Breakup Model Research Articles

Asteroid fragmentation approaches for modeling atmospheric energy deposition

During asteroid entry, energy is deposited in the atmosphere through thermal ablation and momentum-loss due to aerodynamic drag. Analytic models of asteroid entry and breakup physics are used to compute the energy deposition, which can then be compared against measured light curves and used to estimate ground damage due to airburst events. This work assesses and compares energy deposition results from four existing approaches to asteroid breakup modeling, and presents a new model that combines key elements of those approaches. The existing approaches considered include a liquid drop or “pancake” model where the object is treated as a single deforming body, and a set of discrete fragment models where the object breaks progressively into individual fragments. The new model incorporates both independent fragments and aggregate debris clouds to represent a broader range of fragmentation behaviors and reproduce more detailed light curve features. All five models are used to estimate the energy deposition rate versus altitude for the Chelyabinsk meteor impact, and results are compared with an observationally derived energy deposition curve. Comparisons show that four of the five approaches are able to match the overall observed energy deposition profile, but the features of the combined model are needed to better replicate both the primary and secondary peaks of the Chelyabinsk curve.

Interactions of the space debris environment with mega constellations—Using the example of the OneWeb constellation

Recently, several announcements have been published to deploy satellite constellations into Low Earth Orbit (LEO) containing several hundred to thousands of rather small sized objects. The purpose of these constellations is to provide a worldwide internet coverage, even to the remotest areas. Examples of these mega-constellations are one from SpaceX, which is announced to comprise of about 4000 satellites, the Norwegian STEAM network, which is told to contain 4257 satellites, and the OneWeb constellation, which forms one of the smaller constellations with 720 satellites. As example constellation, OneWeb has been chosen. From all announced constellation, OneWeb by far delivered most information, both in regards to constellation design and their plans to encounter space debris issues, which is the reason why it has been chosen for these analyses.In this paper, at first an overview of the planned OneWeb constellation setup is given. From this description, a mission life-cycle is deduced, splitting the complete orbital lifetime of the satellites into four phases. Following, using ESA-MASTER, for each of the mission phases the flux on both single constellations satellites and the complete constellation are performed and the collision probabilities are derived. The focus in this analysis is set on catastrophic collisions. This analysis is then varied parametrically for different operational altitudes of the constellation as well as different lifetimes with different assumptions for the success of post mission disposal (PMD). Following the to-be-expected mean number of collision avoidance manoeuvres during all active mission phases is performed using ARES from ESA's DRAMA tool suite. The same variations as during the flux analysis are considered. Lastly the characteristics of hypothetical OneWeb satellite fragmentation clouds, calculated using the NASA Breakup model, are described and the impact of collision clouds from OneWeb satellites on the constellation itself is analysed.

Applying Different Strategies within OpenFOAM to Investigate the Effects of Breakup and Collision Model on the Spray and in-Cylinder Gas Mixture Attribute

In the current study, a 3-D numerical simulation of two-phase flow has been conducted in a direct injection CI engine using the Eularian-Lagrangian approach and a new breakup model. The newly modified breakup scheme has been implemented for simulating the ultra-high pressure diesel injection. The effects of droplet breakup and collision model on the spray and in-cylinder gas characteristics have been examined using the open source code OpenFOAM. Spray penetration and cone angle are investigated as spray properties and surrounding gas motion are studied by in-cylinder gas velocity and pressure distribution for non-evaporating conditions. In addition, vapor penetration of the evaporating spray is presented to study the effects of current scheme on the evaporating condition. The continuous field is described by RANS equations and dynamics of the dispersed droplet is modeled by Lagrangian tracking scheme. Results of the proposed modified KHRT model are compared against other default methods in OpenFOAM and favorable agreement is achieved. Robustness and accuracy of different breakup schemes and collision models are also verified using the published experimental data. It is demonstrated that the proposed breakup scheme and Nordin collision model display very accurate results in the case of ultra-high pressure injection.

