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Water condensation on a surface strongly affects its effective emissivity, especially in the atmospheric window, a wavelength range essential for outdoor applications related to energetically passive cooling and heating. The evolution of emissivity of a silicon surface during dropwise and filmwise water deposition is studied. The evolution of the spectral radiative properties shows that the increase in effective emissivity due to the growth of a droplet pattern is steeper than for a growing water film of equivalent thickness. The change of surface emissivity takes place in the first moments of condensation where droplets as small as 10 µm drastically impact the reflectance of the pristine surface. The upper limit of effective emissivity is reached for a droplet radius or film thickness of 50 µm. During dropwise condensation, effective emissivity is weighted by the drop surface coverage and then remains within an asymptotic maximum value of 0.8, while in case of filmwise condensation, it is shown to reach 0.9 corresponding to water emissivity. Micrometer‐scale spatially‐resolved infrared spectral images enable to correlate the spatial variation of spectral properties to the droplet size and localization. Such findings are of interest to the implementation of moisture‐controlled emissivity tuning and radiative sky‐coolers for dew harvesting. [ABSTRACT FROM AUTHOR]

The phase transformations of water droplets in the humid air flow for water injection into the flue gas in biofuel combustion technology under typical boundary conditions have been simulated. The numerical study was performed in two stages. The first one defines the influence of radiation on the thermal state of the water droplets and on the cycle of phase transformation modes. It is shown that the influence of radiation in a flue gas flow of 150℃→200℃ temperature on the thermal state of quantitatively injected water droplets is not significant, but it induces qualitative changes in the temperature field and influences phase transformations cycle of the droplets. In the second step, the cycling of the droplet phase transformation modes for water injection into the exhaust flue gas prior to a condensing economiser under typical boundary conditions was numerically investigated. It was justified that for efficient cooling and humidification of the flue gas before the condensing economiser it is necessary to inject water heated above the dew-point temperature by dispersing it into fine droplets. [ABSTRACT FROM AUTHOR]

Varying the depth that a dispersion tooth is inserted into water jet can cause significant differences in the hydraulic performance of irrigation sprinklers. The effect of insertion depth on jet breakup was investigated by combining the fluid volume method, overset grid technology, and using adaptive grid refinement. Jet fragmentation mode, droplet characteristics, and entropy production were analysed, and effects on sprinkler pattern radius loss, water application rate, and combination uniformity were discussed. Results showed that as water insertion depth increased (from 1.5 to 4.5 mm) the number of ligament produced increased. This was due to enhanced air entrainment, which also increased the number of droplets. However, the relative frequency change in droplets with a diameter up to 400 μm exceeded 20%, whilst that of 400–600 μm diameter droplets remained within 10%. Factors such as high and low velocity transfer, backflow, and air entrainment caused reductions in sprinkler pattern radius with a total entropy production increase of 167.8%. The relationship between total entropy production and radius loss was described using an exponential function with a correlation coefficient of 0.91. When the sprinklers were arranged in a square formation, and the spacing between the sprinklers was equal to the throw radius, an optimal combination of uniformity was achieved by inserting the water dispersion tooth into the central axis of the jet, resulting in a maximum uniformity value of 75.6%. Findings from this study provide a reference for the analysis of sprinkler hydraulic performance. • A numerical simulation of the sprinkler irrigation impinging jet derived. • Relationship between total entropy production and pattern radius loss obtained. • Key reasons behind the changes in sprinkler hydraulic performance explored. [ABSTRACT FROM AUTHOR]

Introducing a water dispersal needle has been shown to be an effective way of improving the uniformity of water distribution from irrigation sprinklers. However, the jet breakup mechanism remains unknown. Here, the impacts of key parameters, including the insertion jet depth (h), cone angle (θ), and distance from the nozzle outlet (L), on jet breakup phenomena were investigated by simulation. A comprehensive computational approach was used, which integrated the Volume-of-Fluid method with the SST k-ω model, overset grids, and adaptive mesh refinement technique. The results showed distinct jet field zones characterised by stable velocity, descent, rebound, and fluctuation zones, which were delineated by the axial average velocity profile. It was found that increasing h , θ , or reducing L results in a significant reduction of 7.73%, 5.04%, and 5.54% respectively in axial average velocity within the fluctuation zone. Augmentation of large-scale eddies, vortex bands, wave-like eddies, and vortex ring structures intensified the local entropy production rates, increased energy dissipation. The findings showed how this greatly influenced the throw radius of the sprinkler. Moreover, increasing h , θ , or decreasing L also increased air entrainment rates within the velocity decrement zone. This phenomenon was significant in the rebound and fluctuation zones, heightening the jet breakup and increasing the number of detached water droplets. Such dynamic interaction significantly influences the predicted water application rate within a 6-m radius of the sprinkler. Thus, this simulation study serves as a reference for comprehending the intricate jet breakup characteristics and the consequent sprinkler system hydraulic performance. • Numerical simulation for sprinkler irrigation with needle impinging jet developed. • Experimental rig for precise control of the needle penetration depth was designed. • Key reasons for changes in sprinkler hydraulic performance were explored. • Full optimisation of key water dispersal needle parameters was achieved. [ABSTRACT FROM AUTHOR]

