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Droplet flows, termed misting, are significant lubrication flow mechanisms to, in and around the piston assembly. Therefore, these are important in piston assembly tribology and engine performance. Crankcase lubricant degradation rate has been hypothesised to be influenced by lubricant droplet flows through the piston assembly and crankcase, but not previously confirmed. Lubricant was sampled from the sump, top ring zone (TRZ), and mist and aerosol from the crankcase during an extended run. The physical and chemical degradation of these samples was characterised. Droplet flows were intermediate in degradation and fuel dilution between TRZ and sump. Flows with smaller droplet sizes were more degraded that those with larger droplets. The degradation of polymers was dependent on their molecular architecture. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study focuses on the precise production of droplets in a droplet-based microfluidic device, where monodisperse oil-in-water emulsions with controlled droplet sizes are generated. The primary objective is to achieve uniform emulsions by examining key parameters such as additives in the continuous aqueous phase, internal phase flow rates, and the microfluidic device's geometric characteristics. Initially, the geometric parameters of the microchip for emulsion formation were selected using numerical simulations, and the results were validated through experimental tests of emulsion production with the microchip. The precision of the outcomes is enhanced using an innovative 3D printing method for microchip manufacturing, enabling the creation of identical microdevice copies. In the experimental phase, the optimal conditions for producing uniform droplets were identified by examining the effects of various additives in the external aqueous phase, different internal phase flow rates, and the geometric parameters of the microfluidic device. The results demonstrate that the distance between the two capillaries can control droplet size and frequency, the internal phase flow rate, and the type of additive in the external phase, allowing for emulsions with droplet sizes ranging from 500 to 1000 microns. Specifically, the distance between the capillary tubes significantly affects droplet size, contributing to 30% of the variation when this distance is increased sixfold. Additionally, the study reveals that the increase in droplet diameter due to a higher internal phase flow rate varies with different additives in the external phase. For instance, sodium dodecyl sulfate (SDS) results in a 6.65-fold increase in droplet production frequency with a sixfold increase in the internal phase flow rate. Furthermore, the type of additive in the external phase can independently control droplet size. For example, with a specific internal-to-external phase ratio, oil droplets measure 600.8 μm in an external phase containing SDS, 582.2 μm with polyvinyl alcohol (PVA), and 615.4 μm with Triton X-100. This method can precisely control droplet size and frequency, making it suitable for generating precursor emulsions for engineered micro- and millimeter-sized polymer particles aimed at drug delivery or cell culture applications. The study successfully ensures consistent and uniform emulsions by manipulating these critical parameters through this combined approach of numerical simulations and experimental validation.

This study presents the breakup mechanisms and droplet features of a liquid jet introduced into a low-speed cross air flow. The main aim of this study is to investigate the spray behavior of water when exposed to a uniform crossflow of air at very low velocities. A shadow sizing system is employed to collect comprehensive data for analyzing the interactions between liquid jets and crossflowing air. Three different nozzles were used to examine the distribution, penetration, and breakup characteristics of water jets in an air crossflow. It is worth highlighting that the Weber number in this experiment was maintained at a very low level. Both the jet Weber number (1.3 < Wej < 119) and the gas Weber number (0 < Weg < 1), along with the momentum flux ratio (2 < q < 14400), are crucial dimensionless parameters significantly affecting various droplet properties such as size, velocity, shape, and breakup behavior. This study investigates the structural features, trajectory of the jet, and duration of breakup near the nozzle. Subsequently, the experimental results are tabulated for future numerical and analytical studies. As the air crossflow velocity increases, the liquid jet bends in the direction of the airflow. The breakup length decreases with increasing air velocity. The nozzle with medium diameter shows the maximum dimensionless breakup length. At a constant air velocity, the breakup length initially increases and then decreases with an increasing momentum flux ratio. Higher liquid flow rates result in a higher density of smaller droplets. The liquid jets shift upstream with increasing q values; however, due to the wide range of q values, existing empirical relations in the literature fail to accurately predict this behavior. [ABSTRACT FROM AUTHOR]

