Comparative study of droplet and liquid film velocities in sprays

Abstract

This study presents a comparative analysis of droplet and conical liquid film velocities in sprays by a pressure swirl injector with Abramovich geometric constant K = 1.986. The velocities were measured simultaneously by schlieren image velocimetry and sequential images of the liquid film, using a high-speed camera with 8192 fps and shutter of 2 μs. Other parameters, such as discharge coefficients, spray cone angles and breakup lengths were also determined, using water as test fluid, for injection pressures from 0.05 to 0.5 MPa. Experimental velocity data were compared to results from different semi-empirical equations. The breakup lengths decreased continuously from around 20 mm to 15 mm for injection pressures from 0.1 to 0.5 MPa, while spray cone angles increased continuously from about 42°–53°, for pressures from 0.2 to 0.5 MPa. Mean axial droplet velocities varied from 4.7 m s−1 to 14.5 m s−1, while the mean total droplet velocities varied from 5 m s−1 to 16.2 m s−1 and the total liquid film velocity increased from 5.7 m s−1 to 20.2 m s−1, approximately, for increasing injection pressure. Liquid film velocities were about 15%–28% higher than the droplet velocities in the pressure range considered, due to the energy required for liquid film breakup and the air drag on the droplets. The current findings underscore that significant discrepancies may arise when relying on inadequate velocity data, particularly when employed in the computation of key parameters such as the Reynolds and Weber numbers.