Breakup Effects Research Articles

Coupled Wall Boiling and Population Balance Model for High Void Fraction Flows Under Sub-Cooled Nucleate Boiling Regime: Model Development and Validation

Abstract The subcooled flow boiling of water in a vertical annulus channel is studied numerically at low-pressure conditions. The two-fluid model is developed with flow-regime dependent interfacial transfers for mass, momentum, and energy using the algebraic interfacial area density (AIAD) framework. A discrete population balance model is used to mechanistically determine the vapor bubble diameter in the flow channel by considering the bubble aggregation and breakup effects. Energy balance at the heated wall for the subcooled nucleate boiling is handled using a suitable wall boiling model. A coupling is achieved between the discrete population balance and the wall boiling model for the nucleation and the growth rate of the vapor bubbles along the heated wall. The developed model simulates the reference experimental cases of flow boiling in a vertical channel for various flow and thermal conditions. At low wall heat flux, the wall boiling generates vapor bubbles near the heated wall and within the bubbly flow regime. With an increase in the wall heat flux, the aggregation and evaporation cause the formation of larger bubbles, which progress toward the flow channel core region, a phase that is representative of the transitional flow regime. The model's capability to predict such flow regime transition is validated with the experimental results. The bubble aggregation is found to be dominant compared to the breakup, and thus, proper choice of the aggregation factor is important for the accurate prediction of vapor parameters for the subcooled flow boiling at low-pressure conditions.

Effect of Parasocial Commitment and Breakup with a Fictional Character on Purchase Intention

Effect of Parasocial Commitment and Breakup with a Fictional Character on Purchase Intention

Research of Bubble Breakup and Influencing Factors in Flotation Machine

As the core factor of flotation, bubbles have an important effect on flotation. The rotor speed, initial gas parameters and impeller structure of the flotation machine will affect the formation and movement of bubbles. It is very important to study the influence mechanism of operating parameters of flotation machine on the bubble breakup process for flotation machine design and structure optimization. This paper takes KYF-0.2m<sup>3</sup> flotation machine as the research object, establishes a single bubble analysis model, adopts the VOF (Volume of Fluid) method to analyze the influence of different initial positions of bubbles on the bubble breakup behavior, and studies the influence of impeller speed and initial position of bubbles on the bubble breakup. Result show that the breakup of bubbles mainly occurs near the stator region. With the increase of rotational speed of the impeller, the centrifugal force and the disturbance of the convection field will become greater, the time of the bubble breakup become shorter, more bubbles breakup and generate more smaller ones. With the bubble position is closer to the rotating axis of the impeller, the impact of reflow becomes stronger and the bubble breakup effect will be better, and if the bubble initial position closer to the impeller cover, the influence of impeller on the bubbles become greater and the distribution of bubbles will be more uniform.

Investigation of the Projectile Breakup Effects on Elastic Scattering and Fusion for 9Be + 209Bi System at Around Barrier Energies

Investigation of the Projectile Breakup Effects on Elastic Scattering and Fusion for 9Be + 209Bi System at Around Barrier Energies

Study on the bubble breakup and internal flow characteristics in the pulsed jet ejector

To intensify the bubble breakup in the ejector, a novel pulsed jet ejector is designed in this work. The pulsed jet is introduced into the ejector by one fluidic oscillator. A high-speed camera experiment is conducted to capture the progress of bubble breakup. The intensification mechanism of pulsed jet on bubble breakup in ejector is investigated by numerical simulation. The experimental results indicate that the introduction of the pulsed jet effectively induces the occurrences of pressure fluctuations and vortex collision, prompting the deformation of bubbles to produce microbubbles. It is also found that the bubble diameter and number of microbubbles mainly depend on the process of bubble breakup in the divergent section, and the bubble diameter distribution is significantly influenced by the variation of Reynolds number. The variations of the vortex structure are induced by the pulsed jet, which is a key factor influencing mixing efficiency and bubble breakup effects. In addition, pulsed jet ejectors have superior mixing performance compared to conventional ejectors.