Copyright of Advanced Textile Technology is the property of Zhejiang Sci-Tech University Magazines and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The primary cause of premature failure of silicone insulators in humid conditions is the loss of hydrophobicity due to partial discharges. It has been experimentally studied how pre-soaking the surface of a silicone rubber sample in NaCl solution affects the process of hydrophobicity loss. Partial discharges occur from droplets rolling down an inclined sample under AC voltage of 35 kV, which corresponds to the average electric field strength of 3.5 kV cm-1. It is demonstrated that the pre-soaking of the sample within 336 hours significantly reduces the rate of droplet runoff, the time of onset of the first partial discharges, and the duration of full hydrophobicity loss. This is observed for three different types of silicone rubber: Silfor, Powersil, RTV. [ABSTRACT FROM AUTHOR]

Contact electrification (CE) in water has attracted much attention, owing to its potential impacts on the chemical reactions, such as the recent discovery of spontaneous generation of hydrogen peroxide (H2O2) in water microdroplets. However, current studies focus on the CE of bulk water, the measurement of CE between micrometer-size water droplets is a challenge and its mechanism still remains ambiguous. Here, a method for quantifying the amount of charge carried by the water microdroplets produced by ultrasonic atomization is proposed. In the method, the motions of water microdroplets in a uniform electric field are observed and the electrostatic forces on the microdroplets are calculated based on the moving speed of the microdroplets. It is revealed that the charge transfer between water microdroplets is size-dependent. The large microdroplets tend to be positively charged while the small microdroplets tend to receive negative charges, implying that the negative charges transfer from large microdroplets to the small microdroplets during ultrasonic atomization. Further, a theoretical model for microdroplets charging is proposed, in which the curvature-induced surface potential/energy difference is suggested to be responsible for the charge transfer between microdroplets. The findings show that the electric field strength between two microdroplets with opposite charges during separation is strong enough to convert OH- to OH*, providing evidence for the CE-induced spontaneous generation of H2O2 in water microdroplets. [ABSTRACT FROM AUTHOR]

Lipid oxidation is an inevitable event during the processing, storage, and even consumption of lipid‐containing food, which may cause adverse effects on both food quality and human health. Water‐in‐oil (W/O) food emulsions contain a high content of lipids and small water droplets, which renders them vulnerable to lipid oxidation. The present review provides comprehensive insights into the lipid oxidation of W/O food emulsions. The key influential factors of lipid oxidation in W/O food emulsions are presented systematically. To better interpret the specific mechanisms of lipid oxidation in W/O food emulsions, a comprehensive detection method, oxidative lipidomics (oxidomics), is proposed to identify novel markers, which not only tracks the chemical molecules but also considers the changes in supramolecular properties, sensory properties, and nutritional value. The microstructure of emulsions, components from both phases, emulsifiers, pH, temperature, and light should be taken into account to identify specific oxidation markers. A correlation of these novel oxidation markers with the shelf life, the organoleptic properties, and the nutritional value of W/O food emulsions should be applied to develop targeted protective approaches for limiting lipid oxidation. Accordingly, the processing parameters, the application of antioxidants and emulsifiers, as well as packing and storage conditions can be optimized to develop W/O emulsions with improved oxidative stability. This review may help in emphasizing the future research priorities of investigating the mechanisms of lipid oxidation in W/O emulsion by oxidomics, leading to practical solutions for the food industry to prevent oxidative rancidity in W/O food emulsions. [ABSTRACT FROM AUTHOR]

In recent years, there has been a quest to accelerate the search for efficient and sustainable energy harvesting technologies due to challenges from fossil fuel depletion and environmental concerns. There is also a continous demand for autonomous sensing in our growing connected world. The liquid-solid triboelectric nanogenerator (L-S TENG) has emerged as a viable alternative, notably for generating mechanical energy from water. Despite extensive study into liquid-solid contact electrification techniques, a significant need remains to improve energy harvesting efficiency in L-S TENG systems. This comprehensive analysis delves into recent advances in energy harvesting from water, with a particular emphasis on understanding the interaction dynamics between liquid-solid interfaces when using triboelectric nanogenerators for energy conversion. This review summarizes recent developments in the structural design and applications of liquid-solid triboelectrification, focusing on improving TENG output performance. In addition, new insights are provided on the potential impact and future technical hurdles facing L-S TENG technologies. By offering new insights into current knowledge and future research directions, this review aims to guide progress in the field of L-S TENG energy harvesting. [Display omitted] • Trends discussed for enhancing energy harvesting efficiency in liquid-solid TENG system. • Mechanisms, design and materials employed in liquid-solid TENG are outlined. • The latest developments in liquid-solid TENG are comprehensively summarized. • Challenges and prospects for future research on liquid-solid TENGs are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] Liquid marbles i.e. droplets coated by hydrophobic particles may be formed not only on the solid substrates but also on the floating layers of hydrophobic powders such as fluorinated fumed silica or polytetrafluoroethylene. Formation and growth of liquid marbles on fluorinated fumed silica or polytetrafluoroethylene powder floating on a heated water-vapor interface is reported. Marbles emerge from condensation of water droplets levitating above the powder layer. The kinetics of the growth of droplets is reported. Growth of droplets results from three main mechanisms: water condensation, absorption of small droplets and merging of droplets with neighboring ones. Growing droplets are coated with the hydrophobic powder, eventually giving rise to the formation of stable liquid marbles. Formation of hierarchical liquid marbles is reported. Growth of liquid marbles emerging from water condensation follows the linear temporal dependence. A phenomenological model of the liquid marble growth is suggested. [ABSTRACT FROM AUTHOR]

