Compressed air atomization

In conventional spraying, atomization is the result of external mechanical forces, i.e., the exchange of momentum between two free jets (air and paint). Atomization may be classified as compressed air atomization (air 0.02-0.7 MPa, paint 0.02-0.3 MPa), airless atomization (paint 8 40 MPa), air-assisted airless atomization, also termed airmix process (air 0.02 0.25 MPa, paint 2-8 MPa), and special technologies (Table 8.3). 

The combined airmix process operates at a lower paint pressure (2-8 MPa). Additional low-pressure air jets (0.02-0.25 MPa) from the air-cap bores impinge on the spray jet to mix and homogenize it. In addition to the atomizer and a compressed air generator (airless pump), the airmix unit therefore also requires compressed air for postatomization. Advantages over the airless method are the less sharply defined spray jet and the smaller droplet size. Compared with compressed air atomization, a low-mist coating is possible. 

The equipment used in the spray-pyrolysis technique consists basically of an atomizer and a temperature controller. There are several types of atomizers. The most common ones are compressed air atomizers [2] (when the spray of the precursor solution is produced by a jet of air), electric field atomizers [3] (when the spray of the precursor solution is produced by an electric field) and ultrasound atomizers [4] (when the spray of the precursor solution is produced through high frequencies). 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

A variation of airless atomization is called air-assisted airless. A small amount of compressed air at 35—170 kPa (5—25 psi) is introduced adjacent to the airless nozzle and impinges upon the thin sheet of fluid as it exits from the nozzle. This air aggravates the turbulence in the fluid and results in improved atomization at lower fluid pressures. Often, material that caimot be properly atomized using straight airless atomization can be using the... 

Solid particulates are captured as readily as hquids in fiber beds but can rapidly plug the bed if they are insoluble. Fiber beds have frequently been used for mixtures of liqmds and soluble sohds and with soluble solids in condensing situations. Sufficient solvent (usually water) is atomized into the gas stream entering the collector to irrigate the fiber elements and dissolve the collected particulate. Such nber beds have been used to collect fine fumes such as ammonium nitrate and ammonium chloride smokes, and oil mists from compressed air. 

Steam is the preferred atomizing medium, since it is more economic than compressed air. Steam consumption is typically less than 0.5 per cent of the fuel burnt on a mass basis, although this rises in direct proportion to turndown ratio. On very large burners, the steam flow is modulated in proportion to fuel burnt. Turndown ratios range from about 5 1 for small shell boilers to 12 1 in watertube applications, making this one of the most versatile burners. The steam condition is important in that it must be dry saturated or slightly superheated at the nozzle to avoid condensate formation. On small or non-continuously running plant where no steam is available for start-up a compressed air supply must be provided until steam becomes available from the boiler. 

The apparatus shown in Fig. 2 is assembled in a good hood. One liter of liquid ammonia and 0.5 g. of hydrated ferric nitrate are placed in the 2-1. three-necked flask A, which is equipped with a stirrer and a special reflux condenser cooled with Dry Ice. This condenser is attached to a soda-lime tower which is connected to a source of compressed air through the T-tube C. Over a period of about forty-five minutes, 92 g. (4 gram atoms) of clean sodium shavings is added to the liquid ammonia, and the mixture is stirred until the blue color disappears (one to two hours). 

F = Mixing Chamber for Fuel Gas, Compressed Air, and Atomized Liquid Sample,... 

In the usual design, humidistats call for supplementary atomizer water in order to achieve a desired processing workplace humidity. The atomizers are turned on and off by applying compressed air to... 

With aerosol cleaning products, a quick spray and a blow-dry with compressed air, or a wipe with a dry rag or towel is all that is required to remove the unwanted soil. Another benefit of spraying is the motive force of the spray, which assists in soil removal. Because of the tendency for aerosol products to finely atomize the cleaning solvent and increase air emissions, some air-quahty agencies are mandating the use of low-vapor-pressure solvents in hand-pump dispensers. This action reduces solvent loss to the atmosphere and increases the amount of waste solvent, which must be collected and stored for subsequent recycling or disposal. 

The three different nozzles have slight differences in the configuration of the liquid insert and air cap (the path for the atomizing air), but the largest difference is in the size of the annulus between these components to permit the higher volume of compressed air to flow at the same atomizing pressures for atomization of the liquid stream (Fig. 18). 

Gas atomizing nozzle (two-fluid nozzle) the two-fluid (binary) nozzle where the binder solution (first fluid) is atomized by compressed air (second fluid) is the most commonly used nozzle for the fluid-bed granulation (Fig. 9A and B). 

The oldest method, which is still in use today, is employing compressed air guns in which the stream of the liquid is driven through the nozzle orifice by pressures 1-5 kPa (1.5-7 psi). In general, they are less expensive than other spray guns and atomization... 

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