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Gallium (Ga)-based liquid metals (LMs), as an emerging functional material, stand out among many candidates due to their combination of fluidic and metallic attributes, and they have extensively attracted the attention of academic researchers. When fabricated into droplet form, these metals are imbued with many fantastic characteristics, such as a high specific surface area and self-healing properties. Additionally, Ga-based liquid metal droplets (LMDs) achieve higher response accuracy to external stimuli, satisfying the demands of many applications requiring micro-size and precise stimulus-responsivity. Herein, we focus on reviewing the properties of Ga-based LMs and their droplets, the fabrication strategies of metal droplets, their stimulus-response motion under different external fields, and their applications in microfluidic systems, biomedical applications, and micromachines. To further advance the development of responsive Ga-based LMDs, the future outlooks with key challenges related to their further applications are also presented here. [ABSTRACT FROM AUTHOR]

The evaporation characteristics of unsymmetrical dimethylhydrazine droplets with different initial diameters in a subcritical environment were experimentally investigated with the temperature–pressure separation technique. The evaporation processes of unsymmetrical dimethylhydrazine droplets with different initial diameters in this environment have the same general pattern. All the studied droplets exhibit a short transient heating phase and a steady-state evaporation phase obeying d 2 . Notably, the expansion of the transient heating phase gradually increases with increasing ambient pressure. The change in diameter squared ∆ d 2 m a x increases from 1.03% at 1 MPa to 12.48% at 5 MPa. Under subcritical conditions, the evaporation rate decreases linearly with decreasing droplet diameter, and the droplet evaporation lifetime increases linearly. Changes in the initial droplet diameter may still have a large effect on droplets smaller than those studied here. When the ambient pressure is not greater than 3 MPa, the change in the steady-state evaporation time for both medium- and large-diameter droplets accounts for more than 70% of the variation in the droplet evaporation lifetime. As the ambient pressure increases to 4 MPa and 5 MPa, the percentage of the change in the transient heating time contributing to the variation in the droplet evaporation lifetime gradually increases to more than 45%. [ABSTRACT FROM AUTHOR]

A three-dimensional Navier–Stokes and continuity equation model is employed to numerically predict the resonant modes of sessile droplets on horizontally vibrating substrates. A dynamic contact angle model is implemented to simulate the contact angle variations during vibrations. The four resonant modes (n = 1, 2, 3 and 4) of a droplet under horizontal vibrations are investigated. Simulations are compared to experimental results for validation. Excellent agreement is observed between predicted results and experiments. The model is used to simulate the internal flow patterns within the droplet under resonant modes. It is found that the flow in all four resonant modes can be divided into the Stokes region, the gas–liquid interface region, and the transition region located in between. Numerical simulations show that the average velocity within the droplet increases with the increase in frequency, while the fluctuations in average velocity after reaching the steady state show different trends with the increase in frequency. It is also found that with an increase in the order of resonant modes, the contact angle difference between the two sides of the droplet increases, and the contact angle difference of the droplet is maximized when the applied frequency is the resonant frequency of the specified mode. [ABSTRACT FROM AUTHOR]

In this paper, under the background of low-temperature steam waste heat recovery technology, the pressure oscillation characteristics of direct-contact condensation between continuously falling droplets and saturated steam at sub-atmosphere pressure were studied. An experimental device of pressure oscillation based on an acceleration oscillation sensor was established to investigate the influence of vapor pressure and fluid velocity on the oscillation characteristics of direct-contact condensation. The results showed that as the absolute pressure increases, the peak value of oscillation decreases gradually and the time-domain periodic waveform becomes fluctuating. When the liquid flow rate is low, the condensation oscillation shows a single-peak waveform and the dominant frequency moves towards a higher frequency. When the liquid velocity increases gradually, the RMS (root mean square) of pressure oscillation remains unchanged at first and then decreases obviously. The dominant frequency of oscillation decreases from 23.68 Hz to 7.16 Hz continuously, and the amplitude of oscillation decreases in a parabolic pattern. The auto power spectrum showed that the frequencies with higher energy become unconcentrated and show fluctuation characteristics. The amplitude of the dominant frequency is about 0.0004 (m/s2)2, while that of the other peak frequencies is about 0.00010–0.00015 (m/s2)2. In practical applications, excessive flow velocity and reduced vacuum degree should be avoided to prevent low-frequency vibration, which may lead to fatigue damage or even failure of the equipment due to resonance. In addition, the direct-contact condensation state can be inferred from the vibration signal to reduce environmental noise. [ABSTRACT FROM AUTHOR]

Gene editing tools have triggered a revolutionary transformation in the realms of cellular and molecular physiology, serving as a fundamental cornerstone for the evolution of disease models and assays in cell culture reactions, marked by various enhancements. Concurrently, microfluidics has emerged over recent decades as a versatile technology capable of elevating performance and reducing costs in daily experiments across diverse scientific disciplines, with a pronounced impact on cell biology. The amalgamation of these groundbreaking techniques holds the potential to amplify the generation of stable cell lines and the production of extracellular matrix hydrogels. These hydrogels, assuming a pivotal role in isolating cells at the single-cell level, facilitate a myriad of analyses. This study presents a novel method that seamlessly integrates CRISPR-Cas9 gene editing techniques with single-cell isolation methods in induced pluripotent stem cell (hiPSC) lines, utilizing the combined power of droplets and hydrogels. This innovative approach is designed to optimize clonal selection, thereby concurrently reducing costs and the time required for generating a stable genetically modified cell line. By bridging the advancements in gene editing and microfluidic technologies, our approach not only holds significant promise for the development of disease models and assays but also addresses the crucial need for efficient single-cell isolation. This integration contributes to streamlining processes, making it a transformative method with implications for enhancing the efficiency and cost-effectiveness of stable cell line generation. As we navigate the intersection of gene editing and microfluidics, our study marks a significant stride toward innovative methodologies in the dynamic landscape of cellular and molecular physiology research. [ABSTRACT FROM AUTHOR]

Motivated by the increasing need of optimised micro-devices for droplet production in medical and biological applications, this paper introduces an integrated approach for the study of the liquid–liquid droplet creation in flow-focusing micro cross-junctions. The micro-junction considered is characterised by a restriction of the channels cross-sections in the junction, which has the function of focusing the flow in the region of the droplet formation. The problem is studied numerically in the OpenFOAM environment and validated by a comparison with experimental results obtained by high-speed camera images and micro-PIV measurements. The analysis of the forces acting on the dispersed phase during the droplet formation and the diameter of the droplets obtained numerically are considered for the development of a model of the droplet breakup under the squeezing regime. On the basis of energy balancing during the breakup, a relation between interfacial tension, the size of the cross-sections in the junction, and the time interval needed for droplet creation is obtained, which yields a novel correlation between the dimensionless length of the droplet and the dimensionless flow rate. This research expands our knowledge of the phenomenon of drop creation in micro-junctions with restrictions providing new aid for the optimal design of micro-drop generators. [ABSTRACT FROM AUTHOR]

