Heterogeneous Droplet Research Articles

Microphysics of mass-transport in coupled droplet-pairs at low Reynolds number and the role of convective dynamics

Interfacial mass-transport and redistribution in the micro-scale liquid droplets are important in diverse fields of research interest. The role of the “inflow” and the “outflow” type convective eddy-pairs in the entrainment of outer solute and internal relocation are examined for different homogeneous and heterogeneous water droplet pairs appearing in a tandem arrangement. Two micro-droplets of pure (rain) water interact with an oncoming outer air stream (Re ≤ 100) contaminated by uniformly distributed SO2. By virtue of separation/attachment induced non-uniform interfacial shear-stress gradient, the well-defined inflow/outflow type pairs of recirculating eddy-based convective motion quickly develops, and the eddies effectively attract/repel the accumulated outer solute and control the physical process of mass-transport in the droplet-pair. The non-uniformly shear-driven flow interaction and bifurcation of the circulatory internal flow lead to growth of important micro-scale “secondary” eddies which suitably regroup with the adjacent “primary” one to create the sustained inflow/outflow type convective dynamics. The presently derived flow characteristics and in-depth analysis help to significantly improve our understanding of the micro-droplet based transport phenomena in a wider context. By tuning “Re” (defined in terms of the droplet diameter and the average oncoming velocity of the outer air) and gap-ratio “α,” the internal convective forcing and the solute entrainment efficiency could be considerably enhanced. The quantitative estimates for mass entrainment, convective strength, and saturation characteristics for different coupled micro-droplet pairs are extensively examined here for 0.2 ≤ α ≤ 2.0 and 30 ≤ Re ≤ 100. Interestingly, for the compound droplets, with suitably tuned radius-ratio “B” (of upstream droplet with respect to downstream one) the generated “inflow” type coherent convective dynamics helped to significantly augment the centre-line mass flow, which in turn facilitate faster saturation of the upstream droplet. However, for heterogeneous droplet-pairs containing solid nucleus, while increased solid-fraction “S” (the ratio between the radius of the solid nucleus and that of the droplet) through 0.25 ≤ S ≤ 0.45 caused gradual reductions of convective strength and mass absorption rate (RSO2) for the upstream droplet, beyond a critical value S ≥ 0.45 the RSO2 therein continued to rise again owing to the reduced film thickness.

Aerosol indirect effects on glaciated clouds. Part I: Model description

Various improvements were made to a state‐of‐the‐art aerosol–cloud model and comparison of the model results with observations from field campaigns was performed. The strength of this aerosol–cloud model is in its ability to explicitly resolve all the known modes of heterogeneous cloud droplet activation and ice crystal nucleation. The model links cloud particle activation with the aerosol loading and chemistry of seven different aerosol species. These improvements to the model resulted in more accurate prediction especially of droplet and ice crystal number concentrations in the upper troposphere and enabled the model to directly sift the aerosol indirect effects based on the chemistry and concentration of the aerosols. In addition, continental and maritime cases were simulated for the purpose of validating the aerosol–cloud model and for investigating the critical microphysical and dynamical mechanisms of aerosol indirect effects from anthropogenic solute and solid aerosols, focusing mainly on glaciated clouds. The simulations showed that increased solute aerosols reduced cloud particle sizes by about 5 μm and inhibited warm rain processes. Cloud fractions and their optical thicknesses were increased quite substantially in both cases. Although liquid mixing ratios were boosted, there was however a substantial reduction of ice mixing ratios in the upper troposphere owing to the increase in snow production aloft. These results are detailed in the subsequent parts of this study.

Numerical Investigation of the Main Characteristics of Heat and Mass Transfer while Heating the Heterogeneous Water Droplet in the Hot Gases

The processes of heat and evaporation of heterogeneous water droplet with solid (by the example of carbon) inclusion in hot (from 800 K to 1500 K) gases were investigated by the developed models of heat and mass transfer. We defined the limited conditions, characteristics of the droplet and the gas medium which are sufficient for implementing the “explosive” destruction of heterogeneous droplet due to intensive vaporization on an inner interface, and intensive evaporation of liquid from an external (free) droplet surface. The values of the main characteristic of the process (period from start of heating to “explosive” destruction) obtained in response to using various heat and mass transfer models were compared.

Intensive evaporation and boiling of a heterogeneous liquid droplet with an explosive disintegration in high-temperature gas area

The using of the high-speed (not less than 105 frames per second) video recording tools (“Phantom”) and the software package (TEMA Automotive) allowed carrying out an experimental research of laws of intensive vaporization with an explosive disintegration of heterogeneous (with a single solid nontransparent inclusion) liquid droplet (by the example of water) in high-temperature (500-800 K) gases (combustion products). Times of the processes under consideration and stages (liquid heat-up, evaporation from an external surface, bubble boiling at internal interfaces, growth of bubble sizes, explosive droplet breakup) were established. Necessary conditions of an explosive vaporization of a heterogeneous droplet were found out. Mechanisms of this process and an influence of properties of liquid and inclusion material on them were determined.