We introduce a variant of the Smoluchowski coagulation equation as a kinetic equation with both position and velocity variables, which arises as the scaling limit of a system of second-order microscopic coagulating particles. We focus on the rigorous study of the PDE system in the spatially homogeneous case, proving existence and uniqueness under different initial conditions in suitable weighted spaces, investigating also the regularity of such solutions. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Continuous ceramic membrane emulsification is a promising and scalable technique to prepare water‐in‐heavy oil (W/O) emulsions. The droplet size of W/O emulsions is comprehensively influenced by phase parameters, operational parameters, and membrane parameters, which collectively impact the forces acting on water droplets. In this work, a droplet size prediction model involving multiple factors is established. The forces are analyzed by considering the influence of transmembrane pressure and the viscosity ratio between the dispersed and continuous phases, which are not well considered by current researchers. Additionally, the effects of pore size, crossflow velocity, temperature, and transmembrane pressure were experimentally verified. The experimental results show a high degree of agreement with the predictions. Also, based on the relaxation time difference in oil and water, magnetic resonance imaging was used for the first time to assess the stability of W/O emulsions which was found to be stable for 4 months. [ABSTRACT FROM AUTHOR]

3D printers utilize cutting-edge technologies to create three-dimensional objects and are attractive tools for engineering compact microfluidic platforms with complex architectures for chemical and biochemical analyses. 3D printing's popularity is associated with the freedom of creating intricate designs using inexpensive instrumentation, and these tools can produce miniaturized platforms in minutes, facilitating fabrication scaleup. This work discusses key challenges in producing three-dimensional microfluidic structures using currently available 3D printers, addressing considerations about printer capabilities and software limitations encountered in the design and processing of new architectures. This article further communicates the benefits of using three-dimensional structures, including the ability to scalably produce miniaturized analytical systems and the possibility of combining them with multiple processes, such as mixing, pumping, pre-concentration, and detection. Besides increasing analytical applicability, such three-dimensional architectures are important in the eventual design of commercial devices since they can decrease user interferences and reduce the volume of reagents or samples required, making assays more reliable and rapid. Moreover, this manuscript provides insights into research directions involving 3D-printed microfluidic devices. Finally, this work offers an outlook for future developments to provide and take advantage of 3D microfluidic functionality in 3D printing. [ABSTRACT FROM AUTHOR]

Shear-induced droplet formation is important in many industrial applications, primarily focusing on droplet sizes and pinch-off frequency. We propose a one-dimensional mathematical model that describes the effect of shear forces on the droplet interface evolution. The aim of this paper is to simulate paraffin wax droplets in a co-flowing fluid using the proposed model to estimate the droplet volume rate for different flow velocities. Thus, the study focuses only on the dripping regime. This one-dimensional model has a single parameter that arises from the force balance on the interface. This parameter is related to the shear layer thickness and hence influenced by the change in quantities like velocity, viscosity, and surface tension. The correlation describing the dependence of the parameter on these quantities using non-dimensional numbers is presented. The model is then cross-validated with the previous computational and experimental data. We use PETSc, an open-source solver toolkit, to implement our model using a mixed finite element discretization. We present the simulation results for liquid paraffin wax under fast-moving airflow with a range of velocities. [ABSTRACT FROM AUTHOR]

We study the formation of oil droplets from an initially trapped large oil ganglion under surfactant flooding, using a microfluidic device consisting of a two-dimensional array of regularly spaced square posts. We observe that above a critical capillary number for oil mobilization, breakage of the ganglion results in the formation of either trapped patches spanning multiple pores or numerous mobile droplets that exit the device at a velocity comparable to the average flooding fluid velocity. These mobile droplets, however, are only observed when above a secondary capillary number threshold. The formation of these droplets is found to involve the simultaneous occurrence of three different passive droplet generation mechanisms where a droplet is formed as it is pulled by perpendicular fluid flow, as it is pulled by co-axial fluid flow, and or as it splits due to collision with a post. Our results show that oil breakthroughs only occur when the oil is in the form of mobile droplets, suggesting that droplet formation can be an important condition for the mobility of residual oil in porous media. Additionally, this post-array microfluidic device can be used for the production of monodisperse droplets whose size can be controlled by the spacing of the posts. [ABSTRACT FROM AUTHOR]

Coupled free-flow–porous medium systems are of great importance in various natural and industrial applications. Modeling of such systems is always challenging, especially when droplets form at the interface between the two domains. We propose a new concept to take droplet formation, growth and detachment at the interface into account. In this concept, we use pore-network modeling to describe the porous medium and the Navier–Stokes equations for the free-flow domain. New coupling conditions are developed which include droplet interactions with the free flow and the porous medium. Impacts of using different descriptions of the forces acting on the triple contact line and contact angle hysteresis on the predicted onset of the droplet detachment are examined. In addition, we compare the new approach with another model built using ANSYS Fluent based on the volume of fluid method. The results show that the new model is able to describe the droplet formation, growth and then detachment by the free flow. The proposed model provides a base for further developments to handle formation of multiple droplets at the interface between a free flow and a porous medium as well as to include the evaporation in future works. [ABSTRACT FROM AUTHOR]

