Flash-Boiling Atomization of Liquids under Tensile Conditions

When a flash boiling atomization is considered, a higher-pressure difference across the atomization unit (higher upstream or lower downstream pressures) is expected to result in a finer spray. Here we study, in theoretical terms, the effect of lowering the downstream pressure to its value at near the spinodal, well below the absolute zero (a negative pressure). A negative pressure in a continuous liquid phase can be accomplished when outward forces are applied to produce tensile stresses within the liquid. This state is a metastable liquid state. The negative pressure is a new emerging technology that is already being used in some applications from drug and DNA delivery, gene therapy by sonoporation, tissue ablation (histotripsy), nanoparticles generation by sonochemistry, nuclear material detection and monitoring, to synthetic trees to capture carbon-dioxide by using hydro-gels and reverse osmosis. Here we evaluate the bubbles’ growth rate and their size at burst time as a result of homogeneous nucleation under negative pressure conditions. Further we stress that the bubbles’ size at burst is a reasonable indication of the droplets’ size and uniformity. We also examine the effect of the pressure negativity on the efficiency of transforming the input energy to the bubbles’ energy at burst. We conclude that the negative downstream pressure does not necessarily contribute to obtain smaller droplets’ or higher efficiency of the atomization process.