Breakup Dynamics Research Articles

The effects of poly(ethylene glycol) grafting density on the extensional solution flows of high molecular weight polyacrylamide

AbstractControlling the extensional rheological properties of solutions is of great interest for a number of applications, such as printing and coatings, as polymeric additives can modify a fluid's droplet size, formation, and breakup. We have measured the extensional flows of polyacrylamide graft poly(ethylene glycol) amine (PAM‐g‐PEGa) solutions as a function of grafting density. PAM‐g‐PEGa is synthesized with grafting densities of 2.5%, 5.5%, 8%, and 30% and extensional flow was analyzed with drop‐on‐substrate rheology. Flow time scales and profiles are then compared to understand the effects of backbone extension from the addition of side chains. At low grafting densities, the viscous friction from the added side chains is comparable to, and in some cases, counteracts the losses in extensibility to the graft polymer's backbone, leading to increases in the relaxation time of the polymer. At higher grafting densities, the extension of the backbone reduces the relaxation time. By characterizing the effects of the graft density architecture on extensional flows, we are able to fine‐tune and control the breakup dynamics of elastic solutions.

Dynamics of 7Li breakup and its influence on elastic scattering: a study of 7Li + 144Sm system* *This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (AP19680284). A.A.Ibraheem express his appreciation to the Deanship of Scientific Research at King Khalid University, Saudi Arabia, for funding this work

The angular distributions of 7Li + 144Sm elastic scattering over the energy range of 21.6–52 MeV are reanalyzed utilizing various interaction potentials. The analysis aims to study the consistency of the implemented potentials in representing the considered data and investigate the cluster nature of the weakly bound 7Li projectile. This will aid in the better understanding the impacts of 7Li breakup on the elastic scattering channel. Strong coupling to the breakup channel has a substantial impact on the elastic data and reproduces a repulsive dynamical polarization potential, which drastically diminishes the real potential strength. This reported impact was simulated by introducing a semi-microscopic repulsive DPP and by implementing the method of continuum discretized coupled channels. The analysis was also extended to understand the impact of triton transfer on the elastic scattering data.

Breakup dynamics of water-in-water droplet generation in a flow-focusing microchannel

In ATPS, the ultra-low interfacial tension makes the stable generation of droplets very difficult. In this paper, the stable and homogeneous preparation of ATPS droplets is achieved over a wide range of flow rates, and the self-similarity analysis and formation dynamics of the droplets are studied. Formation of ATPS droplets show good self-similarity. The generation process of ATPS droplets can be divided into slow squeezing, fast squeezing and rapid pinch-off stages. In the slow squeezing stage, the dimensionless minimum neck width wm/wc is linear with the time, and the absolute value of the slope increases with the capillary number of continuous phase Cac. In the rapid squeezing and rapid pinch-off stages, the wm/wc satisfies the power-law relationship with time, and the absolute value of the power-law indexes decrease with increasing Cac, and the pre-exponential factor of pinch-off stage increases with increasing Cac.

Aerial photogrammetry to characterise and numerically model an ice jam in Southern Quebec

Abstract Collecting data on the dynamic breakup of a river's ice cover is a notoriously difficult task. However, such data are necessary to reconstruct the events leading to the formation of ice jams and calibrate numerical ice jam models. Photogrammetry using images from remotely piloted aircraft (RPA) is a cost-effective and rapid technique to produce large-scale orthomosaics and digital elevation maps (DEMs) of an ice jam. Herein, we apply RPA photogrammetry to document an ice jam that formed on a river in southern Quebec in the winter of 2022. Composite orthomosaics of the 2-km ice jam provided evidence of overbanking flow, hinge cracks near the banks and lengthy longitudinal stress cracks in the ice jam caused by sagging as the flow abated. DEMs helped identify zones where the ice rubble was grounded to the bed, thus allowing ice jam thickness estimates to be made in these locations. The datasets were then used to calibrate a one-dimensional numerical model of the ice jam. The model will be used in subsequent work to assess the risk of ice interacting with the superstructure of a low-level bridge in the reach and assess the likelihood of ice jam flooding of nearby residences.

