Experimental Investigation of Effervescent Atomization, Part Ii: Internal Flow and Spray Characterization With Novel Darpa Suboff Afterbody Streamline Aerator

Abstract

This experimental work reports, for the first time, observations of internal flow field involving an DARPA SUBOFF afterbody design aerator body in an inside-out type of effervescent atomizer. The effect of operating parameters like air-to-liquid ratio (ALR), operating pressure, aerator orifice diameter, aeration area and mixing chamber diameter on internal flow within the effervescent atomizer is studied. The effect of increasing ALR on the internal flow is quantified by identifying different gas injection mechanisms at the aerator orifice (into the mixing chamber) and two-phase mixing chamber flow regimes using high-speed shadowgraphy. In particular, it is observed that as ALR is systematically increased the gas injection mechanism transits in the following sequence: single bubbling, pulsed bubbling, elongated jetting, atomized jetting and evacuated chamber. The range of ALRs within which these mechanisms are observed are employed to draw up a flow regime map. Similar analysis on two-phase mixing chamber flow regimes yielded corresponding regime map for internal two-phase stabilized flow in the mixing chamber. The flow regime transited from bubbly flow to slug flow to churn flow and finally to annular flow as the ALR was increased. The spray characteristics (size and velocity) at the nozzle exit are reported using Phase Doppler Anemometry (PDA) measurements. It is observed that dense bubbly and bubbly-slug flow regimes produce stable sprays with droplet sizes in the range of 50-80 µm in the range of 0.25%-1.50% ALR.Dependence of internal flow on other parameters such as orifice aerator diameter (with constant total aerator orifice area), mixing chamber diameter and operating pressure are also studied.

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“…The obtained data are interesting from the point of view of designing new atomizers, in particular, two-phase atomizers. Niland et al [33] also undertook a study on an effervescent atomizer equipped with an aerator. In this experimental work, an internal flow field in the atomizer was presented for the first time, and an attempt was made to explain the complex mechanisms of the effervescent atomization process.…”