Mixer propeller

Finish removers are manufactured in open or closed ketdes. Closed ketdes are preferred because they prevent solvent loss and exposure to personnel. To reduce air emissions from the solvents, condensers are employed on vent stacks. Mild steel or black iron ketdes are used for neutral or basic removers stainless steel (316 or 317) or reinforced polyethylene ketdes are used for acidic removers. The ketdes are heated to increase dispersion of paraffin waxes and aid in the mixing of other ingredients. Electric or air driven motors drive either sweeping blade or propeller mixers that give sufficient lift to rotate and mix the Hquid. Dispenser-type mixers are used to manufacture thick and viscous removers. Ketde, fittings, mixer, and fill equipment must be fabricated with materials resistant to the chemicals in remover formulas. 

For suspension of free-settling particles, circulation of pseudoplastic slurries, and heat transfer or mixing of miscible liqiiids to obtain uniformity, a speed of 3.50 or 420 r/min should be stipulated. For dispersion of dry particles in hquids or for rapid initial mixing of hquid reactants in a vessel, an 11.50- or 1750- r/min propeller should be used at a distance Df/4 above the vessel bottom. A second propeller can be added to the shaft at a depth below the hquid surface if the submergence of floating hquids or particiilate solids is other wise inadequate. Such propeller mixers are readily available up to 2.2 kW (3 hp) for off-center sloped-shaft mounting. 

Propeller mixers are used for mixing liquids with viscosities up to 2,000 cp. They are suitable for the formation of low-viscosity emulsions, for dissolving applications and for liquid-phase chemical reactions. For suspensions, the upper limit of particle size is 0.1 to 0.5 mm, with a maximum dry residue of 10%. 

Propeller mixers are unsuitable for suspending rapid settling substances and for the absorption of gases. Propellers are designed on the basis of data obtained from properly executed modeling experiments. 

For turbine mixers that the width of a baffle should not exceed more than one-twelfth of the tank diameter and, for propeller mixers, no more than one-eighteenth the tank diameter. With side-entering, inclined or off-center propellers, as shown in Figure 13, baffles are not required. Instead, shrouded impellers and diffuser rings may be used to suppress vortex formation. These devices contribute to flow resistance and reduce circulation by creating intense shear and abnormal turbulence... 

Figure 5-9. Theoretical circulating capacity of single propeller mixers. By permission, Fluid Agitation Handbook, Chemineer, Inc.

Figure 5-20 illustrates a vertical propeller mixer assembly, with vertical mounting with gear box and motor. Figure 5-21 is a typical right angle, vertical impeller shaft with horizontal gear and motor drive. 

Figure 5-20. Portable Vektorf vertical propeller mixer assembly. By permission, Lightnin (formerly Mixing Equipment Co.), a unit of General Signal.

Figure 5-23G. Side-entering propeller mixer position, large tanks. By permission, Rushton, J. H., Petroleum Refiner, V. 33, 1954, p. 101 [17].

Baffles can be omitted when propeller mixers are top mounted at an angular off-center position (see Figure 5-23D) and vortex swirling is prevented. This is not recommended for large povver systems on large tanks, due to shaft fatigue. 

Volume entrained into circular jet from propeller mixer, cu ft/sec Flow, gal/min Scale-up ratio... 

A solution of sodium hydroxide of density 1650 kg/m3 and viscosity 50 mN s/m2 is agitated by a propeller mixer of 0.5 m diameter in a tank of 2.28 m diameter, and the liquid depth is 2.28 m. The propeller is situated 0,5 m above the bottom of the tank. What is the power which the propeller must impart to the liquid for a rotational speed of 2 Hz ... 

Figure 7.9. Flow pattern from propeller mixer...

For producing an oil-water emulsion, two portable three-bladed propeller mixers are available a 0.5 m diameter impeller rotating at 1 Hz and a 0.35 m impeller rotating at 2 Hz. Assuming turbulent conditions prevail, which unit will have the lower power consumption ... 

Weber, A.P. Selecting Propeller Mixers, Chemical Engineering, Sept. 2, 1963, pp. 91-98. 

Applications. The munitions industry has several applications suited for infrared detectors. Conveyor belts passing through large covered ducts and explosive and propellant mixers are examples of the controlled environment necessary for proper application. 

Weber, A.P., Selecting propeller mixers, Chemical Engineering, 70, pp. 91-8 (2 Sept 1963). 

Another type of testing, that of electrostatic sensitivity, has been demonstrated in some cases to be more properly a delicate test of the ignitability of the material under localized thermal stress which correlates best to the friction sensitivity of the system under test rather than to electrostatic hazards. On the other hand, electrostatic tests done in the supposed atmosphere above a propellant mixer were reduced in absolute value by more than an order of magnitude when the ammonium perchlorate dust actually present was introduced in the test since this altered the potential path for spark discharge within the system. 

Sometimes it is desired to have a large working area in a tank where, for example, a conveyor belt containing car bodies can be passed through for electrostatic painting. One way to accomplish this is to put a series of propeller mixers in a side arm of the long side of the tank, so that the flow is directed into the middle zone, but there are no mixer shafts or impellers in the center to impede the flow of the parts through the equipment. 

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