We investigate the dynamics and instabilities of a droplet that floats on a liquid substrate. The substrate is cooled from below. In the framework of the slender droplet approximation and the precursor model, the problem is studied numerically. Oscillatory and stationary regimes of thermocapillary convection have been observed. The influence of a two-dimensional spatial inhomogeneity of temperature on the droplet dynamics is investigated. The two-dimensional spatial temperature inhomogeneity can suppress oscillations, changing the droplet's shape. In a definite region of parameters, the two-dimensional spatial modulation can lead to the excitation of periodic oscillations. The influence of the Biot number on the shape of the droplets is studied. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) poses several issues concerning the management of hospital-acquired infections, leading to increasing morbidity and mortality rates and higher costs of care. Multidrug-resistant (MDR) bacteria can spread in the healthcare setting by different ways. The most important are direct contact transmission occurring when an individual comes into physical contact with an infected or colonized patient (which can involve healthcare workers, patients, or visitors) and indirect contact transmission occurring when a person touches contaminated objects or surfaces in the hospital environment. Furthermore, in recent years, toilets in hospital settings have been increasingly recognised as a hidden source of MDR bacteria. Different sites in restrooms, from toilets and hoppers to drains and siphons, can become contaminated with MDR bacteria that can persist there for long time periods. Therefore, shared toilets may play an important role in the transmission of nosocomial infections since they could represent a reservoir for MDR bacteria. Such pathogens can be further disseminated by bioaerosol and/or droplets potentially produced during toilet use or flushing and be transmitted by inhalation and contact with contaminated fomites. In this review, we summarize available evidence regarding the molecular features of MDR bacteria contaminating toilets of healthcare environments, with a particular focus on plumbing components and sanitary installation. The presence of bacteria with specific molecular traits in different toilet sites should be considered when adopting effective managing and containing interventions against nosocomial infections potentially due to environmental contamination. Finally, here we provide an overview of traditional and new approaches to reduce the spreading of such infections. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic wetting manipulation plays a major role in modern microfluidic technologies such as lab-on-a-chip applications and digital microfluidics. Liquid dielectrophoresis (LDEP) is a common driving mechanism, which induces hydrodynamic motion in liquids by the application of nonhomogeneous electrical fields. Among strategies to analyze droplet movement, systematic research on the influence of different frequencies under AC voltage is missing. In this paper, we therefore present a first study covering the motion characteristics of LDEP-driven droplets of the dielectric liquids ethylene glycol and glycerol carbonate in the driving voltage frequency range from 50 Hz to 1600 Hz. A correlation between the switching speed of LDEP-actuated droplets in a planar electrode configuration and the frequency of the applied voltage is shown. Hereby, motion times of different-sized droplets could be reduced by up to a factor of 5.3. A possible excitation of the droplets within their range of eigenfrequencies is investigated using numerical calculations. The featured fluidic device is designed using larger-sized electrodes rather than typical finger or strip electrodes, which are commonly employed in LDEP devices. The influence of the electrode shape is considered simulatively by studying the electric field gradients. [ABSTRACT FROM AUTHOR]

Emulsions form a large group of food materials. Many foods are either partly or wholly emulsions or are in the form of emulsion at some stage of the production process. A good understanding of the rheological properties of emulsions, especially their shear viscosity, is essential in the design, formulation, and processing of food emulsions. The texture and mouthfeel of food emulsions are also largely influenced by emulsion viscosity. Therefore, it is of practical importance to be able to correlate and predict emulsion viscosity as a function of droplet concentration and other relevant variables. In this article, the recent developments made in the viscosity modeling of concentrated emulsions are reviewed. The viscosity models for concentrated emulsions published in the twenty-first century are discussed, compared, and evaluated using a large body of experimental viscosity data available on emulsions. The effects of droplet size distribution and capillary number on the viscosity of concentrated emulsions are also discussed in detail. A new generalized viscosity model is developed for concentrated emulsions that includes the effect of capillary number and is accurate with small average percent relative error (within 3%). [ABSTRACT FROM AUTHOR]

The liquid–liquid two-phase flow and size prediction of slug droplets in flow-focusing microchannels with different downstream orifice sizes were investigated experimentally. Aqueous solution of 50%-glycerol and mineral oil with 4 wt.% surfactant sorbitanlauric acid ester (Span 20) were used as the dispersed and continuous phases, respectively. Three characteristic flow patterns were identified: slug flow, dripping flow, and jetting flow. The slug flow region decreased but the jetting flow region increased with the decrease in the size of the channel orifice. Afterwards, the universal flow pattern maps of the liquid–liquid two-phase in three microchannels were obtained based on dimensionless analysis. Furthermore, two slug droplet formation regions were found: when φ−1Cac < 0.01, the droplet formation was mainly driven by the squeezing force Fp, while when φ−1Cac > 0.01, both the squeezing force Fp and shear force Fτ contributed to droplet formation. Additionally, the prediction correlations of the dimensionless sizes of the slug droplets in both regions were established based on the flow rate ratio of the two-phase, the dimensionless orifice size, and the Capillary number of the continuous phase. The predicted results are in good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

This review focuses on the development of surface acoustic wave-enabled acoustic drop ejection (SAW-ADE) technology, which utilizes surface acoustic waves to eject droplets from liquids without touching the sample. The technology offers advantages such as high throughput, high precision, non-contact, and integration with automated systems while saving samples and reagents. The article first provides an overview of the SAW-ADE technology, including its basic theory, simulation verification, and comparison with other types of acoustic drop ejection technology. The influencing factors of SAW-ADE technology are classified into four categories: fluid properties, device configuration, presence of channels or chambers, and driving signals. The influencing factors discussed in detail from various aspects, such as the volume, viscosity, and surface tension of the liquid; the type of substrate material, interdigital transducers, and the driving waveform; sessile droplets and fluid in channels/chambers; and the power, frequency, and modulation of the input signal. The ejection performance of droplets is influenced by various factors, and their optimization can be achieved by taking into account all of the above factors and designing appropriate configurations. Additionally, the article briefly introduces the application scenarios of SAW-ADE technology in bioprinters and chemical analyses and provides prospects for future development. The article contributes to the field of microfluidics and lab-on-a-chip technology and may help researchers to design and optimize SAW-ADE systems for specific applications. [ABSTRACT FROM AUTHOR]

