Breakup Of Liquid Jet Research Articles

Liquid flow mode transition and hysteresis under passive control

The liquid flow mode exerts a significant influence on the dynamics of droplet breaking, with consequential effects on factors like droplet size and monodispersity. In various applications, including but not limited to inkjet printing, microcapsule preparation, and cell encapsulation, diverse production methods are employed, but they typically rely on some form of droplet breakup or liquid jet breakup to ultimately generate droplets. During the process of droplet formation, smaller satellite droplets, which are considerably smaller than the main droplet, are inevitably generated. These smaller droplets can lead to wastage of raw materials and reduced production efficiency. Passive control methods, which involve modifications to the structure of the dropper, effectively suppress the formation of satellite droplets, and prove to be more practical and manageable in actual production scenarios when compared to active control methods. In contrast to the jetting mode, the dripping mode of droplet molding exhibits greater stability and size uniformity, thereby better meeting the requirements for particle uniformity in the preparation of traditional Chinese medicine. This paper specifically investigated the transition from the jetting mode to the dripping mode and explored the hysteresis of this transition under the influence of gravity utilizing a passive control method. By incorporating a drainage device within the dropper along with a Y-channel, a drainage system was established to achieve passive control. The effects of the length and diameter of the drainage device, as well as the mass fraction of the solution, on the conversion of flow modes were analyzed.

Experimental and Numerical Simulation of Flow Modes in Flow Focusing/Blurring Nozzle

The flow mode of the flow focusing/blurring nozzle was studied through experimental and numerical simulation methods. The experimental results indicate that the flow mode of the nozzle can be classified into flow focusing, transition, and flow blurring based on the location of the liquid jet breakup. Numerical simulation studies have found that the transformation of flow mode is mainly related to viscous shear force, gas pressure on the jet surface, and liquid inertia force. The increase in the gas flow rate changes the flow mode by affecting the viscous shear force. The increase in the liquid flow rate changes the flow mode by affecting the liquid inertial force. When the liquid flow rate is high, the increase in the liquid flow rate affects the flow mode by affecting the gas pressure on the jet surface. The study also found that excessive gas flow rates can hinder the flow of liquid inside the nozzle, while excessive liquid flow rates can hinder the breakup of liquid inside the nozzle. Therefore, the normal operation of the flow focusing/blurring nozzle requires ensuring that the gas and liquid flow rates are within the normal range.

Electrospray modes of liquids in electrohydrodynamic atomization: A review

Liquid is sprayed from a capillary tube and further disperses into fine drops in various means, when subjected to an externally electric field, where the process of liquid jet formation and breakup into drops is usually named as electrohydrodynamic atomization or electrospray (ES). Electrospray has been extensively applied into many fields because uniform and highly charged drops, easy controllability in size and motion, and various ES modes are available to match the requirements of various applications. In present work, recent progresses in theory and numerical work to explain electrospray structure and drop formation were summarized. According to the geometry of liquid ejection and its further disintegration, main ES modes including dripping, micro-dripping, spindle, cone-jet, multi-jet, and simple-jet have been designated. The transformation of ES modes due to variation of electric potential, liquid flow rate, and physical parameters, the formation of curved liquid surface, and jet fragmentation behavior in these ES modes were also reviewed, as well as generated drops dynamics. In a rational range of flow rate, dripping, micro-dripping, spindle, cone-jet, multi-jet modes successively emerge with an increase in electric potential, and otherwise, an irregular instability may occur. In addition, the simple jet mode occurs in a relatively large flow rate. The insight into ES modes may fully understand mechanism and technology of electrospray and further promote more extensive application in industrial fields.

