Analysis of acoustic emissions from gas atomisation

It is well known that during close-coupled gas atomization introduction of the melt into the gas stream affects the emitted noise. However, there has been virtually no study of this ‘acoustic signature’. In this paper we present a quantitative comparison of this acoustic signature for an atomizer under gas only and gas + melt flow. We find that upon introduction of the melt there is strong absorption of frequencies in the 1-8 kHz range. These frequencies are characteristic of the resonance of droplets with 150-600 m diameters and may be indicative of the dynamics of the initial breakup of melt ligaments. Moreover, during atomisation we find that there are considerable low frequency (< 30 Hz) fluctuations in the intensity of the acoustic emissions. We show this may be related to atomizer pulsation, the quasi-periodic low frequency variation in the melt volume instantaneously at the atomizer tip.