Modelling of the breakup process of viscous fluids by a high-speed rotary atomizer
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Spray drying is a preferred method of drying and successful agglomeration of various materials and is widely used in the chemical, food, pharmaceutical and in the power industry, e.g. to produce polymers, dairy products, foodstuff, pharmaceutics or for flue gas cleaning, etc. In spray drying applications very often rotary atomizers are used for atomization of highly viscous and rheologically complex liquids. The resultant droplet size distribution has to be adapted to customer needs, since it directly influences the resultant powder size distribution and the morphology, porosity and packing density of the powder particles. In the present experimental and theoretical study, the size and the velocity of drops generated by a rotary atomizer is measured using a phase Doppler instrument for Newtonian liquids of different viscosities. A theoretical model is developed for the liquid flow through the radial openings of the atomizer wheel, considering a thin annular film flow and a rivulet-type flow. These two types of flow have also been observed in the experiments. Finally, a semi-empirical model for the average diameter of drops in the spray is developed, accounting for the different mechanisms of atomization of the rivulet and the thin film flows.
This work is partly funded by the Innovation Fund Denmark (IFD) under File no. 4135-00129B. The authors would like to thank Prof. Peter Walzel for numerous fruitful discussions.
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