High speed imaging techniques for the analysis of close-coupled gas atomisation

We describe two complimentary, high speed imaging techniques for studying close-coupled gas atomisation. In the first technique a high frame rate (18,000 fps) video camera is used to film a continuous sequence of images, whilst in the second a pulsed Nd:YAG laser is used to obtain pairs of still images with an effective 6 ns exposure time. By combining these techniques we are able to 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.