To investigate droplet formation in a microchannel with different walls, simulations were conducted based on a pseudopotential model using the exact difference method force scheme. The variable surface tension was obtained using Laplace's law, and the static contact angle was estimated using a first-order linear equation of the corresponding control parameter of the model. The droplet motion in microchannels was simulated using our model, and the effects of surface wettability and the Bond number on the droplet motion were investigated. The droplet motion for the intermediate microchannel wall took a significantly shorter time than that for the hydrophilic wall, and the wet length also depended on the contact angle. As the Bond number increased, the wet length of the droplet decreased on the hydrophilic surface. The droplet formation in a T-junction device was also simulated using the proposed model, and the effects of the capillary number and viscosity ratio on droplet formation were discussed in detail, and some empirical correlations between the capillary number and dimensionless droplet length are presented according to different viscosity ratios. The three flow patterns of droplet formation were categorized by the different capillary numbers as the dripping–squeezing, jetting–shearing, and threading regimes. In the dripping–squeezing regime, the droplet volume was nearly independent of the viscosity ratio, but the viscous effect was more prone to occur in the jetting–shearing regime. In the jetting–shearing regime, as the capillary number increased, the effect of the viscosity ratio on droplet formation became more significant. [ABSTRACT FROM AUTHOR]

Microfluidic technology has advantages in producing high-quality droplets with monodispersity which is promising in chemical engineering, biological medicine and so on. An in-depth study on the underlying mechanism of droplet formation in microfluidics is of great significance, and to understand it, numerical simulation is highly beneficial. This article reviews the substantial numerical methods used to study the fluid dynamics in microfluidic droplet formation, mainly including the continuum methods and mesoscale methods. Moreover, the principles of various methods and their applications in droplets formation in microfluidics have been thoroughly discussed, establishing the guidelines to further promote the numerical research in microfluidic droplet formation. The potential directions of numerical modelling for droplet formation in microfluidics are also given. [ABSTRACT FROM AUTHOR]

The present work reports the influence of wall velocity slip during microfluidic droplet generation in a T-junction. A two-phase numerical model based on the level set technique is used to simulate the thermally excited droplet formation under velocity slip conditions. An experiment is performed to validate the present numerical model. The influence of velocity slip and flow rate ratio of the dispersed and continuous phase on the droplet length has been investigated. The length of the droplet increases with the slip length and the flow rate ratio. With an increase in slip length, the droplet quickly achieves a stable state within a small distance. As the slip length increases, the front interface of the droplet tends to wet the channel wall, whereas the rear interface tries to dewet the channel wall. The leakage flow in the main channel decreases with the increase in slip length. The heat transfer rate between the dispersed phase and the continuous phase decreases with the increase in slip length. [ABSTRACT FROM AUTHOR]

The tribological performance of the piston assembly of an automotive engine is highly influenced by the complex flow mechanisms that supply lubricant to the upper piston rings. As well as affecting friction and wear, the oil consumption and emissions of the engine are strongly influenced by these mechanisms. There is a significant body of work that seeks to model these flows effectively. However, these models are not able to fully describe the flow of lubricant through the piston assembly. Some experimental studies indicate that droplets of lubricant carried in the gas flows through the piston assembly may account for some of this. This work describes an investigation into the nature of lubricant misting in a fired gasoline engine. Previous work in a laboratory simulator showed that the tendency of a lubricant to form mist is dependent on the viscosity of the lubricant and the type and concentration of viscosity modifier. The higher surface area-to-volume ratio of the lubricant if more droplets are formed or if the droplets are smaller is hypothesised to increase the degradation rate of the lubricant. The key work in the investigation was to measure the size distribution of the droplets in the crankcase of a fired gasoline engine. Droplets were extracted from the crankcase and passed through a laser diffraction particle sizer. Three characteristic droplet size ranges were observed: Spray sized (250–1000 μm); Major mist (30–250 μm); and Minor mist (0.1–30 μm). Higher base oil viscosity tended to reduce the proportion of mist-sized droplets. The viscoelasticity contributed by a polymeric viscosity modifier reduced the proportion of mist droplets, especially at high load. [ABSTRACT FROM AUTHOR]