Effect of breakup and coalescence kernels on polydispersed bubbly flow in continuous casting mold

Previous studies on polydispersed bubbly flow in continuous casting (CC) mold were mainly attentive to the modeling of shear-induced turbulence, interfacial force, and bubble swarm effects. The current study reveals the coalescence and breakup mechanisms of bubbles in CC mold. Then, a calibration factor of coalescence kernel is proposed based on local gas holdup to harmonize the imbalance between coalescence and breakup rates. The effect of bubble coalescence and breakup models on the Sauter mean diameter, gas holdup, and liquid velocity were studied and against with the experimental data. The results show that the Turbulent and Liao models underestimate the bubbles coalescence rate and the Luo coalescence model overestimates the bubbles coalescence rate. Meanwhile, turbulence shear and surface instability overestimate the bubble breakup frequency, and turbulent impact is the most important mechanism used to describe bubble breakup phenomenon in the CC mold. Furthermore, the turbulent fluctuation, buoyancy driven, and wake entrainment should be considered to define the bubbles collision frequency, while the viscous shear and eddy capture mechanisms could be neglected. The Luo-Prince model could accurately predict the bubble size distribution and the fan-shaped distribution of bubble clusters, which comprehensively considers three collision mechanisms. Finally, the combination form of calibration factors could effectively describe the influence of local gas holdup on bubble collision frequency. The proposed calibration factor can predict bubble size distribution more accurately in the CC mold. The relative error of mean bubble diameter prediction is reduced from 63.53 % to 17.86 %.

Further investigation on the fusion of 6Li with 209Bi target at near-barrier energies

Abstract The complete and incomplete fusion cross sections for 6Li+209Bi were measured via the in-beam γ-ray method around the Coulomb barrier. The cross sections of (deuteron captured) incomplete fusion (ICF) products were re-quantified experimentally for this reaction system. The results reveal that the ICF cross section is equivalent to that of complete fusion (CF) above the Coulomb barrier and dominant near or below the barrier. A theoretical calculation based on the Continuum Discretized Coupled Channel (CDCC) method is performed for the aforementioned CF and ICF cross sections, and the result is consistent with the experimental ones. The universal fusion function (UFF) is also compared with the measured CF cross section with different barrier parameters, demonstrating that the CF suppression factor is quite sensitive to the choice of potential, which can reflect both dynamic and static effects of breakup on the fusion process.

Controlling nonlinear rogue-wave formation using the coherence length of phase noise

Weak phase noise present on an optical field can be amplified by a self-focusing nonlinearity (n2>0) and form intense “rogue-wave” features. Here, we study the effect of the coherence length (or grain size) of this phase noise on the likelihood of rogue-wave formation in the presence of a self-focusing nonlinearity. We show that while the likelihood of rogue-wave formation increases with laser power when the coherence length is only slightly smaller than the beam diameter, the likelihood is minimally affected by a change in laser power when the coherence length is significantly smaller than the beam diameter. Our study provides insight into the interaction of nonlinearity with phase instabilities on a field and could be useful in applications such as reducing the effect of turbulence-induced breakup of intense laser beams, and developing radiance limiters to reduce the focusable power in a beam. Published by the American Physical Society 2024

Detailed analysis of the 6Li breakup in the field of the 209Bi nucleus

Abstract At energies between 24 and 50 MeV, the angular distributions of 6Li + 209Bi elastic scattering are reanalyzed phenomenologically as well as microscopically. The performed analysis adds to previous studies and aims to further explore the cluster nature of the 6Li nucleus by examining the associated breakup effects on the elastic scattering channel, in addition to probing the consistency of the different implemented potentials in reproducing the considered data. The strong coupling to the breakup channel has a strong influence on elastic data and reproduces a repulsive dynamical polarization potential (DPP), which dramatically reduces the real potential strengths. Such an observed effect was simulated by introducing a semi-microscopic repulsive DPP as well as by applying the continuum discretized coupled channels (CDCC) method. The analysis was extended to check the effect of direct deuteron stripping 209Bi(6Li,d)211Po on the elastic 6Li + 209Bi channel.

Monitoring Canadian Arctic seabirds at the Prince Leopold Island Field Station, 1975–2023

The research station at Prince Leopold Island (PLI), initiated in 1975, was the first seabird monitoring site created in the Canadian Arctic. The island supports 150 000 breeding pairs of seabirds, principally thick-billed murres ( Uria lomvia Linnaeus 1758), black-legged kittiwakes ( Rissa tridactyla Linnaeus 1758) and northern fulmars ( Fulmarus glacialis Linnaeus 1761), along with ∼70 pairs of glaucous gulls ( Larus hyperboreus Gunnerus 1767) and several thousand black guillemots ( Cepphus grylle Linnaeus 1758). Baseline observations of seabird breeding biology were made during 1975–1977. Subsequent monitoring has taken place in 22 of the 47 seasons, with work during 2001–2003 replicating the original baseline studies. Population trends of breeding seabirds have shown kittiwakes (sharply) and murres (gradually) increasing, while gulls (definitely) and fulmars (likely) have declined. The most striking scientific findings from PLI were related to the effect of annual ice break-up on seabird phenology, clutch size, and reproductive success. For contaminant research, PLI has become one of the core monitoring sites in Canada and internationally, documenting dramatic changes in concentrations of various contaminants in the Arctic marine environment. Given the international impact of research and monitoring at PLI for almost five decades, the continuation of seabird research at PLI, the most important seabird colony in the Canadian Arctic, is essential.

