for use with different types of reactors and different modes of operation. For stirred tanks the reactor contents are uniform in temperature and composition throughout, and it is possible to write the energy balance over the entire reactor. In the case of a batch reactor, only the first two terms need be retained. For continuous flow systems operating at steady state, the accumulation term disappears. For adiabatic operation in the absence of shaft work effects the energy transfer term is omitted. For the case of semibatch operation it may be necessary to retain all four terms. For tubular flow reactors neither the composition nor the temperature need be independent of position, and the energy balance must be written on a differential element of reactor volume. The resultant differential equation must then be solved in conjunction with the differential equation describing the material balance on the differential element. 

The responses of a single ideal stirred tank reactor to ideal step and pulse inputs are shown in Figure 11.4. Note that any change in the reactor inlet stream shows up immediately at the reactor outlet in these systems. This fact is used to advantage in the design of automatic control systems for stirred tank reactors. 

In this work Ketjen CK. 3QD type alumina was used as support.Different particle size were used depending on the application (0.03--0.05 mm and D. 11-0.63 mm for stirred tank and trickle bed reactors,... 

In Equation 2.21, the index i refers to all compounds of the reaction mass and to the reactor itself. However, in practice, for stirred tank reactors, the heat capacity of the reactor is often negligible compared to that of the reaction mass. In order to simplify the expressions, the heat capacity of the equipment can be ignored. This is justified by the following example. For a 10 m3 reactor, the heat capacity of the reaction mass is in the order of magnitude of 20000kJ K 1 whereas the metal mass in contact with the reaction medium is about 400 kg, representing a heat capacity of about 200 kj K"1, that is, ca. 1% of the overall heat capacity. Further, the error leads to a more critical assessment of the situation, which is a good practice... 

Figure 1.1 Design and development cycle for equipment-based design using pre-decided equipment, a mixing configuration is chosen by correlations and experience. For stirred tanks this configuration is given, e g., by the power-to-volume ratio P/V and the impeller diameter N. Then, CFD models are made to describe the flow field [1],...

The optimum proportions for stirred tank reactors are when the liquid level is equal to the tank diameter, but at high pressures slimmer proportions are economical. 

Table 7 lists these and a number of other scale-up criteria for stirred tanks. Here it is assumed that the fluid is the same on scale up, i.e. density and viscosity are both constant, and that the vessel is operating in the fully turbulent, constant power number regime. 

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. 

Much more information is available on the product ky a than on kl and a separately. For low solids concentrations it may be assumed that the solids do not affect the value of A a, so that the existing relations for two-phase gas-liquid reactors can be applied. For reviews on these relationships, see Lee and Foster [76], for draft tube slurry reactors Goto et al. [77], for bubble columns Deckwer and Schumpe [78] and Deckwer [79], and for stirred tank reactors Mann [80] and Schluter and Deckwer [81]. Despite of much research published on the influence of solids on k a there is still no universally applicable relation describing the influence of all types of particles in any weight fraction in any liquid. 

The approach based on the energy dissipation rate is not limited to a particular type of slurry reactor. Therefore, equations of type 46 and 52 have also been proposed for stirred-tank reactors. For e the total energy dissipation rate originating from both gas and power inputs via the stirrer must then be used. Hence,... 

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