Dispersion spraying

The electric field and gas flow work together to provide a finely dispersed spray of charged droplets. An electric potential of about 3-5 kV is used for capillaries of about 50-100-pm diameter. 

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Streudiise, /. spray nozzle, streuen, v.t. scatter strew spread disperse spray dust. 

Zerstkubung, /, comminution, flne disintegration, atomization spatt-ering, scattering dispersion spraying, spray (of mercury) flouring (cathode) sputtering,... 

G. P. Lindblom. Measurement and prediction of depositional accuracy in dispersant spraying from large airplanes. In Proceedings Volume, pages 325-328. 10th Bien API et al Oil Spill (Prev, Behav, Contr, Cleanup) Conf (Baltimore, MD, 4/6-4Z9), 1987. 

The droplet size distribution produced by vaporization-condensation technique is strongly dependent on the chemical composition and properties of the liquid. If well controlled on a small scale, vaporization-condensation technique can produce moderately mono-disperse sprays with geometric standard deviations ranging from about 1.2 to 1.8.[88]... 

The studies on the performance of effervescent atomizer have been very limited as compared to those described above. However, the results of droplet size measurements made by Lefebvre et al.t87] for the effervescent atomizer provided insightful information about the effects of process parameters on droplet size. Their analysis of the experimental data suggested that the atomization quality by the effervescent atomizer is generally quite high. Better atomization may be achieved by generating small bubbles. Droplet size distribution may follow the Rosin-Rammler distribution pattern with the parameter q ranging from 1 to 2 for a gas to liquid ratio up to 0.2, and a liquid injection pressure from 34.5 to 345 kPa. The mean droplet size decreases with an increase in the gas to liquid ratio and/or liquid injection pressure. Any factor that tends to impair atomization quality, and increase the mean droplet size (for example, decreasing gas to liquid ratio and/or injection pressure) also leads to a more mono-disperse spray. 

Detonations will also propagate through liquid fuel droplet dispersions (sprays) in air and through solid-gas mixtures such as dust dispersions. Volatility of the liquid fuel plays an important role in characterizing the detonation developed. For low-volatility fuels, fracture and vaporization of the... 

The basic assumptions implied in the homogeneous model, which is most frequently applied to single-component two-phase flow at high velocities (with annular and mist flow-patterns) are that (a) the velocities of the two phases are equal (b) if vaporization or condensation occurs, physical equilibrium is approached at all points and (c) a single-phase friction factor can be applied to the mixture if the Reynolds number is properly defined. The first assumption is true only if the bulk of the liquid is present as a dispersed spray. The second assumption (which is also implied in the Lockhart-Martinelli and Chenoweth-Martin models) seems to be reasonably justified from the very limited evidence available. 

Formation of free milk fat in DWM powder particles as a result of atomization and drying may also contribute significantly to poor solubility and dispersibility. Free milk fat, which is extractable from the powder by a 50 50 mixture (v/v) of ethyl and petroleum ether (Brunner, 1974), probably coats the powder particles and prevents their rehydration. The physical state of the milk fat, as controlled by the liquid-to-solid ratio and the presence of free milk fat on the particle surface, strongly influences DWM particle dispersibility. Spray coating of DWM particles with lecithin or other surfactants and dispersion in warm water improve their dispersibility. 

Spray onto dispersed powder (cf. powder clustering, agitation methods above) Atomized liquid feed is sprayed into circulating dispersion of already-dried particles. Hot gases maintain dispersion. Spray granulation, spouted and fluidized bed granulation Fluidized and spouted beds, Wurster apparatus... 

Throughout this chapter, two-phase flows are treated like mono-disperse sprays, an assumption which is not mandatory in EE methods but which makes their implementation easier. Results also suggest that in many flows, this assumption is reasonable. Considering the lack of information on size distribution at an atomizer outlet in a real gas turbine, this assumption might be a reasonable compromise in terms of complexity and efficiency tracking multi-disperse sprays with precision makes sense only if the spray characteristics at the injection point are well known. In most cases, droplets are not yet formed close to the atomizer outlet anyway and even the Lagrange description faces difficulties there. 

The resulting set of equations Eqs. 8.2 to 8.2 is equivalent to the La-grangian description of the dispersed phase (without collision terms and for mono-disperse sprays) and leads to the same solutions, as shown in [348]. 

Polymer dispersion, spray binder for HF-waddings, tion of fish nets. 

Babington, R.S. (1962) Method of atomising Liquid in a Mono-Dispersed Spray , US Patent... 

Babington R. S. (1969) Method of atomizing liquid in a mono-dispersed spray, U.S. Patent 3,421,692. 

Dispersed, Spray or Mist close to vapor velocity >200... 

Dispersed, Spray, or Mist Flow. Here, all of the liquid is entrained as fine droplets by the gas phase. Dispersed flow occurs for gas velocities greater than 200 ft/sec (60 m/sec). 

The key properties of the spray dispersion that influence the size of the droplets formed are its dynamic surface tension and its viscosity (Elliott and Wilson, 1983 Dexter and Huddleston, 1998) although it should be noted that poor spray machinery setup and use can play a more important role than the physical properties of the spray dispersion (Spray Drift Taskforce, 1977). 

Fig. 10.33. HTUoc without end effects, extraction of FeCU from aqueous HCl by isopropyl ether, ether dispersed spray tower, 1.448 in. diam., Uc = 56.8-68.3 (30). With permission of American Chemical Society.)...

Conventionally, fluid-fluid reactions are carried out in agitated vessels, centrifugal devices, columns (in spray, packed, plate and vibrating varieties) and straight or coiled tubes. The contacting methods involved are bubbling, film formation or dispersive spraying of one fluid into the other. 

It is important to note that dispersant must be applied with a system designed specifically for that purpose. For example, the spray volume of pesticide spraying equipment is generally 10 to 50 times less than a dispersant spray system. In addition, pesticide spraying equipment is designed to apply pesticide as a fine spray or mist with droplet sizes of about 50 to 200 pm. It was thought that dispersants are best applied in larger droplets, 400 to 700 pm in size, so that the droplets will not blow away and an adequate amount of dispersant will be deposited onto the oil slick. 

Figure 11. The dispersant spray system, ADDSPAK, in operation from a Hercules aircraft.

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