Fraction Of Droplets Research Articles

Numerical simulations of two-phase flow in open-cell metal foams with application to aero-engine separators

Oil/air separation is a critical process in aero engines since a two-phase flow is created in bearing chambers with closed-loop oil systems. This work describes an application of a two-phase pore-scale modeling method to open-cell metal foams, which are used in secondary oil separation in aero-engine separators. The dispersed oil-phase flow through open-cell foams was studied using a Lagrangian approach: discrete phase model (DPM) and investigated on foam structures of pore densities 10–50 ppi and porosities 75, 85 and 95%. The simulations were performed over flow velocities ranging from 5 m/s to 50 m/s, and for separate uniform droplets of diameters ranging from 0.5 to 15 μm, with the commercial CFD analysis package Ansys Fluent. Results indicated that the fraction of non-captured droplets decreased when the flow velocity rose, and the higher the foam porosity, the higher the number of non-captured oil droplets. The flow velocity had a significant impact on the oil capture for intermediate droplet diameters of 1–3 μm. The fraction of non-captured oil droplets increased as the pore density of the open-cell foam increased at the normalized position of x/dp = 5. Foams with a larger pore size and smaller specific surface area showed an increased oil capture when compared with foams with smaller pore sizes and larger specific surface area. For Stokes numbers below 0.1, the oil capture efficiency was small and remained rather constant independent of the Stokes number. However, for 0.1 < Stokes numbers < 1.0, the oil capture efficiency increased substantially with increasing Stokes numbers. Stokes number values above 1.0 were associated with a high capture efficiency, which remained stable with increasing Stokes numbers.

Unraveling the Athlete’s Paradox—Higher Insulin Sensitivity and Lower PKC? Activation Despite Higher Bioactive Lipids in Endurance-Trained Athletes

High intramyocellular lipid (IMCL) content associates negatively with insulin sensitivity (IS) in insulin resistant, but not in endurance-trained humans. It has been hypothesized that different cellular distribution of bioactive lipids such as diacylglycerols (DAG) and ceramides (CER) could interfere with insulin action and underlie this “athlete’s paradox.” We examined endurance-trained athletes (ATH; n=9) and sedentary individuals (SED; n=12) with comparable total IMCL, as measured by 1H-magnetic resonance spectroscopy, who underwent spiroergometry and hyperinsulinemic-euglycemic clamps to assess maximal oxidative capacity and IS, respectively. In skeletal muscle biopsies, translocation of protein kinase C (PKC) θ and ε were determined by Western blotting and concentrations of DAG and CER were measured using targeted LC-tandem mass spectrometry upon separating fractions of cellular membranes, lipid droplets and cytosol by ultracentrifugation. Maximal oxidative capacity and IS were 46% and 47% higher in ATH than in SED (both p&amp;lt;0.01), respectively. The membrane:cytosol ratio of PKCθ, which reflects PKCθ activity, was 62% lower in ATH consistent with their increased IS (p&amp;lt;0.01), while there was no group difference for PKCε. Total and membrane DAG (40% and 48%, both p&amp;lt;0.01) as well as membrane CER (15%, p&amp;lt;0.05) were higher in ATH while the respective concentrations in lipid droplets and cytosol did not differ. In SED, IS correlated inversely with all stereoselective subspecies of lipid-droplet DAG. On the other hand, cytosolic sn-1,2 (C16:0-C18:2) and sn-1,3 (C18:1-C18:0) DAG correlated positively with IS in ATH. In conclusion, higher IS in endurance-trained ATH can be explained by lower muscle PKCθ activation, which may be due to differences in the stereoselectivity and/or subcompartmentation of cellular DAG between ATH and insulin resistant SED. Disclosure D. Pesta: None. E. Anadol-Schmitz: None. S. Gancheva: None. D.F. Markgraf: None. O.P. Zaharia: None. H. Katsuyama: None. Y. Kupriyanova: None. J. Hwang: None. D. Zhang: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk Inc.. Research Support; Self; Gilead Sciences, Inc. M. Roden: Speaker's Bureau; Self; Boehringer Ingelheim GmbH. Research Support; Self; Boehringer Ingelheim GmbH. Consultant; Self; Poxel SA. Research Support; Self; Danone Nutricia Early Life Nutrition, GlaxoSmithKline plc., Nutricia Advanced Medical Nutrition, Sanofi.

