Droplet Size Distribution Measurements Research Articles

Effect of Surfactants on 1,2-Dichloroethane-in-Water Droplet Impacts at Electrified Liquid-Liquid Interface

In this work, we used the electrified liquid-liquid interface (eLLI) to study the fusion of oil-in-water organic droplets (soft particles) upon coming into contact with the soft interface. Our focus was to define the effect of the neutral (1-tetradodecanol) and ionic (cetyltrimethylammonium bromide and sodium dodecylsulfonate) surfactants that stabilize the colloidal solution on the electroanalytical output of the impact events. The electrochemically and interfacially active salt used in our work (tetramethylammonium tetrakis(4-chlorophenyl)borate) was always initially dissolved in the organic phase droplets. When the potential drop at the interface was set below the formal Galvani potential of the tetramethylammonium cation ion transfer, we observed ionic current events upon the fusion of the droplets at the eLLI, as studied by chronoamperometry. This phenomenon was found to be severely affected by the surfactants. Our system was investigated with several methods, including cyclic voltammetry, chronoamperometry, interfacial tension measurements, and finally zeta potential and droplet size distribution measurements based on dynamic light scattering.

Estimating droplet size distribution of emulsions using turbidity measurements: A soft sensor based on artificial neural network

Ability to characterise droplet size distribution (DSD) of emulsions in real-time is essential for on-demand production of customised emulsions. In this work, for the first time, we demonstrate a possibility of estimating full DSD of oil in water emulsions from turbidity measurements using a single wavelength light source. We used recently published data of DSD and turbidity measurements of rapeseed oil in water emulsions (oil volume fractions of 0.15, 0.3 and 0.45) produced with vortex based hydrodynamic cavitation device. Measured DSDs are represented by weighted sum of three log-normal distributions. We developed an approach and a methodology based on artificial neural network (ANN) to estimate DSD from a single measurement of turbidity. A mathematical model is developed to simulate measured turbidity profiles using the known DSDs. The validated model was then used to generate simulated data of turbidity and oil volume fraction pairs (105 pairs). This synthetic data was used to train ANN which used turbidity and volume fraction as input and eight parameters of DSD as output. The developed ANN was able to capture the experimentally measured characteristic diameters and DSDs very well for three oil volume fractions and four different number of passes. The presented methodology and results will be useful for developing an in-line soft sensor based on turbidity measurements for real time estimation of full DSDs of emulsions.

Fabrication and characterization of dual-functional porous starch with both emulsification and antioxidant properties

Starchy materials with good antioxidant, emulsification and adsorption properties have potential applications in industry. To improve these properties, a Dual-functional porous starch was prepared through one-pot synthesis. In this case, octenyl succinic anhydride (OSA) and syringic acid (SA) were selected to modify the porous starch (PS) by esterification, with subsequent signals recorded by 1H NMR at 1.2 ppm and FT-IR at 1743 cm−1, indicating the formation of Dual-functional porous starch grafted by OSA and SA. N2 adsorption analysis further proved that the porous structure (2.9 m2g−1) was still maintained after modification. This was followed by measurements of droplet size distribution (34.18 ± 3.80 μm), zeta potential (−39.62 ± 1.89 mV) and emulsion index (85.10 ± 1.76 %), all of which indicated good emulsifying capacity. Meanwhile, results of radical scavenging assay proved that the Dual-functional porous starch had considerable antioxidant properties due to the introduction of SA groups. Besides, the Dual-functional porous starch also showed good resistance to digestion. These findings not only provide a novel strategy for constructing multi-functionalized starchy materials, but also open up potential applications of starch in the food and pharmaceutical industries.

Measuring diameters and velocities of artificial raindrops with a neuromorphic event camera

Abstract. Hydrometers that measure size and velocity distributions of precipitation are needed for research and corrections of rainfall estimates from weather radars and microwave links. Existing optical disdrometers measure droplet size distributions, but underestimate small raindrops and are impractical for widespread always-on IoT deployment. We study the feasibility of measuring droplet size and velocity using a neuromorphic event camera. These dynamic vision sensors asynchronously output a sparse stream of pixel brightness changes. Droplets falling through the plane of focus of a steeply down-looking camera create events generated by the motion of the droplet across the field of view. Droplet size and speed are inferred from the hourglass-shaped stream of events. Using an improved hard disk arm actuator to reliably generate artificial raindrops with a range of small sizes, our experiments show maximum errors of 7 % (mean absolute percentage error) for droplet sizes from 0.3 to 2.5 mm and speeds from 1.3 to 8.0 m s−1. Measurements with the same setup from a commercial PARSIVEL disdrometer show similar results. Both devices slightly overestimate the small droplet volume with a volume overestimation of 25 % from the event camera measurements and 50 % from the PARSIVEL instrument. Each droplet requires processing of 5000 to 50 000 brightness change events, potentially enabling low-power always-on disdrometers that consume power proportional to the rainfall rate. Data and code are available at the paper website https://sites.google.com/view/dvs-disdrometer/home (Micev et al., 2023).

