Breakup Point Research Articles

Single bubble breakup in the flow field induced by a horizontal jet—The experimental research

AbstractBubble breakup in multiphase reactors has a direct and important impact on the mass transfer and reaction process. This paper experimentally investigated the single bubble behaviors of deformation and breakup under the affecting of a jet submerged in a water‐filled tank. The dispersed phase motion was captured by a high speed camera, while the continuous phase flow field was analyzed by Particle Image Velocimetry. By changing the downstream location of bubble generation, the liquid flow rate and the initial bubble size, the breakup processes were analyzed and discussed. The breakup point, break pattern, and distribution of daughter bubbles were summarized. The position where the bubble gets the maximum acceleration was defined as the shear position, and the forces on the bubble at the shear position had a significant impact on whether breakup will occur. The expected bubble number, which could reflect a combination of the breakup probability and daughter bubbles distribution, was defined and found to be directly proportional to the capillary number of bubbles at the shear position. The research result will contribute to promoting the understanding and control of multiphase flow, and providing a theoretical basis and technical support for the design and optimization of multiphase reactors.

Laterally Confined Volcanic Successions (LCVS); recording rift-jumps during the formation of magma-rich margins

Seaward Dipping Reflectors (SDRs) are a characteristic feature of magma-rich margins, and represent the generation of large volumes of flood basalts at the point of continental breakup. A number of recent studies provide new insights into the emplacement and tilting of SDRs and conclude that the majority of SDRs are contained within new magmatic crust that has a close affinity to oceanic crust. However, the process by which these initial magmatic systems evolve into a fully established spreading centre remains poorly understood. Several characteristic features of magma-rich margins may be explained by the occurrence of rift-jumps during SDR emplacement, yet the cause and prevalence of such rift-jumps remain unknown.Here we constrain the 3D geometry of the continent–ocean transition in the Orange Basin, offshore South Africa. This allows us to test if, where and why such rift jumps occur. Our results demonstrate an order of along-strike segmentation previously unobserved in these settings. We demonstrate that the SDR belt is disrupted by the occurrence of a volcanic-stratigraphic package, defined as the Laterally Confined Volcanic Succession (LCVS), not previously identified on a rifted margin. We interpret this as a magmatic spreading centre that was abandoned by a subsequent rift-jump. Identification of LCVSs is important for two reasons. First, we argue that the LCVS formed via the same process as SDRs, and hence provides a unique example of SDR geometry prior to their separation onto conjugate plates. Second, as we can map out the 3D geometry of the LCVS and SDRs, we propose that rift-jumps during magma-rich margin formation may be fundamental to the establishment of a laterally continuous incipient spreading centre.

Particle directed dual-fluid flow driven by electrowetting for controllable multiway light valves

High efficiency and position controllable multiway light valves are achieved by electrowetting-driven and magnetic particle (MP)-directed oil film dewetting in microscale spaces. The non-transparent oil phase can be attracted to oleophilic MPs and repelled from hydrophilic MPs to adjust the oil film distribution in a microwell (valve area). Thus, in an oil-water dual-fluidic system, the dewetting and breakup point of an oil film can be modulated when driven by electrowetting. By introducing a MP, both the switching speed and opening ratio of a light valve (microwell) are increased, and the time of both starting to open and reaching the maximum opening ratio is reduced. Oleophilic MPs with larger size show better controllability than hydrophilic MPs with smaller size. A 16-way spatial valve is achieved by magnetically moving one MP in a single microwell. Such a phenomenon is also demonstrated on a large area device with high-density microwells, suggesting high potential for optical valves or display applications.

Rayleigh Instability-Assisted Satellite Droplets Elimination in Inkjet Printing.

Elimination of satellite droplets in inkjet printing has long been desired for high-resolution and precision printing of functional materials and tissues. Generally, the strategy to suppress satellite droplets is to control ink properties, such as viscosity or surface tension, to assist ink filaments in retracting into one drop. However, this strategy brings new restrictions to the ink, such as ink viscosity, surface tension, and concentration. Here, we report an alternative strategy that the satellite droplets are eliminated by enhancing Rayleigh instability of filament at the break point to accelerate pinch-off of the droplet from the nozzle. A superhydrophobic and ultralow adhesive nozzle with cone morphology exhibits the capability to eliminate satellite droplets by cutting the ink filament at breakup point effectively. As a result, the nozzles with different sizes (10-80 μm) are able to print more inks (1 < Z < 38), for which the nozzles are super-ink-phobic and ultralow adhesive, without satellite droplets. The finding presents a new way to remove satellite droplets via designing nozzles with super-ink-phobicity and ultralow adhesion rather than restricting the ink, which has promising applications in printing electronics and biotechnologies.