Drop-on-demand (DOD) inkjet printing enables exact dispensing and positioning of single droplets in the picoliter range. In this study, we investigate the long-term reproducibility of droplet formation of piezoelectric inkjet printed drug solutions using solvents with different volatilities. We found inkjet printability of EtOH/ASA drug solutions is limited, as there is a rapid forming of drug deposits on the nozzle of the printhead because of fast solvent evaporation. Droplet formation of c = 100 g/L EtOH/ASA solution was affected after only a few seconds by little drug deposits, whereas for c = 10 g/L EtOH/ASA solution, a negative affection was observed only after t = 15 min, while prominent drug deposits form at the printhead tip. Due to the creeping effect, the crystallizing structures of ASA spread around the nozzle but do not clog it necessarily. When there is a negative affection, the droplet trajectory is affected the most, while the droplet volume and droplet velocity are influenced less. In contrast, no formation of drug deposits could be observed for highly concentrated, low volatile DMSO-based drug solution of c = 100 g/L even after a dispensing time of t = 30 min. Therefore, low volatile solvents are preferable to highly volatile solvents to ensure a reproducible droplet formation in long-term inkjet printing of highly concentrated drug solutions. Highly volatile solvents require relatively low drug concentrations and frequent printhead cleaning. The findings of this study are especially relevant when high droplet positioning precision is desired, e.g., drug loading of microreservoirs or drug-coating of microneedle devices. [ABSTRACT FROM AUTHOR]

A simplified experimental device was designed to simulate the shear flow in a liquid-liquid cyclone reactor. And the dispersed phase droplet formation process in the shear flow in dripping regime was investigated. Four characteristic parameters, droplet growth time (T g), shrink time (T s), formation time (T f) and size (d) were used to describe the formation process. All the parameters presented fluctuation with different serial droplet numbers. Therefore, the effect of dispersed phase inlet flow rate (v d) on the value and uniformity of the parameters are analyzed. The results indicate that with the increase of v d , T g , T s , T f decrease firstly and then increase, while the droplet size gradually increases. Meanwhile, the uniformity of T g decreases first and then basically tends to be stable, while that of T s , T f and d decreases firstly and then increases. Eventually, the optimal range of v d under different continuous phase inlet flow rate is provided. [Display omitted] ● The brightness of fluorescent oil under ultraviolet light was adopted in the dynamic capture of droplet formation. ● Four characteristic parameters were used to describe the droplet formation process in dripping regime. ● The uniformities of characteristic parameters was proposed to evaluate the fluctuation of droplet formation process. [ABSTRACT FROM AUTHOR]

Microfluidic devices (MFDs) printed in 3-D geometry using digital light projection to polymerize monomers often have surfaces that are not as hydrophobic as MFDs made from polydimethylsiloxane. Droplet microfluidics in these types of devices are subject to droplet adhesion and aqueous spreading on less hydrophobic MFD surfaces. We have developed a post-processing technique using hydrophobic monomers that renders the surfaces of these devices much more hydrophobic. The technique is fast and easy, and involves flowing monomer without initiator into the channels and then exposing the entire device to UV light that generates radicals from the initiator molecules remaining in the original 3-D polymerization. After treatment the channels can be cleared and the surface is more hydrophobic, as evidenced by higher contact angles with aqueous droplets. We hypothesize that radicals generated near the previously printed surfaces initiate polymerization of the hydrophobic monomers on the surfaces without bulk polymerization extending into the channels. The most hydrophobic surfaces were produced by treatment with an alkyl acrylate and a fluorinated acrylate. This technique could be used for surface treatment with other types of monomers to impart unique characteristics to channels in MFDs. [ABSTRACT FROM AUTHOR]

For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel. [ABSTRACT FROM AUTHOR]

• Droplet formation from SiO 2 -based nanofluids in T-junction microchannels has been studied experimentally. • The SiO 2 -based nanofluids exhibit non-Newtonian rheology, notably shearthickening properties. • As nanoparticle concentration increases, nanofluids exhibit elevated viscosity, interfacial tension, and contact angle. • Increased nanoparticle concentrations result in larger droplet size and reduced droplet generation frequency. Due to its precise control over droplet sizes and generation rates, droplet-based microfluidics has become widely utilized across various fields, such as food processing, medical diagnostics, and drug delivery. The integration of nanoparticles has notably advanced droplet synthesis by preventing undesirable coalescence. However, despite these advancements, a thorough comprehension of how nanoparticles influence microdroplet generation within microfluidic channels remains elusive. In this experimental study, we have explored the impact of SiO 2 nanofluid as a dispersed phase at various concentrations within a T-junction microchannel, with silicone oil serving as the continuous phase. This investigation elucidates the non-Newtonian characteristics of SiO 2 nanofluid, demonstrating shear thickening behavior that correlates with elevated viscosity, interfacial tension, and contact angle as nanoparticle concentration rises. The distinct regimes and stages of droplet generation for different concentrations of nanoparticles have been reported. The increase in nanoparticle concentration typically leads to extended production times and larger droplet sizes, primarily driven by simultaneous viscosity and surface tension increments. Increased primary phase flow rates lead to a decrease in droplet length alongside an increase in droplet formation frequency. Elevating the flow rate of the secondary phase fluid results in an augmentation of both droplet length and droplet generation frequency. This study highlights the interplay between rheology and the microfluidic generation of nanofluid droplets, marking a significant milestone in colloid science. [ABSTRACT FROM AUTHOR]

