Critical Mass-Flow in Orifice-Nozzles at the Disintegration of Superheated Liquids

Flashing atomization is initiated when the superheated liquid is exposed to a sudden pressure drop below saturation vapor pressure at the prevailing temperature. Superheated atomization is used to enhance atomization where conventional pressurized liquid injection cannot achieve the desired fine sprays. Essentially flashing is initiated by in situ bubble nucleation followed by bubble growth. If the internal flow conditions are such that stable cavitation bubbles can form, then such bubbles promote the atomization of the base liquid already in the capillary of the nozzle. Bubble creation via cavitation can be achieved by changing the nozzle geometry such as the orifice length-to-diameter ratio, the inlet corner radius, the surface conditions of the nozzle material and the flow velocity in the orifice. In case of superheated atomization, the mass flow and thus the flow velocity in the orifice can just be indirectly set by the combination of superheat temperature upstream the nozzle and the difference between high pressure level upstream and ambient pressure downstream the orifice. Consequently the internal geometry and the material of the nozzle are of vital impact on the atomization process of the ejected liquid.