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22.8.4 The Flat-Fan Atomizer Model

The flat-fan atomizer is very similar to the pressure-swirl atomizer, but it makes a flat sheet and does not use swirl. The liquid emerges from a wide, thin orifice as a flat liquid sheet that breaks up into droplets. The primary atomization process is thought to be similar to the pressure-swirl atomizer. Some researchers believe that flat-fan atomization, because of jet impingement, is very similar to the atomization of a flat sheet. The flat-fan model could serve doubly for this application.

The flat-fan atomizer is available only for 3D models. An image of the three-dimensional flat fan is shown in Figure  22.8.6. The model assumes that the fan originates from a virtual origin. You need to provide the location of this origin, which is the intersection of the lines that mark the sides of the fan as well as the location of the center point of the arc from which the fan originates. FLUENT will find the vector that points from the origin to the center point in order to determine the direction of the injection. You also need to provide the half-angle of the fan arc, the width of the orifice (in the normal direction) and the mass flow rate of the liquid to use the flat-fan atomizer model.

Figure 22.8.6: Flat Fan Viewed from Above and from the Side
figure

The breakup of the flat fan is calculated very much like the breakup of the sheet in the pressure-swirl atomizer. The sheet breaks up into ligaments which then form individual droplets. The only difference is that for short waves, the flat fan sheet is assumed to form ligaments at half-wavelength intervals. Hence the ligament diameter for short waves is given by


 d_L = \sqrt{\frac{16h}{K_s}} (22.8-36)

In this case, $d_L$ in Equation  22.8-36 is taken to be the most probable diameter, with a Rosin-Rammler spread parameter of 3.5 and a default dispersion angle of 6 $^{\circ}$. This angle can be set in the Set Injection Properties panel. In all other respects, the flat-fan atomizer model is like the sheet breakup portion of the pressure-swirl atomizer.


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Up: 22.8 Atomizer Model Theory
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© Fluent Inc. 2006-09-20