Propeller-type impellers

Use well-designed, specialized polymer dissolution systems wherever possible (such as those from the U.S. Filter, Inc. subsidiary, Strandco ), especially for emulsion polymers, rather than simple dissolving tanks and mixers with propeller-type impellers. This prevents undissolved lumps of polymer (fish-eyes) and the breakdown of polymer chains. Always install a strainer to prevent possible pump clogging. 

Naturally, the patterns of liquid movements will vary with the type of impeller used. When marine propeller-type impellers (which often have two or three blades see Figure 7.7c) are used, the liquid in the central part moves upwards along the tank axis and then downwards along the tank wall. Hence, this type of... 

Propeller types pump li( uid. Every revolution of a square pitch prop discharges a column of liquid approximately equal to the diamf ter of the propeller. The flow is iixial. Such pumps are used primarily for high-speed applications and side-entry mixers. Duel propellers are used on vessels with H/D ratios greater than 1. The axial flow decreases mLx time. They are heavier and cost more than pitched-blade turbines. Propeller-to-vessel-diameter ratio is usually Vs- A propeller-type impeller is used for high flow. 

As mentioned earlier, these impellers operate at relatively high speeds and are effective only in low to medium viscosity liquids. In most cases, the main flow in the vessel tends to be transitional and/or turbulent. For shearthinning polymer solutions and particulate suspensions agitated by paddle, turbine and propeller type impellers, many correlations of varying complexity and form are available for the estimation of the outside film coefficient. One such correlation, based on wide ranges of conditions (400 < Re < 10 4 < Pr < 1900 0.65 < /ieff < 283mPa s), is due to Edney and Edwards [1976] ... 

For propeller-type impellers, there is an almost constant power number in the region of 0.2 < D < 0.5. In contrast to this, for the disk turbine the power number decreases in the same range by about 20% with increasing diameter. 

The draft tubes of the reaetor are hollow in order to allow eooling or heating fluid to eireulate. The 300-ml laboratory-seale reaetor (1) is geometrieally similar to the larger reaetors. A marine-type impeller (propeller) provides a smooth and even flow field throughout the reaetor. 

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. 

Jacketed cast iron hemispherical bottom vessel Propeller—no baffles T/D = 2.5 U-Type impeller—no baffles. T/D = 1.05 0.67 1... 

Axial flow impellers, 16 672-673, 684 Axial-flow propeller-type pumps, 22 67, 68 Axially split pumps, 22 67, 68 Axial Peclet number, 10 763 Axial undulations, in hemodialysis, 26 830-831... 

Figure 7.10. Some types of impellers for centrifugal pumps, (a) Open impeller, (b) Semiopen impeller, (c) Shrouded impeller, (d) Axial flow (propeller) type, (e) Combined axial and radial flow, open type, (f) Shrouded mixed-flow impeller, (g) Shrouded impeller (P) in a case with diffuser vanes (V). (h) Turbine impeller.

Propeller jacket 2 x 103 D 0.54 0.67 0.25 0.14 Limited data, but a large 5 ft diameter tank used, marine-type impeller used at 45° pitch and located at the midpoint of tank. No baffles used 34... 

Flow patterns in a mechanically agitated reactor with disk turbine, pitched-blade turbine, and propeller types of agitator are schematically illustrated by Joshi et al. (1982). The flow pattern in the presence of gas is described later in the section on slurry reactors. In each of these cases, the dimensionless velocity profile with respect to the impeller tip velocity has been found to be independent of the impeller speed and has shown slight dependence on the impeller diameter. 

Loiseau et al. (1977) found that their data for nonfoaming systems agreed well with Eq. (3.3). Calderbank (1958), Hassan and Robinson (1977), and Luong and Volesky (1979) have also proposed correlations for power consumption in gas-liquid systems. Nagata (1975) suggested that power consumption for agitated slurries can be reasonably predicted from these correlations by the correction factor psi/pL, where psl is the density of the slurry. Power consumption for a gas-liquid-solid system has also been studied by Wiedmann et al. (1980). They examined the influence of gas velocity, solid loading, type of stirrer, and position of the stirrer blades on power consumption plots of power numbers vs. Reynolds numbers for propeller and turbine type impellers proposed by them are shown in Fig. 13. 

Horizontal contactors are essentially bubble columns with an aspect ratio less than one, and the gas is sparged at the bottom as turbulent jets. In order to get fairly uniform gas-liquid dispersion, multiple injection points are employed for the gas. The gas-liquid contact can be further improved using impellers (Fig. 33). The impellers are of a modified propeller type and are mounted on a horizontal shaft. 

Figure 4.4 shows various types of impellers that are used in centrifugal pumps. The one in a is used for axial-flow pump. Axial-flow pumps are pumps that transmit the fluid pumped in the axial direction. They are also called propeller pumps, because the impeller simply propels the fluid forward like the movement of a ship with propellers. The impeller in d has a shroud or cover over it. This kind of design can develop more... 

In reactor 1, plastic particles are fed into the top of a bed of glass beads as the heat-medium-particles, and the particles are then melted and adhered to the beads. The glass beads are stirred slowly by two equipped impellers, one of which is the propeller-type of impeller, and the other is an anchor-type of impeller located at the bottom of the bed of glass beads. The propeller-type of impeller is turned to lift the particles. In this manner, the glass beads at the top layer of the bed of glass beads are replaced continuously by... 

In a vertical cylindrical tank, the depth of the liquid should be equal to or somewhat greater than the diameter of the tank. If greater depth is desired, two or more impellers are mounted on the same shaft, and each impeller acts as a separate mixer. Two circulation currents are generated for each impeller, as shown in Fig. 9.5. The bottom impeller, either of the turbine or the propeller type, is mounted about one impeller diameter above the bottom of the tank. 

The V-Al oxide precursor was prepared by co-precipitation of ammonium metavanadate and aluminum nitrate solutions [2,7,8]. At the lab-scale (up to 100 g of solid), a 6-liter temperature-regulated glass reactor (LabMax from Mettler) equipped with a U-type impeller was used for the precipitation. This apparatus allows to control and record the pH, temperature, rates of reactants addition, and stirring during the whole precipitation process. At pilot-scale (1 kg of solid), an 80-liter stainless steel precipitation tank was used. This tank is equipped with a double jacket for heating or cooling the slurry, pH and temperature control systems. The stirring in the tank was achieved with a propeller (boat-like) at about 200 rpm. For both scales, the pH... 

Inferential meters include instruments in which the volumetric flow rate is inferred by the movement of a turbine, propeller, or impeller. The fluid impinging on a blade causes it to rotate at an angular velocity that is proportional to the flow rate. The early anemometers made with plates and cups are examples. These types of meters are becoming less and less common due to the need to calibrate and compensate for effects like viscosity. According to Crabtree (2009), the Coriolis and ultrasonic meters are replacing the turbine meters in most industrial applications. 

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