Evaluation of Passive Containment Cooling with an Advanced Water Film Model in a Lumped-Parameter Code

Falling water films have been employed for passive containment cooling in several Generation III pressurized water reactor designs. In this paper, the lumped-parameter (L-P) containment code system COCOSYS with an advanced water film model is applied to evaluate the performance of a passive containment cooling system (PCCS) during accidents. Based on the recent work and with further modification, an integrated water film model is developed. The new model considers different flow regimes of a liquid film as it flows downward and is being evaporated. The integrated model has been adapted to the L-P code and then implemented into COCOSYS. The new model enables the containment code to capture previously neglected phenomena, including the behavior of film breakup due to the reduction in mass; the formation of rivulets; the change in coverage rate and the development of rivulets; the change of velocity distribution as well as film thickness by considering the interfacial shear stress created by countercurrent air on the film surface; the hysteresis of rivulets, i.e., the process of advancing or retreating, involving changes in contact angles; and the influence of waves on the film surface.The new model is validated against existing test results and experimental observations in the authors' recent work and is further modified in this paper taking into account the influence of waves and the processes of rivulet hysteresis. The model is then assessed based on test nodalization, and the expected phenomena are observed. Afterward, the new model is applied to evaluate the performance of PCCS film cooling employed in the AP1000 containment.It is concluded that the original film model tends to underestimate the pressure loads due to the absence of film breakup, rivulet behavior, and shear stress models. The coverage rate, as a new factor captured in the new model, limits the evaporation rate and thus restricts the cooling efficiency of the falling film. The sensitivity analysis reveals that the contact angle and hysteresis phenomenon, which were not previously considered in the code, play significant roles in PCCS film cooling. The advancing contact angle of the rivulets is a decisive factor for the peak pressure, while the retreating contact angle is influential in the later phase of cooling. It can be inferred from the study that the ideal situation for PCCS cooling is that in which the water film is approaching complete dryout at the bottom of the containment. The newly developed liquid film model helps improve the accuracy and reliability of the simulation results.

Lagrangian conditional moment closure model with flame group interaction for lifted turbulent spray jet flames

A new Lagrangian conditional moment closure (CMC) model is developed for multiple Lagrangian groups of sequentially evaporating fuel in turbulent spray combustion. Flame group interaction is taken into account as premixed combustion by the eddy breakup (EBU) model in terms of the probability of finding flame groups in the burned and the unburned state. Evaporation source terms are included in the two phase conditional transport equations, although they turn out to have negligible influence on the mean temperature field during combustion. The Lagrangian CMC model is implemented in OpenFOAM [1] and validated for test cases in the Engine Combustion Network (ECN) [2,3]. Similar ignition delays and lift-off lengths are predicted by the incompletely stirred reactor (ISR) and the Eulerian CMC models due to relatively uniform conditional flame structure in the domain. The improved Lagrangian CMC model shows no abrupt reaction or oscillatory behaviour with an appropriate model constant K and gives results in better agreement with measurements lying between the predictions by ISR and Lagrangian CMC without flame group interaction.

Kinetics of the Change in Droplet Size during Nanoemulsion Formation.

The evolution of droplet size during nanoemulsion formation is critical for the rational design of nanoemulsions in areas such as drug delivery and materials synthesis. In this article, we discuss the relative importance of various time scales involved in nanoemulsion formation and propose a population balance model for droplet breakup that takes into account the droplet's internal viscosity. The proposed model gives a qualitative agreement between average droplet size and polydispersity data for nanoemulsions prepared by high-pressure homogenization and ultrasonication. On the basis of these modeling results, we propose a correlation to obtain a parity plot for the droplet size data. We show that our model and correlation also work well with data from the existing literature. The proposed model and correlation can be used to guide future population balance studies and experimental preparation of nanoemulsions.

Sensitivity of (d, p) Reactions to High n-p Momenta and the Consequences for Nuclear Spectroscopy Studies.

Theoretical models of low-energy (d, p) single-neutron transfer reactions are a crucial link between experimentation, nuclear structure, and nuclear astrophysical studies. Whereas reaction models that use local optical potentials are insensitive to short-range physics in the deuteron, we show that including the inherent nonlocality of the nucleon-target interactions and realistic deuteron wave functions generates significant sensitivity to high n-p relative momenta and to the underlying nucleon-nucleon interaction. We quantify this effect upon the deuteron channel distorting potentials within the framework of the adiabatic deuteron breakup model. The implications for calculated (d, p) cross sections and spectroscopic information deduced from experiments are discussed.

