Evolution Of Droplets Research Articles

Stable quantum droplets with high-order vorticity in zero-order Bessel lattice

A theoretical framework is presented to investigate the stability of novel two-dimensional quantum droplets within zeroth-order Bessel lattices. The evolution of quantum droplets is studied by the Gross–Pitaevskii equations with Lee–Huang–Yang corrections. The circular groove structure inherent in the zeroth-order Bessel lattice potential facilitates the formation of distinct configurations, including stable zero-vorticity annular quantum droplets and annular quantum droplets featuring embedded vorticity. The stability region of these quantum droplets is achieved through direct numerical simulations. It is found that the lower limit of the stability range for quantum droplets under this optical lattice remains unaffected by vorticity. Conversely, the upper limit exhibits a discernible dependence on vorticity. Subsequently, the study extends to the construction of stable composite states, manifesting as nested concentric multiring structures. Numerical results not only validate the feasibility of nesting vortical quantum droplets under the influence of a zeroth-order Bessel lattice potential but also establish that the vorticity of the smaller droplet within nested vortical quantum droplets does not surpass half of that observed in the larger droplet. Moreover, a comparative analysis highlights the enhanced stability of nested quantum droplets with varying vorticities when contrasted with their counterparts possessing identical vorticities.

Influence of thermal effects on the dynamic behavior of blood droplets on a superhydrophobic surface

The high temperatures generated during the operation of high-frequency surgical electrodes can cause biological tissues (especially blood) to crust and adhere to the electrode surface, seriously affecting the quality and efficiency of the procedure. Currently, an effective anti-adhesion approach is to construct superhydrophobic microstructures on the electrode surface. However, the micro-mechanisms of antiadhesion under the influence of high temperatures are still incomplete. Herein, this study focuses on the dynamic growth and evolution of blood droplets on a superhydrophobic microstructured surface (SMS) under thermal effects above 100 °C. The research demonstrated that as the substrate temperature increases gradually, the internal fluid perturbation of the blood droplets intensifies, and the air layer trapped by the SMS is subjected to thermal expansion. Consequently, the SMS is unable to provide sufficient adhesion for the growth of the blood coagulum, leading to a significant decrease in the stability of its binding to the substrate and thus the formation of self-desorption. Particularly, it was discovered for the first time that the shell wall of the blood coagulum is layered, a phenomenon related to mass transfer in the Marangoni flow within the droplet under thermal effects. These detailed findings facilitate comprehension of the anti-adhesion mechanism of SMSs, thereby providing a theoretical foundation for the optimization of future surgical electrodes.

Estimating Coalescence Time in Disdrometer Drop Size Distributions: A PYSDM Cloud Modeling Approach

Cloud droplet evolution is influenced by microphysical processes such as nucleation, condensation, evaporation, and coalescence, all of which impact precipitation. Models simulating droplet growth help improve rainfall predictions by providing insight into these processes. In this study, we investigate the coalescence time of droplets, using ground truth data from Disdrometer Observations with a size range of 156.5 to 2800.25 µm, applying the Python Super Droplet Model (PySDM) to simulate the evolution of droplet size over time. Focusing on the coalescence process, we analyzed the time-dependent progression of droplet formation. Our results revealed a relationship between coalescence time (CT) and drop size distribution (DSD). Larger droplets were found to coalesce rapidly upon impact, quickly reaching a precipitation-ready state, while smaller droplets experienced more frequent bouncing, requiring more time for coalescence. The mean coalescence time was estimated to be approximately 12,550 sec.

Catalytic Pyrolysis of Plastic Waste using Red Mud and Limestone: Pyrolytic Oil Production and Ignition characteristics

This study investigated the catalytic pyrolysis of polypropylene (PP) and low-density polyethylene (LDPE) using 10 wt.% red mud and 10 wt.% limestone catalysts in a batch reactor. The process was conducted at an operating temperature of 350°C with retention times of 30, 60, and 90 minutes. The effects of adding red mud and limestone catalysts on the yields of liquid, solid, and gas pyrolysis products were analyzed. The pyrolytic oil was further evaluated using droplet evaporation measurements, equipped with a K-type thermocouple and a CCD camera to monitor droplet evolution within an atmospheric chamber. The addition of catalysts enhanced the liquid product yield while reducing the solid yield. The catalytic pyrolysis successfully facilitated the isomerization of plastic polymers, breaking the carbon chains of PP with 10 wt.% red mud. Olefin content increased by up to 7.3% for both 10 wt.% red mud and 10 wt.% limestone. Furthermore, the evaporation rate constant of the catalytic pyrolysis oils improved by up to 8.3%. This study aims to provide new insights into utilizing local waste materials to enhance the quality of pyrolytic plastic products.

