Rotor-stator machine

Due to the fact that [78] the energy input was split into mass-related (E/pV) and kinetic (E n) energies, an earlier paper concerning the emulsification process should also be referred to [79]. As emulsifyer, a teeth-rimed rotor-stator machine was used and the results (dso) were correlated with both power per unit volume (P/V) and work per unit volume (Pt/m3). This paper is also of special interest because the evaluation is performed in a dimensional-analytical manner. The dimensionally formulated result reads. 

Figure 5.5 Influence of the specific energy input and the emulsifier adsorption kinetics on the emulsification result when using either a rotor-stator machine (RSM) or a high-pressure homogenizer (HPH) [33],...

In Figure 5.5, the achievable droplet diameter in a high-pressure homogenizer is depicted over the specific energy input for two different emulsifiers in comparison to results achieved by producing the same formula in a rotor-stator machine (RSM). 

FIGURE 11.6 Active part of some emulsifying machines, (a) Rotor-stator type stirrer ( ultra-turrax ). (b) Colloid mill, (c) Valve of a high-pressure homogenizer. The slit width in (b) and (c) is greatly exaggerated. 

The stirrers are mainly of the flat-blade, disk, propeller, or turbine type [7.16]-[7.19]. Rotor-stator systems are also used as continuous mixers (Fig. 7.5). These machines are employed particularly if an emulsion or an emulsion-like product has to be produced (e.g., waterborne paints) [7.20]-[7.22]. 

Actually head of the Process Technology Department. Publications High-speed rotor-stator dispersion machines... 

Colloid milling is instead based on a high speed rotor/stator system, in which the processed material is grinded, dispersed, or emulsified as a consequence of its exposure to intense shear stresses, friction, and high frequency vibrations. Colloid mills are constituted by smooth or toothed rotors and stators, gear-rim dispersion machines, and intensive mixers. ... 

The power density Py is the characteristic quantity of turbulent flow. It determines the size of the smallest eddies and the intensity of microturbulence. In addition, it is a measure of the shear intensity in laminar flows or the intensity of cavitation in ultrasonic fields (see above). The power input P in the dispersion zone can be derived from the pressure drop (e.g. in pipes and nozzles) or can be measured caloricafly (e.g. for rotor-stator systems and ultrasonication Pohl 2005 Kuntzsch 2004). Additionally, P can be roughly approximated by the electric power consumption of the dispersion machine (e.g. for ultrasonication Mandzy et al. 2005 Sauter et al. 2008), even though the real values may be lower by a factor of 2 to 5. A further source of uncertainty is the volume of the dispersion zone (Vdisp). since the stress intensities are not uniformly distributed in dispersion apparatuses. In particular, this applies to agitated vessels, where the highest dissipation rates are obtained in the vicinity of the stirring instmment (Henzler and Biedermann 1996),... 

Many types of emulsification equipment are widely appUed in industry, such as high pressure homogenizers and rotor-stator systems. In these machines the premix droplets are deformed and disrupted in the flow field of the emulsification device [1]. In addition to these techniques, alternative methods for the production of emulsions using microporous devices have been developed since the early 1990s. 

In Fig. 4.33 a refiner with cylindrical rotor/stator geometry is shown. The stock enters the center of the machine via the hollow center shaft and is refined during its helical horizontal path to the two stock outlet pipes. The refining energy is controlled by the gap between the rotor and the stator which is adjusted by cone-shaped means. 

Another popular rotor-stator design is the Silverson Machines or Ross type. The rotor is a radial impeller that rotates inside a stationary housing with slots as shown in Figure 8-3a. The rotor moves the fluid radially out of the mixer head through the slots or holes in the stator. Superimposed on the radial flow is a... 

Figure 8-3 Silverson Machines or Ross rotor-stator design (a) head assembly (b) general purpose disintegrating head (c) high-shear screen (d) slotted-screen disintegrating head.

Figure 8-5 Batch or semibatch rotor-stator assemblies (a) Silverson Machines batch mixer on hydraulic double-lift stand (b) IKA Works batch mixa-. (Myers, 1999, reproduced with permission of AIChE 1999.)...

Direct-current motor fields are on the stator. The rotor is the armature. The magnetic field does not rotate like the field in ac machines. Current in the armature reacts with the stator field to produce torque. 

Adequate single-phase protection is provided on low-voltage ac motor starters by three overload relays, which are now standard. Rotor heating is not particularly a problem on smaller motors which have more thermal capacity, but it is important to protect the stator windings of these machines against burnout. 

Depending upon its size, a machine may adopt more than one cooling system, with separate systems for the stator and the rotor and. sometimes even for bearings. To define the cooling system of such a machine, each system must be separately described. For more details refer to lEC 6(X)34-6. 

Thc.se systems were evolved to provide a variable -frequency supply source to feed directly the stator terminals of the a.e. motor or its rotor through the slip-rings, The motors had to be invariably a combination of two or more slip-ring motors to receive the rotor frequency voltage from the other machine or feed back the rotor frequency voltage to another machine. The easiest method was to have a variable-frequency supply source, which was not possible, unless the supply source itself was captive and specified for this drive alone or a combination of these drives on the same bus. 

Let us consider the simple equivalent motor circuit diagram as shown earlier in Figure 1.15. The no-load component of the current, / , that feeds the no-load losses of the machine contains a magnetizing component, produces the required magnetic field, (p, , in the stator and the rotor circuits, and develops the rotor torque so that... 

Nole In both the above case.s. which are almost similar, so far as the sw itching heats of the stator or the rotor are concertied, the overcurrent protection (noted at serial no. 4) is redundant, as its time constant is much higher (of the order of several minutes) compared to the temperature rise, particularly of the rotor, which is linear and much more rapid under such conditions. Therefore, such protection saves the machine from excessive thermal stresses. 

Bearings and bearing housings in a rotating machine, in view of the very small gap between the stator and the rotor. 

The synchronous motor is a constant-speed machine. Unlike the induction motor which inherendy has slip from losses, the synchronous motor uses an excitation system to continually keep the rotor in synchronous speed with current flowing through the stator. Within its designed torque characteristics, it will operate at synchronous speed regardless of load variations. 

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