The Importance of Widespread Temperature Conditions on Breakup Characteristics: The Case of Sagavanirktok River, Alaska, USA

Daily average springtime air temperatures from four weather stations distributed along north–south and nearly east–west directions within or on the divide of the Sagavanirktok River watershed in Arctic Alaska were studied and compared with discharge measurements and field observations made from 2015 to 2021 during breakup. The results indicate that under widespread air temperature events, during El Niño, rapid and dynamic breakup can occur (promoting sediment transport along the stream), while during La Niña, slow and thermal breakup can be expected. Due to these climate pattern effects, open channel conditions (i.e., ice-free channels) are reached earlier (18 May 2015) during El Niño and later (7 June 2021) during La Niña.

Characterizing the SpraySyn burners with MMC-LES

This paper presents a detailed validation of a modeling framework and its implementation for the simulation of flame spray pyrolysis (FSP) using different nozzle geometries of the so-called SpraySyn burner. Gas, liquid and particulate dynamics are compared against experimental data from literature as well as our own laser-Doppler anemometry, phase-Doppler anemometry and multi-line OH laser-induced fluorescence thermometry imaging measurements. The modeling framework consists of large eddy simulations (LES) coupled to the sparse-Lagrangian multiple mapping conditioning (MMC) model, a Lagrangian spray solver and a sectional description of the population balance equation. Simulations start downstream of the burner exit planes where turbulent inlet data for the gas and liquid phases are generated by independent LES that use a 1-Fluid method to capture the dynamics of the liquid jet break-up. The gas and liquid dynamics are validated and analyzed for an ethanol spray flame in the SpraySyn1 and SpraySyn2 burners. In these burners iron(III) oxide particulates are synthesized from iron pentacarbonyl (IPC)-ethanol solutions with varying IPC concentrations. The results demonstrate the very good predictive capabilities of the MMC modeling framework for the gas and liquid phases. The predictions of the particulate formation are validated by comparison of elastic light scattering (ELS) signals from experiments against synthetic ELS signals calculated from the simulations. Results are of reasonable accuracy for the SpraySyn1 FSP series but indicate an imbalance between particulate growth and dilution with the surrounding gas. Predictions for the SpraySyn2 FSP series are consistent with SpraySyn1 results and indicate an increased product particulate size due to an increased residence time downstream of the heat release zone.

Breakup of thin liquid films with viscous interfaces

Thin liquid films are ubiquitous in nature and have many practical applications. From biological films to the curtain coating process, thin films are present in both large and small scales. Despite their importance, understanding the stability of these films remains a significant challenge due to the fluid–fluid interface that is free to deform, affected by interfacial tension and complex rheological behavior. Instabilities in thin films are often caused by van der Waals attractions, which can lead to the rupture of the layer. To investigate the rupture dynamics, numerical methods are commonly used, such as asymptotic derivations of the lubrication theory or interface tracking methods. In this paper, we present a computational study of the breakup dynamics of a stationary thin liquid sheet bounded by a passive gas with a viscous interface, using the arbitrary Lagrangian–Eulerian method and the Boussinesq–Scriven constitutive law to model the rheological behavior. Our results demonstrate that the stability of thin liquid films is influenced by both surface rheology and disjoining effects and that the viscous character of the interface can delay sheet breakup, leading to more stable films.

Impact of hybrid surfaces on the droplet breakup dynamics in microgravity slug flow: A dynamic contact angle analysis

