Oil droplet breakup during pressure swirl atomization of emulsions: Influence of emulsion viscosity and viscosity ratio

Abstract

The atomization of oil-in-water emulsions for spray drying is a common task in food engineering. During atomization with pressure swirl atomizers, the emulsions are subjected to high stresses that can lead to deformation and breakup not only of the liquid itself but also of the disperse oil droplets therein. In this study, the effect of the viscosity ratio λ of the emulsion (0.2–33) and of the emulsion viscosity (5–50 mPa⋅s) on oil droplet breakup during atomization was investigated at atomization pressures between 50 and 250 bar. A systematic influence of λ on the oil droplet size was observed with maximum oil droplet breakup for λ between 0.2 and 1.2. At a constant viscosity ratio of ∼ 1, the resulting oil droplet size was almost independent of the emulsion viscosity, even when volume flow rates and spray droplet sizes during atomization showed a clear dependence on this parameter. A model based on existing knowledge on droplet breakup in laminar shear flow is developed, by which oil droplet sizes after atomization can be predicted. This model may serve as a tool to control oil droplet size after atomization by defining appropriate atomization conditions and emulsion formulation. This is especially relevant for spray drying applications in which the oil droplet size in the powder is an important quality parameter. • Viscosity ratio λ influences oil droplet breakup during pressure swirl atomization. • At λ ∼ 1 the emulsion viscosity per se has little influence on oil droplet breakup. • Oil droplet breakup follows the theory of droplet breakup in laminar shear flow. • A model is proposed that serves as a tool to predict oil droplet breakup.