Alternative marine fuels are needed to help reduce the exhaust emissions of ships. In this study, we performed an analysis to verify the potential applicability of a fuel based on Bunker-C oil, a low-grade marine heavy oil, as a novel alternative marine fuel. Bunker-C oil and water were mixed in the presence of a 0.8–1.2% emulsifier in four steps from 0% to 25% to produce a special type of emulsified fuel oil. Confocal microscopy images of samples after stabilization for approximately three days at room temperature showed no variation in the pattern at the 0% condition with no water, but a relatively homogenous mixed state of water droplets was found across all domains at the 5–25% conditions. The open-source software Image-J indicated the extraction of 166, 3438, and 5636 water droplets with mean diameters of 1.57, 1.79, and 2.08 μm, as well as maximum diameters of 7.31, 21.41, and 25.91 μm, at the 5%, 15%, and 25% conditions, respectively. For all three conditions, the mean particle diameter was approximately 2 μm, below the 20 μm reported in previous studies, with uniform distributions. This suggests that the mixed state was adequately homogenous. [ABSTRACT FROM AUTHOR]

In this study, rapid inactivation of Escherichia coli (E. coli) by surface micro-discharge (SMD) plasma is studied by comparing the inactivation effects in air with and without water droplets (WDs) under different distances (d) between the samples and the grounded electrode. The discharge current, discharge power and spatial–temporal developments of SMD are also compared. The pH value, conductivity and the concentrations of reactive oxygen and nitrogen species (RONS) of condensed water are determined with the presence of WDs. In addition, the role of water vapor on the sterilization process is analyzed by evaluating the inactivation efficiency of E. coli treated with plasma effluent through the gas outlet. The measurements imply that the variation in discharge power may not be the main factor affecting E. coli inactivation in WD-tuned air. The results of sterilization display that with the presence of WDs, the log value of remaining E. coli on the surface of the sample can be rapidly reduced to 0.05 in 5 s by SMD plasma treatment as the sample surface stained with E. coli backing on the grounded electrode (GND) at d = 1.1 mm. However, a significant decrease in E. coil survival without WDs takes more than 30 s or longer. It also suggests that WD-tuned SMD can significantly contribute to the generation of reactive species associated with water, thus leading to the rapid inactivation of E. coli. These species may be transferred to the surface of the treated samples through air or water clusters. [ABSTRACT FROM AUTHOR]

Water is one of the most sustainable resources in the world, offering an abundance of hydro energy. Getting a large amount of electricity through conventional water energy harvesting is expensive, with complex mechanisms and bulky installation systems. In the case of the small amount of energy for some portable electronic devices and sensor systems, water droplet harvesting as a sustainable energy resource has become a forward‐looking step to meet the future demand for green energy. The ultimate demand for green energy in the future requires all the possible sustainable energy sources surrounding human society. The emerging potential of water droplet‐driven energy‐harvesting nanogenerators can meet a significant portion of the green energy demand. In this review, the recent developments in droplets‐driven nanogenerators for effective energy scavenging is summarized. It also includes an extensive discussion about the device structures from the material selection and output performance aspects. This review also gives a brief discussion on the applications of droplet‐based nanogenerators and outlines the future possibilities via the current improvement in designs and fabrication strategies that have been introduced by the field. [ABSTRACT FROM AUTHOR]

This study has been carried out experimentally to reveal motion behaviors of a water droplet in silicone oil with an electric field. The study used the radial electric field formed by the inner surface of a metal cylinder, and a thin metal wire which had been installed coinciding with the central axis of the cylinder. After a water droplet was supplied between the electrodes, a high voltage of 10 - 16 kV DC was applied between the electrodes. The motion behavior of single water droplet in each experiment was recorded using a high-speed video camera and then observed precisely and analyzed. As a result, it was observed that the water droplet reciprocated repeatedly between each electrode. Detailed observation revealed that the water droplet always stopped a few millimeters in front of the wire electrode, and the water droplet interface contacted and exchanged charges by forming an interface with a shape like a Taylor cone with a pointed tip extending to the surface of the wire electrode. The contact time of the water droplet on each electrode was approximately 5ms in contact with the wire electrode and 25 ms with the inside surface of the cylindrical electrode. From these results, it was clarified that the reciprocating behavior under a non-uniform electric field and the contact behavior for each electrode were different, and especially, water droplets stopped just before the wire electrode. By using the general solution of the equation of motion of the water droplet, its charge quantity was estimated through four view points, and calculated velocity by use of each calculated charge. The evaluation was carried out by comparing the calculated result with the experimental value.