Instability of gas-surrounded Rayleigh viscous jets: Weakly nonlinear analysis and numerical simulation

The instability of gas-surrounded Rayleigh viscous jets is investigated analytically and numerically in this paper. Theoretical analysis is based on a second-order perturbation expansion for capillary jets with surface disturbances, while the axisymmetric two-dimensional, two-phase simulation is conducted by applying the Gerris code for jets subjected to velocity disturbances. The relation between the initial surface and velocity disturbance amplitude was obtained according to the derivation of Moallemi et al. [“Breakup of capillary jets with different disturbances,” Phys. Fluids 28, 012101 (2016)], and the breakup lengths resulting from these two disturbances agree well. Analytical and numerical breakup profiles also coincide satisfactorily, except in the vicinity of the breakup point, which shrinks forcefully. The effects of various parameters (i.e., oscillation frequency, Reynolds number, Weber number, and gas-to-liquid density ratio) have also been examined by comparing spatial growth rate, second-order disturbance amplitude, breakup length, and the breakup profiles at low frequency, where obvious satellite droplets form, versus different parameters. In addition, the competition between Rayleigh instability and Kelvin-Helmholtz instability has been examined using an energy approach.

A novel noninvasive ocular surface analyzer for the assessment of dry eye with Meibomian gland dysfunction.

Meibomian gland dysfunction (MGD) is a major cause of dry eye, and the purpose of the present study was to evaluate the differences between dry eye patients with MGD and controls using a novel noninvasive ocular surface analyzer. A total of 33 dry eye patients with MGD and 31 controls were enrolled in the present study. Testing included administration of the Ocular Surface Disease Index (OSDI), followed by Keratogragh 5M (Oculus, Wetzlar, Germany), measurements of the noninvasive tear film break-up times (NITBUTs), the first tear film break-up point and the morphology of meibomian gland. Meibomian gland loss (MGL) on the upper lid was evaluated using noncontact meibography. The first NITBUT (NITBUTf) was significantly shorter than the average NITBUT (NITBUTav; Mann-Whitney U-test, P<0.01). There was a weak negative Spearman correlation between NITBUTf and OSDI (rs=-0.251, P=0.046) as well as between NITBUTav and OSDI (rs=-0.250, P=0.046). Furthermore, MGL showed a statistically significant Spearman correlation with OSDI (rs=0.562; P<0.01). In the MGD group, NITBUTf was significantly shorter (P<0.01), and MGL and OSDI score were significantly greater (P<0.01 and <0.01, respectively) than in the control group. In the MGD group, the first tear film break-up point was most frequently located in the inferonasal quadrant, while it was most frequently located in the supertemporal quadrant in the control group, and there was a significant difference with this regard (χ2=3.937, P=0.047). In the MGD group, there were significantly more breakups in the lower quadrant than in the upper quadrant (P=0.011), whereas no differences in the number of breakups in each quadrant were observed in the control group (P=0.429). Furthermore, there was no significant difference in the breakups in the lower quadrants of the two groups (χ2=0.525, P=0.469). In the MGD group, there were significantly more breakups in the lower quadrant than in the upper quadrant (P=0.011), whereas no differences in the number of breakups in each quadrant were observed in the control group (P=0.429). Furthermore, there was no significant difference in the breakups in the lower quadrants of the two groups (χ2=0.525, P=0.469). As the NITBUTs showed only a weak correlation with OSDI, they may not be a strong indicator of the OSDI. However, MGL indicated changes of meibomian gland morphology in the MGD group and the first tear film break-up point was likely located in the inferonasal quadrant in the MGD group.

Bubble pinch-off in Newtonian and non-Newtonian fluids

Bubble pinch-off is a rapid process and until now is not well-understood especially for the final stage near the breakup point. In this work, we aim at investigating the air bubble pinch-off at a submerged nozzle in various fluids, including Newtonian and non-Newtonian fluids. Different fluids exert different effects on the pinch-off dynamics as well as shape evolution immediately after pinch-off. A scaling law was applied to describe the bubble pinch-off in Newtonian fluids and the exponents: b=0.5 for low viscosity fluids and b=1 for high viscosity fluids, are in a good agreement with the conventional values predicted by the numerical simulation. For bubbles in non-Newtonian fluids, the pinch-off dynamics is mainly governed by the fluid rheology. The universal scaling exponent exists between 0.5 and 1 for low shear-thinning fluids while a non-universal character occurs for bubble pinch-off in high shear-thinning fluids. Our experimental results were confirmed by the numerical simulation.

