Spraying-spray rate

Scale-Up Considerations Spraying-Spray Rate and Droplet... 

A steady-state rocket-type combustion spray unit has been developed, called high velocity oxy fuel (HVOF), that creates a steady state, continuous, supersonic spray stream (1.2—3 mm dia) resembling a rocket motor exhaust. The portable device injects and accelerates the particles inside a barrel (rocket nozzle). It produces coating quaHty and particle velocities equal to the D-gun at 5—10 times the spray rate with significantly reduced coating costs. 

The drop distribution and spray rate of binder fluid have a major influence on wetting. Generally, finer drops wiU enhance wetting as well as the distribution of binding fluid. The more important question, however, is how large may the drops be or how high of a spray rate is... 

Improve spray distrihiition. Improve atomization hy lowering hinder fluid viscosity. Increase wetted area of the bed per unit mass per unit time hy increasing the number of spray nozzles, lowering spray rate, increase air pressure or flow rate of two-fluid nozzles. 

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). 

Scale Up of Process. The scale up of fluidized bed coating processes has received little attention in the literature. Current practices in the pharmaceutical industry are reviewed by Mehta (1988). The basic approach described by Mehta (1988) is to scale the airflow and liquid spray rates based on the cross-sectional area for gas flow. This seems reasonable except for the fact that in the scaling of the equipment, the height of the bed increases with increasing batch size. For this reason, a time scale factor is also required. 

Test runs using a 150 mm diameter fluid bed coater indicated that a batch of 2 kg of material could be coated using a liquid spray rate of 10 ml/min for 50 minutes and a fluidizing gas rate of 40 scfm. It is desired to scale-up this process to a batch size of 200 kg of bed material. For the scaled up process, determine the bed size the liquid and airflow rates and the new run time. 

From Table 2 choose a 800 mm diameter bed with 3-225 mm diameter draft tubes. The air flow and liquid spray rates are scaled on draft tube diameter ... 

Figure 20. The influence of the extent and rate of penetration on average granule size in drum granulation for different spray rates. (From Gluba et al., 1990.)...

Ultrasonic Atomization Nebulizers 1-5 (55kHz, 0.12 1/min) 30-60 (50 kHz) l-200[88] Medical spray. Humidification. Spray drying. Acid etching. Printing circuit. Combustion Very fine and uniform droplets, Low spray rates Incapable of handling high liquid flow rates... 

Mild steel plates obtained from ARCELOR, France were washed with distilled water and ethanol prior to sample treatments. Pre-rasted samples were prepared by subjecting the mild steel plates to the salt spray chamber according to the ASTM B 117 [16] standard procedure (6 hours exposure in 5% (w/v) NaCl at 98% humidity, l.OmLhour spray rate, 1.0 kg cm of pressure and followed by drying in an oven at 40°C)... 

A generalized comparison of equivalent fire protection for structural steel using water spray rates recommended in NFPA 15 and fire-resistive insulation used alone or in combination is provided in Table 8-9 (NFPA 15). 

Solution spray rate Outlet filter type... 

The spray nozzle (or nozzles) in the production machine would need to be of a size such that this increased spray rate is within its performance envelope (similar droplet size, uniform in distribution), or equivalence in granule size would be impossible. Figure 17 illustrates the concept that atomizing air pressure must be adjusted to attain similar average droplet sizes in all three scales of process equipment at the desired spray rate (data from... 

Figure 17 Average droplet sizes as a function of spray nozzle t5 pe (lab, pilot, and production), spray rate and atomizing air pressure.

Low-viscose liquids can use small ports, and thicker solutions somewhat larger orifices to allow some back pressure to build in the spray nozzle. In this manner, if a port should become clogged, increasing the spray rate through the remaining ports, the total liquid line pressure will rise. An operator can intervene to correct the problem before the larger droplet size results in an increased granule size. 

Figure 20 Droplet size as a function of 1.2mm and 3.0 mm nozzle ports spray rates of 1200 and 2500 mL/min using water.

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