Investigation of Influence of High Pressure on the Design of Deep-Water Horizontal Separator and Droplet Evolution

Investigation of Influence of High Pressure on the Design of Deep-Water Horizontal Separator and Droplet Evolution

Numerical analysis of the interaction between a droplet and an air boundary layer

The deformation and movement of droplets are widely utilized in many industrial applications. The present work investigates the evolution of a single droplet interacting with an air boundary layer numerically and validated by wind tunnel experiments. The volume of fluid method is employed to study the interaction from the micro-perspective. The influences of airflow velocity, droplet size, and depression angle on interactions are comprehensively discussed. The outcomes indicate that droplet diameter and airflow velocity significantly influence the interaction. Based on the morphological evolution of the droplets, the regimes of the interaction can be classified into three categories. It is shown that the airflow velocity, depression angle, and droplet diameter influence the droplet maximum streamwise spreading length. Furthermore, only the airflow velocity and droplet diameter influence the maximum height. The scaling law for the maximum streamwise spreading factor is revealed. Finally, the velocity profile of the boundary layer above the droplet maximum height is also analyzed, revealing a power-law relationship in its curve. These results provide valuable insight for further investigation on the droplet–air boundary layer interaction.

Radial Mass Flow Rate Partition on LOx/GCH4 Pintle Injector Configurations

This study focuses on an oxidizer-centered pintle injector engine fueled with gaseous methane (GCH4) and liquid oxygen (LOx), using two rows of discrete radial injectors. The impact of varying the mass flow rate ratio between these two rows of injectors on flame topology, chamber pressure, and combustion efficiency was investigated through a series of three-dimensional reacting unsteady Reynolds-averaged Navier–Stokes simulations relying on an optimized skeletal mechanism and the Eulerian–Lagrangian approach for the evolution of liquid droplets. When most of the oxidizer is injected from the primary injectors, the annular flow reaches and cools the pintle head, thereby negatively affecting the combustion efficiency. Conversely, increasing the mass flow rate of the secondary injectors allows the radial jets to divert the annular flow, enhancing both mixing and combustion efficiency at the cost of significantly elevated temperatures at the pintle tip. When the mass flow rate of the secondary injectors exceeded that of the primary injectors, a distinctive impact on the interaction between the gas, liquid, and reactive processes was observed. Furthermore, pressure oscillations inside the chamber were observed when the blocking effect of the secondary injectors became relevant. These oscillatory phenomena appear to be related to hydrodynamic mechanisms and their interaction with intrinsically oscillatory combustion processes.

Leidenfrost effect in the flash vaporization of hydrogen peroxide and water mixtures

The Leidenfrost effect, a phenomenon where a droplet levitates on a heated surface due to rapid vaporization, has been extensively studied with various liquids. However, the behavior of binary mixtures, specifically those involving hydrogen peroxide (H2O2) and water, remains relatively unexplored. This study investigates such mixtures, focusing on the ejection dynamics of secondary droplets under different temperatures and solution concentrations. High-speed imaging is used to capture the evolution of droplets upon impacting a hot surface. The results reveal a significant increase in droplet fragmentation and ejection with increasing temperature and hydrogen peroxide concentration. Droplet ejection volume increased by a factor of 2.5 when the temperature was 60 °C over the Leidenfrost point, while it increased by a factor of 1.7 when comparing a solution of 10% wt. H2O2 up to a concentration of 50%. A comprehensive analysis of the observed phenomena is proposed. The impact of hydrogen peroxide's thermal decomposition on systems such as H2O2 vapor decontamination enclosures is revealed. The main difficulty in obtaining highly concentrated H2O2 gas is attributed to the Leidenfrost effect ejecting secondary droplets.

