Water Droplet Size Research Articles

Long term water trapping in Pickering emulsions undergoing compositional ripening.

One approach to achieving low-calorie foods is to substitute regions of high-calorie content with water droplets, forming water-in-oil emulsions. However, in complex food systems consisting of multiple species of dispersed phases, compositional ripening may occur in which the emulsified water undergoes mass transfer to droplets filled with a species that is less soluble in the continuous phase, for example sugar. Here we present two model systems and use them to study compositional ripening for water-in-oil Pickering emulsions. Water-in-dodecane and water-in-tributyrin emulsions stabilised by PMMA particles were prepared and combined with similar emulsions that included sugar in the water. We use confocal microscopy as a function of time combined with particle tracking to explore how these systems evolve in time. For dodecane, as the system evolves, the pure water droplets appear to crumple due to the loss of water; in extreme cases, they eventually 'explode'. Simultaneously, the sugar-filled droplets expand and slowly coalesce. Evidently, our interfacial coating of particles is unable to suppress compositional ripening. In contrast, pure water droplets in tributyrin crumple into small stable structures, potentially retaining water. We show that decreasing the concentration of the sugar solution also decreases the rate of change of water droplet size for both oils. Observations of droplet 'explosions' confirm that the driving force can overcome the trapping of the particles at the interface, in contrast to the case of Ostwald ripening. However the crumpled states in the tributyrin system provide some indication that this effect can be overcome.

DOES INTERNAL CONVECTION PROMOTE MICRO-EXPLOSION OF W/O EMULSION DROPLETS?

W/O emulsions are considered as a beneficial alternative to the use of fossil hydrocarbon fuels and not treated vegetable oils. The presence of a dispersed phase composed of water allows to reduce pollutant emissions and also increases combustion efficiency because of the so-called micro-explosion phenomenon. This micro-explosion has a strong stochastic behavior, and its realization depends on several parameters such as water droplet size distribution and motion during heating. This paper aims to provide a better understanding of the impact of the water droplet behavior on the atomization rate. PLIF technique is used to visualize and track the motion of the water droplets dispersed inside heated emulsion drops. Natural convection of the water droplets is observed, and its impact on coalescence and atomization rate is investigated. Emulsion with small size distributions and high droplet velocity tends to show a low or nonexistent micro-explosion rate, while coarse emulsions show an important coalescence rate, resulting in a high micro-explosion occurrence. Finally, a dimensionless indicator measuring dispersed-phase motion intensity is proposed.

Promotion and inhibition effects of wax on methane hydrate formation and dissociation in water-in-oil emulsions

Clarifying the effect of wax on hydrate formation and dissociation are important for the safe and high-efficient development of deep-water oil and gas fields. In this study, a series of experiments on the effect of wax on hydrate formation and dissociation in water-in-oil emulsions were systematically studied based on the variation analysis of temperature, pressure, torque, oil–water interface area morphology and water droplet size in emulsions. Microscopic images reveal that wax crystals form shell barriers on the oil–water interface, which increases transfer resistance, and the particle focused beam reflectance illustrates that the wax crystals decrease the water droplet size, which increases the oil–water interface area in emulsions. With increasing wax concentration, the hydrate induction time and growth rate show a bimodal shape because of the dual regulation of wax in emulsions, involving the inhibition effect of the transfer barrier layer and the promotion effect of the increasing water–oil interface area. The inhibition effect on hydrate formation was dominant when the wax concentration exceeds 6 wt%, resulting in a rapid decrease in both the growth rate and conversion ratio with increasing wax concentration. Compared with the bimodal shape of hydrate formation, the inhibition effect of wax on hydrate dissociation is the dominant regulation factor. The duration of complete hydrate dissociation by depressurization increased linearly with the increasing wax concentration, which increased the operation difficulty of hydrate plug removal. These experimental results provide valuable references for hydrate risk assessment and optimization of the project design of flow assurance for deep-water oil and gas fields.