Numerical investigation of liquid methanol evaporation and oxy-combustion inside a button-cell ITM reactor

A numerical study is conducted to investigate the performance of a button-cell LNO-ITM reactor utilizing the soot-free oxygenated liquid methanol under oxy-combustion condition. The Euler-Lagrange approach is utilized to solve discrete phase model. Taylor analogy breakup (TAB) model is used due to its convenience with the cases of low injection speed. A plain orifice atomizer is used for fuel atomization and CO2 is used as sweep gas. A semi-empirical oxygen permeation model (ABn model) is validated with the available experimental data and is, then, applied in the present model. Over a wide range of inlet fuel concentrations, the results showed increase in oxygen permeation flux of about five times in cases of reacting conditions as compared to the cases of non-reacting cases. The results showed high oxygen permeation flux at low inlet fuel concentrations due to the improvement in the oxygen to fuel ratio toward the stoichiometric conditions. At inlet gas temperatures of 1223K, 1123K, 1023K and 923K, the combustion temperature approached 1423K, 1347K, 1284K and 1231K, respectively, indicating an average combustion efficiency of 43% at moderate inlet gas temperatures. High fuel concentration at low inlet sweep flow resulted in high oxygen flux and high combustion temperature.

Effect of water-in-heavy fuel oil emulsion on the non-reacting spray characteristics under dierent ambient conditions and injection pressures: A CFD study

Emulsi ed fuel is one of the main strategies to substitute the conventional fossil fuel for the purpose of emission control and enhancement of fuel eciency. Accordingly, non-reacting spray characteristics of water-in-Heavy Fuel Oil (HFO) emulsion are numerically investigated in the present study via CFD analysis. Three di erent volumetric percentages of water in HFO are investigated and compared with pure HFO. E ects of four di erent injection pressures on injected fuel spray characteristics are studied. Moreover, in fluences of three di erent ambient back pressures and two ambient temperatures are considered. For these purposes, the characteristics of spray penetration, cone angle, volume, and SMD are evaluated through the analyses of non-dimensional numbers. For modeling the interaction of the fuel discrete phase and the gaseous continuous phase, Eulerian- Lagrangian multiphase formulation in OpenFOAM CFD toolbox is implemented. Fuel droplet tracking in Lagrangian scheme is applied by Lagrangian Particle Tracking method. Also, KH-RT as a hybrid breakup model for liquid fuel core breakup and standard model of k ???? in RANS for turbulence modeling are utilized. Numerical results are validated against existing experimental data with suitable accordance. Longer spray penetration length, larger cone angle, and greater spray volume are achieved for the emulsi ed fuels.

Fiber formation model for electrospinning. II. Stable jet voltage

The major concern in electrospinning process is the occurrence of jet formation. In order to study physical properties of the solution and process parameters, stable jet voltage model is developed to predict the stabilized jet in electrospinning. Break-up frequency model, that predicts behavior of drop breaking, is the theoretical background for stable jet voltage model. This newly developed model based on the previous work gives a clue to produce stable nano thickness fibers and the results are compared with the experimental data by PVP electrospinning. The result of stable jet voltage modeling shows that surface tension is the most important factor and molecular weight and concentration are both negligible for surface tension of solutions. Surface tension of the solution depends on the types of solvent. Therefore, surface tension of solution has different values of stable jet voltage. The stable jet voltage model that predicts the most similar experimental value is SIC hemispherical model under force mode.

Modeling of Effervescent Spray with Secondary Atomization within a Furnace

Objective: To analyze the droplet distribution characteristics of an effervescent injector by using kerosene within a furnace. Approach: A computational approach has been adopted to study and analyze the droplet distribution statistics. For primary breakup, effervescent injector model has been used and for secondary atomization, the WAVE breakup model has been adopted. Euler-Lagrange frame is employed to simulate the interaction between gas phase and droplet phase. Contributions: In this work, the effect of the variation of model constant C 2 of WAVE breakup model on droplet distribution has been studied. Around 30000 droplet samples are collected for each case (at different value of C 2 ). Validation of the work has been done with the literature available. Findings: However it has been observed that at the minimal and maximal droplet size is predicted well at radial positions away from the axis at any C 2 . The similar trend has been found for the Sauter Mean Diameter (SMD). However near the axis, the prediction is not good enough irrespective of any C 2 . Also it has been found that with higher value of C2, the computational results deviates much from the measured value.

