Jet Breakup Length Research Articles

Breakup length determination of continuous ink jets: Application to a shear-thinning industrial fluid

The theory of the so-called Rayleigh–Plateau instability of fluid jets has been widely studied and can be used to predict the breakup length of liquid jets. Recently, in the work of Rosello et al. [J. Fluids Eng. 140(3), 031202 (2018)], the linear theory was enhanced to accurately predict the breakup length of continuous ink jets of Newtonian fluids by accounting for the influence of the nozzle geometry. In the present work, the influence of a shear-thinning behavior is addressed for both the breakup morphologies and breakup lengths in a linear regime. A comparison with the experimental data shows an excellent agreement extending the model of Rosello et al. to a non-Newtonian shear-thinning fluid.

Varicose-whipping instabilities transition of an electrified micro-jet in electrohydrodynamic cone-jet regime

A cone-jet regime in electrohydrodynamic atomization (EHDA) is widely applied into printing, electro-spinning, spray-coating, and biological mass spectrometry. Regulating different instabilities of jet is crucial for optimizing its operating parameters. In present work, an atypical, hemispherical capillary with inner diameter of 0.40 mm and cap size of 6.20 mm was employed as atomization nozzle, through which a steady cone-jet regime was confirmed versus suitable feeding liquid flow rate and electric potential. A permanent and highly charged jet emits from a Taylor cone apex and further disintegrates into fine highly charged drops in the form of varicose or whipping instabilities. The results indicate that a steady cone-jet is observed in the specific ranges of the feeding liquid flow rate, electric potential and conductivity. The typical breakup instabilities including varicose and whipping are clearly observed with an increase in liquid flow rate for a fixed electric potential for most of liquids, and the transition from varicose to whipping instability easily occurs. For a steady cone-jet, the jet breakup instabilities usually depends on the competition between interfacial forces on the electrified jet. The transition process involving a low-viscosity jet with a large flow rate is observed, and the general parameter G=Γ2δμ0.52 is calculated to account for surface charge, surface tension, and viscosity effects, where Γ is the electric force to surface tension ratio and δμ is the inertia to viscous force ratio. Finally, the varicose, transition regime, and whipping are classified with first and second critical threshold values G = 40 and G = 102, respectively. Meanwhile, as the electrified jet transforms from varicose to whipping instabilities, the jet breakup length shows a trend of increasing first and then decreasing.

Controllable multiple mixing monodisperse droplet streams generation using wavelength-modulated disturbances

In this paper, we study the breakup of a circular jet disturbed by wavelength modulation to produce periodic but non-uniform patterns of droplet sizes. Instead of a single wavelength disturbance, a series of perturbations containing two different wavelengths in one cycle was applied to excite the jet. Jet breakup patterns and droplets formation under composite disturbances were derived based on the classic linear theory of instability. Experiments indicate that the jet breakup length and the resultant droplet size can be precisely controlled. The length of the coexistence stage of two sizes of droplets depends on the difference in the growth rates of each disturbance. By applying three and four wavelengths in the perturbation, we also demonstrate the potential of this concept to generate more mixing droplet streams. This active droplet generation method with well processed control of non-uniform droplets would be advantageous in various potential applications.

Liquid jet core characterization in a model crossflow airblast atomizer

Detail characterization of the liquid jet core in a model cross-stream airblast atomizer by application of the Optical Connectivity (OC) technique is the goal of the present paper. The unique ability of the technique in imaging the fluorescence signal exclusively from the jet core region facilitates simultaneous visualization of the liquid jet from the side- and the front-view with high background contrast. This allows measurement of some important primary breakup characteristics. The jet penetration and breakup length are obtained from the side-view images, while the front view images provides the jet width and the spreading angle. The above parameters are measured for a wide range of injector operating conditions. The measurement of mean jet trajectory and mean penetration/breakup length indicated large difference in comparison to the past studies based on experiments conducted in wind-tunnels. This is attributed to air flow confinement within the atomizer in the present case and also accurate measurement of breakup location in the OC technique. The range of the measured mean width of the jet and spreading angle indicated ’sheet breakup mode’ of the liquid jet for all injector operating conditions. Correlations are obtained to describe the evolution of different mean quantities with respect to relevant non-dimensional numbers. The fluctuations of jet breakup parameters are also measured. Some interesting correlations are obtained between fluctuations of different primary breakup characteristics which are discussed in the paper.