Droplet Size-Assisted Polysiloxane Architecting

(Super)antiwetting shielding around engineering materials and protecting them against harsh environmental conditions have been achieved via growing various geometry polysiloxane (or silicone) patterns around them by using a droplet-assisted growth method, where the polymerization takes place inside of the water droplets acting as reaction vessels. The size and distribution of these reaction vessels are the main factors in making different geometry silicone patterns; however, very little is known about the fate of these droplets throughout the polymerization. Here, we propose keeping the relative humidity (% RH) inside the reactor stable throughout the polymerization as a new coating parameter to force the size of the reaction vessel water droplets to be the same for building simply shaped silicone rods with controlled geometry and distribution. In this manner, we grew simple geometry cylindric microrods on surfaces and could tune their length, diameter, inter-rod spacing, and thus the (super)hydrophobicity. Here, we also demonstrate that with changes in the amplitude and stability of the % RH, it is possible to fabricate different (super)hydrophobic nanograsses, conical silicone microrods, and isotropic silicone nanofilaments. The proposed new way of tuning initial and in situ reaction vessel droplet size can be used as a single factor to formulate different geometry silicone patterns with tunable dimensions, leading to different roughness and hydrophobicity. To a certain extent, the droplet size-assisted silicone shaping in this work provides a new way to control the length, diameter, morphology, inter-rod spacing, and thus the (super)hydrophobicity of the silicone patterns, especially those in the shape of simple cylindrical microrods. This control over silicone architecting will help to prepare new (super)hydrophobic coatings with more controlled morphology and thus wettability; on the contrary, it will support surface scientists modeling the connection between surface geometry and (super)antiwetting of such irregular pillared surfaces that remain elusive.

Dynamics of non-coalescence in unequal sized, conducting multi-droplet system suspended in an insulating medium under an electric field

An intriguing experimental observation in electrocoalescence of water-in-oil emulsions is the occurrence of a very low critical electric field, beyond which chaining of droplets and shorting of electrodes is observed, as compared with the experimental and theoretical predictions based on two equal sized water droplets in oil. Motivated by these observations, a numerical, analytical and experimental study on the interaction between multiple, unequal sized, perfectly conducting droplets in a perfectly dielectric medium under an electric field is presented here. We show that the critical capillary number ( $Ca_c$ ), based on the bigger droplet, in a two droplet system, reduces as the radius ratio of the smaller to bigger drop decreases. Secondly, in a system of three equally sized droplets, it is expected that the $Ca_c$ will be smaller than a two equal sized droplet system, since the electric field experienced by the central droplet is higher when surrounded by two droplets instead of one. Our results show that nonlinearity in the system due to both the asymmetric shape deformation and the electrostatic interaction between the multiple droplets, leads to significant reduction in $Ca_c$ for onset of non-coalescence in an unequal sized two droplet system or for equal and unequal sized three droplet systems, as compared with $Ca_c$ for two equal sized droplets. This is possibly one of the underlying mechanisms for observing much smaller $Ca_c$ in emulsions as compared with a system of two equal sized droplets, and could be responsible for a polydisperse water-in-oil emulsion being exceptionally susceptible to chaining under an electric field.

Effect of centrifugal force (G) on stability of natural emulsions (water/oil) present in fresh virgin olive oils

Fresh virgin olive oils (VOOs) just obtained has a cloudy appearance, due to the presence of emulsified water and solid dispersed particles. The stability of these emulsions mainly depends on the water droplet size distribution and the presence of natural emulsifying agents in the oils. In this work, the effect of centrifugation force and time on fresh unfiltered VOOs from the horizontal decanter centrifuge (HDC) and vertical centrifuge separator (VCS) has been studied. The turbidity, moisture, insoluble impurities and phenol content of the oils were analyzed. The increasing of centrifugation force and time decrease the parameters studied of the unfiltered VOOs studied. The VCS oils showed a higher stability of the emulsion, since presented slightly higher values of the parameters studied after application the different centrifugation treatments. Fresh VOOs obtained in the mills can be considered metastable natural emulsions difficult to break with the current centrifugation systems of the olive extraction process.

