Droplets

This work explores the methodology for micron-scale water droplet contact angle derivation for the warty surface of octocoral sclerites. The calcite-made sclerites of the Red Sea octocoral Dendronephthya hemprichi have been chosen as a model for this study. Water droplet condensation on the sclerites has been in-situ investigated using Quanta 200 FEG (field emission gun) ESEM (environmental scanning electron microscope) under wet environmental conditions. Two different analysis methods of droplet top and side views have been applied to determine the contact angle based on the secondary electron images. The ESEM image analysis for the sclerites indicates that their surface is hydrophilic. The microscopic contact angle is measured to be 45.3 ± 6.3. The macroscopic contact angle has been calculated by using the Wenzel model for the surface texturing of the sclerites.

h i g h l i g h t s Multi-dimensional, quasi-discrete model for gasoline fuel droplets. An analysis of the time evolutions of the droplet surface temperatures and radii. Effects of the approximation of gasoline fuel on droplet heating and evaporation.

Understanding the upward motion of CO 2 droplets or CH 4 bubbles in oceanic waters is prerequisite to predict the vertical distribution of the two most important greenhouse gases in the water column after these have been released from the seabed. One of the key parameters governing the fate of droplets or bubbles dissolving into the surrounding seawater as they rise, is the terminal velocity, u T. The latter is strongly influenced by the ability of both compounds to form skins of gas hydrate, if pressure and temperature satisfy thermodynamic framework conditions. Experimental efforts aiming to elucidate the rise properties of CO 2 droplets and CH 4 bubbles and specifically the influence of hydrate skins open the possibility to obtain a parameterization of u T applicable to both hydrate-coated and pure fluid particles of CH 4 and CO 2. With the present study, we report on experimentally determined terminal velocities of single CH 4 bubbles released to pressurized and temperature-regulated seawater. Hydrate skins were identified by high bubble sphericities and changed motion characteristics. Based on these experiments as well as published data on the rise of hydrate-coated and pure liquid CO 2 droplets and physical principles previously successfully used for clean bubbles near atmospheric pressures, a new parameterization of u T is proposed. Model predictions show a good agreement with the data base established from the laboratory-based measurements.

The goal of the present research is to contribute to improve the knowledge about the spray impingement topic through a numerical study that is aimed at investigating the impact of using the dissipative energy terms that are available in the literature when they are embedded into a specific dispersion model. Comparing all the numerical approaches, a non-negligible disagreement is observed between the relationship proposed in the original model and the other ones drawn from the literature. This fact evidences the influence of the energy dissipated term on the secondary atomization outcome. The present work also provides a comprehensive study on the estimation of the energy dissipated during the splash event. This is a major contribution to the permanent literature since the few works found only addressed the spread regime. In addition, this paper gives an in-depth analysis on the influence that an enhanced treatment of the boundary layer in the region close to the wall may have in the simulation of such flows. The work revealed that this near-wall droplets tracking method provides an alternative way to increase the accuracy of the dispersed phase and achieve more consistent results without the necessity of a direct mesh refinement.

Drop size distributions (DSDs) were continuously and simultaneously measured by laser raindrop-sizing instruments (LD gauges) in an open site and in three forest stands consisting of Japanese cypress (CY: Chamaecyparis obtusa), Japanese cedar (CD: Cryptomeria japonica), and sawtooth oak (SO: Quercus acutissima), during three rainfall events in Tokyo, Japan. Drop data during the whole observation period were used in an hourly based data set and divided into three meteorological condition groups: calm, heavy rain, and strong wind. Evaluating the influence of canopy species and meteorological factors on the D 50 and DSD difference revealed some throughfall DSD characteristics. First, throughfall had different DSDs among canopy species under conditions of little canopy vibration with low rainfall intensity and wind speed; D 50 values were 2.00, 2.93, and 3.60 mm in CY, CD, and SO, respectively. Second, throughfall contained smaller drops under conditions of severe canopy vibration, with high rainfall intensity and/or high wind speed, than under calm meteorological conditions. Vibration of the canopy could reduce water coalescence and increase spattered rainwater from canopies. Third, the influence of meteorological factors was different between canopy species; SO was readily influenced but CY was not. Moreover, results from this study implied that throughfall consisted of three drop components -free throughfall, drips, and splash droplets -and suggested a process for generating throughfall DSD that could explain the variations in throughfall DSDs between canopy species and that influenced by meteorological factors.

A detailed comparative analysis of transport and thermodynamic properties of biodiesel fuels and components of these fuels is presented. Five types of biodiesel fuels are considered: Palm Methyl Ester, produced from palm oil; Hemp Methyl Esters, produced from hemp oil in the Ukraine and European Union; Rapeseed oil Methyl Ester, produced from rapeseed oil in the Ukraine; and Soybean oil Methyl Ester, produced from soybean oil. Up to 16 components (methyl esters in most cases) of these fuels are considered. The results are applied to the analysis of biodiesel fuel droplet heating and evaporation in conditions relevant to internal combustion engines, using the model described elsewhere.