Influence of coupled factors on premixing and fragmentation of mild thermal interaction

After core melt jets drop into the water pool, they break up into several parts and premix with water, and subsequently fine-fragmentation may take place, leading to steam explosions. Besides, mild thermal interaction can also occur in fuel–coolant interactions (FCIs) during core melt accidents in light water reactors. However, this phenomenon is not fully understood owing to the various coupled mechanisms involved. Therefore, we conduct an experimental study to understand the influence of the underlying factors and thermal interaction mechanisms on the premixing and fragmentation processes of FCIs within a confined space. Based on the morphology method, the coupled effects of melt mass, water level, and melt superheating temperature are investigated, quantified in terms of jet breakup length, solidification time, and fragments size distribution. Based on the corresponding pressure and temperature histories, two types of influencing factors are studied in detail: the effect of melt properties coupled with the water level; and the effect of melt superheating temperature coupled with the water level. Finally, a new bubble dynamic phenomenon called the premix expansion is featured based on Rayleigh’s equation. These experimental data on mild thermal interaction are expected to be of significance in the development of models and validation of codes.

Numerical simulation on jet breakup in the fuel-coolant interaction using smoothed particle hydrodynamics

In a severe accident of light water reactor (LWR), molten core material (corium) can be released into the wet cavity, and a fuel-coolant interaction (FCI) can occur. The molten jet with high speed is broken and fragmented into small debris, which may cause a steam explosion or a molten core concrete interaction (MCCI). Since the premixing stage where the jet breakup occurs has a large impact on the severe accident progression, the understanding and evaluation of the jet breakup phenomenon are highly important. Therefore, in this study, the jet breakup simulations were performed using the Smoothed Particle Hydrodynamics (SPH) method which is a particle-based Lagrangian numerical method. For the multi-fluid system, the normalized density approach and improved surface tension model (CSF) were applied to the in-house SPH code (single GPU-based SOPHIA code) to improve the calculation accuracy at the interface of fluids. The jet breakup simulations were conducted in two cases: (1) jet breakup without structures, and (2) jet breakup with structures (control rod guide tubes). The penetration depth of the jet and jet breakup length were compared with those of the reference experiments, and these SPH simulation results are qualitatively and quantitatively consistent with the experiments.

Study on melt jet breakup behavior with nonorthogonal central-moment MRT color-gradient lattice Boltzmann method

In this paper, the melt jet breakup behavior are numerically studied in 3D with nonorthogonal central-moment MRT color-gradient lattice Boltzmann method, which could significantly enhance the numerical stability and accuracy when applied to flows with very high Reynolds number. Firstly, the methodology to simulate immiscible two-phase flow is validated by conducting droplet oscillation tests. Then the ability of this model to accurately predict melt jet breakup in water is validated by simulating molten Wood's metal jet breakup experiments. Meanwhile, the breakup mechanisms are clarified. For the leading edge, the breakup of the side part is due to large eddies, the main part of the leading edge starts breakup owning to Rayleigh-Taylor instability. For the jet column, small droplets and filaments are stripping due to Kelvin-Helmholtz instability, segment breakup of the jet column is owning to Rayleigh-Taylor instability. Finally, the model is employed to simulate molten corium jet breakup in water. The hydrodynamic characteristics such as jet penetration depth, jet breakup length and fragment size are analyzed in detail. It is found that the simulation results are basically consistent with the dimensionless jet breakup length predicted by Epstein et al.‘s correlation when E0=0.1, but relatively shorter. RTI theory significantly overestimates mass median diameter while critical Weber number and KHI theories underestimate it.

