Blade Turbines water

Calderbank (Cl) obtained similar results for the air-water system with a six-blade turbine. His data for gas holdup could be expressed as... 

Harriot (1962) measured the mass transfer coefficients in baffled tanks, using six-blade turbines and several liquids such as water and glycerine. According to that study,... 

Fig. 6. Continuous extraction of w-butylamine from kerosene into water with 6-in. flat-bladed turbines. Vessel diameter = 14.75 in., 7.5 g.p.m. kerosene, 4.78 g.p.m. water, residence time = 1.08 min. Data of Overcashier et al. (03).

Figure 10.11. Power consumption, (a) Ratio of power consumptions of aerated and unaerated liquids. Q is the volumetric rate of the gas (O) glycol ( X ) ethanol ( ) water. [After Calderbank, Trans. Inst. Chem. Eng. 36, 443 (1958)]. (b) Ratio of power consumptions of aerated and unaerated liquids at low values otQ/Nd3. Six-bladed disk turbine ( ) water ( ) methanol (10%) (A) ethylene glycol (8%) (A) glycerol (40%) Pg = gassed power input P = ungassed power input Q = gas flow rate IV = agitator speed d = agitator-impeller diameter. [Luong and Volesky, AIChE J. 25, 893 (1979)].

For an unaerated agitated vessel with a six-bladed turbine stirrer, the data for oxygen-water were also correlated using the relation... 

Rushton et al. (R16) also made a few measurements on turbines, using the same concentric tank arrangement but somewhat modified as shown by the dotted lines in Fig. 1. For turbines with flat blades mounted on the edge of a disk, the discharge was about 0.063 ft.3/revolution for a 6-in. diameter turbine with three blades, and about 0.074 ft 3/revolution for one with four blades. In a later publication Rushton (Rll) has stated (without data) that the flow of water from a similar six-blade turbine can be computed by the relation ... 

Tennant (T2) also studied velocity distributions, using a six-blade turbine and two viscous corn syrup solutions as well as water. For impeller speeds in the range of 100-200 r.p.m., his results generally confirm those of Sachs. A 300-fold increase in viscosity reduces the fluid velocity by about 30%. Comparison with Sachs data indicates that increasing the number of turbine blades from four to six increases the radial velocities by roughly 10-50%, depending on impeller speed and on radial position in a manner as yet undefined. 

Early data on impeller power requirements (H9) indicated a proportionality between power input and roughly the cube of impeller speed for a sand-water mixture. Data taken by Mack and Marriner (M4), using flat-blade turbines in baffled tanks, also have shown the power requirements to vary with the cube of impeller speed. These sketchy results seem to suggest the use of the one-liquid-phase power correlations of Section III, possibly with some appropriate density and viscosity corrections as in the case of liquid-liquid systems. If the opportunity exists, actual measurements on the system of interest should be made. 

Oyama and Endoh (012) studied the solution of sugar in water in 6.7- and 10.8-in. baffled vessels using paddles and flat-blade turbines. They report a mass-transfer coefficient which was proportional to the cube root of the particle diameter and to the cube root of the impeller power consumption per unit mass of agitated liquid. 

Rushton et al. (R15) gave the first data on the use of vertical coils to act as baffles as well as heat transfer surfaces. Using Mixing Equipment Company flat-blade turbines, they noted that the heat transfer was best when the turbine was midway between tank bottom and water surface, based on tests with the liquid depth equal to tank diameter. The entries in Table VI are for this condition. Values of heat transfer coefficients on the order of 300-1200 B.T.U./(hr.) (ft.2) (°F.) were observed. Only one liquid was used and only a small Reynolds-number range was covered. 

The plant operation utilized a curved-blade turbine (CBT) impeller and a subsurface addition line that was suspected to be in a nonoptimum position and was too large in diameter. Presumably, the CBT was causing excessive shear and generating fines from the agglomerates. The position of the subsurface line, and its size, were suspected of promoting nucleation in the immediate region of the water stream inlet, an issue discussed in Section 6.4.4.1. 

In a baffled vessel with flat bottom and a pitched-blade turbine the flow conditions were made qualitatively visible by laser sheet flow visualization and quantified by LDA-measurements [376]. The measurements with water and glycerine solutions were limited to turbulent and intermediate range. The flow visualization showed turbulent macro-instabilities as vortices between the stirrer and the liquid surface. These macro-structmes characterised an organized modification of the flow pattern, creating a transient violent flow activity in the upper part of the vessel which contradicted the view that turbulence had a completely random character. 

