Viscous Forces Research Articles

Effect of gravity number on soil contamination during dynamic adsorption of heavy metal ions: A lattice Boltzmann study

Contamination of soils and aquifers as a result of heavy metal ions adsorption is an extremely negative environmental phenomenon associated with natural or industrial disasters. This paper presents the first systematic study of the dynamic adsorption of heavy metal ions in soils during water-air immiscible displacement induced by pressure drop and gravitational force. This study addresses three objectives. The first purpose is to determine a representative elementary volume to estimate the adsorbed amount of heavy metal ions during two-phase flow with density contrast. The second objective is to study the effect of different balances between viscous and gravitational forces, described by the gravity number, on the adsorbed amount at drainage and imbibition regimes. And the final task is to identify the effect of the pore space heterogeneity on the adsorbed amount for various gravity numbers and wetting conditions. As samples of study, we examine two-dimensional granular digital images characteristic of soils. The lattice Boltzmann method, verified on the problem of capillary-gravitational equilibrium of a meniscus, was used as a research tool. It has been established that the scale of 4–5 mm is sufficient to be representative for estimating the adsorbed amount of heavy metal ions. An increase in gravity number promotes the destabilization of the interfacial front both in the drainage and imbibition regimes and results in suppression of the adsorbed amount. The effect of gravity number on the adsorbed amount is stronger in the drainage mode compared to the imbibition regime. It has been found that pore space heterogeneity is a factor negatively affecting the adsorbed amount of heavy metal ions. The strength of the heterogeneity effect is independent of wetting conditions and gravity numbers.

Multiple jets in a rotating annulus model with an imposed azimuthal magnetic field

Zonal flows driven by rotation and convection are found commonly within astrophysical and geophysical bodies. Multiple jets are most famously observed on the surface of Jupiter, with prograde and retrograde zonal flows making up part of its banded structure of zones and belts. Non-magnetic studies of convection in a rotating annulus model have previously been shown to produce multiple jet structures, similar to those observed in atmospheres of giant planets such as Jupiter. These giant planets have strong magnetic fields which impact on convection in the electrically conducting regions of their atmospheres. Therefore the effect of a magnetic field on the multiple jet solutions of the annulus model is of astrophysical interest. In this work we impose a uniform azimuthal magnetic field to the annulus model and vary its strength and other control parameters to determine the parameter space where multiple jets exist. Zonal flows and multiple jet solutions are found at weak magnetic field strength and, indeed, the magnetic field can promote the production of these features. Simulations with a weak magnetic field or no magnetic field are also found to match well with the Rhines scaling theory. For cases with multiple jets, a strong inertial force must be present, combined with either a weak Lorentz force, or a Lorentz force entering the main balance with increased contributions from the viscous force. At strong magnetic field strengths two regimes are found. For weak magnetic diffusion zonal flows can be retained, albeit without the multiple jet structure. For larger magnetic diffusion non-axisymmetric solutions without clear bands are found. In these regimes, the Lorentz force appears in the primary balance of forces and zonal flows are only retained at strong driving when inertia is able to also enter the balance at leading order.

Evidence of stretching/moving sheet-triggered nonlinear similarity flows: atomization and electrospinning with/without air resistance