Size distribution of migrating particles and droplets under gravity in concentrated dispersions measured with static multiple light scattering

HypothesisLight scattering techniques can provide a non-intrusive measurement of particle and droplet size distribution but are limited to relatively diluted liquid dispersions. Measurement of particle velocity distributions (PVD) and particle/droplet size distributions (PSD) in diluted to highly concentrated solid suspensions and emulsions can be performed by coupling the static multiple light scattering technique (SMLS) to mathematical models describing the vertical motion under gravity of polydisperse particles and droplets. ExperimentsMeasurement of the PSD using SMLS was performed on silica particles dispersed in water with monomodal, bimodal and trimodal PSDs ranging from 570 nm and 7.90 µm. Quasi-monodisperse certified latex particles with 815 nm mean diameter dispersed in water and non-controlled emulsions of hexadecane-water emulsions at volume fractions ranging from 0.005 % to 20 % were also characterized with SMLS. These measurements were compared to certified size distributions, and to laser diffraction and dynamic light scattering measurements. FindingsRobust, highly resolutive and concentration-dependent measurement of the PVD and PSD of solid particles and droplets was achieved for diluted to highly concentrated liquid dispersions. As interactions between particles or droplets are dependent on the dispersed phase concentration, accurate characterization of as-formulated industrial liquid dispersions can be performed with SMLS.

In situ characterization of particle formation in spray flame synthesis using wide-angle light scattering

Wide-angle light scattering (WALS) was used for in situ measurements of droplet and nanoparticle size distributions during the synthesis of titania and iron oxide particles from liquid precursor solutions in the standardized SpraySyn burner for spray flame synthesis. Titania was synthesized from titanium tetraisopropoxide (TTIP) and iron oxide from iron(III) nitrate nonahydrate (INN) using ethanol (EtOH) as solvent. Scattering images were taken at heights up to 120 mm above the burner surface and classified into droplet and particle scattering. Droplet size distributions were derived from a sequential analysis of scattering data containing the oscillating Mie pattern, the lognormal size distribution parameters for spherical and fractal particle fractions from a multivariate approach on averaged particle scattering data. The results show that the precursor addition leads to altered evaporation behavior and even droplet disruption probably induced by puffing or micro-explosions compared to pure EtOH. In the case of TTIP (a hygroscopic alkoxide), the synthesis of a large fraction of spheres was observed, while the nitrate INN leads to the formation of mostly fractal aggregates.

Effects of Salinity Beyond Coalescence on Submicron Aerosol Distributions

AbstractBubbles entrained by ocean waves rise to the surface and burst, creating a shower of droplets which contribute to sea spray aerosols. Submicron‐sized droplets, of which an estimated 60%–80% come from a bursting bubble film cap, play a key role in global climate atmospheric processes. However, many aspects of predicting the number and size of submicron drops emitted from a bursting bubble remain unknown. It is well‐documented that higher salinity increases submicron droplet production, which has been attributed to the role of salt in the suppression of bubble coalescence. We experimentally show that submicron drop production increases with salinity despite using a salt that does not affect bubble coalescence, indicating that salinity plays a role in the physics of submicron aerosol formation beyond coalescence. Laboratory experiments are conducted using sodium acetate solutions of salinity S = 0.001–0.1 M with millimeter‐sized bubbles generated via a needle. Unlike previous studies, the measured droplet size distributions are converted to formation diameter, revealing that the peak aerosol formation diameter decreases with higher salinity. Applying this diameter conversion to past studies, we find the peak formation diameter exhibits a scaling of Dform ∼ S−0.32 across three orders of magnitude in salinity and for a variety of salts, bubble coalescence behaviors, and bubble generation mechanisms. This result suggests that salinity has a systematic effect on the length scale of the rupturing bubble film which generates the aerosols. Consequently, salinity likely impacts the submicron aerosol production in oceanic environments even if bubble coalescence is negligible.