Microfluidic devices, which enable precise control and manipulation of fluids at the microscale, have revolutionized various fields, including chemical synthesis and space technology. A comprehensive understanding of fluid behavior under diverse conditions, particularly in microgravity, is essential for optimizing the design and performance of these devices. This paper aims to investigate the effects of discontinuous wettability on droplet breakup structures under microgravity conditions using a microchannel wall. The approach we adopt is underpinned by the volume-of-fluid methodology, an efficient technique renowned for its accurate resolution of the fluid interface in a two-phase flow. Furthermore, a modified dynamic contact angle model is employed to precisely predict the shape of the droplet interface at and near the wall. Our comprehensive model considers influential parameters such as slug length and droplet generation frequency, thereby providing crucial insights into their impact on the two-phase interface velocity. Validated against existing literature data, our model explores the impact of various configurations of discontinuous wettability on breakup morphology. Our findings highlight the significance of employing a dynamic contact angle methodology for making accurate predictions of droplet shape, which is influenced by the wall contact angle. Emphasis is placed particularly on the effects of slug length and droplet generation frequency. Notably, we demonstrate that the use of a hybrid surface at the junction section allows for precise control over the shape and size of the daughter droplets, contrasting with the symmetrical division observed on uniformly hydrophilic or superhydrophobic surfaces. This study contributes valuable insights into the complex dynamics of the droplet breakup process, which has profound implications for the design and optimization of microfluidic devices operating under microgravity conditions. Such insights are further poised to augment applications in space exploration, microreactors, and more.

The dynamics of bubble breakup in heart-shaped microchannels: Effect of structure

Heart-shaped microreactor (Advanced Flow Reactor, AFR) has been widely applied in industry, in which heart-shaped structure is important to break droplet or bubble up for mass transfer enhancement. The dynamics of bubble breakup in AFR (Channel A) and an improved AFR (Channel B) was visually investigated. Breakup regime with permanent obstruction was observed to undergo three stages: squeezing, transition and pinch-off. Results indicated that bubble breakup in Channel B has wider operating range, shorter time than those in Channel A. Moreover, the influences of various factors on bubble breakup in Channel B were studied systematically. It was found that the mother length (l0/wc) has only slight impact on breakup process, total capillary number (Ca) has always positive promoting effect on breakup during each stage, increasing liquid phase viscosity (μL) could facilitate the breakup in the squeezing and transition stages, while delay the thinning rate of bubble neck in the pinch-off stage.

A comprehensive field investigation of the dynamic break-up processes on the Chaudière River, Quebec, Canada

Abstract The Chaudière River in Quebec, Canada, is well known for its frequent ice jam flooding events. As part of a larger watershed research program, an extensive field campaign has been carried out during the 2018–2019 and 2019–2020 winter seasons to quantify the spatiotemporal characteristics of the break-up processes along the Chaudière River. The results showed that mid-winter ice jams have formed in the Intermediate Chaudière and persisted until spring break-up. Spring break-ups were initiated in the Upper Chaudière, and then, almost simultaneously, in the Intermediate and Lower Chaudière reaches. The break-up in the Intermediate Chaudière usually lasts longer than the rest of the river since the slope is much milder, and the occurrence of mid-winter ice jams has been seen to delay the ice clearing. A reach-by-reach characterization of the cumulative degree day of thawing and discharge thresholds for the onset of break-up has been identified. During the field campaign, 51 ice jams were documented together with their location, length, date of formation, and the morphological feature triggering jam formation. Break-up patterns, hydrometeorological thresholds of ice mobilization, and ice jam sites identified in this study can serve as a basis for the implementation of an early warning system.

An improved three-dimensional lattice Boltzmann-volume of fluid (LB-VOF) method for simulation of laminar liquid jet breakup with high density ratio

Lattice Boltzmann method (LBM) has been widely developed in the past decade, while most of the previously presented LBMs are confined to two-phase problems with a low-density ratio. In the present study, we developed the free surface model based on the volume of fluid (VOF) method to a three-dimensional two-phase LBM (LBM-VOF) and utilized this new model to simulate the breakup of a water jet in the air. This problem is characterized by high density and viscosity ratios with the values of about 830 and 58, respectively. Numerical codes are implemented in the open-source library of parallel Lattice Boltzmann solver (PALABOS), and the results are compared and validated against experimental and published numerical outcomes. It is shown this new model could properly confine spurious currents. Afterward, the LBM-VOF model is used to simulate different water jet regimes, including periodic dripping, dripping faucet, and jetting regimes. Furthermore, the dynamics of fluid jet formation and droplet breakup are comprehensively discussed in different ranges of the Weber number (0.063 < We < 6) and three nozzles with different sizes. Results show that the proposed LBM-VOF model is capable of simulating all the three mentioned regimes and their specific characteristics. The proposed model accurately predicts the ranges of critical Weber number (2.4 < We < 2.84) at which the regime transition from periodic dripping to jetting occurs; which is in agreement with the theoretical relation. Moreover, when the dripping to jetting transition occurs, the length of breakup and the frequency of droplet production increased sharply by approximately 3.6 and 3, respectively, while the volume of produced droplets decreased by about 2.4.

