Simultaneous measurements of the phase-averaged velocity distribution and the underlying discharge quantities of a dielectric barrier discharge plasma actuator (PA) are performed at $10~\text{k}\text{Hz}$ discharge frequency to investigate the interplay of the discharge and the surrounding flow. The underlying velocity information for the force estimation is obtained by means of phase-averaged particle image velocimetry; the discharge quantities are determined from a Lissajous-figure analysis. The results uncover a clear cause–effect relation between the phase-dependent effective discharge capacitance of the PA and the resulting spatiotemporal volume-force distributions. From this novel insight, it must be concluded that the instantaneous effective discharge intensity dominates the momentum-transfer rate rather than the formerly assumed operating voltage.

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Rotary atomizers are widely used for spray drying processes to produce powders in various industrial applications. The atomization regime and therefore the droplet size distribution have a substantial impact on the process outcome. Depending on the intended use of the dried powder particles, various droplet size distributions are desired, which should be adjustable by the main operating parameters (e.g. mass flow rate and wheel speed). In this study the spray of a rotary atomizer wheel, operated under normal ambient conditions, is characterized for different mass flow rates, wheel speeds and viscosities with the help of a phase Doppler measurement system. Visual investigations of the spray with a high resolution camera system help to get a better understanding of the atomization process, as well as the thickness of the liquid jets exiting the atomizer. Keywords rotary atomizer, spray drying, phase Doppler analyser IntroductionThe intended use of the dried powder obtained with a rotary atomizer in a spray drying process [1] or for flue gas cleaning [2] determines the desired size distribution of the powder particles, their morphology and porosity. It is important to understand the influencing parameters on the droplet size distribution for a given geometry of an atomizer to be able to change them to achieve a desired droplet size distribution. In rotary atomizers the liquid is first supplied to the internal atomizer reservoir, flows from there into several (ceramic-) inserts (mainly driven by the centrifugal force due to the atomizer rotation) and is then ejected into the surrounding air. The jets of the processed liquid then breakup and atomize into drops with a certain size distribution. Besides the spray drying industry [3,4,5] rotary atomizers [6,7] and ligament based atomization is also used in numerous other applications, e.g. painting, coating, and generation of agricultural sprays (spreading of pesticides) [8]. The primary atomization process for laminar operating rotary atomizers has already been expressed in terms of dimensionless numbers [9,10], but such atomizers operate at much lower rotational speeds and mass flow rates compared to the atomizers investigated in this study.

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