Breakup Conditions Research Articles

Puffing/micro-explosion of two-liquid droplets: Effect of fuel shell composition

Theoretical research into the heat and mass transfer, hydrodynamic and physicochemical processes in combustion chambers of gas turbine engines usually implies that multi-component jet fuels are modeled using single-component liquids (saturated or cyclic hydrocarbons) and their substitutes. Due to an insoluble dispersed phase (e.g., water) in their composition, droplets consist of a noncombustible core and a liquid fuel shell. During heating, water droplets coalesce in fuel droplets to produce explosion-triggering volumes of liquid superheated to the boiling point. When heated, these heterogeneous droplets breakup in the micro-explosion and puffing modes. This study reports the numerical simulation results providing the temporal characteristics of heating and evaporation of heterogeneous droplets until puffing/micro-explosive breakup, when varying the composition of the fuel shell in the homologous series of saturated and cyclic (as illustrated by monocycloparaffins) hydrocarbons from C7 to C16. The conducted research has revealed that the variations in the breakup delay times in the homologous series of saturated and cyclic hydrocarbons are nonlinear. The breakup delay rates were found to increase substantially in the boundary points of the investigated series. Mechanisms to control droplet fragmentation delay time were identified for different initial and boundary conditions. A dimensionless complex reflecting the correlation between the critical conditions of composite liquid droplet breakup and the physicochemical properties of the fuel shell components was proposed.

Dynamics of a droplet in shear flow by smoothed particle hydrodynamics

The behavior of a droplet under shear flow in a confined channel is studied numerically using a multi-phase smoothed particle hydrodynamics (SPH) method. With an extensive range of Reynolds number, capillary number, wall confinement, and density/viscosity ratio between the droplet and the matrix fluid, we are able to investigate systematically the droplet dynamics such as deformation and breakup. We conduct the majority of the simulations in two dimensions due to economical computations, while perform a few representative simulations in three dimensions to corroborate the former. Comparison between current results and those in literature indicates that the SPH method adopted has an excellent accuracy and is capable of simulating scenarios with large density or/and viscosity ratios. We generate slices of phase diagram in five dimensions, scopes of which are unprecedented. Based on the phase diagram, critical capillary numbers can be identified on the boundary of different states. As a realistic application, we perform simulations with actual parameters of water droplet in air flow to predict the critical conditions of breakup, which is crucial in the context of atomization.

A hydrologic and river ice modelling framework for assessing ungauged sub-basin streamflow impact in a large cold-region river basin

ABSTRACT Modelling snow- and ice-affected streamflow in cold regions is challenging. Neglecting the streamflow from ungauged regions/sub-basins of a river basin in the inflow boundaries of a river ice model adds further uncertainties. This study combined a river ice model (River1D) with a hydrological model (Soil and Water Assessment Tool, SWAT) to investigate the impacts of ungauged sub-basin streamflow on peak flow simulation under both open water and river ice breakup conditions in the Peace River Basin (PRB). Results showed that ungauged sub-basins of the PRB can greatly affect peak flow simulation of the River1D for both open water and river ice breakup events, especially for flood events. Although they represent only about 26.54% of the whole modelled area in the PRB, the SWAT model simulated results show that the ungauged sub-basins can contribute nearly 50% of peak flow for the open water and river ice breakup flood events.

Discriminant analysis of the freeze-up and break-up conditions in the Inner Mongolia Reach of the Yellow River

Abstract This study divided the total storage potential in a natural channel into the ice production volume and the water storage capacity volume. Thermal factors, hydraulic processes, topography, and ice formation were selected to derive a discriminant equation for freeze-up and break-up conditions in the Inner Mongolia Reach of the Yellow River. The trends observed from data for the freeze-up dates, break-up dates, and total frozen days from 2017 to 2020 conform to the principle that the river is gradually frozen from the downstream to the upstream and later thawed from the upstream to the downstream. The number of frozen days in the downstream is greater than in the upstream. Results indicate that freeze-up typically occurs when the proportion of ice in the channel is relatively high. Higher temperatures and greater discharges are required to facilitate the break-up of the river when the equilibrium ice thickness is greater. This study can provide a theoretical basis and framework for establishing an accurate freeze-up and break-up forecast model to prevent and mitigate ice-induced disasters.

