Drop Size Research Articles

Drop deformation in a planar elongational flow: impact of surfactant dynamics.

Drops in extensional flow undergo a deformation, which is primarily fixed by a balance between their surface tension and the viscous stress. This deformation, predicted and measured by Taylor on millimetric drops, is expected to be affected by the presence of surfactants but has never been measured systematically. We provide a controlled experiment allowing us to measure this deformation as a function of the drop size and of the shear stress for different surfactants at varying concentrations. Our observation is that the deformation predicted by Taylor is recovered at zero and high surfactant concentration, whereas it is smaller at concentrations close to the critical micellar concentration. This is in contradiction to the existing analytical models. We develop a new analytical model, taking into account the surfactant dynamics. The model predicts a transition between a deformation similar to that of a pure liquid and a smaller one. We show that the transition is driven by a parameter KL, which compares adsorption and desorption dynamics. Finally, the concentration C*, at which we observe this transition in the extensional flow is in good agreement with the one predicted by independent measurements of KL.

Statistical Characteristics of Drop Size Distributions in the Warm Season over the Sea of Japan

Statistical Characteristics of Drop Size Distributions in the Warm Season over the Sea of Japan

High-pressure homogenizer valve design modifications allowing intensified drop breakup without increasing power consumption. I. Optimization of current design-principle

This study uses a model-based design approach (CFD coupled to well-established emulsification correlations) to investigate how to choose the valve dimensions of a high-pressure homogenizer so as to achieve intensified drop breakup without increasing the power consumption. Results show how design modifications influence the thermodynamic efficiency of the homogenizer via two effects, a friction factor and a factor related to how high a dissipation rate of turbulent kinetic energy that the design delivers in the centre of the jet. By simple design modifications, thermodynamic efficiency can be increased by 4 % (compared to a representative contemporary valve design) by decreasing the inlet chamber angle, and an additional 5 % by carefully adjusting the outlet chamber angles so as to ensure that the jet exits the gap free of the wall, but then bends and re-attaches to the wall further downstream. The modifications are predicted to allow for achieving the same resulting drop size but with a 17 % lower power draw, compared to a standard contemporary valve, or alternatively a smaller resulting drop diameter at constant power draw.

Optical and Electrical Properties of Nano Magnesium Oxide Doped with Polyvinylpyrrolidone (PVP) Thin Films

A thin film of polyvinylpyrrolidone (PVP) polymer doped with different weight ratios of magnesium oxide nanoparticles produced by using the low-temperature hydrothermal method was prepared, and the morphology of the doped thin film was verified using a scanning electron microscope and an atomic force microscope. The X-ray diffraction pattern showed that magnesium oxide has a multi cubic crystal structure with a diffraction peak of high density associated with the level (200) (at the diffraction angle of 42.69◦) and a crystal drop size of 25 nm. Measurements of the Fourier A transformation of the infrared spectrum of a polyvinylpyrrolidone polymer doped with metal oxides was carried out. It showed a clear difference from the pure polymer, where a (Mg-O-Mg) bond appeared at a wavelength of 450 cm^-1 to confirm the effect of MgO addition on the chemical bonding of polyvinylpyrrolidone. Optical properties, including absorbance, maximum wavelength, and energy gap, have been studied. Determined by ultraviolet examination. The band gap decreased when MgO was doped with PVP films, and the Hall coefficient effect was used to calculate the electrical properties, including the conductivity, kinetics of charge carriers, and their type. The highest conductivity was (0.1*10^-2 Sm), and the tainted membrane was of the n type), where it can be used in optical applications.

In Vitro and In Vivo Performance of Pickering Emulsion-Based Powders of Omega-3 Polyunsaturated Fatty Acids.

