Multiple Breakup Research Articles

Modeling of Supercooled Large Droplet Physics in Aircraft Icing

This paper aims to investigate phenomena that are related to SLD conditions in aircraft icing including gravity, non-spherical droplets, droplet breakup and droplet splash using an in-house computational tool. The in-house computational tool involves four modules for the computation of the flow field, droplet trajectories, convective heat transfer coefficients and ice growth rates. Droplet trajectories are computed using the Lagrangian approach, while ice growth rates are calculated using the Extended Messinger Model. In order to extend the capabilities of the computational tool to include SLD-related phenomena, empirical models that represent SLD physics are implemented. An extensive study has been performed using MS317 and NACA0012 airfoils, that aims to bring out the relative importance of the SLD-related phenomena, particularly on water catch rates and ice formation. The results of the study pointed to some important new conclusions that may shed further light on SLD physics. For example, multiple droplet breakup has been observed under certain conditions and droplet breakup emerged as a more important effect than previously reported. It was also seen that droplet splash influences both the energy balance and the mass balance in the icing process, which has been shown to have an important effect on the final ice shape, especially for very large droplets.

Gondwanan flood basalts linked seismically to plume-induced lithosphere instability

Delamination of the continental lithospheric mantle is well recorded beneath several continents. However, the fate of the removed continental lithosphere has been rarely noted, unlike subducted slabs reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5 horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500 to 700 km depths beneath former Gondwana, with slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone and mid-mantle above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2 to 4 × 106 km3, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high-wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

Inverse ECG imaging as a novel solution for acute coronary syndrome classification from standard 12-lead ECG in the emergency department

Spiral wave reentry is a potential mechanism of atrial fibrillation (AF), but is difficult to differentiate clinically from multiple wavelet breakup using standard bipolar recordings. We developed a new methodology using bipolar recordings to estimate the direction of local activation wavefronts during AF by calculating the electrogram conformation (Egm-C). We subsequently used recurrence quantification analysis (RQA) of Egm-C to differentiate regions of spiral wave reentry from wavelet breakup.A 2D computer simulation was created with regions containing a stable spiral wave and also regions of wavebreak. A grid of 40 × 40 unipolar electrodes was superimposed. At each site, the actual wavefront direction (WD) was determined by comparing relative activation timings of the local intracellular recordings, and the estimated wavefront direction (Egm-C) was determined from the morphology of the local bipolar electrogram. RQA of Egm-C was compared to RQA of actual WD in order to differentiate AF mechanisms.RQA of actual WD and Egm-C both distinguished regions of spiral wave reentry from wavelet breakup with high correlation between the two methods (recurrence rate, r = 0.96; determinism, r = 0.61; line max, r = 0.95; entropy, r = 0.84; p < 0.001 for all). In areas of stable spiral wave reentry, the recurrence plots of both Egm-C and actual WD demonstrated stable, periodic dynamics, while regions of wavelet breakup demonstrated chaotic behavior largely devoid of repetitive activation patterns.Calculation of Egm-C allows RQA to be performed on bipolar electrograms during AF and differentiates regions of spiral wave reentry from multiple wavelet breakup.

Behaviors of multiple pulsing in high power saturable-absorber mode-locked Yb:KGW laser

By investigating the mode-locked pulse characteristics with varying pump power, we report on the soliton pulse breakup and multiple pulsing of a high power femtosecond Yb:KGW laser at a 10 W level of output power. The pulse breakup from single to double pulses at an output power of 6.3 W, exhibits a step-like abrupt change in the spectrum and temporal duration. Even under multiple pulsing operation, the mode-locked pulses follow the soliton-like pulse formation model such that the pulse duration is inversely proportional to the pulse energy and the time-bandwidth product is close to the transform limit. The multiple pulsing and breakup characterized in this study provide an efficient and reliable method to confirm the single pulse operation of high power mode-locked solid-state lasers.

