Jet Drop Research Articles

Size and velocity of jet drops produced by bursting bubbles at the interface of a water jet

Bursting bubbles at the free surface of aerated faucet water jets may spread pathogens through the released droplets. Many studies focused on the production of jet drops from bursting bubbles at a planar interface, particularly for the first jet drop. The extent to which previous findings apply to bubbles in aerated jets remains unknown. In this study, we produce a wide range of bubble size distributions within different jet diameters and characterize the diameter and velocity of jet drops released from individually bursting bubbles. Several similarities with the planar case are recovered, such as the overall dependence of the jet drop diameter and bursting dynamics on the bubble diameters and the formation of secondary jet drops. However, we observe asymmetries in the ejection of the droplets, and droplets ejected horizontally appear to have the highest ejection velocity among all jet drops. By modeling the evolution of the ejected drops for the different bubble size distributions, we find that for a mean Laplace number Labub=ρwσwRbubμw2≲6×104, a fraction of the drops ejected can become airborne. Droplets deposit within 9 cm for a mean Labub≲2.1×104 and within 33 cm for a mean 2.1×104≲Labub≲1.8×105 from a faucet jet, assuming a countertop situated 20 cm below the faucet outlet. A bubble size distribution with a mean Labub of 6×104 would minimize both the risk of airborne pathogen transmission and that resulting from surface contamination.

Thin-film flow due to an asymmetric distribution of surface tension and applications to surfactant deposition

Thin-film equations are utilised in many different areas of fluid dynamics when there exists a direction in which the aspect ratio can be considered small. We consider thin free films with Marangoni effects in the extensional flow regime, where velocity gradients occur predominantly along the film. In practice, because of the local deposition of surfactants or input of energy, asymmetric distributions of surfactants or surface tension more generally, are possible. Such examples include the surface of bubbles and the rupture of thin films. In this study, we consider the asymmetric thin-film equations for extensional flow with Marangoni effects. Concentrating on the case of small Reynolds number $ Re $ , we study the deposition of insoluble surfactants on one side of a liquid sheet otherwise at rest and the resulting thinning and rupture of the sheet. The analogous problem with a uniformly thinning liquid sheet is also considered. In addition, the centreline deformation is discussed. In particular, we show analytically that if the surface tension isotherm $\sigma = \sigma (\varGamma )$ is nonlinear (surface tension $\sigma$ varies with surfactant concentration $\varGamma$ ), then accounting for top–bottom asymmetry leads to slower (faster) thinning and pinching if $\sigma = \sigma (\varGamma )$ is convex (concave). The analytical progress reported in this paper allows us to discuss the production of satellite drops from rupture via Marangoni effects, which, if relevant to surface bubbles, would be an aerosol production mechanism that is distinct from jet drops and film drops.

Modeling the Concentration Enhancement and Selectivity of Plastic Particle Transport in Sea Spray Aerosols

AbstractBursting bubbles transport bacteria, viruses, and other marine particles across the air‐sea interface. This effect is enhanced when particles are hydrophobic and cling to the bubbles as they rise. Recent studies suggest that plastic particles, a major ocean pollutant, can also be transported by sea spray. However, estimates of plastic transport via this pathway have large uncertainties due to limited size detection techniques in field studies and few lab studies. An understanding of the number and size of particles carried in the smallest drops, which have the longest residence time in the atmosphere, is missing from current literature. Here, we develop a modeling framework to provide bounds on the number, area, and volume transport of non‐scavenged hydrophilic and fully‐scavenged hydrophobic particles of radii between 0.1 and 100 μm for a range of jet and film drops. For droplets containing plastic particulates, we predict particle enrichment is significantly higher in jet drops than film drops. For particles in these jet drops, our results suggest that in the absence of bubble scavenging, the number distribution is dominated by smaller plastics, the mass/volume distribution by larger plastics, and surface area distribution is balanced across plastic size. Whereas for hydrophobic particles, scavenging dramatically modifies these distributions, enhancing certain particle–droplet size combinations by over four orders of magnitude. Our predictions suggest critical effects of enrichment in air‐sea particle transport and highlight the variable dependencies on bubble and particle size, improving our theoretical understanding of plastic and marine particle transport and identifying modeling assumptions to refine with experimental measurements.