Improving Separation of Oil and Water With a Novel Coalescing Centrifugal Pump

Summary A novel centrifugal pump that increases oil-droplet sizes in produced water has been developed. This paper investigates a concept of pumping-pressure optimization, with respect to downstream separation efficiency, for the new pump. The investigation shows that the coalescing centrifugal pump always increased the separation efficiency of a downstream hydrocyclone. Furthermore, it is shown that the pumping pressure can be adjusted to maximize the improvement. Experimental results demonstrate how pumping conditions that minimize the volume fraction of droplets with a diameter smaller than the cut size of the hydrocyclone maximize the separation efficiency. Finally, it is demonstrated how the concept of pumping-pressure optimization can be implemented in a typical produced-water-treatment plant.

Modification of the surface layers with plasma of a vacuum-arc discharge by controlling the energy of precipitating particles

In this paper we consider one of the most effective ways to improve the performance properties of metals – their treatment by intense flows of metal plasma generated by a vacuum-arc discharge. The change in the thermal regime and the duration of the plasma treatment allows controlling both the thickness of a modified layer and the distribution of implanted ions into its depth. At the first stage of part processing the preliminary cleaning of the surface is carried out using a glow discharge in argon. In the second stage, vacuum-arc plasma sources are used, that provide surface treatment with ions of the sprayed material. To weaken and purify the plasma flow special separation systems were used to ensure the creation of an impassable barrier for the droplet fraction. Modification of the treated surface layer is achieved either due to the high energy of the deposited particles, or due to the implementation of the diffusion processes deep into the substrate. The presence of a modified surface layer allows improving the quality of the working coating that is deposited further.

How supercooled superhydrophobic surfaces affect dynamic behaviors of impacting water droplets?

Water droplet icing on the supercooled surface is ubiquitous and presents gigantic harmfulness on the power transmission lines, aircraft and outdoor equipment. Therefore, a good understanding of droplet impact and freezing process on the supercooled superhydrophobic surface is crucial. In this paper, aluminium sheet was adopted as the substrate to prepare the superhydrophobic (SH) surface. A high-speed camera was applied to explore the dynamic behaviors of a water droplet impacting on the SH surface with various supercooling degrees visually. Moreover, the droplet spreading factor, dimensionless height, characteristics time, rebounding energy and mass fraction of the secondary droplets were adopted to reflect the dynamic behaviors. The results indicate that the dynamic behaviors of a droplet (with an initial temperature of 15 °C, equivalent diameter of 2.94 mm and impacting velocity of 0.99 m·s−1) impacting on the SH surface (160° in static contact angle) with a lower supercooling degree is consisted of three regimes: spreading, retraction and rebounding. Whereas, the retraction and rebounding regime are limited at −17 °C and −24 °C, respectively. Moreover, in the retraction regime, the governing factor of the droplet frozen onset time transforms from the interface heat transfer ability into incubation time at the surface temperature below −34.4 °C. Furthermore, the droplet separating and rebounding are prevented once the remaining energy at the end of the retraction regime is lower than 35% of the droplet initial energy.

Phase change and deposition of inhaled droplets in the human nasal cavity under cyclic inspiratory airflow