Effects of Nozzle Screw Structure on Breakup Length of Jet

Effects of Nozzle Screw Structure on Breakup Length of Jet

Uniform breaking of liquid-jets by modulated laser heating

We report a theoretical and experimental study of the breaking of liquid jets under external periodic heating by laser pulses. In this case, jet breaking is controlled by the competition between the growth of the initial disturbances, which possess a wide wavenumber spectrum and result in the classical Rayleigh–Plateau (RP) unstable modes, and the growth of the disturbance caused by the surface tension perturbation corresponding to the periodic temperature modulation by pulsed laser heating, which appears as the thermocapillary (TC) unstable modes driven by the Marangoni flow. Our linear stability analysis shows that both the RP modes and the TC modes obey the same dispersion relation. We obtain analytical results on the range of the laser pulsing frequency that produces uniform jet breaking, at which the principal TC mode dominates the RP modes and the jet breaks at exactly the laser heating frequency, and the resulting liquid drops are uniform in size. Our theoretical prediction agrees well with experimental observations. In the uniform jet breaking range, our stability analysis also gives the growth rates of the TC modes and the jet breakup length, both of which are supported by experimental measurements. In the experiments, we also observed the growth of higher-order modes, which can again be explained quantitatively by our stability analysis.

Visualization on electrified micro-jet instability from Taylor cone in electrohydrodynamic atomization

Abstract The cone-jet in electrohydrodynamic atomization has been widely applied into numerous industrial fields owing to micro-sized drops with narrow distribution and high charge. The electrified jet emits from a single capillary sheathed with quartz tube is visualized versus operating parameters and physical properties, and breakup instabilities are also discussed. The range of operating parameters for a steady cone-jet broadens, as well as the minimum flow rate. Taylor cone angle decreases with an increase in flow rate, while increases as electric potential increasing. The jet breakup length decreases with an increase in flow rate and conductivity, while increases as electric potential increasing. The diffusion angle increases as flow rate increasing, while decrease as electric potential and conductivity increasing. Much clearer whipping instabilities are observed with an increase in “electro-Weber” number and conductivity. The completion in disturbance or/and suppression from axial and radial stresses, drag force dominates the variation. Meanwhile, for a large flow rate, the transition from varicose instabilities to whipping instabilities is found. The whipping instabilities are clearly observed for high conductivity due to much more free ions in liquid. For much higher conductivity, an intermittent electrified jet appears and shows an umbrella plume, and breakup length sharply shortens.

Ejection and breakup behaviors of a novel direct contact thermal storage using ejection PCM

To solve the blocking issue of direct contact thermal storage and further improve the heat exchange efficiency, a novel method that ejecting the molten phase change material (PCM) into the heat transfer fluid (HTF) was proposed in this paper. The experiments were carried out to understand the ejection and breakup behaviors of PCM and investigate the feasibility of this concept. Two properties about ejection and breakup, i.e. jet breakup length (LP) and angle (β), were discussed. The relationship between operation parameters, including ejection velocity, nozzle size, ejection temperature, and particle diameters were quantificationally analyzed. The results shown that there exist four obvious stages of ejection and breakup behaviors: i) 0-40 mm: an approximate horizontal liquid column with smooth surface; ii) 40-110 mm: a slight curvulate liquid column with unstable and fluctuate surface; iii) 110-210 mm: peel-off and superficial breakage; iv) From 210 mm: deposition of PCM droplets. The two properties LP and β shows negative and positive correlation with ejection velocity, respectively. The LP varies from 72.2 mm to 30.2 mm, the β varies from 17.5 ° to 21.0 °. However, the correlation between above two properties and nozzle size and also ejection temperature is on the contrary. The diameter of most PCM particle is in the range of 0-8 mm. The higher ejection velocity, smaller nozzle size, and lower ejection temperature results in smaller particle diameters in breakup processes. Compared with the traditional direct contact thermal storage, the novel method can not only solve the blocking issue but also dramatically enlarge heat transfer area by dispersing molten PCM, which can provide an insight of development of new direct contact thermal storage.