Improved Taylor analogy model for predicting droplet breakup and large deformation in planar extensional flow

The application of the Taylor analogy has been proven effectively in predicting the breakup of droplet within a spray system. Recently, a model of small deformation at steady and transient states within extensional flow with low Reynolds numbers has been successfully proposed by approaching the Taylor analogy. The objective of this study is to improve the Taylor analogy in laminar flow for the prediction of breakup and large deformation of the droplet in planar extensional flow by theoretical modeling and numerical analysis. The performance of the suggested model is collated using a three-dimensional numerical simulation with vast viscosity ratios and capillary numbers. The available experimental data from the literature is likewise compared with the numerical analysis outcomes for validation purposes. The proposed model could accurately predict the critical breakup condition and large deformation of droplet in extensional flow. These improvements hold significant importance for droplet dynamics studies within microfluidic systems.

Hydrodynamics of vapor-liquid flows in curvilined channels of separation devices of power plants

The main factor that affects the efficiency of the separation process is the lack of contact with the surface of the shutter when moving in the flow of small droplets of wet steam. This process depends on the physical and chemical properties of the wet vapor, the dispersion of the droplets, the parameters of the movement of the two-phase medium, adhesion and edge angle, and the geometry of the channel. Purpose. Determination of the limit modes of operation of separation shutter devices depending on the dispersion and quantity of droplet liquid, flow parameters and geometric characteristics of curved channels. Methodology. The methodology is based on the analysis of the physical model of the movement of a two-phase medium under the action of mass and gravitational forces in a curved horizontal channel. Findings. A mathematical model is presented for determining the trajectory of a liquid droplet in a curvilinear corrugation channel of the louvered package of a separator-superheater. The main conditions of film destruction and dynamic droplet break-up are defined. A method for expanding the range of stable operation of separation devices is proposed. Based on the obtained correlations, the design of the blind package is optimized. Originality. Based on the analysis of the physical model of the movement of a two-phase medium in a curved horizontal channel, a mathematical model was developed and the limit of capture of the dispersed phase was determined. Practical value. The presented results allow optimization of separation devices of boiler drums, horizontal steam generators and steam superheater separators of the II circuit of VVER-1000, fuel preparation systems of GTU.

Fog Intermittency and Critical Behavior

The intermittency of fog occurrence (the switching between fog and no-fog) is a key stochastic feature that plays a role in its duration and the amount of moisture available. Here, fog intermittency is studied by using the visibility time series collected during the month of July 2022 on Sable Island, Canada. In addition to the visibility, time series of air relative humidity and turbulent kinetic energy, putative variables akin to the formation and breakup conditions of fog, respectively, are also analyzed in the same framework to establish links between fog intermittency and the underlying atmospheric variables. Intermittency in the time series is quantified with their binary telegraph approximations to isolate clustering behavior from amplitude variations. It is shown that relative humidity and turbulent kinetic energy bound many stochastic features of visibility, including its spectral exponent, clustering exponent, and the growth of its block entropy slope. Although not diagnostic, the visibility time series displays features consistent with Pomeau–Manneville Type-III intermittency in its quiescent phase duration PDF scaling (−3/2), power spectrum scaling (−1/2), and signal amplitude PDF scaling (−2). The binary fog time series exhibits properties of self-organized criticality in the relation between its power spectrum scaling and quiescent phase duration distribution.

