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

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.

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Impact of Viscosity Ratio on the Dynamics of Droplet Breakup in a Microfluidic Flow Focusing Device

10.1063/1.2964920 ◽

2008 ◽

Cited By ~ 2

Author(s):

Wingki Lee ◽

Lynn M. Walker ◽

Shelley L. Anna ◽

Albert Co ◽

Gary L. Leal ◽

...

Keyword(s):

Viscosity Ratio ◽

Droplet Breakup ◽

Flow Focusing ◽

Microfluidic Flow

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Droplet Breakup in Shear and Elongation Dominated Flows in Microfluidic Devices

Microelectromechanical Systems ◽

10.1115/imece2005-80625 ◽

2005 ◽

Author(s):

Shelley L. Anna ◽

Gordon F. Christopher ◽

Nadia Noharuddin

Keyword(s):

Drop Size ◽

Viscosity Ratio ◽

Volume Fraction ◽

Microfluidic Devices ◽

Droplet Breakup ◽

Formation Mechanisms ◽

Liquid Form ◽

Droplet Sizes ◽

Elongational Flows ◽

Viscous Stresses

Microfluidic devices have recently been demonstrated as an effective platform for generating monodisperse drops and bubbles, which is important for applications from emulsification to drug delivery and lab on a chip. Here we compare drop formation mechanisms in microfluidic devices in which flows can be either predominantly shear flows, or predominantly elongational flows. In either case, drops of an aqueous liquid form due to viscous stresses imposed by a second oil phase. We show that the two flow types lead to dramatically different ability to control droplet sizes. We characterize the drop size over a large number of experiments by varying capillary number, volume fraction, and viscosity ratio. We observe distinct breakup modes depending on these three dimensionless parameters, and the flow type.

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Breakup and Coalescence of Oil Droplets in Protein-Stabilized Emulsions During the Atomization and the Drying Step of a Spray Drying Process

Food and Bioprocess Technology ◽

10.1007/s11947-021-02606-1 ◽

2021 ◽

Author(s):

Martha L. Taboada ◽

Doll Chutani ◽

Heike P. Karbstein ◽

Volker Gaukel

Keyword(s):

Spray Drying ◽

Droplet Size ◽

Concentration Ratio ◽

Oil Content ◽

Droplet Breakup ◽

Drying Process ◽

Oil Droplets ◽

Oil Droplet ◽

Oil Concentration ◽

Oil Droplet Size

AbstractThe goal of this study was to investigate the changes in oil droplet size in whey protein–stabilized emulsions during the atomization and the subsequent drying step of a spray drying process. For this purpose, experiments were performed in an atomization rig and a pilot spray dryer with two commercial pressure swirl atomizers. By comparing the oil droplet size before atomization, after atomization, and after spray drying, the changes in oil droplet size during each process step were quantified. The effect of oil droplet breakup during atomization was isolated by atomizing emulsions with 1 wt.% oil content and a protein to oil concentration ratio of 0.1. At 100 bar, the Sauter mean diameter of oil droplet size was reduced from 3.13 to 0.61 μm. Directly after breakup, coalescence of the oil droplets was observed for emulsions with a high oil content of 30 wt.%, leading to a droplet size after atomization of 1.15 μm. Increasing the protein to oil concentration ratio to 0.2 reduced coalescence during atomization and oil droplets with a mean diameter of 0.92 μm were obtained. Further coalescence was observed during the drying step: for an oil content of 30 wt.% and a protein to oil concentration ratio of 0.1 the mean droplet size increased to 1.77 μm. Powders produced at high oil contents showed a strong tendency to clump. Comparable effects were observed for a spray drying process with a different nozzle at 250 bar. The results confirm that droplet breakup and coalescence during atomization and coalescence during drying have to be taken into consideration when targeting specific oil droplet sizes in the product. This is relevant for product design in spray drying applications, in which the oil droplet size in the powder or after its redispersion determines product quality and stability.