The present paper intends to provide an analysis of how the process of calefaction occurs in a selective catalytic reduction (SCR) system and the mechanisms by which the deposition of AdBlue crystals on a hot surface evolve. Experimentally, two aluminium samples heated to 200 °C were used, over which AdBlue droplets with different atomisation rates were dropped, maintaining the same dynamic flow parameters, in order to observe the influence of temperature effects on the degree of deposition of crystallised sediment on the surface. The authors proposed the use of calefaction in an ultrasonic environment to prevent deposition and to increase droplet fragmentation by a break-up process. To prove the performance of this method one sample was subjected to a normal flow regime while a second sample was exposed to ultrasound. Both samples were assembled on a magneto-strictive concentrator operating at a frequency of 20 kHz. The obtained results indicated that the sample exposed to ultrasound demonstrated lower urea crystallisation compared to the sample that was not exposed to this treatment. Thus, it can be seen that the proposed method of injecting AdBlue into an ultrasonic zone gives the desired results. [ABSTRACT FROM AUTHOR]

Digital microfluidics, which relies on the movement of drops, is relatively immune to clogging problems, making it suited for micro-reactor applications. Here, graphene oxide paper of 100 μm thickness, fabricated by blade coating sedimented dispersions onto roughened substrates, followed by drying and mechanical exfoliation, was found to be relatively free of cracks and curling. It also exhibited high wettability and elasto-capillary characteristics. Possessing low enough stiffness, it could rapidly and totally self-wrap water drops of 20 μL volume placed 2 mm from its edge when oriented between 0 and 60° to the horizontal. This complete wrapping behavior allowed drops to be translated via movement of the paper over long distances without dislodgement notwithstanding accelerations and decelerations. An amount of 2 drops that were wrapped with separate papers, when collided with each other at speeds up to 0.64 m/s, were found to eschew coalescence. This portends the development of robust digital microfluidic approaches for micro-reactors. [ABSTRACT FROM AUTHOR]

The features of the local mean and fluctuational flow structure, carrier phase turbulence and the propagation of the dispersed phase in the bubbly and droplet-laden isothermal round polydispersed jets were numerically simulated. The dynamics of the polydispersed phase is predicted using the Eulerian–Eulerian two-fluid approach. Turbulence of the carrier phase is described using the second-moment closure while taking into account the presence of the dispersed phase. The numerical analysis was performed in a wide range of variation of dispersed phase diameter at the inlet and particle-to-fluid density ratio (from gas flow laden with water droplets to carrier fluid flow laden with gas bubbles). An increase in the concentration of air bubbles and their size leads to jet expansion (as compared to a single-phase jet up to 40%), which indicates an increase in the intensity of the process of turbulent mixing with the surrounding space. However, this makes the gas-droplet jet narrower (up to 15%) and with a longer range in comparison with a single-phase flow. The addition of finely dispersed liquid droplets to an air jet suppresses gas phase turbulence (up to 15%). In a bubbly jet, it is found that small bubbles (Stk < 0.1) accumulate near the jet axis in the initial cross-sections, while concentration of the large ones (Stk > 0.2) along the jet axis decreases rapidly. In the gas-droplet jet, the effect of dispersed phase accumulation is also observed in the initial cross-section, and then its concentration decreases gradually along the jet axis. For gas bubbles (Stk < 0.1), small turbulence attenuation (up to 6%) is shown. [ABSTRACT FROM AUTHOR]

Microfluidic-based platforms have become a hallmark for chemical and biological assays, empowering micro- and nano-reaction vessels. The fusion of microfluidic technologies (digital microfluidics, continuous-flow microfluidics, and droplet microfluidics, just to name a few) presents great potential for overcoming the inherent limitations of each approach, while also elevating their respective strengths. This work exploits the combination of digital microfluidics (DMF) and droplet microfluidics (DrMF) on a single substrate, where DMF enables droplet mixing and further acts as a controlled liquid supplier for a high-throughput nano-liter droplet generator. Droplet generation is performed at a flow-focusing region, operating on dual pressure: negative pressure applied to the aqueous phase and positive pressure applied to the oil phase. We evaluate the droplets produced with our hybrid DMF–DrMF devices in terms of droplet volume, speed, and production frequency and further compare them with standalone DrMF devices. Both types of devices enable customizable droplet production (various volumes and circulation speeds), yet hybrid DMF–DrMF devices yield more controlled droplet production while achieving throughputs that are similar to standalone DrMF devices. These hybrid devices enable the production of up to four droplets per second, which reach a maximum circulation speed close to 1540 µm/s and volumes as low as 0.5 nL. [ABSTRACT FROM AUTHOR]

Diffusiophoresis of a weakly charged liquid metal droplet (LMD) is investigated theoretically, motivated by its potential application in drug delivery. A general analytical formula valid for weakly charged condition is adopted to explore the droplet phoretic behavior. We determined that a liquid metal droplet, which is a special category of the conducting droplet in general, always moves up along the chemical gradient in sole chemiphoresis, contrary to a dielectric droplet where the droplet tends to move down the chemical gradient most of the time. This suggests a therapeutic nanomedicine such as a gallium LMD is inherently superior to a corresponding dielectric liposome droplet in drug delivery in terms of self-guiding to its desired destination. The droplet moving direction can still be manipulated via the polarity dependence; however, there should be an induced diffusion potential present in the electrolyte solution under consideration, which spontaneously generates an extra electrophoresis component. Moreover, the smaller the conducting liquid metal droplet is, the faster it moves in general, which means a smaller LMD nanomedicine is preferred. These findings demonstrate the superior features of an LMD nanomedicine in drug delivery. [ABSTRACT FROM AUTHOR]

We have shown in a previous work that the combination of the emulsion solvent evaporation technique and droplet-based microfluidics allows for the synthesis of well-defined monodisperse mesoporous silica microcapsules (hollow microspheres), whose size, shape and composition may be finely and easily controlled. In this study, we focus on the crucial role played by the popular Pluronic® P123 surfactant, used for controlling the mesoporosity of synthesised silica microparticles. We show in particular, that although both types of initial precursor droplets, prepared with and without P123 meso-structuring agent, namely P123+ and P123− droplets, have a similar diameter (≃30 μm) and a similar TEOS silica precursor concentration (0.34 M), the resulting microparticles exhibit two noticeably different sizes and mass densities. Namely, 10 μm and 0.55 g/cm3 for P123+ microparticles, and 5.2 μm and 1.4 g/cm3 for P123− microparticles. To explain such differences, we used optical and scanning electron microscopies, small-angle X-ray diffraction and BET measurements to analyse structural properties of both types of microparticles and show that in the absence of Pluronic molecules, P123− microdroplets divide during their condensation process, on average, into three smaller droplets before condensing into silica solid microspheres with a smaller size and a higher mass density than those obtained in the presence of P123 surfactant molecules. Based on these results and on condensation kinetics analysis, we also propose an original mechanism for the formation of silica microspheres in the presence and in the absence of the meso-structuring and pore-forming P123 molecules. [ABSTRACT FROM AUTHOR]

