Rotor-stator mechanism

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). 

The working principle of a DC motor is relatively simple, but its mechanical design is quite complicated. The rotor s conductors are permeated by the stator s magnetic field. Commutation (guidance of current density in the rotor) occurs mechanically. To this end, switches (brush collectors) are affixed to the axle that are activated by the rotation of the... 

Asynchronous motors (squirrel cage induction motors, the rotor-stator part of slipring induction motors) and the rotor-stator part of synchronous motors are within the scope of increased safety due to the omission of sparks and arcs assuming an appropriate construction of rotor and windings. Tire standards IEC 60079-7 and EN 50019 contain mechanical and thermal requirements that follow this aim. 

Sulfur-asphalt binders can be prepared by various mechanical means. One conventional method is to combine liquid sulfur and asphalt at 285°-300°F in a Gifford Wood colloid mill. A rotor stator gap setting of 0.02 in. at 7000 rpm for 8 min will prepare satisfactory emulsions. This emulsion is immediately mixed with preheated aggregate. The laboratory binder was prepared by TTI (Texas Transportation Institute) scientists in cooperation with SNPA (Societe Nationale des Petroles d Aquitaine) scientists and is believed to be comparable with the binders prepared by the turbine in the field trials. The need for dispersing sulfur in the asphalt is discussed by Garrigues (9) and by Kennepohl et al., Deme, and McBee et al. elsewhere in this volume. 

The word homogenization is somewhat inconclusive and is typically defined as used in context. Two processes are considered here the first is a fine clearance valve homogenizer, and the second is a rotor-stator-type mechanical homo-genizer. Homogenization is similar to sonication and produces submicron droplets by a combination of mechanical shearing and cavitation. 

The rotor-stator-type mechanical homogenizer generates submicron droplets by forcing the emulsion through small openings in the stationary... 

Fluid viscosity and volume to be mixed are the most significant factors. Propellers viscosity <3000 mPa-s volumes <750 m Turbines and paddles viscosity <50,000 mPa-s volumes <75 m Liquid jets viscosity <1000 mPa s volumes >750 m Air agitation viscosity <1000 mPa-s volumes >750 mT Anchors viscosity <100,000 mPa-s Re <10,000 volumes <30 mT Kneaders viscosity 4,000 to 1.5 x 10 mPa s volumes 3 to 75 m Roll mills viscosity 10 to 200,000 mPa s volumes 60 to 450 m For viscosity >10 consider extruders, Banbury mixers, and kneaders. Paddle reel/stator-rotor gentle mechanical mixing for coagulation, viscosity <20 mPa s volumes large. Motionless mixers viscosity ratio <100,000 1 continuous and constant flow rates residence times <30 min and flow rate ratio of <100 1. Other related sections are size reduction (Sections 16.11.8.1 and 16.11.8.3), reactors (Section 16.11.6.10), and heat transfer (Section 16.11.3.5). 

Traditional methods of emulsification include high-pressure homogenizers, rotor-stator systems, and ultrasound homogenizers [110, 111], The first two examples employ high mechanical shear rates to produce small droplets of the... 

Paddle reel/stator-rotor gentle mechanical mixing for coagulation, viscosity < 20 mPa s, volumes large. Size increase for particles, with details in Section 9.3. 

The other type of mechanical homogenizer is represented by the blade homogenizers ( blenders ) commonly used to produce extracts from plant and animal tissues. The cutting blades rotate at speeds of 6000-50 000 rpm. Blenders are not suitable for disruption of microorganisms unless glass beads or other abrasives are added to the media, but this leads to the same problems of foaming and aerosol formation as mentioned above for rotor-stator homogenizers (Yacko 2007). 

Emulsions can be produced by a wide range of industrially applied processes. Most often, droplets are formed and disintegrated mechanically (Figure 20.5). Rotor-stator devices and high-pressure homogenizers are emulsification techniques have been... 

In the practice of pharmacy preparations, it is usual to try to distribute the dispersed phase more finely with a rotor-stator mixer or a simple mechanical (paddle) mixer (pourable emulsions), or, for semisolid emulsions, with a mortar and pestle or a mixing device. Magnetic stirrers are unsuitable. Impaction of air should be avoided because the liberation of air bubbles can accelerate the creaming process (in case of pourable emulsions) and promote possible oxidation of the lipid base or of an active substance. A Stephan mixer with vacuum (see Sect. 28.6.1) is a suitable device for the preparation of emulsions without inclusion of air. 

Crystallinity Impurity Solvate Incomplete dissolution pH Temp Amount Miscibility w/solvent Mixer type(high-shear in-line versus suspended mixer homogenizer) Mixer design Rotor/stator design and gap Tip speed S/AS flow rates and ratio Batch size Processing time Temperature Too slow Incomplete removal of solvent Temp. Time Air flow Humidity Shear/temp Milling mechanism... 

When the flow is laminar, either single or multiphase, there is only one design class option static or motionless mixers. Other pipeline mixing devices described for turbulent flow are not usable for even the simplest mixing applications in the laminar regime. All rely on turbulence and cannot function at low Reynolds numbers. The only alternative technology is in-line dynamic mixers, which include extruders, rotor-stator mixers, and a variety of rotating screw devices. None of these has the benefits of simplicity and the little or no maintenance characteristic of static mixers. In-line mechanical mixers are discussed briefly later in the chapter. 

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. 

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