Numerical investigation of droplet impacting, spreading and penetration on porous substrates

Numerical investigation of droplet impacting, spreading and penetration on porous substrates

High-Fidelity Sensing Modality for Anomaly Detection in Inkjet Printing

Abstract Inkjet three-dimensional (3D) printing has emerged as a transformative manufacturing technique, finding applications in diverse fields such as biomedical, metal fabrication, and functional materials production. It involves precise deposition of materials onto a moving substrate through a nozzle, achieving submillimeter scale resolution. However, the dynamic nature of droplet deposition introduces uncertainties, challenging consistent quality control. Current process monitoring, relying on image-based techniques, is slow and limited, hindering real-time feedback in erratic droplet ejection. In response to these challenges, we present the zero-dimensional ultrafast sensing (0-DUS) system, a novel, cost-effective, in situ monitoring tool designed to assess the quality of drop-on-demand inkjet printing. The 0-DUS system leverages the sensitivity of the light-beam field interference effect to rapidly and precisely detect and analyze localized droplets. Two core technical advancements drive this innovation: first, the exploration of integral sensing of the computational light-beam field, which allows for efficient extraction of temporal and spatial information about droplet evolution, introducing a novel in situ sensing modality; second, the establishment of a robust mapping mechanism that aligns sensor data with image-based data, facilitating accurate estimation of droplet characteristics. We successfully implemented the 0-DUS system within a commercial inkjet printer and conducted a comparative analysis with ground truth data. Our experimental results demonstrate a detection accuracy exceeding 95%, even at elevated speeds, allowing for an impressive in situ certification throughput of up to 500 Hz. Consequently, our proposed 0-DUS system meets the stringent quality assurance requirements, thereby expanding the potential applications of inkjet printing across a wide spectrum of industrial sectors.

Transient microstructural behavior of methanol/n-heptane droplets under supercritical conditions

Supercritical fluids exist widely in nature and have enduringly attracted scientific and industrial interest. In power systems like liquid rocket engines, fluids undergo the trans-critical process transferred from the subcritical state to the supercritical state, and the phase change process exhibits different features distinguished from subcritical evaporation. In this work, we conducted a series of molecular dynamics studies on the behavior of methanol (MeOH), n-heptane (C7), and binary C7/MeOH droplets under supercritical nitrogen environments. The emphasis is on clarifying the transient characteristics and physical origins of the trans-critical evolution of droplets. During the trans-critical process, droplets are found to experience an unstable period without a spherical shape, where the droplet diameter no longer decreases, violating the traditional d2-law rule. The occurrence of nonspherical droplets is related to the microstructural behavior of trans-critical droplets. Two types of microscopic structures within the droplet are identified: large-scale thermally induced clusters for long-chain C7 and hydrogen-bond connected network-like structures for MeOH, which contains hydroxyl (–OH) groups. Based on these findings, the mechanism behind the evolution of trans-critical droplets is illustrated. Finally, we determine the boundary of ambient conditions in the form of dimensionless expressions Tr−1=a(pr−1)−b, which dictate whether droplets can maintain a spherical shape during the trans-critical process.

Dynamic Behavior of Impacting Droplet on the Edges of Different Wettability Surface.

The dynamic behavior of impacting droplet shearing by the surface edge with different wettabilities is complicated and has great significance for engineering application. The morphological evolution of droplet with various Weber numbers (We) and wettability impacting on the edge of square substrate is investigated by high-speed photography. Moreover, the effects of the contact angle (α) and Weber numbers (We) on the shear breaking process of droplets are obtained. There are three types morphological evolution of impacting droplet are observed experimentally, including unbroken, tensile breakup, and shear breakup. Contact angle and Weber number have been proved to be the significant factors affecting the type of droplet morphological evolution. Meanwhile, the critical Weber number of different types are obtained quantitatively. Moreover, as α increases, the critical Weber numbers for breakup increase. In the shear breakup process, the mass ratio between the droplets remaining on the substrate and the initial droplets is maintained at 50%. Particularly, a reliable prediction model for the spreading of droplet impacting the side wall is proposed and compared with the experimental data. Overall, this study provides new direction and guidance for exploring droplet breakup kinetics.