In many situations, inhaled droplets experience phase change in the human nasal passages during the breathing cycle. The associated size change of droplets can significantly influence the transport and deposition patterns in the nasal cavity. In this study, the transport, evaporation, and deposition of inhaled droplets under unsteady cyclic breathing conditions were simulated. A computational model of the nasal cavity was developed from magnetic resonance imaging (MRI) scans of the nose of a healthy male and a computational fluid dynamics (CFD) method was used to solve the governing equations of airflow and droplet motion. The Lagrangian trajectory approach was then used to investigate the transport and deposition of droplets. The size change of droplets was simulated using a convection–diffusion controlled model. In order to evaluate the effects of evaporation on transport and deposition of droplets, two inhaled compounds (water and linalool) with different saturation vapor pressures were simulated. The results showed substantial differences between the evaporation behavior of water and linalool droplets. Water droplets, which is more volatile than linalool drops, with the initial diameter ≤ 8 µm completely evaporated while complete evaporation of linalool droplets was observed for the initial diameter < 2 µm. During the time-varying inspiratory airflow, the minimum evaporation rates were observed when the airflow rate was near its maximum value. Comparing the deposition fractions of water droplets in the presence and absence of evaporation showed that droplet evaporation decreases the deposition of droplets by about 10–20% mainly due to the reduced inertial impaction effects. Furthermore, it was shown that a steady airflow simulation does not accurately estimate the deposition and evaporation of droplets in the human nasal cavity.

Experimental investigation on effect of ethanol and di-ethyl ether addition on the spray characteristics of diesel/biodiesel blends under high injection pressure

In this work, a comprehensive experimental investigation on spray characteristics of four blended fuels, including diesel (D100), diesel-biodiesel (DB), diesel-biodiesel- ethanol (DBE), and diesel-biodiesel-diethyl ether (DBDE) has been conducted by using high pressure common rail injection system (up to 200 MPa). The transient spray behavior under various conditions was recorded by high speed photography with scattering light illumination. It is shown that higher injection pressure significantly accelerates the spray tip penetration (STP) evolution due to increased inertia of spray while increase in ambient pressure reduces the STP evolution due to higher gas resistance. With the addition of diethyl ether (DEE) into biodiesel, the STP of blended fuel tends to go down and corresponding projected area increases a lot when compared to DB. By means of particle droplet image analysis (PDIA) optical diagnostic method, spray microscopic parameters such as Sauter Mean Diameter (SMD), droplet diameter distribution probability curve, cumulative volume curve and characteristic diameter have been investigated. Results show that both the injection pressure and ambient pressure have significant influence on the spray microscopic characteristics. In addition, for fixed injection pressure and ambient pressure, when DEE is added into DB blends, the number fraction of smaller droplets increases, though the statistic diameter with peak probability is fixed at a certain value. Furthermore, SMD of the four tested fuels decreases sequentially in the order of DB, D100, DBE, and DBDE, indicating that DEE addition favors the atomization process.

Shrinking of Rapidly Evaporating Water Microdroplets Reveals their Extreme Supercooling.

The fast evaporative cooling of micrometer-sized water droplets in a vacuum offers the appealing possibility to investigate supercooled water-below the melting point but still a liquid-at temperatures far beyond the state of the art. However, it is challenging to obtain a reliable value of the droplet temperature under such extreme experimental conditions. Here, the observation of morphology-dependent resonances in the Raman scattering from a train of perfectly uniform water droplets allows us to measure the variation in droplet size resulting from evaporative mass losses with an absolute precision of better than 0.2%. This finding proves crucial to an unambiguous determination of the droplet temperature. In particular, we find that a fraction of water droplets with an initial diameter of 6379±12 nm remain liquid down to 230.6±0.6 K. Our results question temperature estimates reported recently for larger supercooled water droplets and provide valuable information on the hydrogen-bond network in liquid water in the hard-to-access deeply supercooled regime.

Effect of Channel Geometry and Properties of a Vapor–Gas Mixture on Volume Condensation in a Flow through a Nozzle

A method of direct numerical solution of the kinetic equation for the droplet size distribution function was used for the numerical investigation of volume condensation in a supersonic vapor–gas flow. Distributions of temperature for the gas phase and droplets, degree of supersaturation, pressure, fraction of droplets by weight, the number of droplets per unit mass, and of the nucleation rate along the channel were determined. The influence of nozzle geometry, mixture composition, and temperature dependence of the mixture properties on the investigated process was evaluated. It has been found that the nozzle divergence angle determines the vapor–gas mixture expansion rate: an increase in the divergence angle enhances the temperature decrease rate and the supersaturation degree raise rate. With an increase or decrease in the partial pressure of incondensable gas, the droplet temperature approaches the gas phase temperature or the saturation temperature at the partial gas pressure, respectively. A considerable effect of the temperature dependence of the liquid surface tension and properties on gas phase parameters and the integral characteristics of condensation aerosol was revealed. However, the difference in results obtained with or without considering the temperature dependence of evaporation heat is negligible. The predictions are compared with experimental data of other investigations for two mixtures: a mixture of heavy water vapor with nitrogen (incondensable gas) or n-nonane vapor with nitrogen. The predictions agree quite well qualitatively and quantitatively with the experiment. The comparison of the predictions with numerical results from other publications obtained using the method of moments demonstrates the usefulness of the direct numerical solution method and the method of moments in a wide range of input data.