A mathematical model is provided for heat and mass transfer processes of a semi-transparent droplet. The model was validated by checking the calculated instantaneous evaporation rate of a large water droplet and comparing it with experimental data in the case of combined radiative-convective heating. The condensation, transitional and equilibrium evaporation regimes were modelled for droplets at a temperature of 40 °C. Flue gases were considered as hot and humid air flow in 150°C-1000 °C and humidity of 0.4 according to water vapour volumetric fraction, where droplets are slipping with initial velocity up to 60 m/s and their diameter is 50–1000 μm. In phase change regimes a detailed assessment is provided for heat and mass transfer parameters for droplets slipping in radiating high temperature humid gas flow. It was confirmed that the change in thermal and energy states of water droplets is dependent on their dispersity, flue gas temperature and humidity factors, which also define the droplet equilibrium evaporation temperature. The state and phase changes of droplets are influenced by the heat transfer regime change in them from radiative-convective to conductive, which is caused by rapidly decreasing droplet slipping velocity during transient phase change regime and radiation absorption weakening during their equilibrium evaporation. • Original software was used for the investigation. • Circulation inside droplet weakens when velocity is close to the flue gas velocity. • Radiation absorption weakens during droplet evaporation. • Droplet geometrical parameters in phase change regimes change individually. • Results define optimal waste heat recovery conditions in the humid flue gas. [ABSTRACT FROM AUTHOR]

[Display omitted] The shape of the "freezing tip" formed by the crystallization of water droplets demonstrated remarkable universality - no dependence on the cooling rate and physico-chemical properties of the substrate has been observed. At the same time, the spatial orientation of the freezing cone may be varied. We hypothesized that the orientation of the freezing tip is determined by the direction of heat flux at the base of the sessile droplet. This direction is expected to be changed when the substrate with a low thermal diffusivity is not cooled uniformly. We studied the freezing of water droplets placed on the inclined surface of wedges made from a variety of materials (polymers: Polymethylmethacrylate, Polytetrafluoroethylene, Polyurethane and metal: Titanium), which were cooled from below. The shape of the frozen droplets was controlled in situ. The computational model was suggested for the transient temperature field in the polymer wedge to determine a time variation of the local heat flux under the droplets. A comparison of numerical results and the measurements enabled us to confirm the aforementioned hypothesis relating the orientation of the freezing tips to the direction of the heat flux. It was established that the orientation of the freezing cone axis depends on the location of the frozen droplet on the inclined surface of the wedge. Calculations of the transient temperature field of the wedge confirmed our hypothesis about the physical reason of the various spatial orientations of the freezing cones. [ABSTRACT FROM AUTHOR]

Contact electrification between water and a solid surface is crucial for physicochemical processes at water-solid interfaces. However, the nature of the involved processes remains poorly understood, especially in the initial stage of the interface formation. Here we report that H2O2 is spontaneously produced from the hydroxyl groups on the solid surface when contact occurred. The density of hydroxyl groups affects the H2O2 yield. The participation of hydroxyl groups in H2O2 generation is confirmed by mass spectrometric detection of 18O in the product of the reaction between 4-carboxyphenylboronic acid and 18O-labeled H2O2 resulting from 18O2 plasma treatment of the surface. We propose a model for H2O2 generation based on recombination of the hydroxyl radicals produced from the surface hydroxyl groups in the water-solid contact process. Our observations show that the spontaneous generation of H2O2 is universal on the surfaces of soil and atmospheric fine particles in a humid environment. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The blast-mitigation effect produced by water droplets sprayed into a confined geometry was studied. When a one-dimensional blast wave interacts with a layer of water droplets, blast mitigation occurs that can be expected to reduce the damage from an accidental explosion. Focus was on the blast-mitigation effect produced by the quasi-steady drag force between the shocked air and the stationary water droplets. Momentum transfer due to the drag mitigated the blast wave, and the maximum blast-wave mitigation occurred just behind the layer of droplets. The study parameters (the volume fraction of water droplets, the location ancj length of the region with sprayed water droplets, and the mass of the high explosive) demonstrated that higher momentum loss from the air resulted in greater mitigation. The momentum loss was evaluated using the volume fraction and length of the layer of water droplets and the quasi-steady drag force when the shock wave reached the layer. Relationships were formulated between the initial conditions, the momentum loss, and the blast-mitigation effect, which made it possible to evaluate quantitatively the mitigation effect on the blast wave caused by the water droplets. [ABSTRACT FROM AUTHOR]

Recently, the trend towards sustainable energy production and pollution control has motivated the increased consumption of ultra-low-sulfur diesel (ULSD) or bio-fuels. Such fuels have relatively low surface tension with water and therefore, the separation of water from fuel has become a challenging problem. The separation process relies on using porous structures for the collection and removal of water droplets. Hence, understanding the interaction between water droplets and the separators is vital. The simplest geometry of a separator is the wire mesh screen, which is used in many modern water–diesel separators. Thus, it is considered here for systematic study. In this work, pore-scale computational fluid dynamics (CFD) simulations were performed using OpenFOAM® (an open-source C++ toolbox for fluid dynamics simulations) coupled with a new accurate scheme for the computation of the surface tension force. First, two validation test cases were performed and compared to experimental observations in corresponding bubble-point tests. Second, in order to describe the interaction between water droplets and wire mesh screens, the simulations were performed with different parameters: mean diesel velocity, open area ratio, fiber radii, Young–Laplace contact angle, and the droplet radius. New correlations were obtained which describe the average reduction of open surface area (clogging), the pressure drop, and retention criteria. [ABSTRACT FROM AUTHOR]