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We developed a broadband highly sensitive optofluidic detection system, which enabled us to show for the first time that Rhodamine-B dye molecules can exhibit standard photoluminescence as well as blue-shifted photoluminescence. We demonstrate that this phenomenon originates from the interaction between the pump laser beam and dye molecules when surrounded by the low thermal conductive fluorocarbon oil, generally used as a carrier medium in droplet microfluidics. We also show that when the temperature is increased, both Stokes and anti-Stokes fluorescence intensities remain practically constant until a temperature transition is reached, above which the fluorescence intensity starts to decrease linearly with a thermal sensitivity of about − 0.4 % / ° C for Stokes emission or − 0.2 % / ° C for anti-Stokes emission. For an excitation power of 3.5 mW, the temperature transition was found to be about 25 ° C, whereas for a smaller excitation power (0.5 mW), the transition temperature was found to be about 36 ° C. [ABSTRACT FROM AUTHOR]

Evaporation of a sessile drop is ubiquitous in nature and has many industrial applications. Despite extensive studies over recent decades, a critical issue, i.e., how temperature varies near contact lines, remains elusive. In this work, we report to date the first direct experimental measurement showing the microscopic temperature distribution near contact lines of an evaporating pinned sessile drop. Using a fluorescence-based thermometry, we find that the temperature at the free interface near contact lines varies drastically along the radial direction, engendering a concentric fringe pattern that evolves over the evaporation lifespan. The formation of such fringe patterns is attributed to a combined mechanism of locally enhanced evaporative cooling at the drop edge and the development of interfacial convective vortices due to Bénard-Marangoni instability. We also study the evaporation dynamics at different initial contact angles and find that the characteristics of this fringe pattern vary as the initial contact angle decreases. Our experimental investigation and theoretical analysis in this work reveal insights to the understanding of droplet evaporation dynamics in various heat transfer systems. [ABSTRACT FROM AUTHOR]

A mathematical model has been developed and a numerical study of vapor bubble growth as a result of acoustic evaporation of an encapsulated perfluorocarbon droplet in a viscoelastic liquid is presented. The viscoelasticity of the droplet shell and the carrier liquid is taken into account according to the Kelvin–Voigt rheological model. The problem is reduced to solving a system of ordinary differential equations for the radius and temperature of the bubble, the radius of the droplet and the shell together with the thermal conductivity equation for the internal liquid. Spatial discretization of the thermal conductivity equation is carried out using an implicit finite difference scheme. ODEs are solved by the fifth order Runge–Kutta method with an adaptive computational step. To check the correctness of the numerical calculation in a particular case, the theory has been compared with known experimental data. The influence of the shear modulus of the shell and the carrier liquid, and the shell thickness on the radial dynamics of a vapor bubble inside an encapsulated droplet in an external viscoelastic liquid is demonstrated. [ABSTRACT FROM AUTHOR]

The wetting behavior of ionic liquids (ILs) on the mesoscopic scale considerably impacts a wide range of scientific fields and technologies. Particularly under vacuum conditions, these materials exhibit unique characteristics. This work explores the effect of the deposition rate and substrate temperature on the nucleation, droplet formation, and droplet spreading of ILs films obtained by thermal evaporation. Four ILs were studied, encompassing an alkylimidazolium cation (CnC1im) and either bis(trifluoromethylsulfonyl)imide (NTf2) or the triflate (OTf) as the anion. Each IL sample was simultaneously deposited on surfaces of indium tin oxide (ITO) and silver (Ag). The mass flow rate was reproducibly controlled using a Knudsen cell as an evaporation source, and the film morphology (micro- and nanodroplets) was evaluated by scanning electron microscopy (SEM). The wettability of the substrates by the ILs was notably affected by changes in mass flow rate and substrate temperature. Specifically, the results indicated that an increase in the deposition rate and/or substrate temperature intensified the droplet coalescence of [C2C1im][NTf2] and [C2C1im][OTf] on ITO surfaces. Conversely, a smaller impact was observed on the Ag surface due to the strong adhesion between the ILs and the metallic film. Furthermore, modifying the deposition parameters resulted in a noticeable differentiation in the droplet morphology obtained for [C8C1im][NTf2] and [C8C1im][OTf]. Nevertheless, droplets from long-chain ILs deposited on ITO surfaces showed intensified coalescence, regardless of the deposition rate or substrate temperature. [ABSTRACT FROM AUTHOR]

We study a gas of bosonic dipolar atoms in the presence of a transverse harmonic trapping potential by using an improved variational Bethe ansatz, which includes the transverse width of the atomic cloud as a variational parameter. Our calculations show that the system behavior evolves from quasi-one dimensional to a strictly one-dimensional one by changing the atom–atom interaction, or the axial density, or the frequency of the transverse confinement. Quite remarkably, in the droplet phase induced by the attractive dipolar interaction the system becomes sub-one dimensional when the transverse width is smaller than the characteristic length of the transverse harmonic confinement. [ABSTRACT FROM AUTHOR]

The objective of this research work is to propose a phase diagram that can be used to find a proper operating condition for generating droplets of different types. It is found that the phase diagram of QR versus CaD can effectively classify the droplet generation into three vivid regimes: dripping, jetting and tubing. For the dripping regime, its operating condition is in the range of either CaD < 10−4 and QR < 50 or 10−3 < CaD < 10−4 and QR < 1. For the jetting regime, its operating condition is in the range of either CaD < 1.35 × 10−2 and QR > 100 or CaD > 1.35 × 10−2 and QR > 1. For the tubing regime, its operating condition is in the range of CaD > 1.35 × 10−2 and QR < 1. [ABSTRACT FROM AUTHOR]

The present review describes the current achievements in the applications of a planar laser-induced fluorescence (PLIF) method for the diagnostics of liquid films, bubbles, individual droplets, and sprays. Such flows are related with strongly curved interphases, which often results in additional high errors during the PLIF data quantification because of laser light reflection, refraction, and absorption. The present review demonstrates that a two-color PLIF approach and a PLIF modification for regularly structured illumination resolves the reflection- and refraction-caused errors. The latter modification ensures proper phase separation in the measurement cross-section and visualization of the interface dynamics. The former approach provides the accurate evaluation of the local temperature and concentration both in liquid and gaseous phases even in the case of strong variations of the laser sheet intensity. With intensified cameras, the PLIF method is used for multi-parameter diagnostics of the two-phase combustion of sprays in combustion chambers with optical access. It visualizes and quantifies the liquid fuel evaporation and mixing, to measure temperature in the gas and liquid phases and to reveal the regions of pollutant formation. The PLIF technique can also be easily combined with a particle image (or tracking) velocimetry method, to evaluate local heat and mass transfer. [ABSTRACT FROM AUTHOR]