Experimental and theoretical study of jet hydrodynamic breakup behavior with air entrainment

Molten jet breakup is a vital phenomenon during Fuel-Coolant Interaction (FCI), which can be strongly affected by hydrodynamic behaviors around the jet surface. When a liquid jet plunges into another liquid surface, air entrainment may occur and influence the jet breakup process. In this paper, the hydrodynamic breakup behavior of liquid jets accompanied by air entrainment is investigated experimentally and theoretically. Mercury and Benzyl benzoate is used as jet material with density ratios of 13.63 and 1.12 respectively. The experimental results show that the air is entrained into the water and wrapped around the liquid jet. The cause for this air entrainment phenomenon is the momentum loss of liquid jet when injecting into the water surface. In the low-density ratio cases, the air entrainment effect is more remarkable due to greater loss of jet momentum. This phenomenon has a delay effect to jet breakup process by preventing contact between the jet column and water. The existing correlations are not enough for predicting the jet breakup length with air entrainment. A revised correlation equation is proposed in which jet breakup length is the sum of maximum air void depth and the existed jet breakup length correlation. The proposed correlation shows good agreements with both the high-density ratio and the low-density ratio experimental results. Conclusions in this paper are helpful in understanding the hydrodynamic jet breakup behavior with air entrainment, offering the accidental scenarios an applicable reference.

Jet Fragmentation Characteristics During Molten Fuel and Coolant Interactions

Jet fragmentation greatly influences the possibility of steam explosion and the formation of a debris bed when a molten corium jet falls into subcooled coolant during a severe accident of a nuclear reactor—which is called fuel and coolant interaction (FCI). The characteristics of different jet fragmentation mechanisms and the conditions under which they play a major role are still in doubt. Experiments were carried out to investigate the fragmentation characteristics of melt jet interaction with water at medium temperature (~680°C) and high temperature (1800°C to 2150°C). Molten metal [tin or Type 304 stainless steel (304SS)], oxide (alumina), and their mixture (304SS-alumina) were used as melt materials to obtain different fragmentation mechanisms. In addition, the effects of melt temperature, water subcooling, and water depth on jet fragmentation were also studied. Through comprehensive analysis of high-speed photography, dynamic pressure, water temperature variation, and jet breakup length during interactions as well as the morphology and size of debris after interactions, it was found that the characteristics of jet fragmentation varied greatly at different melt temperatures and water subcooling due to competition between hydrodynamic fragmentation and thermodynamic fragmentation caused by boiling. In addition, under high-temperature conditions, fragmentation of alumina was much greater than 304SS due to the fracture of solidifying melt caused by thermal stress. Finally, five kinds of mechanisms of melt jet fragmentation under different conditions are summarized.

Liquid jet breakup and spray formation with annular swirl air

Spray formation is important for liquid fuel combustion from the perspective of emissions and sustaining combustion. Employing swirl flow increases turbulent intensity, which leads to a much-desired outcome for sprays in a reduction of the jet breakup length, better air-fuel mixing and vaporization characteristics, and stabilizes the combustion operation. The present investigation endeavors to characterize the near field spray developing region of a swirl airblast atomizer. The high-speed digital imaging system is employed to record the unsteady dynamics when the liquid jet breaks to form mono-disperse or poly-disperse drop size distribution depending upon the atomizing air to liquid jet momentum ratio. The coherent spatial nature of the atomization process is identified using Proper Orthogonal Decomposition (POD) of acquired high-speed images of the spray in the near field. The simultaneous droplet size and velocities (axial, radial, and tangential) are measured through Phase Doppler Particle Analyzer (PDPA) technique to quantify the effect of the flow field on spray characteristics in the near field of an atomizer. Joint probability distributions of drop size and velocity along with Weber number distribution provide insight into the spray developing near field region. The spatial variations in the drop size distribution are found to be a function of turbulent Weber number (Wet) and shear Weber number (Wes) distribution. Double Gaussian function representing superimposed distributions for larger and smaller droplets provides the highest confidence fit for both velocity and dropsize distributions throughout the flow field. The volume-averaged statistics are proposed for a better description of the actual spray quality.

