Abstract
The goal of this study was to investigate oil droplet breakup in food emulsions during atomization with pressure swirl (PS), internal mixing (IM), and external mixing (EM) twin-fluid atomizers. By this, new knowledge is provided that facilitates the design of atomization processes, taking into account atomization performance as well as product characteristics (oil droplet size). Atomization experiments were performed in pilot plant scale at liquid volume flow rates of 21.8, 28.0, and 33.3 L/h. Corresponding liquid pressures in the range of 50–200 bar and air-to-liquid ratios in the range of 0.03–0.5 were applied. Two approaches were followed: oil droplet breakup was initially compared for conditions by which the same spray droplet sizes were achieved at constant liquid throughput. For all volume flow rates, the strongest oil droplet breakup was obtained with the PS nozzle, followed by the IM and the EM twin-fluid atomizer. In a second approach, the concept of energy density EV was used to characterize the sizes of resulting spray droplets and of the dispersed oil droplets in the spray. For all nozzles, Sauter mean diameters of spray and oil droplets showed a power-law dependency on EV. PS nozzles achieved the smallest spray droplet sizes and the strongest oil droplet breakup for a constant EV. In twin-fluid atomizers, the nozzle type (IM or EM) has a significant influence on the resulting oil droplet size, even when the resulting spray droplet size is independent of this nozzle type. Overall, it was shown that the proposed concept of EV allows formulating process functions that simplify the design of atomization processes regarding both spray and oil droplet sizes.
Highlights
The atomization of oil-in-water emulsions for spray drying is a common task in food engineering for the production of, e.g., infant formula, coffee creamer and for the encapsulation of lipid-soluble active ingredients, flavors, and colorants [1]
The breakup of oil droplets in emulsions during atomization was investigated for a pressure swirl, an internal mixing and an external mixing twin-fluid atomizer
When operating the nozzles at constant volume flow and comparable spray droplet sizes, the strongest oil droplet breakup was obtained with the pressure swirl nozzle, followed by the internal mixing and the external mixing twin-fluid atomizer
Summary
The atomization of oil-in-water emulsions for spray drying is a common task in food engineering for the production of, e.g., infant formula, coffee creamer and for the encapsulation of lipid-soluble active ingredients, flavors, and colorants [1]. During the atomization step of the spray drying process, an oil-in-water emulsion is dispersed into fine spray droplets, which are dried to powder by contact with a hot air stream [2]. After drying—i.e., evaporating of the water molecules from the continuous phase—the oil droplets remain encapsulated in solid particle, formed by the matrix material, which has been dissolved in the continuous phase prior to spray drying. Matrix materials are usually carbohydrates such as maltodextrins, which are dissolved in the water phase in the feed emulsion [3]. The size of the encapsulated oil droplets in the powder after spray drying is an important quality parameter as it determines the stability and functional properties of the product [4,5]. Submicron oil droplets (
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