Flow Behavior and Breakup of Liquid Jets Issued from Rectangular Nozzles

Flow Behavior and Breakup of Liquid Jets Issued from Rectangular Nozzles

Enhancing Rayleigh-regime liquid jet breakup with MHz-order acoustic waves

We present a new device that effectively reduces the breakup of cylindrical Rayleigh-regime liquid jets in quiescent air. The device is made of lithium niobate, a piezoeletric material, to convert input electrical power into oscillation. A 10x10 mm crystal with a through hole of 1 mm in diameter placed at the outlet of the liquid's nozzle, the device creates 7 MHz acoustic waves that disrupt the stability of the jet. We show its effectiveness over a range of different input powers and Weber and Ohnesorge numbers. Furthermore, we show modelling results in COMSOL and equations that describe this new instability mechanism. This opens new doors for droplet-on-demand applications.

Experimental Investigation on Atomization of JP-10 Slurry Jets Containing Boron Nanoparticles

The present work aims to experimentally investigate the atomization of JP-10 based slurry jets containing boron nanoparticles. A coaxial airblast injector is used to atomize the slurry fuel. Different injector operating conditions are realized by varying the air and the fuel flow rates through the atomizer. For each case, different particle-to-fuel mass loading ratios ϕ (equal to 0, 5, 10, and 20%) are investigated. Time-resolved imaging is performed near the nozzle exit and 30Dl downstream of the injector exit to visualize the primary liquid jet breakup process and the resulting spray droplets, respectively. The instantaneous jet breakup length, droplet size, and velocity are obtained by processing the raw images. The influence of particle loading on the mean and fluctuations of jet breakup length, droplet size, and droplet size/velocity correlation is investigated in detail. The results highlight degradation in atomization quality for higher particle loading ratio in the base fuel. A monotonic increase in the mean jet breakup length with particle loading ratio is identified. The Sauter mean diameter increases by about 100% when ϕ is increased from 0 to 20%. It is found that ϕ must be accounted for, in addition to conventional nondimensional numbers, in the experimental correlations for jet breakup length and droplet size for nanofuel slurry.

Study on the spray characteristics of transverse jets with elliptical nozzles in supersonic crossflows using the volume of fluid–discrete phase model

The atomization characteristics of liquid jets injected transversely into a supersonic crossflow significantly affect the performance of scramjet engines. Existing research on this topic has mainly focused on circular nozzles, while the influence of nozzle geometry, particularly elliptical nozzles, has received relatively limited attention. Therefore, this study employs a numerical simulation method coupling the volume of fluid and discrete particle model to investigate the breakup and atomization characteristics of transverse liquid jets from elliptical nozzles with different aspect ratios under supersonic crossflow conditions, as well as the total pressure loss. The simulation model is validated against experimental data obtained from a pulse wind tunnel, including measurements of the liquid jet penetration depth and the Sauter mean diameter (SMD). The results indicate that for elliptical nozzles with an aspect ratio (AR) greater than 1, columnar breakup occurs earlier, and the columnar breakup length is shorter compared to circular nozzles. As the AR increases, the jet penetration depth decreases, while the spray expansion angle increases. Furthermore, the SMD of the atomized spray field from the circular nozzle is larger than that from the elliptical nozzles, and the SMD of the spray field is smallest for an elliptical nozzle with AR of 4. Finally, the elliptical nozzles exhibit a higher total pressure recovery coefficient, indicating reduced total pressure loss in the combustion chamber. This reduction in pressure loss is expected to improve the thrust performance of the scramjet engine.

Analysis of the explicit volume diffusion subgrid closure for the [formula omitted] model to interfacial flows over a wide range of Weber numbers

The explicit volume diffusion (EVD) method was recently proposed for simulating interfacial flows based on the volume of fluid method. In this work, the EVD equations are derived rigorously from the Σ−Y (surface density and mass fraction) perspective under the large eddy simulation (LES) framework. Volume averaging is applied over an explicit length scale ℓV that is grid-independent. The sub-volume flux and stress are closed through gradient diffusion and viscosity models that account for the presence of an interface and turbulence, and have the correct limits in the absence of interface vorticity and in the pure phases. An EVD equation for Σ is introduced for the first time to model the volume averaged surface tension. The EVD model and closures are tested for three different liquid jet breakup cases: a series of laminar round jets in the Rayleigh-Plateau regime (12<Wel<34), a turbulent coaxial air-blast jet (Weg=75) and a high Weber number turbulent crossflow (Weg=330). Numerical convergence and sensitivity to ℓV are investigated, along with comparisons to linear theory, experimental data, empirical correlations and previous simulations. The effects of the closures on flow dynamics and key dimensionless numbers are also analysed.