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are essential nutrients for human health and have been linked to a variety of health benefits, including reducing the risk of cardiovascular diseases. In this paper, a spray-dried powder formulation based on Pickering emulsions stabilized with cellulose nanocrystals (CNC) and hydroxypropyl methylcellulose (HPMC) has been developed. The formulation was compared in vitro and in vivo to reference emulsions (conventional Self-Emulsifying Drug Delivery System, SEDDS) to formulate n-3 PUFA pharmaceutical products, specifically in free fatty acid form. The results of in vivo studies performed in fasted dogs showed that Pickering emulsions reconstituted from powders are freely available (fast absorption) with a similar level of bioavailability as reference emulsions. In the studies performed with dogs in the fed state, the higher bioavailability combined with slower absorption observed for the Pickering emulsion, compared to the reference, was proposed to be the result of the protection of the n-3 PUFAs (in free fatty acid form) against oxidation in the stomach by the solid particles stabilizing the emulsion. This observation was supported by promising results from short-term studies of chemical stability of powders with n-3 PUFA loads as high as 0.8 g oil/g powder that easily regain the original emulsion drop sizes upon reconstitution. The present work has shown that Pickering emulsions may offer a promising strategy for improving the bioavailability and stability as well as providing an opportunity to produce environmentally friendly (surfactant free) and patient-acceptable solid oral dosage forms of n-3 PUFA in the free fatty acid form.

Droplet Size Distribution in Emulsions.

The droplet size in emulsions is known to affect the rheological properties and plays a crucial role in many applications of emulsions. Despite its importance, the underlying mechanisms governing droplet size in emulsification remain poorly understood. We investigate the average drop size and size distribution upon emulsification with a high-shear mixer for model oil-in-water emulsions stabilized by a surfactant. The size distribution is found to be a log-normal distribution resulting from the repetitive random breakup of drops. High-shear emulsification, the usual way of making emulsions, is therefore found to be very different from turbulent emulsification given by the Kolmogorov-Hinze theory, for which power-law distributions of the drop size are expected. In agreement with this, the mean droplet size does not follow a scaling with the Reynolds number of the emulsification flow but rather a capillary number scaling based on the viscosity of the continuous phase.

Spray characteristics of a multi-slit type throttleable pintle injector with different slit heights

A pintle injector is a type of variable-area injector that has been effectively applied in throttleable rocket engines. Among the several types of pintle injectors, multi-slit type pintle injectors are advantageous in terms of combustion efficiency and suitability for continuous throttling. However, the spray characteristics of multi-slit type pintle injectors have been rarely investigated. Therefore, spray characteristics such as pressure drop, spray angle, and droplet size for a multi-slit type pintle injector were analyzed in this study based on slit height and throttling level. Cold flow experiments and numerical simulations using two types of pintle tips with different slit heights were conducted under a wide throttling range of 20–100 %. The experimental and numerical results indicated that adopting a vertically heightened slit significantly reduces the pressure drop, spray angle, and droplet size at high throttling levels, which can be beneficial in terms of combustion performance and combustion chamber durability. Moreover, changes in spray characteristics over a wide range of throttling levels can be alleviated by applying a vertically heightened slit. The numerical simulation models used in this study were validated such that these could be applied to predict the spray characteristics of multi-slit type pintle injectors.

Rain Attenuations Based on Drop Size Distribution (DSD) Model and Empirical Model at Low THz Frequencies

Rain attenuation based on the drop size distribution (DSD) with different rainfall rates (R) at low THz frequencies is investigated in this paper. The rain attenuation is calculated using the DSD measured for one year and the extinction cross-section (ECS) by the Mie scattering theory. Moreover, the obtained specific rain attenuation is verified by the empirical model using the measurement system consisting of a transmitter, a receiver, and weather measurement units. We measured the received power against the uniform transmitted power at 240, 270, and 300 GHz on the rooftop of the National Radio Research Agency (RRA) in Korea during the same period as the DSD measurement period. After curve fitting by regression analysis, we compared both rain attenuations obtained in two methods with the recommendation International Telecommunication Union Radiocommunication Sector (ITU-R) P.838-3. The root mean square errors (RMSEs) of the DSD model are 2.8977, 2.8646, and 2.8331 at 240, 270, and 300 GHz, respectively. The calculated result using the Mie scattering and the measured DSD methods shows the best fit to the data of the ITU-R recommendation for a rainfall rate of up to 5 mm/h. On the other hand, the empirical results using the T/Rx antenna system are slightly higher compared to the data of the ITU-R recommendation. As the rainfall rate increases, the difference between our results and ITU-R recommendation increases. This study will be useful for predicting rain attenuation for terrestrial wireless links operating at low THz frequencies.

