Portable mixer

For a wide range of applications, a portable mixer which can be clamped on the top or side of the vessel is often used. This is commonly fitted with two propeller blades so that the bottom rotor forces the liquid upwards and the top rotor forces the liquid downwards. The power supplied is up to about 2 kW, though the size of the motor becomes too great at higher powers. To avoid excessive strain on the armature, some form of flexible coupling should be fitted between the motor and the main propeller shaft. Units of this kind are 

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Porous solid as pseudo-homogeneous medium 635 effective diffusivity 635 Portable mixers 306 Positive displacement pumps. 315... 

Power tools, portable mixers, hairdryer housings. .. 

Portable mixers may be clamped on the side of an open vessel in the angular, off-center position shown in Fig. 18-14 or bolted to a flange or plate on the top of a closed vessel with the shaft in the same angular, off-center position. This mounting results in a strong top-to-bottom circulation. 

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 6-4 Angular top-entering mixer for small tanks with portable mixers.

Figure 21-1 Direct-drive portable mixer. (Courtesy of Lightnin.)...

Obviously large, custom motors would never be applied to a portable mixer, but explosion-proof motors wonld. 

Single-voltage motors can have simplified wiring because the other connections are made internal to the motors. Portable mixers, especially those with single-phase motors, can be prewired with a suitable electric cord. 

Except for some portable mixers, high-shear mixers, and a few special mixers, most mixers operate below standard motor speeds. Typical motor speeds of 1800 or 1200 rpm (30 or 20 rps) are reduced to between 350 and 30 rpm (5.8 and 0.5 rps) for most mixer applications. Portable and side-entering mixers usually operate near the upper portion of this speed range from 420 to 170 rpm (7 to 2.8 rps). Turbine mixers operate in the middle range, from 125 to 37 rpm (2.1 to 0.6 rps), and high viscosity mixers operate from 45 to 20 rpm (0.75 to 0.33 rps) and slower. 

In the upper portion of the speed range for mixers, a single speed reduction with either gears or belts is used. Gear reduction is used with most low-speed portable mixers, and belts are used with many side-entering mixers. Turbine mixers can use single-, double-, or triple-reduction enclosed gear drives. Sometimes a... 

The concern about natural frequency is that an excitation such as mixer operating speed could cause undamped vibrations. Undamped vibrations occur when no resisting forces are present to diminish the amplitude of vibration. Such vibrations could result in sudden and catastrophic failme of the mixer shaft. The most dangerous conditions usually occur when the mixer is operated in air. Large mixers normally operate below the first natmal frequency. Small portable mixers, which accelerate quickly, often operate above the first natural frequency. In either case, operating at or near the natmal frequency must be avoided for both mechanical reliability and safety. 

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