Recently developed approaches to droplet and spray modeling in computational fluid dynamics (CFD) codes are reviewed. It is emphasized that the modeling of spray primary break-up needs to take into account the transient nature of sprays, while the modeling of droplet heating and evaporation needs to take into account a number of factors, including recirculation and finite thermal conductivity of liquid, semi-transparency of droplets and the kinetic effects. This modeling needs to take place in realistic three-dimensional enclosures, which makes it essential to find a compromise between the accuracy of the models and their CPU efficiency. Evaporation 6 S. SAZHIN Periodica 4, 2009, 1 droplet break-up, heating and evaporation in engineering computational fluid dynamics (CFD) codes. Some of the new models have been implemented into the customized version of the KIVA 2 computational fluid dynamics (CFD) code. The implementation of these models into other CFD codes seems to be a straightforward task.

We discuss the stability of bubbles to coalescence when undergoing a pressure drop and their stability to disproportionation under quiescent conditions, studied using previously established 'single bubble layer experimental' techniques, focussing on the effects on stability of the inclusion of a low volume fraction (0.25%) of stable oil droplets. Detailed measurements of the surface dilatational elasticity (3 s ) and surface shear viscosity (h s ) of systems in the presence and absence of oil droplets have been performed. The surface rheology and stability have been measured as a function of adsorption time and pH, between pH 4.5 and 7, by including glucono-d-lactone (GDL) as an acidification agent. Commercial sodium caseinate (SC) and purified b-lactoglobulin (b-L) were used at 1 wt% bulk concentration as bubble stabilizing agents. The emulsion oil droplet phase was n-tetradecane (TD) or 1-bromohexadecane (BHD), with a mean droplet size of (d 43 ) ¼ 0.59 and 0.67 mm, respectively. The emulsion droplets were completely stable to coalescence and did not enter or spread at the air-water (A-W) interface. With SC at all pH values the values of h s were markedly higher in the presence of TD droplets than in their absence, but particularly when the pH was lowered to pH 5.5 such that the SC started to aggregate. The increase in h s correlated with the increase in coalescence stability under the same conditions. With neutrally buoyant BHD droplets the increase in h s was not as great, but h s was still significantly higher than in the absence of droplets, indicating that the rise to, and packing of, TD droplets at the A-W interface due to gravity was not solely responsible for their observed effects. The values of 3 s did not increase much at all for either b-L or SC as the pH was lowered and/or TD droplets were added, except at very low pH values, when the effects with SC were obscured by the tendency for the bulk SC to gel. In agreement with the relatively insignificant changes in 3 s as the pH was lowered or droplets were added, the resistance to disproportionation of bubbles did not change very much either.

Based on the fact that water can be collected from fog under favorable topographical and atmospheric conditions. The small water droplets present in the fog precipitate when they come in contact with solid objects. The frequent fogs that occur in the southwestern region of Kingdom of Saudi Arabia have the potential to provide an alternative source of freshwater in this otherwise dry region if harvested through the use of simple and low-cost collection systems known as fog collectors. A fog collection project has been carried out in Asir region of Saudi Arabia. Three Standard Fog Collectors (SFC) were designed and manufactured with locally available materials and imported mesh. These SFCs were installed in April 2006. Three different sites were chosen based on topography and altitude and data from April 2006 to April 2007 were obtained. Measurements with the SFCs were made for regions with 2,260 to 3,200 m elevation. The results indicate that at highest altitudes (at Alsooda), it is feasible to obtain an average water production of 6.215 L/m 2 day over the studied period, and in the lower altitudes, which are in Abha city, it is possible to collect more than 3.3 L/m 2 day. The highest water collection was 24 L/m 2 day and recorded in Dec. 20, 2006 at Al-Sahab park station, and furthermore for the same site, the best average water production of 11.5 L/m 2 day was obtained in winter 3 months period namely (December, November and January). Data about the weather conditions has been collected for the studied region. An analysis of fog collection effectiveness was carried out and compared with international standards. The obtained results indicate that fog can be a useful source of water supply in the southwest region of Saudi Arabia.

Nanoparticles have been a research focus for more than two decades. The advent of microfluidic technology provides alternative strategies for the synthesis of nanoparticles in reactors having a micrometer length scale. The integration of nanoparticle and microreactor technologies delivers enormous opportunity and impetus for the further development of novel materials and reactors. In this article, recent achievements in the synthesis of nanoparticles in microfluidic reactors are reviewed. A variety of strategies for synthesizing nanoparticles are presented and compared, including continuous flow, gas-liquid segmented flow and droplet-based microreactors. Different categories of nanoparticles manufactured in microreactors are summarized to highlight the wide application of microfluidic systems in the development of novel nanomaterials. The control of nanoparticle synthesis is also briefly discussed.

We report the results of a comparative study of microfluidic emulsification of liquids with different viscosities. Depending on the properties of the fluids and their rates of flow, emulsification occurred in the dripping and jetting regimes. We studied the characteristic features and typical dependence of the size and of the size distribution of droplets in each regime. For each liquid, we identified a range of hydrodynamic conditions promoting generation of highly monodisperse droplets. Viscosity played an important role in emulsification: highly viscous liquids were emulsified into larger droplets with lower polydispersity. Although it was not possible to provide a unified scaling for the volumes of the droplets, our results suggest that the break-up dynamics of the lower viscosity fluids resembles the rate-of-flow-controlled break-up, as reported earlier for the formation of bubbles in flow-focusing geometries [Garstecki P, Stone HA, Whitesides GM (2005) Phys Rev Lett 94:164501]. The results of this study can be helpful for a rationalized selection of liquids for the controlled formation of droplets with a predetermined size and with a narrow distribution of sizes.