Polymorphic phase transitions in triglycerides and their mixtures studied by SAXS/WAXS techniques: In bulk and in emulsions

Triacylglycerols (TAGs) exhibit a monotropic polymorphism, forming three main polymorphic forms upon crystallization: α, β’ and β. The distinct physicochemical properties of these polymorphs, such as melting temperature, subcell lattice structure, mass density, etc., significantly impact the appearance, texture, and long-term stability of a wide range products in the food and cosmetics industries. Additionally, TAGs are also of special interest in the field of controlled drug delivery and sustained release in pharmaceuticals, being a key material in the preparation of solid lipid nanoparticles. The present article outlines our current understanding of TAG phase behavior in both bulk and emulsified systems. While our primary focus are investigations involving monoacid TAGs and their mixtures, we also include illustrative examples with natural TAG oils, highlighting the knowledge transfer from simple to intricate systems. Special attention is given to recent discoveries via X-ray scattering techniques. The main factors influencing TAG polymorphism are discussed, revealing that a higher occurrence of structural defects in the TAG structure always accelerates the rate of the α → β polymorphic transformation. Diverse approaches can be employed based on the specific system: incorporating foreign molecules or solid particles into bulk TAGs, reducing drop size in dispersed systems, or using surfactants that remain fluid during TAG particle crystallization, ensuring the necessary molecular mobility for the polymorphic transformation. Furthermore, we showcase the role of TAG polymorphism on a recently discovered phenomenon: the creation of nanoparticles as small as 20 nm from initial coarse emulsions without any mechanical energy input. This analysis underscores how the broader understanding of the TAG polymorphism can be effectively applied to comprehend and control previously unexplored processes of notable practical importance.

Evaluating the In Vivo Virulence of Environmental Pseudomonas aeruginosa Using Microinjection Model of Zebrafish (Danio rerio).

(1) Background: Microinjection of zebrafish (Danio rerio) embryos offers a promising model for studying the virulence and potential environmental risks associated with Pseudomonas aeruginosa. (2) Methods: This work aimed to develop a P. aeruginosa infection model using two parallel exposition pathways on zebrafish larvae with microinjection into the yolk and the perivitelline space to simultaneously detect the invasive and cytotoxic features of the examined strains. The microinjection infection model was validated with 15 environmental and clinical strains of P. aeruginosa of various origins, antibiotic resistance profiles, genotypes and phenotypes: both exposition pathways were optimized with a series of bacterial dilutions, different drop sizes (injection volumes) and incubation periods. Besides mortality, sublethal symptoms of the treated embryos were detected and analyzed. (3) Results: According to the statistical evaluation of our results, the optimal parameters (dilution, drop size and incubation period) were determined. (4) Conclusions: The tested zebrafish embryo microinjection infection model is now ready for use to determine the in vivo virulence and ecological risk of environmental P. aeruginosa.

Experimental study on droplet breakup in an orifice jet mixer

AbstractThe droplet breakups in an orifice jet mixer are studied to gain a deeper understanding of the breakup mechanism and establish breakup models used as population balance model source terms for accurate predictions. The breakup process and details are captured in situ using a high‐speed photomicrography system. Experiments are performed with different levels of pressure drop and mother droplet size. A complete breakup process consists of several different sub‐breakup events, hence the cascade breakup definition is adopted to determine statistical results. High breakup frequency is achieved under high pressure drop and small mother droplet size. The average number of daughter droplets is 102–105 and is positively correlated with the pressure drop and mother droplet size. The daughter droplet size distribution has a tailing phenomenon and is mainly affected by the pressure drop. New breakup models based on the above features are established and predict well with the experimental results.