PurposeThe purpose of this study is two-fold. First, it aims to differentiate the response of a stretching jet encountering a quadratic air resistance from the classical jet shape formed in a frictionless medium. Second, it investigates how the resulting jet forms with and without air resistance, seeking evidence that supports the similarity flows frequently studied for stretching/moving thin bodies under the boundary layer approximation.Design/methodology/approachThis study extends the established electrohydrodynamic stretching jet theory, used to model electrospinning or jet printing in the absence of air resistance, to encompass the impact of the retarding force on the jet stretching in both the cone and final regimes before it impinges on a substrate.FindingsA close examination of the nonlinear governing equations reveals that the jet rapidly thins near the nozzle because of the combined action of viscous and electrical forces. In this region, the exponentially decaying jet receives further support from the air resistance, resulting in a closer alignment with the observed experimental jet. This exponential decay, accelerated by the inversely quadratic speed of the liquid particles, serves as clear evidence for the existence of a similarity flow over an exponentially stretching sheet. Furthermore, in the final regime, the jet stretching exhibits an algebraic decay in the absence of air friction, while with air resistance, it decays exponentially to reach a limiting speed. In the former case, a square root dependence of the stretching jet speed leads to the emergence of a similarity flow over a thin stretching jet, while in the latter case, a Sakiadis’ similarity flow appears over a continuously moving flat surface.Practical implicationsThe analysis goes beyond jet hydrodynamics, delving into the interplay of electrostatic forces (including Coulomb’s law) and quadratic air drag, drawing upon experimental data on glycerol liquid presented in earlier publications.Originality/valueFinally, the asymptotic behavior of the stretching jet under the combined influence of electrostatic pull and its electric currents because of bulk conduction and surface convection is validated through a comprehensive numerical simulation of the nonlinear system.

Assessing Subsurface Gas Storage Security for Climate Change Mitigation and Energy Transition

AbstractSubsurface gas storage is crucial for achieving a sustainable energy future, as it helps to reduce CO2 emissions and facilitates the provision of renewable energy sources. The confinement effect of the nanopores in caprock induces distinctive thermophysical properties and fluid dynamics. In this paper, we present a multi‐scale study to characterize the subsurface transport of CO2, CH4, and H2. A nanoscale‐extended volume‐translated Cubic‐Plus‐Association equation of state was developed and incorporated in a field‐scale numerical simulation, based on a full reservoir‐caprock suite model. Results suggest that in the transition from nanoscale to bulk‐scale, gas solubility in water decreases while phase density and interfacial tension increase. For the first time, a power law relationship was identified between the capillary pressure within nanopores and the pore size. Controlled by buoyancy, viscous force and capillary pressure, gases transport vertically and horizontally in reservoir and caprock. H2 has the maximum potential to move upward and the lowest areal sweep efficiency; in short term, CH4 is more prone to upward migration compared to CO2, while in long term, CH4 and CO2 perform comparably. Thicker caprock and larger caprock pore size generally bring greater upward inclination. Gases penetrate the caprock when CH4 is stored with a caprock thickness smaller than 28 m or H2 is stored with a caprock pore size of 2–10 nm or larger than 100 nm. This study sheds light on the fluid properties and dynamics in nanoconfined environment and is expected to contribute to the safe implementation of gigatonne scale subsurface gas storage.

The role of cavity shapes in improving the performance of a heat sink incorporating nano-enhanced phase change material

Improving the cooling performance of heat sink is critical for providing better thermal management to compact electronic devices. Thus, analyzing various cavity shapes for a heat sink containing Nano-enhanced Phase Change Material is of utmost necessity. The present study focuses on a two-dimensional conjugate heat propagation in a Heat sink with Rectangular (HRC), Trapezoidal (HTC), and Wavy (HWC) cavities. Various cavity shapes are examined to identify the ideal shape for a heat sink containing nano-enhanced Phase Change Material (Ne-PCM). The copper oxide (CuO) nanoparticle enhanced paraffin is considered as Ne-PCM. The analysis encompasses identification of the potent cavity shape, its optimum geometric parameters, the dominant mode of heat transfer and ultimately the desirable thermophysical properties of the Ne-PCM. Among HRC, HTC, and HWC, the heat sink with HRC performs the best by maintaining the lowest base temperature. The HTC, has a better initial performance than the HRC, though HTC has low PCM content. Nevertheless, as time progresses, HTC fails to inhibit the base temperature rise. In contrast, due to increased contact surface area, PCM in HWC experiences a stronger opposing viscous force. Consequently, HWC has conduction-dominated heat transfer and the slowest melting of PCM that elevates the base temperature, accumulating heat near cavity walls. Shortening the relative pitch distance and elongating the relative height of the HRC further lowers the base temperature of the heat sink. Notably, the heat transfer mode analysis reveals that in the cavity with maximum height, heat diffusion dominates convective heat transfer. Heat diffusion increases away from the cavity walls towards the middle of the cavity. Ultimately, it is noted that a denser PCM with high thermal conductivity and low viscosity effectively maintains a low heat sink base temperature. A denser PCM imparts more sensible and latent heat absorption capability and maintains a lower base temperature. On complete melting, the convective heat transfer is much higher in a denser PCM. A PCM with higher thermal conductivity marginally lowers the base temperature with a small increase in PCM melting rate.