Modal Analysis of Breakup Mechanisms for a Liquid Jet in Crossflow

Abstract Liquid fuel jet in crossflow (LJIC) is a vital atomization technique significant to the aviation industry. The hydrodynamic instability mechanisms that drive a primary breakup of a transverse jet are investigated using modal and traveling wavelength analysis. This study highlights the primary breakup mechanisms for aviation fuel Jet-A, utilizing a method that could be applied to any liquid fuel. Mathematical decomposition techniques known as POD (proper orthogonal decomposition) and Robust MrDMD (multiresolution dynamic mode decomposition) are used together to identify dominant instability flow dynamics associated with the primary breakup mechanism. Implementation of the Robust MrDMD method deconstructs the nonlinear dynamical systems into multiresolution time-scaled components to capture the intermittent coherent structures. The Robust MrDMD, in conjunction with the POD method, is applied to data points taken across the entire spray breakup regimes: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The dominant frequencies of breakup mechanisms are extracted and identified. These coherent structures are classified with an associated time scale and Strouhal number. Three primary breakup mechanisms, namely, ligament shedding, bag breakup, and shear breakup, were identified and associated with the four breakup regimes outlined above. Further investigation portrays these breakup mechanisms to occur in conjunction with each other in each breakup regime, excluding the low Weber number enhanced capillary breakup regime. Spectral analysis of the Robust MrDMD modes’ entire temporal window reveals that while multiple breakup mechanisms are convolved, there is a dominant breakup route for each breakup regime. An associated particular traveling wavelength analysis further investigates each breakup mechanism. Lastly, this study explores the effects of an increased momentum flux ratio on each breakup mechanism associated with a breakup regime.

An investigation on the bubble transportation of a two-stage series venturi bubble generator

In this paper, we designed a new venturi bubble generator, which mainly consist of two serial rectangular perspex venturi channels with the same geometrical dimension. Visualization experimental method combined with digital image analysis was adopted to study the motion, deformation and breakup process of bubbles when the micro-bubble generator was installed vertically. The bubble foaming frequency which is defined as the amount of forming bubbles within one second from the air injection hole was significantly enhanced with the increase of water flow rate, but was not sensitively affected by the air flow rate. The discrete bubbles moved in a two-stage venturi channel and experienced collapse or breakup in the divergent section. The Sauter mean diameter of bubbles which recorded in each divergent outlet decreased gradually. The Reynolds numbers of water had a significant effect on the breakup characteristics of bubbles. With the increasing of Re, the bubbles experienced binary breakage and multiple breakup successively. Under the effect of complex turbulence vortex, the bubbles presented different breakup patterns in each stage. When Reth>19793, the bubble breakup ratio of the first stage divergent section was larger than that of the second stage, and the difference of the generated bubble Sauter mean diameter in each divergent outlet was minimized accordingly. The surface stability of the daughter bubble was enhanced, and it was difficult to breakup significantly under the effect of recirculation flow. The numerical simulation results by Computational Fluid Dynamics (CFD) indicated that the area of the vortex was increased for larger second stage divergent angle, which intensify the phase interaction and promote the possibility of sub-micron bubble breakup.

Regime mapping of multiple breakup of droplets in shear flow by phase-field lattice Boltzmann simulation

Multiple breakup refers to a sequence of events through which a single droplet eventually produces multiple daughter droplets in a shear flow. It is a more common phenomenon than binary breakup. Using a phase-field lattice Boltzmann method, this work investigates the effects of Reynolds number, capillary number and soluble surfactant on multiple breakup in shear flow. We find that the regime map for a droplet in a surfactant-free shear flow can be segmented into the non-breakup, elementary breakup, multiple breakup, filament and coalescence regimes. By contrast, the multiple-breakup regime widens and the coalescence regime narrows in the system of surfactant. This difference on macroscale regimes originates from the mesoscale behaviour caused by the interaction of surfactant and shear flow. While surfactant hinders droplet breakup at lower Re, it promotes breakup at higher Re. The interfaces around the breaking points are stretched by the opposite reaction of Marangoni stress. While the regime map gives the number of daughter droplets in a given shear flow, a correlation is proposed to calculate the composition of breakup events, viz. the number of binary breakup and of ternary breakup events.

Transformation of single drop breakup from binary to ternary and multiple in turbulent jet flows

By releasing liquid drops in turbulent jet flows, we investigated the transformation of single drop breakup from binary to ternary and multiple. Silicone oil and deionized water were the dispersed phase and continuous phase, respectively. The probability of binary, ternary, and multiple breakup of oil drops in jet flows is a function of the jet Reynolds number. To address the underlying mechanisms of this transformation of drop breakup, we performed two-dimensional particle image velocimetry (PIV) experiments of single-phase jet flows. With the combination of drop breakup phenomenon and two-dimensional PIV results in a single-phase flow field, these transformation conditions can be estimated: the capillary number ranges from 0.17 to 0.27, and the Weber number ranges from 55 to 111.

