Spherical Droplets Research Articles

Boundary Value Problem of Mass and Heat Transfer of an Evaporating Spherical Droplet

Boundary Value Problem of Mass and Heat Transfer of an Evaporating Spherical Droplet

Atomization characteristics of a bluff body-assisted sonic twin-fluid atomizer

This study examines the gas dynamic effect and atomization behaviour of the sonic bluff body-assisted twin-fluid atomizer with three distinct geometry configurations based on cone distances (Lc) as 6.0 mm, 8.0 mm, and 10.0 mm. The atomization characteristics of these atomizers employing a 280 µm annular liquid sheet with a central bluff body (cone) are compared based on a range of air and liquid flow rates. The spray-bluff body impacted secondary atomization was characterized through volume-normalized droplet size distribution (DSD) & cumulative droplet distribution, excentricity plots, Sauter mean diameter (SMD), and relative span factor (Δ). When plotted for a given liquid flow rate, the DSD & cumulative droplet distribution becomes more uniform with the increase in the airflow rate independent of the cone distance (Lc). Excentricity plots exhibited high excentricity droplets at the spray centreline and a large fraction of nearly spherical droplets at off-centre spray locations. SMD and RSF (Δ) showed opposite trends when plotted against the air-to-liquid ratio (ALR) as SMD increases while RSF decreases with radial locations, respectively. When plotted for all radial locations, Sauter mean diameter (D32) and relative span factor (Δ) show a cluster formation. Larger SMD values correspond to lower RSF (Δ) values and vice-versa.

Axisymmetric free-surface flow simulation using the moving surface mesh particle method and application to drop formation

It is difficult to accurately simulate axisymmetric free-surface flows with surface tension and topological changes, such as drop formation through a nozzle. A promising numerical method that can achieve this goal is the moving surface mesh particle method. It incorporates a moving surface mesh to explicitly represent a free-surface boundary, which enables accurate free-surface tracking and surface tension calculation. In the present study, this method is extended to an axisymmetric coordinate system. In the axisymmetric simulation, particles moving in a Lagrangian fashion result in significantly non-uniform particle distributions, leading to numerical instabilities. To circumvent this issue, a new algorithm is developed for determining the particle movement in an ALE fashion by considering a two-dimensional continuity equation. Moreover, in order to deal with the topological change arising from breakup of liquid domain, a simple algorithm employing surface mesh splitting is developed. The proposed method is verified using fundamental test cases such as axisymmetric cavity flow, axisymmetric patch test, spherical droplet oscillation, and hanging droplet. Therein, precise agreements to reference solutions are confirmed. Furthermore, the proposed method is applied to the numerical simulation of dripping faucet. As a result, complex drop formation phenomena are successfully simulated with reasonable computational cost. The numerical results are also shown to agree well with the experimental measurement in the literature, from which the validity of the proposed method is demonstrated.

A QUANTUM FRACTALS THEORY OF THE PIONS CHAOS AND THEIR FUTURISTIC APPLICATIONS WITH GRANULAR SOURCES

Higher-order correlations measured in lead collisions examined the geometrical strength as well as the coherence–chaotic characteristics of the particles creation region. The three- and four-particle quantum correlations can delineate the system of pions at small relative momentum region and observe a significant innovative penchant about the granular sources with various parameters. Such conglomerate of correlation functions and their corresponding genuine correlations are rarely analyzed at higher-order quantum computation via invariant momenta to search the granular structure of pion emanation sources. We evince and examine the pions excretion from a dispersed collection of fluid droplets with coherence snippets that produce quantum interferences to explore the nature of the fluid and the characteristics of the chaos fraction in collisions of heavy nuclei. The cumulant correlations and the normalized correlators with their intercepts contained the existence of amalgamation facet of hadronic particles, and the partons plasma. Specifically, we analyze such hybrid fluid with various correlations functions via droplet numbers to probe the trifle of chaos–coherence fraction of pions condensate by using the source with spherical structure droplets.