Internal blocking and bonding to strengthen the mechanical properties and prevent collapse and leakage of fragmented coalbed methane (CBM) reservoirs by cohesive drilling fluids

Exploiting coalbed methane (CBM) not only provides clean energy but also reduces the risk of gas explosions in coal mining. CBM reservoirs have low mechanical strength due to poor continuity, strong heterogeneity, and rich natural fractures, which bring about wellbore collapse and leakage during the drilling operations of CBM wells. As for fragmented coalbed methane reservoirs, plugging the leakage channel and increasing the density of drilling fluid would result in new collapse problems and leakage. To achieve this, we developed a cohesive fuzzy ball drilling fluid (FBDF) to adhere fragmented coal particles from the discontinuous phase to the continuous phase and strengthen their mechanical properties to prevent collapse and leakage. The microcosmic interaction of coal seams with different fluid systems and adhesive properties have been comprehensively evaluated. The mechanical parameters of coal plugs treated with common potassium chloride drilling fluid (PCDF), polymer drilling fluid (PDF), and FBDF were carefully compared through uniaxial and triaxial experiments. Additionally, the adhesive mechanism of FBDF to coal fines was comprehensively discussed. The results showed that the FBDF would form an elastic mesh structure through hydrophobic association, and bond the small particles of coal debris together to form a stable structure similar to “steel bar-concrete” “macromolecule-particle”. The viscous force on the surface of coal rocks treated by FBDF was higher than that of coal plungers treated by PCDF or PDF. The uniaxial compressive strength of core samples treated by FBDF was increased by 47.1%, while the modulus of elasticity, Poisson's ratio, and brittleness coefficient were decreased by 19.94%, 11.95%, and 4%, respectively, compared to dry coal plug. FBDF also showed preferential plugging and permeability recovery abilities. The FBDF fluids have been successfully applied in two CBM wells characterized by “top leakage and bottom collapse”, neither collapse nor leakage occurred during the drilling process. It provided a new internal blocking and bonding technology for fragmented reservoirs.

Viscous Current-Induced Forces.

We study the motion (translational, vibrational, and rotational) of a diatomic impurity immersed in an electron liquid and exposed to electronic current. An approach based on the linear response time-dependent density functional theory combined with the Ehrenfest dynamics leads to a system of linear algebraic equations, which account for the competing and counteracting effects of the current-induced force (electron wind) and the electronic friction. We find and emphasize the coupling between the center of mass motion and that of the nuclei relative to each other, the feature due to the mediation of the two-body interaction by the environment. The current-induced forces, by means of the dynamic exchange-correlation (xc) kernel f_{xc}(r,r^{'},ω), include the electronic viscosity contribution. Starting from the ground state at the equilibrium internuclear distance and applying a current pulse, we observe three phases of the motion: (i)acceleration due to the prevalence of the current-induced force, (ii)stabilization upon balancing of the two forces, and (iii)deceleration due to the friction after the end of the pulse. At lower, but still metallic, electron densities, the dynamic xc contribution to the force significantly affects the acceleration (deceleration) at the first (third) phase of the process. For the Cs density (r_{s}≈6 a.u.), this correction amounts up to 40% in the rotation regime.

Microscale Diffractive Lenses Integrated into Microfluidic Devices for Size-Selective Optical Trapping of Particles.