Metal-based droplet deposition technique is a promising method for obtaining 3D circuits and micro-sized conductive structures. Practically, direct part manufacturing can be achieved via droplet generator systems efficiently. In this study, micro-scale droplets are formed by a vibrated actuator. Furthermore, vibration stroke can be adjusted by means of a precise mechanical restrictor. The effects of the input ejection parameters are investigated over the droplet properties such as diameter, velocity and deposition conditions. The deposition morphologies with different layouts are first classified through theoretical equations. Experiments are then performed to obtain the predicted deposition patterns. As a result, it is observed that the vibration amplitude and voltage directly affect the flight velocity, diameter and wetting characteristic of the droplet, thus the deposition performance. In this context, it has been proven that droplets can be deposited in desired patterns when ejection parameters are properly configured. With such system, metallic structures can be obtained in non-laboratory environments such as space stations and aerospace vehicles those have limited access to the equipment. The presented device is designed to be modifiable, maintainable and compact structure. Given the freedom of design and flexibility in manufacturing, such devices become promising candidates for use in space environments involving different gravitational conditions. [ABSTRACT FROM AUTHOR]

The droplet size distribution in liquid–liquid dispersions is a complex convolution of impeller speed, impeller type, fluid properties, and flow conditions. In this work, we present three a priori modeling approaches for predicting the droplet diameter distributions as a function of system operating conditions. In the first approach, called the two‐fluid approach, we use high‐resolution solutions to the Navier–Stokes equations to directly model the flow of each phase and the corresponding droplet breakup/coalescence events. In the second approach, based on an Eulerian–Lagrangian model, we describe the dispersed fluid as individual spheres undergoing ongoing breakup and coalescence events per user‐defined interaction kernels. In the third approach, called the Eulerian–Parcel model, we model a sub‐set of the droplets in the Eulerian–Lagrangian model to estimate the overall behavior of the entire droplet population. We discuss output from each model within the context of predictions from first principles turbulence theory and measured data. [ABSTRACT FROM AUTHOR]

The presence of lubricant droplets in the gas that flows through the piston assembly and crankcase of an internal combustion engine (generically termed oil misting) has important implications for performance, particularly lubricant supply to the upper piston assembly, oil consumption and lubricant degradation. A significant source of these droplets is thought to be oil shearing and blow-through by blow-by gas flows in the piston assembly. An experimental rig was developed to simulate the high velocity gas and lubricant film interactions at a top piston ring gap where the flow conditions are most severe. Flows of lubricant droplets were produced and characterised in terms of the proportion of the oil flow that formed droplets in the gas flow and the size distribution of the droplets produced. Considering various aspects of a commercial automotive crankcase formulation, the effect of lubricant viscosity was found to be particularly important. Of the lubricant additives evaluated, viscosity modifiers were found to have the greatest effect on the tendency to form droplets: Detailed study on a range of viscosity modifiers identified that the influence of their molecular architectures on viscoelasticity was the key mechanism. [ABSTRACT FROM AUTHOR]

The use of processing units for the production of mineral fertilizers in the industry in today’s market requires improved product quality and increased productivity. As a result, there is a need to change the design of existing units or some structural elements. Rotary vibroprillers, having a relatively simple design, can be of different designs that directly affect the productivity indicators mentioned above. The study considers the influence of the shape of the basket bottom on the quality of the rotational vibroprillers. After using the governing equation of prills motion in the airflow, a program was developed for automatic control of the rotational speed of the priller based on changes in melt loads. It is established that the size of the spray swath can be changed by varying the rotational speed of the priller. There is a tendency to affect the vibropriller performance by controlling the rotational speed and shape of the basket bottom without performance degradation.

