Water Microdrops Research Articles

High order Fano resonance in the time domain for a freezing water microdroplet

Fog is a collection of micro drops of water suspended in the air, formed as a result of cooling of moist air. In supercooled air, water droplets freeze, forming ice fog at air temperatures below − 10–15° C. As the ice drop freezes, it forms a core-shell structure. In such a particle, a high-Q Fano resonance is possible, which entails the formation of a magnetic pulse. Our theoretical calculations have predicted the time-dependent formation of Fano resonances in a freezing the outside in water droplet. Time-varying unconventional Fano resonance with magnetic field enhancement yield new method to manipulate light–matter interactions in a freezing water droplet. To the best of our knowledge this mechanism was not discussed previously.

Microstructure and crystal order during freezing of supercooled water drops.

Supercooled water droplets are widely used to study supercooled water1,2, ice nucleation3-5 and droplet freezing6-11. Their freezing in the atmosphere affects the dynamics and climate feedback of clouds12,13 and can accelerate cloud freezing through secondary ice production14-17. Droplet freezing occurs at several timescales and length scales14,18 and is sufficiently stochastic to make it unlikely that two frozen drops are identical. Here we use optical microscopy and X-ray laser diffraction to investigate the freezing of tens of thousands of water microdrops in vacuum after homogeneous ice nucleation around 234-235 K. On the basis of drop images, we developed a seven-stage model of freezing and used it to time the diffraction data. Diffraction from ice crystals showed that long-range crystalline order formed in less than 1 ms after freezing, whereas diffraction from the remaining liquid became similar to that from quasi-liquid layers on premelted ice19,20. The ice had a strained hexagonal crystal structure just after freezing, which is an early metastable state that probably precedes the formation of ice with stacking defects8,9,18. The techniques reported here could help determine the dynamics of freezing in other conditions, such as drop freezing in clouds, or help understand rapid solidification in other materials.

The Three-Phase Contact Potential Difference Modulates the Water Surface Charge

The surface charge of an open water surface is crucial for solvation phenomena and interfacial processes in aqueous systems. However, the magnitude of the charge is controversial, and the physical mechanism of charging remains incompletely understood. Here we identify a previously overlooked physical mechanism determining the surface charge of water. Using accurate charge measurements of water microdrops, we demonstrate that the water surface charge originates from the electrostatic effects in the contact line vicinity of three phases, one of which is water. Our experiments, theory, and simulations provide evidence that a junction of two aqueous interfaces (e.g., liquid-solid and liquid-air) develops a pH-dependent contact potential difference Δϕ due to the longitudinal charge redistribution between two contacting interfaces. This universal static charging mechanism may have implications for the origin of electrical potentials in biological, nanofluidic, and electrochemical systems and helps to predict and control the surface charge of water in various experimental environments.

Nucleate boiling heat transfer during water–IN–oil emulsion drop impact onto a heated solid surface

The phenomenon of collision of fuel droplets with the walls of the combustion chamber largely determines the formation of the air-fuel mixture. The main attention in the study is paid to establishing the influence of the hydrodynamic parameters of the drop-wall interaction on the heat transfer during nucleate boiling of a drop of an n-decane-based water-in-oil emulsion. A drop of emulsion impacts onto a quartz glass surface heated to a temperature from 140 °C to 260 °C at Weber numbers (We) from 20 to 1000 and Reynolds numbers (Re) from 250 to 8000. The contact (evaporation) time of liquid droplets is measured experimentally. As a result, it becomes possible to derive an empirical model of the contact time τc, taking into account the dimensionless temperature of the heat exchange surface θ, as well as the main driving forces of the drop-wall interaction (inertia, viscosity and surface tension) at Re from 40 to 3000 and We from 1 to 1085. A complex mechanism of nucleate boiling in an emulsion drop is proposed. It involves injecting an intense vapor flow into a growing bubble from a near-wall microlayer and from the entire surface of the bubble, which is in contact with the n-decane and microdrops of water. An empirical model is introduced to predict the heat flux density at the solid-liquid interface during the contact of emulsion drops with a heated surface at nucleate boiling, q″, and tested at Re from 50 to 8000 and We from 20 to 1000. The empirical models allow evaluating the considered characteristics of heat transfer during the formation of an air-fuel mixture in the combustion chamber of the engine, taking into account the effects of the nucleate boiling nonlinearity and the collision of drops with the wall.

