Power rotor-stator

Sparks, T. G., Brown, D. E. and Green, A. Assessing rotor/stator mixers for rapid chemical reactions using overall power characteristics (BHR conference series. Publication 18. Mechanical Engineering Publications Ltd. London, 1995). 

Colloid Mills. Colloid mills are another form of rotor stator mill. A colloid mill is composed of a conical rotor rotating in a conical stator (Fig. 8.5). The surface of the rotor and stator can be smooth, rough, or slotted. The spacing between the rotor and stator is adjustable by varying the axial location of the rotor to the stator. The gap can be as little as a few hundred microns to a couple of millimeters.18 Varying the gap varies not only the shear imparted to the particles but also the mill residence time and the power density applied. Particle size is affected by adjusting the gap and the rotation rate. It is possible to produce particles in the 1-10 pm size range. 

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. 

The above expressions indicate the importance of a maximum change in inductance in the stator windings as the rotor changes one pole position. Torque is noted to be proportional to the second power of stator current. 

In all of the preceding motors the developed torque has been directly proportional to the second power of stator currents and remains constant regardless of speed of rotation. A linear relationship can be obtained if the rotor contains... 

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),... 

Table 5.2 Experimental exponents a for power law dependency (232) dispersion of p5nx)genic powders with rotor-stator systems (RS), high pressure systems (HP), and ultrasonication (US) the applied power density Ey and achieved mean particle size x ean are indicated, values for a were derived from data or cited from source references Mandzy et al. (2005), Pohl et al. (2004), Pohl et al. (2005), Sauter and Schuchmann (2008), Sauter et al. (2008)...

Still very popular for in-line dispersion are the class of rotor-stator mixers. These devices look more like pumps than like stirred tanks. Volumes are small but rotational speeds and powers are high, giving high local energy dissipation. They are often staged with several rotors separated by stators that reduce bypassing. 

There are few published data for power draw and pumping capacity in either batch or in-line rotor-stator mixers. Even less is known about the velocity fields in these devices, so there is little hard evidence to support proposed mechanisms for dispersion and emulsification. As a result it is often necessary to rely on equipment vendors for scale-up rules. Although many vendors have facilities for customer trials, few have well-equipped laboratories for acquisition of basic data for performance characterization. In reality, it is difficult to know how many vendor data are available, since many consider the information to be proprietary. Until recently, there has been little academic interest in high-shear mixers. This work is only starting to appear in the open literature, and it is important for the practitioner to stay informed as a body of knowledge evolves. 

It is important to recall from the discussion above that for turbulent flow the actual shear rate in the rotor-stator gap varies substantially from y. and that gap shear rate does not directly control power draw and dispersion. However, tip speed may control turbulence characteristics, especially if the spacing between stator elements (teeth or stator openings) as well as the shear gap width do not change on scale-np. 

Local Power Per Mass Approach. Davies (1987) showed that values of dmax for a wide variety of dispersion devices could be correlated with local power per mass if a rough estimate of Smax/ avg could be obtained. By extending the ideas of McManamey (1979), he argued that this could be accomplished by assuming that all the power is dissipated in a localized, device-specific volume. The results of his analysis of literature data for dilute inviscid dispersed phases, corrected for interfacial tension, are shown in Figure 12-11. The slope of the line bounding the data is as predicted by eq. (12-21). The rotor-stator data discussed above would lie between the data for agitated vessels and liquid whistles. 

The power transferred by the stator to the rotor, P, also known as air gap power at synchronous speed, can be expressed in kW by ... 

---