Experimental investigation on a novel external-mixing prefilming atomizer for advanced aircraft engines

As a crucial component of aircraft engine combustors, the external-mixing prefilming atomizer exhibits significant advantages in enhancing combustion efficiency and reducing pollutant emissions. However, the intricate relationship between spray characteristics, droplet breakup mechanisms, flow fields, and geometric parameters of the external-mixing prefilming atomizer remains poorly understood. This paper presents a novel external-mixing prefilming atomizer, aiming to address this knowledge gap. Additionally, particle image velocimetry (PIV), high-speed Schlieren photography, and particle image analysis (PIA) measuring systems were employed to gain insights into the spray characteristics and droplet breakup mechanism of the external-mixing prefilming atomizer under various swirl flow fields. The obtained results reveal the formation of two distinct regions, namely a low-density area and a high-density area. Notably, the number of droplets in the low-density area, located within 0–2 cm from the central axis, is significantly lower compared to the high-density area situated further away from the central axis. The breakup of droplets in the low-density region is primarily attributed to the inner swirl airflow, while the outer swirl airflow induces droplet breakup in the high-density region. As the Reynolds number of the incoming flow increases, the air-liquid ratio (ALR) and Weber number also increase, thereby enhancing the fuel breakup effect. The Schlieren results reveal a two-stage spray development process. The initial stage is characterized by the dominant momentum of the dense spray, with the spray tip penetration (STP) exhibiting a relatively slow increase. The aerodynamic force of airflow plays a crucial role in governing the breakup and transport of droplets, leading to a linear variation of STP over time. As the swirl number increases, there is an enhanced momentum exchange between droplets and airflow, resulting in accelerated spray penetration and droplet breakup.

Comprehension of breakup fusion reactions using forward recoil range distribution measurements

To understand the break-up fusion reaction dynamics, the forward recoil range distribution (FRRD) measurements of 12C + 165Ho system at the incident projectile energy of ≈ 88 MeV has been performed. The recoil catcher activation technique followed by the off-line gamma ray spectroscopy was implemented. It is observed that the FRRD measurements of the evaporation residues (ERs) populated via xn and pxn channels have a single Guassian peak at large cumulative thickness. This is attributed to complete momentum transfer from the projectile to the target nucleus. However, in case of the FRRD measurements of the ERs populated via αxn, αpxn and 2αxn emitting channels, in addition to peak corresponding to complete momentum transfer, the Gaussian peaks at lower cumulative thicknesses are also observed. This is accredited to the breakup fusion. Moreover, the effect of projectile breakup on complete fusion cross section is also studied. The suppression in fusion cross section is observed when compared with the universal fusion function, thus indicating the breakup probability of 12C projectile.

Effects of secondary breakup, collision dynamics, gravity and evaporation on droplet size distribution in a pressure-swirl JET A-1 spray

Size and velocity of droplets in pressure-swirl sprays vary with distance downstream the nozzle. This study aims to explain the phenomena contributing to size-resolved spatial variation of the drop size distribution for Jet A-1 spray from a small pressure swirl atomizer injected into quiescent ambient air at atmospheric conditions. The effects of secondary breakup, droplet collisions, gravity, drag-driven spray dispersion, and evaporation are evaluated. Phase Doppler anemometer (PDA) was used to resolve the velocity and size of the droplets in radial profiles at several axial distances (Z) from the nozzle exit at injection pressures between 0.5 and 1.5 MPa. The droplet motion and collision dynamics were qualitatively characterised by high-speed imaging. The analysis focused on areas along 1) the spray axis and 2) the liquid sheet direction. The first area covers small droplets with marginal evolution, while the mean drop size in the second area significantly increases downstream. The local drop size distribution and its axial evolution results from a combined effect of ballistic filtering (drifting of small droplets from periphery to spray centre and large droplets vice versa), centrifugal and turbulent droplet dispersion, and droplet collisions (increasing drop size with distance). The relative droplet-gas velocity was found at investigated Z positions too small for drag-driven secondary droplet breakup to occur. Evaporation of Jet A-1 sprayed at room temperature and pressure into still atmosphere reduces the drop size marginally. Trajectory of all drop sizes is insignificantly altered by gravity. The smallest droplets are strongly drag-driven to the spray axis, while large ones disperse centrifugally and have sufficient momentum to neglect the gravity. Combining results from imaging and laser diagnostics, various collision outcomes were identified, with a conclusion that these depend on the size and velocity of colliding droplets. Coalescing collisions dominate and strongly increase the mean drop size downstream the spray at off-axis positions while insignificantly contribute along the spray axis. The drop size span factor reduces with Z as separative collisions between large droplets and mixed-type collisions between small and large droplets narrow the drop size distribution. The above effects can be most easily amplified for drop size reduction via modification of physical properties of sprayed liquid by its heating.