A slender drop in a nonlinear extensional flow

The deformation of a slender drop in a nonlinear axisymmetric extensional and creeping flow has been theoretically studied. This problem, which was first suggested by Sherwood (J. Fluid Mech., vol. 144, 1984, pp. 281–295), is being revisited, and new results are presented. The problem is governed by three dimensionless parameters: the capillary number ($\mathit{Ca}\gg 1$), the viscosity ratio ($\unicode[STIX]{x1D706}\ll 1$), and the nonlinear intensity of the flow ($E\ll 1$). Contrary to linear extensional flow ($E=0$), where the local radius of the drop decreases monotonically (in the positive $z$ direction), in a nonlinear extensional flow ($E\neq 0$), two possible steady shapes exist: steady shapes (stable or unstable) with the local radius decreasing monotonically, and steady shapes (unstable) where the local radius of the drop has a local maximum, besides the one at the centre of the drop. Similar to linear extensional flow, the addition of nonlinear extensional effects does not change the end shape of the steady drop, which has pointed ends. A stability analysis has been done to distinguish between stable and unstable steady shapes and to determine the breakup point. Time-dependent studies reveal three types of breakup mechanism: a centre pinching mode, indefinite elongation, and a mechanism that remind us of tip-streaming, where a cusp is developed at the end of the drop.

Penetration and breakup of liquid jet in transverse free air jet with application in suspension-solution thermal sprays

The penetration and breakup of water jets in transverse free air jets are experimentally studied at room conditions. After coming out of an orifice and forming a cylindrical jet, water interacts with a free air jet and disintegrates. In the current work, the effects of the instabilities of cylindrical liquid jets, the distance between the liquid orifice and gas nozzle, and the ratio of liquid orifice diameter to the gas nozzle diameter, on the breakup mechanisms and liquid structure are investigated. Moreover, general correlations for spray trajectory and location of the liquid column breakup point are developed. Experimental results indicate that the breakup mechanisms are mainly controlled by the gaseous and liquid Weber numbers. Like other studies, four breakup regimes, namely capillary, bag, multimode, and shear breakup are observed. It is found that, due to the presence of instabilities on the cylindrical liquid jet, large ligaments are formed close to the interaction point of liquid and gas flows. Furthermore, results indicate that the location of liquid column breakup point is mainly dependent on the momentum flux ratio, and perturbations on the liquid jet. This fundamental study is essential to investigate the spray structure of a suspension-solution jet in plasma spray.

Regional Differences in Tear Film Stability and Meibomian Glands in Patients With Aqueous-Deficient Dry Eye.

To noninvasively investigate regional differences in tear film stability and meibomian glands in patients with aqueous-deficient dry eye. Forty-nine dry eyes and 31 normal eyes were analyzed. A corneal topographer with a tear film scanning function was used for noninvasive tear film break-up time (NI-TFBUT) measurements and meibomian gland observations. The NI-TFBUT values and location of the first tear film break-up point were recorded in four quadrants. Meibomian gland loss was graded for each eyelid using meiboscores. Lid margin abnormality was scored from zero to four according to the number of existing abnormalities. The NI-TFBUT values and meiboscores were compared between two groups, and regional differences in NI-TFBUT values and meiboscores were analyzed. Also, the correlation between the NI-TFBUT and ocular surface examination results were investigated. The NI-TFBUT values and meiboscores were significantly lower and higher, respectively, for the dry eye group than for the normal group. In the dry eye group, the occurrence rate for first tear film break-up was the highest in the inferior nasal quadrant, and the mean meiboscore was significantly higher for the upper eyelids than for the lower eyelids. The NI-TFBUT and lid margin abnormality scores showed a weak negative correlation, and the NI-TFBUT values and meiboscores showed no correlation. Compared to normal eyes, aqueous-deficient dry eyes show significant regional differences in tear film stability and meibomian glands. Considering these regional differences, the overall observation of the ocular surface, including both upper and lower eyelids, will aid clinicians in understanding this condition better.