This paper presents the Eulerian-Lagrangian approach for numerical modeling of highspeed gas-droplet flows and aeroacoustics. The proposed hybrid approach is implemented using the OpenFOAM library and two different methods. The first method is based on a hybrid convective terms approximation method employing a Kurganov-Tadmor and PIMPLE scheme. The second method employs the regularized or quasi-gas dynamic equations. The Lagrangian part of the flow description uses the OpenFOAM cloud model. Within this model, the injected droplets are simulated as packages (parcels) of particles with constant mass and diameter within each parcel. According to this model, parcels moving in the gas flow could undergo deceleration, heating, evaporation, and breakup due to hydrodynamic instabilities. The far-field acoustic noise is predicted using Ffowcs Williams and Hawking's analogy. The Lagrangian model is verified using the cases with droplet evaporation and motion. Numerical investigation of water microjet injection into the hot ideally expanded jet allowed studying acoustic properties and flow structures, which emerged due to the interaction of gas and liquid. Simulation results showed that water injection with a mass flow rate equal to 13% of the gas jet mass flow rate reduced the noise by approximately 2 dB. This result was in good coincidence with the experimental observations, where maximum noise reduction was about 1.6 dB. [ABSTRACT FROM AUTHOR]

The present study is devoted to the detailed numerical analysis of the combustion wave propagation in the confined vessel filled with the lean 15% hydrogen-air mixture containing suspended micro-droplets of water. Considered gaseous mixtures possesses a relatively low reactivity, and so the intensity of the combustion is moderate. Herewith, it is found that the flame can be noticeably accelerated in the presence of suspended micro-droplets with a diameter larger than 50 μm. Numerical analysis of the flame structure performed via in-house computational package developed by authors showed that the interaction between the flame and the droplets results in the intensification of the flame instability and small scale flame front wrinkling. It is demonstrated that along with the scales associated with intrinsic hydrodynamic and thermo-diffusive modes of flame front instability, smaller wrinkles are excited as a result of the local effect of micro-droplets on the flame front. The rapid growth of the corrugated flame surface leads to the combustion intensification, and in the considered system, the burnout process can proceed up to 2.2 times faster in the presence of micro-droplets of 200 μm diameter than in the pure gaseous mixture. It is expected that distinguished mechanisms of the influence of water droplets on the flame front structure are relevant for the other two-phase combustible systems, such as reactive gaseous mixtures with suspended fuel droplets or solid particles. • Presence of water micro-droplets is shown to intensify the lean hydrogen-air combustion. • Water droplets intensify the combustion via triggering flame instability development. • The combustion intensification is more pronounced in case of larger droplets. • Greatest intensification is achieved when inter-droplet distance matches intrinsic instability scale. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to compare the blast mitigation performances of water layers, whose mass ratios to an explosive were m W / m E = 12.2 , 44.5 , and 107.2 , with water droplets surrounding the explosive. The blast waveforms were measured using pressure transducers, and the motion of the water layer was recorded using a high-speed camera. When mW/mE was equivalent between the water layer and water droplets, the water layer exhibited less mitigation of the peak overpressure and positive impulse than the water droplets. The results demonstrated high efficiency of the water droplets in blast mitigation and the existence of an optimal apparent density of the water barrier. The velocities of the water layers determined using high-speed photography agreed with the prediction model of the barrier material accelerated by explosion. It suggested that the primary cause of the blast overpressure mitigation by the water layer was the allocation of the explosion energy into the kinetic energy of the water. [ABSTRACT FROM AUTHOR]

Self-propelled droplets made of organic materials can be an influential candidate for understanding cell migration from the viewpoint of nonequilibrium physics and have attracted significant attention with regard to soft-matter-type rovers. Because self-propelled droplets are soft enough to be easily deformed, they should be useful as chemically artificial rovers that can move in small areas with many obstacles in water and can be applied as 'motile' carriers for exploring and curing of biological bodies or remediation of the natural environment. Here, we review recent research progress on designing self-propelled droplets of micrometer size. Image 1 [ABSTRACT FROM AUTHOR]

To prepare surfaces with stable anti-icing properties, square-column micro/nanocomposite structures were fabricated using wire-cut electrical discharge machining. Smooth and hydrophobic/superhydrophobic surfaces were tested for wettability and were subjected to mechanistic analysis. Droplets were found to produce an 'air cushion effect' upon contact with the microstructure, which reduced the contact area between the droplets and the aluminium substrate and increased the contact angle of the droplets on the surface. The icing experiment quantitatively evaluated the anti-icing performance of the surfaces by observing the cooling time and out-of-phase icing time of water droplets. It was found that the anti-icing effect is influenced by the wettability of the material and that the superhydrophobic surface has excellent anti-icing properties. Combined with the one-dimensional heat transfer theory for analysing the mechanism of icing, the results show that the 'air cushion' reduces the heat transfer between the solid and liquid and increases the thermodynamic barrier to ice core formation. The stability of the sample surface was tested by icing-melting experiments and friction experiments, and the test piece exhibited stable wettability and anti-icing performance. [ABSTRACT FROM AUTHOR]

An experimental research method and an analysis of the results of a water droplet phase change in the additionally humidified air flow are presented. The diagrams of variation of the equivalent diameter of convectively heated water droplets are presented and analysed. The influence of initial water temperature and additionally humidifying air flow on the phase change of a droplet in transient regime is experimentally substantiated. [ABSTRACT FROM AUTHOR]

