Jet Drop Research Articles

Jet drops from bursting bubbles: How gravity and viscosity couple to inhibit droplet production.

When a bubble ruptures at a liquid surface the collapsing cavity produces a central jet that frequently breaks up into a series of droplets. Current experiment and theory predict that the production of jet drops will be limited by either viscous or gravitational effects. However, while there are a number of studies focusing on these two limiting cases, less is understood about the production of jet drops when both gravitational and viscous effects are significant. Here, we uncover the existence of an intermediate region where both gravitational and viscous effects play a critical role in jet-drop formation. We propose that the role of gravity is most important before rupture, and carry out simulations that demonstrate the importance of the equilibrium bubble shape in the production of jet drops.

Periodic Breakup of Laminar Liquid Jet and Uniform Drop Formation by Oblique Oscillation of Cylindrical Nozzle

Periodic Breakup of Laminar Liquid Jet and Uniform Drop Formation by Oblique Oscillation of Cylindrical Nozzle

CFD study of capillary jets under superimposed destabilizing conditions for microdroplet formation

Initial numerical studies on the capillary laminar instability of continuous polymeric jets subjected to controlled destabilization and their comparison with experimental results obtained from a microparticle formation technique are addressed. Continuous jet instabilities and drop formation are challenging free-surface flow problems that require sophisticated interface tracking methods. The assessment of a Coupled Volume of Fluid and Level Set (CLSVOF) commercial code and its potential application to more complex systems are considered. The data obtained from the numerical simulations under different operating conditions showed good qualitative results, in agreement with the trends experimentally obtained. Nevertheless, the use of generalized Newtonian models instead of more complex constitutive equations accounting for the polymer viscoelasticity preclude the obtaining of better comparisons. However, it can be concluded that the use of CLSVOF under the described conditions deals reasonably well with the tracking of the interface, making its use adequate in capillary laminar instabilities.

Erratum: Periodic Breakup of Laminar Liquid Jet and Uniform Drop Formation by Oblique Oscillation of Cylindrical Nozzle

Erratum: Periodic Breakup of Laminar Liquid Jet and Uniform Drop Formation by Oblique Oscillation of Cylindrical Nozzle

Whipping of electrified liquid jets.

We apply an electric field to a moderately conducting liquid surrounded by another coflowing liquid, all inside a glass-based microfluidic device, to study nonaxisymmetric instabilities. We find that the bending of the electrified jet results in a steady-state, helicoidal structure with a constant opening angle. Remarkably, the characteristic phase speed of the helicoidal wave only depends on the charge carried by the jet in the helicoidal region and its stability critically depends on the properties of the coflowing liquid. In fact, the steady-state helical structure becomes chaotic when the longest characteristic time is that of the inner liquid rather than that of the outer coflowing liquid. We also perform a numerical analysis to show that the natural preference of the jet is to adopt the conical helix structure observed experimentally.

605 ノズルの斜め方向加振による平滑液体噴流の規則分裂と均一液滴の生成(GS 流体現象と解析)

605 ノズルの斜め方向加振による平滑液体噴流の規則分裂と均一液滴の生成(GS 流体現象と解析)

Simulation Experiments to Model the Inkjet Printing Behavior of Functional Inks

Flow simulations of jetting of ink jet drops are presented. The Z number of Fromm is used to characterize jettability. Simulation results are comparable to jetting behavior observed by the drop watcher on a Dimatix 2800 Materials Printer.

Adult rat retinal ganglion cells and glia can be printed by piezoelectric inkjet printing

We have investigated whether inkjet printing technology can be extended to print cells of the adult rat central nervous system (CNS), retinal ganglion cells (RGC) and glia, and the effects on survival and growth of these cells in culture, which is an important step in the development of tissue grafts for regenerative medicine, and may aid in the cure of blindness. We observed that RGC and glia can be successfully printed using a piezoelectric printer. Whilst inkjet printing reduced the cell population due to sedimentation within the printing system, imaging of the printhead nozzle, which is the area where the cells experience the greatest shear stress and rate, confirmed that there was no evidence of destruction or even significant distortion of the cells during jet ejection and drop formation. Importantly, the viability of the cells was not affected by the printing process. When we cultured the same number of printed and non-printed RGC/glial cells, there was no significant difference in cell survival and RGC neurite outgrowth. In addition, use of a glial substrate significantly increased RGC neurite outgrowth, and this effect was retained when the cells had been printed. In conclusion, printing of RGC and glia using a piezoelectric printhead does not adversely affect viability and survival/growth of the cells in culture. Importantly, printed glial cells retain their growth-promoting properties when used as a substrate, opening new avenues for printed CNS grafts in regenerative medicine.

