Spray Droplets Research Articles

What determines the drop size in sprays of polymer solutions?

The effect of viscoelasticity on sprays produced from agricultural flat fan nozzles is investigated experimentally using dilute aqueous solutions of polyethylene oxide (PEO). Measurements of the droplet size distribution reveal that polymer addition to water results in the formation of overall bigger droplets with a broader size distribution. The median droplet size is found to increase linearly with the extensional relaxation time of the liquid and to be well captured by a simple empirical expression in terms of non-dimensional Weber and Deborah numbers. We show that the increase in droplet size with increasing viscoelasticity can be partly attributed to an increase of the wavelength of the flapping motion responsible for the sheet breakup, resulting in the formation of larger ligaments from which droplets are formed. We also show that droplet size distributions, rescaled by the average drop size, are well described by a compound gamma distribution with parameters n and m encoding for the ligament corrugation and the width of the ligament size distribution, respectively. These parameters are found to saturate to values n = 4 and m = 4 at sufficiently high polymer concentrations. • Viscoelasticity leads to larger droplets in sprays for agricultural flat fan nozzles. • Polymer additives can therefore be used to reduce airborne spray drift. • The median droplet size increases linearly with the extensional relaxation time. • Droplet sizes are Gamma distributed with broad drop and ligament sizes with polymers.

Investigation of cross-stream spray injection and wall impingement in a circular channel for SCR application

A parametric study of cross-stream pulsed spray injection and wall impingement characteristics in a circular channel has been carried out with an objective to investigate performance improvement in selective catalytic reduction (SCR) systems for exhaust gas after-treatment in diesel engines. The spray computations are performed based on a combined Eulerian and Lagrangian based modeling approach for the continuous and the discrete phases respectively. The simulation results are validated using the in-house experimental data for water injection in both open atmospheric and channel flow conditions. The spray structure, penetration, and droplet size are compared and good agreement between the experiments and simulations is demonstrated. Though the focus of the present work is on studying the influence of liquid preheating on post-impingement spray and wall-film characteristics as well as evolution of species mass fraction, the effect of air mass flow rates, and temperature, and the choice of the working liquid (water or Urea Water Solution (UWS)) are also investigated. While the mass flow rate of air and the selection of the above liquids for spray injection are found to have marginal influence on the results, the liquid preheating is shown to strongly affect the droplet evaporation and thus, the spray impact process. Especially, the liquid injection temperature that leads to flash evaporation results in reduced wall filming, higher ammonia generation rate and spatial uniformity of NH 3 across the channel. This paper demonstrates preheating as a promising approach for the improvement of SCR performance. • Spray injection and wall impingement in a duct air flow relevant to SCR systems is numerically investigated. • The predicted post-impingement droplet size and spatial distribution compared well against the in-house experiments. • Marginal influence of air mass flow rate and choice of the liquid (water or UWS) is observed. • Preheating the injected liquid is a viable alternate for performance optimization of the SCR systems. • Especially, the flash evaporation condition ensures reduced wall filming and, higher rate of NH 3 and its spatial uniformity.

Numerical analysis of injection and spray characteristics of diesel fuel and rapeseed oil in a diesel engine

Vegetable oil-based biofuels are promising carbon-neutral fuels to replace fossil fuels. The study focuses on a comparative analysis of injection and spray characteristics of DF and RO and the relationship between spray and emission formation. Steady nozzle flows were simulated in Ansys Fluent. Free sprays were modeled with 0D spray models, and the relationships between atomization parameters and TKE at the orifice exit were analyzed. Sprays of DF/RO blends in real combustion chamber conditions were simulated with a multi-zone spray model in DIESEL-RK. The influence of RO content on fuel atomization and fuel-air mixture formation were analyzed. Compared with DF, RO has lower injection velocity and TKE at the orifice exit. The empirical correlations of mean droplet diameters and spray angle with TKE were developed by using a complex TKE/ν 0.5 with correlation coefficients above 0.988. The increase of the RO content from 0 to 100% leads to a reduction in spray angle by 24% and an increase in spray tip penetration by 15.5%, SMD by 62.1%, and the mass fraction of fuel injected onto the combustion chamber walls from 17.1 to 42%. A correlation between NOx emissions and SMD was fitted with a correlation coefficient of 0.9968.