EXPERIENCES OF MULTIPLE ROMANTIC RELATIONSHIPS MAKEUP AND BREAKUP AMONG ADOLESCENTS

Experiences of multiple romantic relationships makeup and breakup among adolescents is a very common issue in this era. The rationale of this research is to know the reasons and after effects of multiple romantic relationships make up and break up among adolescence. Semi structure interview of 3 females and a male of age fifteen years to twenty-six years is conducted to collect the data

Experimental Investigation on Single‐Droplet Deformation and Breakup in a Concave‐Wall Jet

AbstractLiquid droplets are released in the concave‐wall jet to investigate their deformation and breakup characteristics. CCl4 and water are the dispersed and continuous phases. The study reveals that the three modes of single droplets in the concave‐wall jet are non‐breakup, binary breakup, and multiple breakup. When the Weber (We) number is less than 30, the mode of binary‐breakup is primary for the droplets, however, there are only multiple‐breakup modes when We &gt; 47. The non‐breakup and binary‐breakup modes are beneficial to the gravity and centrifugal separation because of little deformation and high axial velocity of the droplet. Effects of continuous‐phase tangential velocity and shear rate distribution on the droplet image sequence are studied. Droplet breakup occurs mainly in the region of high shear rate.

Numerical study on electrohydrodynamic multiple droplet interactions.

We present a numerical study of inviscid multiple droplet coalescence and break-up under the action of electric forces. Using an embedded potential flow model for the droplet hydrodynamics, coupled with an unbounded exterior electrostatic problem, we are able to perform computations through various singular events and analyze the effects of the electrical field intensity on droplet interactions. Laboratory experiments on the electrodynamics of droplet pairs show a much richer, and sometimes unexpected, behavior than that of isolated droplets. For example, it has been found that opposite charged droplets tend to repel each other when the electric field intensity is above a certain critical value. Although the mathematical model employed in this work incorporates very simple flow and electric assumptions, many of the droplet coalescence patterns seen in laboratory experiments can be reproduced. In this model, the interaction pattern of two droplets of radii R_{0} separated a distance D_{0}, depends on the ratio X_{0}=D_{0}/R_{0} and the applied uniform electric field intensity, E_{∞}. By performing a vast number of numerical simulations we are able to characterize the coalescence modes before and after drop merging as a function of these two parameters. The simulations predict that droplet repulsion occurs within a narrow interval of E_{∞} values, different for each X_{0}. Surprisingly, in this E_{∞} interval, a sharp transition between two power-law precoalescence flow regimes is seen. The evolution of several flow characteristics before and after coalescence, and the shape of the deformed droplets at coalescing time and the double cone angle, are also addressed and analyzed in detail. Cone angles below 35^{∘} lead to droplet coalescence for any X_{0} value, which is in accordance with previously reported studies. Finally, it is shown that the model and algorithm can handle multiple droplet interactions. The simulations qualitatively match results from water in oil experiments in microchannels, despite the fact that the exterior fluid is not considered in the mathematical model.

Location and pattern of non‐invasive keratographic tear film break‐up according to dry eye disease subtypes

To compare the non-invasive keratographic tear film break-up time (NIKBUT) and the location and pattern of non-invasive keratographic tear film break-up between normal group and each group of three dry eye disease (DED) subtypes. We enrolled 55 normal subjects and 250 patients with DED, who underwent tear meniscus height and NIKBUT measurements using the Keratograph® 5M. Ocular surface parameter assessments such as the fluorescein tear break-up time, ocular surface staining, Schirmer's test, and lid margin and meibomian gland examinations were performed, and the ocular surface disease index was determined. These parameters, including the proportion of the first tear film break-up location and simultaneous multiple tear film break-up pattern, were compared amongst the normal and DED subtypes. Aqueous-deficient dry eye disease (ADDE) and ADDE/meibomian gland dysfunction (MGD) subtypes showed lower NIKBUTs than those of the normal group, whilst NIKBUTs of the MGD subtype did not differ from those of the normal group. The NIKBUTs showed a good diagnostic ability in diagnosing dry eye except MGD only. The occurrence of the first tear film break-up in the central location was significantly higher in both the ADDE and ADDE/MGD subtypes, comprising approximately 40% in both subtypes (p<0.001). The proportion of a simultaneous multiple tear film break-up pattern was higher in the ADDE and ADDE/MGD subtypes, at 60.9% and 45.5%, respectively (p<0.001). The NIKBUTs and the location and pattern of non-invasive tear film break-up were different between normal group and each group of three DED subtypes.