Liquid crystal droplets formation and stabilization during phase transition process

Abstract The study of phase transition processes in liquid crystals (LCs) remains challenging. Most thermotropic LCs exhibit a narrow temperature range and a rapid phase transition from the isotropic (ISO) to the nematic (N) phase, which make it difficult to capture and manipulate the phase transition process. In this study, we observed the evolution of small droplets during the ISO–N phase transition in ferroelectric nematic (NF) LC RM734. After doping with metal nanoparticles (NPs), the temperature range of the phase transition broadened, and the droplets formed during the phase transition remained stable, with their diameter increasing linearly with temperature. In addition, droplets doped with NPs can be well controlled by an external electric field. This discovery not only aids in understanding the fundamental mechanisms of LC phase transitions but also provides a simple alternative method for preparing droplets, which is potentially valuable for applications in optoelectronic devices and sensors.

Triboelectrically Empowered Biomimetic Heterogeneous Wettability Surface for Efficient Fog Collection.

Biomimetic engineering surfaces featuring heterogeneous wettability are vital for atmospheric water harvesting applications. Existing research predominantly focuses on the coordinated regulation of surface wettability through structural and chemical modifications, often overlooking the prevalent triboelectric charge effect at the liquid-solid interface. In this work, we designed a heterogeneous wettability surface by strategic masking and activated its latent triboelectric charge using triboelectric brushes, thereby enhancing the removal and renewal of surface droplets. By examining the dynamic evolution of droplets, the mechanism of triboelectric enhancement in the water collection efficiency is elucidated. Leveraging this inherent triboelectric charge interaction, fog collection capacity can be augmented by 29% by activating the system for 5 s every 60 s. Consequently, the advancement of triboelectric charge-enhanced fog collection technology holds both theoretical and practical significance for overcoming the limitations of traditional surface wettability regulation.

Dynamic behavior of droplet impacting on superhydrophobic cylinder with different macro-ridge orientations

Dynamic behavior of droplet impacting on superhydrophobic cylinder with different macro-ridge orientations

Polystyrene Particle Size Distribution with the Use of Modified Time Increment Monte Carlo Model

AbstractIn the present study, a dynamic Monte Carlo (MC) model is applied for predicting the dynamic evolution of monomer Droplet Size Distribution (DSD) and polymer Particle Size Distribution (PSD) within the presence of an inventive time step in the MC algorithm for both non‐reactive (liquid–liquid dispersion) and reactive systems. Besides, a combining approach as a second inventive strategy is introduced for implementing the MC simulation with a high number of droplets. An optimization process generated the dimensionless Model Parameters (MPs) and is applied to the MC simulation. The MC algorithm is validated with the experimental data from the literature. The novel time step can predict the dynamic evolution of monomer droplets and polymer particles in the reactive systems and diminish the time of the simulation. The combining approach is an excellent strategy for mixing the same or different number of droplets for decreasing time consumption of MC simulation. Extraordinary findings depicted the model's effectiveness and the validity of the time step and combining strategies.

Characterization Of The Electrothermal Conversion Mechanisms Of A Plasma Actuator For Icing Control

The characterization of a new icing protection system, specifically a dielectric barrier discharge (DBD) plasma actuator, is conducted in this study. The system operates by establishing an AC high voltage between two electrodes arranged on opposite sides of a dielectric material. This setup generates a plasma on the dielectric surface, which in turn induces a significant temperature rise (about 30°C) in both the dielectric surface and the surrounding air. To gain a comprehensive understanding of the electrothermal conversion mechanisms involved in the discharge, a Planar Laser Induced Fluorescence technique is employed. Using a two-colour one-dye ratiometric method (PLIF2c1d), the technique provides measurements of the temperature evolution of an ice droplet deposited on the actuator during its melting process by the discharge. An annular actuator configuration is chosen to minimise the effect of the generated ionic wind and maintain the droplet in the discharge. A pyranine and sucrose solution is identified and temperature calibrated. The calibration process involves depositing a droplet of the solution in a temperature-controlled enclosure capable of reaching temperatures as low as -22°C. Through detailed spectral analysis, two specific detection spectral bands are selected for the imaging applications. These bands enable measurements of the ice temperature with a sensitivity of 7.61%/°C. The effects of laser light scattering by ice and fluorescence reabsorption are also investigated by varying the ice thickness. They are found to have limited influence on the fluorescence emission when the solution in ice form. Finally, the capacity of the technique is evaluated by measuring the ice temperature evolution during the melting induced by a plasma discharge. Droplets are deposited on two dielectric materials, namely PTFE and Sapphire, which possess distinct thermal and dielectric properties. Comparisons under varying plasma discharge power levels provide valuable insights into the optimization of DBD plasma actuators for effective icing protection.

