Fan spray atomization

Fan spray atomizers have been widely used in the spray coating industry (Fig. 2.5), in some small annular gas turbine combustors, and in other special applications that require a narrow elliptical spray pattern rather than the normal circular pattern. In particular, fan spray atomizers are ideal for small annular combustors because they can produce a good lateral spread of fuel, allowing to minimize the number of injection ports. 

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Fan spray atomizers Fansteel process Faradaic current... 

The flow characteristics inside Hquid atomizers have been studied by numerous investigators (4—8). Of special interest to designers is the work reported on swid atomizers (4), fan spray atomizers (6,7), and plain jets (8). The foUowing discussion focuses on the flow characteristics of a swid atomizer. 

Fanning friction factor, 73 260 Fan spray atomizers, 23 179 Fan sprays, 23 182 Fansteel process, 24 319 FAO Flax Group, 77 592 Faraday, Michael, 77 398 Faraday constant (F), 3 410 Faraday cup construction, 74 444 Faraday s law of electrolysis, 24 748 Faraday s laws, 9 593, 772 77 669 Far-Go/Triallate, 2 549t Farina, 26 284... 

In practical fan sheet breakup processes, sheet thickness diminishes as the sheet expands away from the atomizer orifice, and liquid viscosity affects the breakup and the resultant droplet size. Dombrowski and Johns[238] considered these realistic factors and derived an analytical correlation for the mean droplet diameter on the basis of an analysis of the aerodynamic instability and disintegration of viscous sheets with particular reference to those generated by fan spray atomizers ... 

Various correlations for mean droplet size generated using pressure-swirl and fan spray atomizers are summarized in Tables 4.4 and 4.5, respectively. In the correlations for pressure-swirl data, FN is the Flow number defined as FN = ml/APlpl) )5, l0 and d0 are the length and diameter of final orifice, respectively, ls and ds are the length and diameter of swirl chamber, respectively, Ap is the total inlet ports area, /yds the film thickness in final orifice, 6 is the half of spray cone angle, and Weyis the Weber number estimated with film... 

Table 4.5. Correlations for Mean Droplet Sizes Generated by Fan Spray Atomizers...

In fan spray atomization, the effects of process parameters on the mean droplet size are similar to those in pressure-swirl atomization. In general, the mean droplet size increases with an increase in liquid viscosity, surface tension, and/or liquid sheet thickness and length. It decreases with increasing liquid velocity, liquid density, gas density, spray angle, and/or relative velocity between liquid and surrounding air. 

Fan Spray 100-1000 High-pressure painting/coat ing, Annular combustors Good atomization, Narrow elliptical spray pattern High supply pressure... 

As mentioned in the previous section, a major drawback of the simplex atomizer is the poor atomization quality at the lowest flow rate due to too-low pressure differential if swirl ports are sized to allow the maximum flow rate at the maximum injection pressure. This problem may be resolved by using dual-orifice, duplex, or spill-return atomizers. Alternatively, the atomization processes at low injection pressures can be augmented via forced aerodynamic instabilities by using air or gas stream(s) or jet(s). This is based on the beneficial effect of flowing air in assisting the disintegration of a liquid j et or sheet, as recognized in the application of the shroud air in fan spray and pressure-swirl atomization. 

The liquid properties of primary importance are density, viscosity and surface tension. Unfortunately, there is no incontrovertible evidence for the effects of liquid viscosity and surface tension on droplet sizes, and in some cases the effects are conflicting. Gas density is generally considered to be the only thermophysical property of importance for the atomization of liquids in a gaseous medium. Gas density shows different influences in different atomization processes. For example, in a fan spray, or a swirl jet atomization process, an increase in the gas density can generally improve... 

A number of techniques have been evolved to disperse liquids in gases in the form of fine droplets. The various atomizing techniques are jet injections, fan sprays, centrifugal nozzles, twin fluid atomizers, impinging jets, and rotary... 

Z. Han, L. Fan, and R. D. Reitz, Multidimensional modeling of spray atomization and air-fuel mixing in a direct-injection spark-ignition engine, SAE Technical Paper 970884, Society of Automotive Engineers, Warrendale, 1997. 

Figure 3 shows fine atomization and feed distribution of the fan spray pattern generated by the feed nozzle of Chen and Dewitz (1998) during a pilot plant test. 

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). 

Nozzles that spray water as a sheet of liquid produce a pattern known as a fan. At the extreme are nozzles that atomize the liquid stream into a mass of very fine droplets. These nozzles are generally referred to as fog nozzles. 

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