Atomizer rotating wheel

Atomizing spray wheels rotate at speeds to 20,000 rpm with peripheral speeds of 250-600 ft/sec. With nozzles, the length to diameter ratio of the dryer is 4-5 with spray wheels, the ratio is 0.5-1.0. For the final design, the experts say, pilot tests in a unit of 2 m dia should be made. 

Proper atomization of feed is the key to successful spray drying. The three devices of commercial value are pressure nozzles, pneumatic nozzles, and rotating wheels of various designs. Usual pressures employed in nozzles range from 300 to 4000 psi, and... 

Rotary atomizer uses the energy of a high-speed rotating wheel to divide bulk liquid into droplets. Feedstock is introduced at the center of the wheel, flows over the surface to the periphery, and disintegrates into droplets when it leaves the wheel (Table 21.3). 

In contrast, a vaned wheel directs the flow of the liquid feed across the surface of an inner liquid distributor in which liquid slippage over the surface of the distributor occurs until there is contact with the vane or channel. The feed then flows outward due to centrifugal force and forms a thin film across the surface of the vane. As the liquid film leaves the edge of the vane, droplet formation occurs as a result of the radial and tangential velocities experienced. Atomizer wheel characteristics that influence droplet size include speed of rotation, wheel diameter, and wheel design, e.g., the number and geometry of the vanes. 

The relationship of the wheel-rim-type structure of 62 to the metal can be demonstrated by a 30° rotation of the two centered Alg rings followed by a shift of the six rings towards each other (cf. Figure 2.3-13) [92], The other possibility of the formation of an Al14 polyhedron with point symmetry by displacement of the two naked central atoms in the direction of a polyhedral entity has been shown to be energetically unfavorable by quantum chemical calculations i.e., the observed metalloid structure (Figure 2.3-13) is favored over the anticipated polyhedral structure as described by Wade-Mingos [5, 96] (see Chapter 1.1.2). 

The main variables in the operation of atomizers are feed pressure, orifice diameter, flow rate and motive pressure for nozzles and geometry and rotation speed of wheels. Enough is known about these factors to enable prediction of size distribution and throw of droplets in specific equipment. Effects of some atomizer characteristics and other operating variables on spray dryer performance are summarized in Table 9.18. A detailed survey of theory, design and performance of atomizers is made by Masters (1976), but the conclusion is that experience and pilot plant work still are essential guides to selection of atomizers. A clear choice between nozzles and spray wheels is rarely possible and may be arbitrary. Milk dryers in the United States, for example, are equipped with nozzles, but those in Europe usually with spray wheels. Pneumatic nozzles may be favored for polymeric solutions, although data for PVC emulsions in Table 9.16(a) show that spray wheels and pressure nozzles also are used. Both pressure nozzles and spray wheels are shown to be in use for several of the applications of Table 9.16(a). 

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