Impeller flat blade disc turbine

Radial-flow impellers include the flat-blade disc turbine, Fig. 18-4, which is labeled an RlOO. This generates a radial flow pattern at all Reynolds numbers. Figure 18-17 is the diagram of Reynolds num-ber/power number curve, which allows one to calculate the power knowing the speed and diameter of the impeller. The impeller shown in Fig. 18-4 typically gives high shear rates and relatively low pumping capacity. 

Problem A recently built reactor, equipped with a flat-blade disc turbine, does not satisfy the process requirements. By examining the hquid surface, the operator suspects that the gas is rising straight through the impeller to the hquid surface. In other words, the impeller is flooded. The mass-transfer rate is usually lower when the impeller is flooded than when it is able to completely disperse the gas. Pertinent information about the reactor is T = 2m D = 0.8m N = 1.13rps Qg = 0.12m /s /i = 1 cP p = 1,000 kg/m Na = 0.21 Npr = 0.1. 

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). 

The most common impellers are the marine impeller or disc flat-blade turbine the flowpatterns which typically result are illustrated in Fig. 15-22. 

Figure 7.21. Variation in turbine impeller designs (a) Flat blade (b) Disc flat blade (c) Pitched vane (d) Curved blade (e) Tilted blade (/) Shrouded (g) Pitched blade (h) Pitched curved blade (7) Arrowhead...

The impellers used in this study are shown in Figure 1. They are both of the radially discharging type which is characterized by a strong radial jet of fluid that moves out to the vessel walls while entraining fluid from above and below. Near the wall it splits into two circulation zones. The flat blade turbine (FBT) is commonly used in industry and consists of a disc with several paddles fixed normal to the disc which serve to generate the radial flow. The novel impeller design... 

Three types of impellers are commonly used in the low viscosity region, propellers, Fig. 1 turbines. Fig. 2 and axial flow turbines. Fig. 3. Impellers used on small portable mixers shown in Fig. 4, are oflen inclined at an angle as well as being off-center to give a good top-to-bottom flow pattern in the system. Fig. 5. Large top-entering drives usually use either the axial flow turbine or the radial flow flat blade turbine. For aerobic fermentation, the radial flow disc turbine is most common and is illustrated in Fig. 6. 

Figure 16.2 S values for three different impellers, (a) propeller (b) disc turbine (c) flat paddle (two blades, width 0.5D) ...

Figure 4.1. Stirred vessels with baffles, and common impeller types flat disc turbine, propeller, and pitched blade impeller.

We find then that the coefficient P is between 2 and 4 for propellers and pitched blade impellers, and between 1 and 2 for flat disc turbines. That would mean that the latter are the most power-effective mixers. 

In those gas/liquid processes where the gas flow is not sufficient for obtaining an effective contact between the phases, a stirrer can be used for disperging the gas. This applies particularly to small and medium sized reactors. A turbine impeller combined wiA baffles is quite effective (see figure 4.1). The gas can best be introduced via a perforated ring that is placed underneath the impeller. Another well known impeller type has a hollow shaft and hollow blades, through which the gas is sucked from the gas space and introduced into the liquid at the blade tips. When a common flat disc turbine is used, the gas phase is dispersed into small bubbles that circulate with the liquid in upward and downward directions (compare section 4.2.1). Particularly in the zones with lower flow rates, the bubbles will coalesce at a certain rate. A fraction of the larger bubbles will return with the circulating liquid flow to the impeller zone, where they are redispersed, but the... 

Rushton turbine A type of impeller used for gas dispersion such as in biochemical reactors and consists of a flat disc with six vertical flat blades mounted on the circumference (see Fig. 54). It therefore provides radial-flow mixing. It is named after American chemical engineer John Hetuy Rushton (1905-85), who was noted for his work on mixing. There have been many subsequent modiflcations and improvements to the basic design. 

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