Assessment of subgrid dispersion models for large-eddy simulations of turbulent jet flows with dilute spray droplets

High-fidelity simulations for polydispersed sprays in the Eulerian–Lagrangian framework need to incorporate subgrid-scale effects in the particle evolution equations. Although the quasi-linear evaporation rate formulation captures evaporating droplet statistics, further improvement is required when subgrid-scale velocity effects become essential. The subgrid dispersion model strongly affects droplets spatial distribution, and subsequently net evaporation rate, depending on how rapidly they are dispersed into the dry air region. The main original contribution of this study is to assess the performances of a number of commonly used dispersion models in a consistent manner, against a reference direct simulation results. The models considered are (i) discrete random walk, (ii) approximate deconvolution method, (iii) stochastic model based on the Langevin equation, and (iv) combined approximate deconvolution method with the Langevin equation. Mass and enthalpy transfer source terms together with droplet diameters and particle distributions were compared against corresponding direct numerical and large-eddy simulations without a model as reference cases. Numerical results at low Stokes and moderate Reynolds numbers indicate that the dispersion model choice does not affect Eulerian field averages or fluctuations. However, proper dispersion models are essential to capture droplet distributions in the far-field region after jet breakup for Stokes number smaller than unity. The unclosed Lagrangian momentum equation without any dispersion model most accurately reproduces direct numerical simulation in the near field.

Three-dimensional measurement of the droplets out of focus in shadowgraphy systems via deep learning-based image-processing method

For the shadowgraphy techniques with a single camera, it is difficult to accurately obtain the shape, size, and depth location of the droplets out of focus due to the defocus blur. This paper proposed a deep learning-based method to recover the sharp images and infer the depth information from the defocused blur droplets images. The proposed model comprising of a defocus map estimation subnetwork and a defocus deblur subnetwork is optimized with a two-stage strategy. To train the networks, the synthetic blur data generated by the Gauss kernel method are utilized as the input data, which mimic the defocused images of droplets. The proposed approach has been assessed based on synthetic images and real sphere blur images. The results demonstrate that our method has satisfactory performance both in terms of depth location estimation and droplet size measurement, e.g., the diameter relative error is less than 5% and the location error is less than 1 mm for the sphere with a diameter of more than 1 mm. Moreover, the present model also exhibits considerable generalization and robustness against the transparent ellipsoid and the random background noise. A further application of the present model to the measurement of transparent water droplets generated by an injector is also explored and illustrates the practicability of the present model in real experiments. The present study indicates that the proposed learning-based method is promising for the three-dimensional (3D) measurement of spray droplets via a combination of shadowgraphy techniques using a single camera, which will greatly reduce experimental costs and complexity.

Evaluation of Spray Droplets Characteristics Depending on the Configuration of Boomless Nozzle

Using hollow cone nozzles is a common in different spraying processes for controlling the pests. The aim of the study was to evaluate the spray droplet characteristics deposited on the eggplant plants at flowering vegetative growth stage. The study was performed in a Complete Block Random Design (CBRD) with a 3x4 factorial scheme, consisting of three working pressures 2, 3, and 5 bar, and four spray patterns of nozzles with three blocks. For obtaining micro details about spray droplets characteristics, white paper cards were used, which later had their images digitized and analyzed by the ImageJ software. The following values were measured in this study: volume median droplet diameter, spray coverage percentage, and droplet density per centimeter square. Then, the values found were subjected to analysis to show the significance between them. These values were compared by t test at 5% probability level. For each factor, separately, the coefficients of variation were analyzed and then the correlation between these factors was performed. The main results showed that the spray droplet characteristics were affected by both of operating pressure and spray pattern configuration. Higher operating pressure of 5bar produced the smallest median diameter and greatest number of droplets, and spray coverage percentage. Results also showed that the using of a combination spray pattern led to an increase in droplet density thereby coverage percentage into plant canopy in comparison to other pattern configurations.