A Simple Model for the Viscosity of Pickering Emulsions

A new model is proposed for the viscosity of Pickering emulsions at low shear rates. The model takes into consideration the increase in the effective volume fraction of droplets, due to the presence of an interfacial layer of solid nanoparticles at the oil-water interface. The model also considers aggregation of droplets and eventual jamming of Pickering emulsion at high volume fraction of dispersed phase. According to the proposed model, the relative viscosity of a Pickering emulsion at low shear rates is dependent on three factors: contact angle, ratio of bare droplet radius to solid nanoparticle radius, and the volume fraction of bare droplets. For a given radius of nanoparticles, the relative viscosity of a Pickering emulsion increases with the decrease in bare droplet radius. For O/W Pickering emulsions, the relative viscosity decreases with the increase in contact angle. The W/O Pickering emulsion exhibits an opposite behavior in that the relative viscosity increases with the increase in contact angle. The proposed model describes the experimental viscosity data for Pickering emulsions reasonably well.

Dissociation of intramyocellular lipid storage and insulin resistance in trained athletes and type 2 diabetes patients; involvement of perilipin 5?

Intramyocellular lipid storage is negatively associated with insulin sensitivity. However, endurance trained athletes and type 2 diabetes mellitus (T2DM) patients store similar amounts of lipids in their muscle; the so-called athlete's paradox. Compared to T2DM, trained athletes possess higher levels of perilipin 5 (PLIN5), a lipid droplet (LD) coating protein. We examined whether coating LD with PLIN5 affects the pattern of muscle lipid (LD size and number) in relation to the athlete's paradox. Despite differences in PLIN5 protein content, we observed that coating the LD with PLIN5 could not explain the observed differences in LD size and number between athletes and T2DM. PLIN5-coated LDs were positively associated with oxidative capacity but not with insulin sensitivity. We conclude that coating of LDs with PLIN5 cannot causally explain the athlete's paradox. Intramyocellular lipid (IMCL) hampers insulin sensitivity, albeit not in endurance-trained athletes (Trained). Compared to type 2 diabetes mellitus (T2DM) patients, Trained subjects have high levels of perilipin 5 (PLIN5). In the present study, we tested whether the fraction of PLIN5-coated lipid droplets (LDs) is a determinant of skeletal muscle insulin sensitivity and contributes to the athlete's paradox. Muscle biopsies were taken from eight Trained, Lean sedentary, Obese and T2DM subjects. Trained, Obese and T2DM subjects were matched for total IMCL content. Confocal images were analysed for lipid area fraction, LD size and number and PLIN5+ and PLIN5- LDs were measured. A stepwise linear regression was performed to identify factors explaining observed variance in glucose infusion rate (GIR). Trained and T2DM subjects stored IMCL differently; Trained subjects had a higher number of LDs compared to T2DM subjects (0.037±0.004μm-2 vs. 0.023±0.003μm-2 , P=0.024) that were non-significantly smaller (0.27±0.01μm2 vs. 0.32±0.02μm2 , P=0.197, Trained vs. T2DM). Even though total PLIN5 protein content was almost double in Trained vs. T2DM subjects (1.65±0.21AU vs. 0.89±0.09AU, P=0.004), PLIN5 coating did not affect LD number or size significantly. Of the observed variance in GIR, the largest fraction by far (70.2%) was explained by maximal oxygen uptake. Adding PLIN5 protein content or PLIN5+ LDs increased the explained variance in GIR (74.7% and 80.7% for PLIN5 protein content and PLIN5+ LDs, respectively). Thus, the putative relationship between PLIN5 and insulin sensitivity is at best indirect and is apparent only in conjunction with maximal oxygen uptake. Hence, PLIN5 abundance cannot be causally linked to the athlete's paradox.