Fires are considered among the most dangerous accidents on manned spacecraft. That is why several programs of combustion experiments were implemented at the International Space Station (ISS) since 2008. In the experiments with n-heptane and n-dodecane droplet combustion, a new phenomenon was discovered, namely, the phenomenon of the radiative extinction of a burning droplet with subsequent multiple flashes of flame. In this paper, n-dodecane droplet ignition, combustion, radiative extinction, and subsequent low-temperature oxidation with multiple flashes of cool, blue, and hot flames under microgravity conditions are studied computationally. The mathematical model takes into account multiple elementary chemical reactions in the vicinity of a droplet in combination with heat and mass transfer in liquid and gas, heat release, convection, soot formation, and heat removal by radiation. The model is based on the non-stationary one-dimensional differential equations of the conservation of mass and energy in liquid and gas phases with variable thermophysical properties within the multicomponent diffusion concept in the gas phase. Calculations confirm the important role of the soot shell formed around the droplet and low-temperature reactions in the phenomenon of droplet radiative extinction with multiple flame flashes in the space experiment at the ISS. Calculations reveal the decisive role of the blue flame, arising due to the decomposition of hydrogen peroxide, in the multiple flame flashes. Calculations with forced ignition of the droplet reveal the effect of the ignition procedure on droplet evolution in terms of the timing and the number of cool, blue, and hot flame flashes, as well as in terms of the combustion rate constant of the droplet. Calculations with droplet self-ignition reveal the possible existence of new modes of low-temperature oxidation of droplets with the main reaction zone located very close to the droplet surface and with only partial conversion of fuel vapor in it. [ABSTRACT FROM AUTHOR]

The reuse of decontaminated disposable medical face masks can contribute to reducing the environmental burden of discarded masks. This research is focused on the effect of household and laboratory washing at 50 °C on the quality and functionality of the nonwoven structure of polypropylene medical masks by varying the washing procedure, bath composition, disinfectant agent, and number of washing cycles as a basis for reusability. The barrier properties of the medical mask were analyzed before and after the first and fifth washing cycle indirectly by measuring the contact angle of the liquid droplets with the front and back surface of the mask, further by measuring air permeability and determining antimicrobial resistance. Additional analysis included FTIR, pH of the material surface and aqueous extract, as well as the determination of residual substances—surfactants—in the aqueous extract of washed versus unwashed medical masks, while their aesthetic aspect was examined by measuring their spectral characteristics. The results showed that household washing had a stronger impact on the change of some functional properties, primarily air permeability, than laboratory washing. The addition of the disinfectant agent, didecyldimethylammonium chloride, contributes to the protective ability and supports the idea that washing of medical masks under controlled conditions can preserve barrier properties and enable reusability. [ABSTRACT FROM AUTHOR]

Aiming at the mode of liquid ligament disintegration into droplets in the process of the centrifugal granulation of molten blast furnace slag using a spinning cup, in order to gain an in-depth understanding of the behavior and mechanism of droplet formation by liquid ligament disintegration and to obtain appropriate conditions to control the size of the produced slag granules, a three-dimensional CFD model describing water–air two-phase flow with a free surface was established in this work for simulating the process of a single water ligament breakup into droplets under the action of gravity, surface tension and inertial forces, so as to compare with the process of a molten slag ligament disintegration into droplets due to centrifugal force exerted by the spinning cup. By studying the disintegration behavior and mechanism of a single water ligament, the similar phenomenon of a molten slag ligament disintegration is examined. The numerical simulation results on the breakup of a single water ligament show that the length of the ligament before its disintegration and the diameter of the droplets formed both increase with the increase of the velocity of the ligament initially exiting a capillary nozzle. In addition, an experimental set-up was established in the laboratory to conduct cold physical model simulation experiments on single water or liquid paraffin ligament disintegration. The experimental results are compared with the numerical simulation results so that the reliability of the CFD model is verified. The results of the present study show that, in the centrifugal granulation process of blast furnace slag using a spinning cup operated in the ligament disintegration mode, the breakup of a single molten slag ligament is very similar to that of a single water or liquid paraffin ligament, and both approximately follow the Rayleigh Disintegration Mechanism, which provides a theoretical basis for analyzing the breakup process of the ligaments of different liquids as references for guiding the operation of centrifugal granulation of molten slag. [ABSTRACT FROM AUTHOR]

Woodland fires are a major issue worldwide. The aviation method of extinguishing forest fires is one of the main ones. However, the use of the latter is carried out according to the results of experiments, bench or flight tests in the absence of models that adequately describe the mechanisms for suppressing the combustion of forest combustible materials with specific fire extinguishing compositions (solutions, emulsions or suspensions). Therefore, the task of studying the evaporation and interaction of single drops with the surfaces of combustible materials is relevant and practically significant in the field of fire hazards. The paper presents the experimental research findings on the evaporation of specialized composition droplets for extinguishing fires under different heat supply schemes. The compositions under study included a group of widely used fire extinguishing agents: water; flame retardant FR-Les (5% solution); FR-Les (20% solution); bentonite slurry (1%); bentonite slurry (5%); bischofite solution (5%); bischofite solution (10%); fire extinguishing agent OS-5 (5% solution); fire extinguishing agent OS-5 (10% solution); fire extinguishing agent OS-5 (15% solution); foaming agent emulsion (1%); foaming agent emulsion (5%); fire retardant (5% solution). Specialized composition droplets were heated using conductive, convective and radiant heating. Empirical coefficients were obtained. [ABSTRACT FROM AUTHOR]

We are proposing a model mathematical description of droplet evaporation using the kinetic approach. We have obtained the basic equation of the theory by using the law of conserving the full power of the vapor–liquid system, which has not been done before. We have found the range of droplet sizes at which it is stable. We have given a comparison of the obtained results with the known traditional ones. We have given numerical estimates for the critical size of the fine-dispersed phase up to the value of which ordinary evaporation takes place (that is for Knudsen number K n = l R , inequality K n ≪ 1 must be fulfilled, where l − is the free path of the molecule and R − is the droplet radius). We have given the optimal droplet size which is the most effective from the point of view of technical use in extinguishing flammable oil transformers. [ABSTRACT FROM AUTHOR]

Analysing the penetration and droplet deposition characteristics in the canopy of fruit trees is critical for optimising the operational parameters of air-assisted spraying equipment, achieving precise application of chemicals, and improving the effectiveness of fruit tree pest and disease control. We used a mobile LIDAR system to detect the tree canopy characteristics and optical porosity and conduct wind tunnel experiments to investigate the interaction between the tree canopy, the airflow field, and the droplet penetration ratio in the canopy of fruit trees. The results show that the relative wind velocity decreases rapidly during canopy penetration, and that the minimum value occurs at the back of the canopy. The smaller the optical porosity, the greater the reduction in wind velocity is. The quadratic exponential regression model had the highest coefficient of determination (R2) (0.9672) and the lowest root mean square error (RMSE) (5.56%). This paper provides information on optimising the spraying parameters, improving the pesticide utilisation rate, and selecting the optimum spraying conditions and application parameters. [ABSTRACT FROM AUTHOR]

