Flat Blade Disk Turbine

The actual mixing effect is predominantly in the shear zone of the radial emerging jet. 

---

For tbe flat-blade disk turbines, at a spacing equal to 1.5d or greater, tbe combined power for both will approximate twice tbat for a single turbine. 

Suppose that a flat-blade disk turbine with six blades is used and the agitation rate is 800 rpm. For the other characteristics of the tank assume a typical design configuration. 

Estimate the mass-transfer coefficient for the oxygen dissolution in water 25°C in a mixing vessel equipped with flat-blade disk turbine and sparger bv using Calderbank and Moo-Young s correlations. 

Calderbank (1958) correlated the mterfacial areas for the gas-liquid dispersion agitated by a flat-blade disk turbine as follows ... 

The power required by an impeller in a gas sparged system Pm is usually less than the power required by the impeller operating at the same speed in a gas-free liquids Pmo. The Pm for the flat-blade disk turbine can be calculated from Pmo (Nagata, 1975), as follows ... 

A cylindrical tank (1.22 m diameter) is filled with water to an operating level equal to the tank diameter. The tank is equipped with four equally spaced baffles, the width of which is one tenth of the tank diameter. The tank is agitated with a 0.36 m diameter, flat-blade disk turbine. The impeller rotational speed is 4.43 rps. The air enters through an open-ended tube situated below the impeller and its volumetric flow rate is 0.0217 m3/s at 1.08 atm and 25°C. Calculate ... 

Flat blade disk turbine 4.6 Radial with high shear effect... 

With the help of experimental data in three (12.2, 19.0, and 22.9 cm diameter) flat-bottom vessels with an eight-flat-blades disk turbine stirrer and four baffles, they obtained a relationship... 

Calculate the mass transfer coefficient, kL, for dissolution of oxygen from the air into 25°C water at 1 atm in a mixing vessel equipped with a flat-blade disk turbine and sparger. At those conditions, the diffusivity of oxygen in water, DAB, is 2.5 x 10 9 m2/s, the viscosity of water is 8.904 x 10-4 kg/(m-s), and the density of water is 997.08 kg/m3. Use Calderbank and Moo-Young s correlations (see Ref. 14). 

Laity and Treybal (LI) report on experiments with a variety of two-phase systems in a covered vessel which was always run full, so that there was no air-liquid interface at the surface of the agitated material. Under these circumstances no vortex was present, even in the case of operation without baffles. Mixing Equipment Company flat-blade disk-turbines were used in 12- and 18-in. diameter vessels whose heights were about 1.07 times their diameters. Impeller diameter was one-third of tank diameter in each case. For operation without baffles, using only one liquid phase, the usual form of power-number Reynolds-number correlation fit the data, giving a correlation curve similar to that given in Fig. 6 for disk-turbines in unbaffled vessels. In this case, however, the Froude number did not have to be used in the correlation because of the absence of a vortex. For two-phase mixtures, Laity and Treybal could correlate the power consumption results for unbaffled operation by means of the same power number-Reynolds number correlation as for one-phase systems provided the following equations were used to calculate the effective mean viscosity of the mixture For water more than 40% by volume ... 

Bakker, Smith, and Myers combined the results of Nienow and those of Warmoeskerken and Smith to establish an equation for the determination of the transition point at which the gas becomes completely dispersed in the liquid (in the regions both below and above the impeller). For flat-blade disk turbines, the expression that they found... 

The multiplying constant for concave-blade disk turbines is 0.058 instead of 0.025. This constant has a weak dependence (to the power of about 0.2) on the scale of the equipment. This inequality defines two regions delimited by a vertical line in the Fr vs. Flo flow map, for a given value of the D/T ratio. Nienow, Wisdom, and Middleton developed a relationship to predict the agitation speed of a flat-blade disk turbine at which gas recirculation occurs for a given gas rate. This expression... 

The equations above allow one to predict the operating conditions in any coalescing gas-liquid system equipped with a flat-blade disk turbine. A similar analysis and flow map have been produced for a concave-blade impeller such as the... 

The value of g/u in Eq. (6) can easily fall as low as 0.4 for 6-blade flat-blade disk turbines (Fig. 6) and downflow pitched-blade turbines and hydrofoils (Table 3). However, for modern impellers with parabolic concave blades (e.g., Scaba SRGT, Chemineer BT6, Lightnin R-130), g/u typically falls to only about 0.9 (and then only at high FIq values). The ability to deliver high power makes these impellers highly suitable for gas-liquid operations. 

Flat-blade disk turbine [27] Reactor diameter 0.33 0.54... 

---