Large eddy simulations of complex multicomponent diesel fuels in high temperature and pressure turbulent flows

A multicomponent droplet evaporation model, which discretizes the one-dimensional species and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and used for large-eddy simulations of high speed diesel sprays in high temperature and pressure closed chambers. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting conditions. The multicomponent liquid model used together with the Kelvin–Helmholtz – Rayleigh–Taylor droplet breakup model is found to reasonably well predict the experimentally observed non-linear behavior of spray penetration with changing ambient conditions for n-hexadecane and 4 different multicomponent surrogate diesel fuels with 2–8 components. The effects of various modeling assumptions and gas and liquid parameters on the drop and spray evolution and evaporation are investigated in details.

Analysis of the mechanism of gas bubble break-up in liquids during the self-aspirating impeller operation

Abstract Feasibility of a model of gas bubble break-up and coalescence in an air-lift column enabling determination of bubble size distributions in a mixer with a self-aspirating impeller has been attempted in this paper. According to velocity measurements made by the PIV method with a self-aspirating impeller and Smagorinski’s model, the spatial distribution of turbulent energy dissipation rate close to the impeller was determined. This allowed to positively verify the dependence of gas bubble velocity used in the model, in relation to turbulent energy dissipation rate. Furthermore, the range of the eddy sizes capable of breaking up the gas bubbles was determined. The verified model was found to be greatly useful, but because of the simplifying assumptions some discrepancies of experimental and model results were observed.

Complete kinematical study of the 3 $\alpha$ breakup of the 16.11 MeV state in 12C

The reaction $^{11}B+p$ has been used to populate the $(J^{\pi},T)=(2^+,1)$ state at an excitation energy of 16.11 MeV in $^{12}$C, and the breakup of the state into three $\alpha$ particles has been studied in complete kinematics. A two-step breakup model which includes interference effects is found to provide the most accurate description of the experimental data. The branching ratio to the ground state of $^8$Be is determined to be 5.1(5)% in agreement with previous findings, but more precise by a factor of two, while the decay to the first-excited state in $^8$Be is found to be dominated by $d$-wave emission.

Floculação: considerações a partir da análise clássica e da avaliação direta da distribuição de tamanho de partículas

RESUMO: Este artigo apresenta algumas considerações sobre a floculação a partir da análise clássica e da avaliação direta da distribuição de tamanho de partículas. Para tal, foram realizados experimentos em escala de bancada. Os resultados foram avaliados à luz da abordagem clássica, dada pelo adimensional número de Camp (GT) e pela cinética de agregação e ruptura, e da distribuição de tamanhos de partículas. Verificou-se que o emprego isolado do produto GT não é adequado para representar as variações de desempenho na floculação e que o modelo clássico de agregação e ruptura pode ser influenciado pela medida indireta de turbidez, bem como pelo uso da sedimentação como etapa intermediária. Por outro lado, a avaliação direta de desempenho por meio da distribuição de tamanhos de partículas, representada pela função contínua linearizada, pode constituir ferramenta promissora na avaliação dedicada da floculação.

Process modeling pressure-swirl-gas-atomization for metal powder production

The paper aims at integral process modeling and simulation of the pressure-swirl-gas-atomization process for metal powder production. A numerical analysis is applied in this way to the atomization and spray process of a molten metal for metal powder production. The primary disintegration process of swirling conical sheets of the molten metal is described by the Volume of Fluid (VOF) approach, while the subsequent droplet spray process is simulated through the Eulerian-Lagrangian approach by taking the secondary breakup of produced droplets as well as in-flight spray phenomena such as drag and droplet solidification into account. The characteristics of liquid sheet fragmentation such as primary droplet size and velocity are derived and compared with measurements. The coupled simulation is realized by setting the outcomes of liquid sheet fragmentation as the initial conditions for the droplet spray process simulation. An assessment of classical secondary breakup models is shown in comparison with measurements. The droplet solidification behaviour in a spray process is investigated. Finally, the powder particle size distribution will be derived from the process modeling and simulation.