Simulation and experimental study on measurement of droplet size distribution based on a novel ultrasonic attenuation scheme

Simulation and experimental study on measurement of droplet size distribution based on a novel ultrasonic attenuation scheme

Comparison between shadow imaging and in-line holography for measuring droplet size distributions

A direct comparison of the droplet size and number measurements using in-line holography and shadow imaging is presented in three dynamically evolving laboratory scale experiments. The two experimental techniques and image processing algorithms used to measure droplet number and radii are described in detail. Droplet radii as low as r = 14 µm are measured using in-line holography and r = 50 µm using shadow imaging. The droplet radius measurement error is estimated using a calibration target (reticle) and it was found that the holographic technique is able to measure droplet radii more accurately than shadow imaging for droplets with r le 625 µm. Using the measurements of droplet number and size we quantitatively cross-validate and assess the accuracy of the two measurement techniques. The droplet size distributions, N(r), are measured in all three experiments and are found to agree well between the two measurement techniques. In one of the laboratory experiments, simultaneous measurements of droplets (r ge 14 µm, using holography) and dry aerosols (0.07 lessapprox r lessapprox 2 µm, using an scanning mobility particle sizer and 0.15 lessapprox r lessapprox 5 µm using an optical particle sizer) are reported, one of the first such comparison to the best of our knowledge. The total number and volume of droplets is found to agree well between both techniques in the three experiments. We demonstrate that a relatively simple shadow imaging technique can be just as reliable when compared to a more sophisticated holographic measurement technique over their common droplet radius measurement range. The agreement in results is shown to be valid over a large range of droplet concentrations, which include experiments with relatively sparse droplet concentrations as low as 0.02 droplets per image. Advantages and disadvantages for the two techniques are discussed in the context of our results. The main advantages to in-line holography are the greater accuracy in droplet radius measurement, greater spatial resolution, larger depth of field, and the high repetition rate and short pulse duration of the laser light source. In comparison, the main advantages to shadow imaging are the simpler experimental setup, image processing algorithm, and fewer computer resources necessary for image processing. Droplet statistics like number and size are found to be very reliable between the two methods for large range of droplet densities, {mathcal {P}}_{r>50}, ranging from 10^{-4} le {mathcal {P}}_{r>50} le 10^{-1} cm^{-3}, when the two techniques are implemented as shown in this paper.

Theoretical and experimental studies on the oil-based emulsion spray.

Oil-based emulsion is a common herbicide formulation in agricultural spray, and its atomization mechanism is different from that of water spray. In this paper, a theoretical model based on the characteristics of spray sheets was proposed to predict the spray droplet size for oil-based emulsion spray. An image processing method was used to measure droplet size distributions for different spray pressures and nozzle configurations, and the measured results were used to validate the theoretical model. The results show that oil-based emulsion spray is characterized by the web structure constituted by perforations. The liquid originally occupied by spray sheets eventually gathers in these web structures. The proposed theoretical model is based on the size of the nozzle exit, the angle of spray sheets, and the perforation number in the web structure, which are relatively easy to obtain. The theoretical droplet size is in inverse proportion to the square root of the perforation number in the web structure while in proportion to the square root of the area of the nozzle exit. The captured images of spray sheets and the measured droplet size distribution show consistency with the theoretical prediction. The difference between theoretical results and measured volumetric median diameter is less than 10% for different spray pressures and nozzles.

Measurements of Droplet Size and Velocity Distributions During Rod Bundle Core Reflood

As part of the Organisation for Economic Co-operation and Development/Nuclear Energy Agency Rod Bundle Heat Transfer (RBHT) project, an experimental study was performed to investigate the entrained droplet sizes and velocities in a rod bundle under reflood conditions. Experimental results were obtained from the U.S. Nuclear Regulatory Commission/The Pennsylvania State University RBHT test facility using advanced dual laser measurement systems that allow for the simultaneous measurement of droplet behaviors at two axial locations during reflood transients. The RBHT facility is highly instrumented and contains a 7×7 electrically heated bundle with dimensions matching those in commercial pressurized water reactors. The combination of the measurement capabilities of the RBHT facility and the choice of appropriate experimental conditions allows for the measurement of unique droplet size and velocity distributions under different transient reflood conditions.

Categorization of Sprays by Image Analysis with Convolutional Neuronal Networks

AbstractSpray characterization has been an issue for process and product characterization for decades. Because of this, a convolutional neuronal network was developed to determine the droplet size from spray images. The images were taken using a digital camera, a light source, and a dark room. These were subsequently employed to design and train a convolutional neuronal network using open‐source software packages and a desktop computer. The accuracy of the network droplet size determinations was checked with additional, independent images. The median drop size was assessed with a high accuracy of more than 99.8 % as the mean spray performance indicator. Additionally, the droplet size distribution measurements from the neural network method deviated from those from the reference method (laser diffraction) by less than 1.5 %. Convolutional neuronal networks can be applied to determine the spray performance using spray cone images. This approach could be useful for multiple applications.