Performance evaluation of electro-spark eroded high-volume fraction of Cr-Fe-Ni superalloy

Current research aims to execute a viability study of electro-spark erosion technique to process Inconel 690, a high-volume fraction of Cr-Fe-Ni superalloy (∼32% Cr). The Box-Behnken design of response surface methodology with varying processing conditions is used to execute the experimental trails. Process performance is examined in terms of material removal rate and surface topography. The surface conditions of the processed surface are studied using scanning electron microscopy. The tool wear character and tribological behavior of the processed surface are also scrutinized to check the post-process consequences. The study explores the formation of oxide layers, craters, spherical droplets, and micro-cracks on the surface processed at Ton: 118 mu; Toff: 45 mu; Ip: 130 mu; Sv: 50 V ( parametrical settings for maximum material removal rate), and at Ton: 118 mu; Toff: 30 mu; Ip: 220 mu; Sv: 50 V ( parametrical settings for maximum surface roughness) attributing a deteriorating surface quality. The maximum material removal rate of 9.38 mm3/min and minimum surface roughness of 0.47 μm are achieved. A significant improvement of approximately 20 HV in micro-hardness is detected owing to the formation of a recast layer on the processed surface. Consequently, a noticeable improvement is observed in the wear resistance of the processed surface.

Polymer Crystallization with Configurable Birefringence in Double Emulsion Droplets

Biodegradable semicrystalline polymers are broadly used in microfluidic techniques to create microdroplets for various applications. However, it remains a fundamental challenge to modulate polymer crystallization and optical properties in microdroplets which have complicated spatial geometries. Here we investigate the crystallization of double emulsion droplets formed by poly(1,4-butylene adipate) (PBA), polycaprolactone (PCL), and their blends. Crystallization of these polymers drives the spherical liquid droplets to anisotropic solid microcapsules. Crystal growth shows a linear relationship with time, irrespective of flat-on, edge-on, or continuous twisting lamellar arrangement in the shell. We further reveal that the anisotropic shape and lamellar arrangement impart the crystallized microcapsule with orientation-sensitive birefringence. A representative feature is that all anisotropic microcapsules show two types of Maltese cross, depending on the microcapsule orientation. The PBA shell with flat-on lamellar arrangement always shows positive birefringence, while the PCL shell with edge-on lamellar growth may present negative or positive birefringence at specific orientation angles. Microcapsules of PCL/PBA blends are regulated by the composition of two polymers (fPCL), realizing the transition from PBA-dominated shell to PCL-dominated shell across fPCL = 0.5. We emphasize the peculiarities of crystallization behavior in double emulsion droplets by comparing with crystallization on plane substrate. This work may serve as a fundamental reference for understanding polymer crystallization and further expanding potential applications of semicrystalline polymers for optical microdevices.

3D locating and sizing of volumetric metal droplets with astigmatic dual-beam interferometric particle imaging at panoramic scattering angle

This work goes insight into the feasibility of astigmatic dual-beam interferometric particle imaging (ADIPI) to enable the measurement of three-dimensional (3D) positions and sizes of spherical metal droplets at panoramic scattering angle. The ADIPI signal exists at arbitrary angle except the two laser beam axes, defined as backward scattering region, forward scattering region, and sideward scattering region according to the angle of light scattering. A generalized model for three types of scattering situation is derived and an algorithm based on the ellipse detection and two-dimensional (2D) Fourier transform is applied to locate the centroid of each pattern and extract the spatial frequency and the inclination angle of fringes. Experiments are designed and performed, showing that the results in both of the depth position and size measuring of the same droplets measured from different angles are essentially identical. The average deviation values of the depth positions both are 1% for forward-sideward situation and backward-sideward situation. For backward-forward situation, backward-sideward situation and forward-sideward situation, the average deviation values in size measuring are 6%, 13% and 9%, respectively. The flexibility of ADIPI, breaking the strict requirements for equipment arrangement, can be carried out over a wide range of angles, facilitating its great potential in metal droplet measurement.

Model droplet formation in extensional filament stretching within a Filament Extension Atomizer

Further innovation in the field of selective laser sintering (SLS) is strongly connected to the availability of new materials since the market is dominated by polyamide 12 (>90%). The aim of this publication is to develop a descriptive model for the droplet formation process in a Filament Extension Atomizer to predict the applicability to exploit further polymers for the SLS process. The feasibility was tested, investigated and characterized using a “Dripping out of a nozzle” setup for uniaxial extension. The droplet formation process was then observed via high-speed camera imaging and classified for certain parameters. The experiments were carried out using semi-diluted polyethylene oxide (600–4000 kg/mol), glycerol and water solutions as model fluids. Driven by the Plateau-Rayleigh instability, different types of spherical droplets were observed and various droplet formation mechanisms demonstrated and analyzed. Based on the experimental results, a predictive model is derived to describe various essential parameters.