The droplet size distribution following pesticide application practices can significantly impact droplet drift and non-target organisms (animals and plants). However, the relationship among liquid sheet breakup, drop formation, and droplet drift is an area that has been studied over the past 65 years but is still not fully understood. The objectives of this study were severalfold: to examine the liquid sheet breakup following the use of different adjuvants (sodium dodecyl sulfate, aerosol OT, and silicone at 1%) and their effects on the drift via three commonly used commercial spray nozzles (XR, AIXR, and TXVK). The spray sheet and initial droplet size spectrum for each spray was detected by a particle image velocimetry (PIV) system, and the drift for each treatment was measured in a wind tunnel. The nozzle type and the spray solution were found to significantly affect the liquid sheet breakup characteristics. AIXR produced large droplets, and TXVK with short liquid sheet length produced more small droplets. All adjuvants used in these experiments increased the formation of large droplets upon atomization while simultaneously reducing driftable fines (e.g., drops %<150 µm). The drift potential can be reduced by up to 66.1% when switching from a fine spray quality (TXVK) to a coarse spray quality (AIXR). The SDS adjuvant provided the most effective drift reduction for XR and TXVK nozzles showing reduced drift potential by 69.2% and 66.3%, respectively, while the silicone adjuvant showed the largest drift reduction for AIXR of 78.3%. The correlation between the liquid sheet length and DV0.5 was positive for XR and TXVK nozzles, and there was a significant positive correlation between %<150 µm and drift potential for all nozzles. This work suggests that the drift can be reduced significantly by changing the nozzle type and adding pesticide adjuvant into spray solution, which provided data support for the drift reduction of plant protection drones. [ABSTRACT FROM AUTHOR]

High-aspect-ratio (HAR) micropillar arrays offer a wide range of applications in micro-contact printing, switchable transparent optical windows, superhydrophobic surfaces, mechanical sensors, and actuators, due to their properties such as large surface area and excellent mechanical compliance. However, owing to their high aspect ratio, these microstructures are prone to lateral deflection by elastocapillary forces in liquid environments, which is known as top-gathering, limiting their manufacturing processes and applications. Here, the impact of symmetry on evaporation triggered top-gathering of micropillars was studied numerically. The initiation of the micropillar deflection due to capillary forces under varying force distributions was simulated using a COMSOL Multiphysics simulation package. The simulation was carried out for the configurations of two, four, and an array of micropillars. For the four micropillar configuration, a new equation was suggested for calculating the micropillar deflection due to elastocapillary forces, using force distributions around the micropillars. The suggested equation was verified by comparison with the experimental observations. The effect of droplet evaporation on deflection/top-gathering of micropillars was also investigated. It was found that initiation of deflection is due to asymmetry at the rim of the droplet, generating domino-like deflection of the other micropillars. This study provides a new equation/criterion for estimating deflection of the micropillars, suggesting array designs that are resistant to such deflections when interacting with liquids. [ABSTRACT FROM AUTHOR]

The convenient division of aqueous samples into droplets is necessary for many biochemical and medical analysis applications. In this article, we propose the design of a cost-effective droplet generator for potential bio-chemical application, featuring two symmetric tubes. The new droplet generator revisits the relationship between capillary components and liquid flow rates. The size of generated droplets by prototype depends only on generator dimensions, without precisely needing to control external flow conditions or driving pressure, even when the relative extreme difference in flow rate for generating nL level droplets is over 57.79%, and the relative standard deviation (RSD) of the volume of droplets is barely about 9.80%. A dropper working as a pressure resource is used to verify the rapidity and robustness of this principle of droplet generation, which shows great potential for a wide range of droplet-based applications. [ABSTRACT FROM AUTHOR]

In recent decades, electronic devices have tended towards miniaturization, which necessitates the development of new cooling systems. Droplet cooling on a heated wall is effectively used in power devices with high heat flux densities. The use of a surfactant leads to an increase in the diameter of the wetted spot and the rate of droplet evaporation. Despite the wide interest and numerous works in this area, there are still unexplored questions regarding the influence of surfactant and wall temperature on convection, of nonisothermality, and of the decrease in the partial pressure of vapor with increasing surfactant concentration. This work experimentally studies the effect on the rate of droplet evaporation of wall temperature in the range 20–90 °C and of the concentration of surfactant in an aqueous solution of sodium lauryl sulfate (SLS) from 0 to 10,000 ppm. It is shown for the first time that an inversion of the evaporation rate related to the droplet diameter occurs with increasing wall temperature. The influence of key factors on the evaporation of a water droplet with SLS changes with temperature. Thus, at a slightly heated wall, the growth of the droplet diameter becomes predominant. At high heat flux, the role of nonisothermality is predominant. To determine the individual influence of the surfactant on the partial pressure of water vapor, experiments on the evaporation of a liquid layer were carried out. The obtained results and simplified estimates may be used to develop existing calculation models, as well as to optimize technologies for cooling highly heated surfaces. [ABSTRACT FROM AUTHOR]

Research in the field of the evaporation of liquid droplets placed on surfaces with special wetting properties such as biphilic surfaces is of great importance. This paper presents the results of an experimental study of the heat and mass transfer of a water droplet during its evaporation depending on the direction of the gravitational force. A special technique was developed to create unique substrates, which were used to physically simulate the interaction of liquid droplets with the surface at any angle of inclination to the horizontal. It was found that the suspended and sessile droplets exhibited fundamentally different evaporation dynamics. It was shown that the suspended droplets had a higher temperature and, at the same time, evaporated almost 30% faster. [ABSTRACT FROM AUTHOR]

The effect of supersonic air temperature on the mixing characteristics of liquid hydrocarbon fuel injected into three different supersonic airflows elevated in three steps from 373 K to 673 K was investigated numerically. Compressible Reynolds-averaged Navier–Stokes (RANS) equations were solved together with species conservation equation using ANSYS Fluent for two-phase flow simulations including fuel droplet breakup and evaporation. The turbulence model needed to close the RANS equations used the Shear Stress Transport (SST) k-ω model. The Eulerian–Lagrangian model was employed to track fuel droplets in mainstream air, and the Kelvin–Helmholtz and Rayleigh–Taylor (KH-RT) models were used to simulate the droplet breakup process. Numerical solutions were validated using experimental data. The higher the air temperature, the stronger the streamwise vortices downstream of the pylon. When the air temperature was 373 K, the liquid fuel hardly evaporated, but as the air temperature increased, and the mass fraction of the vaporized fuel and the mixing efficiency increased linearly downstream of the pylon. At air temperatures of 523 K and 673 K, the mixing efficiencies were 10% and 51% at the combustor outlet, respectively. The total pressure loss decreased slightly due to droplet evaporation as the temperature increased from 373 K to 673 K. [ABSTRACT FROM AUTHOR]