Accelerating intelligent microfluidic image processing with transfer deep learning: A microchannel droplet/bubble breakup case study

Deep learning has recently been leveraged in the microfluidic research for intelligent image processing. However, it usually requires massive human efforts to label sufficient images for obtaining a precise deep learning model. We herein propose an integrated microfluidic image processing method based on transfer deep learning for the rapid deployment of Mask R-CNN, which is capable of reutilizing models trained in previous microfluidic domains to accelerate the analysis of droplets and bubbles in the images of the target microfluidic domain. The transfer deep learning is validated in the microfluidic research with a constrictive microchannel, which is commonly used to break large droplets or bubbles to enhance emulsification. With only 40 labeled images and about 10 min training, the integrated image processing method achieves precise recognition results for both droplets and bubbles in the microfluidic experiments. Applying the trained Mask R-CNN to unlabeled images, the breakup of droplets is found to be highly dependent on the low flow rate, but the bubble breakup is much easier to happen in the same microfluidic equipment. Critical conditions of droplet breakup and size laws of droplet and bubble are precisely determined based on the recognition results of the trained Mask R-CNN.

NEW EXPERIMENTAL DATA OF CHILD DROPLETS IDENTIFICATION AFTER TWO-LIQUID DROPLET BREAKUP

New experimental data of child droplets characteristics (times to puffing/microexplosion, distribution of sizes, and ratio of the evaporation surface area before and after puffing/microexplosion) of heated two-liquid droplets in puffing and microexplosion modes are presented. Different droplet configuration effects (fuel liquid (rapeseed oil) - shell, water-core, vice versa) are discussed. The experiments were carried out with two-liquid droplets in which coal particles were added to meet nonpremixed spray technologies into the combustion chambers. Breakup conditions of water/fuel droplets in monodisperse and polydisperse aerosols are determined. The difference in secondary atomization effects of water and fuel is described. The effect of gas temperature in the range 720-1070 K on child droplets characteristics is discussed.

A prediction model for the rockslide-generated wave amplitude under the condition of bedrock mass breakup

Landslides along coastlines and rivers can cause landslide-generated waves and pose a threat to the offshore banks, navigation vessels and coastal buildings. The maximum amplitude of the landslide-generated wave, which is strongly related to the size and geometry of the landslide and gradually decreases with the increase of the propagation distance, is one of the important indexes to evaluate the secondary hazard caused by landslides. The fragmentation of rockslide has an influence on the effect of rockslide on water body. This study proposes a relationship between the maximum rockslide-generated wave amplitude and the number of fragmentation blocks which is defined to present different degrees of landslide bedrock mass breakup. The computational fluid dynamics (CFD) numerical method is used to simulate the whole process of landslide and wave propagation. The orthogonal array experiment algorithm is used to design the numerical simulation schemes. The Gauss-Newton algorithm is adopted to analyze the results and elect the optimal model with the strongest correlation. A series of conducted physical model experiments prove the applicability and accuracy of the optimal model. This optimal numerical model can offer a reference for rockslide-generated wave analysis when considering bedrock mass breakup.

Limiting Conditions for Droplet Fragmentation of Stabilized Suspension Fuels

The main barrier to the wide use of composite liquid fuels in the energy sector is the significant sedimentation of solid particles during fuel storage and transportation. As a result, the composition of fuel slurries changes quite fast and considerably when yet another portion of fuel is pumped from a storage tank. Stabilizing additives are one of the possible solutions to this problem. The technology of primary and secondary slurry fuel atomization is generally considered promising for obtaining a spray of small fragments (droplets and particles). This way, droplets of liquid components and solid particles can be produced with a size of less than 10 μm. A fuel aerosol with particles and droplets this small burns out rapidly. The most effective secondary droplet atomization technology is based on their microexplosive breakup in combustion chambers by superheating the water in the fuel to exceed its nucleation (boiling) point. As part of this research, we studied the impact of the main stabilizing additives to slurry fuels on droplet breakup behavior: heating time until breakup, breakup delay and duration, and the number, size, and velocities of secondary fragments. Soy lecithin and sodium lignosulfonate were used as stabilizers. The main components of the fuel slurries were water, rapeseed oil, diesel fuel, coal processing waste (filter cake), coking bituminous coal, soy lecithin, and sodium lignosulfonate. Droplets were heated at an ambient gas temperature ranging from 450 to 1050 K until the breakup conditions were achieved. Mathematical expressions were obtained for the relationship between input parameters and the key characteristics of the process. Principal differences and overall patterns of droplet breakup were established for slurries with and without stabilizing additives.