The experimental research into water droplet collisions resulting in their secondary atomization has been performed. The temperature of the first and second droplets was 20°С and 90°С, respectively. The interaction regime maps using the dimensionless linear collision parameter and the Weber number have been plotted. We also determined the integral characteristics of child droplets: size and number. When droplets with a temperature of 90°С were used, the critical Weber numbers went down by 10–30% for disruption, 5–15% for separation, and 15–35% for coalescence. For bounce, they increased by 50–80%. The number of newly formed child droplets for droplets with a temperature of 90°С increased by 5–20% relative to the droplets with a temperature of 20°С. The integral characteristics of child droplets and interaction regime maps of droplets with different temperatures can be used to optimize heat and mass transfer technologies. Unlabelled Image • Interaction time of droplets heated up to 90 °С was 10–30% longer than at 20 °С. • Weber number for bounce was 50–80% higher than without liquid heating. • Weber numbers for coalescence and disruption were 30–50% lower at the heating. • Child droplets number from heated droplet was 10–20% higher than without heating. • When We >180, heated and non-heated droplets interact under the same conditions. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental studies of the collisions characteristics for water droplets in an aerosol at its entry into the air counter flow. The temperature of the latter ranged from 20 °C to 500 °C. Experiments were also carried out with the flow of combustion products having a temperature of 800- 850 °C. The initial dimensions (radii) of the droplets in the aerosol were 50-1000 μm. Visualization of the droplet motion in the counter flow of air and combustion products required the use of a hollow cylinder made of quartz glass with a height of 1 m and an internal diameter of 0.15 m, a cross-correlation complex and optical methods (particle image velocimetry, particle tracking velocimetry, interferometric particle imaging). The characteristics of the droplet interaction (size, velocity, total surface area of the liquid before and after) were controlled using a high-speed video camera and tracking algorithms in the TEMA AUTOMOTIVE software package. The main modes of drops interaction have been identified: bounce, coagulation, scatter, and breakup. The statistical information database has been obtained to describe the interaction modes using diagrams, taking into account the ratio of the sizes of colliding drops, velocities of their motion, and an angle between trajectories of motion. The influence of gas temperature on the probabilistic criteria of droplet collisions, as well as the integral criterion characterizing the change in the liquid surface area due to the intensification of droplet collisions in the gas medium has been established. [ABSTRACT FROM AUTHOR]

The authors have presented results of experimental investigations into the process of collisions of water droplets in a gas medium with variation of the basic parameters in wide ranges corresponding to advanced gas-vapor-droplet technologies: sizes (radii) 0.1–1 mm, velocities of travel 0–10 m/s, angles of interaction (attack) 0–90o, relative volume concentration 0.1–10–3–8.5·10–3 m3 of water/m3 of the gas, velocity of motion of the flow 0–10 m/s, and temperature 20–1000oC; directions of flows: opposing, codirectional, and lateral. In processing the experimental results, the emphasis was on the influence of the relative volume concentrations of the droplets on the characteristics of their interaction. The relative probabilities of four typical regimes of interaction of the droplets have been calculated: recoil, coagulation, spread, and breakup (reduction in size). Parametric ranges have been shown for droplets for which the concentration growth of the latter in an aerosol leads to an increase in the probability of coagulation, recoil, and size reduction. Also, the authors have presented ranges of variation of the concentration of droplets in a gas medium, in which the probabilities of all the investigated interaction schemes are high. The experimental results have been processed with the existing approaches to generalization by calculating the angular factor of interaction and the Weber number. [ABSTRACT FROM AUTHOR]

[Display omitted] • After drops fall on solid surface, the properties of the water and gases dissolved in it change. • After drops fall on solid surface, the luminescence of water is observed. • After drops fall on solid surface, the formation of ROS is observed. • Explanation may have been found for the healing properties attributed to rainwater and waterfalls. It has been shown that when drops fall on a solid surface, the physicochemical properties of water change. After drops fall on a solid surface, water saturated with atmospheric gases luminesces in the blue region of the spectrum. The luminescence intensity decreases exponentially after exposure. The concentration of gases (molecular oxygen and carbon dioxide) in water decreases. In this case, both the size and the number of nano-sized gas bubbles in the water do not change. It has been established that when drops fall on a solid surface in water saturated with atmospheric gases, hydrogen peroxide and hydroxyl radicals are formed. As the fall height increases, the intensity of generation of hydrogen peroxide and hydroxyl radical increases. The formation of hydrogen peroxide is probably associated with two independent mechanisms. [ABSTRACT FROM AUTHOR]

The contact angle of water droplets decreases above certain absorbed doses in the case of heavy ions (He, C and Kr ions). Similarly, monotonic decreases are seen due to exposures to corona discharge and UV lights. The present trends indicate that the hydrophilicity of PADC surface increases by the contribution of hydroxyl groups. In comparison, the contact angle increases due to proton irradiations up to 1.3×105 Gy. Then it begins to decrease monotonically with increasing the absorbed dose. The present anomalous trend is discussed based on the combination of the track overlapping model and the Young's formula. [ABSTRACT FROM AUTHOR]

Poor performance in the condensers in power plants and chemical plants is due to the fact that condensed water is deposited on the heat transfer pipes. The dynamics of condensed water droplets forming on the surface of heat transfer pipes have a significant effect on the heat transfer efficiency of heat exchangers. In the present study, a numerical approach using a coupled level-set and volume of fluid (CLSVOF) method was adopted to investigate the impact of water droplets on cylindrical pipes. The numerical model was verified by an experiment, and both sets of results showed qualitative and quantitative agreements. The effects of the surface wettability, impact velocity and relative size of the droplet to the pipe on the droplet impact dynamics are systematically investigated. Moreover, the regularities of the contact area between the liquid and the pipe during the impacting process as well as the volume of residual liquid remaining on the pipe post-impact are also analyzed; these two parameters are the key factors which affect the heat transfer efficiency of heat transfer pipes, and they cannot be acquired very accurately using experiments.

