Surface Of Liquid Jet Research Articles

Study of the effects of the injector length/diameter ratio on the surface properties of turbulent liquid jets in still air using X-ray imaging

The disintegration of turbulent liquid jets in gases, a process termed turbulent primary breakup, has many industrial applications, especially in liquid injection systems whose injector internal flow results in enhanced turbulence generation. An investigation was carried out by using X-ray diagnostics at the Advanced Photon Source (APS) facility of Argonne National Laboratory on two injectors with a smooth entry followed by round passage with different length-to-diameter ratios of 10 and 40, operating at the same injection speed. The test matrix was designed to eliminate cavitation and to isolate the effect of length/diameter ratio of the injector passage and to determine the importance of jet turbulence compared to aerodynamic forces. The X-ray diagnostics used allowed the surface and internal topography of liquid jets to be visualized and the spatial distribution of the surface ligaments to be revealed in the near-injector region. The present results show that the separation distance between a ligament and its neighbors depends on the ligament sizes, and the injector length/diameter ratio affects the rates of breakup.

Application of maximum entropy method for droplet size distribution prediction using instability analysis of liquid sheet

This paper describes the implementation of the instability analysis of wave growth on liquid jet surface, and maximum entropy principle (MEP) for prediction of droplet diameter distribution in primary breakup region. The early stage of the primary breakup, which contains the growth of wave on liquid–gas interface, is deterministic; whereas the droplet formation stage at the end of primary breakup is random and stochastic. The stage of droplet formation after the liquid bulk breakup can be modeled by statistical means based on the maximum entropy principle. The MEP provides a formulation that predicts the atomization process while satisfying constraint equations based on conservations of mass, momentum and energy. The deterministic aspect considers the instability of wave motion on jet surface before the liquid bulk breakup using the linear instability analysis, which provides information of the maximum growth rate and corresponding wavelength of instabilities in breakup zone. The two sub-models are coupled together using momentum source term and mean diameter of droplets. This model is also capable of considering drag force on droplets through gas–liquid interaction. The predicted results compared favorably with the experimentally measured droplet size distributions for hollow-cone sprays.

Electrostatic instability of the lateral surface of a viscous liquid finite-conductivity jet in a collinear electrical field

The influence of the finiteness of the charge transfer rate on the electrostatic instability of the lateral surface of a viscous liquid jet is studied. The study is based on the analysis of a dispersion relation for flexural-deformation capillary waves on the surface of the jet with allowance for charge relaxation. The jet is subjected to a superposition of two electrostatic fields one of which is collinear with the jet’s axis and the other is directed radially to the former. It is found that the finiteness of the potential equalization rate influences jets of a poorly conducting liquid most strongly. The charge relaxation shows up in the appearance of both periodic and aperiodic “purely relaxation” flows. Relaxation flows give rise to electrostatic instability in low-permittivity liquids. When the conductivity of the liquid drops, the instability growth rate of relaxation waves grows and their spectrum expands toward shorter waves. An increase in the charge surface diffusion coefficient introduces destabilization into the relaxation flows of the liquid, which may eventually become unstable.

Mechanisms controlling supercritical antisolvent precipitate morphology

Supercritical antisolvent precipitation (SAS) has been successfully used to micronize several kinds of materials. A great variety of morphologies, such as nanoparticles with mean diameters in the 30–200 nm range, spherical microparticles in the 0.25–20 μm range, hollow expanded microparticles with diameters between about 10 and 200 μm, and crystals with various habits and micrometric dimensions have been frequently obtained. However, a comprehensive analysis of the mechanisms that control the attainment of the different particle size and morphologies has not been proposed, yet. In this work, the interactions among high-pressure vapor–liquid equilibria, surface tension variations, jet fluid dynamics, mass transfer, nucleation and growth are indicated as the responsible for the observed SAS morphologies. The possible particle formation mechanisms are indicated and discussed on the basis of the experimental results. Liquid jet break-up and surface tension vanishing at supercritical conditions are indicated as the processes in competition to produce spherical microparticles or nanoparticles. Two possible mechanisms can be involved in crystals formation: (1) droplets drying followed by a fast crystallization kinetics, that can led to the formation of crystals with a spherical predominant shape; (2) the precipitation from an expanded liquid phase that can led to crystals with various habits and dimensions, depending on the interactions with the liquid solvent used.