This study deals with the diagenetic evolution of dolostones of the Romaine Formation, from cores and outcrops on Anticosti and Mingan islands, and reports evidence for hydrocarbon migration in secondary porosity generated by high temperature / hydrothermal alteration. Four types of calcite (grouped into early (C1) and late (C2) assemblages) and six types of dolomite (grouped into 3 different (D1, D2 and D3) assemblages) are distinguished. According to fluid-inclusion and stable C-O isotope data, the early calcite group, which consists of sedimentary micrite, replacement microspar and early pore-filling calcite records near surface diagenetic environments. Early and pervasive replacement dolomites (RD1 and RD2 in the first dolomite (D1) assemblage) were formed during early burial, and are not related to porosity generation. Later replacement dolomites (RD3 and RD4 in the second dolomite (D2) assemblage) and pore-filling dolomite cements (PD1 and PD2 in the third dolomite (D3) assemblage) as well as minor sphalerite were formed from warm, saline fluids, which were likely hydrothermal in origin. Vuggy porosity was produced through brecciation and fracturing, and through some dissolution of the D1 dolomite assemblage by these hydrothermal fluids. Intercrystalline porosity was also created during formation of the D2 dolomite assemblage. The vugs were partly occluded by late-stage pore filling dolomite and calcite cements, pyrite and barite. Bitumen droplets in vugs together with hydrocarbon inclusions recorded in C2 calcite and in contemporaneous barite indicate a hydrocarbon migration event after the porositygenerating processes.

Applicability of two kinds of computational-fluid-dynamics method adopting Cahn-Hilliard (CH) and Allen-Cahn (AC)-type diffuse-interface advection equations based on a phase-field model (PFM) is examined to simulation of motions of microscopic incompressible two-phase fluid on solid surface. A capillarity-driven gas-liquid motion in rectangular channel is simulated by use of a PFM method for solving Navier-Stokes (NS) equations and a CH equation, whereas an immiscible liquid-liquid flow in a microchannel with T-junction and square cross section is simulated by use of another PFM method proposed in this study, which adopts a lattice-Boltzmann method based on fictitious particles kinematics as numerical scheme for solving NS equations and an AC equation that is modified to improve volume-of-fluid conservation. The major findings are as follows: (1) effect of capillary force on the dynamic two-phase fluid system with a high density ratio is well predicted for cross-sectional aspect ratio of the channel = 1 and 2; (2) mono-dispersed slug flow pattern transition is reproduced in good agreement with experimental observations in terms of variation in length and interval of droplets as increasing their volumetric flow rates at a constant flow rate ratio = 1. These results prove that the PFM methods can be used for analyzing two-phase fluid motions in various microfluidic devices and micro fabrication processes.

There are many processes in nature and technology in which the time needed for fluid fragmentation or coalescence is comparable to the characteristic time of the investigated macroscopic physical phenomenon. Thus methods and models are needed to generalize laboratory observations, in order to adequately model fragmentation and coalescence dynamics and their influence on system behavior of flows.

The one-step synthesis of barium titanate (BaTiO 3 ) nanoparticles was studied by employing a low-pressure spray pyrolysis (LPSP) method. The effects of temperature, pressure, and the addition of urea to the precursor were investigated experimentally. The results were compared with the experimental data of the conventional (atmospheric) spray pyrolysis method. It was shown that the BaTiO 3 nanoparticles could be synthesized by the low-pressure method, while only spherical hollow particles with smooth surfaces could be produced by the conventional spray method. The addition of urea greatly improved the crystal growth and particle breakup due to extra heat supplied during the combustion reaction coupled with the evolution of gases. The dispersity of nanoparticles increased with the quantity of urea and with a decrease in pressure. The possible mechanism of the formation of BaTiO 3 nanoparticles in the LPSP process was also proposed.

The later part of year 2019 saw a potential threat to humans in the form of covid-19 viruses. The worry regarding this covid-19 viruses is that it spreads so fast among humans. Spreading of this type of viruses must be detected and controlled. At present there is no medicine or treatment for this disease. It is considered as a global pandemic disease. Symptoms for this disease are mild fever, shortness of breath, and continuous dry cough. Also a person affected with this will have severe body pain. Lot of methods is involved in detecting the virus. In this paper the author explains few methods of detecting the viruses.

1] In this paper we report on a laboratory study, the Spray Production and Dynamics Experiment (SPANDEX), conducted at the University of New South Wales Water Research Laboratory in Australia. The goals of SPANDEX were to illuminate physical aspects of spume droplet production and dispersion; verify theoretical simplifications used to estimate the source function from ambient droplet concentration measurements; and examine the relationship between the implied source strength and forcing parameters such as wind speed, surface turbulent stress, and wave properties. Observations of droplet profiles give reasonable confirmation of the basic power law profile relationship that is commonly used to relate droplet concentrations to the surface source strength. This essentially confirms that, even in a wind tunnel, there is a near balance between droplet production and removal by gravitational settling. The observations also indicate considerable droplet mass may be present for sizes larger than 1.5 mm diameter. Phase Doppler Anemometry observations revealed significant mean horizontal and vertical slip velocities that were larger closer to the surface. The magnitude seems too large to be an acceleration time scale effect. Scaling of the droplet production surface source strength proved to be difficult. The wind speed forcing varied only 23% and the stress increased a factor of 2.2. Yet, the source strength increased by about a factor of 7. We related this to an estimate of surface wave energy flux through calculations of the standard deviation of small-scale water surface disturbance, a wave-stress parameterization, and numerical wave model simulations. This energy index only increased by a factor of 2.3 with the wind forcing. Nonetheless, a graph of spray mass surface flux versus surface disturbance energy is quasi-linear with a substantial threshold.

