Possible, Impossible and Expected Diameters and Flow Rates of Droplets in Aerosols and Sprays

In our recent work we demonstrated a novel liquid atomization technique to produce micro-sprays which combine into an aerosol of submicron-diameter droplets for pure solvents, suspensions, and solutions. Our droplet generation process is based on disintegration by gas jets of thin liquid films formed as bubbles on a liquid surface. For this system and, in general, for any other droplet aerosol or spray generation system, one of the main questions is how to theoretically predict possible, impossible and expected droplet diameters and flow rates which the system will produce at different regimes. In this work we show that the diameters and flow rates of the produced droplets are governed by the interplay of process timescales including capillary breakup, liquid viscosity, and atomizing gas pressure. Timescale ratios can be converted into the ratios of specific energies and into the ratios of specific energy rates provided by the gas and dissipated by the atomized liquid. Using those ratios, we developed a new theoretical approach to determine the lower and the upper limits and the expected values of droplet diameters and flow rates in a droplet generation process. We introduced atomization diagrams to graphically visualize the respective regions for liquid atomization. Theoretically predicted and measured droplet diameters and droplet flow rates for various liquids (water, gasoline, diesel, and solutions of sodium alginate and sodium benzoate) were in a good agreement for aerosols of submicron-diameter droplets generated by our liquid atomization process, as well as for sprays of regular-size droplets produced by conventional pressure nozzle. Finally, we demonstrate that our approach can serve as a theoretical framework for comparison between different aerosol and spray production techniques.