Experimental study on dynamics of double emulsion droplets flowing through the Y-shaped bifurcation

Dynamic behaviors of double emulsion droplets flowing through the Y-shaped bifurcation are experimentally studied and the influences of droplet length, droplet velocity, and liquid viscosity are particularly discussed. The flow patterns of double emulsion droplets are categorized by typical features in motion, namely the number of interfacial breakups and the coupling effect between interfaces. Critical conditions for the existence of the coupling effect are determined by the relative difference between the residence time of inner and outer droplets. Influences of the droplet length and velocity on the transition laws of flow patterns are summarized, and the corresponding dynamic mechanisms are discussed through characteristics of the interfacial deformations. Breakup conditions of inner and outer droplets are individually identified and their variations in liquid systems with different viscosity ratios are analyzed with the aid of the built theory of single emulsion droplets. Universal phase diagrams of the flow patterns are established by taking into account the physical parameters of both inner and outer droplets, which characterize all working forces including the viscous force, the squeezing force, the interfacial tension, and the coupling force that is the unique feature during the breakup of multiple interfaces.

Acoustic Telemetry Reveals the Complex Nature ofMixed‐StockFishing in Canada's Largest Arctic Char Commercial Fishery

AbstractClimate change is having a myriad of effects on Arctic ecosystems, yet understanding how these changes will influence the spatiotemporal dynamics of harvest in northern commercial fisheries remains unclear. Furthermore, stock mixing continues to complicate fisheries management in Arctic Canada, especially for anadromous stocks, but data on the extent and degree of stock mixing for the majority of northern fisheries are scarce. Here, we used a multiyear (2015–2019) acoustic telemetry data set to test the utility of acoustic telemetry as a potential tool for inferring stock mixing in the Arctic CharSalvelinus alpinuscommercial fishery in Cambridge Bay (Nunavut). We also assessed the effect of annual variation in environmental variables (river breakup and marine ice conditions) on the potential contribution of discrete stocks to commercial harvest at several fisheries. We found that stock mixing during the commercial harvest is common in both marine and freshwater fisheries during the summer/open‐water season, with virtually all stocks potentially being susceptible to harvest at any given commercial fishery. Additionally, in some fisheries, the vulnerability of different stocks to harvest was influenced by annual differences in marine ice and river breakup conditions. We discuss options for fisheries management, including a potential quota‐transfer system, and highlight how changing environmental and climatic conditions may have an effect on the commercial harvest of Arctic Char in the region. Overall, the results of this study demonstrate the utility of acoustic telemetry for informing mixed‐stock fisheries while highlighting the complex and pervasive nature of stock mixing in Canada's largest Arctic Char commercial fishery.

Coupled Electrohydrodynamic and Thermocapillary Instability of Multi-Phase Flows Using an Incompressible Smoothed Particle Hydrodynamics Method

This paper concerns the study of coupled effects of electrohydrodynamic (EHD) and thermocapillary (TC) on the dynamic behaviour of a single liquid droplet. An incompressible Smoothed Particle Hydrodynamic (ISPH) multiphase model is used to simulate EHD-TC driven flows. The complex hydrodynamic interactions are modeled using the continuum surface force (CSF) method, in which the gradient of the interfacial tension and the Marangoni forces are calculated with an approximated error or 0.014% in the calculation of Marangoni force compared to the analytical solutions which is a significant improvement in comparison with previous SPH simulation studies, under the assumption that the thermocapillarity generates sufficiently large stress to allow droplet migration, while the electrohydrodynamic phenomena influences the droplet morphology depending on the electrical and thermal ratios of the droplet and the ambient fluid. This study shows that, when applying a vertical electric field and thermal gradient, the droplet starts to stretch horizontally towards a break-up condition at a high rate of electrical permitivity. The combined effect of thermal gradient and electric field tends to push further the droplet towards the break-up regime. When the thermal gradient and the electric field vector are orthogonal, results show that the droplet deformation would take place more slowly and the Marangoni forces cause the droplet to migrate, while the stretching in the direction of the electric field is not seen to be as strong as in the first case.

