Simplex atomizer pressure-swirl

The simplex atomizer has many other variants. 1 Designs are aimed at achieving good atomization over a wide range of flow rates by varying the effective flow area without the need for excessive hydraulic pressures. In practice, pressure-swirl atomizers used in gas... 

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. 

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

Radcliffe [52] studied a family of simplex/pressure swirl atomizers and demonstrated that at low Reynolds numbers Co decreases with an increase of Reynolds number, and for larger Reynolds numbers, C/j is independent of the Reynolds number. It is also weakly dependent on the injection pressure within the normal operating range [42, 43]. Discharge coefficients for swirl nozzles are provided in [1, 51, 52], among others. 

There has been some development in the numerical modeling of the sheet formation from swirl nozzles. A fully nonlinear model using an axisymmetric boundary element formulation has been developed for simulating the free surface shape and spray formed by simplex/pressure swirl atomizers [30, 32]. A linear instability analysis by Ponstein has been used to predict the number of droplets formed from each ring-shaped ligament shed from the parent surface. 

I-P. Chung, C. Presser, Fluid property effects on sheet disintegration of a simplex pressure-swirl atomizer, J. Propuls. Power 17(1), 212-216 (2001). 

Park et al. [68] derived 24.7.ix for duplex swirl nozzles. It is very similar to 24.5.i-24.5.iii however it does not contain any effect of liquid mass flow rate. The formula was derived based on variations in temperature only, which caused the liquid properties to change independent changes were not applied. The correlation indicates that surface tension has a much smaller impact on SMD in duplex nozzles than simplex nozzle. It also shows that the viscosity plays a much larger role in the atomization process, while the effect of the injection pressure is the same as in simplex nozzles. Figure 24.45 plots this equation as a function of viscosity and injection pressure at various surface tensions, using AP = 300 kPa and mass flow rate = 50 g/s. As expected, an increase in injection pressure leads to a decrease in SMD, and an increase in viscosity leads to an increase in SMD. 

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