THE MODEL OF DESCRIPTION OF EXTRACTION OF URANIUM-235 AND URANIUM-238 ISOTOPES COMPLEXES IN A SUPERCRITICAL CARBON DIOXIDE LAYER HEATED FROM BELLOW

The models and analytical solutions for description of the extraction of 235U and 238U isotopes complexes in case of availability of water microdrops located both in a uniform temperature field and in a non-uniform temperature field of the heated from bellow horizontal layer of the supercritical carbon dioxide are suggested. It has been indicated that in a uniform temperature field the efficiency of supercritical fluid extraction with carbon dioxide complexes of uranium isotopes reaches a maximum at the limit of water solubility in supercritical carbon dioxide. Theoretical calculations have demonstrated that the maximum concentration of 235U isotope complexes heated from below in a supercritical carbon dioxide layer reaches 1.2% and is observed near the lower layer boundary. The procedure for supercritical fluid extraction with carbon dioxide is described, in which the concentration of 235U isotope complexes in the supercritical fluid will be higher than the natural one.

The Magnitude and Waveform of Shock Waves Induced by X-ray Lasers in Water

The high energy densities deposited in materials by focused X-ray laser pulses generate shock waves which travel away from the irradiated region, and can generate complex wave patterns or induce phase changes. We determined the time-pressure histories of shocks induced by X-ray laser pulses in liquid water microdrops, by measuring the surface velocity of the microdrops from images recorded during the reflection of the shock at the surface. Measurements were made with ~30 µm diameter droplets using 10 keV X-rays, for X-ray pulse energies that deposited linear energy densities from 3.5 to 120 mJ/m; measurements were also made with ~60 µm diameter drops for a narrower energy range. At a distance of 15 µm from the X-ray beam, the peak shock pressures ranged from 44 to 472 MPa, and the corresponding time-pressure histories of the shocks had a fast quasi-exponential decay with positive pressure durations estimated to range from 2 to 5 ns. Knowledge of the amplitude and waveform of the shock waves enables accurate modeling of shock propagation and experiment designs that either maximize or minimize the effect of shocks.

Atmospheric Processes Involving Condensed Water

Various mechanisms of formation and growth of water microdrops in the atmosphere include attachment of water molecules to them, coagulation and coalescence processes, and growth of drops during the rain caused by the gravitation. Condensed water cannot be formed under the conditions of standard atmosphere, it results from mixing of humid streams with cold air. Atmospheric water microdrops form the clouds, and their contribution to the atmospheric radiative flux toward the Earth is about 30%. The Mie theory for scattering of infrared radiation on liquid water droplets is represented that uses the measured optical parameters for liquid water. Then, basing on the energetic balance of the Earth and its atmosphere, it is possible to determine the relative mass of condensed water, which is of the order of 1% of the total mass of atmospheric water and is several times less than the analysis of atmospheric electricity suggests.

WATER DROPLET EVAPORATION IN A CHAMBER ISOLATED FROM THE EXTERNAL ENVIRONMENT

With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.

The Evaporation of Liquid Micro-Drops on the Heated Substrate

Evaporation of a heated sessile water micro-drop was studied experimentally at the substrate temperature and surrounding atmosphere from 30 to 50 °C. The studies were performed on the float glass substrate with aluminum nanocoating of optical quality. The research has shown that the specific rate of evaporation (mass loss per unit of the drop surface area) increases with the decrease in droplet volume and at the last stage several times exceeds the initial value.

Taggiasca extra virgin olive oil colonization by yeasts during the extraction process

The opalescent appearance of the newly produced olive oil is due to the presence of solid particles and microdrops of vegetation water in which the microorganisms from the olives’ carposphere are trapped. Present research has demonstrated that the microbiota of the fresh extracted olive oil, produced in the mills, is mainly composed of yeasts and to a lesser extent of molds. The close link between the composition of the microbiota of the olives’ carposphere undergoing to processing, and that of the microbiota of the newly produced olive oil, concerns only the yeasts and molds, given that the bacterial component is by and large destroyed mainly in the kneaded paste during the malaxation process. Six physiologically homogenous yeast groups were highlighted in the wash water, kneaded paste and newly produced olive oil from the Taggiasca variety which had been collected in mills located in the Liguria region. The more predominant yeasts of each group belonged to a single species called respectively: Kluyveromyces marxianus, Candida oleophila, Candida diddensiae, Candida norvegica, Wickerhamomyces anomalus and Debaryomyces hansenii. Apart from K. marxianus, which was found only in the wash water, all the other species were found in the wash water and in the kneaded paste as well as in the newly produced olive oil, while in the six-month stored olive oil, was found only one physiologically homogeneous group of yeast represented by the W. anomalus specie. These findings in according to our previous studies carried out on other types of mono varietal olive oils, confirms that the habitat of the Taggiascas’ extra virgin olive oil, had a strong selective pressure on the yeast biota, allowing only to a few member of yeast species, contaminating the fresh product, to survive and reproduce in it during storage.