Gas–Liquid Flow Dispersion in Micro-Orifices and Bubble Coalescence With High Flow Rates

The flow of microbubbles in millichannels with typical dimensions in the range of few millimeters offers a reduced pressure loss with simultaneous large specific contact surface. The transformation of pressure into kinetic energy creates secondary flow in micro-orifices, which results in continuous bubble dispersion. In this work, bubble flow through different orifices and channel modules with widths up to 7 mm are experimentally and numerically studied. The effect of the orifice dimensions on bubble sizes is evaluated for hydraulic diameters of 0.25–0.5 mm with different aspect ratios. To provide larger residence times of the generated dispersions in the reactor, several channel structures are analyzed to offer less coalescence. Volume flow rates of 10–250 mL/min are studied with various phase ratios. Bubble diameters are generated in the range of less than 0.1–0.7 mm with narrow size distributions depending on the entire flow rate. Opening angles of the orifices above 6 deg resulted in flow detachments and recirculation zones around the effluent jet. The first break-up point is shifted closer to the orifice outlet with increasing velocity and hydraulic diameter. The entire break-up region stays nearly constant for each orifice indicating stronger velocity oscillations acting on the bubble surface. Linear relation of smaller bubble diameters with larger energy input was identified independent from Reynolds number. Flow detachment and coalescence in bends were avoided by an additional bend within the curve based on systematically varied geometrical dimensions.

Two-phase microfluidics in electrowetting displays and its effect on optical performance.

Driving microfluidic flow in micropixels by electrowetting to realize light switches and displays is of both practical and fundamental significance. The electro-optical performance related to microfluidic behavior needs to be clarified to optimize device functions. In this article, the microfluidic performance in electrowetting display devices was categorized according to the oil-water interface shape and response. The oil film movement was divided into vertically "thinning" and transversally "opening," for which the "thinning" process was found the key factor determining the pixel switching speed rather than the "opening" process. Therefore, the breakup point and the oil film thickness were critical, which could be controlled by surface wettability and oil volume. We have also realized a new oil filling method with controllable dosing volume assisted by the microfluidic creation of microdroplets. This study could help quantitatively understand electrowetting display performance in both its theoretical and practical aspects.

A lattice Boltzmann study of the effects of viscoelasticity on droplet formation in microfluidic cross-junctions.

Based on mesoscale lattice Boltzmann (LB) numerical simulations, we investigate the effects of viscoelasticity on the break-up of liquid threads in microfluidic cross-junctions, where droplets are formed by focusing a liquid thread of a dispersed (d) phase into another co-flowing continuous (c) immiscible phase. Working at small Capillary numbers, we investigate the effects of non-Newtonian phases in the transition from droplet formation at the cross-junction (DCJ) to droplet formation downstream of the cross-junction (DC) (Liu and Zhang, Phys. Fluids. 23, 082101 (2011)). We will analyze cases with Droplet Viscoelasticity (DV), where viscoelastic properties are confined in the dispersed phase, as well as cases with Matrix Viscoelasticity (MV), where viscoelastic properties are confined in the continuous phase. Moderate flow-rate ratios Q≈O(1) of the two phases are considered in the present study. Overall, we find that the effects are more pronounced with MV, where viscoelasticity is found to influence the break-up point of the threads, which moves closer to the cross-junction and stabilizes. This is attributed to an increase of the polymer feedback stress forming in the corner flows, where the side channels of the device meet the main channel. Quantitative predictions on the break-up point of the threads are provided as a function of the Deborah number, i.e., the dimensionless number measuring the importance of viscoelasticity with respect to Capillary forces.

Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry.

Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of ∼2.2, and their size is 1.4 ± 0.4 mm, which is large, compared to the Kolmogorov length scale (η = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., dfrag ∼ σ(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude.

Mass transfer around slender drops in an extensional flow: Inertial effects at large peclet numbers

AbstractThe exchange of mass between a slender drop and a viscous liquid in an axisymmetric extensional flow and at large Peclet numbers is examined. Four cases are discussed: an inviscid drop and a viscous drop, under both creeping flow conditions and when the external flow has a weak amount of inertia. Solutions are presented as a function of the capillary number (Ca ≫ 1), the viscosity ratio (κ ≪ 1), the external Reynolds number (Re ≪ 1), and the Peclet number (Pe ≫ 1). The results suggest that the steady mass transfer rate, to or from the slender drop, is proportional to the elongation rate to the (relative) high power of 3/2. In general, as inertia increases, the drop becomes thinner and longer, and the average tangential surface velocity and the surface area increase, resulting in larger mass transfer rates, especially near the breakup point.

Pulsation in Bag Breakup of Round Liquid Jets in Crossflow

An experiment was conducted to investigate bag breakup process of round liquid jets in crossflow. The objective of this study is to research pulsation law. Specifically, this study measures the onset position of bag, the breakup position of bag, the breakup position of the jet. High-speed camera was used to observe the formation and breakup of bags. The diameter of the nozzle used in the experiment was 0.5mm, 0.8mm, 1mm. The test liquid was tap water. Wea number covers the range of 6~30, and liquid-to-air momentum flux ratio varied from 22 to 211. Present results indicate that in the direction perpendicular to the gas flow, the dimensionless pulsating amount of the onset point of bags (yonset/d) is linear to q, while the dimensionless pulsating amount of breakup point of bags (ybag/d) and the dimensionless pulsating amount of breakup point of the jet (yjet/d) is linear to ln (q). The dimensionless pulsating amount of these points in the direction of gas flow is irregular.