Recently, the trend towards sustainable energy production and pollution control has motivated the increased consumption of ultra-low-sulfur diesel (ULSD) or bio-fuels. Such fuels have relatively low surface tension with water and therefore, the separation of water from fuel has become a challenging problem. The separation process relies on using porous structures for the collection and removal of water droplets. Hence, understanding the interaction between water droplets and the separators is vital. The simplest geometry of a separator is the wire mesh screen, which is used in many modern water–diesel separators. Thus, it is considered here for systematic study. In this work, pore-scale computational fluid dynamics (CFD) simulations were performed using OpenFOAM® (an open-source C++ toolbox for fluid dynamics simulations) coupled with a new accurate scheme for the computation of the surface tension force. First, two validation test cases were performed and compared to experimental observations in corresponding bubble-point tests. Second, in order to describe the interaction between water droplets and wire mesh screens, the simulations were performed with different parameters: mean diesel velocity, open area ratio, fiber radii, Young–Laplace contact angle, and the droplet radius. New correlations were obtained which describe the average reduction of open surface area (clogging), the pressure drop, and retention criteria.

Dispersion nature of water droplets over the insulator surface is used for hydrophobicity classification. Stochastic nature of water dispersions makes naive Bayesian classifier a preferable choice, which has been investigated in this work. About 12 features describing the characteristics of water droplets are extracted from the binary image using binary large objects analysis. Ambient light intensity is a significant factor that affects the binary image quality. As these insulators are installed in the outside environment, variations in ambient light intensity are inevitable. An adaptive threshold technique is proposed to compensate for ambient light variations. Six classes of various ambient light intensities have been considered in this study, and the proposed adaptive threshold technique can produce quality binary image consistently. Features extracted from the binary image are ordered according to their principal components (PCs) using PC analysis. Improvement in classification accuracy with the accumulation of ordered features is analysed. Results illustrate the use of the first eight features provides a reliable classification accuracy of 97.6% for test image samples. In comparison to the other existing classifiers, the proposed classifier illustrates optimal performance in terms of classification accuracy and computational time.

This paper presents the Eulerian–Lagrangian approach for numerical modeling of high-speed gas-droplet flows and aeroacoustics. The proposed hybrid approach is implemented using the OpenFOAM library and two different methods. The first method is based on a hybrid convective terms approximation method employing a Kurganov–Tadmor and PIMPLE scheme. The second method employs the regularized or quasi-gas dynamic equations. The Lagrangian part of the flow description uses the OpenFOAM cloud model. Within this model, the injected droplets are simulated as packages (parcels) of particles with constant mass and diameter within each parcel. According to this model, parcels moving in the gas flow could undergo deceleration, heating, evaporation, and breakup due to hydrodynamic instabilities. The far-field acoustic noise is predicted using Ffowcs Williams and Hawking’s analogy. The Lagrangian model is verified using the cases with droplet evaporation and motion. Numerical investigation of water microjet injection into the hot ideally expanded jet allowed studying acoustic properties and flow structures, which emerged due to the interaction of gas and liquid. Simulation results showed that water injection with a mass flow rate equal to 13% of the gas jet mass flow rate reduced the noise by approximately 2 dB. This result was in good coincidence with the experimental observations, where maximum noise reduction was about 1.6 dB.

An experimental investigation was conducted in an explosion pit to mitigate blast wave propagation by the interaction with water droplets. Composition C-4 (8.00 ± 0.01 g) was used as the explosive with No. 6 detonators. Water droplets were supplied around the explosives using a sprinkler having holes with a diameter of 1.0mm. Pressure waveforms of the blast waves were measured using pressure transducers, while controlling the water flow rate and the area sprinkled with the water droplets. This study revealed that the sprinkled area affected the effectiveness of the mitigation of the peak overpressure. Larger pressure mitigation was observed when a smaller area was sprinkled with water for equivalent total masses of water applied. This indicated that the spatial density of the water dropletswasan important factor for the mitigation of the blast waves. [ABSTRACT FROM AUTHOR]

Results of experimental investigations on the suppression of the flame combustion and thermal decomposition of forest combustible materials by aerosol flows of a pure water and aqueous solutions are presented. The characteristics of some sprayers were determined and the densities of wetting of a fire hotbed, provided by them, were calculated. The times of extinguishing hotbeds of model crown and ground forest fi res were measured, and distributions of temperatures and heat flows in them were determined. It is shown that the efficiency of extinguishing a forest fire is mainly determined by the sizes of the aerosol droplets acting on it. [ABSTRACT FROM AUTHOR]