A numerical investigation on the morphology evolution of compound droplets

The volume of fluid-continuum surface force model is used to systematically study the influence of characteristic parameters, internal pressure on the dynamic characteristics, finite deformation mode, and fracture mode of compound droplets in air. The simulation results indicate that the morphology evolution of compound droplets can be divided into two stages: expansion deformation stage and irregular deformation stage. And for the first time, it is proposed that the crushing methods of compound droplets can be divided into two types: overall oscillation and local oscillation. Increasing the internal pressure of the compound droplet will cause severe deformation of the compound droplet, and the time required for the expansion and deformation stage will be reduced. However, the influence of fluid interfacial tension and viscosity on the bottom dynamics of compound droplets is often complex, leading to significant changes in the deformation mode of compound droplets. In addition, the influence of feature parameters We and Ca is further discussed. The research results can provide theoretical guidance for precise control of their arrangement in core–shell driven microfluidic technology.

Experimental investigation of interactions between a water droplet and an airflow boundary layer

The deformation and movement of droplets is widely relevant in many fields of research. The present work experimentally investigates the evolution of a single droplet interacting with an air boundary layer. A series of experiments are carried out using a high-speed photography technique to determine the effects of the airflow velocity, drop height, and droplet size. The morphological characteristics can be classified into three types according to the experiments. The outcomes indicate that both the drop height and the airflow velocity significantly influence the maximum streamwise spreading length, but only the drop height has an impact on the maximum lateral spreading width. The maximum streamwise spreading factor follows a power function relationship with WeRe−0.5. In addition, the crater maximum streamwise and lateral spreading diameters are mainly influenced by the drop height. An energy conversion model is established by considering the effects of the aerodynamic drag force, surface tension, and viscous force. This study provides experimental reference data for the scenario of a droplet interacting with an air boundary layer.

Exploring selection signatures in the divergence and evolution of lipid droplet (LD) associated genes in major oilseed crops

BackgroundOil bodies or lipid droplets (LDs) in the cytosol are the subcellular storage compartments of seeds and the sites of lipid metabolism providing energy to the germinating seeds. Major LD-associated proteins are lipoxygenases, phospholipaseD, oleosins, TAG-lipases, steroleosins, caleosins and SEIPINs; involved in facilitating germination and enhancing peroxidation resulting in off-flavours. However, how natural selection is balancing contradictory processes in lipid-rich seeds remains evasive. The present study was aimed at the prediction of selection signatures among orthologous clades in major oilseeds and the correlation of selection effect with gene expression.ResultsThe LD-associated genes from the major oil-bearing crops were analyzed to predict natural selection signatures in phylogenetically close-knit ortholog clusters to understand adaptive evolution. Positive selection was the major force driving the evolution and diversification of orthologs in a lineage-specific manner. Significant positive selection effects were found in 94 genes particularly in oleosin and TAG-lipases, purifying with excess of non-synonymous substitution in 44 genes while 35 genes were neutral to selection effects. No significant selection impact was noticed in Brassicaceae as against LOX genes of oil palm. A heavy load of deleterious mutations affecting selection signatures was detected in T-lineage oleosins and LOX genes of Arachis hypogaea. The T-lineage oleosin genes were involved in mainly anther, tapetum and anther wall morphogenesis. In Ricinus communis and Sesamum indicum > 85% of PLD genes were under selection whereas selection pressures were low in Brassica juncea and Helianthus annuus. Steroleosin, caleosin and SEIPINs with large roles in lipid droplet organization expressed mostly in seeds and were under considerable positive selection pressures. Expression divergence was evident among paralogs and homeologs with one gene attaining functional superiority compared to the other. The LOX gene Glyma.13g347500 associated with off-flavor was not expressed during germination, rather its paralog Glyma.13g347600 showed expression in Glycine max. PLD-α genes were expressed on all the tissues except the seed,δ genes in seed and meristem while β and γ genes expressed in the leaf.ConclusionsThe genes involved in seed germination and lipid metabolism were under strong positive selection, although species differences were discernable. The present study identifies suitable candidate genes enhancing seed oil content and germination wherein directional selection can become more fruitful.