Many scientific research papers report that jet-like flow during speech is a potent route for viral transmission in the COVID-19 pandemic. Droplet emission occurs during breaking, speaking, singing, coughing and sneezing, which could be affected by the shear-thinning rheology of the liquid. Here we test the viscosity of simple liquid system in many-body dissipative particle dynamics model under different driven forces, which illustrates that the simple liquid system interestingly has shear-thinning property. Based on this, we simulate the process of jet-like flow and capture the rupture of liquid cylinder and the process of drop generation, which implies the jet-induced liquid pinchoff and drop generation can be regulated by initial driven force and its temperature. The results show that larger pressure pulse could generate longer liquid cylinder and larger drops, as well as at lower force frequency. This work can provide an insight in liquid jet-like flow with shear-thining property and yield a better understanding of virus spreading via salivary droplets. [ABSTRACT FROM AUTHOR]

Using variational mode decomposition, we analyze the signal from velocities at the center of the channel of a microfluidics drop-maker. We simulate the formation of water in oil droplets in a microfluidic device. To compare signals from different drop-makers, we choose the length of the water inlet in one drop-maker to be slightly shorter than the other. This small difference in length leads to the formation of satellite droplets and uncertainty in droplet uniformity in one of the drop-makers. By decomposing the velocity signal into only five intrinsic modes, we can fully separate the oscillatory and noisy parts of the velocity from an underlying average flow at the center of the channel. We show that the fifth intrinsic mode is solely sufficient to identify the uniform droplet formation while the other modes encompass the oscillations and noise. Mono-disperse droplets are formed consistently and as long as the fifth mode is a plateau with a local standard deviation of less than 0.02 for a normalized signal at the channel inlet. Spikes in the fifth mode appear, coinciding with fluctuations in the sizes of droplets. Interestingly, the spikes in the fifth mode indicate non-uniform droplet formation even for the velocities measured upstream in the water inlet in a region far before where droplets form. These results are not sensitive to the spatial resolution of the signal, as we decompose a velocity signal averaged over an area as wide as 40% of the channel width. [ABSTRACT FROM AUTHOR]

In order to study the influence of streamwise forcing on the formation mechanism of liquid ligaments and droplets in the primary breakup process of liquid circular jet, the VOF interface capturing method-based direct numerical simulation was adopted, and a range of sinusoidal velocity disturbances with different frequencies were considered. The selected disturbance frequency range is 0–3000 kHz. This work analyzes the evolution process of the jet surface waves at different disturbance frequencies, and the coupling effect of the jet tip and liquid core on the overall spray field from overall structure, liquid ligament, and droplet formation. The results show that different disturbance frequencies affect the droplet shape distribution and size distribution in spray field. Current work provides guidance for the control of the thermoacoustic instability of the engine and design of the nozzle. [ABSTRACT FROM AUTHOR]

Electrospraying is a process that uses electrostatic force to break up a liquid into droplets by using a strong electric field. There are different modes of electrospraying depending on the electric field strength and the liquid flow rate for a specified liquid. The simple-jet mode is among these modes, which can produce monodisperse droplets. This article is aimed at analyzing electrospraying in simple-jet mode of a pesticide—solution issued from the nozzle of a capillary of the spray—system. The analysis includes the formation of a jet charged by conduction at low applied voltages (below corona onset) and by corona discharge at voltages higher than the corona onset value. The electric field distribution in the space between the charged jet and the target is calculated at voltages below and above the corona onset value. The disintegration of the jet into droplets is assessed to determine the jet length and radius as well as the charge and radius of droplets. The current–voltage characteristic of the spray system is calculated and checked experimentally. The agreement between the calculated and measured currents in the spray system at the same applied voltage is satisfactory. [ABSTRACT FROM AUTHOR]

[Display omitted] • The developed methodology measures dynamic interfacial tension down to 3ms. • Surfactant adsorption times can be significant if compared to drop formation times. • Dynamic interfacial tension was observed even with small-molecule surfactants. • The proposed criteria ensure equilibrium interfacial tension during drop formation. Dynamic interfacial tension was studied experimentally during drop formation in a flow-focusing microchannel. A low viscosity silicone oil (4.6 mPa s) was the continuous phase and a mixture of 48% w/w water and 52% w/w glycerol was the dispersed phase. An anionic (sodium dodecylsulfate, SDS), a cationic (dodecyltrimethylammonium bromide, DTAB) and a non-ionic (Triton™ X-100, TX100) surfactant were added in the dispersed phase, at concentrations below and above the critical micelle concentration (CMC). For SDS and DTAB the drop size against continuous phase flowrate curves initially decreased with surfactant concentration and then collapsed to a single curve at concentrations above CMC. For TX100 the curves only collapsed at surfactant concentrations 8.6 times the CMC. From the collapsed curves a correlation of drop size with capillary number was derived, which was used to calculate the dynamic interfacial tension at times as low as 3 ms. The comparison of the surfactant mass transport and adsorption times to the interface against the drop formation times indicated that surfactant adsorption also contributes to the time required to reach equilibrium interfacial tension. Criteria were proposed for drop formation times to ensure that equilibrium interfacial tension has been reached and does not affect the drop formation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microfluidic devices (MFDs) printed in 3-D geometry using digital light projection to polymerize monomers often have surfaces that are not as hydrophobic as MFDs made from polydimethylsiloxane. Droplet microfluidics in these types of devices are subject to droplet adhesion and aqueous spreading on less hydrophobic MFD surfaces. We have developed a post-processing technique using hydrophobic monomers that renders the surfaces of these devices much more hydrophobic. The technique is fast and easy, and involves flowing monomer without initiator into the channels and then exposing the entire device to UV light that generates radicals from the initiator molecules remaining in the original 3-D polymerization. After treatment the channels can be cleared and the surface is more hydrophobic, as evidenced by higher contact angles with aqueous droplets. We hypothesize that radicals generated near the previously printed surfaces initiate polymerization of the hydrophobic monomers on the surfaces without bulk polymerization extending into the channels. The most hydrophobic surfaces were produced by treatment with an alkyl acrylate and a fluorinated acrylate. This technique could be used for surface treatment with other types of monomers to impart unique characteristics to channels in MFDs.

