Top spraying

Paint thinner/removcr Air fresheners Dessert topping sprays ... 

Type of application equipment used for example, using over-the-top spray boom or air blast for grapes. The sprayer should be consistent with local cultural practices for each test site. 

Top spray systems During top-spray cooling of an overheated core, the wall temperature is usually higher than the Leidenfrost temperature, which causes water to be sputtered away from the wall by violent vapor formation and then pushed upward by the chimney effect of the steam flow generated at lower elevations (as shown in Fig. 4.25). A spray-cooling heat transfer test with BWR bundles was reported by Riedle et al. (1976). They found the dryout heat flux to be a function of spray rate and system pressure. The collapsed level required to keep the bundle at saturation for various pressures compared reasonably well with that in the literature (Duncan and Leonard, 1971 Ogasawara et al., 1973). 

Top-spray fiuidized-bed units, 76 448 Top spraying, in fiuidized-bed encapsulation, 77 541-542 Torque, mixer power and, 76 686... 

Dewettinck, K. and Huyghebaert, A., Top-spray fluidized bed coating effect of process variables on coating efficiency, Lebensmittel Wissenschaft Technologie, 31 (1998) 568-575. 

Dewettinck, K., De Visscher, A., Deroo, L. and Huyghebaert, A., Modeling the steady-state thermodynamic operation point of top-spray fluidized bed processing, /. Food Eng., 39 (1999b) 131-143. 

Figure 16 Influence of increasing batch size on product differential pressure and process air volume for a pilot scale top spray layering and coating process.

Nozzle positions (with the possible exception of the top-spray process) are somewhat flxed, and the distances between the nozzle tips and product being coated are often quite small and unlikely to change on scale-up. 

Jones DM. Effect of process air dew point on a top-spray fluidized bed-coating process. Presented in Session 265 Coating in the pharmaceutical industry. Proceedings of AIChE Annual Meeting, 1998. 

Bottom Spray Wurster 2. Top Spray [Granulator) S.Tangenlial Spray (Rotor- processor)... 

The top-spray process, which is a manifestation of the fluid bed granulation process that has long been used in the pharmaceutical industry... 

Top spray Larger batches Limited batch weight Application of ... 

Although these examples are more specific to the Wurster process, similar guidelines can be applied to the top-spray process, in which case the definition for working capacity will be different. When dealing with the tangential-spray process, the quantity of product that is sufficient to ensure that the spray nozzles are completely immersed when the product is in motion will define the minimum starting batch weight. 

Fig. 3. Diagram of a Top Spray Coater. (Courtesy Glatt Air Techniques, Inc.)...

Nozzle port size is also selected to accomodate desired spray rate and viscosity. The position of the nozzle is very significant. In top spray coating operations, the nozzle is positioned to spray liquid counter currently to the flow of product (see Figure 3). In the Wurster system, the nozzle sprays concurrently with the well organized flow of substrate (see Figure 4), and in the rotor technique, the nozzle sprays concurrently in the spiralling bed of product (see Figure 5). 

The top spray system has been used to coat materials as small as 100 microns. Smaller substrates have been coated, but agglomeration is almost unavoidable due to nozzle limitations and the tackiness of most coating substances. Batch sizes range from a few hundred grams to approximately 1,500 kg. Typically, a single nozzle wand with up to six liquid delivery ports is used, but multiple nozzle systems have been applied. 

However, top spraying is the system of choice for coating without... 

The most significant characteristic of the top spray method is that the nozzle sprays countercurrently or down, into the fluidizing particles. The fluidization pattern is very random and... 

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