Theoretical prediction of atomization performance of fibre suspensions and the effect of feed temperature and air velocity

Abstract Atomization performances of juice-fibre suspensions, which are non-Newtonian extensional liquids, inside a two-fluid nozzle were predicted theoretically by using two different relationships, in which one of the relationships does not incorporate the extensional rheological properties in its prediction. A good correlation was obtained between the theoretical and experimental droplet sizes of fibre suspensions when the theoretical droplet sizes were predicted by considering the extensional rheological property which is the relaxation time of the fibre suspensions. This finding confirms that the atomization of fibre suspensions, which the fibre suspensions exhibit significant extensional properties, are dominantly controlled by extensional resistance with minor effects of shear resistance and surface tension. It also implies that the relatively bigger droplet sizes of the fibre suspensions, when compared to Newtonian droplets, were due to the extensional resistance of the suspensions, with little effect by shear viscosity and surface tension. The atomization performance was observed at elevated temperatures ranging between 20 and 70 °C. By using a two-fluid nozzle at a low atomizing air velocity of 150 m/s, the D(v,90) significantly reduced from > 1000 μm to 650 μm when the temperature was increased from 20 to 70 °C. Meanwhile, at a high atomizing air velocity of 240 m/s, the D(v,90) can be said to remain constant between 350 and 400 μm.