Atomization behaviour of juice-fibre suspensions in a two-fluid nozzle

摘要

Atomization of non-Newtonian viscoelastic liquids was carried out using a two-fluid nozzle. Juice-fibre suspension is a shear thinning liquid that exhibits significant extensional resistance when forced through an extensional flow-field. Two types of fibres were used with aspect ratios of 2-3 and 8-10. The atomization behaviour of the suspensions discharging in the air was photographed using a backlit setup to visualise the atomization pattern of viscoelastic fibre suspensions. The effect of the extensional resistance is to delay the droplet formation by forming filamentary structures that link successive droplets together. As a consequence, droplets of viscoelastic fibre suspensions are usually bigger than Newtonian droplets. Using a two-fluid nozzle, at an atomizing air velocity of 150 m/s, the average droplet size of fibre suspension with aspect ratio 2-3 was 450 mu m while the average droplet size of fibre suspension with aspect ratio 8-10 was 530 mu m. Increasing the atomizing air velocity in the two-fluid nozzle yielded better atomization by forming smaller droplets as proved by the droplet size analysis. At the highest tested atomizing air velocity of 240 m/s, both average droplet sizes were reduced to approximately 200-250 mu m.