A thermally-driven seawater desalination system: Proof of concept and vision for future sustainability

Since the 1970s, commercial-scale thermally-driven seawater desalination plants have been powered by low-grade energy sources, drawn either with low-pressure bled-steam from steam turbines or the solar renewable energy harvested that are supplied at relatively low temperatures. Despite the increasing trend of seawater reverse osmosis plants, the role of thermal desalination methods (such as multi-stage flashing and multi-effect distillation) in GCC countries is still relevant in the Arabian Gulf, arising from higher salinity, the frequent algae blooms of seawater and their ability to utilize low temperature heat sources. Given the urgent need for lowering both the capital and operating costs of all processes within the desalination industry and better thermodynamic adaptation of low-grade heat input from renewable sources, the present paper addresses the abovementioned issues by investigating the direct contact spray evaporation and condensation (DCSEC) method. A DCSEC system comprises only hollow chambers (devoid of membranes or tubes, minimal use of chemical and maintenance) where vapor generation (flashing) utilizes the enthalpy difference between the sprayed feed seawater and the saturated vapor enthalpy of the vessels. Concomitantly, vapor is condensed with spray droplets of cooler water (potable) in adjacent condenser vessels, employing a simple design concept. We present detailed design and real seawater experiments data of a DCSEC system for the first time. The water production cost is calculated as $0.52/m 3 , which is one of the lowest figures reported compared to commercial processes presented by Global Water Intelligence.

Salt Spray Corrosion of 2060-T8 Al–Li Alloy in an Aggressive Environment

The phase and microstructure of corrosion product formed on 2060-T8 Al–Li alloy have been investigated effectively by SEM and XRD after salt spray corrosion. It was found that the corrosion product growth rate can be divided into three stages: the main phases of corrosion product were Al2O3, Al(OH)3, and AlOOH phases; as the increasing of salt spray time, the phase angle of A12O3 shifts slightly to the left at 31.8°; and the phase angle of A12O3 first shifts to the left, then to the right at 38.6°. The formation and evolution model of salt spray droplet was built, and the formation mechanism of corrosion product was also analyzed. This alloy shows a sensitive corrosion performance to the salt spray environment.

Count- and mass-based dosimetry of MDI spray droplets with polydisperse and monodisperse size distributions

Most previous numerical studies of inhalation drug delivery used monodisperse aerosols or quantified deposition as the ratio of deposited particle number over the total number of released particles (i.e., count-based). These practices are reasonable when the aerosols have a sufficiently narrow size range. However, spray droplets from metered-dose inhalers (MDIs) are often polydisperse with a wide size range, so using monodisperse aerosols and/or count-based deposition quantification may lead to significant errors. The objective of this study was to develop a mass-based dosimetry method and evaluate its performance in lung delivery in a mouth-lung (G9) geometry with an albuterol-CFC inhaler. The conventional practices (monodisperse and polydisperse-count-based) were also simulated for comparison purposes. The MDI actuation in the open space was studied using both high-speed imaging and LES-Lagrangian simulations. Experimentally measured spray velocities and size distribution were implemented in the computational model as boundary conditions. Good agreement was achieved between recorded and simulated spray plume evolution spatially and temporally. The polydisperse-mass-based predictions of MDI doses compared favorably with the measurements in all three regions considered (device, mouth-throat, and lung). Significant errors in MDI regional deposition were predicted using the monodisperse and count-based methods. The new polydisperse-mass-based method also predicted local deposition hot spots that were one order of magnitude higher in intensity than the two conventional methods. The results of this study highlighted that a presentative polydisperse size distribution and appropriate deposition quantification method should be applied to reliably predict the MDI drug delivery in the human respiratory tract.

Possible, impossible, and expected diameters and production rates of droplets in aerosols and sprays

