Fluid spraying

D. C. Busby and co-workers. Supercritical Fluid Spray Application Technology A Pollution Prevention Technologyfor the Futures PP- 218—239 Proceedings of the 17th Water-Borne and High-Solid Coating Symposiums New Orleans, La., 1990. 

Two-Fluid (Pneumatic) Atomizers This general category includes such diverse apphcations as venturi atomizers and reac tor-effluent quench systems in addition to two-fluid spray nozzles. Depending on the manner in which the two fluids meet, several of the breakup mechanisms may be apphcable, but the final one is high-level turbulent rupture. 

Hydraulic or Pressure (Single Fluid) Spray Nozzles... 

Liquid feed is most often dispersed into the bed by a two-fluid spray nozzle which is flexible in operation and less prone to blockage, especially if heated air is used to atomize crystallizing liquors. Liquid feed may be directed onto the bed surface from the space above the upper bed surface or introduced directly beneath the surface of the bed material. The liquid spray is less likely to dry as a spray before contacting the bed particles in this latter arrangement. 

With two-fluid sprays, the atomizing air tends to dry the liquid feed. Hence an increase in air rate or its temperature reduces the ability of the spray to wet and penetrate the bed material, leading to smaller bed particle size. 

Detailed design of fluid spray dryers must, however, be accompanied by experimental work. It has been noted [22] that even quite similar materials may behave very differently in a spray granulator. Experimental work will indicate such information as the natural mechanism of particle growth (coalescence vs layering), attainable product sizes, the preferred temperature and moisture conditions for the bed material, suitable ranges of bed voidage... 

Pressure nozzle spray diameter 70 to 10,00 pm capacity 0.03 to 0.3 L/s low viscosity and clean fluids. Spinning disc spray diameter 50 to 250 pm capacity 0.0015 to 0.4 L/s for usual fluids and for viscous fluid or fluid containing solids. Twin fluid spray diameter 2 to 80 pm capacity 0.03 L/s increasing the ratio of atomizing fluid to liquid from 1 to 10, will decrease the spray diameter by a factor of 10. Rayleigh breakup to produce uniform drops of diameter 1.8 x diameter of orifice. A related topic is prilling (Section 16.11.9.14). Surface aerators for activated sludge oxidation (instead of diffused air aeration. Section 16.11.8.1). Brush aerators for oxidation ditches. Motionless mixers spray flow. 

The Clean Air Act has set strict limitations on the emission of certain VOCs, so new safer solvents are needed to replace them. One new spray system has been developed that yields a high-quality coating while emitting as much as 80% fewer VOCs of all types and none of the VOCs that are considered hazardous air pollutants. This system is called the supercritical fluid spray process. The solvent mixture for this process still contains some of the slow evaporating solvents that allow the coating to spread evenly but replaces the fast evaporating solvents with high pressure CO2. 

Because carbon dioxide is much less toxic than the VOCs it replaces and because it is nonflammable and relatively inert, it is much safer to use in the workplace. It is also far less expensive. Moreover, because the CO2 can be obtained from the production of other chemicals, the new process does not lead to an increase in carbon dioxide in the atmosphere. In fact, since the VOCs that it replaces can form CO2 in the atmosphere, the supercritical fluid spray process actually leads to a decrease in atmospheric CO2 levels compared to what they would be with the traditional spray process. 

Cristea, E. D. "Contribution to Research on Twin Fluid Spray Burners for Industrial Furnaces." PhD Diss., Polytechnic University of Timisoara-Romania, 1984. 

Meterc D, Petermann M, Weidner E. Drying of aqueous green tea extracts using a supercritical fluid spray process. J Supercrit Fluids. 2008 45(2) 253-259. 

JP-8 and hydraulic fluid sprays flames. The ranking is given in terms of a flame suppression number (on a mass basis), which is defined as the mass of agent relative to the mass of Halon 1301 needed to suppress an equivalent flame. Note that sodium bicarbonate powder (NaHCOs) was as effective a suppressant as Halon 1301 (to be discussed further in the section Powders ). 

Twin fluid spray diameter 2 to 80 pm capacity 0.03 L/s increasing the ratio of atomizing fluid to liquid from 1 to 10 decreases the spray diameter by a factor of 10. 

Supercritical Fluid Spray Process. The supercritical fluid spray process is shown schematically in Figure 1. The reformulated coating, which is called a coating... 

Figure I Schematic diagram of the supercritical fluid spray process.

Nielsen, K. A. Glancy, C. W. Hoy, K. L. Perry, K. M. A New Atomization Mechanism for Airless Spraying The Supercritical Fluid Spray Process. In Proceedings of the Fifth International Conference on Liquid Atomization and Spray Systems Semeijian, H. G., Ed. NIST Pub. 813 Gaithersburg, MD, 1991 pp 361-314. 

---