Liquid jet disintegration memory effect on downstream spray fluctuations in a coaxial twin-fluid injector

This paper intends to investigate the influence of unsteadiness in the liquid jet disintegration process on downstream fluctuations of spray characteristics in a coaxial twin-fluid injector. Time-resolved high-speed shadowgraphic imaging of the spray was obtained for different axial locations downstream of the injector exit at z = 0, 8Dl, and 30Dl, where Dl is the central liquid tube diameter. The primary jet breakup unsteadiness close to the injector exit was characterized by measuring both shear-driven Kelvin–Helmholtz (KH) instability and flapping instability in addition to jet breakup length fluctuations. Downstream of the liquid jet core region, the liquid shedding rate (fshed) was measured at z = 8Dl. The power spectrum of time series data of instantaneous volume mean diameter (VMD) measured at z = 30Dl indicated periodic variation of the droplet size. The corresponding frequency (fVMD) was obtained. It was found that for lower range of gas-to-liquid momentum flux ratio (M < 4), both fshed and fVMD are larger than the frequency of KH instability. Also, for such conditions, larger temporal variation of the droplet size is realized, and this leads to higher fluctuations of the local liquid mass flux. Proper orthogonal decomposition analysis of the shadowgraph images for different axial locations identified similar topology of the dominant mode that corresponds to flapping instability. The results suggest that even far downstream of the injector exit, some memory of the upstream unsteady jet breakup process is retained, which strongly influences spatio-temporal evolution of droplet characteristics, thereby contributing to local spray fluctuations.

Empirical correlation for spray half cone angle in plain-jet airblast atomizers

Plain-jet airblast atomizers are widely used in industrial applications. The literature contains numerous papers on Sauter mean diameter, however, there is no estimation method available for spray cone angle, SCA, which derivation is the primary goal of this study. Four distinct, practical model liquids were analyzed: distilled water, diesel oil, light heating oil, and crude rapeseed oil. The atomizing pressure and liquid preheating temperature were varied in the range of 0.3–2.4 bar and 25–85 °C, respectively. This latter parameter enabled a wide and continuous liquid kinematic viscosity investigation range of 0.33–44.2 mm2/s. The resulting sprays were imaged at various shutter speeds for proper edge detection. An adaptive thresholding algorithm was developed in Matlab software environment to calculate SCA. The methodology is discussed in detail to facilitate the re-implementation of this technique since there is no generally accepted method for SCA measurement. SCA inversely varied with liquid density and followed a power law with the air-to-liquid mass flow ratio; however, the derived expression also performed well by replacing air-to-liquid mass flow ratio by either Mach number or momentum flux ratio. A simple empirical equation was derived, which allows the estimation of SCA of airblast atomization in a wide parameter range within a 3.5% deviation. The measured results were evaluated in the light of high-speed camera images in the vicinity of the nozzle; it was found that increased liquid jet breakup length decreases SCA while intense ligament formation increases it.

Effect of droplet size on the jet breakup characteristics of n-butanol during impact on a heated surface

Jet breakup during droplet impacted on heated surface has received wide concerns due to its regularity. The Weber number (We) is a common used dimensionless parameter to classify and analyze the phenomenon, but it is unable to summarize all detailed phenomenon variations and related theory. Thus, the effect of droplet size on jet breakup was investigated by considering its significant difference in various scenarios. The behavior of n-butanol droplets with diameter range from 1.71 mm to 2.84 mm impacts a heated surface with jet breakup was recorded by backlit technology. Three parameters, the jet breakup time, the jet breakup length and the jet ligament diameter, were analyzed to illustrate the phenomenon. The results showed that these parameters are affected by the droplet size largely at 10 < We < 35, but affected lightly at higher Weber numbers. The sub-droplet diameter reduces with Weber number for all initial size droplets while the larger initial droplet corresponds to larger sub-droplet. The breakup time, breakup length and jet ligament diameter increase with the initial diameter. The time of jet breakup versus agrees well with the theory of Rayleigh instability regardless of droplet diameter. In addition, the jet breakup phenomenon was observed to evolve into pancake bouncing with an ultrafine high-speed jet when the We was above 50. • The dynamics of various size n-butanol droplets impacting on a heated surface was studied. • Jet breakup was impacted significantly by droplet size in a certain We range (10–35). • The ratio of D / D 0 remains near constant for different size droplets while reduces with We. • Breakup length and ligament diameter increase with the increase of initial droplet size. • The time of jet breakup for all tested size droplets agrees well with Rayleigh instability theory.