Modeling the disintegration of modulated liquid jets using volume-of-fluid (VOF) methodology

In this study, we present the numerical investigations on the effect of finite velocity modulations imposed on an otherwise unperturbed cylindrical liquid jet issuing into stagnant gas. Sinusoidal velocity fluctuations of finite frequency and amplitude are imposed at the liquid jet inlet and the resulting liquid jet surface deformation is captured using a volume of fluid (VOF) methodology, utilizing compressive interface capturing scheme for arbitrary meshes (CICSAM) scheme. Variation of the simulation parameters, comprising of the mean liquid jet velocity, modulation amplitude and frequency grouped together using a set of non-dimensional parameters, leads to the formation of a wide gamut of reproducible liquid structures such as waves, upstream/downstream directed bells, chains of droplets similar to those observed in experiments. Elaborate tests on the effect of injection velocity and inlet jet diameter are investigated to characterize the breakup process. The computations efficiently capture the diverse flow structures generated by the evolving modulated liquid jet inclusive of several non-linear dynamics such as growth of surface waves, ligament interaction with shear vortices and its subsequent thinning process. The simulations identify the deterministic behavior of modulated liquid jets to predict liquid disintegration modes under given set of non-dimensional parameters.

Asymptotic analysis of nonlinear nonaxisymmetric waves on the surface of a neutral dielectric jet in a longitudinal electrostatic field

The problem of calculation of finite-amplitude waves on the cylindrical surface of an ideal incompressible dielectric liquid jet in a uniform electrostatic field collinear to the unperturbed jet axis is solved using a second-order asymptotic analytic procedure in ratio of the wave amplitude to the jet radius. Nonlinear corrections to the jet profile, velocity field potential, and electrostatic potentials inside and outside the jet are of resonant nature. The degenerate resonant interaction between the wave determining the initial strain and the waves excited due to nonlinearity of the hydrodynamic equations can take place for waves with different symmetries (different azimuth numbers).

Nozzle-Geometry Effects on Upwind-Surface Properties of Turbulent Liquid Jets in Gaseous Crossflow

An experimental study to investigate the effect of nozzle length-to-diameter ratio and the inlet curvature on the surface properties of turbulent liquid jets in gaseous crossflow was carried out. Straight nozzles with length/diameter ratios of 10, 20, and 40 were used to generate turbulent liquid jets in gaseous crossflow. The radius of curvature ofthe nozzles used was 0.6,1.2, and 2.4. The present study was limited to small Ohnesorge number liquid jets (Oh 110). The diagnostics consisted of double-pulsed holographic microscopy and shadowgraphy. The measurements included liquid-jet surface properties, breakup location of the liquid column as a whole, and the breakup-regime transitions. The measurements were interpreted and correlated using phenomenological analyses. It was observed that the injector passage length plays a role in determining the breakup length and influences the characteristics of the jet upwind surface.

Spray jet penetration and distribution of modulated liquid jets in subsonic cross-flows

Modulated liquid jets injected into subsonic cross-flows are empirically studied by using a mechanical liquid jet modulation apparatus. Experimental investigations were conducted using water over a range of cross-flow velocities from 5 m/s to 143 m/s and with modulated liquid jet frequencies from 35.7 Hz to 166.2 Hz and so on. PDPA(phase Doppler particle anemometry) was employed to measure droplet diameter and velocity with various spray cross-sections from Z/d=20 to Z/d=60. The spray structure, penetration depth, SMD(Sauter mean diameter), volume flux and velocity characteristics of modulated liquid jets injected into cross-flows were examined. As oscillation of the periodic pressure that could make liquid jet moved up and down in cross-flow field, the mixing process was facilitated. This phenomenon has the advantage of mixing the spray concentration from the center area to the outer area. Also, a bulk liquid jet puff was detected in the upper field of the liquid jet surface. The modulation effect appears significant in the extent of the spray oscillation. The correlation equations for the liquid jet boundary of the upper and lower regions which related to the Strouhal number have been presented to predict the spray structure under modulation conditions. Because of the modulation frequency, an inclination of averaged SMD for the structured layer was evanescent which contributed to the promotion of the macroscopic spray mixing process. Cross-sectional characteristics of SMD had the same tendency over a range of various modulation frequencies. As the modulation frequency increased, the region of volume flux distribution also increased.

Measurement of free surface of liquid metal lithium jet for IFMIF target

Lithium (Li) flow experiment was conducted for a Li target of International Fusion Materials Irradiation Facility (IFMIF). In the experiment, Li plane jet of 10 mm in depth and 70 mm in width formed by a two contractions nozzle was tested in the velocity range of less than 15 m/s. In the present report, wave patterns (called as surface wakes) on the Li flow were measured by Pattern Projection Method. This is an image measurement of non-contact and three dimensions. The projected patterns, which were stripes in this study, were observed to be deformed according to the surface up-and-down. Three-dimensional surface shape could be obtained by analyzing the deformed patterns. By the method, surface wakes were successfully measured. The results were compared with a theoretical study and showed good agreement.

