Effervescent atomization is the injection of liquid infused with a super-heated (with respect to downstream conditions) liquid or propellant. As the volatile liquid exits the nozzle, it rapidly changes phase. This phase change quickly breaks up the stream into small droplets with a wide dispersion angle. The model also applies to cases where a very hot liquid is discharged.
Since the physics of effervescence is not well understood, the model must rely on rough empirical fits. The photographs of Reitz and Bracco [ 300] provide some insights. These photographs show a dense liquid core to the spray, surrounded by a wide shroud of smaller droplets.
The initial velocity of the droplets is computed from conservation of mass, assuming the exiting jet has a cross-sectional area that is times the nozzle area, where is a fixed constant, equal to 0.611 as specified in Equations 22.8-3 and 22.8-12.
The maximum droplet diameter is set to the effective diameter of the exiting jet:
The droplet size is then sampled from a Rosin-Rammler distribution with a spread parameter of 4.0. (See Section 22.12.1 for details on the Rosin-Rammler distribution.) The most probable droplet size depends on the angle, , between the droplet's stochastic trajectory and the injection direction:
The dispersion angle multiplier, , is computed from the quality, , and the specified value for the dispersion constant, :