Atomizers spill-return

A spill-return atomizer (Fig. 2.4) is essentially a simplex atomizer. The difference between the two types of atomizers is that the rear wall of the swirl chamber is solid in a simplex, while in a... 

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. 

Spill return nozzles are almost the same as the simplex types however they contain a passageway from which any surplus liquid not atomized can make its way back to the supply source. Hollow cone shapes are the most common shapes produced from this. They tend to yield a very high quality spray since exactly the right amount of liquid is atomized, while the rest is sent back to the supply source. 

Equation 24.92 is a formula for spill-return type of swirl atomizers, as derived by Orzechowski [69]. He attributes Dmax to be a function of exit orifice diameter, injection pressure, surface tension and liquid density and viscosity. 

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