Vibrating drying chambers

Two-stage spray dryer systems are sometimes called Spray-Fluidizers, since a fluid bed is installed at the cone of the spray dryer chamber. Alternatively, a vibrated fluid bed (VFB) is installed at the bottom of the drying chamber. It can produce instantly soluble products, such as instant coffee, milk, cocoa, etc., by agglomeration of the product. It is ideal to handle heat-sensitive products. 

Spray drying is an example of powder production from solution. It is used widely for preparing ferrites, titanates, and other electrical ceramics. Fine droplets produced by an atomizer are sprayed into a drying chamber and the powder is collected (Figure 20.3). There are different types of atomizers. One uses ultrasonic atomization in which the solution is passed over a rapidly vibrating piezoelectric membrane. Droplet sizes in the range of 10 pm to over 100 pm can be produced. 

FIGURE 45.19 Continuous vibrogravitational freeze dryer for liquid and pastes (1) vacuum granulator (2) material feed (3) condenser (4) vacuum pump (5) feeding valve (6) drying chamber (7) radiators and (8) vibrating trays. (From Novikov, P.A. et al., Continuous freeze-dryer for liquid materials, Russian Patent No. 273,734, 1970.)... 

In polymer industries, wherever spray dryers are used they are primarily used as predryers of a multistage system. Final drying is normally done in a fluid bed, which is either stationary or vibrated type. Stationary fluid beds are used when spray-dried powder leaving the drying chamber is directly fluidizable. The vibrated type of fluid bed is used for products that, on leaving the spray dryer, are not readily in a fluidizable state owing to their particle form, size distribution, or wetness. 

Multi-stage operation Reduces size of drying chamber internal water removed in small fluid or vibrated bed dryers or through circulation conveyor dryer... 

It is necessary to modify the edge of the hole in various ways to reduce these stress concentrations. Some methods of modification are priming, plunging, and standard radiusing and polishing methods. In the Dry Low NOx Combustors, especially in the lean pre-mix chambers, pressure fluctuations can set up very high vibrations, which lead to major failures. 

Dosimetry. Ion current measurements required for absolute dosimetry were performed with a Cary 31 ionization chamber and vibrating reed electrometer. Dry nitrogen was used as filling gas for the chamber, and a W value of 34.9 e.v./ion pair was assumed for H-3 beta rays in N2 (27). Deuterium pressures in each of the reaction mixtures were great enough to ensure that less than 1% of the H-3 beta rays reached the walls of the reaction vessel (7). 

Si wafers of n-type and (100) orientation covered by thermally grown 100 nm SiO2 layer fabricated at 1100 °C in dry O2, were used as substrates. The wafers were loaded into an oil free evaporation chamber (Varian VT-460), and the system was evacuated down to lxlO 8 Torr. Ge ingot of 99.999 % purity was supported on a molybdenum plate, and it was evaporated using an electron gun, at an evaporation rate of 0.01-0.03 nm/s, at a pressure of lxlO"7 Torr. During evaporation, and for an additional 1 min after this process, the substrate temperature was kept at 350 °C. The temperatures were monitored by small-heat-capacity Ni-NiCr thermocouples, while the film thicknesses were measured by a vibrating quartz probe. For this study, four different samples have been prepared with different Ge evaporation times of 25, 50, 75, and 100 s for samples No. 1, 2, 3, and 4, respectively. After germanium evaporation, the samples were moved to a cold place inside the vacuum chamber. 

In case (1) of Figure 9.20, the separation occurs outside. In cases (2)-(4) the product is accumulated at the bottom of the chamber and discharged by means of a valve. Vibrators and rotating scrapers help convey the powder when the cone angle is too large or the chamber bottom is flat. When necessary, the air sweeper can be nsed to discharge the dry product along the chamber wall, as in case (4). 

Figure 21.9 presents such a novel design, originally developed for drying of whole egg but successfully used for drying of other biomaterials such as egg white, animal blood, casein, yeast, and soya protein [21]. The dryer comprises a vertical cylindrical chamber with a set of horizontally located and oppositely directed pneumatic nozzles. A grid-type gas distributor supports inert particles. In contrast to the conventional VFB dryers, this grid is freely mounted with a small clearance to the chamber wall and vibrated vertically... 

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