Atomization characteristics on the surface of a round liquid jet

Fundamental mechanisms of liquid jet breakup are identified and quantified. The quality of the atomization of liquids is an important parameter of many technological processes and is, e.g. for fuels and propellants critical in defining engine performance. This investigation takes a look at the jet behavior for a single injector element to determine the influence of the injection conditions on a round liquid jet. The study focuses on the atomization of a liquid forming a classical spray. To adjust the relative velocity between the liquid jet and the gaseous ambient a wind tunnel-like coaxial flow configuration was used. This made it possible to distinguish between effects of aerodynamic forces, chamber pressure and jet velocity, which determine the liquid Reynolds number and thereby the internal jet turbulence. Shadowgraphy and a novel image-processing approach was used to determine the jet surface characteristics: wavelength and amplitude. The absolute injection velocity of the jet seems to affect the structures the most with an increasing velocity causing the wavelengths to be smaller. An increase in chamber pressure seemed to have little influence on the jet with no relative velocity between the gas and liquid jet, but increased the amplitude and drop formation frequency at other testing conditions with relative motion. The wave amplitude trends provide information about the likelihood of drop formation but are limited in maximum size due to this breakup phenomenon of the jet. The study of the direction of the relative velocity demonstrated that injector performance cannot simply be described by scalar geometrical and operational injection parameters (e.g., We , Re or Oh), but has to include the injection direction of the atomizing fluids in relation to each other and to the ambient (e.g., combustion chamber). The undisturbed jet length and the spread angle were investigated, and a correlation for the droplet separation position was proposed. The data led to an extended classification of liquid jet breakup regimes. Large wave instabilities were experimentally analyzed and compared with linear stability theory.

Initial breakup of a small-diameter liquid jet by a high-speed gas stream

The situation of a small-diameter liquid jet exposed to a large-diameter high-speed gas jet (gas-to-liquid nozzle area ratio of order 100 to 1000) is investigated experimentally. Flow visualization and particle-sizing techniques are employed to examine the initial jet breakup process and primary liquid atomization. Observations of the initial breakup of the liquid jet in the near-nozzle region, combined with droplet-size mea-surements, are used in an effort to elucidate the dominant mechanism of primary breakup of the liquid. It is shown that for large aerodynamic Weber numbers, the bulk of the liquid atomization is completed within a few gas-jet diameters of the nozzle exit, inside of the potential cone of the gas flow. Breakup is therefore completed within the zone of constant ambient gas velocity. It is argued that the mechanism of initial jet breakup is similar to that of a liquid drop suddenly exposed to a high-speed gas stream. A phenomenological breakup model is proposed for the initial droplet size, based upon the accelerative, secondary destabilization (via Rayleigh–Taylor instability) of the liquid wave crests resulting from the primary Kelvin–Helmholtz instability of the liquid jet surface. Primary mean droplet sizes are shown to scale well on the most unstable Rayleigh–Taylor wavelength, and the dependence of the droplet diameter on both the atomizing gas velocity and the liquid surface tension are successfully captured by the proposed breakup model.

Numerical simulation on liquid jet behavior issued into still air

AbstractNumerical simulations have been conducted to clarify the effects of turbulence, in the onset of protrusions on liquid jet surfaces. The turbulences in the liquid jet were simulated by the Rankin vortices. The liquid jet surface was tracked numerically by the VOF method. From numerical simulations, the protrusions on the liquid jet surface are induced by the vortices in the liquid, whose rotational direction decelerates the jet surface. Despite the distance between vortices, the displacement of the liquid jet surface from the initial surface location increases linearly, in time, at almost the same growth rate. In the initial region, the growth rate of the displacement increases as the major semiaxis‐to‐minor semiaxis ratio of the ellipsoidal vortex increases. The initial growth rate of displacement is almost proportional to the vortex intensity. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 141–152, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10078

Highly Expanded Flashing Liquid Jets

Results arepresented of experiments with highly expanded e ashing liquid jets along with a one-dimensional numericalmodel.Theexperimentswerecarriedoutwithliquidiso-octanejetsissuing from asmallconical convergent nozzle into a low-pressure chamber. Images of the expanding jet off the nozzle exit section were obtained from a schlieren setup using a charge-coupled device camera. Analyses of these images enabled a qualitative visualization of the e ashing jet structure and geometry. At very low backpressures, it has been observed that the emerging jet wasformedbya central liquid core,and thephasechangeprocessoccurred onthesurfaceofthatliquidcore,giving rise to a sonic two-phase e ow. In addition, it is also inferred that the freshly formed two-phase e ow proceeded further to higher velocities and Mach numbers to terminate eventually with a complex shock wave structure to adjust pressures, as usual. A one-dimensional numerical analysis is carried out. The sudden phase change in the metastable liquid jet surface is modeled as an evaporation wave, for which the jump equations are solved. Next, the supersonic expansion of the two-phase mixture downstream of the evaporation wave is analyzed in a radial direction. Theone-dimensional calculation yielded theradial position of the shock wavelocation. It has been found that the numerical results are consistent with the experimental data.