Frequency selection in a gravitationally stretched capillary jet in the jetting regime

A capillary jet falling under the effect of gravity continuously stretches while thinning downstream. We report here the effect of external periodic forcing on such a spatially varying jet in the jetting regime. Surprisingly, the optimal forcing frequency producing the most unstable jet is found to be highly dependent on the forcing amplitude. Taking benefit of the one-dimensional Eggers & Dupont (J. Fluid Mech., vol. 262, 1994, pp. 205–221) equations, we investigate the case through nonlinear simulations and linear stability analysis. In the local framework, the WKBJ (Wentzel–Kramers–Brillouin–Jeffreys) formalism, established for weakly non-parallel flows, fails to capture the nonlinear simulation results quantitatively. However, in the global framework, the resolvent analysis, supplemented by a simple approximation of the required response norm inducing breakup, is shown to correctly predict the optimal forcing frequency at a given forcing amplitude and the resulting jet breakup length. The results of the resolvent analysis are found to be in good agreement with those of the nonlinear simulations.

Entrainment studies in inverse jet flame port burner

The present investigation aims to investigate the fundamental understanding of entrainment characteristics of a Circumferentially Arranged Fuel Port Inverse Jet Flame Burner (CAFP IJF). The high-speed flame Schlieren visualization is carried out experimentally for 8, 18 and 32 port CAFP IJF burner for varying air–fuel operating conditions to visualize the entrainment characteristics. The region of fuel entrainment is found to occur within the base region whereas intense mixing and combustion is observed in transition and main flame region respectively. The 32 port CAFP IJF burner exhibits enhanced entrainment characteristics and augmented ambient air–jet interactions for similar operating conditions as compared to a lesser number of circumferential fuel ports. The jet breakup length is employed to identify the interaction of ambient air with the combustion driven vorticial structures. The steady laminar flamelet model is used to investigate the entrainment characteristics of a 32 port CAFP IJF burner. The calculated entrainment coefficients at different operating conditions for reacting and non-reacting CAFP IJF indicate that the entrainment rate for reacting jet is lower due to the diminution of density across the flame cross-section at each axial plane. The strong ambient air entrainment is observed within the interstitial space between consecutive fuel ports which promote air–fuel mixing. Additionally, unlike in Normal Jet Flame (NJF), a clear distinction between air and fuel entrainment is found to be essential for the current CAFP IJF burner configuration.

A comprehensive mathematical model for nanofibre formation in centrifugal spinning methods

Motivated by our experimental observations of nanofibre formation via the centrifugal spinning process, we develop a string model to study the behaviours of a Newtonian, viscous curved jet, in a non-orthogonal curvilinear coordinate system including both air-drag effects and solvent evaporation for the first time. In centrifugal spinning a polymeric solution emerges from the nozzle of a spinneret rotating at high speeds around its axis of symmetry and thins as it moves away from the nozzle exit until it finally lands on the collector. Except for the Newtonian fluid assumption, our model includes the key parameters of the curved jet flow, e.g. viscous, inertial, rotational, surface tension, gravitational, mass diffusion within the jet, mass diffusion into air and aerodynamic effects, via Rossby ( ), Reynolds ( ), Weber ( ), Froude ( ), Peclet ( ), air Reynolds ( ) and air Peclet ( ) numbers, and the collector radial position ( ). Our results, including comparison to experiments, reveal that the aerodynamic effects must be considered to enable a correct prediction of the jet trajectory and radius. Decreasing not only renders the jet thinning much faster, but also forces the jet to wrap tighter around the rotation axis. Increasing , and leads to a longer jet. Decreasing causes the jet to wrap tighter around the spinneret but it shows trivial effects on the solvent evaporation. Changes in and do not significantly affect the jet trajectory. Finally, we propose simple relations to estimate the jet radius and the jet breakup length.