An experimental and computational study of the hydrodynamics of high-velocity water microdrops for interproximal tooth cleaning

The flow field and local hydrodynamics of high-velocity water microdrops impacting the interproximal (IP) space of typodont teeth were studied experimentally and computationally. Fourteen-day old Streptococcus mutans biofilms in the IP space were treated by a prototype AirFloss delivering 115µL of water at a maximum exit-velocity of 60ms−1 in a 33-ms burst. Using high-speed imaging, footage was generated showing the details of the burst, and demonstrating the removal mechanism of the biofilms. Footage was also generated to characterize the viscoelastic behavior of the biofilms when impacted by an air-only burst, which was compared to the water burst. Image analysis demonstrated the importance of fluid forces on the removal pattern of interdental biofilms. X-ray micro-Computed Tomography (µ-CT) was used to obtain 3D images of the typodont and the IP spaces. Computational Fluid Dynamics (CFD) simulations were performed to study the effect of changing the nozzle position and design on the hydrodynamics within the IP space. Results confirmed our previous data regarding the wall shear stress generated by high-velocity water drops which dictated the efficacy of biofilm detachment. Finally, we showed how CFD models could be used to optimize water drop or burst design towards a more effective biofilm removal performance.

Ion Chromatography for Rapid and Sensitive Determination of Three Alkylamines in Wastewater after Headspace Single-Drop Microextraction

A novel headspace single drop microextraction method coupled with ion chromatography was developed for the determination of propylamine, sec-butylamine, and butylamine in industrial wastewater. The method was based on a deionized water microdrop (10 µL) which hung in the headspace of the sample bottle. The ammonium ion produced in the microdrop was measured subsequently by ion chromatography. The conditions for the single-drop microextraction process were optimized by employing an orthogonal experimental design. The enrichment factors of propylamine, sec-butylamine, and butylamine were 40, 73, and 45, respectively, under the optimal conditions. Baseline separation of three alkylamines was achieved within 15 min in concentrations varying from 0.5 to 15.0 mg L−1 (, , ) and the detection limits (signal-to-noise ratio of 3) were 0.96, 4.28, and 8.18 µg L−1 by using 30 mmol L−1 methanesulfonic acid as the eluent. The method was successfully employed to determine the three aliphatic amines in industrial wastewater with recoveries of 97.2% to 102.9%. The relative standard deviation, according to peak area, was 0.96%. The experimental results showed that headspace single-drop microextraction combined with ion chromatography is a simple, rapid, and low-cost method for the determination of the alkylamines.

Removal of Interproximal Dental Biofilms by High-velocity Water Microdrops

The influence of the impact of a high-velocity water microdrop on the detachment of Streptococcus mutans UA159 biofilms from the interproximal (IP) space of teeth in a training typodont was studied experimentally and computationally. Twelve-day-old S. mutans biofilms in the IP space were exposed to a prototype AirFloss delivering 115 µL water at a maximum exit velocity of 60 m/sec in a 30-msec burst. Using confocal microscopy and image analysis, we obtained quantitative measurements of the percentage removal of biofilms from different locations in the IP space. The 3D geometry of the typodont and the IP spaces was obtained by micro-computed tomography (µ-CT) imaging. We performed computational fluid dynamics (CFD) simulations to calculate the wall shear stress (τw) distribution caused by the drops on the tooth surface. A qualitative agreement and a quantitative relationship between experiments and simulations were achieved. The wall shear stress (τw) generated by the prototype AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal in the IP space.

Phase transformations of a condensate on a crystal surface in a strong electric field

The evolution of the phase state of the water vapor condensate of the silver iodide crystal surface in an applied electric field up to 10 V/nm is studied by computer simulation. The previously found domain structure of the contact layer is stable against the external field and remains up to the complete break of the molecular film. In a strong electric field, the film condensation mode is changed by the formation of a new phase consisting of molecular nanothreads growing in the direction of the electric field lines. The transition to the new state is sharp. The presence of a phase transition is likely analogous to that accompanying the transformation of water microdrops to the superpolarized state under the action of an external electric field at stratospheric temperatures.