In [655] measurements of the concentration profiles were presented which were measured in a vessel with contoured bottom (see Fig. 5.18a) and a 45°-pitched-blade turbine. Material system glass beads in water. 

Fig. 6.1 Volume density distribution <73 (dp) as a function of dp for the 6-blade turbine stirrer at four different stirrer speeds in the material system trichloroethene/water (y> = 0.2) from [166]... 

Kipke [276] investigated the effect of different stirrer types and their d/D ratios on the droplet size and its distribution. This study utilized the already mentioned coalescence-prone camauba wax/water system (type 2442 p = 825 kg/m, pj = 2 mPa s at 95°C). The wax/water dispersion could be frozen in with ice water and the droplet size distribution determined by sieving. The stirrer types investigated were 2-stage Intermig d/D — 0.5 0.6 0.7) propeller stirrer (d/D = 0.31 0.37) pitched-blade turbine d/D = 0.31) 6-blade turbine stirrer, Pfaudler impeller stirrer (d/D = 0.575). The experimental data are presented in Fig. 6.7. It is evident that in this material system the droplet size distribution extended to dp/d32 = 0.4-1.5. 

Fig. 6.12 Sequences of integral distributions with time. Symbols - experimental data (CCI4, 50% -h iso-octane, 50%)/water 6-blade turbine stirrer from [392]...

This was developed for pitched-blade turbines for air and water as the working fluids. In industrial practice, the physical properties of the fluids are likely to be dramatically different. Therefore, the constant in the equation may vary, but its values can be obtained with a few experiments in the laboratory. The new correlation thus obtained can be used for scale-up. Holdup correlations for other impellers are given elsewhere (Mhetras et al., 1994 McFarlane and Nienow, 1996). 

The power number decreases with an increase of the Reynolds number and reaches a constant value (6 for a flat six-bladed turbine) when the Reynolds number is greater than 10,000. At this point, the power number is independent of the Reynolds number. For the normal operating conditions of gas-liquid contact, the Reynolds number is usually greater than 10,000. For example, for a 3-inch impeller with an agitation speed of 150 rpm, the impeller Reynolds number is 16,225 when the liquid is water. Therefore, for a six flat-bladed turbine, the power number is... 

A fermentation broth contained in a batch-operated, stirred-tank fermentor, with a diameter D of 1.5 m, equipped with a flat-blade turbine with a diameter of 0.5 m, is rotated at a speed N= 3 s. The broth temperature is maintained at 30 °C with cooling water at 15 °C, which flows through a stainless steel helical coil, with an outside diameter of 40 mm and a thickness of 5 mm. The heat evolution by biochemical reactions is 2.5 x 104kJ h 1, and dissipation of mechanical energy input by the stirrer is 3.5 kW. Physical properties of the broth at 30 °C density p = 1,050 kg m , viscosity p — 0.004 Pa s, specific heat cp = 4.2kj kg-1 °C-1, thermal conductivity k = 2.1 kj h 1 m 1 °C 1. The thermal conductivity of stainless steel is 55kJh-1m-loC-1. 

Example 9.5. An agitated vessel 6 ft (1.8 m) in diameter with a working depth of 8 ft (2.44 m) is used to prepare a slurry of 150-mesh fluorspar in water at 70 F. The solid, has a specific gravity of 3.18, and the slurry is 25 percent solids by weight. The impeller is a four-blade pitched-blade turbine 2 ft (0.61 m) in diameter set 1.5 ft above the vessel floor, (a) What is the power required for complete suspension (b) What is the critical stirrer speed ... 

A pilot-plant reactor, a scale model of a production unit, is of such size that 1 g charged to the pilot-plant reactor is equivalent to 500 g of the same material charged to the production unit The production unit is 2 m in diameter and 2 m deep and contains a six-blade turbine agitator 0,6 m in diameter. The optimum agitator speed in the pilot-plant reactor is found by experiment to be 330 r/min. a) What are the significant dimensions of the pilot-plant reactor (b) If the reaction mass has the properties of water at 70°C and the power input per unit volume is to be constant, at what speed should the impeller turn in the large reactor (c) At what speed should... 

---