Statistical Characterization of Bubble Breakup Flow Structures in Swirl-Type Bubble Generator Systems

The bubble breakup pattern on a swirl-type bubble generator (MBG) with water and air fluids was experimentally studied. The bubble breakup pattern was analyzed visually and characterized using several parameters such as Pressure Drop (∆P), Kolmogorov Entropy, Standard Deviation, and DWT (Discrete Wavelet Transform), which were taken from the extraction of pressure signals at the water inlet and outlet of the bubble generator. The wavelet spectrum of the measured signal was shown to identify the overall bubble breakup pattern, and the wavelet variance vector is proposed as a character vector to identify the bubble breakup pattern. The results show that there were three types of different flow breakup patterns: (1) static breakup, (2) dynamic breakup, and (3) tensile breakup. The observed bubble breakup sub-patterns can be categorized into tensile, moderate tensile, high tensile, dynamic, low dynamic, static, and high static sub-patterns. The static clustered breakup pattern has the highest wavelet energy compared to the tensile and dynamic clustered breakup.

Simulation of radioactive plume transport in the atmosphere including dynamics of particle aggregation and breakup

Accurate prediction of the atmospheric transport of debris particles relies heavily on our knowledge of the size distribution of the particles within a debris cloud. Assuming a fixed particle size during simulations is not always viable since the size distribution of the debris can change during transport. Various microphysical processes, such as aggregation and breakup, influence debris particles and dictate any changes to the size distribution. To track those changes that can occur, a population balance model can be adopted and instituted within a model framework. Nonetheless, many of the models that simulate the transport of radioactive debris following a device-driven fission incident have historically neglected to consider these processes. As such, this work describes our effort to develop a modeling framework capable of simulating the transport and deposition of a radioactive plume generated from a fission incident with a dynamic population balance including particle aggregation and breakup. The impact of aggregation and breakup, individually and collectively, on the particle size distribution is explored using the developed framework. When simulating aggregation, for example, six mechanisms, including Brownian coagulation, the convective enhancement to Brownian coagulation, van der Waals-viscous force correction for Brownian coagulation, gravitational collection, turbulent inertial motion, and turbulent shear, are considered. Brownian coagulation and its corrections have, as one would expect, a large impact on relatively small aggregates. Aggregates with a diameter that is less than or equal to 1.0 μm, for instance, comprise 50.6 vol % of all aggregates in the absence of aggregation and 31.2 vol % when Brownian coagulation and its corrections are considered. Gravitational collection and, to a much lesser extent, turbulent shear and turbulent inertial motion are, conversely, of great importance to relatively large aggregates (i.e., diameter greater than 3.0 μm). Additionally, the individual effects of atmospheric and particle parameters, such as wind speed and particle density, are examined. Of the parameters examined, turbulent energy dissipation and aggregate fractal dimension (i.e., aggregate shape with lower values representing more irregular particles) were of substantial importance since both terms directly impact aggregate stability and, by extension, the breakup rate. Large-scale transport and deposition simulations in a dry atmosphere are also presented and discussed as a proof of concept.