A numerical study on bubble dynamics in sinusoidal channels

In the present work, we investigate the dynamics of a bubble, rising inside a vertical sinusoidal wavy channel. We carry out a detailed numerical investigation using a dual grid level set method coupled with a finite volume based discretization of the Navier–Stokes equation. A detailed parametric investigation is carried out to identify the fate of the bubble as a function of Reynolds number, Bond number, and the amplitude of the channel wall and represented as a regime map. At a lower Reynolds number (high viscous force), we find negligible wobbling (path instability) in the dynamics of the bubble rise accompanied only with a change in shape of the bubble. However, at a higher Reynolds number, we observe an increase in the wobbling of the bubble due to the lowered viscous effects. Conversely, at a lower Bond number, we predict a stable rise of the bubble due to higher surface tension force. However, with a gradual increase in the Bond number, we predict a periodic oscillation which further tends to instigate the instability in the dynamics. With a further increase in the Bond number, a significant reduction in instability is found unlike a higher Reynolds number with only change in the shape of the bubble. At lower values of Reynolds numbers, Bond numbers, and channel wall amplitudes, the instability is discernible; however, with an increase in the channel wall amplitude, the bubble retains integrity due to higher surface tension force. At a higher Bond number and channel wall amplitude, a multiple breakup in the form of secondary bubbles is observed. We propose a correlation which manifests the average bubble rise velocity and the fluctuating velocity (due to channel waviness) as a function of Reynolds number, Bond number, and channel wall amplitude. Finally, we conclude that the bubble dynamics pertinent to the offset channels with varying amplitudes does not remain the same as that of the symmetric channel.

An investigation on the performance of a micro-scale Venturi bubble generator

Venturi-type bubble generators exhibit a simple structure, high efficiency, low power consumption, and high reliability. An experimental study was conducted to evaluate the performance of a micro-scale Venturi channel as a bubble generator. In addition, the mechanisms dominating the bubble breakup were analyzed based on observations. With a liquid Reynolds number in the throat part of 0.7–1.2 × 104 and a void fraction below 0.1, the micro-scale Venturi-type bubble generator can produce micro-bubbles with average diameters of approximately 0.2–0.4 mm. Bubble breakups induced by shear stress, shear-off, and interfacial instability were observed in the experiments. The dominating bubble breakup type was multiple breakup arising from interfacial instability and eddy collisions. The recirculation process played a crucial role in the bubble deformation and prolonged the residence time of bubbles in the diverging section, thereby intensifying the energy transmission between the turbulent flow and bubbles. A negative aspect associated with the bubble generator was identified—a limitation of the void fraction to values below 0.1 had to be imposed on the micro-scale bubble generator because it would be very difficult for the bubble generator to produce microbubbles at high void fractions. The larger fragments from bubble breakups would escape the diverging section, thereby experiencing only a small influence from the turbulence flow.

Analysis of Neptune’s 2017 bright equatorial storm

We report the discovery of a large ( ∼ 8500 km diameter) infrared-bright storm at Neptune’s equator in June 2017. We tracked the storm over a period of 7 months with high-cadence infrared snapshot imaging, carried out on 14 nights at the 10 m Keck II telescope and 17 nights at the Shane 120 inch reflector at Lick Observatory. The cloud feature was larger and more persistent than any equatorial clouds seen before on Neptune, remaining intermittently active from at least 10 June to 31 December 2017. Our Keck and Lick observations were augmented by very high-cadence images from the amateur community, which permitted the determination of accurate drift rates for the cloud feature. Its zonal drift speed was variable from 10 June to at least 25 July, but remained a constant 237.4 ± 0.2 m s−1 from 30 September until at least 15 November. The pressure of the cloud top was determined from radiative transfer calculations to be 0.3-0.6 bar; this value remained constant over the course of the observations. Multiple cloud break-up events, in which a bright cloud band wrapped around Neptune’s equator, were observed over the course of our observations. No “dark spot” vortices were seen near the equator in HST imaging on 6 and 7 October. The size and pressure of the storm are consistent with moist convection or a planetary-scale wave as the energy source of convective upwelling, but more modeling is required to determine the driver of this equatorial disturbance as well as the triggers for and dynamics of the observed cloud break-up events.

A method for quantifying recurrent patterns of local wavefront direction during atrial fibrillation