Analysis combustion of fuel droplets release to the atmosphere using homotopy analysis method

In this paper, we investigate the model of combustion of polydisperse fuel spray that release to the atmosphere. The mathematical model using the well-known Eulerian–Lagrangian approach for transient flows of the fuel vapor–droplets mixture. The eddy breakup model is used to describe the combustion of the spray droplets as well as the k–ϵ model is used to describe the turbulence of the process. In order to investigate the mathematical/physical model, we applied the well-known analytic approximate method, the homotopy analysis method (HAM). According to the theory of HAM, the convergence and the rate of solution series are dependent on the artificial convergent control parameter ħ.

Experimental study of the relative effect of pressure drop and flow rate on the droplet size downstream of a pipe restriction

ABSTRACTAn experimental setup consisting of a 100 mm inner diameter pipeline, a butterfly valve with inner diameter of 100 mm, and oil and water pumping capacities of up to 20 m3/h were used to study droplet breakup in two-phase oil–water flow. The tests were performed at atmospheric pressure and under ambient temperatures. A particle-sizing camera was used to quantify droplet sizes. Combinations of different flow rates, water cuts, and pressure drops were tested to determine the relative effects of flow rate and pressure drop over a valve on the droplet breakup process. The test matrix was designed so that it should be possible to determine if the droplet sizes produced were independent of the flow rate. The fluid system consisted of a water phase and a mineral oil with viscosity of 4 mPa · s. Two different droplet breakup models were compared against the measured droplet sizes. The two models considered turbulence and droplet acceleration through the restriction respectively as the main contributor for droplet breakup.

The significance of drop non-sphericity in sprays

This paper presents a new framework to model drop dynamics in Lagrangian sprays. The framework builds on the Taylor Analogy Breakup (TAB) model. Real-fluid (gas-liquid) thermodynamics applicable to multicomponent systems are combined with Gradient Theory to facilitate detailed calculations of drop surface tension forces, oscillations, and breakup processes. This is combined with a more detailed treatment of deforming drop dynamics to construct more accurate representations of the local interfacial exchanges of mass, momentum, and energy. The framework is derived using an energy balance equation that explicitly enforces drop momentum conservation during the breakup process. This facilitates development of a refined set of drop equations that address current shortcomings in the prediction of drop properties over a wide range of relevant breakup conditions. The resulting drag forces, evaporation, and heating rates deviate significantly from the predictions given by contemporary drop models used in modern simulations. These deviations are quantified using Large Eddy Simulation (LES) with a Lagrangian-Eulerian modeling approach. The analysis demonstrates how the model improvements in the new framework provides a more detailed representation of physical complexities that are largely neglected in modern studies.

A modification to the WAVE breakup model for evaporating diesel spray

In order to improve the accuracy of the WAVE breakup model for an evaporating spray, it was calibrated using a series of diesel spray experiments with different orifice diameters, injection pressures, background gas densities and temperatures. The calibration focused on liquid length and spray (vapor) penetration. Based on the calibration results, it is concluded that the standard WAVE model with a constant C2, which is an adjustment parameter for breakup time, accurately predicts liquid length and spray penetration with a variety of orifice diameters, injection pressures and background gas densities. However, the same cannot be said for background temperature. Background temperature strongly affects the C2 value. Particularly, the C2 decreases with an increase in background temperature. Interestingly, the relationship between the C2 value and the background temperature seems to be of approximate inverse proportion. Therefore, due to this relationship between the C2 value and background temperature, and in order to obtain greater simulation accuracy, the proposed WAVE model with a variable C2 was developed and used to simulate a single-cylinder diesel engine. It was found that there is a significant decrease in liquid length alongside the development of the in-cylinder spray and combustion process. This is reasonable because liquid droplets break-up and evaporate faster in a higher temperature environment. Moreover, the result is in accordance with images from optical diesel engine experiments captured and performed by others.