Formation of droplets of yield stress non-Newtonian fluids at T-junctions within parallelized microchannels

The effects of yield stress on the flow pattern, and the breakup mechanism, formation frequency and size of droplets at T-junctions within symmetrical parallelized microchannels are investigated experimentally. Carbopol gel and cyclohexane with 5 wt% span 20 are used as dispersed and continuous phases, respectively. Three flow patterns are observed, including parallel flow, jetting flow-elongated droplets, and dripping flow-slug/cloud droplets. Based on the yield stress characteristics, the breakup dynamics of the liquid–liquid interface during droplet formation under different flow patterns, flow rates and Carbopol concentrations are studied. The results reveal that the yield stress would enlarge the thickness of liquid film, weaken the squeezing force of the continuous phase and enhance the resistance of the dispersed phase, which greatly slow down the droplet formation. Finally, the stable and uniform operating ranges of liquid–liquid two-phase flow in yield stress non-Newtonian fluids are obtained, and the semi-empirical formulas for droplet size prediction are established.

Microscopic stabilization mechanism of nanoparticle-laden droplets under external electric fields: A molecular dynamics study

Electric dehydration process of crude oil is frequently accompanied by water droplet breakup, resulting in efficiency reduction of oil-water separation. To reveal the microscopic stabilization mechanism of nanoparticle-laden droplet, molecular dynamics (MD) simulations were adopted to investigate the electro-deformation and breakup dynamics. Good qualitative and quantitative agreements were observed between the present simulations and the literature experiments. The effects of electric fields (electrocapillary numbers and frequencies) and nanoparticles (concentrations and types) on the droplet stability were analyzed in terms of intermolecular total interactions. The analysis of quantum chemical calculations and weak interactions shows that stable hydrogen bonds can be formed between the silicon dioxide (SiO2) and water (H2O) molecules, enhancing droplet stability. The droplet stability under alternating current (AC) electric fields are higher than that under direct current (DC) electric fields, and the stability increases with increasing AC frequencies. At the total interactions of the nanoparticle-laden droplet system after switch-off electric field stronger than that after switch-on electric field, fast droplet recovered process was observed. The modified SiO2 NPs can efficiently enhance droplet stability, and high nanoparticle (NP) concentrations lead to high droplet stabilities. Eventually, the ranking of NP-laden droplet stabilities is roughly consistent with that of droplet pair electrocoalescence efficiencies, i.e., CAC (SiO2 modified with 6 carboxylic acid chains) > CAAL (SiO2 modified with 3 carboxylic acid chains and 3 alkane chains) > ALC (SiO2 modified with 6 alkane chains) > SiO2. The results of this work will be potentially valuable for optimizing the design of compact and efficient oil-water separators.

Experimental Study on Breakup Characteristics of Hollow Cone Spray in Gas Crossflow

Hollow cone spray with a medium spray half-cone angle (in the range of 36°–45°) exposed to a gaseous crossflow is a situation that has been extensively investigated experimentally. In this experiment, flow visualization techniques are employed to examine the initial liquid sheet thickness at the nozzle orifice exit and the sheet breakup process. The dynamics of the primary breakup of the sheet is analyzed based on the observations of the sheet breakup in the near-nozzle region. The experimental results show that the breakup mechanism of the liquid sheet varies greatly depending on liquid centrifugal momentum and aerodynamic force. Four distinct breakup modes are observed, and the breakup regimes are mapped in the parametric space based on the liquid Weber number (84–2175) and the liquid-to-air momentum ratio (22–8455). It is observed that the leeward side of the sheet is dominated by shear oscillation breakup within the range of the liquid-to-air momentum ratio less than 600. The influences of the aerodynamic Weber number on breakup frequency and the number of surface waves observed on the leeward side sheet are discussed by analyzing the spray images. The breakup-regime transition criteria for hollow cone spray in crossflow and the trajectory of spray in crossflow are proposed by employing a multivariable regression method.