Kinetics and the crystallographic structure of bismuth during liquefaction and solidification on an insulating substrate

Here we study the kinetics of liquefaction and solidification of thin bismuth films grown on an insulating substrate by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) and investigated by in situ electron and X-ray diffraction. By PLD, we can grow films similar to those obtained using MBE, studied by ex-situ AFM, KPFM, XRR, and XRD. The liquefaction-solidification transition is monitored in real-time by RHEED and synchrotron XRD, observing thereby the dewetting phenomenon and the formation of spherical droplets which size depends on the initial film thickness. Studying this phase transition in more detail, we find abrupt liquefaction and solidification, resulting in formation of the nanodots oriented with the (110) crystallographic plane parallel to the substrate. Furthermore, by analysis of the recorded specular diffraction rods, we propose growth by initial deposition, followed by a transformation into nandots, followed by further deposition. Overall, we demonstrate that controlling the growth scenario for Bi nanostructures, here shown by PLD and MBE, one is able to steer its resulting shape, size and corresponding (materials) properties.

Coacervation in polyzwitterion-polyelectrolyte systems and their potential applications for gastrointestinal drug delivery platforms

Traditionally, complex coacervation is regarded as a process whereby two oppositely charged polyelectrolytes self-assemble into spherical droplets. Here, we introduce the polyzwitterionic complex, “pZC”, formed by the liquid-liquid phase separation of a polyzwitterion and a polyelectrolyte, and elucidate a mechanism by which such complexes can assemble using theory and experimental evidence. This system exhibits orthogonal phase behavior-it remains intact in acidic conditions, but disassembles as the pH increases, a process governed by the acid-base equilibria of the constituent chains. We relate the observed phase behavior to physiological conditions within the gastrointestinal tract with a simulation of the gastroduodenal junction, and demonstrate using video microscopy the viability of polyzwitterionic coacervates as technologies for the pH-triggered release of cargo. Such a system is envisaged to tackle imminent problems of drug transport via the oral route and serve as a packaging solution to increase uptake efficiency.

Viscoelasticity, Tensile Properties, and Microstructure Development in Cyclic Olefin Copolymer/Polyolefin Elastomer Blends

AbstractThe new ethylene/cyclic olefin copolymers (COCs) are a major breakthrough in traditional polyolefins made available by metallocenes, but its high brittleness restricts the applications. Ethylene/1‐octene copolymer (POE) with similar backbones is blended with COCs to compensate the rigidity of cyclic segments. Field emission scanning electron microscope photos and Raman spectra demonstrate the existence of abundant phase interfaces between POE and COC, and the phase structure changes from spherical droplets, of partial continuity to cocontinuity with rising POE components. The phase changes are considered as corresponding to the formation, expansion, and coalescence of droplets at melting state according to Van Gurp curves, Han plot, and Cole–Cole plot. Viscoelastic data show that the storage modulus, loss modulus, and complex viscosity reach a high value at medium POE contents. Furthermore, the tensile strength and fracture energy increases and then decreases, the elongation at break increases and Young's modulus reduces with the increment of POE percentage. Because of the large spherical and ellipsoidal structures and abundant interfaces, the synchronous reinforcement and toughness come true at a medium ratio of POEs. Dynamic mechanical analysis confirms the existence of the interfacial layer, and the interfacial layer becomes more pronounced with the rising POE contents exactly as the morphology and rheological findings.

Structural properties and ring defect formation in discotic liquid crystal nanodroplets

In this work, we performed NpT Monte Carlo simulations of a Gay–Berne discotic liquid crystal confined in a spherical droplet under face-on anchoring and fixed pressure. We find that, in contrast to the unbounded system, a plot of the order parameter as function of temperature does not show a clear evidence of a first-order isotropic-nematic transition. We also find that the impossibility of simultaneously satisfy the uniform director field requirement of a nematic phase with the radial boundary conditions, results in the appearance of a ring disclination line as a stress release mechanism in the interior of the droplet. Under further cooling, a columnar phase appears at the center of the droplet.