Characterization of the aerosol produced from an aerated jet

Faucet aerators that form aerated water jets generate aerosols, which can constitute a risk of infection if the water is contaminated, particularly for vulnerable individuals near the sink. In this study, we characterize the size and trajectory of water droplets produced from an aerated jet. The detected particle diameter ranged from 3 to 150μm. The concentration of droplets in the air varied from near-zero to a maximum of 2×1011particles/m3, depending on the location relative to the jet. We found four relevant categories of droplets based on their trajectories following their emission at the jet’s free surface: particles with inertia high enough to escape the immediate vicinity of the jet (category 1), particles moving towards the jet (category 2), particles drawn into the aerator, which only included particles with a diameter smaller than 50μm (category 3), and particles with a near-vertical trajectory (category 4). Tracing category 1 particles to their generation location on the water interface shows a higher emission rate near the aerator. Finally, we employ a numerical model to compute the subsequent trajectories of droplets detected at the limits of the sampled domain. We find that particles whose diameter is smaller than 55μm completely dry and become airborne. Larger droplets deposit within a radius of 7cm around the jet, assuming a surface is located 20cm below the aerator tip. These results increase the fundamental understanding of the emission mechanisms of droplets in aerated jets and their fate in the sink environment.

Effects of plastic-grocery-bag derived oil-water-diesel emulsions on combustion, performance and emission characteristics, and exergoeconomic aspects of compression ignition engine

Waste generation from non-biodegradable plastic-grocery bags (PGB) has raised concerns in recent years due to their massive production and consumption. The other pressing issues include the depletion of fossil fuels, rising prices, and environmental pollution from compression ignition (CI) engines. In the context of reducing emissions from CI engines, emulsified fuel is becoming increasingly popular. Given the above two flaws and the potential of emulsification, this study looks into the prospects of PGB-derived oil-water-diesel emulsions for CI engine application. Three emulsions were prepared at varying diesel percentages. The average water droplet size ranged between 215.4 and 397.4 nm, with more than 93 % stability after 75 days. The lower heating value of the emulsions increased the brake-specific fuel consumption (BSFC). However, the neat BSFC of all the blends was lower than diesel. All the emulsion blends also decreased the nitrogen oxide and smoke emission simultaneously; additionally, the heat sink effect also reduced the exhaust gas temperature. The blend with 10 % diesel incorporation exhibited the lowest increment in carbon monoxide and unburnt hydrocarbon emissions w.r.t diesel. Additionally, it has also the highest exergy efficiency and sustainability index and the lowest specific exergy cost for shaft work amongst the emulsion blends.

Microemulsion Delivery Systems with Low Surfactant Concentrations: Optimization of Structure and Properties by Glycol Cosurfactants.

Extensive use of microemulsions as delivery systems raises interest in the safe ingredients that can form such systems. Here, we assessed the use of two glycols, i.e., propylene glycol and pentylene glycol, and their mixtures to manipulate the properties and structure of microemulsions. Obtained systems with glycols were extensively characterized in terms of capacity to incorporate water phase, droplet size, polydispersity, structure type, and rheological and thermal properties. The results of these studies indicate that the composition, structure, and viscosity of the microemulsions can be changed by appropriate quantification of glycols. It has been shown that the type of glycol used and its amount may favor or worsen the formation of microemulsions with the selected oils. In addition, a properly selected composition of oils and glycols resulted in the formation of microemulsions with a reduced content of surfactants and consequently improved the safety of using microemulsions as delivery systems.

Predicting the drop size passing through a superhydrophobic orifice

Superhydrophobic surfaces can be utilized in various applications, such as enhanced heat transfer, anti-icing, self-cleaning, and viscous drag reduction. In this work, we investigated the water droplet size separation using superhydrophobic surfaces, which is relatively new and unexplored research field, but yet promising for pharmaceutical and medical applications. We developed a theoretical model for predicting the diameter of a droplet passing through a smaller superhydrophobic orifice by considering the balance of forces, geometrical characteristics, and the surface wettability. For verification of the model, experimental water droplet size separation was conducted using a thin superhydrophobic copper foil with a laser-cut orifice with a diameter ranging from 1.2 to 2.1 mm. A comparison of the experimental and analytical results has shown that the error of the model is less than 20% within the model's validity range with the upper limit at the capillary length of the fluid. By moving away from this limit toward smaller droplet diameters, the accuracy of the model improves and reaches an error of less than 7% at the smallest used orifice diameter of 1.2 mm.