Swirling Capillary Instability of Rivlin–Ericksen Liquid with Heat Transfer and Axial Electric Field

The mutual influences of the electric field, rotation, and heat transmission find applications in controlled drug delivery systems, precise microfluidic manipulation, and advanced materials’ processing techniques due to their ability to tailor fluid behavior and surface morphology with enhanced precision and efficiency. Capillary instability has widespread relevance in various natural and industrial processes, ranging from the breakup of liquid jets and the formation of droplets in inkjet printing to the dynamics of thin liquid films and the behavior of liquid bridges in microgravity environments. This study examines the swirling impact on the instability arising from the capillary effects at the boundary of Rivlin–Ericksen and viscous liquids, influenced by an axial electric field, heat, and mass transmission. Capillary instability arises when the cohesive forces at the interface between two fluids are disrupted by perturbations, leading to the formation of characteristic patterns such as waves or droplets. The influence of gravity and fluid flow velocity is disregarded in the context of capillary instability analyses. The annular region is formed by two cylinders: one containing a viscous fluid and the other a Rivlin–Ericksen viscoelastic fluid. The Rivlin–Ericksen model is pivotal for comprehending the characteristics of viscoelastic fluids, widely utilized in industrial and biological contexts. It precisely characterizes their rheological complexities, encompassing elasticity and viscosity, critical for forecasting flow dynamics in polymer processing, food production, and drug delivery. Moreover, its applications extend to biomedical engineering, offering insights crucial for medical device design and understanding biological phenomena like blood flow. The inside cylinder remains stationary, and the outside cylinder rotates at a steady pace. A numerically analyzed quadratic growth rate is obtained from perturbed equations using potential flow theory and the Rivlin–Ericksen fluid model. The findings demonstrate enhanced stability due to the heat and mass transfer and increased stability from swirling. Notably, the heat transfer stabilizes the interface, while the density ratio and centrifuge number also impact stability. An axial electric field exhibits a dual effect, with certain permittivity and conductivity ratios causing perturbation growth decay or expansion.

Statistical analysis of rotary atomization by phase Doppler anemometry

Rotary atomization is used in a wide variety of fields, exploiting the external control option of the spray while no high-pressure fluid is needed. Most papers on rotary atomization deal with liquid jet breakup, while external spray characteristics are rarely evaluated; this is performed currently. The water spray was measured by a two-component phase Doppler anemometer. The optical setup requires a special measurement chamber to avoid spray deposition on the optical components. Therefore, the first goal was to find a proper filter that enables the removal of biased droplets by secondary flows. Since most droplets have a similar radial-to-tangential velocity ratio at each measurement point, i.e., scattering around a line, this was the first component of the best filter. The second component was the need for a positive radial velocity component. This filter efficiently removed droplets originating from alternative processes, increasing the R2 of the line fit. The physical soundness of this filter was checked by evaluating the effect of filtering on the angle of the velocity components of each droplet at a given measurement point. The proposed filter efficiently detected recirculation, a secondary effect of the measurement setup with less regular dataset shapes. Finally, the slope and intercept values of the fitted lines were evaluated and presented. The mean of the former followed the same trend irrespective of the rotational speed and the mass flow rate; it was principally dependent on the radial distance from the atomizer. The intercept showed a regular but less universal behavior.