Influence of surface roughness and porosity of inclusion in water droplet on heat transfer enhancement

Using high-speed camera, the experiments were performed to research evaporation of 10 μl water droplets containing 2 mm solid inclusions in the shape of cube, when heated (up to 850 K) in combustion products of technical ethanol. Adding solid inclusions in water droplets allowed considerably decreasing (by 70%) their evaporation times. Also, the artificial irregularities (roughness and porosity) at the surfaces of solid inclusions were manufactured to increase heat transfer area. Such approach enabled to decrease evaporation times of heterogeneous liquid droplets in high-temperature gases by 40% (when comparing inclusions with artificial irregularities and smooth surface).

Evaporation and Vapor Formation of Graphite Suspensions Based on Water in a High-Temperature Gas Environment: an Experimental Investigation

We performed an experimental research on evaporation and vapor formation of water droplets containing large (2 mm in size) and small (0.05 mm and 0.2 mm in diameter) graphite inclusions, when heated in a high-temperature gas environment. We applied a high-speed (up to 104 fps) video recording to establish mechanisms of the processes considered. Moreover, we revealed the positive influence of addition of small graphite inclusions on intensifying the evaporation of heterogeneous suspension droplets. In addition, we made the assumption on the formation of vapor layer around the 10 and 15 μl suspension droplets, as well as its negative influence on the lifetimes of suspension droplets τh (increasing the times) in a high-temperature gas environment.

고온평판에 충돌하는 비균일혼합액적의 동적거동 특성

In this experiment, a heterogeneous droplet consisted of de-ionized water and olive oil was made through two 31G injection needles. The injection flow rate was and the droplet size was 2 mm. The droplet was impinged onto a sapphire plate which was heated up to by a heater. Two high speed cameras were used for visualization, and the frame rate was 20,000 fps. A 150W metal halite lamp was used for illumination. The dropping height was fixed to 20 mm and the corresponding Weber number was 10.6 based on water. Due to different boiling points of two liquids, partial boiling features of heterogeneous droplet was observed. At the Leidenfrost condition, micro explosion phenomenon has occurred.

Thermokinetics of heterogeneous droplet nucleation on conically textured substrates.

Within the framework of the classical theory of heterogeneous nucleation, a thermokinetic model is developed for line-tension-associated droplet nucleation on conical textures considering growth or shrinkage of the formed cluster due to both interfacial and peripheral monomer exchange and by considering different geometric configurations. Along with the principle of free energy extremization, Katz kinetic approach has been employed to study the effect of substrate conicity and wettability on the thermokinetics of heterogeneous water droplet nucleation. Not only the peripheral tension is found to have a considerable effect on the free energy barrier but also the substrate hydrophobicity and hydrophilicity are observed to switch over their roles between conical crest and trough for different growth rates of the droplet. Besides, the rate of nucleation increases and further promotes nucleation for negative peripheral tension as it diminishes the free energy barrier appreciably. Moreover, nucleation inhibition can be achievable for positive peripheral tension due to the enhancement of the free energy barrier. Analyzing all possible geometric configurations, the hydrophilic narrower conical cavity is found to be the most preferred nucleation site. These findings suggest a physical insight into the context of surface engineering for the promotion or the suppression of nucleation on real or engineered substrates.

Explosion of heterogeneous water droplet in a high-temperature gaseous region

Using high-speed video recording tools (up to 105 frames per second) and «TEMA Automotive» and «Phantom Camera Control» software packages the experimental features of explosive disintegration, boiling and evaporation of water droplets with comparably sized solid inclusions heated in high-temperature (more than 650 K) gaseous region were determined. The necessary and sufficient conditions of explosive vapor formation achievement with the next heterogeneous water droplet disintegration were found.

Evaporation, boiling and explosive breakup of heterogeneous droplet in a high-temperature gas

Experimental investigation of evaporation and boiling was carried out on fixed water droplet containing a single nontransparent solid inclusion and placed in gaseous environment at high-temperature (500–1100K). We carried out experiments with water droplets (diameters 3–5mm) containing graphite inclusions of different shapes (sphere, disk, cone, parallelepiped and polyhedron) with sizes between 2 and 4mm. These droplets were in the hot flux on top of combustion of industrial ethanol. The behavior of the droplets was recorded by high-speed (up to 105 frames per second) video cameras “Phantom” and “TEMA Automotive” software. Conditions for intensive vaporization at solid/liquid interface inside droplets were determined. A phenomenon of explosive disintegration occurred when heating some of the heterogeneous droplets. Time of heating until an explosive disintegration and complete evaporation was recorded. Influence of gas temperature and inclusion sizes were measured.