Effect of Installation Conditions of Water Mist Nozzle on Thermal Radiation Attenuation Performance

In this experimental study, the effect of installation conditions of a water mist nozzle on thermal radiation attenuation performance was investigated. Two types of nozzles (Small_nozzle and Large_nozzle) were used. Experiments were conducted under conditions in which the nozzle was installed near the heater and heat flux sensor (Position_NH and Position_NS, respectively), and water mist was discharged from one and two nozzles (Case_ID and Case_SD, respectively). To characterize the water mist spray, the water supply pressure and droplet size were measured, and visualization of the sprayed water mist was performed. The thermal radiation attenuation performance improved with an increase in the water flow rate, and Small_nozzle showed higher thermal radiation attenuation performance than Large_nozzle. Moreover, Case_SD showed lower thermal radiation attenuation performance than Case_ID_Sum (that is, the Sum of Case_ID & Position_NS and Case_ID & Position_NH) and the difference in thermal radiation attenuation performance between Case_SD and Case_ID_Sum at a higher water flow rate was more significant than that at a lower water flow rate. These might be attributed to the wide overlapping area of water mist discharged from two nozzles in Case_SD and at a higher water flow rate, narrowing the overall width of the water mist.

Water droplets in oil at the inlet of an EHD contact: A dual experimental and numerical investigation

The current study employs both experimental and numerical approaches to investigate water-in-oil flow at the entrance of EHD contacts. In this work, for the first time, a micro-sized water-in-oil emulsion flow was directly observed at the entrance of an EHL point contact using a high-speed camera. To represent the severity of the water-in-oil emulsion, the abscissa of the closest droplets to the contact area is compared to the critical meniscus position of starvation calculated for pure oil EHL condition. A numerical approach was developed based on the experimental observation. The impacts of various operating parameters such as rolling velocity, water droplet size, applied load, and lubricant viscosity on the flow of water-in-oil emulsion have been further investigated. The results of this work give a possible explanation for the contradictory findings in the literature and reveal the critical conditions under which water-in-oil emulsion would influence the EHL contacts.

Continuous preparation of water-in-heavy oil emulsion without emulsifier by SiC membranes at high temperature and its micro-explosion performance

Emulsified heavy oil as an alternative fuel is of great significance for reducing environmental pollution and settling energy crisis. The micro-explosion of the emulsion plays a vital role in improving the fuel efficiency as well as reducing harmful gas emissions. Here, the water-in-heavy oil emulsion was prepared by membrane emulsification at high temperatures (60–100 °C) without using any emulsifier, and its puffing and micro-explosion performance were investigated by the suspended drop method. The water droplet size (D90) of emulsions can be controlled from 3.8 μm to 7.0 μm by controlling the emulsification process parameters (i.e., membrane pore size, the flow rate ratio of the dispersed phase to the continuous phase, the flow rate of the continuous phase on the membrane surface and temperature of continuous phase) using SiC membranes. Moreover, the trend of droplet size can be predicted based on analyzing the forces on an individual droplet that govern by the emulsification parameters. The puffing and micro-explosion probability of the emulsions increased with the increasing water content and droplet size, which can also effectively reduce the coking of heavy oil at 500 °C. As a result, the highest probability of micro-explosion (90%) and the lowest probability of coking (10%) were realized at a water content of 5 vol% and an average droplet size of 6.5 μm. Therefore, the utilization efficiency of heavy oil can be improved by membrane emulsification process.

