Radial-flow turbines

The fluidfoil impellers (shown in Fig. 18-2) usually give more flow for a given power level than the traditional axial- or radial-flow turbines. This is also thought to be an advantage since the heat-transfer surface itself generates the turbulence to provide the film coefficient and more flow should be helpful. This is true to a limited degree in jacketed tanks (Fig. 18-34), but in helical coils (Fig. 18-35), the... 

An example of a typical turboexpander is shown in Fig. 29-46. Radial-flow turbines are normally single-stage and have combination impulse-reaction blades, and the rotor resembles a centrifugal-pump impeller. The gas is jetted tangentially into the outer periphery of the rotor and flows radially inward to the eye, from which the gas is jetted backward by the angle of the rotor blades so that it leaves the rotor without spin and flows axially away. 

Radial-flow turbines have been developed primarily for the production of low temperatures, but they also may be used as power-recovery devices. 

E. Eor radial flow turbine, locate 1.5D to 2.0D apart, with liquid coverage over the top impeller of minimum M to 3.0D, depending on surface motion desired. 

Although low shear emulsification equipment (mechanical stirrers or impellers) can differ in the type of fluid flow imparted to the mixture (axial-flow propeller or radial-flow turbines), no subclasses have been defined. 

Radial flow impellers have a much lower pumping capacity and a much higher macroscale shear rate. Therefore they consume more horsepower for blending or solids suspension requirements. However, when used for mass transfer types of processes, the additional interfacial area produced by these impellers becomes a very important factor in the performance of the overall process. Radial flow turbines are primarily used in gas-liquid, liquid-solid, or liquid-liquid mass transfer systems or any combinations of those. 

A new impeller is now being used for gas-liquid contacting, call the Smith Turbine. It is a radial flow turbine with blades as shown in Fig. 25. It is rotated in the concave... 

For highly exothermic reactions, it is necessary to maintain the temperature at a desired level. In general, the heat-transfer coefficient is proportional to (Pg/F)0 25-033, and the actual power cost varies linearly with (Pt/V) these dependencies lead to an optimum value of the reactor volume. For these reactions, when the demand for mass transfer is not important, the radial-flow turbine (curved blades) can be used for an efficient heat transfer. Optimum stirring conditions in the laminar flow regime have been evaluated by Zlokarnik and Judat (1988) and Pawlowski and Zlokarnik (1972). 

Figure 2. Schematic of velocity flow pattern from radial flow turbine, showing shear rate calculation...

Mass-transfer characteristics on large-scale equipment seem to be quite similar, but the fluidfoil impellers tend to release a larger-diameter bubble than is common with the radial-flow turbines. The blend time is one-half or one-third as long, and solid-suspension characteristics are better so that there have been notable improved process results with these impellers. This is particularly true if the process requires better blending and there is solid suspension. If this is not the case, the results from these impellers can be negative compared to radial-flow turbines. 

Fig. 1.5 Flow patterns in a baffled tank, generated by A - axial-flow propeller and a B - radial-flow turbine stirrer...

Figure 12. Velocity trace with time for three different impeller types, A310fluidfoil,A200 axial flow turbine and RlOO radial flow turbine. The impellers are compared at equal discharge pumping capacity, equal diameter and at whatever speed is required to achieve this flow. The power required increases from left to right.

Figu re 21. Typical velocity pattern coming from the blades of a radial flow turbine showing calculation of the shear rate AVI AY. 

Experiments made with the sulfite oxidation technique evaluate the overall KqO relationship for radial flow turbines and a very typical curve, shown in Fig. 3 8a gives the value of versus power and various gas rates. 

Figure 38. Typical curves oi K a versus power and various gas rates for radial flow turbines, (a) RlOO (b) A-315.

If it is desired to consider axial flow impellers in a gas-liquid system for any reason, it should be remembered that the upward flow of gas tends to negate the downward action ofthe pumping capacity ofthe axial flow turbine. A radial flow turbine must have three times more power than the power in the gas stream for the mixer power level to be fully effective. On the other hand, the axial flow impeller must have eight to ten times more power than in the gas stream for it to establish the axial flow pattern. 

Impellers available in the pre-1960 era would have been limited to four- and six-blade disc turbines (also known as radial-flow turbines or RFT or Rushton turbines), the four- and six-blade 45° pitch blade turbines (PBT), the four- and six-blade flat-blade turbines (FBT), and the three-blade retreat-curve impellers (RCI). 

Swirling flow pattern with a radial-flow turbine in an unbaffled vessel. (j4/ter Otdsluie. )... 

Figure 15.6 Flow patterns in a baffled tank reactor with axial-flow propeller and radial-flow turbine. (From ref. 55.)...

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