Temperature is a critical parameter that can control the morphology of poly (lactic acid) (PLA) porous membranes prepared through phase inversion induced by water droplets. It determines the volatilization rate of the solvent and the exchange rate between the solvent and nonsolvent. In this work, in order to investigate the effect of temperature on the morphology, PLA porous membranes were prepared via phase inversion induced by water droplets at different temperatures. The morphologies of the prepared membranes were observed using scanning electron microscopy, and the volatilization rate of the solvent and the exchange rate between the solvent and nonsolvent were tested separately. The experimental data indicated that the volatilization rate of the solvent was faster than the exchange rate between the solvent and nonsolvent. A uniform porous structure was obtained for the PLA membrane, and the pore size decreased with the increase in temperature from 25 °C to 75 °C. This result indicated that a PLA porous membrane with desired pore size could be achieved by adjusting the ambient temperature. • It benefits to control accurate the phase inversion behaviors. • A simple method was developed for precise control of the pore structure of the porous membrane. • Quantitative study of the phase change process reveals the pore formation mechanism. [ABSTRACT FROM AUTHOR]

The influence of the dimensionless angular and linear parameters of interaction of water droplets shaped as a sphere, an ellipsoid, and a conventionally liquid disk on the characteristics (regimes) of their collisions in air (bouncing, coalescence, separation, or disruption) is studied by using a system of high-speed video recording. Conditions of sustainable implementation of this interaction are determined. Maps of the corresponding regimes are constructed and compared with available data. The characteristic sizes, the number of liquid fragments formed in collisions, and the total areas of the evaporation surface are calculated. It is demonstrated that the liquid surface area in the case of collisions of conventionally liquid disks is significantly (by several times) greater than that in the case of spherical droplets. [ABSTRACT FROM AUTHOR]

One of the perspective types of water-based fuels is the foamed emulsion. Foamed emulsion represents the foam consisting of oxygen bubbles distributed in the oil-in-water emulsion. Paper considers experimentally the issues of combustion of foamed emulsion with the high content of water fraction. For the first time, the synchronized data on the flame speed and the pressure profile along the channel length are obtained. It is shown that flame acceleration in the foam is possibly related to the explosive boiling of the liquid phase of the foam that is accompanied by a formation of weak compression waves. The interaction between these compression waves and the flame front leads to the change in the total burning rate of the foam. The data on the average diameter of water droplets are obtained via photography of multiphase flow of combustion products. It is shown that the average diameter of water droplets decreases with the increase in the flame speed. The conditions required for the combustion of the foamed emulsion with high water content are analyzed. It is shown that the foamed emulsion becomes incombustible with the decrease in oil volatility. [ABSTRACT FROM AUTHOR]

Abstract In this paper, complex processes of water droplet heat and mass transfer are analyzed in a cycle of condensing, transitional evaporation and equilibrium evaporation regimes during phase change which occurs on a droplet's surface. The dynamics of a heated droplet's surface temperature is directly related to the change in the regimes. The definition of the dynamics is based on a numerical iterative scheme which depends on the balance of a droplet surface's heat flux. In this scheme, the energy of phase change and external heat transfer are combined as well as the internal heat transfer occurring in droplets. The numerical investigation results of the water droplets' phase change were used as a basis while defining the inputs provided by the droplet slipping and the radiation absorbed in the flue gas within the interactions between the processes of complex transitional transfers. For this investigation, the conditions have been set to be typical for heat utilization technologies and biofuel furnaces used in flue gas removal. Highlights • Droplet phase change model describes flue gas and dispersed water energy interaction. • Original software was used for the numerical investigation. • Highlighted factors defining the interaction of droplet transfer processes. • Results define optimal utilization conditions for exhausted flue gas heat. [ABSTRACT FROM AUTHOR]

Parametrization of radiation transfer through clouds is an important factor in the ability of Numerical Weather Prediction models to correctly describe the weather evolution. Here we present a practical parameterization of both liquid droplets and ice optical properties in the longwave and shortwave radiation. An advanced spectral averaging method is used to calculate the extinction coefficient, single scattering albedo, forward scattered fraction and asymmetry factor (βext, ϖ, f, g), taking into account the nonlinear effects of light attenuation in the spectral averaging. An ensemble of particle size distributions was used for the ice optical properties calculations, which enables the effective size range to be extended up to 570 μm and thus be applicable for larger hydrometeor categories such as snow, graupel, and rain. The new parameterization was applied both in the COSMO limited-area model and in ICON global model and was evaluated by using the COSMO model to simulate stratiform ice and water clouds. Numerical weather prediction models usually determine the asymmetry factor as a function of effective size. For the first time in an operational numerical weather prediction (NWP) model, the asymmetry factor is parametrized as a function of aspect ratio. The method is generalized and is available on-line to be readily applied to any optical properties dataset and spectral intervals of a wide range of radiation transfer models and applications.

Recently, water has been employed as a supportive agent for the preparation of multiple suppressing agents including aqueous film forming foams (AFFF), which is combined with different kinds of gases for its various applications. In this study, the water mist is chosen for the gas-suppressing agent such as carbon dioxide. Our work investigated the suppression effects of water droplets on the n-heptane pool fire, and its mixture with carbon dioxide, respectively. The size and frequency of droplets with their effect on temperature and suppression was compared to observe the difference in the suppression. Initially, it was found that the droplets having a larger droplet size were found to be more efficient as compared to the smaller droplets with respect to the heat release rate, temperature, and radiation. Afterwards, a mixture of water droplets and carbon dioxide was simultaneously discharged to compare the difference between these two suppressing agents. It was found that the synergistic effect of the mixture has higher advantages over the use of only water suppression. It helps reduce the hot gases that surround the pool fire and allows the water mist to travel efficiently towards the fuel. Both suppression mechanisms were set to similar initial parameters that lead to different outcomes.