Universal non-monotonic drainage in large bare viscous bubbles

Bubbles will rest at the surface of a liquid bath until their spherical cap drains sufficiently to spontaneously rupture. For large film caps, the memory of initial conditions is believed to be erased due to a visco-gravitational flow, whose velocity increases from the top of the bubble to its base. Consequently, the film thickness has been calculated to be relatively uniform as it thins, regardless of whether the drainage is regulated by shear or elongation. Here, we demonstrate that for large bare bubbles, the film thickness is highly nonuniform throughout drainage, spanning orders of magnitude from top to base. We link the film thickness profile to a universal non-monotonic drainage flow that depends on the bubble thinning rate. These results highlight an unexpected coupling between drainage velocity and bubble thickness profiles and provide critical insight needed to understand the retraction and breakup dynamics of these bubbles upon rupture.

Non-Newtonian droplet breakup in a T-junction microdevice containing constriction induced asymmetric parallel branches

Here, we describe the breakup and post-breakup dynamics of a non-Newtonian droplet of xanthan gum aqueous solution in asymmetric parallel branch microdevices. Our experimental results reveal that the droplet breakup regimes, namely, obstruction, tunnel, combined, non-breakup, and parallel, are the functions of xanthan gum concentration and the continuous phase flow rate. We examined the influence of fluid properties on droplet breakup stages by varying the xanthan gum concentration in an aqueous solution that exhibited increasing shear-thinning and elastic properties with its concentration. Four sequential stages (squeezing, transition, pinch-off, and filament thinning) are identified during the droplet breakup process. We found that upstream pressure controlled the squeezing stage, and fluid properties mainly steered the filament rupture stage. A complex interaction between elastic, capillary, and inertial forces further divided the final stage into the stretching and fluid-drainage stages. The Hencky strain characterized the formation of a persistent cylindrical filament in the stretching stage that decayed exponentially in the fluid-drainage stage. Eventually, this study highlights the significance of parallel branches with asymmetric geometric confinements on droplet splitting. Enhanced asymmetry is observed for the elongated filament, emphasizing the dominance of feedback from the downstream confinement.

Evolution of potassium bubbles and its influences on the recrystallization behaviour of swaged tungsten rods with high potassium doping level

Recrystallization temperature (RCT) is a key factor influencing the working temperature window of tungsten (W)-based plasma facing materials (PFMs). To investigate the effects of potassium (K)-bubbles on the recrystallization behaviour of the W rods with a high K-doping level of 96 ppm, large size sintered K-doped W ingot with a diameter of 70 mm (total weight of 42 kg) was fabricated via powder metallurgy route. The ingot was reduced to various diameters with logarithmic strains up to 3.53 by a series of high-speed forging and swaging. Then the rods were treated by 1-h isochronal annealing at temperatures ranging from 1350 °C to 2050 °C in the H2 atmosphere. Results showed that as the logarithmic strain increased, the RCT increased and reached a maximum value of 1820 °C at the logarithmic strain of 2.95. Then, it decreased at a higher logarithmic strain of 3.53. The K-tubes in the rods with heavy deformation have experienced a ‘dynamic break-up’ during swaging. This influenced the evolution and morphology of K-bubbles in the subsequent annealing. The RCT of high K-doped W with heavy deformation was determined by the synergetic effects of the internal stored energy and the morphology of K-bubbles.

Investigating Electrosprayed Droplets Using Particle-into-Liquid Sampling for Nanoliter Electrochemical Reactions

Electrospray ionization (ESI) is a powerful ionization technique that can generate charged solvent droplets and bare analyte ions from sample solutions. Despite seeing extensive use in mass spectrometry due in part to the low internal energy deposited into the ions formed during ionization, some unknowns persist regarding the exact dynamics of droplet breakup and molecule behavior during spray, and research is still underway regarding how various types of molecules acquire charge during the ESI process. Previously, the authors introduced a novel aerosol measurement technique, particle-into-liquid sampling for nanoliter electrochemical reactions (PILSNER). The current work introduces a new method utilizing PILSNER for the examination of the particles generated during ESI using simple analysis techniques with a commercially available potentiostat. This technique is applied in this work for the detection of charges on electrosprayed droplets, including the estimation of the number of charges on individual ESI droplets using a fluorescent proxy. This technique provides an additional tool for the exploration of the complex process of droplet generation and ion liberation during ESI.