Liquid atomization processes generating sprays and aerosols of droplets are used in many delivery and coating systems involving pure solvents, solutions, and suspensions. In our recent experimental work, we introduced a novel liquid atomization process generating micro-sprays and aerosols of submicron-diameter droplets for pure solvents, solutions, and suspensions: gas jets disintegrate thin liquid films that are formed as bubbles approach a liquid surface. Here we develop a theoretical description of droplet sizes and flow rates, using the first principles of conservation of mass and energy, and accounting for the ratios of specific energies and the ratios of specific energy rates provided by the atomizing gas and dissipated by the atomized liquid. We introduce atomization diagrams as a graphical tool to determine possible, impossible, and expected droplet diameters and specific flow rates in aerosols and sprays produced under various conditions. We find a reasonable agreement between the theory and experiments for five different liquids converted into aerosols of submicron-diameter droplets by an atomization process where gas jets disintegrate thin liquid films that are formed as bubbles approach a liquid surface, and also for five traditional pressure nozzles that produce sprays of droplets of hundreds of microns in diameter. Our study explored the overall range of Ohnesorge number between 0.01-100, and the analysis and atomization diagrams contribute to understanding of liquid atomization and can serve as a theoretical framework for comparing different liquid atomization techniques.

Drift Potential Characteristics of a Flat Fan Nozzle: A Numerical and Experimental Study

This study explores the drift potential characteristics of a flat fan nozzle. The atomization and drift characteristics of fan-shaped pressure nozzles were studied at a spraying height of 0.6 m and a lateral wind speed of 0–6 m/s through a combination of computational fluid dynamics (CFD) analyses and wind tunnel experiments. The nozzle Lu 120-03 had a spraying pressure of 0.3 MPa. The results show that as the wind speed varies from 0 m/s to 6 m/s, the spray droplet spectrum also changes, and the droplet volume medium diameter increases. The cumulative droplet ratio and droplet spectral width of M oscillate within certain ranges. The amount of spray drift increases at higher wind speeds. The concentration of droplet deposition on the bottom of the wind tunnel gradually spreads downward in the wind direction. The determination coefficient R2 of the straight-line fitting of the drift characteristics is 0.982, which is highly consistent with the CFD simulation results. A CFD simulation-assisted wind tunnel test method, which is more convenient and repeatable than traditional field tests, is proposed to analyze the droplet spectrum and drift of Lechler series nozzles. The program can accurately simulate the actual drift and provide theoretical and data support for the optimization of atomization and drift characteristics of several types of flat fan nozzles under different spraying pressures and crosswinds in practical applications.

Droplet velocity and thermal state from hot gas atomization of steel melt: Impact on the quality of the spray-formed tubular deposit

The velocity and thermal behavior (temperature, enthalpy, solid fraction) of atomized droplets in a metal spray play the most important role in the spray forming process. These properties mainly determine the materials yield and the final product quality (e.g., porosity, microstructure) of the as-sprayed materials. Changing the gas temperature in the atomization process directly influences these droplet properties in the spray. To understand the droplet behavior in the spray at various atomization gas temperatures (i.e., room temperature RT 293 K, 573 K, 873 K), numerical simulations using computational fluid dynamics (CFD) techniques have been performed and validated by experiments. A series of atomization runs (powder production and spray-forming with AISI 52100 steel) has been conducted at different atomization gas temperatures and pressures with a close-coupled atomizer (CCA). The in-situ temperature detection of the deposit surface (pyrometer) and in the substrate (thermocouples) has been performed to observe the effect of particle properties on the deposit. The result shows that hot gas atomization provides smaller droplets with faster velocity in the spray, affecting the droplet impact and deformation time in the deposition zone. A higher solid fraction of the smaller droplets by hot gas atomization also reduces the deposit surface temperature. Increasing the substrate diameter further decreases the deposit surface temperature without compromising the deposit quality (i.e., porosity) and also refines the grain size. Pre-heating of the substrate up to 573 K results in lower porosity in the vicinity of the substrate.

Lower Inspiratory Breathing Depth Enhances Pulmonary Delivery Efficiency of ProAir Sprays