Laser technology is being widely studied for controlled energy deposition for a range of applications, including flow control, ignition, combustion, and diagnostics. The absorption and scattering of laser radiation by liquid droplets in aerosols affects propagation of the laser beam in the atmosphere, while the ignition and combustion characteristics in combustion chambers are influenced by the evaporation rate of the sprayed fuel. In this work, we present a mathematical model built on OpenFOAM for laser heating and evaporation of a single droplet in the diffusion-dominated regime taking into account absorption of the laser radiation, evaporation process, and vapor flow dynamics. The developed solver is validated against available experimental and numerical data for heating and evaporation of ethanol and water droplets. The two main regimes—continuous and pulsed laser heating—are explored. For continuous laser heating, the peak temperature is higher for larger droplets. For pulsed laser heating, when the peak irradiance is close to transition to the boiling regime, the temporal dynamics of the droplet temperature does not depend on the droplet size. With the empirical normalization of time, the dynamics of the droplet shrinkage and cooling are found to be independent of droplet sizes and peak laser intensities. [ABSTRACT FROM AUTHOR]

Nebulizer is one of inhalation therapy's most widely used aerosol generation devices. Nowadays, the vibrating mesh nebulizer has become popular owing to its compactness and noiselessness. In this study, an experimental system is proposed to measure the deposition fraction (DF) of nebulized sodium chloride (NaCl) droplets in an idealized mouth-throat airway model. The results show that before the DF increases to 58.6% with an increasing flow rate to 60 L/min, there is a decrease in DF from 42.4% to 15.5% when the inhalation flow rate increases from 15 to 22.5 L/min for a normal saline solution. These results substantially differ from the conclusions of dry powder or particle experiments and simulations, which monotonously increases with increasing inhalation flow rate. This suggests that droplet evaporation during aerosol generation and transport in the airway plays an important role. The experiment also showed that droplets generated from solutions with a higher NaCl concentration have higher DFs. [ABSTRACT FROM AUTHOR]

Controlled buckling of colloidal droplets via acoustic levitation plays an important role in pharmaceutical, coating, and material self-assembly. In this study, the evaporation process of PTFE colloidal droplets with two particle concentrations (60 wt% and 20 wt%) was investigated under acoustic levitation. We report the occurrence of surface invagination caused by evaporation. For the high particle concentration droplet, the upper surface was invaginated, eventually forming a bowl-shaped structure. While for the low particle concentration droplet, both the upper and lower surfaces of the droplet were invaginated, resulting in a doughnut-like structure. For the acoustically levitated oblate spherical droplet, the dispersant loss at the equatorial area of the droplet is greater than that at the two poles. Therefore, the thickness of the solid shell on the surface of the droplet was not uniform, resulting in invagination at the weaker pole area. Moreover, once the droplet surface was buckling, the hollow cavity on the droplet surface would absorb the sound energy and results in strong positive acoustic radiation pressure at bottom of the invagination, thus further prompting the invagination process. [ABSTRACT FROM AUTHOR]

This paper presents the results of detailed studies of the processes of droplet formation and its characteristics under conditions of artificially induction of a bag-breakup fragmentation event. A shadow imaging method was used in combination with the high-speed video filming of the side-view fragmentation process. Trajectories and ejection velocity characteristics of the formed droplets are determined by identifying particles in consecutive frames with combined use of Particle Imaging Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). Based on the results of trajectory processing, the distributions of droplet velocities for the selected regions are obtained, and estimates of the ejection velocities at various heights are proposed. [ABSTRACT FROM AUTHOR]

We present a novel device for generating suspension droplets and studying droplet impact against solid substrates. The proposed droplet generator extends beyond previous designs by introducing hydraulic machinery that includes separate hydraulic and test containers. This eliminates mixing between the test liquid and the hydraulic liquid above the latch that connects the two containers, thus ensuring reliable clogless operation. The device can produce droplets of controllable sizes between 0.75 and 4.4 mm, and droplets can contain suspension particles of 45 μm to 300 μm size. Repeatability tests show that, at constant control parameters, the median relative droplet size deviation from the target value is ±0.9% and the maximum relative deviation is ±9.1%. We also explore different collision scenarios, which we change from spreading to bouncing by varying the substrate wettability. In addition, the shape of the stain and the resulting spatial distribution of particles are found to be sensitive to particle size. [ABSTRACT FROM AUTHOR]

In order to compare and analyze the similarities and differences between normal droplet icing shapes and supercooled large droplet icing shapes, SADRI carried out normal droplet and supercooled large droplet icing wind tunnel tests in the NRC−AIWT icing wind tunnel. Taking the typical glaze ice in normal droplet icing conditions as the reference, the freezing drizzle and freezing rain icing tests under the supercooled large droplet conditions were carried out. The test results show that compared with normal droplets, the ice horn height of supercooled large droplets decreases with the increase in droplet particle size, and even the ice horn characteristics are not obvious when the icing condition is freezing rain. At the same time, the range and height of rough element ice shape after the main ice horn of supercooled large droplets are significantly larger and higher than those of the normal droplets, while the difference in the rough element in different supercooled large droplet icing conditions is small. [ABSTRACT FROM AUTHOR]

A novel numerical model was developed to investigate air entrapment in binary droplet impact with solidification microstructure formation under practical plasma spraying conditions. The evolving liquid–gas interface was tracked by the explicit finite difference solution to the Cahn–Hilliard equation, coupled with the Navier–Stokes equations. Another diffuse interface model was invoked to trace solid–liquid and grain–grain boundaries. The model was discretized using an explicit finite difference method on a half-staggered grid. The velocity pressure coupling was decoupled with the projection method. The in-house code was written in Fortran and was run with the aid of the shared memory parallelism, OpenMP. The time duration over which gas compressibility matters was estimated. Typical cases with air entrapment were studied with the model. The effect of droplet porosity on air entrapment was probed into as well: the larger the porosity of a droplet, the bigger the trapped air bubble. The grain growth near the air bubble is skewed. Moreover, a case without air entrapment was also shown herein to stress that air bubbles could be suppressed or even eliminated in plasma spraying by adjusting the landing positions of successive droplets. [ABSTRACT FROM AUTHOR]