IntroductionSpiral wave reentry is a potential mechanism of atrial fibrillation (AF), but is difficult to differentiate clinically from multiple wavelet breakup using standard bipolar recordings. We developed a new methodology using bipolar recordings to estimate the direction of local activation wavefronts during AF by calculating the electrogram conformation (Egm-C). We subsequently used recurrence quantification analysis (RQA) of Egm-C to differentiate regions of spiral wave reentry from wavelet breakup. MethodsA 2D computer simulation was created with regions containing a stable spiral wave and also regions of wavebreak. A grid of 40 × 40 unipolar electrodes was superimposed. At each site, the actual wavefront direction (WD) was determined by comparing relative activation timings of the local intracellular recordings, and the estimated wavefront direction (Egm-C) was determined from the morphology of the local bipolar electrogram. RQA of Egm-C was compared to RQA of actual WD in order to differentiate AF mechanisms. ResultsRQA of actual WD and Egm-C both distinguished regions of spiral wave reentry from wavelet breakup with high correlation between the two methods (recurrence rate, r = 0.96; determinism, r = 0.61; line max, r = 0.95; entropy, r = 0.84; p < 0.001 for all). In areas of stable spiral wave reentry, the recurrence plots of both Egm-C and actual WD demonstrated stable, periodic dynamics, while regions of wavelet breakup demonstrated chaotic behavior largely devoid of repetitive activation patterns. ConclusionCalculation of Egm-C allows RQA to be performed on bipolar electrograms during AF and differentiates regions of spiral wave reentry from multiple wavelet breakup.

CFD-PBM Coupled Simulation of an Airlift Reactor with Non-Newtonian Fluid

Hydrodynamics of an AirLift Reactor (ALR) with tap water and non-Newtonian fluid was studied experimentally and by numerical simulations. The Population Balance Model (PBM) with multiple breakup and coalescence mechanisms was used to describe bubble size characteristics in the ALR. The interphase forces for closing the two-fluid model were formulated by considering the effect of Bubble Size Distribution (BSD). The BSD in the ALR obtained from the coupled Computational Fluid Dynamics (CFD)-PBM model was validated against results from digital imaging measurements. The simulated velocity fields of both the gas and liquid phases were compared to measured fields obtained with Particle Image Velocimetry (PIV). The simulated results show different velocity field profile features at the top of the ALR between tap water and non-Newtonian fluid, which are in agreement with experiments. In addition, good agreement between simulations and experiments was obtained in terms of overall gas holdup and bubble Sauter mean diameter.

Direct measurement of droplet breakage in a pulsed disc and doughnut column

The lack of experimental data for the droplet breakup has been one of the limitations for the application of population balance model (PBM). In this work, a high‐speed camera was used to directly measure the droplet breakup frequency and daughter size distribution in a pulsed disc and doughnut column. It was found from the captured video that multiple breakup events were more frequently observed than binary breakup. The multiple breakup was treated as an original breakup and several intermediate breakups to characterize the process quantitatively. The effects of pulsation intensity, dispersed phase flow rates, and the spatial locations were investigated in detail. Empirical correlations were finally established for both the breakup frequency function and the daughter droplet size distribution function and fitted well with the experimental data. The correlation equations were then used in a simplified PBM to calculate the droplet number density, which further proved the feasibility of the correlations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4188–4200, 2017

Motion of Deformable Drops Through Porous Media

This review describes recent progress in the fundamental understanding of deformable drop motion through porous media with well-defined microstructures, through rigorous first-principles hydrodynamical simulations and experiments. Tight squeezing conditions, when the drops are much larger than the pore throats, are particularly challenging numerically, as the drops nearly coat the porous material skeleton with small surface clearance, requiring very high surface resolution in the algorithms. Small-scale prototype problems for flow-induced drop motion through round capillaries and three-dimensional (3D) constrictions between solid particles, and for gravity-induced squeezing through round orifices and 3D constrictions, show how forcing above critical conditions is needed to overcome trapping. Scaling laws for the squeezing time are suggested. Large-scale multidrop/multiparticle simulations for emulsion flow through a random granular material with multiple drop breakup show that the drop phase generally moves faster than the carrier fluid; both phase velocities equilibrate much faster to the statistical steady state than does the drop-size distribution.

Theoretical model for multiple breakup of fluid particles in turbulent flow field

Generalized phenomenological model, based on the theories of probability and isotropic turbulence, is developed for multiple breakup of fluid particles in turbulent flow field. The approach uses a series of successive binary breakup events occur at a time scale comparable to the colliding eddy turnover time. It was found that the use of energy density, instead of energy, will increase the predicted binary breakup rate which is usually underestimated by the existing models in the literature. Generalization of the binary breakup model for multiple fragmentations is performed by defining a “remaining energy function” for the colliding eddy which means the contribution of original eddy to the later breakup events. For ternary breakage, the model shows a reasonably good agreement with the experimental data. The quaternary fragmentation frequency, however, is of negligible importance at lower energy dissipation rates but its contribution to breakage fraction at higher energy dissipation rates becomes considerable. The results also show that ternary and quaternary breakups have a considerable 90% contribution to the overall fragmentation, while pentenary and further fragmentations are of lower importance at low energy dissipation rates. At higher levels of energy dissipation rate, fragmentations up to six daughter particles contribute to more than 95% of the overall fragmentations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4508–4525, 2016