Spray efficiency

Important design aspects of fixed water sprays include release orientation, release momentum, and release contact with the water sprays. If the release is a two-phase jet and has a momentum that is larger than that of the water spray, the jet will penetrate the water spray with little interaction which will lead to a poor removal efficiency. Water-spray efficiency can be maximized by ensuring that all of the water comes in contact with the vapor cloud, that is, by ensuring that the cloud will spread out across the entire area covered by the water spray such that all the water is used. 

Powder coatings No solvent or water Electrostatic spray efficiency < 100% dust, color change limitations... 

Type and size of pneumatic sulfur spray nozzles. External atomizing nozzles are used as previously described and schematically pictured in Figure 4. The nozzles produce a finely atomized spray in the shape of an elongated oval. Depending on nozzles used, various alterations are needed to maximize the spraying efficiency and to eliminate operational problems associated with start-up and shutdown. The nozzles should be sized for maximum atomization at the spray distance of 4% in. while discharging a sulfur spray with a density of about 2.5 lb/sq in./hr at that distance. 

The above expression represents a first-order approximation if a well-mixed droplet model is used for the spray efficiency. The expression is valid for As values equal to or greater than ten per hour. Aj is to be limited to 20 per hour to prevent extrapolation beyond the existing data for boric acid solutions with a pH of 5 (References...). For Aj values less than ten per hour, analyses using a more sophisticated expression are recommended. 

Another important class of dryer is the fluidized-bed dryers. Some designs combine spray and fluidized-bed dryers. Choice between dryers is usually based on practicalities such as the materials handling characteristics, product decomposition, product physical form (e.g., if a porous granular material is required), etc. Also, dryer efficiency can be used to compare the performance of different dryer designs. This is usually defined as follows -. 

Solutions can be examined by ICP/MS by (a) removing the solvent (direct and electrothermal methods) and then vaporizing residual sample solute or (b) nebulizing the sample solution into a spray of droplets that is swept into the plasma flame after passing through a desolvation chamber, where excess solvent is removed. The direct and electrothermal methods are not as convenient as the nebulization inlets for multiple samples, but the former are generally much more efficient in transferring samples into the flame for analysis. 

Samples to be examined by inductively coupled plasma and mass spectrometry (ICP/MS) are commonly in the form of a solution that is transported into the plasma flame. The thermal mass of the flame is small, and ingress of excessive quantities of extraneous matter, such as solvent, would cool the flame and might even extinguish it. Even cooling the flame reduces its ionization efficiency, with concomitant effects on the accuracy and detection limits of the ICP/MS method. Consequently, it is necessary to remove as much solvent as possible which can be done by evaporation off-line or done on-line by spraying the solution as an aerosol into the plasma flame. 

Introduction of sample solution via a nebulizer may need both spray and a desolvation chamber, but a well-designed, efficient nebulizer needs neither. 

The Z-spray inlet/ion source is a particularly efficient adaptation of the normal in-line electrospray source and gets its name from the approximate shape of the trajectory taken by the ions between their formation and their entrance into the analyzer region of the mass spectrometer. A Z-spray source requires much less maintenance downtime for cleaning. 

To assist in the deposition of these larger droplets, nebulizer inlet systems frequently incorporate a spray chamber sited immediately after the nebulizer and before the desolvation chamber. Any liquid deposited in the spray chamber is wasted analyte solution, which can be run off to waste or recycled. A nebulizer inlet may consist of (a) only a nebulizer, (b) a nebulizer and a spray chamber, or (c) a nebulizer, a spray chamber, and a desolvation chamber. Whichever arrangement is used, the object is to transfer analyte to the plasma flame in as fine a particulate consistency as possible, with as high an efficiency as possible. 

Entrainment occurs when spray or froth formed on one tray enters the gas passages in the tray above. In moderate amounts, entrainment will impair the countercurrent action and hence drastically decrease the efficiency. If it happens in excessive amounts, the condition is called priming and will eventually flood the downcomers. 

Aerosol products are hermetically sealed, ensuring that the contents caimot leak, spill, or be contaminated. The packages can be considered to be tamper-proof. They deUver the product in an efficient manner generating Httie waste, often to sites of difficult access. By control of particle size, spray pattern, and volume deUvered per second, the product can be appHed directiy without contact by the user. For example, use of aerosol pesticides can minimize user exposure and aerosol first-aid products can soothe without applying painful pressure to a wound. Spray contact lens solutions can be appHed directiy and aerosol lubricants (qv) can be used on machinery in operation. Some preparations, such as stable foams, can only be packaged as aerosols. 

Chemical Neutralization. Spray-type air washers are used extensively for removal or neutrali2ation of noxious components from large volumes of air, particularly exhaust air streams. Appropriate reagents are sprayed into the washer to purify the air by neutrali2ation, eg, sodium hydroxide solution is used if the air contains acidic gases. The solution must be continuously reconcentrated and any precipitated salts removed. The contact efficiency of such washers is high, and the simple constmction provides easy maintenance and constant efficiency (see AiRPOLLUTlON CONTROL METHODS). 

Fig. 18. Target efficiency of a single water droplet in a gravitational spray tower (278,279). From Ref. 280,...

Fig. 20. Spray droplet target efficiency in a centrifugal spray tower with a centrifugal field of 100 g (140,281).

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