Study on Numerical Simulation Methods for Hypervelocity Impact on Large-Scale Complex Spacecraft Structures

This paper aims to study the difference of results in breakup state judgment, debris cloud and fragment characteristic parameter during hypervelocity impact (HVI) on large-scale complex spacecraft structures by various numerical simulation methods. We compared the results of the test of aluminum projectile impact on an aluminum plate with the simulation results of the smooth particle hydrodynamics (SPH), finite element method (FEM)-smoothed particle Galerkin (SPG) fixed coupling method, node separation method, and finite element method-smooth particle hydrodynamics adaptive coupling method under varying mesh/particle sizes. Then based on the test of the complex simulated satellite under hypervelocity impact of space debris, the most applicable algorithm was selected and used to verify the accuracy of the calculation results. It was found that the finite element method-smooth particle hydrodynamics adaptive coupling method has lower mesh sensitivity in displaying the contour of the debris cloud and calculating its characteristic parameters, making it more suitable for the full-scale numerical simulation of hypervelocity impact. Moreover, this algorithm can simulate the macro breakup state of the full-scale model with complex structure and output debris fragments with clear boundaries and accurate shapes. This study provides numerical simulation method options for the follow-up research on breakup conditions, damage effects, debris clouds, and fragment characteristics of large-scale complex spacecraft.

Coulomb and nuclear interactions in the dynamics of weakly-bound neutron-halo breakup on heavy target * *LT acknowledge support from Conselho Nacional de Desenvolvimento Científico e Tecnológico [Procs. 304469-2019-0 and 464898/2014-5 (INCT-FNA)], and Fundação de Amparo à Pesquisa do Estado de São Paulo [Projs. 2017/05660-0]

Within our aim to clarify some aspects of the breakup dynamics of loosely-bound neutron-halo projectiles on a heavy target, we apply the continuum discretized coupled-channel formalism to investigate the beryllium 11Be breakup on a lead 208Pb target at = 140 MeV incident energy. By evidencing that the continuum–continuum couplings are much stronger in the nuclear breakup than in the Coulomb breakup, we conclude that the strength of these couplings in the total breakup is dominated by the nuclear contribution, with the diagonal monopole nuclear potential in the projectile–target center-of-mass having negligible effect on the total and nuclear breakup cross-sections. For this kind of reaction, we show that the condition for the total breakup to approach its dominant component in the absorption region is strongly dependent on the continuum–continuum couplings and the diagonal monopole nuclear potential.

Compared structure and evolution of the conjugate Demerara and Guinea transform marginal plateaus

The Demerara and Guinea plateaus are conjugate Transform Marginal Plateaus (TMPs) formed at the junction of the Jurassic Central Atlantic Ocean and the Cretaceous Equatorial Atlantic Ocean. We compare their structure and evolution through a combined industrial/academic seismic dataset tied by well data. We show that these TMPs record a complete evolution history from the Jurassic Central Atlantic to the Equatorial Atlantic breakup and seafloor spreading phases. Both plateaus first formed as volcanic margins displaying successive SDR wedges migrating towards the newly forming Central Atlantic domain. In this context, Demerara and Guinea, conjugates of the Bahamas, seem to have formed in relation to plume activity at the southern end of the Central Atlantic domain. Our dataset suggests that the Demerara and Guinea plateaus initially represented two distinct extrusive centres separated by a crustal basement high. Later, during the Cretaceous Equatorial opening phase, both plateaus separated in a transform mode following this discontinuity. Deformation is notably asymmetric during this phase: Aptian to Albian folding, strike-slip, transtensive deformation and complex vertical movements on the Demerara side and only minor deformation on the Guinean side, except on its divergent Sierra Leone termination. The deformation is sealed on both plateaus by a regional upper Albian erosion unconformity. Extensional reactivation occurs on the Guinea side (probably through a general collapse?). To conclude, this study provides new insights into the nature and origin of TMPs and the key tectono-sedimentary archives they may contain to understand the polyphase breakup conditions of Gondwana.