Airy theory revisited with the method combining vectorial complex ray model and physical optics.

Airy published his theory in the 1830s to remedy the problem of infinite intensity in the rainbow angles of a spherical droplet predicted by geometrical optics. This theory has been studied by mathematicians and physicists since then from different points of view. In what concerns the scattering diagram around the rainbow angles, Airy theory has been improved by researchers in order to predict correctly the intensity of the supernumerary bows. However, it is known that the positions and the intensities of the supernumerary bows predicted by Airy theory differ from those of rigorous Debye theory with increasing order p and the scattering angles from the rainbow angle. In the present Letter, we will show that this discrepancy is caused by the approximations in Airy theory and can be revised by combining the vectorial complex ray model and physical optics (PO). The former permits us to calculate rigorously the amplitudes and phases of all rays and predicts precisely the scattering pattern except for the main bows. The combination with PO predicts very precisely all the supernumerary bows for both perpendicular and parallel polarization. This method can be applied directly to the light scattering of non-spherical particles with smooth surfaces.

The morphology and the electro-optical properties of PDLCs cured in the presence of electric fields

ABSTRACT Polymer dispersed liquid crystals, PDLCs, are composite materials generally formed by spherical liquid crystal droplets embedded in a polymer matrix. Reports of PDLCs with different droplet shape are not widespread. In this work, epoxy/LC mixtures in different weight ratios were polymerised in the presence of an external AC electric field with increasing strengths. The morphology and the electro-optical properties of the obtained PDLCs were found to be dependent from the strength of the electric field applied during the curing process. Common PDLCs with spherical droplets were obtained from samples polymerised under the action of low strength electric fields, but PDLCs with elongated droplets and memory states were found for polymerisation performed in the presence of intermediate electric fields. For larger electric fields, PDLCs were characterised by a morphology with long cylindrical channels and large memory states.

Nanoemulsified <i>Eucalyptus globulus</i> Essential Oil Against Mosquito <i>Aedes aegypti</i> (L.)

In the present study, nanoemulsified essential oil of Eucalyptus globulus was analysed for its chemical composition and larvicidal activity against mosquito Aedes aegypti. GC-MS analysis revealed presence of total 22 compounds, of which the major ones were 1, 8-cineole (42.16%) and P-cymene (14.81%). Non polar fractions of oil were sonicated by mixing it in water with Tween 20 in different ratios, and 1:2 ratio was found to be the most stable. This was characterized using TEM and found to have spherical droplets of 20-40 nm. Nanoemulsified oil was found to be effective at 70 ppm with LC50 and LC90 of 51.95 and 64.21 ppm, respectively. SEM studies showed significant shrinkage and disruption of various larval body parts post treatment.

Stability of a split-core configuration induced by saddle-splay elasticity in a submicron nematic liquid crystal spherical droplet

ABSTRACT We use Landau–de Gennes theory to investigate the configurations of liquid crystals confined to a submicron spherical droplet subject to weak homeotropic anchoring. The results show that in a one-constant approximation, there are three equilibrium configurations: radial hedgehog, ring disclination and uniform, where the radial hedgehog configuration is a stable state. With increasing elastic anisotropy, which is essentially an increase in the splay elastic constant, the radial hedgehog configuration transforms into a split-core configuration, which is metastable. The split-core configuration becomes the lowest-energy state induced by saddle-splay elasticity within appropriate ranges of the radius and elastic anisotropy.

Theory of director fluctuations about a hedgehog defect in a nematic drop.

We present calculations of eigenmode energies and wave functions of both azimuthal and polar distortions of the nematic director relative to a radial hedgehog trapped in a spherical drop with a smaller concentric spherical droplet at its core. All surfaces interior to the drop have perpendicular (homeotropic) boundary conditions. We also calculate director correlation functions and their relaxation times. Of particular interest is a critical mode whose energy, with fixed Frank constants, vanishes as the ratio μ=R_{2}/R_{1} increases toward a critical value μ_{c}, where R_{2} is the radius of the drop and R_{1} that of the inner droplet, and then becomes negative for μ>μ_{c}. Our calculations form a basis for interpreting experimental measurements of director fluctuations relative to a radial hedgehog state in a spherical drop. We compare results with those obtained by previous investigations, which use a calculational approach different from ours, and with our experimental observations.