Numerical Study of Electrostatic Desalting: A Detailed Parametric Study

A systematic process analysis was conducted to study the effect of the main variables in an industrial electrostatic desalter, such as electric field intensity, wash water content, droplet size, and oil viscosity, on the efficiency of the separation of water from oil. The analysis was assessed through an already published and validated CFD multiphase numerical model that considers the expression of the frequency of collisions as a function of the mentioned process variables. Additionally, the study allowed the formal optimization exercise of the operation to maximize the separation efficiency. The most significant variables were the initial water content and the electric field intensity, while the temperature (oil viscosity) had an effect to a lower extent. An increase in the electric field and temperature and a decrease in the water content improved the water separation from oil. Optimum values suggested from the factorial experimental design and the optimization implemented in this work indicated the use of an electric field of 3 kV/cm, water content of 3%, and an oil viscosity of 0.017 kg/ms. At the same time, the droplet size showed no significant effect under the conditions explored in this work.

Behavior and welfare impacts of water provision via misting in commercial Pekin ducks.

Ducks will access water to maintain feather condition and exhibit natural water-related behaviors such as wet preening. Providing water to ducks commercially is challenging as it may reduce litter and air quality leading to higher duck mortality or illness. This research aimed to measure the behavioral and welfare impacts of water provision via a misting system for commercial Pekin grower ducks in Victoria, Australia. Seven grower flocks were observed (four misted and three nonmisted in open-sided sheds) during May and November 2021. From 26 until 33 d of age, treatment ducks were provided 1 h of misting with shed curtains closed in both treatment and control sheds. At the start and end of the misting application period, external health and welfare measures were taken directly on the ducks via transect walks throughout each shed and catch-and-inspect observations on a sample of 150 ducks from each shed. Video recordings were also made of the misted and nonmisted ducks for 3 h representing time periods prior to, during, and after the 1-h misting across all sheds for all 8 d of the treatment period. Observations were made of all behavior that ducks exhibited at 10-min scan sample intervals across four cameras per shed, totaling 4,198 scans across the seven sheds. General linear mixed models showed the misting application predominantly had impacts on the patterns of behavioral change across the treatment time periods between the misted and nonmisted ducks rather than increasing or decreasing the overall expression of specific behaviors (interaction terms all P ≤ 0.003). The misted ducks increased drinking, tail wagging, and walking, and reduced preening, rooting litter, sitting, and stretching during misting relative to what they showed prior. The nonmisted ducks showed less sitting and more panting during misting relative to prior. Pearson's Chi-square tests showed some differences between the treatment groups in feather cleanliness on the back and wings (both P < 0.0001), likely resulting from pre-existing differences between sheds in blood from pin feathers. Most welfare indicators showed no positive or negative effect of the misting treatment. These results indicate overhead misting does affect duck behavior to some degree without compromising their welfare, but further research with larger water droplet sizes resulting in greater accumulation of surface water or extended durations of misting may lead to greater effects.

Brownian motion on an out-of-thermal-equilibrium surface.

The motion of colloidal species on an out-of-thermal equilibrium surface is studied experimentally by optical microscopy. Water droplets of size in the micrometer range, spontaneously formed at a spherical-like interface between water and oil, are the colloidal species. The interface appears as a convex meniscus when putting water on oil with an added nonionic surfactant. Since the water density is greater than that of oil, the interface is produced into the oil. The spontaneously formed water droplets move attached to the interface while still growing from submicrometer sizes to a few micrometers. Although the dynamic nature of the process, with both the interface and the particles still changing, produces heterogeneities in the system, anomalous diffusion was not observed. The motion of the droplets has a well-identified Brownian component with a Gaussian distribution of steps due to the thermal agitation of the media surrounding the droplets and a drift component due to the effect of gravity.