Seamless Combination of High-Pressure Chip-HPLC and Droplet Microfluidics on an Integrated Microfluidic Glass Chip.

We introduce an approach for the integration of high performance liquid chromatography and droplet microfluidics on a single high-pressure resistant microfluidic glass chip. By coupling these two functionalities, separated analyte bands eluting from the HPLC column are fractionated into numerous droplets in a continuous flowing oil phase. The compartmentalization of the HPLC-eluate in a segmented flow was performed with droplet sizes of approximately 1 nL and with droplet frequencies reaching up to 45 Hz. This approach prevents peak dispersion and facilitates post column processing of chromatographic fractions on chip. A reliable generation of droplets is also possible in reversed phase gradient elution mode as demonstrated by applying a solvent gradient from 20% to 100% acetonitrile. A chip design with an incorporated dosing unit enabled the directed postcolumn addition of reagents to individual droplet fractions. The capability of this dosing function was successfully evidenced by post column addition of a reagent which quenches the fluorescence signal of the analytes. The chip-integration of gradient HPLC, fractionation, detection and post column addition of reagents opens up new avenues to perform multistep chemical processes on a single lab-on-a-chip device.

Study on separation abilities of moisture separators based on droplet collision models

Moisture separators are widely used for eliminating the droplets from the gas–water/steam mixture flows. The volume fraction of droplets is often not small in most separators, so the collision behavior of droplets is crucial in changing their velocity, size and number distributions to affect the separation abilities of these separators. In this paper, the collision models of droplets are established to simulate the droplet-laden flows in the moisture separators. First, a stochastic searching algorithm to find the collision droplet pairs is performed by utilizing the collision kernels and defining the mean free path of a droplet. Second, the criteria to distinguish the different regimes of binary droplet collision are carried out. The regime map drawn by these criteria is highly consistent with that from previous experiments. Third, a set of formulas to predict the velocity, size and number distributions of droplets after bouncing, coalescence, reflexive and stretching separation are proposed based on the conservation law and some empirical relations. Finally, the separation abilities of the cyclone and swirl-vane separators are investigated by simulating the droplet-laden flows coupled with the droplet collision models. As for the cyclone, the simulation separation efficiencies are in good agreement with the experimental data. It is further shown that the separation efficiency curve begins to climb up very quickly in the region with small droplet diameters, and then keep constant as the droplet diameter increasing. As for the swirl-vane separators, the simulated separation efficiencies are little larger than those of the experiment within 5% difference, which is mainly due to the fact that coalescence dominates the collision behaviors from the simulation results. The theoretical and simulation results show that these collision models present a new view to study the flowing behaviors of the droplets in the moisture separators.

Droplet sizing and mixture fraction measurement in liquid-liquid flows with rainbow-angle diffractometry.

The capabilities and resolution of the rainbow technique were extended to estimate the size distribution and composition of droplets in liquid-liquid systems. For these droplets, essentially characterized by a low relative refractive index (m≈1.001-1.20), the first-order rainbow is localized in the near-forward to sideways region. It exhibits an unusually higher contrast in the parallel polarization due to the vicinity of the rainbow and the Brewster angles. A numerical study revealed that a few thousand to ten thousand droplets were necessary to obtain reliable estimations of the first moments of typical droplet size distributions when the diffractometer is operated as an ensemble averaging technique. The importance of the accuracy of the light scattering model and the inverse methods used are also documented. Experimental results performed on free-rising submillimeter to millimeter droplets of various compositions showed that a global resolution of 1% to 5% of their mean diameter and about 1.6×10-4 of the dispersion on their refractive index (i.e., 3% in the mixture fraction of oily droplets in water) could be achieved, which enhances the perspectives on mixing and extraction studies in liquid-liquid systems.