Integration of optical components into microfluidic devices can enhance particle manipulations, separations, and analyses. We present a method to fabricate microscale diffractive lenses composed of aperiodically spaced concentric rings milled into a thin metal film to precisely position optical tweezers within microfluidic channels. Integrated thin-film microlenses perform the laser focusing required to generate sufficient optical forces to trap particles without significant off-device beam manipulation. Moreover, the ability to trap particles with unfocused laser light allows multiple optical traps to be powered simultaneously by a single input laser. We have optically trapped polystyrene particles with diameters of 0.5, 1, 2, and 4 μm over microlenses fabricated in chromium and gold films. Optical forces generated by these microlenses captured particles traveling at fluid velocities up to 64 μm/s. Quantitative trapping experiments with particles in microfluidic flow demonstrate size-based differential trapping of neutrally buoyant particles where larger particles required a stronger trapping force. The optical forces on these particles are identical to traditional optical traps, but the addition of a continuous viscous drag force from the microfluidic flow introduces tunable size selectivity across a range of laser powers and fluid velocities.

High-Speed Stress Field Measurement In A Soft Substrate During Droplet Impact

In this study, we utilized high-speed photoelastic tomography to quantify dynamic stress fields within a soft substrate during droplet impact. This manuscript details the measurement technique, which employs a high-speed polarization camera and the principles of photoelastic tomography. Our method successfully enabled the quantitative measurement of dynamic stress fields in a soft substrate during droplet impact. Additionally, we conducted an analysis of the impact force derived through the spatial integration of the measured stress field. The discussion explored the interplay between the maximum impact force, droplet viscosity, and substrate elasticity. Our findings indicate that the maximum impact force 𝐹max can be expressed as a function with a self-similar variable of 𝑅𝑒 / 𝐶𝑎^2 , where 𝑅𝑒 is Reynolds number representing the droplet inertial force and droplet viscous force and 𝐶𝑎 is Cauchy number representing the ratio of the droplet inertial force and substrate elastic force. This combination, 𝑅𝑒 / 𝐶𝑎^2 , represents the relationship between the relaxation time of droplet and substrate deformation ( 𝜂/ 𝐸), the contact time of the droplet (𝑅 / 𝑉), and the ratio of substrate elastic force to droplet inertial force. Consequently, the maximum impact force 𝑅𝑒 / 𝐶𝑎^2 is determined by the balance between the relaxation and contact times. We believe that our developed method will significantly enhance the understanding of droplet impact phenomena. Furthermore, it holds potential for broader applications in various engineering processes, such as analyzing stress distribution in materials caused by liquid jet impact and studying cavitation bubbles in viscoelastic materials. This method's ability to provide detailed quantitative measurements of dynamic stress fields offers a valuable tool for future research and technological advancements in related fields.

Unsteady electroosmotic flow of Carreau–Newtonian fluids through a cylindrical tube