Elastic scattering and total reaction cross sections of 6Li examined via a microscopic continuum discretized coupled-channels model* *Supported by the National Natural Science Foundation of China (U2067205)

We present a systematic study of 6Li elastic scattering and total reaction cross sections at incident energies around the Coulomb barrier within the continuum discretized coupled-channels (CDCC) framework, where 6Li is treated in an α+d two-body model. Collisions with 27Al, 64Zn, 138Ba, and 208Pa are analyzed. The microscopic optical potentials (MOP) based on Skyrme nucleon-nucleon interaction for α and d are adopted in CDCC calculations and satisfactory agreement with the experimental data is obtained without any adjustment on MOPs. For comparison, α and d global phenomenological optical potentials (GOP) are also used in CDCC analysis and a reduction of no less than 50% on the surface imaginary part of deuteron GOP is required for describing the data. In all cases, the 6Li breakup effect is significant and provides repulsive correction to the folding model potential. The reduction on the surface imaginary part of GOP of deuteron reveals a strong suppression of the reaction probability of deuteron as a component of 6Li when compared with that of a free deuteron. Further investigation is performed by considering the d breakup process equivalently within the dynamic polarization potential approach, and the results show that d behaves in a manner similar to a tightly bound nucleus in 6Li induced reactions.

Combined Effect of Bubble Size and Gas Volume Fraction on Natural Convective Heat Transfer Enhancement in Homogeneous Bubbly Flow: Eulerian–Eulerian Numerical Simulations

Abstract Natural convective heat transfer can be enhanced through either fins or riblets, wall roughness elements, or the injection of bubbles in the flow. Bubble injections in a quiescent (pseudo-turbulent) liquid phase or an already turbulent liquid phase had been shown to enhance the natural convective heat transfer from literature. However, study of the combined effect of bubble size and gas volume fraction rather than individual effect on natural convective heat transfer enhancement for homogeneous bubbly flow is lacking. The present work intends to fill in that data gap through conducting numerical simulations to study the combined effect of bubble size and gas volume fraction on natural convective heat transfer enhancement. The present numerical work employs the validated interphase force models and the Eulerian–Eulerian model. ansysfluent is used to simulate a bubbly flow in a three-dimensional rectangular channel with a natural convective heat transfer. Bubbles ranging from microto millimeter diameter with inlet gas volume fraction varied in the range of 0.351–3.725% are injected upward to a quiescent liquid phase in a rectangular channel with a heated left wall and a cooled right wall. The flow regime is homogeneous without bubble coalescence and breakup effect. Validated computational models are employed to study the combined effect of bubble size and gas volume fraction on heat transfer enhancement. A relation between Nusselt number, bubble Reynolds number, Rayleigh number, nondimensional bubble size, and inlet gas volume fraction is constructed using the power regression method.

Numerical simulations of droplet evaporation and breakup effects on heterogeneous detonations

Evaporation and breakup of droplets are critical phenomena in the liquid-fueled, multiphase detonation process. Understanding the relevant conditions and times for each process is crucial for predicting real world behavior. In this paper, the effects of evaporation and breakup on the multiphase detonation process will be explored through Euler-Lagrange (EL) simulations. Various droplet sizes of n-dodecane (C12H26) are reacted with oxygen (O2) utilizing a single-step global reaction mechanism. Droplet processes are modeled using temperature dependent thermophysical properties through the liquid-gas phase change and into the supercritical regime. Two aerodynamic breakup models are considered (based on theorized hydrodynamic instability mechanisms) from both empirical and theoretical approaches. Detonation wave velocity deficits are observed to be sensitive to breakup and evaporation time. It is shown that droplets redistribute fuel vapor mass over their lifetime, perturbing the equivalence ratio and creating vapor rich regions that cannot fully react. It was shown that as the total evaporation time decreases (shorter breakup time), the detonation structure becomes more like the idealized gaseous detonation case.