Data-driven surrogate modelling of multistage Taylor cone–jet dynamics

The Taylor cone jet is an electrohydrodynamic flow typically induced by applying an external electric field to a liquid within a capillary, commonly utilized in colloidal thrusters. This flow generation involves a complex multiphase and multiphysics process, with stability contingent upon specific operational parameters. The operational window is intrinsically linked to flow rate and applied electric voltage magnitude. High voltages can induce atomization instabilities, resulting in the production of an electrospray. Our study presents initially a numerical investigation into the atomization process of a Taylor cone jet using computational fluid dynamics. Implemented within OpenFOAM, our numerical model utilizes a volume-of-fluid approach coupled with Maxwell's equations to incorporate electric body forces into the incompressible Navier–Stokes equations. We employ the leaky-dielectric model, subjecting the interface between phases to hydrodynamic surface tension and electric stress (Maxwell stress). With this model, we studied the droplet breakup of a heptane liquid jet, for a range of operation of 1.53–7.0 nL s−1 and 2.4–4.5 kV of extraction. First, the developed high-fidelity numerical solution is studied for the jet breakup and acceleration of the droplets. Second, we integrate a machine learning model capable of extending the parametric windows of operation. Additionally, we explore the influence of extractor and acceleration plates on colloidal propulsion systems. This work offers a numerical exploration of the Taylor cone–jet transition and droplet acceleration using novel, numerically accurate approaches. Subsequently, we integrate machine learning models, specifically an artificial neural network and a one-dimensional convolutional neural network, to predict the jet's performance under conditions not previously evaluated by computationally heavy numerical models. Notably, we demonstrate that the convolutional neural network outperforms the artificial neural network for this type of application data, achieving a 2% droplet size prediction accuracy.

The breakup and instability structures of liquid jets in subsonic crossflows

The breakup of water and Jet A fuel jets injected transverse into elevated temperature (up to 425 °C), combustion pre-heated, subsonic crossflows was investigated by internally fluorescing the liquid jet column. The fluorescent dye seeded test liquids were illuminated by a pulsed laser light that was transmitted within the injector using a quartz rod light-guide. High-resolution images isolating the intact liquid column from light scattered by the surrounding dense spray facilitated precise measurement of the liquid column breakup position and the size and distribution of windward column instability waves. The injector geometry consisted of a 1 mm circular orifice with an orifice length of 20 mm with a tapered inlet. Liquid jet to gaseous crossflow momentum flux ratios were varied from 6 to 266 and the gas Weber number was varied from 10.7 to 228. Empirical correlations were derived for the liquid column breakup coordinates and breakup time in addition to the average and local maximum instability wavelength and amplitude on the liquid column windward surface. The reported correlations provided key insight into atomization physics and aim to support the quantitative validation of high-fidelity numerical simulations of the liquid jet in subsonic crossflow.

Primary breakup of liquid jet—Effect of jet velocity profile

The present work examines the effect of the velocity profile on primary breakup of liquid jets emanating from fuel injectors. Direct numerical simulation is used to simulate liquid jet breakup. Different velocity profiles are imposed on the liquid and their effect on breakup is examined. It is a common practice in the literature to use flat or uniform velocity profiles in such studies. The validity of this assumption is assessed and its implications are highlighted. Droplet sizes and degree of atomization are compared for all the cases. Further, a detailed comparison of jet breakup structure is made for two cases—parabolic and power-law velocity profiles. The liquid surface is observed to show two-dimensional waves initially, which subsequently transform into three-dimensional waves and give rise to ligament formation and surface breakup. Tip vortex rollup and its role in jet breakup is discussed. The distinction between different velocity profiles is examined in detail in terms of surface waves, degree of atomization, and jet structure.

Primary breakup model development for trajectory prediction of liquid jets in subsonic crossflow