Visualization and numerical investigations on heterogeneous nucleation of water vapor on the surface of SiO2, Fe2O3 and CaSO4 particles

Particles composition has an important influence on heterogeneous nucleation of water vapor on the particles surface and subsequent particles abatement by heterogeneous condensation. In this work, three kinds of single-component particles of typical chemical composition of coal-fired fine particles are selected. First, Environmental Scanning Electron Microscopy (ESEM) system is adopted to directly visualize the heterogeneous condensation process of water vapor on the particles surface. It can be found that when water vapor condenses on the particles, spherical cap-shaped embryo droplets occur, which is significantly consistent with the embryo model theory proposed by Fletcher (1958). Then, according to Fletcher’s nucleation theory, a numerical experimental platform is established by MATLAB programming to predict nucleation parameters. The theoretical critical supersaturation and the experimental results are compared at the same time. It is noted that the classical theory of heterogeneous nucleation underestimates particles nucleation ability and predicts a higher critical supersaturation than that experimentally measured. Finally, the growth rate of droplets on three kinds of particles is obtained experimentally. The results show that with the same initial particle size, the final growth size of CaSO4 is larger than that of SiO2 and Fe2O3 particle, and the growth rate of droplets on CaSO4 is also the largest, showing the best growth performance.Copyright © 2022 American Association for Aerosol Research

Anticancer Activity of Nanoemulsions Loading Biomaterial <i>Amomum kravanh</i> Oil against Oral Cancer Cells

Several biomaterial presented anticancer activities including volatile oil. Interestingly, the volatile oil from Amomum kravanh has been reported as anticancer activity. Nevertheless, the utilization in native oil might be barrier to apply its as anticancer agent because of the limitation of their water solubility. One of the solutions to this challenge is to use nanoemulsions as a carrier for delivery A.kravanh oil (AMO) into oral cancer cell. In this research, the phase inversion temperature method was used to prepared nanoemulsions containning AMO. The physical and anticancer property of various nanoemulsions were comparatively evaluated. The 8AMO:2Soybean oil (SBO) illustrated spherical and small oil droplet around 80 nm. It also presented good physical stability after temperature cycling test. Regarding anticancer property, the 8AMO:2SBO can considerably arrest oral cancer cells with dose dependent manner at IC50 of 0.76% v/v, and the nuclear fragmentation that was remarkable feature of apoptosis was also found in 8AMO:2SBO group. This discovery demonstrated that the AMO loaded nanoemulsions system can be consider to alternative choices for oral cancer prevention and treatment.

Kinetic interplay between droplet maturation and coalescence modulates shape of aged protein condensates

Biomolecular condensates formed by the process of liquid–liquid phase separation (LLPS) play diverse roles inside cells, from spatiotemporal compartmentalisation to speeding up chemical reactions. Upon maturation, the liquid-like properties of condensates, which underpin their functions, are gradually lost, eventually giving rise to solid-like states with potential pathological implications. Enhancement of inter-protein interactions is one of the main mechanisms suggested to trigger the formation of solid-like condensates. To gain a molecular-level understanding of how the accumulation of stronger interactions among proteins inside condensates affect the kinetic and thermodynamic properties of biomolecular condensates, and their shapes over time, we develop a tailored coarse-grained model of proteins that transition from establishing weak to stronger inter-protein interactions inside condensates. Our simulations reveal that the fast accumulation of strongly binding proteins during the nucleation and growth stages of condensate formation results in aspherical solid-like condensates. In contrast, when strong inter-protein interactions appear only after the equilibrium condensate has been formed, or when they accumulate slowly over time with respect to the time needed for droplets to fuse and grow, spherical solid-like droplets emerge. By conducting atomistic potential-of-mean-force simulations of NUP-98 peptides—prone to forming inter-protein beta-sheets—we observe that formation of inter-peptide beta-sheets increases the strength of the interactions consistently with the loss of liquid-like condensate properties we observe at the coarse-grained level. Overall, our work aids in elucidating fundamental molecular, kinetic, and thermodynamic mechanisms linking the rate of change in protein interaction strength to condensate shape and maturation during ageing.