Modelling the atomization process in fire sprinklers has remained a challenge mainly due to the complexity of sprinkler geometry. A review of existing fire sprinkler spray modelling approaches, including film flow and sheet tracking models, showed that they mainly assumed a constant sheet velocity and linear attenuation of the sheet thickness before its disintegration. In the present study, a liquid sheet trajectory sub-model based on the solution of stream-wise conservation equations has been used to predict both sheet thickness and velocity as it radially expands. This will also help to investigate the extent to which a change in the release angle can affect the sheet characteristics. The analysis carried out shows that the proposed approach improves the predictions of mean droplet diameter and initial droplet speed. A semi-empirical approach is further introduced in the study by using experimental volume fraction measurements to characterize sprinkler sprays in the near field. For a given direction predictions have been conducted for droplet volume median diameter, water volume flux and droplet average velocity at different elevation and azimuthal locations. A reasonably good agreement is found for the near field measurements.

The recirculation of ink in an inkjet printhead system keeps the ink temperature and viscosity constant, and leads to the development of a high-performance device. Herein, we propose a recirculating piezo-driven micro-electro-mechanical system (MEMS)-based inkjet printhead that has a pressure chamber, a nozzle, and double restrictors. The design and characteristic analysis are performed using a two-port lumped element model (LEM) to investigate the effect of design parameters on the system responses. Using LEM, the jetting pressure at the pressure chamber, velocity at the nozzle inlet, meniscus pressure, and Helmholtz resonance frequency are predicted and the comparative analysis of the jetting pressure and velocity between LEM and the finite element method (FEM) simulation is conducted to validate our proposed LEM method. Furthermore, the effect of a change in major design parameters on the jetting pressure, velocity, and Helmholtz resonance frequency is analyzed. On the basis of this analysis, the optimized device dimensions are finalized. From our analysis, it is also concluded that the restrictor is more sensitive than the pressure chamber in terms of their variations in depth. As the cross-talk effect can occur due to an array of hundreds or thousands of nozzles, we investigated the effect of a single activated nozzle on the non-activated neighboring nozzles, as well as the effect of multi-activated nozzles on a single central nozzle using our proposed LEM.

Spray flow calculations are usually based upon equations that have been developed by averaging droplet properties locally throughout the flow field. Presently, standard procedure for LES (large-eddy simulations) is to average these averaged equations once again to filter the short-length-scale fluctuations. In this paper, the theoretical foundations for the averaged spray equations are examined; then the volume-averaging process for LES and the volume-averaging process for two-phase flows are unified for the analysis of turbulent, two-phase flows. Comments are provided on the relationship between the averaging volume and the computational-cell volume. This paper provides generality to the weighting-function choice in the averaging process and precision to the definition of the volume over which the averaging is performed. New flux terms that result from the averaging process and appear in the governing averaged partial differential equations are identified and their modelling is discussed. Situations are identified where sufficient stratification of properties on the scale smaller than the averaging volume leads to the significance of these quantities. Evolution equations for averaged entropy and averaged vorticity are developed. The relationship amongst the curl of the average gas-phase velocity, the average of the gas-phase-velocity curl, and the rotation of the discrete droplets or particles is established. The needs and challenges for sub-grid modelling to account for small-vortex/droplet interactions are presented. Applications to spray combustion are discussed.

This review covers experimental results of evaporative lithography and analyzes existing mathematical models of this method. Evaporating droplets and films are used in different fields, such as cooling of heated surfaces of electronic devices, diagnostics in health care, creation of transparent conductive coatings on flexible substrates, and surface patterning. A method called evaporative lithography emerged after the connection between the coffee ring effect taking place in drying colloidal droplets and naturally occurring inhomogeneous vapor flux densities from liquid-vapor interfaces was established. Essential control of the colloidal particle deposit patterns is achieved in this method by producing ambient conditions that induce a nonuniform evaporation profile from the colloidal liquid surface. Evaporative lithography is part of a wider field known as "evaporative-induced self-assembly" (EISA). EISA involves methods based on contact line processes, methods employing particle interaction effects, and evaporative lithography. As a rule, evaporative lithography is a flexible and single-stage process with such advantages as simplicity, low price, and the possibility of application to almost any substrate without pretreatment. Since there is no mechanical impact on the template in evaporative lithography, the template integrity is preserved in the process. The method is also useful for creating materials with localized functions, such as slipperiness and self-healing. For these reasons, evaporative lithography attracts increasing attention and has a number of noticeable achievements at present. We also analyze limitations of the approach and ways of its further development.

