Investigation on the Usage of Effervescent Atomization for Spraying and Spray Drying of Rheological Complex Food Liquids and on the Resulting Particle and Product Properties

Abstract

The effervescent atomizer is an internal mixing pneumatic atomizer in which a two-phase flow prior to the nozzle orifice is created by adding gas in a mixing chamber. The resulting flow pattern is responsible for atomization of the liquid feed. In this study, two different single-phase and two multiphase model feeds were employed. Research was focused on the influence of the flow pattern inside the atomizer and the air-to-liquid ratio by mass (ALR) on the spray performance. The flow pattern inside the mixing chamber of the atomizer was recorded by high-speed cameras, while the one inside the nozzle orifice was determined by an optical sensor. Plug and annular flow was found in the mixing chamber, while a bubbly flow—reported for low viscous liquid feeds in literature—could not be formed due to the feed viscosity investigated in this study. The spray morphology investigations (shadowgraphy imaging and time-resolved spray drop size measurement) showed a clear connection of flow pattern and spray fluctuations. The latter are found for plug flow and have to be avoided for spray drying applications. Annular flow was found to be suitable for fine and stable spray characteristics and consequently atomizer geometry and ALR conditions for annular flow were determined. Moreover, the models of Lund and Geckler [J Fluids Eng 130:61303, 2008, Atomization Sprays, 3:77–89, 1993] were used to predict spray drop sizes. The comparison of these values to measured data gave additional insight in the spray mechanism. To investigate the influence of the atomization process on an inner phase of a multiphase feed, oil-in-water-emulsions were atomized and changes in the oil drop size were determined. Oil drop breakup and coalescence was found and could be described by classical emulsification theory. Finally, the investigated effervescent atomizers were used for spray drying experiments with single-phase feeds. The particle characteristics of the dried products were determined and showed a good agreement with the literature.