The present study aims to investigate the fully developed electroosmotic flow of Carreau–Newtonian fluids within a circular tube, considering two different boundary conditions of zeta potential. The unsteady behavior of Carreau–Newtonian fluids, is attributed to the pulsatile pressure-driven flow. Studying two distinct formulations, slip and no-slip zeta potentials, illustrates the relative movement of fluid particles and the charged surface. The proposed study’s framework is divided into two regions: a central region containing a non-Newtonian Carreau fluid exhibiting both shear-thinning and thickening behavior, and a peripheral region containing a Newtonian fluid with the effect of an electrical double layer at the solid wall of the cylindrical tube. The Poisson–Boltzmann equation under the assumption of Debye–Hückel approximation governs the potential distribution due to the electric double layer, facilitating the examination of electroosmotic flow through tube. Obtaining analytical solutions for the momentum equations in both regions becomes challenging due to the inclusion of pulsatile pressure-driven flow and a non-Newtonian Carreau fluid. Asymptotic series expansions are employed, utilizing small parameters such as the Weissenberg number (We≪1) and a pulsatile Reynolds number (α≪1), to derive velocity expressions for both regions. Wall shear stress fluctuations, as indicated by time-averaged wall shear stress and oscillatory shear index are assessed to gauge the temporal variation of wall shear stress from the dominant blood flow direction. By utilizing potential and hydrodynamic variables, an asymptotic formulation for the streaming potential is developed to ascertain the asymptotic expression of electrokinetic energy conversion efficiency and scrutinize the impacts of pertinent physical parameters on it. The proposed study prominently shows that the Debye–Hückel parameter, Weissenberg number, pulsatile Reynolds number, and time-dependent pressure gradient significantly influence the fluid velocity, flow rate, and flow resistance. The notable determination of the present study is that the velocity amplitude and electrokinetic energy conversion efficiency are enlarged in the slip-dependent case relative to the no-slip zeta potential. It is noteworthy that as inertial forces become more prominent compared to viscous forces, both time-average wall shear stress and oscillatory shear index experience a slight decrease, although the reduction in oscillatory shear index is minimal owing to the absence of obstruction within the tube wall. The NDSolve numerical scheme in Mathematica software is employed to calculate numerical solutions for the governing equations, which are subsequently verified against results obtained through asymptotic analysis. The findings of this study are expected to deepen our understanding of unsteady electroosmotic flows of Carreau fluid and contribute to the design and development of advanced microfluidic devices with enhanced performance for various applications.

A comparison of models for predicting the maximum spreading factor in droplet impingement

The maximum spreading factor during droplet impact on a dry surface is a pivotal parameter of a range of applications, including inkjet printing, anti-icing, and micro-droplet transportation. It is determined by a combination of the inertial force, viscous force, surface tension, and fluid–solid interaction. There are currently a series of qualitative and quantitative prediction models for the maximum spreading factor rooted in both momentum and energy conservation. However, the performance of these models on consistent experimental samples remains ambiguous. In this work, a comprehensive set of 785 experimental samples spanning the last four decades is compiled. These samples encompass Weber numbers ranging from 0.038 to 2447.7 and Reynolds numbers from 9 to 34 339. A prediction model is introduced that employs a neural network, which achieves an average relative error of less than 16.6% with a standard error of 0.018 08 when applied to the test set. Following this, a fair comparison is presented of the accuracy, generality, and stability of different prediction models. Although the neural network model provides superior accuracy and generality, its stability is weaker than that of Scheller's We-Re-dependent formula, chiefly due to the absence of physical constraints. Subsequently, a physics-informed prediction model is introduced by considering a physical loss term. This model demonstrates comprehensive enhancements compared to the original neural network, and the average relative and standard errors for this model are reduce to 13.6% and 0.010 59, respectively. This novel model should allow for the rapid and precise prediction of the maximum spreading factor across a broad range of parameters for various applications.

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.

Motion behaviors of droplets containing Au nanoparticles on a superhydrophobic laser-induced graphene surface

The movement of nanoparticle-containing droplets on solid surfaces significantly affects the distribution of the nanoparticles and is of great interest in the fields of two-phase separation, biosensing detection, inkjet printing, and microarrays. There has been little research on the initiation and motion behaviors of colloidal droplets containing nanoparticles on superhydrophobic surfaces. Here, we prepare superhydrophobic laser-induced graphene (LIG) surfaces with excellent depinning effects using an extremely simple method and explore the formation mechanism of the depinning-LIG surfaces. The reduction of nano-graphene fibers and the increased hydroxyl group ratio after alcohol modification further enhance the hydrophobic properties of depinning-LIG, reducing its surface adhesion. The initial and continuous motion of droplets containing Au nanoparticles (AuNPs) on these superhydrophobic surfaces under airflow is studied using high-speed microscopy. The coupling effects of the droplet size, surface properties, airflow velocity, and nanoparticles on the droplet motion behaviors are analyzed. The dimensionless parameter G is incorporated to obtain the partition diagram of AuNP droplet motion behaviors on depinning-LIG surfaces, which delineate the critical conditions for droplet “oscillation,” “initiate sliding,” and “continuous rolling” as a function of system parameters. For AuNP droplets, the viscous force Fγ,p exerted by the nanoparticles on the contact line significantly affects the droplet movement behaviors. In addition, a mathematical model about the competition of dynamic forces and resistance is established to describe the motion of AuNP droplets, and the critical conditions for different motion behaviors of the droplet are clarified to guide practical applications.