Impact of bacterial ice nucleating particles on weather predicted by a numerical weather prediction model

Bacterial ice-nucleating particles (INP) have the ability to facilitate ice nucleation from super-cooled cloud droplets at temperatures just below the melting point. Bacterial INP have been detected in cloud water, precipitation, and dry air, hence they may have an impact on weather and climate. In modeling studies, the potential impact of bacteria on ice nucleation and precipitation formation on global scale is still uncertain due to their small concentration compared to other types of INP, i.e. dust. Those earlier studies did not account for the yet undetected high concentration of nanoscale fragments of bacterial INP, which may be found free or attached to soil dust in the atmosphere. In this study, we investigate the sensitivity of modeled cloud ice, precipitation and global solar radiation in different weather scenarios to changes in the fraction of cloud droplets containing bacterial INP, regardless of their size. For this purpose, a module that calculates the probability of ice nucleation as a function of ice nucleation rate and bacterial INP fraction was developed and implemented in a numerical weather prediction model. The threshold value for the fraction of cloud droplets containing bacterial INP needed to produce a 1% increase in cloud ice was determined at 10−5 to 10−4. We also found that increasing this fraction causes a perturbation in the forecast, leading to significant differences in cloud ice and smaller differences in convective and total precipitation and in net solar radiation reaching the surface. These effects were most pronounced in local convective events. Our results show that bacterial INP can be considered as a trigger factor for precipitation, but not an enhancement factor.

Pronounced limb and fibre type differences in subcellular lipid droplet content and distribution in elite skiers before and after exhaustive exercise.

Although lipid droplets in skeletal muscle are an important energy source during endurance exercise, our understanding of lipid metabolism in this context remains incomplete. Using transmission electron microscopy, two distinct subcellular pools of lipid droplets can be observed in skeletal muscle - one beneath the sarcolemma and the other between myofibrils. At rest, well-trained leg muscles of cross-country skiers contain 4- to 6-fold more lipid droplets than equally well-trained arm muscles, with a 3-fold higher content in type 1 than in type 2 fibres. During exhaustive exercise, lipid droplets between the myofibrils but not those beneath the sarcolemma are utilised by both type 1 and 2 fibres. These findings provide insight into compartmentalisation of lipid metabolism within skeletal muscle fibres. Although the intramyocellular lipid pool is an important energy store during prolonged exercise, our knowledge concerning its metabolism is still incomplete. Here, quantitative electron microscopy was used to examine subcellular distribution of lipid droplets in type 1 and 2 fibres of the arm and leg muscles before and after 1h of exhaustive exercise. Intermyofibrillar lipid droplets accounted for 85-97% of the total volume fraction, while the subsarcolemmal pool made up 3-15%. Before exercise, the volume fractions of intermyofibrillar and subsarcolemmal lipid droplets were 4- to 6-fold higher in leg than in arm muscles (P<0.001). Furthermore, the volume fraction of intermyofibrillar lipid droplets was 3-fold higher in type 1 than in type 2 fibres (P<0.001), with no fibre type difference in the subsarcolemmal pool. Following exercise, intermyofibrillar lipid droplet volume fraction was 53% lower (P=0.0082) in both fibre types in arm, but not leg muscles. This reduction was positively associated with the corresponding volume fraction prior to exercise (R2 =0.84, P<0.0001). No exercise-induced change in the subsarcolemmal pool could be detected. These findings indicate clear differences in the subcellular distribution of lipid droplets in the type 1 and 2 fibres of well-trained arm and leg muscles, as well as preferential utilisation of the intermyofibrillar pool during prolonged exhaustive exercise. Apparently, the metabolism of lipid droplets within a muscle fibre is compartmentalised.

Measuring the Transition Rates of Coalescence Events during Double Phase Separation in Microgravity.