Detonation wave driven by aerosolized liquid RP-2 spray

Detonation-based engines such as Rotating Detonating Engines (RDEs) have been of significant interest for aerospace propulsion. However, most detonation-related studies have focused on gaseous reactants with the majority of investigations focusing on liquid water interactions with gaseous detonations and shocks. This study explores the dynamics of detonation waves driven by aerosolized liquid fuel sprays. An unlike-doublet impinging-jet injector is used to atomize RP-2 and water into aerosolized liquid droplet cloud of measured droplet size distribution where the detonation wave interacts with the cloud mixture. Evidence of RP-2 driving the detonation phenomenon is quantified using dynamic pressure measurements and four simultaneous optical diagnostic measurements: high-speed schlieren, CH* chemiluminescence, formaldehyde planar laser-induced fluorescence (PLIF), and particle Mie scatter. The results show formaldehyde and CH* generation along with a substantial increase in pressure and wave speed when the detonation wave interacts with the RP2 mixture cloud. On the contrary, the detonation pressure and wave speed decrease are observed when the detonation wave interacts with the water droplet cloud. The investigation provides supporting information on liquid fuel droplet burning and heat release driving the detonation wave.

Modelling of dispersed oil/water flow in a near-horizontal pipe

A gravity-diffusion model was implemented for predicting water concentration profiles in dispersed oil-continuous oil–water flows. In this model, the measured droplet size distributions were used instead of a droplet size closure law. The turbulent diffusion was modelled assuming single-phase flow while the gravitational drift was based on closure laws from the literature, including hindrance effects. The results showed that including the effect of turbulence on the drag force was important, where the turbulent fluctuations cause an increase in the average drag because of the non-linearity of the drag law. The model yielded a good match with the experimental data reported by Gonzales et al. (Gonzalez et al., 2022), especially at the highest flow rates.We also concluded that the following model simplification could be introduced without changing the results significantly:1)The droplet size distributions could be replaced by the Sauter mean droplet size.2)The diffusivity profile model could be replaced by a uniform diffusivity model.

Development of innovative clean label emulsions stabilized by vegetable proteins

SummaryThe consumer's perception that food is one of the main determining factors for health increases the demand for foods in line with this trend. The food industry is researching new ingredients, formulations, and technologies aiming to respond to this demand. Namely, product formulations are increasingly less complex, with fewer additives, and manufactured with commonly known ingredients, leading to the concept of clean label products. The present work aimed to develop a vegan and clean label mayonnaise by replacing egg yolk with vegetable protein, obtaining a product aligned with current food trends. Emulsions with 1.5% (w/w) powdered aquafaba, green pea, lupin, and faba bean proteins were prepared and compared to the commercial standard Mendes Gonçalves' mayonnaise. Texture (TPA) and rheology (SAOS) measurements showed that emulsions with lupin and faba bean protein had significant differences (P < 0.05) from the standard. Thus, these two proteins were assessed in a mixed system using different proportions – total protein content of 1.5% (w/w). Additionally, lupin protein showed a significant impact on mayonnaise structure and consistency. Backscattering and droplet size distribution measurements indicated that, except for faba bean, all the emulsions studied are stable and have a high potential for scale‐up.

Effect of Liquid–Liquid Interfacial Area on Biphasic Catalysis Exemplified by Hydroformylation

Biphasic catalysis enables the effective recycling of homogeneous catalysts by their immobilization in an additional liquid phase immiscible with the products. The introduced liquid–liquid interfacial area implies mass transfer limitations that play an important role in understanding these catalytic systems, with many rate enhancement strategies revolving around optimizing said area. In this contribution, the relationship between liquid–liquid interfacial area and catalytic activity is elucidated by applying a methodology that utilizes an image-based in situ measurement of the transient droplet size distribution. When the industrially highly relevant aqueous biphasic hydroformylation of the long-chain olefin 1-octene is taken as the model reaction, it is found that the product nonanal and the addition of the ligand increases the interfacial area by a factor of up to 5. The rate of conversion is found to depend on the stirring speed. By variation of the catalyst concentration, it is shown that an accumulation of the catalyst species at the interface is unlikely. Using a mathematical model, it is highlighted that the effect of the aqueous–organic interfacial area on the catalytic activity is not linear as was previously assumed in the literature. Instead, a change in the interfacial composition is proposed that causes a shift in the dependence of catalytic activity on said area. Thus, the dynamic physical properties of a lean gas–liquid–liquid system were linked to the catalytic performance of the system.