An open question in cloud physics is how rain forms in warm cumulus as rapidly as it is sometimes observed. In particular, the growth of cloud droplets across the size gap from 10 to 50 m in radius has not been fully explained. In this paper, the authors investigate the growth of cloud droplets by collisioncoalescence, taking into account both the gravitational mechanism and several enhancements of the collision-coalescence rate due to air turbulence. The kinetic collection equation (KCE) is solved with an accurate bin integral method and a newly developed parameterization of turbulent collection kernel derived from direct numerical simulation of droplet-laden turbulent flows. Three other formulations of the turbulent collection kernel are also considered so as to assess the dependence of the rain initiation time on the nature of the collection kernel. The results are compared to the base case using the Hall hydrodynamicalgravitational collection kernel. Under liquid water content and eddy dissipation rate values typical of small cumulus clouds, it is found that air turbulence has a significant impact on the collection kernel and thus on the time required to form drizzle drops. With the most realistic turbulent kernel, the air turbulence can shorten the time for the formation of drizzle drops by about 40% relative to the base case, applying measures based on either the radar reflectivity or the mass-weighted drop size. A methodology is also developed to unambiguously identify the three phases of droplet growth, namely, the autoconversion phase, the accretion phase, and the larger hydrometeor self-collection phase. The important observation is that even a moderate enhancement of collection kernel by turbulence can have a significant impact on the autoconversion phase of the growth.

A computational fluid dynamics algorithm that uses a volume of fluid method to model immiscible phase behaviour is adapted to simulate the flow of viscoelastic fluids. Two-dimensional Cartesian simulations of a viscoelastic droplet passing through a contraction are compared against experimental results generated using a three-dimensional planar contraction. Viscoelastic effects are simulated using the Oldroyd-B rheological model. The physical and numerical models capture the deformation process well, particularly the characteristic forked tail that develops on the viscoelastic droplet while it is within the contraction. Encapsulation of continuous phase fluid is observed in the experiments, but not predicted by the simulations. We suggest this is due to inadequate mesh refinement at the length scale of a fine thread entrainment process. The numerical results show the existence of an elastic stress within the droplet that could cause the entrainment and subsequent encapsulation. The process has application potential in the manufacture of micron-sized drug and chemical delivery capsules.

In this work the effect of flash boiling on liquid break up and atomization is first reviewed and then described in detail for the sprays produced by two high pressure multistream gasoline direct injectors. They were operated at 120bar and 200bar pressure with a fuel injection duration of 0.8ms into sub-atmospheric pressures between 1 and 0.1bar and four temperatures between 20°C and 100°C. The sprays were injected into an optically accessed chamber whose temperature and pressure were independently controlled to recreate the conditions found in an engine likely to cause flash boiling. Shadowgraph imaging with a single shot CCD camera was applied to obtain images of the spray morphology under a matrix of the above conditions. The interaction between spray streams is particularly complex under flash boiling conditions being a function of the nature of the fuel and the geometry of the injector. In this investigation, three different fuels, regular RON-95 gasoline and single components fuels, n-heptane and iso-octane were used with two different injectors, one with a 60 degree and the other with a 90 degree nominal external cone angle. In total, five variables were investigated: fuel pressure, ambient pressure, ambient temperature, fuel composition and injector geometry. Once processed, the recorded images allowed measurement of spray tip 2 penetration and cone angle. Qualitative data on the change in shape of the spray was also available. The results showed that flash boiling has potential to reduce droplet diameters and improve fuel vaporisation, however, the associated change in spray shape must be taken into account to avoid problems with spray impingement.

This work deals with the modeling and the direct numerical simulation of the absorption of a gas component into a spherical liquid droplet in free fall, where the absorbed component takes part to a chemical reaction. This study is realized by computing the flow fields and the concentration fields simultaneously in the gas and liquid phases. The time evolution of the droplet global mass absorption rate is studied for various regimes characterized by the Reynolds and the Hatta numbers. The monitoring of the time evolution of the concentration fields in the droplet enables the understanding of the interactions between the diffusive and convective mass transports and the chemical reaction. The phenomena controlling the mass transfer rate and how they evolve during the mass absorption process can then be identified. In a first stage, the case of the physical absorption is studied. Moreover, analytical expressions are developed to correlate the time evolution of the Sherwood number with the Reynolds number and the absorption time. In a second stage, the influence of the coupling with a chemical reaction is studied. It is observed that several rate-limiting mechanisms successively control the global absorption rate, enlightening the complex interactions between convective and diffusive mass transport and the chemical reaction.

This paper presents the assessment of the capability of Shan-Chen (SC) Multiphase Lattice Boltzmann Model (LBM) to accurately predict the liquid-gas interface in multiphase flow. Multiphase flow can be found in various applications, as for example, in CO 2 sequestration. One of the challenges for numerical models of such multiphase flows is being able to capture correctly the interface where liquid/gas phase transition happens. In this study, we analyse how parameters such as density ratio and temperature range affect the magnitude of unphysical velocity fields at the interface. The assessment of the model is performed by observing the change in unphysical velocity at the vicinity of the interface under input variations and as the result of domain discretization limits. Several static droplet tests were performed with different conditions of input variables using DL_MESO Lattice Boltzmann Equation (LBE). The SC model is found to present numerical instability for liquid-gas density ratios above 33 and at reduced temperature of below 0.67, and the magnitude of unphysical velocity also increases dramatically. The results of the assessment demonstrate the current limitations of SC LBM when used in the simulation of liquid/gas flows at moderate or low temperatures and high liquid-gas density ratios.