Experimental evaluation of individual effects of water mist spray characteristics on thermal radiation attenuation using twin‐fluid nozzles with full‐cone spray pattern

AbstractIn this study, the effects of water mist spray characteristics on thermal radiation attenuation were experimentally investigated using five types of external and internal mixing twin‐fluid nozzles with a full‐cone spray pattern. To the best of our knowledge, this may be the first attempt to experimentally examine the separate effects of water mist spray characteristics on thermal radiation attenuation. Water and air supply pressures were measured, and their values were 1.3–55.5 and 29.8–316 kPa, respectively. The Sauter mean diameter and volume median diameter of the water mist were measured to be 20–99 μm and 21–108 μm, respectively. The spray angle and width of the water mist were approximately 20° and 110 mm, respectively. The thermal radiation attenuation afforded by the water mist discharged from the twin‐fluid nozzle increased with increasing water and air flow rates and decreasing droplet sizes. Within the experimental range, the thermal radiation attenuation was approximately 6.9%–28.4%. Based on experimental data, the effects of the water flow rate and droplet size on thermal radiation attenuation were examined independently. The dependence of the thermal radiation attenuation on the droplet size was greater than that on the water flow rate.

Characterization of water droplets size distribution in aviation turbine fuel: Ultrasonic homogeniser vs high shear speed mixer

Pumps, pressure drops across fittings, and flight operations (such as turning manoeuvres, take-off, and landing) are some of the many sources of turbulence mixing and shearing in aircraft fuel systems, therefore, making it an inevitable condition. Literature established that shearing conditions would influence the droplets and droplets size distribution in an oil/water emulsion. So, low intensity shearing conditions could be beneficial as it promotes droplets coalescence, which could be a driving force for a weak emulsion. However, to date no experimental data has shown the influence homogenising intensity and total water content has on dispersed water droplets size distribution in aviation fuel. Therefore, to expand knowledge of quantification of measurements of dispersed water droplets in aviation fuel, this study characterizes dispersed water droplets in aviation turbine fuel, varying available laboratory homogenising devices and water content. Results presented show that droplets count increases with water concentration and shearing effect. To provide more statistical evidence, kurtosis and skew values were calculated from the extrapolated data and compared with data from a hexanol/water mixture given that hexanol is likely to form a stable emulsion. Experimental results show that the higher the homogenising intensity the more stable the emulsion is likely to be with a higher kurtosis and skew value close to that for the hexanol/water mixture. Therefore, observations show that mild shearing conditions (high shear mixing in this case) could help promote droplets coalescence, leading to a better separation ability.

Facile formulation of sustainable and stable oil-in-dispersion emulsion: A release agent with high demoulding efficacy

In the hunt of new sustainable release agents for concrete removal with improved demoulding efficacy, oil-in-dispersion (OD) release agents have appeared as favourable emulsions, since they display augmented performance in contrast to conventional oil-in-water (O/W) emulsions. This work presents a novel and facile methodology for sustainable preparation of OD release agent employing emulsifiers as active components to produce stable emulsion, leading to a superior and easier commercial product formulation. The new type of OD release agent is optimized by varying the composition of two food grade emulsifiers named as span-80 and AEO-3 from 2.4 to 7.4% in the formulation. The stability and performance of new OD release agents are studied comprehensively through various parameters like creaming index, viscosity, density, pH tests, water contact angle, droplet size and shape. After dilution five times with water, the OD based release agent containing 5.4–7.4% mixed emulsifier concentrations demonstrate excellent stability even after six months of storage and performed well in physico-chemical lab testing. Moreover, OD release agents showed good application results during on-field industrial trials on iron mould surfaces. The formulated OD release agents on the mould took only 12–15 min to generate a smooth and uniform film that was demoulded easily by sledgehammering about 3–5 times. Thus, easily prepared and highly stable OD release agent could be revolutionary in construction industry for sustainable and rapid removal of mould concrete with high efficacy.

Simulation of Separation of Salt Solution from Crude Oil in a Hydrocyclone

In this study, separating water from oil is studied numerically. In this simulation, the Reynolds Stress Model and the mixture multiphase model are used for coupling the velocity and pressure equations using the SIMPLE algorithm. The simulated geometry is taken from an experimental setup. It results that, in the case of the crude oil as the discrete phase, by increasing the diameter of the discrete phase (crude oil) droplets, the separation efficiency increases. If the diameter of the oil droplets is greater than 100 microns, the percentage of oil output from the spillway reaches 99.5%. In the case of the water phase as the discrete phase, if the water droplets size is considered equal to 200 microns, the water separation efficiency in the spillway reaches 69%.