Cell-encapsulation is used for preventing therapeutic cells from being rejected by the host. The technology to encapsulate cells in immunoprotective biomaterials, such as alginate, commonly involves application of an electrostatic droplet generator for reproducible manufacturing droplets of similar size and with similar surface properties. As many factors influencing droplet formation are still unknown, we investigated the impact of several parameters and fitted them to equations to make procedures more reproducible and allow optimal control of capsule size and properties. We demonstrate that droplet size is dependent on an interplay between the critical electric potential (Uc,), the needle size, and the distance between the needle and the gelation bath, and that it can be predicted with the equations proposed. The droplet formation was meticulously studied and followed by a high-speed camera. The X-ray photoelectron analysis demonstrated optimal gelation and substitution of sodium with calcium on alginate surfaces while the atomic force microscopy analysis demonstrated a low but considerable variation in surface roughness and low surface stiffness. Our study shows the importance of documenting critical parameters to guarantee reproducible manufacturing of beads with constant and adequate size and preventing batch-to-batch variations. [ABSTRACT FROM AUTHOR]

To achieve efficient preparation of emulsion droplet, this paper uses a two-dimensional mathematical model coupled with the phase field model and the electrostatic field model to calculate the droplet formation in parallel flow focusing multichannel, and analyzed the effect of electric field strength on the droplet formation process. In addition, the effects of different capillary numbers and dispersed phase viscosity on droplet formation were also analyzed. The results show that the emulsion in the channel always generates droplet by dripping regime, and the droplet have the best monodispersity. Applying appropriate electric field strength can realize droplet formation frequency and size regulation. Increasing the dispersed phase viscosity increases the breakup thread of the dispersed phase fluid, and the droplet size obtained gradually decreases, the difference in droplet size can be slowed down by applying the electric field. Increasing the electrostatic force leads to a higher droplet deformation rate. The droplet shape classification is plotted using the capillary number (Ca) and electrostatic number (Ca E). It is found that the droplet flow pattern in the channel remains a circle only when Ca and Ca E are sufficiently small. [Display omitted] [ABSTRACT FROM AUTHOR]

Double emulsions (DEs) have attracted researchers' attention to be utilized as a promising platform in biomedical and chemical applications. Several actuation mechanisms have been proposed for the generation of DEs. The conventional DE formation approaches (e.g. two-stage emulsification) suffer from low monodispersity. The electric actuation (i.e. coaxial electrospray technology) has been demonstrated as a controllable method for the DE formation, while the capability of magnetic actuation has not been studied yet. In the present study, the generation of ferrofluid double emulsions (FDEs), made from water-based ferrofluid as a core and oil as a shell, under the magnetic actuation of a permanent magnet with a steady magnetic field and an electromagnet with DC and pulse width modulation (PWM) magnetic fields was investigated with a simple controllable setup fabricated using 3D printing. The effect of various parameters affecting the FDE formation, such as the fluid flow rates, the magnetic field type, the magnetic flux density, and the PWM frequency and duty cycle, on the FDE formation characteristics, including the inner and outer equivalent diameters, and the formation frequency was studied. Under the steady magnetic field, two regimes of the FDE formation were identified: inertia-dominated and magnet-dominated. Wireless power-free magnetic actuation provides better control over the FDE formation, enhancing this process by increasing the FDE formation frequency with high monodispersity. The PWM magnetic field offers excellent controllability over the FDE formation with low-volume or no, in some cases, satellite droplets by tuning the PWM frequency and the duty cycle. [Display omitted] • Several magnetic actuation mechanisms have been proposed for the ferrofluid double emulsion (FDE) formation using a simple 3D-printed setup. • The effect of various parameters affecting the FDE formation have been investigated. • Two regimes of the FDE formation were identified: inertia-dominated and magnet-dominated. • The PWM magnetic field offers excellent controllability over the FDE formation with low-volume satellite droplets by tuning the PWM frequency and the duty cycle. [ABSTRACT FROM AUTHOR]