Experimental Study on the Characteristics of Jet and Drop Formation Related to a Fluidization Method for Ice Slurry Production

The new fluidization method of liquid-liquid circulating fluidized bed proposed for ice slurry production was investigated experimentally. Multiple small water-drops were formed in another immiscible liquid coolant by a single-nozzle atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to research the dynamic behaviors of jet and drops formation in the ice making system by the high resolution digital camera and image processing. The photos of jet development, breakup and drop formation were obtained. The affects of the shape of jet breakup, jet length and its surface fluctuation on drops size were revealed. The range of drop sizes and the sloping extent have always increased with the jet rate increasing. And varying jet shape directly results in the jet breakup into droplets under different time and test conditions, so the variation laws of the jet shape contribute most to the quality of the liquid drop, such as drop size distribution.

Quantitative Risk Estimation for a Legionella pneumophila Infection Due to Whirlpool Use

Quantitative microbiological risk assessment was used to quantify the risk associated with the exposure to Legionella pneumophila in a whirlpool. Conceptually, air bubbles ascend to the surface, intercepting Legionella from the traversed water. At the surface the bubble bursts into dominantly noninhalable jet drops and inhalable film drops. Assuming that film drops carry half of the intercepted Legionella, a total of four (95% interval: 1-9) and 4.5×10(4) (4.4×10(4) - 4.7×10(4) ) cfu/min were estimated to be aerosolized for concentrations of 1 and 1,000 legionellas per liter, respectively. Using a dose-response model for guinea pigs to represent humans, infection risks for active whirlpool use with 100 cfu/L water for 15 minutes were 0.29 (∼0.11-0.48) for susceptible males and 0.22 (∼0.06-0.42) for susceptible females. A L. pneumophila concentration of ≥1,000 cfu/L water was estimated to nearly always cause an infection (mean: 0.95; 95% interval: 0.9-∼1). Estimated infection risks were time-dependent, ranging from 0.02 (0-0.11) for 1-minute exposures to 0.93 (0.86-0.97) for 2-hour exposures when the L. pneumophila concentration was 100 cfu/L water. Pool water in Dutch bathing establishments should contain <100 cfu Legionella/L water. This study suggests that stricter provisions might be required to assure adequate public health protection.

Protein spheres prepared by drop jet freeze drying

In spray freeze drying (SFD) solutions are frozen by spraying into a very cold environment and subsequently dried by sublimation. In contrast to conventional freeze drying, spray freeze drying has the possibility to produce flowable lyophilizates which offers a variety of new pharmaceutical applications. Here, a drop jet nozzle is proposed as liquid dispenser that is able to produce droplets with a very narrow size distribution compared to standard methods. The drop jet nozzle is mounted in a spray tower designed to prevent direct contact of the product with the freezing medium. Various formulations have been tested containing lysozyme as model protein and stabilizers such as bovine serum albumin, polyvinylpyrrolidone or dextran in various concentrations and mannitol. Excellent free flowing and nearly monodispersed, porous particles are produced where particle properties can be controlled by formulation and process conditions. The particle diameter varied between 231 ± 3 μm and 310 ± 10 μm depending on the formulation composition. The lysozyme activity was >94 ± 5% for all formulations exhibiting a full preservation of enzyme activity. This new method is very promising for the production of nearly monodisperse particulate lyophilizates in various therapeutic applications.

Slender-body theory for the generation of micrometre-sized emulsions through tip streaming

