Impellers disc-type turbines

Impeller types usually used with mixing and listed in decreasing order of high volume ability (hence in increasing order of high head ability or requirement) are paddle, turbine, propeller, sawtooth impeller or propeller, cut-out impeller disc (no blades), colloid mill. 

Recently, in contrast to the traditional small impellers, a large impeller has been manufactured in Japan. In general, it has been said that the disc turbine-type, turbine-type, and pitched-type impellers mainly produce radial, tangential,... 

A more common impeller classification is by flow leaving the impeller zone. Impellers can be classified into radial or axial flow impellers. Some examples of radial flow impellers are the Narcissus impeller (NS), concave blade disc turbine (Figure 6.11), (Chemineer) BT-6, and the multibladed disc turbine. A six-bladed disc turbine, shown in Figure 6.12, is often referred to as a Rush ton-type turbine (RT) (Ulbrecht and Patterson, 1985). The standard blade is DJ long and D,/5... 

Concave blade disc turbines are of interest in gas-liquid dispersion because they are able to handle more gas than Rushton-type turbines before flooding (Smith et al., 1977 Vasconcelos et al., 2000). The mass transfer capacity for the concave blade disc turbine is very similar to the Rushton-type turbine, but Chen and Chen (1999) found that the blade curvature could be optimized for a certain power input to produce higher gas-liquid mass transfer coefficients. Unlike the Rushton-type turbine, the concave blade disc turbine requires the cup orientation to be in the direction of impeller rotation (Tatterson, 1994). 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

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

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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