Jet break up of liquid metal in twin fluid atomisation

For melt disintegration in spray forming and metal powder production, the liquid metal typically is atomised by means of twin fluid atomisation e.g. with inert gases. The first stage of the atomisation process is covered by the initialisation and development of surface perturbations on the liquid jet surface that subsequently grow and finally lead to the break up of the melt jet. The primary disintegration process affects all further stages of the atomisation process and hence influences the resulting spray characteristics. In this contribution, the influence of different material properties on the primary disintegration process of a metal melt in a free fall atomiser configuration is investigated. Surface instabilities of liquid metal jets up to the primary break up are analysed experimentally as well as analytically. Results of a linear instability analysis are discussed and compared to evaluations of high-speed video images. In comparison of both results the periodicity and main mechanism of the initialisation process is analysed.

Liquid breakup at the surface of turbulent round liquid jets in still gases

An experimental study of liquid column breakup lengths and turbulent primary breakup properties at the surface of turbulent round liquid jets in still air at standard temperature and pressure is described. Jet exit conditions were limited to non-cavitating water and ethanol flows, long length/diameter ratio (greater than 40:1) constant-diameter round injector passages, jet exit Reynolds numbers of 5000–200,000, jet exit Weber numbers of 235–270,000 and liquid/gas density ratios of 690 and 860, at conditions where direct effects of viscosity were small (e.g., liquid jet Ohnesorge numbers were smaller than 0.0053). Three liquid column breakup modes were observed, as follows: a weakly turbulent Rayleigh-like breakup mode observed at small jet exit Weber and Reynolds numbers, a turbulent breakup mode observed at moderate jet exit Weber numbers, and an aerodynamic bag/shear breakup mode observed at large jet Weber numbers. The turbulent primary liquid column breakup mode was associated with conditions where drop diameters resulting from turbulent primary breakup along the liquid surface were comparable to the diameter of the liquid column itself. The bag/shear liquid column breakup mode was observed when liquid turbulence caused large deformations of the liquid column so that portions of it were in a gaseous cross flow; this resulted in bag or shear liquid column breakup, very similar to the breakup of non-turbulent liquid jets in gaseous cross flow. Mean streamwise drop velocities after breakup were comparable to mean streamwise velocities within the jet whereas mean cross stream drop velocities after breakup were comparable to cross stream velocity fluctuations within the liquid. Rates of primary breakup at the liquid surface are reported as surface efficiency factors (the fraction of the maximum possible cross stream drop liquid flux at the surface based on the mean relative cross stream velocity of the drops at the surface and the liquid density). The resulting surface efficiency factors varied from small values near the onset of liquid surface breakup to values of the order of unity as conditions near breakup of the liquid column as a whole were approached.

Numerical simulation on the behavior of a liquid jet into an air flow

AbstractA numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001

Short capillary waves on the surface of a stretching cylindrical jet of a viscous liquid

This paper presents asymptotic formulas describing the evolution of short–wave perturbations on the surface of a cylindrical viscous liquid jet with the radius decreasing in time. The effects of Reynolds and Weber numbers and the initial wavenumber on the decay of the perturbations are analyzed.

206 静止気体中に噴出した液体同軸二重噴流の乱れ初生(流体工学)

206 静止気体中に噴出した液体同軸二重噴流の乱れ初生(流体工学)

Free-Surface Shear Layer Instabilities on a High-Speed Liquid Jet

The instabilities of the shear layer beneath the free surface of high-speed liquid jets are investigated. Such instabilities will generate waves on liquid-metal jet targets, affecting adversely the target performance. The most unstable wave number and the spatial growth rate of perturbation are predicted with linear stability theories and are shown to agree fairly well with experimental data for water jets. The effects of fluid surface tension and streamline curvature on the instabilities are analyzed to evaluate the applicability of water data to liquid-metal curved jets. It is shown that the surface tension effects are negligible when the Weber number based on the shear layer thickness is greater than six, and also the streamline curvature effects are negligible when the radius of curvature is more than 30 times greater than the shear layer thickness.

Disintegration Model of Liquid Jet Injected from Coaxial Airblast Atomizer.

The atomization model of the liquid jet injected from a coaxial airblast atomizer was newly proposed. The atomization model is based on the JE technique. The disturbance wave on the liquid jet surface grows according to the linear instability theory, and the droplets detach from the surface wave when the wave amplitude exceeds the critical value. The liquid jet itself disintegrates into a liquid clump when the amplitude of an asymmetric wave exceeds the critical value, and the liquid clump disintegrates again into finer droplets according to the TAB model. The calculated breakup length shows the smaller value compared to the empirical equation, especially at low air velocity. The Sauter's mean diameter calculated from the model almost coincides with the Nukiyama-Tanasawa's equation at high air velocity. However, at low air velocity the calculated mean diameter shows much larger value compared to the equation.