Characterization of the hypergolic ignition of green fuels with hydrogen peroxide by drop test and jet impingement

This work presents an experimental study on the hypergolic behavior of variants of N,N,N’,N’-tetramethylethylenediamine (TMEDA)/N,N-dimethylethanolamine (DMEA) system, named PAHyp 0, with 93 wt% hydrogen peroxide. Two different copper-based catalyst and one cobalt-based catalytic agent were dissolved in the fuels to trigger the pre-ignition reactions. When employing copper chloride dihydrate, the resultant fuel requires methanol (ternary system) as a stabilizing agent, whereas both carboxylic salts of copper and cobalt dissolved in TMEDA/DMEA deliver a stable formulation (binary system) without the need for any organic solvent. Shadowgraph high-speed imaging was used to capture the ignition process and pressure wave development of over 30 fuel samples in a modified drop test. An ignition/stability envelope was proposed to map the safe and unstable formulations. It was demonstrated that the concentration of TMEDA should be no more than 50% in the binary system, while the amount of methanol should fall within a concentration window of 33 to 50% in the ternary system. Lower loadings of catalyst, ranging from 0.5 to 1.0 wt%, are required to deliver stable fast-igniting fuels. Three promising formulations catalyzed with 1 wt% copper salts were selected to perform impinging jet fire experiments. Impinging jets yielded significantly lower ignition delay times than drop tests due to the better mixing conditions. However, it was verified that ignition may fail for low values of jet velocities, below 0.8 m/s, and for high jet velocities, exceeding 14 m/s. An attempt to explain the ignition and non-ignition events was made by using the fundamentals of explosion limits of the hydrogen/oxygen system and oxidation reactions at low temperature. Remarkably, ultra-fast ignitions of about 10 ms were measured by the impinging jet setup within near-optimal operational conditions. Therefore, TMEDA/DMEA-based fuels with reduced catalyst loadings (0.5–1.0 wt%) offer new opportunities in aerospace propulsion and should be further studied.

Water–air transfer rates of microplastic particles through bubble bursting as a function of particle size

Microplastic (MP) particles can be ejected into the air by jet drops when gas bubbles burst at water surfaces. For a qualitative and quantitative understanding of this transport mechanism from the hydrosphere to the atmosphere, we studied the transfer of MP due to bubble bursting at the air–water interface in laboratory experiments. Gas bubbles were produced with filtered air that was pushed through a stainless-steel frit at two different volume flow rates in a glass flask filled with polystyrene (PS) particles of six different diameters (0.35 µm, 0.5 µm, 0.75 µm, 1 µm, 1.5 µm, 2 µm) suspended in deionized water. Airborne PS particle concentrations were measured by an optical particle counter. Additionally, size and volume of the bursting bubbles and the resulting jet droplets were analyzed with a camera. Depending on the volume flow rates, bubble bursting rates from 688 s−1 to 1176 s−1 and mean diameters of the bursting bubbles from 0.76 mm to 0.81 mm were observed. The mean diameters of the top jet drops were estimated to be between 0.10 mm and 0.11 mm. The measured number of jet droplets ranged from 2092 s−1 to 2391 s−1. For particle diameters from 0.35 µm – 2.0 µm, the airborne MP particle concentrations ranged from 4.2 l−1 to 348 l−1. We determined size-dependent transfer factors for the water–air transfer and found a maximum for 1 µm particles. For MP particles up to 1 µm diameter, the particle concentration in the jet droplets was enhanced compared to the bulk water concentration, indicating an enrichment of MP particles at the water–air-interface of bubbles.

Effect of surface viscoelasticity on top jet drops produced by bursting bubbles.

Jet drops resulting from bubble bursting at a liquid surface play a key role in various mass transfer processes across the interface, including sea spray aerosol generation and pathogen transmission. However, the impact of structurally compound interfaces, characterized by complex surface rheology introduced by surface-active contaminants, on the jet drop ejection still remains unclear. Here, we experimentally investigate the influence of surface viscoelasticity on the size and velocity of the top jet drops from surface bubble bursting, examining both pure protein and mixed protein-surfactant solutions. We document that for bubble bursting at a pure-protein-laden surface where surface elasticity dominates, the increase in Ec, i.e. the interfacial elastocapillary number as the ratio between the effects of interfacial elasticity and capillarity, efficiently increases the radius and decreases the velocity of the top jet drop, ultimately inhibiting the jet drop ejection. On the other hand, considering the mixed protein-surfactant solution, we show that the top jet drop radius and velocity exhibit a different variation trend with Ec, which is attributed to the additional dissipation on the capillary waves as well as the retardation and resistance on the converging flow for jet formation from surface viscoelasticity. Our work may advance the understanding of bubble bursting dynamics at contaminated liquid surfaces and shed light on the potential influence of surface viscoelasticity on the generation of bubble bursting aerosols.

