Dual-orifice atomizers

Hollow Sprays. Most atomizers that impart swid to the Hquid tend to produce a cone-shaped hoUow spray. Although swid atomizers can produce varying degrees of hoUowness in the spray pattern, they aU seem to exhibit similar spray dynamic features. For example, detailed measurements made with simplex, duplex, dual-orifice, and pure airblast atomizers show similar dynamic stmctures in radial distributions of mean droplet diameter, velocity, and Hquid volume flux. Extensive studies have been made (30,31) on the spray dynamics associated with pressure swid atomizers. Based on these studies, some common features were observed. Test results obtained from a pressure swid atomizer spray could be used to iUustrate typical dynamic stmctures in hoUow sprays. The measurements were made using a phase Doppler spray analyzer. 

Figure 12.5. Photograph of microdispensing system depositing an inorganic dielectric dispersion onto a patterned, metallized polyester film. The pattern is of a transistor gate electrode array. The microdispensing head atomizes the dispersion, generating a liquid spray much like a dual orifice atomizer found on an airbrush.

Dual- Orifice 20-200 A variety of aircraft and industrial gas turbines Good atomization, Turndown ratio 50 1, Relatively constant spray angle Poor atomization in transition range, Complexity in design, Susceptibility of small passages to blockage... 

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. 

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