The effect of nozzle width on the droplet formation in the wedge-shaped step microchannel devices was investigated, and the applicability of the devices with different nozzle widths were evaluated in generating droplets with various viscosities. The glycerol aqueous solution with different viscosities and the silicone oil were used as the dispersed phase and the continuous phase, respectively. The dripping, transition, and jetting flow patterns were found in the experiment and the dripping flow was mainly discussed. The effect of the nozzle width, the flow rates, and the viscosities of the dispersed phase on the droplet size, the formation frequency, the size-stable range, and the variation coefficient of the droplet diameter were discussed. In addition, the effect of nozzle width on droplet formation dynamics was analyzed. An empirical formula for the influence of nozzle width and dispersed phase viscosities on the average stable size of droplets generated in size-stable zones was proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

The dynamic formation characteristics of droplets in a cross-junction can be captured via a high-speed image setup. The experimental results show four flow regimes: slug, dripping, jetting (threading and tubing), and viscous displacement. When Cad and Cac are small, the slug regime occurs. The dripping regime occurs when Cac is relatively high. The jetting regime appears when Cad increases to a considerable value. When Cac is much smaller than Cad, the viscous displacement regime occurs. In the slug and dripping regimes, the dispersed phase will experience growing, squeezing, and pinching off stages in the formation of droplets. These four flow regimes are strongly affected by Cac and Cad. In addition, the flow rates of the two phases can be changed to adjust the sizes of the generated droplet in the cross-junction under the slug regime and dripping regime. The dimensionless droplet length l* can be predicted via l* = (0.248 + 0.55Q)Cac−0.203. [ABSTRACT FROM AUTHOR]

Issues of the formation of dust particles in high-temperature technological reactors are considered with an emphasis on the processes occurring in electrothermal ore-reduction furnaces of phosphorus production, when dust serves as a source of sludge that contaminates the product. A model of dust formation is proposed based on the hydrodynamic interaction of gas bubbles with liquid when they exit at the interface, when the destruction of bubbles leads to the appearance of drops carried away by the gas flow. Consideration of the stability positions for maximum perturbations in cylindrical liquid jets makes it possible to estimate the droplet sizes above the liquid surface and obtain qualitative and quantitative estimates for droplets carried away by the gas flow. Analytical dependencies for dust formation in a phosphoric furnace make it possible to relate the dust content to the operating parameters characterizing the operation of the furnaces (the temperature in the reaction zone) and the properties of the melt and control parameters (the voltage on the electrodes and the dosage of coke). Calculations based on the ratios show a satisfactory correlation with experimental data on the formation of dust in phosphoric, open-hearth furnaces, as well as bubbling heat and mass transfer installations. A model of thermophysical processes in an electrothermal reduction reactor is presented in the approximation of lumped-distributed parameters, which takes into account the interaction of zones of different phase compositions, making it possible to analyze the operating modes of the reactor from the main control parameters—voltage on the electrodes and the proportion of reducing coke. The results can be used to optimize the operating modes of the equipment within the limits of permissible dust emissions. [ABSTRACT FROM AUTHOR]

The flow-focusing method is a technology for microfluidic droplet control, and the temperature can effect on the droplet formation. In this study, the droplet formation in the flow-focusing method during the squeezing of dispersed phase by the continuous phase is simulated using CLSVOF, with the consideration of the effects of temperature on droplet size, shape and frequency. The simulation results are consistent with experimental data. The simulated results demonstrate that the droplet size increases with the increase of inlet phase temperature, while the shape regularity and forming frequency decrease, the maximum increase of droplet size is 16%, the biggest drop of droplets number is 29%, and the biggest drop of the roughness parameter is 5%. When the inlet temperatures of the continuous phase are not equal, dripping and jetting are observed in the flow regime of droplet dispersed phase. The mechanism of the temperature influence on droplet formation and the detailed process of droplet formation under different flow regimes are discussed. At the same time, the radial size of droplet breakup point under different flow regimes is compared. The simulation results provide insights in better selection of the control parameters for droplet formation technology.