Radial flat blade disk turbine

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

A typical form of the radial flow impeller is the flat blade disk turbine, its typical flow pattern being illustrated in Figure 13.4. 

The effect of impeller elevation C on the power number is small for turbine impellers, especially the radial flow impellers. Figure 6-16 shows this effect for pitched blade (PBT), flat-blade (FBT), and disk flat-blade (DFBT) turbines with... 

To disperse gas, the gas is usually injected into the liquid from the bottom of the tank or near the impeller to enhance dispersion. Disk style turbines are found to be most convenient for gas dispersion because the disk disturbs the freely rising gas bubbles. The turbines with flat blades give radial flow and are very useful for gas dispersion where the gas is introduced just below the impeller at its axis and drawn up to the blades and chopped into fine bubbles. 

The power consumption of an impeller is the product of the pumping capacity (circulation fiow rate) and the velocity head, which is directly related to shear rate and turbulence. Depending on the type and size of the impeller, either the flow or the turbulence can be favored [110]. Axial flow impellers usually produce a fluid motion that is downward at the central axis of the vessel and upward in the wall region. They are designed to produce a high flow/power ratio with little turbulent loss. The designs of axial-flow impellers are derived from three-blade propellers. Radial-flow turbines produce a radial fluid motion from the impeller to the wall, where the radial flow separates into an upper and a lower circulation loop. They are characterized by a relatively low flow/power ratio, with much of the energy dissipated by turbulence around the impeller. Radial-flow turbines have flat blades or a disk with flat blades. 

Radial flow Flat-blade impeller, disk turbine (Rushton), hollow-blade turbine (Smith)... 

If it is turning at suitable speed, the impeller will break the gas up into very fine bubbles, which are swept out radially from the tip. In the imme ate vicinity of the impeller tip, the specific interfacial area is consequently very large. Coalesc-nece of the bubbles in the slower-moving liquid in other parts of the vessel increases the bubble diameter and lowers the local area. For moderate impeller speeds, only the gas fed to the impeller produces the specific interfacial area designated as but at higher impeller speeds, especially in small vessels, gas drawn from the space above the liquid contributes importantly to produce the larger mean specific area a. For disk flat-blade turbines, the specific area can be estimated from [23, 24, 84] ... 

Two different types of impellers for turbulent flow exist, radial impellers and axial impeller, as sketched in Fig. 7.2. The radial impellers project the fluid radially out from the blade towards the tank wall. The flow splits at the tank wall, and approximately 50 % of the fluid circulates towards the surface while the rest to the bottom, creating two regions of low mean velocity. The flow exiting the impeller blade forms a sharp velocity gradient with a strong peak at the impeller blade horizontal center line. Examples of radial flow impellers are disk style flat blade turbines (Rushton... 

Radial flow impellers may either have a disk (Rushton turbine) or be open (FBT) and may have either flat or curved blades (backswept mrbine). Impellers without the disk do not normally pump in a true radial direction since there is pressure difference between each side of the impeller. This is also true when the impellers are positioned in the tank at different off-bottom clearances. They can pump upward or downward while discharging radially. Radial discharge flow patterns can cause stratification or compartmentalization in the mixing tank. Disk-type radial impellers provide more uniform radial flow pattern and draw more power than open impellers. The disk is a baffle on the impeller, which prevents gas from rising along the mixer shaft. In addition, it allows the addition of a large number of impeller blades. Such blade addition cannot be done easily on a hub. A disk can also be used with a pitched blade turbine for use in gas-liquid mixing. 

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