Investigation of the dispersing characteristics of antral contraction wave flow in a simplified model of the distal stomach

The dispersing characteristics of antral contraction wave (ACW) flow in the antrum are investigated by reproducing the flow generated by an ACW and determining its effect on liquid drops. The goal is to gain information about the flow field and mechanical stresses, which are responsible for the food disintegration. Toward this end, a model antrum prototype was constructed, consisting of a cylinder that was closed at one end to represent the antrum and closed pylorus. A moving hollow piston with a parabolic inner contour was used to model an ACW. A computational model was developed that reflects this prototype. Experiments and simulations were first performed for fluids with different rheological properties, two relative occlusions (0.60 and 0.75), and several ACW speeds (1.0–7.5 mm/s). The simulations were validated with velocity measurements, and the characteristics of the retropulsive jet were quantified at different Reynolds numbers (0.5–105.3). Experiments were then performed in which liquid drops of different viscosity were placed in a highly viscous fluid with low interfacial tension, similar to conditions in a stomach. It was found that the viscosity ratio (0.001–0.1) influences the retraction dynamics of a drop's tail after stresses are relaxed. The flow and stress information from the simulations was used to analyze fluid transport in the antrum and to quantify drop breakup conditions. It was found that a drop broke up if both a critical capillary number of 0.51 was exceeded and the drop passed within a critical dimensionless distance of 0.3 to the wave apex.

Orbital Migration and Circularization of Tidal Debris by Alfvén-wave Drag: Circumstellar Debris and Pollution around White Dwarfs

Abstract A significant fraction of white dwarfs (WDs) exhibit signs of ongoing accretion of refractory elements at rates ∼103–107 kg s−1, among which, 37 WDs were detected to harbor dusty debris disks. Such a concurrence requires not only fertile reservoirs of planetary material but also a high duty cycle of metal delivery. It has been commonly suggested that this material could be supplied by solar system analogs of Main Belt asteroids or Kuiper Belt objects. Here we consider the primary progenitors of WD pollutants as a population of residual high-eccentricity planetesimals, devolatilized during the stellar giant phases. Equivalent to the solar system’s long-period comets, they are scattered to the proximity of WDs by perturbations from remaining planets, Galactic tides, passing molecular clouds, and nearby stars. These objects undergo downsizing when they venture within the tidal disruption limit. We show quantitatively how the breakup condition and fragment sizes are determined by material strength and gravity. Thereafter, the fragments’ semimajor axes need to decay by at least ∼6 orders of magnitude before their constituents are eventually accreted onto the surface of WDs. We investigate the orbital evolution of these fragments around WDs and show that WDs’ magnetic fields induce an Alfvén-wave drag during their periastron passages and rapidly circularize their orbits. This process could be responsible for the observed accretion rates of heavy elements and the generation of circum-WD debris disks. Speculative implications are that giant planets may be common around WDs’ progenitors and that they may still be bound to some WDs today.

Theoretical model for predicting the break-up of ice covers due to wave-ice interaction

An approximate solution for wave transmission and reflection between open water and a finite viscoelastic ice cover is developed in the present study, in which both the water part and the ice cover are treated as a continuum, each governed by its own equation of motion. The interface conditions include matching velocities and stresses between the two continua. In this study, only two modes of the dispersion relation are considered, and horizontal boundary conditions are approximated by matching mean values. The reflection and transmission coefficients are determined for simplified cases to compare with earlier theories. Behaviors of the resonance are obtained for pure elastic ice covers. The effect of viscosity is also investigated for viscoelastic ice covers. According to the above wave-ice interaction model, the stress and strain are calculated in the ice cover. By using a stress failure criterion, the break-up condition of ice covers with different thickness and length under the interaction of waves and sea ice is determined. Finally, a dynamic evolution model of the ice floe size distribution function in the marginal ice zone is established. The present study is useful for modeling the wave-in-ice climate on a geophysical scale.