Short communication: Concentrated impacts by tree canopy drips – hotspots of soil erosion in forests

Abstract. The degradation of ground vegetation cover caused by large grazing herbivores frequently results in enhanced erosion rates in forest ecosystems. Splash erosion can be caused by drop impacts with a high throughfall kinetic energy (TKE) from the tree canopy. Notably larger canopy drips from structurally mediated woody surface points appear to induce even higher TKE and generate concentrated impact locations causing severe focus points of soil erosion. However, TKE at these locations has rarely been reported. This pilot study investigated the intensity of TKE at a concentrated impact location and compared it with general TKE locations under the canopy and freefall kinetic energy (FKE) outside the forest. We measured precipitation, TKE and FKE using splash cups at seven locations under Japanese beech trees and five locations outside the forest during the leafless and leafed seasons in 2021 in a mixed forest with evergreen coniferous trees and deciduous broadleaved trees in Japan. The TKE at the concentrated impact location was 15.2 and 49.7 times higher than that at the general locations under the beech and FKE, respectively. This study confirmed that canopy drip from woody surfaces could be a hotspot of soil erosion in temperate forest ecosystems. Throughfall precipitation at the concentrated impact location was 11.4 and 8.1 times higher than that at general locations and freefall, respectively. TKE per 1 mm precipitation (here, “unit TKE”) at the concentrated impact location (39.2 ± 23.7 J m−2 mm−1) was much higher than that at general locations (22.0 ± 12.7 J m−2 mm−1) and unit FKE (4.5 ± 3.5 J m−2 mm−1). Unit TKE in the leafless season was significantly lower than in the leafed season because of fewer redistribution of canopy drips induced only by woody tissue. Nevertheless, unit TKE at the concentrated impact location in the leafless season (36.4 J m−2 mm−1) was still higher than at general locations in the leafed season. These results show that potentially high rates of sediment detachment can be induced not only by throughfall precipitation but also by larger throughfall drop size distributions at the concentrated impact location, even in the leafless season. Further studies with more replication building on this first report are necessary to investigate how many of these concentrated impact locations may occur on average with different tree species to better assess the extent of the erosion risk under forests.

Liquid-liquid surfactant partitioning drives dewetting of oil from hydrophobic surfaces

HypothesisSessile droplets solubilizing in surfactant solution are frequently encountered in practice, but the factors governing their non-equilibrium dynamics are not well understood. Here, we investigate mechanisms by which solubilizing, sessile oil droplets in aqueous surfactant solution dewet from hydrophobic substrates and spread on hydrophilic substrates. ExperimentsWe quantify the dependence of droplet contact line dynamics on drop size and oil, surfactant, and substrate chemistries. We consider halogenated alkane oils as well as aromatic oils and focus on common nonionic nonylphenol ethoxylate surfactants. We correlate these results with measurements of the interfacial tensions. FindingsCounter-intuitively, under a range of conditions, we observe complete dewetting of oil from hydrophobic substrates but spreading on hydrophilic substrates. The timescales needed to reach a steady-state contact angle vary widely, with some droplets examined taking over a day. We find that surfactant surface adsorption governs the contact angle on shorter timescales, while partitioning of surfactant from water to oil, and oil solubilization into the water, act on longer timescales to facilitate the complete dewetting. Understanding of the role played by surfactant and oil transport presents opportunities for tailoring sessile droplet behaviors and controlling droplet dynamics under conditions that would previously not have been considered.

Evaporation of flammable liquids droplets in an electric discharge

Evaporation of a liquid drop under the action of a high-frequency electric discharge is considered. The drops were suspended on a thermocouple and were in air at room temperature. The analysis was carried out under the assumption that the action of the discharge is thermal. It is shown that pure liquid fuel drop (ethanol and diesel fuel) evaporates according to the d2-law. At the same time, the rate of evaporation takes a maximum value depending on the distance to the electrode. Analysis of the rate of drop mass reduction made it possible to estimate the thermal power of the discharge, which also passes through a maximum when the electrode is moved away from the drop. When evaporating emulsion droplets (50%/50% fuel/water) after the heating stage, pulsations of geometric size are observed. The drop size periodically changes near some average value with a certain frequency, which decreases with the time of "evaporation". A physico-mathematical model of droplet heating under the thermal action of a discharge was constructed. The pulsations are explained by the evaporation of water globules inside the emulsion drop, the subsequent increase in the size of the vapor bubbles before the "micro-explosion" of the drop. The loss of emulsion material under the action of an electric discharge occurs mainly due to emissions during microexplosions. That is, the electric discharge leads to the dispersion of emulsions droplets with a high water content, in contrast to individual flammable liquids droplets. A decrease in the water content and the power of the electric discharge leads to an increase in the period of pulsations.