A simplified model is developed, which allows us to perform computer simulations of the particles transport in an evaporating droplet with a contact line pinned to a hydrophilic substrate. The model accounts for advection in the droplet, diffusion and particle attraction by capillary forces. On the basis of the simulations, we analyze the physical mechanisms of forming of individual chains of particles inside the annular sediment. The parameters chosen correspond to the experiments of Park and Moon [Langmuir 22, 3506 (2006)], where an annular deposition and snakelike chains of colloid particles have been identified. The annular sediment is formed by advection and diffusion transport. We find that the close packing of the particles in the sediment is possible if the evaporation time exceeds the characteristic time of diffusion-based ordering. We show that the chains are formed by the end of the evaporation process due to capillary attraction of particles in the region bounded by a fixing radius, where the local droplet height is comparable to the particle size. At the beginning of the evaporation, the annular deposition is shown to expand faster than the fixing radius moves. However, by the end of the process, the fixing radius rapidly outreaches the expanding inner front of the ring. The snakelike chains are formed at this final stage when the fixing radius moves toward the symmetry axis.

The remote marine aerosol and the cloud droplet number concentration (CDNC) are examined with an aerosol microphysics box model in an attempt to better understand the processes involved in the formation and transformation of the marine aerosol. Emission of submicrometre sea-salt and dimethylsulfide (DMS) have been included together with aerosol dynamics, gas and liquid phase chemistry and cloud processing representative for the marine boundary layer atmosphere. Our simulations are able to reproduce a bimodal submicrometre size distribution with realistic number concentrations even when new particle formation by nucleation is neglected. This indicates that ultrafine primary sea-salt flux is an important source of Aitken mode particles and CDNC. However, sulphate still constitutes 20-80% of the Aitken and accumulation mode masses. The temperature dependence of the sea-salt source function leads to a 23% decrease in total number concentration when the temperature increases from 12 to 20 • C. The influence of DMS emission on the aerosol and CDNC is minimal but the size distribution and mass concentration of sulphate is changed, mostly due to in-cloud processes. The wind speed is the dominant factor determining the CDNC, although entrainment of aerosols from free troposphere can have a substantial effect.

Thermocapillary manipulation of a droplet in a planar microchannel with periodic actuations has been demonstrated by both theoretical simulation and experimental characterization. The driving temperature gradients are provided by four micro heaters embedded in the boundaries of the planar channel. The temperature distributions corresponding to the periodic actuations are calculated, and are coupled to the droplet through the surface tensions which drive the droplet. The results show that the droplet will be driven to move along closed loops whose patterns can be designed and controlled by the periodic heating schemes and actuation frequencies. Qualitative agreement between the simulation and experimental observation, in terms of the temperature distributions and droplet moving tracks, has been obtained.

The main results of the aerothermodynamic hypersonic characterization of the intermediate experimental vehicle, by means of both computational fluid dynamics simulations and wind-tunnel measurements, have been reported and analyzed in this work, developed in the frame of ESA Future Launcher Preparatory Program. A test campaign has been carried out at the von Kármán Institute Free Piston Longshot wind tunnel in a cold hypersonic regime. The numerical simulations, rebuilding the von Kármán Institute wind-tunnel conditions, have been performed by the Italian Aerospace Research Center, the goal being to support the procedure of extrapolation-to-flight of the measurements and the general aerothermal characterization. A detailed comparison of all measured and predicted hypersonic relevant phenomena and aerothermodynamic parameters, such as surface pressure and heat flux, is reported in the paper, together with a detailed description of the configuration, freestream conditions, and model attitude effects. The reproducibility of flight conditions in the von Kármán Institute Longshot test campaign is qualitatively very good, both in terms of flow features and surface properties as indicated by wind-tunnel numerical simulations. The comparisons of numerical and experimental results indicate a good agreement in terms of external flow structure, i.e., bow shock, shock layer, expansion at the junction on windward side, shock-wave boundary-layer interaction in the flap area, and multiple-shock interaction above the flap. Sideslip, angle-of-attack, and flapdeflection effects are correctly reproduced by computational fluid dynamics in terms of pressure coefficient and heat flux.

A new phenomenon of turbulent thermal diusion is discussed. This eect is related to the dynamics of small inertial particles in low-Mach-number compressible turbulent¯uid¯ows. Turbulent thermal diusion is caused by the correlation between temperature and velocity¯uctuations of the surroundinḡ uid and leads to relatively strong nondiusive mean¯ux of inertial particles in regions with mean temperature gradients. It is shown that turbulent thermal diusion under certain conditions can cause a large-scale instability of spatial distribution of particles. Particles are concentrated in the vicinity of the minimum (or maximum) of the mean temperature of the surrounding¯uid depending on the ratio of material particle density to that of the surrounding¯uid. At large Reynolds and Peclet numbers the turbulent thermal diusion is much stronger than the molecular thermal diusion. Turbulent thermal diusion can be important in various naturally occurring and industrial multiphase¯ows. In particular, this eect may cause formation of inhomogeneities in spatial distribution of fuel droplets in internal combustion engines. It is conceivable to suggest that the eect of turbulent thermal diusion can play an important role in a process of soot formation in¯ames and in atmospheric dynamics of pollutants, e.g. smog and aerosol clouds formation. #