AbstractWe report experiments in which a flow rate ${Q}_{i} $ of a fluid with a viscosity ${\ensuremath{\mu} }_{i} $ discharges into an immiscible liquid of viscosity ${\ensuremath{\mu} }_{o} $ that flows in parallel with the axis of the injector. When the outer capillary number verifies the condition ${\mathit{Ca}}_{o} = {\ensuremath{\mu} }_{o} {U}_{o} / \sigma ~\geqslant ~5$, where ${U}_{o} $ and $\sigma $ indicate, respectively, the outer velocity and the interfacial tension coefficient, and if the inner-to-outer velocity ratio is such that ${U}_{i} / {U}_{o} = {Q}_{i} / (\lrm{\pi} {U}_{o} { R}_{i}^{2} )\ll 1$, with ${R}_{i} $ the inner radius of the injector, a jet is formed with the same type of cone–jet geometry as predicted by the numerical results of Suryo &amp; Basaran (Phys. Fluids, vol. 18, 2006, p. 082102). For extremely low values of the velocity ratio ${U}_{i} / {U}_{o} $, we find that the diameter of the jet emanating from the tip of the cone is so small that drops with sizes below $1~\lrm{\ensuremath{\mu}} \mathrm{m} $ can be formed. We also show that, through this simple method, concentrated emulsions composed of micrometre-sized drops with a narrow size distribution can be generated. Moreover, thanks to the information extracted from numerical simulations of boundary-integral type and using the slender-body approximation due to Taylor (Proceedings of the 11th International Congress of Applied Mechanics, Munich, 1964, pp. 790–796), we deduce a third-order, ordinary differential equation that predicts, for arbitrary values of the three dimensionless numbers that control this physical situation, namely, ${\mathit{Ca}}_{o} $, ${\ensuremath{\mu} }_{i} / {\ensuremath{\mu} }_{o} $ and ${U}_{i} / {U}_{o} $, the shape of the jet and the sizes of the drops generated. Most interestingly, the influence of the geometry of the injector system on the jet shape and drop size enters explicitly into the third-order differential equation through two functions that can be easily calculated numerically. Therefore, our theory can be used as an efficient tool for the design of new emulsification devices.

Primary and secondary tip coronae from splashing water drops in electric fields

An enquiry has been carried out into millimetre size water drops falling through vertical electric fields, at terminal and near terminal velocities, and impacting a water surface. A laboratory method was devised to electronically observe the splashing event, together with the onset, duration and magnitude of all ensuing coronae. The production of a secondary jet tip and the discovery of a previously unknown corona were originally recorded by Kinsey (1986) and are here described in detail. Emanating from the secondary jet tip, the corona is synonymous with the release and electrification of an airborne water drop and its nC range of charge transfer (being field/momentum dependant) offer low level luminosity to the dark adapted eye (mentioned by ur Rahman and Saunders, 1988).For terminal and near terminal velocity drops, the resulting water jets follow under-damped sinusoidal oscillation and, in fields above a critical value (Ec), their primary tips often support more than one corona, thus yielding charge to the aerosol and space charge below oceanic thunderstorms. Secondary tip, or jet drop, corona data show the phenomenon to occur in fields of 100Vcm−1 and maybe even lower. The role of such drops, in oceanic thunderstorm electrification, being subject to drop size, ambient field, updraft and wind shear speeds. Oscilloscopic and photographic evidence is presented in support of the discovered corona and oscillographs, photographs and data are taken from P. B. Kinsey Ph.D. thesis (1986).

Jet Fluctuations and Drop Velocity Jitter: Confirmation of a Causal Model

In continuous inkjet devices, an applied perturbation, such as acoustic vibration or thermal modulation, is used to drive the Rayleigh-Plateau instability to cause regular breakup of liquid microjets into droplets of controlled size. Background fluctuations and other processes contribute to subtle variations in droplet velocity within the droplet stream. These velocity variations&#x2014;droplet velocity jitter&#x2014;can be observed by stroboscopy or by laser detection. The fluctuations in droplet position or period are influenced by the details of the jet breakup process, and measurement of the droplet fluctuations as a function of distance along the droplet stream provide estimates of the fundamental noise on the jet.

Numerical simulation of drop impact and jet buckling problems using the eXtended Pom–Pom model

This work presents numerical simulations of two fluid flow problems involving moving free surfaces: the impacting drop and fluid jet buckling. The viscoelastic model used in these simulations is the eXtended Pom–Pom (XPP) model. To validate the code, numerical predictions of the drop impact problem for Newtonian and Oldroyd-B fluids are presented and compared with other methods. In particular, a benchmark on numerical simulations for a XPP drop impacting on a rigid plate is performed for a wide range of the relevant parameters. Finally, to provide an additional application of free surface flows of XPP fluids, the viscous jet buckling problem is simulated and discussed.