Spray characteristics from nasal spray atomization

In addition to topical delivery, nasal sprays offer an alternative drug administration route to the systemic circulation, therefore avoiding the need for painful, invasive delivery techniques. Studies on the efficacy of nasal drug delivery to date have been conflicting despite its potential. In particular computational studies, e.g. Computational Fluid Dynamics (CFD), of nasal spray deposition require realistic initial spray conditions, which are lacking in the literature. This study aims to provide benchmark experimental data for CFD inputs by characterizing four different types of commercially available nasal sprays used in an ENT (Ear Nose Throat) clinic. Spray characteristics were obtained via high-speed videography, while droplet size distribution (DSD) measurements were obtained with laser diffraction. Three actuation forces were evaluated, representing the use-case of an average adult, average child and the maximum force applied to the spray device. The results demonstrated that actuation force influenced spray velocity, spray duration, DSD, and breakup length. Quantitative data of Rosin–Rammler diameter distributions, spray cone angles, dispersion angles and breakup lengths were found, assisting computational models with realistic values, thereby improving future CFD studies of nasal spray drug delivery in the nasal cavity.

Experiments and fully transient coupled CFD-PBM 3D flow simulations of disperse liquid-liquid flow in a baffled stirred tank

Liquid-liquid disperse multiphase flow in a baffled tank stirred by a Rushton turbine is investigated by experiments and 3D simulations for different impeller speeds and volume fractions. Droplet size distributions are experimentally measured with an inline shadowgraphic probe and compared with fully transient coupled CFD-PBM simulations using the Eulerian multi-fluid framework, the inhomogeneous Multiple Size Group approach and a statistical turbulence model. The simulation model is assessed by a variation of size class and velocity group numbers, grid resolution and simulation domain extent. The model parameters for the breakup and coalescence kernels are fitted to match the measured droplet size distribution at a selected operation point. A subsequent application to different operation points shows that experimental droplet size trends are captured, albeit aside from the fitting point, deviations to data increase. The resulting droplet size distribution is analyzed by an assessment of the turbulent mixing, breakup and coalescence time scales.

Measurements of bimodal droplet size distribution of emulsions using ultrasonic spectroscopy in the long and intermediate wavelength regimes

Ultrasonic spectroscopy has a great potential to measure the particle sizes in suspensions and emulsions of many industrial sectors. However, one significant challenge is measuring particle sizes in a broader range and concentrated systems due to the lack of theoretical models covering large particle wave-particle interaction mechanisms. An alternative way lies with the simultaneous application of ultrasonic theories that operate in long and intermediate wavelength regimes. This work used acoustic spectroscopy to measure size droplets of water-in-sunflower oil emulsions for a volume concentration range of 10 to 50% considering bimodal distributions. The observed attenuation spectra results were compared with the simplest acoustic models applied for the long and intermediate wavelength regimes. The results of ultrasonic spectroscopy agreed with those obtained by laser diffraction and indicate that the methodology used in this study is suitable to measure bimodal droplet distributions with diameters from 0.1 to 1000 μm and concentrations up to 40% vol.

Wine lees: From waste to O/W emulsion stabilizer

Wine lees are the major waste from wine production, containing a noticeable amount of biomass (yeast, stalks, and peels), they could be used for the stabilization of dispersed systems such as emulsions. This work is focused on the determination of techno-functional properties of whine less produced from white grapes and industrial-grade blueberries. The interfacial characterisation was carried out by means of dilatational and interfacial shear rheology, whereas the characterisation of emulsion microstructure was assessed by droplet size distribution, rheological characterisation and backscattering measurements. The results obtained indicated that a high amount of polyphenols were present in wine less obtained from grape fermentation with industrial-grade blueberries as an additive, moreover, their presence also caused better interfacial properties (reducing the interfacial tension up to ca. 15 mN/m). However, the comparison of dilatational and interfacial-shear rheology determined that the interfacial response was caused by a densely packed structure. Fairly low droplet sizes (⁓ 320 nm) were obtained after ultraturrax® homogenization and further passing through the Microfluidizer® device, where the emulsions were stable only in presence of xanthan gum (0.06, 0.12 and 0.25 wt%). However, the suitable amount of XG gum was 0.06 and 0.12 wt% since no phase separation was observed in the emulsions generated over storage time, although flocculation phenomena took place. The results obtained exhibited emulsions with a suitable texture for the preparation of milk-shakes and brewages products, evidencing the potential of wine lees for these products.