Effective pulmonary drug delivery using a metered-dose inhaler (MDI) requires a match between the MDI sprays, the patient’s breathing, and respiratory physiology. Different inhalers generate aerosols with distinct aerosol sizes and speeds, which require specific breathing coordination to achieve optimized delivery efficiency. Inability to perform the instructed breathing maneuver is one of the frequently reported issues during MDI applications; however, their effects on MDI dosimetry are unclear. The objective of this study is to systemically evaluate the effects of breathing depths on regional deposition in the respiratory tract using a ProAir-HFA inhaler. An integrated inhaler mouth-throat-lung geometry model was developed that extends to the ninth bifurcation (G9). Large-eddy simulation (LES) was used to compute the airflow dynamics due to concurrent inhalation and orifice flows. The discrete-phase Lagrangian model was used to track droplet motions. Experimental measurements of ProAir spray droplet sizes and speeds were used as initial and boundary conditions to develop the computational model for ProAir-pulmonary drug delivery. The time-varying spray plume from a ProAir-HFA inhaler into the open air was visualized using a high-speed imaging system and was further used to validate the computational model. The inhalation dosimetry of ProAir spray droplets in the respiratory tract was compared among five breathing depths on a regional, sub-regional, and local basis. The results show remarkable differences in airflow dynamics within the MDI mouthpiece and the droplet deposition distribution in the oral cavity. The inhalation depth had a positive relationship with the deposition in the mouth and a negative relationship with the deposition in the five lobes beyond G9 (small airways). The highest delivery efficiency to small airways was highest at 15 L/min and declined with an increasing inhalation depth. The drug loss inside the MDI was maximal at 45–60 L/min. Comparisons to previous experimental and numerical studies revealed a high dosimetry sensitivity to the inhaler type and patient breathing condition. Considering the appropriate inhalation waveform, spray actuation time, and spray properties (size and velocity) is essential to accurately predict inhalation dosimetry from MDIs. The results highlight the importance of personalized inhalation therapy to match the patient’s breathing patterns for optimal delivery efficiencies. Further complimentary in vitro or in vivo experiments are needed to validate the enhanced pulmonary delivery at 15 L/min.

Flash-Boiling Characterization During Ingress of Coolant Event for Dust Issue in ITER

Abstract Dust resuspension inside the vacuum vessel (VV) is one of the safety issues of the fusion reactor ITER. Plasma interaction with the plasma facing components (PFC) leads to their erosion, generating dust. One of the accident scenarios leading to dust resuspension is the ingress of coolant event (ICE) where a leak of the coolant pipes inside the VV conducts to injection and flash atomization of the cooling water. The metallic dust, produced by the erosion, is then oxidized by water throughout an exothermic reaction that produces hydrogen leading to a loss of confinement risk due to hydrogen and dust combustion. The steam flow, produced by the flash atomization of the liquid leaking from the breach, is considered to be the main source of dust resuspension. Therefore, experimentations about the two-phase flow generated by the flashing liquid jet are important to identify the main physical phenomena involved in the aerosol particles resuspension for ITER-like conditions that impose in particular low pressure level. Flash-boiling experiments were conducted under primary vacuum conditions. We studied the behavior and the structure of the flow resulting from superheated water injection into low pressure environment. Using shadowgraphy and particle image velocity (PIV), qualitative information and quantitative measurements on the two-phase flow that develops for different superheat conditions were gathered. The measured spray lateral spreading and droplets velocity are shown to increase with the superheat level. The use of a transparent nozzle also confirmed the strong coupling between the external structure of the atomized spray and the two-phase flow that develops upstream of the coolant circuit breach.

Comment on Scheepers et al. Comparative Performance Testing of Respirator versus Surgical Mask Using a Water Droplet Spray Model. Int. J. Environ. Res. Public Health 2021, 18, 1599.

In the article "Comparative Performance Testing of Respirator versus Surgical Mask Using a Water Droplet Spray Model" by Scheepers et al. [...].

Extinguishment of a transformer fire with a long projection water mist system

When large oil-immersed power transformer fire happens, scenarios such as bushing explosion, oil pool fire, oil spray fire and oil flowing fire are commonly observed. As the nozzles of current water mist or sprinkler system are arranged in the fire region, they are at risk of damage during the explosion or under high temperature. This paper presents a long projection water mist technique based on axial flow inducing to effectively extinguish the fire at far distance. The droplet size, spray density, and effective spray distance were characterized via Laser diffraction technique, water collection method and laser distance measurement. Fire extinguishment tests were conducted through setting up a full-scale 800 kV converter transformer model to verify its capability. The results indicate that the proposed system can extinguish the 800 kV converter transformer fire within dozens of seconds, due to its long spray distance, small droplet size, and large spray density. This study will provide a new method for water mist generation and references for system design for large transformer fire or oil fire extinguishment in open space.