Effects of deuteron breakup and nucleon-transfer reactions on d+^{11}B elastic scattering

A set of experimental data consisting of angular distributions of d+^{11}B elastic and inelastic scattering and (d,t) reaction obtained at deuteron energy of 14.5 MeV as well as data sets for (d,p) (E_d = 21.5 MeV), (d,n) (E_d = 15.4 MeV) and (d,^3He) (E_d = 11.8 MeV) nucleon transfer reactions were analysed using the continuum-discretized coupled-channel (CDCC) and coupled-reaction channel (CRC) methods. It was found that at forward scattering angles the elastic scattering data are well described by parameter-free CDCC calculations which include breakup of the deuteron, but at more backward angles virtual effects due to target excitation and neutron-transfer reactions play an important role. The strongest effects are due to the excitation of ^{11}B and the neutron pickup reaction, reflecting their large cross sections. The effects induced by proton-transfer reactions are found to be negligible.

Three-dimensional simulations of liquid/gas flow through radial centrifugal pumps and the effect of bubble coalescence and breakup on the formation of gas accumulations

Three-dimensional liquid/gas flow mixture simulations of a centrifugal pump are performed by a hybrid two-phase solver, which comprises a blending between a Volume-of-Fluid-like interface-sharpening scheme and a classical homogeneous mixture two-fluid model. The hybrid solver is combined with a population balance model and a turbulence-scale adaptive simulation approach. The experimentally measured head drop due to adherent gas pockets at elevated gas loadings is well reproduced. By a thorough validation with optical measurement data, it is shown that the transition from dispersed bubbles to coherent gas accumulations as well as the steady core of gas pockets and their unsteady wake could be captured without any parameter fitting of coalescence and breakup kernels. Regions of high coalescence activity correlate with locations of gas accumulations, stabilizing the gas pockets in the impeller region. Bubble breakup, in contrast, was primarily found in the wake of the accumulation zones where the tip leakage flow of the semi-open impeller re-enters the blade passage. The particular hybrid solver architecture, together with the resolution of turbulence scales and bubble populations, facilitates the reproduction of bubble coalescence and breakup effects on the formation of gas pockets in centrifugal pumps.

Thermochronometry constraints on south West Greenland passive continental margin development

Passive continental margins (PCMs) represent the interface between the marine and terrestrial realms. However, topographic evolution of PCMs is often difficult to decipher due to paucity of the preserved geological record. Here, we report uranium-thorium-helium ((U-Th)/He) analysis of the Precambrian crystalline basement from southern West Greenland that help constrain the process of rifting between Greenland and North America and contributes to the debate about the West Greenland PCM development. The majority of zircon (U-Th)/He dates (220-580 Ma) imply several kilometres of burial of the basement by Paleozoic (and potentially Mesozoic) sediments. Apatite (U-Th)/He dates (80-230 Ma) record thermal processes associated with extensional tectonism starting in the Late Triassic and passive margin formation in the Early Cretaceous. Our data provide no evidence of thermal activity during Cenozoic times, suggesting that the thermal effects of Paleogene rifting and break-up were negligible and the magnitude of Cenozoic erosion was <3.5 km in the study area.

Single-particle spectroscopic strength from nucleon transfer reactions with a three-nucleon force contribution

The direct reaction theory widely used to study single-particle spectroscopic strength in nucleon transfer experiments is based on a Hamiltonian with two-nucleon interactions only. We point out that in reactions with a loosely-bound projectile, where clustering and breakup effects are important, an additional three-body force arises due to three-nucleon (3N) interaction between two nucleons belonging to different clusters in the projectile and a target nucleon. We study the effects of this force on nucleon transfer in (d,p) and (d,n) reactions on 56Ni, 48Ca, 26mAl and 24O targets at deuteron incident energies between 4 and 40 MeV/nucleon. Deuteron breakup is treated exactly within a continuum discretized coupled-channel approach. It was found that an additional three-body force can noticeably alter the angular distributions at forward angles, with consequences for spectroscopic factors' studies. Additional study of transfer to 2p continuum in the 25F(p,2p)24O reaction, involving the same overlap function as in the 24O(d,n)25F case, revealed that 3N force affects the (d,n) and (p,2p) reactions in a similar way, increasing the cross sections and decreasing spectroscopic factors, although its influence at the main peak of (p,2p) is weaker. The angle-integrated cross sections are found to be less sensitive to the 3N force contribution, they increase by less than 20%. Including 3N interactions in nucleon removal reactions makes an essential step towards bringing together nuclear structure theory, where 3N force is routinely used, and nuclear direct reaction theory, based on two-nucleon interactions only.