A triple emulsion droplet in a uniform flow

The fluid mechanics problem of a triple emulsion droplet in a uniform creeping flow is theoretically studied. The triple emulsion, submerged in an external fluid 1, is composed of an inner spherical drop (fluid 4), covered by a spherical shell (fluid 3), which is subsequently covered by another spherical shell (fluid 2). In the absence of a body force, eight parameters are governed: the Capillary number (Ca), three viscosity ratios (λ21, λ32, λ43), two radii ratios (K, k), and two-surface tension ratios (M, m). If all surfaces remain spherical and concentric, five parameters (λ21, λ32, λ43, K, k) are sufficient. Expressions for the stream functions and the drag forces were obtained to calculate the terminal velocity of the triple emulsion falling or rising in a stagnant fluid under the influence of gravity. With gravity, four additional parameters are needed: the ratio of the buoyancy force to the external viscous force (B), and three density ratios (γ21, γ31, γ41). To remain concentric, all surfaces must have the same velocity (magnitude and direction). This results in two restricted parameters, but even then, not every combination of parameters leads to a physical solution. Our findings suggest that the terminal velocity of a triple emulsion is equal to or lower than that of a double emulsion, which is subsequently equal to or lower than that of a single drop. Similar to single and double emulsion droplets, no deformation takes place in a concentric spherical triple emulsion subjected to a gravitational field under creeping flow conditions.

Numerical simulation of submarine landslide tsunamis based on the smoothed particle hydrodynamics model

This paper establishes a SPH (Smoothed Particle Hydrodynamics) model for simulating underwater landslides based on the mixture theory. This model requires only one layer of particles, which greatly improves the computational efficiency compared with the traditional two-layer particle simulation for a mixture theory scheme. In the numerical model, based on a mixture theory, submerged landslide flow is regarded as a mixture of water and sediment phases and is discretized into a series of SPH mixed particles employing the volume fraction of the sediment phase. Using this volume fraction, a convection–diffusion term is calculated to represent the material transport between the water phase and the sediment phase. In addition, based on this volume fraction, the SPH mixed particles at any location in the considered domain are classified into three categories: (i) pure water, (ii) low-concentration suspended sediment, and (iii) high-concentration sediment. Pure water is treated as a Newtonian fluid. High-concentration sediment is modeled as a non-Newtonian fluid, and the Herschel–Bulkley–Papanastasiou rheological model is used to describe the viscous forces. The viscosity of the low-concentration suspended sediment, which acts as a transition layer between pure water and high-concentration sediment, is derived from the Chezy relation. A comparison of the numerical and experimental results demonstrates the high accuracy of the present numerical scheme. Using this validated numerical model, underwater landslides are simulated. Specifically, the effects of landslide deformation and compaction degree on the amplitudes of the surge wave crest and trough are investigated.

Preparation of ethyl cellulose bimodal nanofibrous membrane by green electrospinning based on molecular weight regulation for high-performance air filtration