Phase transition is a ubiquitous phenomenon in nature, science and technology. In general, the phase separation from a homogeneous phase depends on the depth of the temperature quench into the two-phase region. Earth’s gravity masks the details of phase separation phenomena, which is why experiments were performed under weightlessness. Under such conditions, the pure fluid sulphur hexafluoride (SF) near its critical point also benefits from the universality of phase separation behavior and critical slowing down of dynamics. Initially, the fluid was slightly below its critical temperature with the liquid matrix separated from the vapor phase. A 0.2 mK temperature quench further cooled down the fluid and produced a double phase separation with liquid droplets inside the vapor phase and vapor bubbles inside the liquid matrix, respectively. The liquid droplets and the vapor bubbles respective distributions were well fitted by a lognormal function. The evolution of discrete bins of different radii allowed the derivation of the transition rates for coalescence processes. Based on the largest transition rates, two main coalescence mechanisms were identified: (1) asymmetric coalescences between one small droplet of about 20 m and a wide range of larger droplets; and (2) symmetric coalescences between droplets of large and similar radii. Both mechanisms lead to a continuous decline of the fraction of small radii droplets and an increase in the fraction of the large radii droplets. Similar coalescence mechanisms were observed for vapor bubbles. However, the mean radii of liquid droplets exhibits a evolution, whereas the mean radii of the vapor bubbles exhibit a evolution.

Microfluidic Generation of High-Viscosity Droplets by Surface-Controlled Breakup of Segment Flow.

Fluids containing high concentration polymers, sols, nanoparticles, etc., usually have high viscosities, and high-viscosity fluids are difficult to be encapsulated into uniform droplets. Here we report a surface-controlled breakup method to generate droplets directly from various aqueous and nonaqueous fluids with viscosities of 1.0 to 11.9 Pa s and a dispersed-to-continuous viscosity ratio up to 1000, whereas the volume fraction of droplets up to 50% can be achieved. It provides a straightforward method to encapsulate high viscosity fluids, in a well-controlled manner in the rapid developing droplet-based applications, including materials synthesis, drug delivery, cell assay, bioengineering, etc.

On the upward flux of sea‐spray spume droplets in high‐wind conditions

AbstractIt has been speculated that the spume droplets torn off from ocean waves in high wind speeds (larger than about 9 m s−1) enhance air‐sea fluxes. However, the vertical transport of spume droplets in the high‐wind atmospheric boundary layer (ABL) is little researched and lacks the support of numerical simulations. Based on observational data and the characteristics of high‐wind ABL above the ocean, the vertical transport of spume droplets is studied and simulated. It is revealed that the existence of gusty wind with coherent structure during high winds is favorable for the vertical transport of the large‐size droplets. The trajectories of 1000 spume droplets with different sizes under different wind speeds in the range 10–35 m s−1 are calculated, and the uplifting fraction of spume droplets that can reach the 100 m height in the ABL is parameterized by using a nondimensional factor U102/(r80g), where U10 is the wind speed at 10 m height, r80 the equilibrium radius of droplet at an equivalent 80% relative humidity, and g the gravitational acceleration. Then, the upward flux of large‐size spume droplets and the mass concentration at 100 m height are evaluated. These numerical results are comparable to some observational data and show that the large‐size spume droplets can be entrained into the ABL during high winds and then contribute to the air‐sea mass fluxes.

Pattern Evolution during Double Liquid-Vapor Phase Transitions under Weightlessness.

Phase transition in fluids is ubiquitous in nature and has important applications in areas such as the food industry for volatile oils’ extraction or in nuclear plants for heat transfer. Fundamentals are hampered by gravity effects on Earth. We used direct imaging to record snapshots of phase separation that takes place in sulfur hexafluoride, SF6, under weightlessness conditions on the International Space Station (ISS). The system was already at liquid-vapor equilibrium slightly below the critical temperature and further cooled down by a 0.2-mK temperature quench that produced a new phase separation. Both full view and microscopic views of the direct observation cell were analyzed to determine the evolution of the radii distributions. We found that radii distributions could be well approximated by a lognormal function. The fraction of small radii droplets declined while the fraction of large radii droplets increased over time. Phase separation at the center of the sample cell was visualized using a 12× microscope objective, which corresponds to a depth of focus of about 5 m. We found that the mean radii of liquid droplets exhibit a evolution, in agreement with growth driven by Brownian coalescence. It was also found that the mean radii of the vapor bubbles inside the liquid majority phase exhibit a evolution, which suggest a possible directional motion of vapor bubbles due to the influence of weak remaining gravitational field and/or a composition Marangoni force.