1] Ice formation in atmospheric clouds is crucial to our understanding of precipitation and cloud radiative properties. In recent work it was shown that heterogeneous ice nucleation rates can be strongly enhanced by a form of surface crystallization . Here we present new laboratory data and consider the implications for contact nucleation and its relevance to ice nucleation in atmospheric clouds. Our observations contradict three leading hypotheses for contact nucleation and suggest, instead, that the notion of contact nucleation should be generalized to include surface crystallization from particles contacting a supercooled drop from the inside out, as well as from the outside in. Our findings lead to the hypothesis that the freezing temperature of an evaporating drop will suddenly become higher once the drop surface contacts an immersed ice nucleus. This mechanism for evaporation freezing is therefore a plausible explanation for the abundant observations of high ice concentrations associated with cloud dilution and droplet evaporation. Citation: Durant, A.

The Marine Stratus/Stratocumulus Experiment (MASE) field campaign was undertaken in July 2005 off the coast of Monterey, California to evaluate aerosol-cloud relationships in the climatically important regime of eastern Pacific marine stratocumulus. Aerosol and cloud properties were measured onboard the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft. One cloud that was clearly impacted by ship emissions as well as the ensemble of clouds observed over the entire mission are analyzed in detail. Results at both the individual and ensemble scales clearly confirm the Twomey effect (first indirect effect of aerosols) and demonstrate drizzle suppression at elevated aerosol number concentration. For the ship track impacted cloud, suppressed drizzle in the track led to a larger cloud liquid water path (LWP) at the same cloud thickness, in accord with the so-called second indirect effect. Ensemble averages over all clouds sampled over the entire 13-flight mission show the opposite effect of aerosol number concentration on LWP, presumably the result of other dynamic influences (e.g., updraft velocity and ambient sounding profile). Individual polluted clouds were found to exhibit a narrower cloud drop spectral width in accord with theoretical prediction (M.-L. Lu and J. H. Seinfeld, Effect of aerosol number concentration on cloud droplet dispersion: A large-eddy simulation study and implications for aerosol indirect forcing, Journal of Geophysical Research, 2006). This field experiment demonstrates both the indirect aerosol effect on ship track perturbed clouds, as well as the subtleties involved in extracting these effects over an ensemble of clouds sampled over a 1-month period.

The pore-scale effects of seismic stimulation on two-phase flow are modeled numerically in random 2D grain0pack geometries. Seismic stimulation aims to enhance oil production by sending seismic waves across a reservoir to liberate immobile patches of oil. For seismic amplitudes above a welldefined ͑analytically expressed͒ dimensionless criterion, the force perturbation associated with the waves indeed can liberate oil trapped on capillary barriers and get it flowing again under the background pressure gradient. Subsequent coalescence of the freed oil droplets acts to enhance oil movement further because longer bubbles overcome capillary barriers more efficiently than shorter bubbles do. Poroelasticity theory defines the effective force that a seismic wave adds to the background fluid-pressure gradient. The lattice-Boltzmann model in two dimensions is used to perform pore-scale numerical simulations. Dimensionless numbers ͑groups of material and force parameters͒ involved in seismic stimulation are defined carefully so that numerical simulations can be applied to field-scale conditions. Using the analytical criteria defined in the paper, there is a significant range of reservoir conditions over which seismic stimulation can be expected to enhance oil production.

Abstract A study of heat transfer and film dynamics caused by single and multiple streams of
impinging droplets using HFE-7100 as the cooling liquid under constant heat flux conditions
is presented. Single and multiple streams of mono-dispersed droplets were produced using
a piezoelectric droplet generator with the ability to adjust parameters such as droplet
impingement frequency, droplet diameter, droplet velocity, and spacing between adjacent
impinging droplet streams.

Micro-and nanotechnology can provide us with many tools for the production, study and detection of colloidal and interfacial systems. In multiphase flow in micro-and nanochannels several immiscible fluids will be separated from each other by flexible fluidic interfaces. The multiphase coexistence and the small-volume confinement provide many attractive characteristics. Multiphase flow in microfluidic systems shows a complicated behavior but has many practical uses compared to a single-phase flow. In this paper, we discuss the methods of controlling multiphase flow to generate either micro-or nano-droplets (or bubbles) or stable stratified interfaces between fluidic phases. Furthermore, applications of the droplets and interfaces in microchannels are summarized.

Most materials of practical interest are neither completely wetting nor completely non-wetting. Through careful design, it is possible to alter the natural wettability of a surface to be more omniphilic or omniphobic. This is principally realized by modifying the physics and/or the chemistry of the surface. In this work, the effects of external uniform magnetic fields on the behavior of the static contact angle of different oil-based ferrofluid droplets were examined for a handful of horizontal surfaces of varying wettability. Experimental results show that the static contact angle of ferrofluid droplets in a magnetic field is not constant around the periphery of the droplet on a horizontal surface, rather it varies in a rich, yet predictable way with the azimuthal angle and magnetic field strength. In addition, the spontaneous motion of two oil-based ferrofluid droplets on a wedge-shaped surface tension gradient was studied for two distinct surface tension gradient orientations in the presence of different external uniform magnetic fields (0-250G). Various wedge angles from 10° to 17° were studied. It was observed that for a given ferrofluid droplet size, larger wedge angles generally produced larger overall surface tension driving forces. As a result, higher droplet velocities were generally achieved in this case, but also shorter overall travel distances. Eventually, for each ferrofluid that was studied, a magnetic field was found above which the droplet was "pinned" on the surface, and droplet movement was stopped despite the underlying presence of the surface tension gradient force.