Preparing bio-based air filtration membrane through green electrospinning strategy is a vital approach to alleviating environmental and energy crises. However, the development of related biomaterials and method for regulating membrane structure are still lacking. In this study, ethyl cellulose (EC) bimodal nanofibrous membrane was prepared by electrospinning using ethanol and water as solvents to achieve high-performance air filtration. A new strategy for bimodal fiber molding based on molecular weight modulation was proposed. The EC polymer chains with medium molecular weights were subject to the highest degree of inhomogeneity of solvent intrusion, and there were significant differences in viscous forces “microscopically”, leading to the formation of bimodal structure by inhomogeneous stretching of the jet. The well-defined bimodal structure endowed EC membrane with excellent air filtration performance. The filtration efficiency for PM0.3, pressure drop, quality factor were 99.11 %, 42.2 Pa, and 0.112 Pa−1, respectively. Compared to the commonly used zein, EC cost just 12.77 %, and its solution had a 50 % longer shelf life, making it a more desirable biomaterial. This work will facilitate the application of more biomaterials in air filtration, promote the green fabrication of high-performance air filtration membranes, and realize sustainable development.

A novel electric field-assisted material extrusion process for clean additive manufacturing

Material extrusion (MEX) is a type of additive manufacturing technique that is widely used in a variety of applications. However, the issue of reduced quality of printed parts caused by degraded polymer debris accumulation on the nozzle surface during the MEX process has received very limited attention. This work presents a novel electric field-assisted MEX (E-MEX) method to solve the quality issue by significantly reducing the accumulations of polymer debris on the nozzle. By applying a high-voltage power source between the nozzle and the build plate, an electrostatic force was generated to overcome the which showed great potential to reduce the accumulation of molten thermoplastic material on the nozzles. Both the E-MEX and conventional MEX methods were used to print test specimens for specific amounts of time to confirm the efficacy of the E-MEX method. 3D scanning was used to quantify the volumes of debris that had accumulated on the nozzle. Compared to the conventional MEX method, the E-MEX printing reduced debris accumulation by 47 % after about 5 h and over 80 % after about 15 h of the printing process. The changes in electric field intensity over orienting height were analyzed using numerical simulations. The relationship between electric field intensity and time spent by the nozzle during the printing process at a specific height was established. The polymer accumulation in the E-MEX process was found to be dependent on the electric field intensity and the continuous time spent by the nozzle in the weaker electric field enhanced polymer debris accumulations on the nozzle surfaces. The presented study integrates experimental observations with simulation results, revealing the mechanism of debris accumulation on the nozzle when the electric field decreased to a certain level during printing process. A numerical simulation model was developed to understand the traveling of accumulated polymer debris from the nozzle's outer surface to the printing layer under the influence of electrostatic force. The simulation results showed that the dragging of polymer debris towards the build plate occurs when the electric force acting in the tangential and normal direction is sufficient to overcome the viscous force and normal force in the polymer debris. The simulation results also showed some part of the debris remained in the crease area of the nozzle surface due to the viscous and surface tension forces prevailing over the electric force.

Mechanism and experimental investigation on the formation of micro‐triangle stepped jet in composite spinning solution

AbstractIn the field of nanotechnology, rotary jet spinning technology has garnered attention due to its unique advantages in fabricating composite nanofibers. The composite nanofibers prepared using this technology exhibit exceptional purity, uniformity, and consistency, thereby enhancing reliability and controllability in practical applications. During the process of rotary jet spinning, the spinning solution flows into the nozzle and converges at a micro‐triangle under the combined influence of centrifugal force, viscous force, surface tension, and gravity. Stepped jet refers to the flow phenomenon occurring within a channel with a gradually decreasing cross‐sectional area. In this process, an increase in the flow velocity of the composite spinning solution aids in stabilizing stretching at the micro‐triangle which is crucial for forming continuous jets. This article analyzes cone formation mechanisms for composite spinning solutions and stepped jet principles while establishing corresponding models that reflect relationships between solution velocity magnitude and parameters such as rotational speed, concentration, and nozzle diameter. Finally, polyethylene oxide (PEO)/polyvinylpyrrolidone (PVP) composite nanofibers were prepared using a rotary jet spinning device where experimental investigation focused on examining how parameters such as rotational speed, solution concentration, and nozzle diameter impact motion of spinning solution within micro‐triangle.Highlights Preparation of PEO/PVP composite nanofibers by rotary jet spinning. Presentation of cone formation mechanisms for composite solutions. The stepped injection principle was proposed. Modeling of composite solution motion. Rotational speed, solution concentration, and nozzle diameter impact motion.