Splitting a droplet into several segments is of great significance in many applications such as the detection of tiny liquid samples, whereas the surface tension tends to hold liquid to remain as one drop, causing difficulty in separating the droplet into pieces. In this work, a method is proposed to split an impacting droplet with a relatively high velocity or Weber number into two halves by a superhydrophobic wire. The effects of the wire wettability and the impact velocity of the droplet on the splitting phenomena and the efficacy to an anti-icing application are investigated. Compared to a hydrophilic wire, a superhydrophobic wire splits an impacting droplet at a relatively high speed of the Weber number greater than 3.1 and inhibits ice accretion at the temperature as low as −20 °C. The results suggest that a superhydrophobic wire can be utilized in the droplet manipulation and anti-icing applications such as power lines in high latitude areas. [ABSTRACT FROM AUTHOR]

Micro-structured surfaces can affect heat transfer mechanisms because of enlarged specific surface areas. However, employing the Leidenfrost effect during liquid nitrogen (LN2) droplet cooling of a heated micro-structured surface possessing a fin with a spacing much smaller than the diameter of the droplet has not yet been explored. In the present work, a direct numerical simulation (DNS) is carried out to investigate heat transfer mechanisms of the LN2 droplet, whose diameter is sufficiently larger than the structured spacing of fin, impinging on a micro-structured surface with variable velocities. For a comparative study, a smooth surface is also employed in numerical simulations. The spreading mechanisms and vaporization behavior of the droplet along with liquid film morphology at various conditions are investigated. Results show that a smaller fin size inhibits LN2 in entering into the grooves between the fins and left the surface untouched by the droplet completely, and eventually, a thinner liquid film is spread out in contrast to the smooth surface. Notably, at a low Weber number, the droplet can be shrunk or even rebounded away from the wall after impinging on the wall. The fastest vaporization behavior for both surfaces, namely smooth and micro-structured, is obtained at a Weber number of 180. Additionally, an effective heat transfer upon the micro-structured surface is observed at a low impinging velocity of the droplet. [ABSTRACT FROM AUTHOR]

Water collection remains a fundamental challenge to stable and efficient operation of the solar desalination system. Functional surfaces that can realize self-actuation of droplets have shown great potential in improving droplet dynamics without external energy. Therefore, a surface that can make a droplet move spontaneously along a curve was designed for smart droplet manipulation, and the mechanism of the droplet motion was revealed through molecular dynamics simulations. Influences of the wettability difference between the curved track and the background, the width of curved track, and the temperature were evaluated via simulations. The results show that the surface on which the curved track and the background are both hydrophobic enables a faster actuating velocity of the droplet than the hydrophilic-hydrophobic surface and the hydrophilic-hydrophilic surface. The width of the curved track also affects the actuating velocity of the droplet and increasing the TRACK width can increase the actuating velocity of the droplet. However, actuation of the droplet slows down if the width of the curved track is too large. Overall, the mechanism driving the motion of the droplet along the curve was investigated, which opens new opportunities for the application and manufacturing of water collection in solar desalination. [ABSTRACT FROM AUTHOR]

Background: A cough is known to transmit an aerosol cloud up to 2 m. During the COVID-19 pandemic of 2020 the United Kingdom's National Health Service (NHS), other UK government agencies and the World Health Organization (WHO) advised people to cough into their elbows. It was thought that this would reduce viral spread and protect the public. However, there is limited peer reviewed evidence to support this. Objectives: To determine if cough related interventions reduce environmental contamination, protecting members of the public from infection. Methods: Scientists and engineers at the Health and Safety Executive (HSE) laboratory used a human cough simulator that provided a standardised cough challenge using a solution of simulated saliva and a SARS-CoV-2 surrogate virus; Phi6. Pseudomonas syringae settle plates were used to detect viable Phi6 virus following a simulated cough into a 4 × 4 m test chamber. The unimpeded pattern of contamination was compared to that when a hand or elbow was placed over the mouth during the cough. High speed back-lit video was also taken to visualise the aerosol dispersion. Results and Discussion: Viable virus spread up to 2 m from the origin of the cough outwards in a cloud. Recommended interventions, such as putting a hand or elbow in front of the mouth changed the pattern of cough aerosol dispersion. A hand deflected the cough to the side, protecting those in front from exposure, however it did not prevent environmental contamination. It also allowed for viral transfer from the hand to surfaces such as door handles. A balled fist in front of the mouth did not deflect the cough. Putting an elbow in front of the mouth deflected the aerosol cloud to above and below the elbow, but would not have protected any individuals standing in front. However, if the person coughed into a sleeved elbow more of the aerosol seemed to be absorbed. Coughing into a bare elbow still allowed for transfer to the environment if people touched the inside of their elbow soon after coughing. Conclusions: Interventions can change the environmental contamination pattern resulting from a human cough but may not reduce it greatly. [ABSTRACT FROM AUTHOR]

The suitability of airflow velocity in airborne spraying operations in orchards is mostly evaluated on the basis of inlet and outlet based on the airflow velocity at the canopy. However, the airflow velocity required to penetrate into the inner layer of the canopy, which is prone to pests and diseases, is still unclear due to variation in the geometry of the plant canopies. In this study, pear trees were selected as an example to explore the variations in the law of airflow attenuation in the inner canopy. Furthermore, we examine mist droplet formation in the inner canopy to determine a suitable inner canopy airflow end velocity (ICAEV) for air-assisted application. We also conducted a field validation test. The results showed that the majority of airflow velocity loss occurred in the middle and outer part of the canopy; rapid decline of airflow occurred in the 0–0.3 m section, whereas the slow decline of airflow occurred in the 0.3–0.8 m section. When the ICAEV is in the range of 2.70–3.18 m/s, the spraying effect is better. The droplet deposition variation coefficient was 42.25% compared with 51.25% in the conventional airflow delivery mode. Additionally, the droplet drift was reduced by 12.59 μg/cm2. The results of this study can identify a suitable ICAEV for air-assisted spraying in orchards. [ABSTRACT FROM AUTHOR]

For structures and load-bearing beams under extreme impact loading, the prediction of the transmitted peak impact force is the most challenging task. Available numerical and soft computing-based methods for finding peak impact force are not very accurate. Therefore, a simple and user-friendly predictive model is constructed from a database containing 126 impact force experiments of the simply supported RC beams. The proposed model is developed using gene expression programming (GEP) that includes the effect of the impact velocity and the impactor weight. Also identified are other influencing factors that have been overlooked in the existing soft computing models, such as concrete compressive strength, the shear span to depth ratio, and the tensile reinforcement quantity and strength. This allows the proposed model to overcome several inconsistencies and difficulties residing in the existing models. A statistical study has been conducted to examine the adequacy of the proposed model compared to existing models. Additionally, a numerical confirmation of the empirical model of the peak impact force is obtained by reference to 3D finite element simulation in ABAQUS. Finally, the proposed model is employed to predict the dynamic shear force and bending moment diagrams, thus rendering it ideal for practical application. [ABSTRACT FROM AUTHOR]