Semi-Empirical Model of Droplet Size Distribution From the Maximum Entropy Principle in Sodium Spray

When a sodium leakage accident occurs in the sodium-cooled fast reactor, the leaked sodium reacts violently with the air in the form of droplets, resulting in the phenomenon of sodium spray fire. The droplet size distribution formed by liquid sodium injection is the key factor affecting the accident analysis of sodium spray fire. Based on the theory of the maximum entropy principle, a semi-empirical model of sodium spray droplet size distribution is constructed, which is constrained by the mass equation or the momentum equation with viscous resistance, respectively. Based on the existing liquid fuel droplet size distribution experiment results and the sodium spray fire experiment results, the semi-empirical model is verified, which shows that the prediction result with the semi-empirical model constrained by the momentum equation is in good agreement with the experimental result with the error of about 20%. Furthermore, the proposed sodium spray droplet model is compared with other models of the empirical model, the semi-empirical model, and the model based on the maximum entropy principle constrained by the simplified mass equation. The simulation result with the proposed model matches the experimental data better with minor error.

Effects of spray droplet size on pronamide control of Poa annua

AbstractAnnual bluegrass (Poa annua L.) is a problematic weed in turfgrass that has evolved resistance to 12 different herbicide sites of action. The mitotic inhibiting herbicide pronamide has both pre‐ and postemergence activity on susceptible annual bluegrass populations, but on certain resistant populations, postemergence activity is hypothetically compromised due to lack of root uptake or due to an unknown foliar resistance mechanism. Spray droplet size may affect foliar and soil deposition of pronamide, thus potentially explaining variation in population control or differential shoot and root uptake. Greenhouse experiments were conducted to quantify pronamide, flazasulfuron, and pronamide + flazasulfuron (a common tank mixture) deposition on annual bluegrass as affected by spray‐droplet size. Five droplet sizes (200, 400, 600, 800, and 1,000 μm) were sprayed in an enclosed spray chamber on two‐ to three‐leaf stage annual bluegrass plants. Fluorescent dye was added to each treatment solution to quantify the effects of herbicide and spray droplet size on herbicide deposition. Results indicate that spray droplet size affects deposition of pronamide and flazasulfuron, applied alone and in combination, on annual bluegrass. The highest foliar deposition was produced with 400‐μm spray droplets in pronamide treatments and with 200 μm spray droplets in flazasulfuron and pronamide + flazasulfuron treatments. The addition of flazasulfuron to pronamide did not affect herbicide deposition when compared with pronamide‐alone treatments. Results suggest that 200‐ to 400‐μm spray droplets are optimal for foliar deposition of pronamide. Alternatively, larger droplet sizes may facilitate better soil deposition of pronamide where root uptake is optimal.

Numerical study of kerosene spray and combustion characteristics using an air-blast atomizer

In this study, a computational model for a cylindrical combustor with an air-blast atomizer was created to investigate the effect of changing air to liquid mass ratio (ALR) on spray characteristics without combustion and the effect of changing ALR on combustion characteristics under different swirl numbers with constant kerosene fuel mass flow rate using computational fluid dynamics (CFD) code. The study aim is to define the ALR at which the pollutants concentrations at combustion exhaust will be the least. Eight values of ALR were considered and these include 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.4 and 1.5. The cold spray characteristics including the number of droplets, Sauter Mean Diameter, droplets penetration length and droplets contours were obtained in addition to combustion characteristics that were studied by describing the reverse flow zone (RFZ) boundary, flow pathlines, temperatures maps, outlet temperatures at combustor exit and species concentrations. The results indicate that increasing ALR and consequently spray droplet diameter decrease does not always translate into superior emissions performance and it depends on several parameters including swirling intensity where the modernistic capabilities of CFD code including flow visualization and calculated recirculated mass flow ratio are used to justify the reasons behind this exceptional behavior. In addition, the results show that the spray Sauter Mean Diameter decreases by increasing ALR but the droplet diameter reduction effect was steeper at lower ALR than higher ones. The length of the RFZ is decreasing with the increase of ALR and shifts upstream closer to the combustor swirler. The recirculated flow mass ratio and the outlet average temperature are decreasing with the increase of ALR.

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 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.