Unified closure relationship for slug liquid holdup

AbstractSlug flow is a common flow pattern in pipes operating with gas–liquid mixtures. The slug flow's periodic behaviour affects the performance of multiphase transportation systems, which is generally predicted using mechanistic models. Mechanistic models are based on one‐dimensional mass and momentum conservation equations and require additional relationships to define a complete system of equations. These additional equations are usually called closure relationships. The slug liquid holdup () is one of the required closure relationships. In this paper a unified closure model for is proposed considering the energy balance and the interaction between inertial, gravitational, viscous, and surface tension forces. The model parameters' behaviour is described as a function of a new dimensionless number. The experimental data analysis shows that this number can quantitatively define two flow categories: ‘low viscosity flow’ and ‘medium/high viscosity flow’. Slug liquid holdup changes its behaviour in these regions due to the predominance of inertial–surface tension forces or gravitational–viscous forces, respectively. The proposed closure performs better than the existing mechanistic and empirical models.

Analysis of Injury Metrics From Experimental Cardiac Injuries From Behind Armor Blunt Trauma Using Live Swine Tests: A Pilot Study.

Warfighters are issued hard body armor designed to defeat ballistic projectiles. The resulting backface deformation can injure different thoracoabdominal organs. Developed over decades ago, the behind armor blunt impact criterion of maximum 44 mm depth in clay continues to be used independent of armor type or impact location on the thoracoabdominal region covered by the armor. Because thoracoabdominal components have different energy absorption capabilities, their mode of failures and mechanical properties are different. These considerations underscore the lack of effectiveness of using the single standard to cover all thoracoabdominal components to represent the same level of injury risk. The objective of this pilot study is to conduct cardiac impact tests with a live animal model and analyze biomechanical injury candidate metrics for behind armor blunt trauma applications. Live swine tests were conducted after obtaining approvals from the U.S. DoD. Trachea tubes. An intravenous line were introduced into the swine before administering anesthesia. Pressure transducers were inserted into lungs and aorta. An indenter simulating backface deformation profiles produced by body armor from military-relevant ballistics to human cadavers delivered impact to the heart region. The approved test protocol included 6-hour monitoring and necropsies. Indenter accelerometer signals were processed to compute the velocity and deflection, and their peak magnitudes were obtained. The deflection-time signal was normalized with respect to chest depth along the impact axis. The peak magnitude of the viscous criterion, kinetic energy, force, momentum and stiffness were obtained. Out of the 8 specimens, 2 were sham controls. The mean total body mass and soft tissue thickness at the impact site were 81.1 ± 4.1 kg and 3.8 ± 1.1 cm. The peak velocities ranged from 30 to 59 m/s, normalized deflections ranged from 15 to 21%, and energies ranged from 105 to 407 J. The range in momentum and stiffness were 7.0 to 13.9 kg-m/s and 22.3 to 79.9 N/m. The maximum forces and impulse data ranged from 2.9 to 11.7 kN and 1.9 to 5.8 N-s. The peak viscous criterion ranged from 2.0 to 5.3 m/s. One animal did not sustain any injuries, 2 had cardiac injuries, and others had lung and skeletal injuries. The present study applied blunt impact loads to the live swine cardiac region and determined potential candidate injury metrics for characterization. The sample size of 6 swine produced injuries ranging from none to pure skeletal to pure organ trauma. The viscous criterion metric associated with the response of the animal demonstrated a differing pattern than other variables with increasing velocity. These findings demonstrate that our live animal experimental design can be effectively used with testing additional samples to develop behind armor blunt injury criteria for cardiac trauma in the form of risk curves. Injury criteria obtained for cardiac trauma can be used to enhance the effectiveness of the body armor, reduce morbidity and mortality, and improve warfighter readiness in combat operations.