On the characterization of spray unsteadiness and its influence on oil drop breakup during effervescent atomization

• Annular flow was achieved for ALR values between 0.1–0.7 (stable atomization).
• At an ALR of 0.02, slug flow was predominant in 2 atomizers resulting in spray unsteadiness.
• A low time-averaged x1,2 is not necessarily a predictor for a stable atomization process.
• At all conditions oil drops were broken during atomization (min. x1,2; oil = 1.7 μm).

The present study focused on the effervescent atomization of oil-in-water emulsions with a special look at the unsteadiness occurring in the internal mixing pneumatic atomizer at certain process conditions. Spray drop size measurements were conducted using a laser diffraction spectrometer at a data acquisition rate of 250 Hz to analyze changes over time. Different characteristic values for the spray morphology and behavior were studied for their suitability to describe timely changes and their effect on spray results. It was found that the flow pattern inside the mixing chamber of the atomizer not only influences the averaged spray drop size but also its temporal fluctuation. Oil drops of atomized emulsions broke up at all investigated ALR, however, no measurable influence of spray unsteadiness was found with the chosen nozzle design.

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