A comprehensive theoretical model for the primary breakup of liquid jets in subsonic crossflow was developed. The model theoretically analyzed the jet deformation process, mass stripping process, and the influence of several critical forces and consequently provided highly accurate predictions of the jet trajectory. Deformation of the liquid jet cross section was considered as a two-stage process based on the physical characteristics, including the spring-mass analogy deformation and the mass stripping induced deformation. The mass stripping process was modeled as an exponential function of time based on experimental findings for liquid jets and droplets. Balance of critical forces acting on the jet were analyzed, both along the gas and jet flow directions, which included aerodynamic drag, viscous force, surface tension, and gravitation. The model provided precise prediction to the jet trajectory against experimental data without any initial jet velocity assumption across a wide range of gaseous Weber numbers and gas to liquid momentum ratios. In addition, quantitative effects of viscous force, surface tension force, and aerodynamic drag on jet trajectory were fully investigated based on the new model, which provided more insight into jet breakup characteristics and the effects of fuel properties on jet trajectory and deformation. Furthermore, the three-dimensional structure of the jet was reconstructed through the present model, which matched well against numerical results. Importantly, the current mathematical primary breakup model could be integrated with Lagrangian methods, obtaining more detailed vortex structures and accurate droplet dispersion with reduced computational time.

Review of atomization characteristics of liquid jets in crossflow

The atomization process of liquid fuels is vital in scramjet engines. The level of atomization directly impacts the subsequent evaporation, mixing, and combustion processes. Therefore, understanding the atomization mechanism of liquid jets in crossflow is necessary to promote the mixing process of scramjet engines and improve the combustion efficiency. This article overviews the atomization process of liquid jets in transverse airflow based on the breakup mechanism, atomization characteristics, and factors affecting atomization. The deformation and fragmentation of droplets are influenced primarily by the Weber number and have little correlation with the Reynolds number. There are similarities in the properties between the primary fragmentation of liquid jets and the breakup of liquid droplets in crossflow. The primary breakup of liquid jets in crossflow is characterized primarily by continuous jet column breakup. The Rayleigh–Taylor instability causes columnar breakup, while the Kelvin–Helmholtz instability causes surface breakup in the jet. The size distribution of droplets follows C-, I-, or S-shaped distributions, while the velocity distribution of droplets follows an inverse C-shape. Finally, the shortcomings of current research are pointed out, namely, the lack of research on the jet breakup mechanism in crossflow under actual scramjet engine configurations and inflow conditions. In the future, it can be combined with artificial intelligence to reveal the jet breakup mechanism under actual working conditions and establish a wide range of theoretical prediction models.

The Primary Breakup and Atomization Characteristics of Liquid Jet in Crossflow at the Fixed Momentum Ratio and Weber Number

ABSTRACT The primary breakup behaviors of injected fuel were investigated by high fidelity simulation. The influence of various parameters on the breakup and atomization was analyzed at the fixed momentum ratio and Weber number. The results indicated that a simultaneous increase of the surface tension coefficient and the velocity of crossflow will hardly affect axial waves. The air density primarily affected the friction acting on the liquid column near the nozzle, while the liquid density affected the liquid flow in the liquid column to the sides. These variations lead to differences in breakup modes. The evolution of liquid column shape at different penetration heights suggested that the formation of sheet-like structures on the sides of liquid column was one of the main reasons for its deflection. The deflection of liquid column was enhanced by the increase of air density, and it was weakened at the increase of surface tension coefficient. In addition, it was also observed that for different parameters, the change of the boundary of spray plume in the y direction corresponded to variations in liquid column deflection. The diameter distribution of droplets generated by the primary breakup was predominantly influenced by density, with only a slight impact from the surface tension coefficient.