The current NASA Decadal mission planning effort has identified Venus as a significant scientific target for a surface in-situ sampling mission. The Venus environment represents several extremes including high temperature (460 o C), high pressure (~9 MPa.), and potentially corrosive (condensed sulfuric acid droplets that adhere to surfaces during entry) environments. This technology challenge requires new actuator and sensor designs that can withstand these extreme conditions. In addition a variety of industrial applications could benefit from an extended operating temperature range of actuators and sensors. Piezoelectric materials can potentially operate over a wide temperature range reaching as low as -270 o C to as high as +650 o C. Single crystals, like LiNbO 3 , have a Curie temperature that is higher than +1000 o C. In order to investigate the feasibility of producing actuators/sensors that can operate under these conditions we have initiated a study of the properties of a variety of piezoelectric materials in the temperature range 25 0 C to 500 0 C. These piezoelectric materials were chosen because they are solid state and can be designed as actuators to provide high torque, stroke, and speed. However the feasibility of this critical actuation capability has never been demonstrated under the extreme conditions mentioned above. We will present the results of our measurements on a variety of piezoelectric materials that can be operated at temperatures above 460 o C. The data for small signal resonance analysis (ring, radial and thickness extensional modes) of disk and ring samples made of BST-PT and BMT-PT (TRS Technologies Inc.) and Bismuth Titanate BT (Ferroperm Piezoceramics A/S, Sinoceramics) as a function of the temperature will be presented.

The rates of the reduction of Cr(VI) with S(IV) were measured in deaerated NaCl solution as a function of pH, temperature and ionic strength. The rates of the reaction were found to be first order with respect to Cr(VI) and second order with respect to S(IV), in agreement with previous results obtained at concentrations two order higher than the present study. The reaction also showed a first-order dependence of the rates on the concentration of the proton and a small influence of temperature with an apparent energy of activation DH app of 22.8 F 3.4 kJ/mol. The rates were independent of ionic strength from 0.01 to 1 M. The rate of Cr(VI) reduction is described by the general expression (M. Pettine).

Numerical simulation of flow and heat transfer in two adjacent channels is conducted with one of the channels partially blocked. This system simulates typical channels of a material testing reactor. The blockage is assumed due to the buckling of one of the channel plates inward along its width. The blockage ratio considered in this work is defined as the ratio between the cross-sectional area of the blocked and the unblocked channel. In this work, we consider a blockage ratio of approximately 40%. However, the blockage is different along the width of the channel, ranging from 0% at the end of the channel to 90% in the middle. The channel walls are sandwiching volumetric heat sources that vary spatially as chopped cosine functions. Interesting patterns are highlighted and investigated. The reduction in the flow area of one channel results in the flow redistributing among the two channels according to the changes in their hydraulic conductivities. The results of the numerical simulations show that the maximum wall temperature in the blocked channel is well below the boiling temperature at the operating pressure.

We calculate ion distributions near a planar oil-water interface within non-linear Poisson-Boltzmann theory, taking into account the Born self-energy of the ions in the two media. For unequal self-energies of cations and anions, a spontaneous charge separation is found such that the water and oil phase become oppositely charged, in slabs with a typical thickness of the Debye screening length in the two media. From the analytical solutions, the corresponding interfacial charge density and the contribution to the interfacial tension is derived, together with an estimate for the Yukawa-potential between two spherical water droplets in oil. The parameter regime is explored where the plasma coupling parameter exceeds the crystallization threshold, i.e. where the droplets are expected to form crystalline structures due to a strong Yukawa repulsion, as recently observed experimentally. Extensions of the theory that we discuss briefly include numerical calculations on spherical water droplets in oil, and analytical calculations of the linear PB-equation for a finite oil-water interfacial width.

This study investigates pattern formation during evaporation of water based nanofluid sessile droplets placed on a smooth silicon surface at various temperatures. An infrared thermography technique was employed to observe the temperature distribution along the air-liquid interface of evaporating droplets. In addition, an optical interferometry technique is used to quantify and characterize the deposited patterns. Depending on the substrate temperature, three distinctive deposition patterns are observed; a nearly uniform coverage pattern, a "dual-ring" pattern and multiple rings corresponding to "stick-slip" pattern. At all substrate temperatures, the internal flow within the drop builds a ring-like cluster of the solute on the top region of drying droplets, which is found essential for the formation of the secondary ring deposition onto the substrate for the deposits with the "dual-ring" pattern. The size of the secondary ring is found to be dependent on the substrate temperature. For the deposits with the rather uniform coverage pattern, the ringlike cluster of the solute does not deposit as a distinct secondary ring instead it is deformed by the contact line depinning. In the case of the "stick-slip" pattern, the internal flow behavior is complex and found to be vigorous with rapid circulating flow appears near the edge of the drop.