Post-breakup solutions of Navier-Stokes and Stokes threads

We consider the breakup of a fluid thread, neglecting the effect of the outside fluid (or air). After breakup, the solution of the fluid equations consists of two threads, receding rapidly from the point of breakup. We show that the bulk of each thread is described by a similarity solution of slender geometry (which we call the thread solution), but which breaks down near the tip. Near the tip of the thread the thread solution can be matched to a solution of Stokes' equation, which consists of a finger of constant spatial radius, rounded at the end. Very close to breakup, the thread solution balances inertia, viscosity, and surface tension (Navier-Stokes case). If however the fluid viscosity is large (as measured by the dimensionless Ohnesorge number), some time after breakup the thread solution consists of a balance of surface tension and viscosity only (Stokes case), and the thread profile can be described analytically.

Evolution of core–shell structure: From emulsions to ultrafine emulsion electrospun fibers

Due to the relative ease for fabricating fibers with a core–shell structure, emulsion electrospinning has been investigated intensively for making nanofibrous delivery vehicles for local and sustained release of biomolecules such as growth factors. In this investigation, water-in-oil (w/o) emulsions consisting of deionized (DI) water or phosphate buffer saline (PBS), poly(lactic-co-glycolic acid) (PLGA) solution and a surfactant were electrospun into fibers for studying the evolution of core–shell structures in emulsion electrospun fibers. Optical microscopy, high speed imaging, fluorescence microscopy and transmission electron microscopy were employed to examine the morphology of the water phase in fibers at different locations of the jet (or fiber) trajectory during emulsion electrospinning. The results indicated that the water phase in emulsion jets underwent multi-level stretching and breakup. When the jet (or fiber) diameter was large (i.e., for the jet near the Taylor cone), the water phase within the jet (or fiber) exhibited a discrete morphology whereas in ultrafine fibers collected beyond certain distance from the Taylor cone, a mostly continuous water phase core was formed. The Rayleigh/capillary instability determined the breakup point of the deformed water phase. When the water phase in emulsions for electrospinning was changed from DI water to PBS, it changed from a continuous state to a discontinuous state in electrospun nanofibers.

Explorative, authentic and cohesive

Using a comparative approach, this article looks at the different elements contributing to the success of boy band comebacks, primarily by contrasting the Take That reunion with the somewhat flopped reformation of their precursors, New Kids on the Block, but also by drawing on British examples such as the Spice Girls, East 17, and Boyzone. Firstly, the parameters of the breakup are analysed as possible predictors for the success of a reunion, especially, here, the popularity at the point of breakup, its staging and framing. Secondly, the parameters of the reunion are scrutinised, in particular the mode of re-entry into the market (explorative or assumptive), the discourse (re-) established in the comeback video (typical or atypical boy band theme) and the marketing strategy as such. Thirdly, the article examines the dynamics within the band and its personalities as factors influencing the potential success of a reunion (particularly problematic in the case of East 17). And finally, the article considers the impact which successful solo careers of individual band members may have upon the success of a reunion, arguing that the immense popularity of Robbie Williams kept Take That relevant even during their latency and increased Take That’s chances of finding large audiences again (a dramatic factor which is unique to Take That).

Analysis of the transition from laminar annular flow to intermittent flow of steam condensation in noncircular microchannels

The condensation liquid was pulled into the corner of the noncircular microchannels due to the effect of surface tension. The thickness in the meniscus region increased along the channel with the decrease of the thin-liquid film region. The condensation annular flow completed when the short side wall of the microchannel was entirely covered by the meniscus region. At this point, the vapor liquid interface presented a circular shape, and the transition flow occurred. The location of transition flow depends on the short side length and the meniscus area ratio (MAR) at the breakup point under the same experimental conditions. The location of the transition flow moves toward the outlet with the increase of the short side length and decrease of the aspect ratio in the rectangular and trapezoidal microchannels. The transition flow occurs further downstream, and the annular flow regime is expanded in the trapezoidal and triangular microchannels compared with the rectangular microchannel with the same hydraulic diameter. The analysis was compared with the experimental data for different cross section shape microchannels. Most predicted values provided good predictions of the experimental data with a MRD of 30.50% and a MAD of 5.15mm. Based on the numerical results, a dimensionless correlation with a new parameter MAR was also introduced to predict the transition flow location at different cross section shape microchannels.