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

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 lambda 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 lambda on the oil droplet size was observed with maximum oil droplet breakup for lambda between 0.2 and 1.2. At a constant viscosity ratio of ~& nbsp;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.

Automated summary

The effect of viscosity ratio and emulsion viscosity on oil droplet breakup during atomization was investigated, and a model for predicting oil droplet sizes after atomization was developed.