FUNDAMENTAL INVESTIGATION OF LIQUID INJECTION IN SUPERSONIC CROSSFLOW: AN EXPERIMENTAL STUDY

Experimental investigation of the liquid injection into a Mach 2.2 supersonic crossflow through a transverse single circular injector has been carried out in the present study. High-speed visualization techniques such as back-lit imaging, shadowgraphy, and schlieren imaging have been employed to investigate the flow and the liquid jet features. The present study provides a detailed analysis of the breakup behavior of a liquid jet introduced into a crossflow with a Mach number of 2.2 by categorizing it into distinct zones. The liquid jet breakup was induced by surface instabilities, leading to the formation of a protrusion structure that traveled downstream along the jet. The schlieren photographs captured the essential flow dynamics resulting from the liquid injection, such as the bow shock wave and the separation shock wave. Observations indicated that the location where the bow shock wave interacts with the upper wall shifts in the upstream direction as the liquid injection pressure is increased. Furthermore, a parametric analysis was conducted to assess the penetration height of the injected liquid and its variation relative to the injection pressure. The analysis revealed that the penetration of the jet was greatest at an injection pressure of 7 bar, succeeded by 5 bar and 3 bar, respectively. The minimal penetration height was recorded at an injection pressure of 1 bar. In a quantitative analysis, the penetration of a liquid jet was measured at various injection pressures at a normalized axial distance of 5. It was found that the penetration of the liquid jet with an injection pressure of 7 bar was 3.67 times greater than the liquid injection with an injection pressure of 1 bar.

Numerical investigation of particle dispersion and collision in a liquid jet flow

A numerical simulation with the Eulerian–Lagrangian point-particle approach is used to study the dispersion of nanoparticles in liquid jet flows. The volume of fluid method is used to simulate the motion of the gas–liquid interface. The particle motion is resolved by the Lagrangian point-particle model, and the collisions among particles are considered. According to the simulation results, the liquid jet atomization process can be divided into four different periods. Moreover, the nanoparticles lead to an increase in the liquid density and viscosity. The influence of the particle motion on the liquid jet breakup process is discussed. The simulation results show that the collisions would restrain particle dispersion. However, the motions and collisions of the particles would help the breakup of the liquid jet.

Experimental study of breakup and atomization characteristics of liquid carbon dioxide jet under high-pressure environment

Considering the working conditions of a Mg/CO2 rocket engine for Mars exploration, an experimental investigation was carried out to study the breakup and atomization properties of a liquid CO2 jet in a high-pressure environment. It is shown that the pressure ratio has a significant effect on the location and process of jet evaporation, resulting in significant difference in jet morphology and breakup characteristic. Two dividing points were identified, one near the CO2 triple point and the other near the saturation point. As the pressure ratio increases, the thermodynamic driving force for jet breakup weakens, leading to larger droplet sizes. The breakup length of the free round jet and Sauter mean diameter are functions of the Weber number and Jacob number, which are influenced by vapor content, injection velocity, and gas-liquid density ratio, in the mass flowrate range of 5.9–9.1 g/(mm2·s). A thermodynamic mechanism dominates when the ambient pressure in the atomize room is low enough, resulting in an unimodal distribution of droplet sizes. When the ambient pressure is in the range of 1–2.5 MPa, both thermodynamic and mechanical breakup mechanisms are active, resulting in a bimodal distribution of droplet sizes.

Vorticity dynamics in transcritical liquid jet breakup

A transcritical domain with a sharp two-phase interface may exist during the early times of liquid hydrocarbon fuel injection at supercritical pressure. Thus, two-phase dynamics are sustained before substantial heating of the liquid and drive the early three-dimensional deformation and atomisation. A recent study of a transcritical liquid jet showed distinct deformation features caused by interface thermodynamics, low surface tension and intraphase diffusive mixing. In the present work, the compressible vortex identification method $\lambda _\rho$ is used to study the vortex dynamics in a cool liquid n-decane transcritical jet surrounded by a hotter oxygen gaseous stream at supercritical pressures. The relationship between vortical structures and the liquid surface evolution is detailed, along with the vorticity generation mechanisms, including variable-density effects. The roles of hairpin and roller vortices in the early deformation of lobes, the layering and tearing of liquid sheets and the formation of fuel-rich gaseous blobs are analysed. At these high pressures, enhanced intraphase mixing and ambient gas dissolution affect the local liquid structures (i.e. lobes). Thus, liquid breakup differs from classical sub-critical atomisation. Near the interface, liquid density and viscosity drop by up to 10 % and 70 %, respectively, and the liquid is more easily affected by the vortical motion (e.g. liquid sheets wrap around vortices). Despite the variable density, compressible vorticity generation terms are smaller than the vortex stretching and tilting. Layering traps and aligns the vortices along the streamwise direction while mitigating the generation of new rollers.