Conditions of Intensive Evaporation of Heterogeneous Water Droplet in High Temperature Gas Environment

AbstractThe results of a numerical simulation of heat and mass transfer during evaporation of a water droplet with solid inclusion in air at temperature as high as 1000K are presented. Typical heating steps of droplet until it reaches the conditions of intensive evaporation (i.e.the interface “solid inclusion – liquid” reaches the boiling temperature) are described. The roles played by the external air temperature and by the main properties of inclusion are detailed. The droplet size, the relation between the sizes of inclusion and a liquid layer during the heating up is determined. The necessary and sufficient conditions of intensive evaporation in the system “water droplet with solid inclusion in high-temperature air” are pointed out.

High-Throughput, Quantitative Enzyme Kinetic Analysis in Microdroplets Using Stroboscopic Epifluorescence Imaging

Droplet-based microfluidic systems offer a range of advantageous features for the investigation of enzyme kinetics, including high time resolution and the ability to probe extremely large numbers of discrete reactions while consuming low sample volumes. Kinetic measurements within droplet-based microfluidic systems are conventionally performed using single point detection schemes. Unfortunately, such an approach prohibits the measurement of an individual droplet over an extended period of time. Accordingly, we present a novel approach for the extensive characterization of enzyme-inhibitor reaction kinetics within a single experiment by tracking individual and rapidly moving droplets as they pass through an extended microfluidic channel. A series of heterogeneous and pL-volume droplets, containing varying concentrations of the fluorogenic substrate resorufin β-d-galactopyranoside and a constant amount of the enzyme β-galactosidase, is produced at frequencies in excess of 150 Hz. By stroboscopic manipulation of the excitation laser light and adoption of a dual view detection system, "blur-free" images containing up to 150 clearly distinguishable droplets per frame are extracted, which allow extraction of kinetic data from all formed droplets. The efficiency of this approach is demonstrated via a Michaelis-Menten analysis which yields a Michaelis constant, Km, of 353 μM. Additionally, the dissociation constant for the competitive inhibitor isopropyl β-d-1-thiogalactopyranoside is extracted using the same method.

Determination of interfacial parameters of a soluble particle in a nonideal solution from measured deliquescence and efflorescence humidities

Abstract. In order to study the growth/shrinking of a hygroscopic nanoparticle during hydration/dehydration in an atmosphere of water vapour, we have employed a thermodynamic approach proposed by Shchekin et al. (2008). This approach uses the mechanic and thermodynamic concept of disjoining pressure of thin films and allows, among others, the prediction of the humidity growth factor of both (i) a homogeneous solution droplet with completely dissolved residual core and (ii) a heterogeneous solution droplet with partially dissolved residual core as a function of the ambient relative humidity. For application to a nanometric sodium chloride particle we have extended the original approach by (i) considering the nonideality of the solution through the dependence of molecular volumes of the solvent and solute molecules and the solute and solvent activities on the solution concentration, (ii) deriving an equation for the estimation of the efflorescence properties of a homogeneous solution droplet, and (iii) combining the empirical power law fittings for the size dependence of the deliquescence and efflorescence relative humidity values by Biskos et al. (2006a). It was demonstrated how the solution/solute interface energy and the correlation length of a thin solution film can be determined from a combination of experimentally determinable efflorescence and deliquescence humidities with the present calculus. The solution/solute interface energy was found to be in close agreement with some previous values reported in the literature, while it strongly differs from data of some other sources. The calculated deliquescence humidity shows a low sensitivity to the choice of the numerical value for the film correlation length. The estimated film correlation length of 1 nm for a nanometric sodium chloride particle with dry particle radius of 5 nm was found to be reconcilable with available a priori estimates of the correlation length from the literature when the measurement uncertainty of the deliquescence humidity is considered. Considering the combination of an extensive calculus, a comprehensive set of thermophysical constraints, and independent measurements of the deliquescence and efflorescence humidities as functions of dry particle radius, the obtained values of the solution/solute interface energy and the correlation length are in close agreement with previous estimations. The humidification of sodium chloride particles in the initial hydration stages was found to be very sensitive to the specification of the disjoining pressure. The enhancement of the wettability of the particle surface leads to an earlier onset of hygroscopic growth.

Difference Of Evaporation and Boiling for Heterogeneous Water Droplets in a High-Temperature Gas

Experimental investigation of vapor formation was carried out on water droplets on fixed graphite substrate and heterogeneous droplets (containing solid single inclusions) when heating in high-temperature gas. High-speed video shooting (up to 10 5 frames per second), optical method (Particle Image Velocimetry) and TEMA Automotive software were used. We revealed two phase change mechanisms of heterogeneous liquid droplets. Effect of evaporation and boiling on evaporation times of water droplets was determined.