Impact of feeding conditions on continuous liquid-liquid gravity separation, part II: Inlet/outlet drop size distribution and fractional separation efficiency

The effect of the feeding conditions and operating temperatures on the separation process was investigated in a continuous gravity-driven separator, following the analysis of the outlet drop size, and formation/shape of dense-packed zone. The inlet and outlet drop size distributions (DSDs) were considered in combination with the separation efficiency. The inlet and outlet DSDs were found to be self-similar across varied feeding conditions and operating temperatures. An increase of operating temperatures from 20 to 40∘C had a tiny impact on the inlet DSDs and resulted in an 1% - 3% increase in separation efficiency but an 8% - 13% reduction in outlet drop size. A novel concept of integrating separation efficiency and DSDs was introduced, allowing for a more comprehensive assessment of the separation process. The fractional separation efficiency was introduced, and it was evaluated based on the self-similarity of inlet and outlet DSDs.

New Formulation of a Subunit Vaccine Candidate against Lawsonia intracellularis Increases Humoral and Cellular Immune Responses.

Previously, we designed a subunit vaccine candidate based on three L. intracellularis antigens with promising results in pigs. In this study, antigens were produced individually to achieve an even antigen ratio in the formulation. The emulsion characterization included the drop size and the mechanical and thermal stability. Immune response was evaluated by indirect and sandwich ELISAs, qPCR, and flow cytometry. The vaccine candidate's safety was assessed by histopathology and monitoring the clinical behavior of animals. The average production yielded for the chimeric antigen as inclusion bodies was around 75 mg/L. The formulation showed mechanical and thermal stability, with a ratio Hu/Ho > 0.85 and a drop size under 0.15 nm. Antigens formulated at a ratio of 1:1:1 induced a significant immune response in inoculated pigs that persisted until the end of the experiment (week 14). The dose of 200 μg significantly activated cellular response measured by transcriptional and translational levels of cytokines. The cell proliferation assay revealed an increment of lymphocytes T CD4+ at the same dose. Animals gained weight constantly and showed proper clinical behavior during immunization assays. This research demonstrated the immunological robustness of the new subunit vaccine candidate against Porcine Proliferative Enteropathy evenly formulated with three chimeric antigens of L. intracellularis.

Effects of secondary breakup, collision dynamics, gravity and evaporation on droplet size distribution in a pressure-swirl JET A-1 spray

Size and velocity of droplets in pressure-swirl sprays vary with distance downstream the nozzle. This study aims to explain the phenomena contributing to size-resolved spatial variation of the drop size distribution for Jet A-1 spray from a small pressure swirl atomizer injected into quiescent ambient air at atmospheric conditions. The effects of secondary breakup, droplet collisions, gravity, drag-driven spray dispersion, and evaporation are evaluated. Phase Doppler anemometer (PDA) was used to resolve the velocity and size of the droplets in radial profiles at several axial distances (Z) from the nozzle exit at injection pressures between 0.5 and 1.5 MPa. The droplet motion and collision dynamics were qualitatively characterised by high-speed imaging. The analysis focused on areas along 1) the spray axis and 2) the liquid sheet direction. The first area covers small droplets with marginal evolution, while the mean drop size in the second area significantly increases downstream. The local drop size distribution and its axial evolution results from a combined effect of ballistic filtering (drifting of small droplets from periphery to spray centre and large droplets vice versa), centrifugal and turbulent droplet dispersion, and droplet collisions (increasing drop size with distance). The relative droplet-gas velocity was found at investigated Z positions too small for drag-driven secondary droplet breakup to occur. Evaporation of Jet A-1 sprayed at room temperature and pressure into still atmosphere reduces the drop size marginally. Trajectory of all drop sizes is insignificantly altered by gravity. The smallest droplets are strongly drag-driven to the spray axis, while large ones disperse centrifugally and have sufficient momentum to neglect the gravity. Combining results from imaging and laser diagnostics, various collision outcomes were identified, with a conclusion that these depend on the size and velocity of colliding droplets. Coalescing collisions dominate and strongly increase the mean drop size downstream the spray at off-axis positions while insignificantly contribute along the spray axis. The drop size span factor reduces with Z as separative collisions between large droplets and mixed-type collisions between small and large droplets narrow the drop size distribution. The above effects can be most easily amplified for drop size reduction via modification of physical properties of sprayed liquid by its heating.