Fouling-release Property of Water-filled Porous Elastomers

Since the fouling-releasing ability of silicone elastomers increased as their modulus decreases, we designed and prepared composites with embedded tiny NaCl crytals that were soluble after their immersion in water, resulting in water-filled porous elastomers. The scanning electron microscope images confirmed such a designed water-filling porous structure. The existence of many micro-drops of water in these specially designed elastomers decreased the shear storage modulus and increased the loss factors. The decrease of shear modulus plays a leading role here and is directly related to a lower critical peeling-off stress of a pseudo-barnacle on them. Therefore, such a novel preparation with cheap salts instead of an expensive silicone provides a better way to make fouling-release paints with a lower modulus, a lower critical peeling-off stress and a better fouling-release property without a significant decrease of the cross-linking density.

Numerical simulation of formation of cyclone vortex flows in the intratropical zone of convergence and their early detection

Mechanisms of formation of cyclonic vortices in the tropical atmosphere of the Earth are investigated in the intratropical zone of convergence using numerical simulation made with the complete system of equations of gas dynamics taking into account transport of infrared radiation, phase transitions of water vapor into microdrops of water and ice particles, and sedimentation of these drops and ice particles in the field of gravity force. Observational data on the structure of dominant air streams, which are formed in the intratropical zone of convergence over the North Atlantic in the periods of its highest thermodynamic intensity and instability, are used in the initial and boundary conditions of the model. Formation of cyclonic vortex flows is obtained numerically at sufficiently strong bending of the intratropical zone of convergence. The results of numerical modeling are compared with the data of satellite microwave monitoring: global radio thermal fields of the Earth from the electronic collection GLOBAL-Field allowing one to study the structure of atmospheric motions in a wide range of space-time scales.

A mechanism of formation of polar cyclones and possibility of their prediction using satellite observations

Using numerical simulation, a mechanism of formation of polar cyclones in the region of location of the arctic front in the winter troposphere of the Northern Hemisphere is studied. The simulation was performed with the help of the complete system of gas dynamics equations taking into account the transport of infrared radiation, phase transitions of water vapor into micro-drops of water and ice particles, and with allowance made for sedimentation of these drops and ice particles in the gravity field. In the initial and boundary conditions of the model, observational data on the structure of dominating air flows in the region of the arctic front over Norwegian Sea in January are used. Formation of large-scale cyclonic vortex flows in 15–20 hours at the presence of a bend of the central line of the shear flow in the arctic front 500–600 km long with northward or southward deviations by 100 km and more is obtained numerically. On the basis of the simulation results, a method of short-term forecast of formation and motion of polar cyclones is suggested.

Non-equilibrium and Nonlinear Effects in Water-in-Oil Emulsion Flows in Porous Media

The nonlinear behavior of emulsions in hydrodynamics is mostly pronounced when such emulsions flow in microchannels in experiments involving a permanent pressure gradient at the channel. It has been discovered that, despite the permanent pressure gradient, the flow of the water-in-oil emulsion almost completely ceases with time. This effect is known as dynamic blocking. It becomes pronounced when the emulsions flow through a cylindrical microchannel, in the case of a plane flow in the elements of a fracture, and when the emulsion flows through a 3D capillary structure, such as a core. The sizes of the water microdrops in the emulsion are an order of magnitude smaller than the cross-section sizes of the microchannels. However, the structure that is formed of such microdrops blocks not only individual microchannels but also the entire microchannel system, including cores. The physical nature of the dynamic blocking of emulsions is connected to the deformations of the emulsion microdrops as the pressure grad...

Features of water microdrop dispersion flow in microchannels

A remarkable property of inverse water-hydrocarbon emulsions, which is manifested during their flow in microchannels, has been discovered and called dynamic blocking. According to this phenomenon, the flow of emulsion through a microchannel ceases with the time despite the presence of a continuously applied pressure gradient. Experiments show that this effect can be observed for the flow of emulsions with different compositions and rheological properties. The effect is manifested at rather significant pressure gradients, although it is accompanied by a partial degradation of dispersions. A physical mechanism is proposed to explain the dynamic blocking of water-hydrocarbon emulsions in microchannels, which is based on the notion of an interaction between nanodimensional surface shells consisting of surfactant molecules that surround water microdrops.

Transition in the Evaporation Kinetics of Water Microdrops on Hydrophilic Surfaces

We describe a technique that allows measurement of the mass and shape of sessile liquid microdrops during evaporation. Therefore, the microdrops are deposited by an inkjet onto a silicon microcantilever, and the bending and the shift in resonance frequency are monitored. From hydrophobized surfaces, microscopic water drops evaporate with the same kinetics as macroscopic drops; we verify the validity of known evaporation laws to drops with diameters from 100 microm to below 10 microm. From hydrophilic surfaces, the evaporation is slowed down during the last approximately 100 ms; we believe that this occurs due to flattening of the drops, which are then stabilized by interfacial forces and disjoining pressure.