Study of sea salt particles launched by bubble burst

Sea salt particles launched from bursting bubbles and lofted in a drying tube were collected so that their morphology and size could be observed. Such particles can act as cloud condensation nuclei. Both film and jet drops were captured and desiccated so that their morphology was not perturbed by deliquescence and redrying. The mass of sea salt ejected from known bubble diameters was measured gravimetrically using a discrete bubble generator. The launch of droplets by bubble burst was recorded by high speed camera and illustrates the subtle momentum exchange as the jet breaks up to give widely different launch velocities and droplet heights. The distribution of heights attained by droplets in still air was recorded by addition of dye and printing of droplets on paper. The study is intended to underpin emergent technologies for climate restoration (geoengineering) aimed at increasing oceanic albedo and optical depth of clouds.

Characteristics of jet droplet produced by bubble bursting on the free liquid surface

Droplet formation that follows gas bubble bursting at a free liquid surface, being known as “entrainment”, is a common phenomenon in many fields. Though there were a couple of investigations focusing on entrainment, specific characteristics of jet drops produced by bubble bursting on free surface are still unknown in the current stage. Efforts were performed to try to determine the expression of critical bubble size, above which the bubble does not produce any drops by bursting on liquid surface. Dimensionless analyses show that in air–liquid systems, ReFr−0.5, ReWe−0.5 and WeFr−0.5Re−1 can be readily correlated to Mo. Error analysis demonstrated the following expression: Dcr=100.1914σL0.5517ρL−0.4830g−0.5170μL−0.0688 can give the most accurate prediction of Dcr as a universal expression. Further, for correlating the number of droplets to bubble diameter in air–water and air–iron system, Dcr was used as the length scale to normalize the bubble diameter. Through curve fitting, a universal expression has been obtained to predict the number of droplets produced by bubble bursting on free liquid surface in any air–liquid system: Ndr=7.9exp(−DB/(0.338Dcr))−0.41. Comparison shows that this expression is able to give more accurate prediction than the previous empirical expressions. The most significant innovation is that it is a universal model that can be used in various gas–liquid systems.

Analysis of surfactant laden liquid–liquid dispersion using an axisymmetric laminar jet

AbstractThe contacting of multiple liquid phases is a complex process; and one that is often difficult to study experimentally. However, many multiphase mixers function by forcing an immiscible fluid through an orifice or nozzle, which can be modelled using an axisymmetric jet. Despite the extensive literature on jets, there is little information on the role played by surfactants in determining jet breakup length and drop diameter.Experiments involving the discharge of oil jets into otherwise quiescent aqueous surfactant solutions were performed over a broad range of conditions. Jet length was found to increase with surfactant concentration, while droplet diameter was found to decrease (dependent on jet regime). These results compare favourably with, and can aid the interpretation of similar experiments in high shear mixers.

The Numerical Study of Oil Drop Jet from Oil-Air Lubrication Nozzle

Nozzle is an important part of oil-air lubrication system. This paper uses Computational Fluid Dynamics (CFD) software FLUENT to study the flow field of oil air, and different air pressure and nozzle throat size are discussed. The results show that: When air pressure is increased from 0.05Mpa to 0.1Mpa, the maximum diameter (2mm) percentage reduces, but the diameters distribution is almost unchanged as the air pressure is increased to 0.3MPa. The throat diameter is decreased, the mean Sauter diameter of oil drop reduces. This paper will provide a theoretical basis for oil-air lubrication nozzle design and selection.

Estimating Flow Characteristics of Different Weir Types and Optimum Dimensions of Downstream Receiving Pool

Estimating Flow Characteristics of Different Weir Types and Optimum Dimensions of Downstream Receiving PoolThis paper presents the results of a laboratory study on the flow characteristics of sharp-crested weirs, broad-crested weirs, and labyrinth weirs. The variation of the maximum bubble penetration depth for different weir types is investigated depending on overfall jet expansion, discharge, and drop height. Moreover, most efficient depth, length and width of the downstream receiving pool in an open channel system are studied by considering the penetration depth, overfall jet expansion, jet trajectory and the bubble zone. The results show that overfall jet expansion at the labyrinth weirs is significantly wider than the rectangular sharp-crested weirs and the trapezoidal sharp-crested weir. It is demonstrated that the labyrinth weirs have the lowest values of bubble penetration depth among the weirs tested. Furthermore, it is found that the rectangular and the trapezoidal weirs are observed to have the highest bubble penetration depth among all weirs. Consequently, empirical equations are obtained for predicting the maximum penetration depth of bubbles, trajectory of free overfall nappe, jet expansion of free overfall nappe, and the length of the bubble zone.