High speed imaging of the flow during close-coupled gas atomisation: Effect of melt delivery nozzle geometry

We describe the application of a high-speed still imaging technique to the study of close-coupled gas atomisation. A pulsed Nd:YAG laser is used to obtain pairs of still images with an effective 6 ns exposure time, from which velocity maps of the flow of the atomised fluid can be reconstructed. We demonstrate directly that the melt spray cone consists of a jet precessing around the surface of a cone. Further, we demonstrate that the width of this jet is directly related to the geometry of the melt nozzle. By applying Particle Image Velocimetry techniques we are also able to map the flow field in both the primary and secondary atomisation zones, demonstrating an asymmetric recirculation eddy exists at the circumferential edge of the gas–melt interface in the primary atomisation zone.

► 1st application of Particle Image Velocimetry (PIV) to the gas atomisation process.
► Direct observation that spray cone comprises fine melt filament.
► Direct observation of precession of melt filament.
► Complex, asymmetrical circumferential gas circulation eddies identified.