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Heavy Fuel Oil Droplet Breakup and Dispersion Study

Proceedings of the 4th International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT'17) ◽

10.11159/ffhmt17.192 ◽

2017 ◽

Author(s):

Masoud Darbandi ◽

Ali Fatin ◽

Gerry E. Schneider

Keyword(s):

Droplet Breakup ◽

Fuel Oil ◽

Heavy Fuel Oil ◽

Oil Droplet

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Droplet breakup of a high-viscosity-ratio system in a nonuniform temperature field under laser irradiation

Physics of Fluids ◽

10.1063/5.0055235 ◽

2021 ◽

Vol 33 (7) ◽

pp. 073108

Author(s):

Gea Fardias Mu'min ◽

Tatsuya Kawaguchi ◽

Takushi Saito

Keyword(s):

Temperature Field ◽

Laser Irradiation ◽

Viscosity Ratio ◽

High Viscosity ◽

Droplet Breakup ◽

Nonuniform Temperature ◽

Nonuniform Temperature Field

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Influence of the Emulsifier System on Breakup and Coalescence of Oil Droplets during Atomization of Oil-In-Water Emulsions

ChemEngineering ◽

10.3390/chemengineering4030047 ◽

2020 ◽

Vol 4 (3) ◽

pp. 47

Author(s):

Martha Taboada ◽

Nico Leister ◽

Heike Karbstein ◽

Volker Gaukel

Keyword(s):

Molecular Weight ◽

Whey Protein ◽

Spray Drying ◽

Protein Isolate ◽

Droplet Breakup ◽

Low Molecular Weight ◽

Oil Droplets ◽

Oil Droplet ◽

Emulsifier System ◽

Coalescence Times

Spray drying of whey protein-based emulsions is a common task in food engineering. Lipophilic, low molecular weight emulsifiers including lecithin, citrem, and mono- and diglycerides, are commonly added to the formulations, as they are expected to improve the processing and shelf life stability of the products. During the atomization step of spray drying, the emulsions are subjected to high stresses, which can lead to breakup and subsequent coalescence of the oil droplets. The extent of these phenomena is expected to be greatly influenced by the emulsifiers in the system. The focus of this study was therefore set on the changes in the oil droplet size of whey protein-based emulsions during atomization, as affected by the addition of low molecular weight emulsifiers. Atomization experiments were performed with emulsions stabilized either with whey protein isolate (WPI), or with combinations of WPI and lecithin, WPI and citrem, and WPI and mono- and diglycerides. The addition of lecithin promoted oil droplet breakup during atomization and improved droplet stabilization against coalescence. The addition of citrem and of mono- and diglycerides did not affect oil droplet breakup, but greatly promoted coalescence of the oil droplets. In order to elucidate the underlying mechanisms, measurements of interfacial tensions and coalescence times in single droplets experiments were performed and correlated to the atomization experiments. The results on oil droplet breakup were in good accordance with the observed differences in the interfacial tension measurements. The results on oil droplet coalescence correlated only to a limited extent with the results of coalescence times of single droplet experiments.

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Shape and rheology of droplets with viscous surface moduli

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.930 ◽

2019 ◽

Vol 862 ◽

pp. 385-420 ◽

Cited By ~ 2

Author(s):

Vivek Narsimhan

Keyword(s):

Inclination Angle ◽

Viscosity Ratio ◽

Droplet Breakup ◽

Constitutive Law ◽

Lateral Migration ◽

Droplet Deformation ◽

Insoluble Surfactant ◽

Dilute Suspension ◽

Normal Stress Differences ◽

Extra Stress

We develop perturbation theories to describe the flow dynamics of a droplet with a thin layer of insoluble surfactant whose mechanics are described by interfacial viscosity, i.e. a Boussinesq–Scriven constitutive law. The theories quantify droplet deformation in the limit of small capillary number, large viscosity ratio, or large shear Boussinesq number, to a sufficient level of approximation where one can extract information about nonlinear rheology and droplet breakup. In the first part of this manuscript, we quantify the Taylor deformation parameter and inclination angle in shear and extensional flows, developing expressions that resolve discrepancies between current analytical theories and boundary element simulations. Interestingly, the theories we develop appear to accurately describe the inclination angle of a clean droplet over a wider range of viscosity ratios and capillary numbers than previous works. In the second part of the manuscript, we calculate how interfacial viscosity alters the extra stress of a dilute suspension of droplets, in particular the shear stress, normal stress differences, shear thinning and extensional thickening. The normal stresses are intimately related to the lateral migration of droplets in wall-bound shear flow, and we explore the influence of interfacial viscosity on this phenomenon. We conclude by discussing how one can use these theories to describe droplet breakup, and how one can incorporate additional effects into the perturbation theories such as viscoelastic membranes and/or Marangoni flows.

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