Vibrated beds

Another separation device that may be used is the mineral jig. This unit produces a loose vibrating bed of particles in a Hquid medium. The vibrations segregate the soHds into layers of density. The dense nonferrous metals, primarily lead, 2inc, and copper are at the bottom while organics are at the top. The middle layer is primarily glass. 

Fluidized bed (2) Moving beds Microspheres, spheroids Slurries, inclined bed, tumbled beds, vibrated beds, beds with pulsed flow, Raschig rings... 

Shah, R.M. and Goyel, S.K., Drying characteristics of tea fluidised on a vibrating bed. 11 Handling of dust grades and its impact on quality. Drying Tech., 13 (1995) 1523-1541. 

Nonagitated Perforated band Through-circulation Atmospheric band/belt, vibrated bed... 

Closed-system dryers, spray dryers, fluidized bed dryers Batch or continuous tray, vibrated bed dryers Use dielectric heating (microwave or radio frequency) over part of drying... 

Vibrated beds, impinging jet-fluidized beds, mechanically fluidized beds, rotary, or conveyor dryers may be used. Each type of dryer has its own advantages and limitations, so a careful evaluation of all the key criteria noted earlier in this chapter must be made before the final selection. 

It should be pointed out that many new dryers cannot conveniently fit the classification suggested earlier. For example, a pulsed combustion dryer for pasty solids or waste sludge, the Remaflam process for drying textiles by controlled combustion of solvent (alcohol) on the wet fabric itself, and vibrated bed drying of pastes cannot be placed under any one single category of dryers. Such a coarse classification is stiU of interest in that it allows one to home in on a limited number of possible dryers, which can then be evaluated in depth. 

Pakowski, Z., Mujumdar, A.S., and Strumillo, C., Theory and application of vibrated beds and vibrated fluid beds for drying processes, in Advances in Drying, Vol. 3, Mujumdar, A.S. (ed.), Hemisphere Publishing, New York, 1984, pp. 245-306. 

Figure 21.25 presents immersed wall-to-bed heat transfer coefficients in vibro-rotational and vibrating beds of the same geometry and at the same amplitude-frequency of vibration [41]. The superiority of the VRB results from particle circulation superposed on bed vibration, which improves the contact of the particles with the heat transfer snrface. An additional advantage of the VRB is its efficient operation under vacuum the heat transfer coefficient at 0.2 atm is only 7%-ll% lower than that at atmospheric pressure [39]. 

FIGURE 21.25 Wall-to-bed heat transfer coefficient in VRB (1), vibrated bed (2), and fluidized bed (3). (From Nikitin, V.S. and Martenov, O.G., Heat and Mass Transfer in Dispersed Systems, Minsk, AN BSSR, 1982, pp. 130-135 (in Russian).)... 

Vibration causes the pseudofluidized particulate material to move downward along the tray. At the same time, the material is dried by the hot gas stream passing through the vibrated bed at a superficial velocity determined by heat and mass transfer requirements. This superficial velocity is usually lower than the fluidization velocity and varies from 0.7 to 3 m/s, depending on the material characteristics. 

Rysin, A.P. and Ginzburg, A.S. 1982. Theory and technology of food product drying in fluidized vibration bed. In Drying of Solids (A.S. Mujumdar, Ed.), Oxford, India, pp. 86-124. 

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