On the dynamics of a big drop in acoustic levitation

The acoustic levitation of a drop is a complex process that needs a high-intensity non-linear acoustic field; the sound pressure level has to be sufficient to raise the drop but not too large to avoid its atomization, limiting the maximum size of a levitated drop. In this paper, we present an experimental study of big drops levitation with a volume up to 166±2μl and with an effective diameter 6.82±0.03mm, figures one magnitude order larger than the maximum drop volume reported in the literature. Our acoustic levitator produces an acoustic field with a different shape than the field produced by a typical levitator. Our measurements and simulations of the acoustic field and drop dynamics suggest that the levitation of big drops is possible because the distribution of radiation pressure over the drop surface in our system differs from that in a typical acoustic levitator; its maximum value appears on the top surface of the drop and not in its equator. In addition, we determined the upper and lower limits of sound pressure necessary for the levitation of drops of various sizes that allow our system.

Interplay of Drop Shedding Mechanisms on High Wettability Contrast Biphilic Stripe-Patterned Surfaces.

To improve the rate of DWC, numerous studies have adjusted the distribution of drops through biphilic surface patterning and wettability gradients to control the nucleation and drop shedding rates on the condensing surface, yet the connection between drop shedding mechanisms and surface wettability patterning remains unclear. Moreover, wettability patterning places geometric bounds on the governing forces (i.e., gravity, capillary, and inertia), which drive the droplet shedding mechanisms. Thus, the subsequent influence of droplet distribution along the DWC regions on the shedding mechanisms may not be known a priori. In this study, the area fraction, ADWC, of the DWC and also the DWC region width, LN, were varied between 10 and 50% and 0.5-1.5 mm, respectively, to probe the dominant droplet shedding mechanisms on a high wettability contrast surface (i.e., the contact angle on the DWC was 159 ± 3.4° and the hysteresis 9 ± 3.6°, whereas the FWC was nearly perfectly wetting). Humid air was introduced inside a custom-built chamber with the upright steady-state condensation imaged by both real-time and high-speed imaging techniques. We found that the droplet shedding mechanisms changed with increasing LN where the sliding drop radii are reduced with LN while the jumping drop radii remained unchanged with LN. The maximum drop size for shedding also decreased by 13%, which we attribute to the secondary droplet inertia, which helps gravity overcome the capillary retention force. Lastly, although many studies have probed DWC enhancements via surface wettability patterning, an optimal combination of ADWC and LN provided in this study significantly aids in the improvement of future DWC-based condensers and water collector applications.

Quantifying the dependence of drop spectrum width on cloud drop number concentration for cloud remote sensing

Abstract. In situ measurements of liquid cloud and precipitation drop size distributions from aircraft-mounted probes are used to examine the relationship of the width of drop size distributions to cloud drop number. The width of the size distribution is quantified in terms of the parameter k=(rv/re)3, where rv is the volume mean radius and re is the effective radius of the distributions. We find that on small spatial scales (∼100 m), k is positively correlated with cloud drop number. This correlation is robust across a variety of campaigns using different probe technology. A new parameterization of k versus cloud drop number is developed. This new parameterization of k is used in an algorithm to derive cloud drop number in liquid phase clouds using satellite measurements of cloud optical depth and effective radius from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor on Aqua. This algorithm is compared to the standard approach to derive drop number concentration that assumes a fixed value for k. The general tendency of the parameterization is to narrow the distribution of derived number concentration. The new parameterization generally increases the derived number concentration over ocean, where N is low, and decreases it over land, where N is high. Regional biases are as large as 20 % with the magnitude of the bias closely tracking the regional mean number concentration. Interestingly, biases are smallest in regions of frequent stratocumulus cloud cover, which are a regime of significant interest for study of the aerosol indirect effect on clouds.