Влияние показателя поглощения тушащей жидкости на интенсивность кипения и испарения неоднородной капли в пламени

The numerical model and methodology of experimental researches of heat and mass transfer during the heating, boiling and evaporation of heterogeneous water droplet in a high-temperature area are presented in the work. The results of numerical and experimental researches of evaporation of water droplet with a solid graphite inclusion in a flaming combustion area are introduced. The conditions of an explosive vaporization mode realization in a contact zone of solid inclusion and liquid film (temperature of gaseous area is Tf > 1050 K and water film thickness is 5R > 0.210 -3 m) are determined. The main stages of studying process are fixed on video: the droplet heat-up, the beginning of bubble formation of vapor at the interface solid inclusion - liquid, the volume increase of vapor bubble, the droplet fission. The influence of optical water characteristic (absorption coefficient of radiant energy k x )onthe typical period t h from the beginning of heterogeneous liquid droplet heating to the realization of an explosive vaporization conditions is analyzed. It is shown that for droplets with liquid film size SR ~ 0.510 3 m the change of the absorption coefficient of radiant energy in a wide range =10 -3 ^10 2 m -1 doesn't influence on t h significantly. The application possibility of water unprepared (in the case of optical properties) in a special way (for example from open ponds at forest fire extinguishing) for extinguishing composition is substantiated, provided accounting of the absorption coefficient of the liquid in the process of selecting the characteristic sizes of the generated droplets.

Explosive Breakup of a Water Droplet with a Nontransparent Solid Inclusion Heated in a High-Temperature Gaseous Medium

This paper investigates the evaporation of a droplet with a comparably sized solid nontransparent in a high-temperature (500-800 K) gas medium. Water evaporates from the free surface of the inclusion. During this process, intensive vapor formation occurs on the inner interface water droplet - solid inclusion with the subsequent explosive decay of the droplet. Experiments have been conducted using high- speed (up to 10 5 fps) video cameras and software Phantom Camera Control. The conditions of the explosive vapor formation of the heterogeneous droplet were found. The typical phase change mechanisms of the heterogeneous droplet under the conditions of intensive heat exchange were determined.

Light and electron microscopic studies on the pigmented epithelium and photoreceptors of the retina of common buzzard (Buteo buteo)

The current study is essentially carried out to reveal the histological and ultra-structural details of the retinal pigmented epithelium (RPE) and photoreceptors cell layers of a common buzzard (Buteo buteo). The recorded results revealed that the neural retina of common buzzard consisted of seven distinct cell layers. The inner nuclear layer was markedly revealed as the thickest one among these layers. A highly melanized RPE was recorded in between the choroid and neural retina. Histologically, the RPE was represented by a single layer of cuboidal epithelial cells with centrally located nucleus. Ultrastructurally, the RPE cells showed numerous melanosomes, mitochondria, phagosomes, myeloid bodies, smooth endoplasmic reticulum (SER), but very rare rough endoplasmic reticulum (RER). The photoreceptor cell layer was represented by three categories of photoreceptor cells: few single rods, numerous single and double cones. Each double cone consisted of a short accessory cone and a long principle cone. The photoreceptor outer segment consisted of bi-membranous discs that are enclosed by outer membrane. Moreover, the inner segment of rods consisted of an ellipsoid and an inner hyperboloid. The hyperboloid was rich with RER, polysomes, Golgi apparatus and autophagic vacuoles. Furthermore, the inner segment of single cone and accessory cone consisted of an ellipsoid, paraboloid and myoid regions, while, the inner segment of principle cone lacked the paraboloid regions. At the proximal end of each inner segment for all types of cones, there was a large heterogeneous oil droplet. The paraboloid region was markedly rich with glycogen granules. The myoid region exhibited the same organelles but with little glycogen granules when compared with hyperboloid.

Numerical Simulation of Rapid Solidification Process for Micrometer Level Solder Ball Used in BGA Packaging

We numerically simulated the containerless rapid solidification for micrometer level solder ball used in BGA packaging, based on prior models for heterogeneous droplet nucleation and non-equilibrium solidification, to predict the solidification microstructure of solder ball. Results of simulations for Sn-5mass%Pb solder ball produced under different conditions are discussed.

Modeling the surface tension of complex, reactive organic–inorganic mixtures

Abstract. Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic–inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2–6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski–Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic–inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

519 不均一な燃料液滴群の蒸発および燃焼挙動(GS-5・6 燃焼)

519 不均一な燃料液滴群の蒸発および燃焼挙動(GS-5・6 燃焼)