Image Tracking of Fire Extinguishing Jet Drop Point Based on Improved ENet and Robust Adaptive Cubature Kalman Filtering

Image Tracking of Fire Extinguishing Jet Drop Point Based on Improved ENet and Robust Adaptive Cubature Kalman Filtering

Visual predictive control of fire monitor with time delay model of fire extinguishing jet

Controlling the fire monitor through visual sensors is crucial for achieving automatic fire extinguishing. Since it takes a certain time for the water jet drop point (JDP) to respond the action of fire monitor, the controller with the image of the JDP will lead to jet oscillation and long adjustment time, which will reduce the effectiveness of fire extinguishing. To solve these problems, first of all, a kinematic model of the JDP with delay is constructed by scrutinizing the movement of particles in the water jet. This model quantifies the delay mechanism of the JDP and lessens its detrimental effects. Then, the visual predictive controller with visibility and structural restrictions is used to achieve the desired angles of the fire monitor in various degrees of freedom. Finally, the dynamic model of the fire monitor is derived to achieve accurate tracking control for the desired angles, and a controller with the linear extended state observer is proposed to account for unknown terms resulting from factors such as jet reaction forces. Comparative experiments are conducted on a real fire-extinguishing robot to verify the effectiveness of the proposed kinematic model and controller.

Field-theoretic analysis of hadronization using soft drop jet mass

Field-theoretic analysis of hadronization using soft drop jet mass

Ocean emission of microplastic.

Microplastics are globally ubiquitous in marine environments, and their concentration is expected to continue rising at significant rates as a result of human activity. They present a major ecological problem with well-documented environmental harm. Sea spray from bubble bursting can transport salt and biological material from the ocean into the atmosphere, and there is a need to quantify the amount of microplastic that can be emitted from the ocean by this mechanism. We present a mechanistic study of bursting bubbles transporting microplastics. We demonstrate and quantify that jet drops are efficient at emitting microplastics up to in diameter and are thus expected to dominate the emitted mass of microplastic. The results are integrated to provide a global microplastic emission model which depends on bubble scavenging and bursting physics; local wind and sea state; and oceanic microplastic concentration. We test multiple possible microplastic concentration maps to find annual emissions ranging from 0.02 to 7.4-with a best guess of 0.1-mega metric tons per year and demonstrate that while we significantly reduce the uncertainty associated with the bursting physics, the limited knowledge and measurements on the mass concentration and size distribution of microplastic at the ocean surface leaves large uncertainties on the amount of microplastic ejected.

Jetting Dynamics of Viscous Droplets on Superhydrophobic Surfaces.

We investigated the dynamics of liquid jets engendered by the impact of droplets on a fractal superhydrophobic surface. Depending on the impact conditions, jets emanate from the free liquid surface with several different shapes and velocities, sometimes accompanied by droplet ejection. Experimental outcomes exhibit two different regimes: the singular jet and columnar jet. We found that droplet impacts at a lower impact velocity and low viscosity result in singular jets, attaining a maximum velocity nearly 20-fold higher than the impact velocity. The high-speed video frames reveal that the formation and subsequent collapse of the cylindrical air cavities within the droplet favor the formation of these high-speed singular jets. In contrast, the capillary wave focusing engenders columnar jets at a moderate to high impact velocity. With an increase in viscosity, singular jets are suppressed at lower impact velocities, whereas columnar jets are seen regularly. The columnar jets ascend and grow over time, feeding a bulbous mass, and subsequently the bulb separates itself from the parent jet due to capillary pinch-off phenomena. The quantitative analysis shows that columnar jets' top jet drop size varies nonmonotonically and is influenced by preceding jetting dynamics. At moderate viscosity, the drop size varies with jet velocity, following a power-law scaling. At very high viscosities, both singular and columnar jetting events are inhibited. The results are relevant to several recent technologies, including microdispensing, thermal management, and disease transmission.

Secondary Bubble Entrainment via Primary Bubble Bursting at a Viscoelastic Surface.

Bubble bursting at liquid surfaces is ubiquitous and plays a key role for the mass transfer across interfaces, impacting global climate and human health. Here, we document an unexpected phenomenon that when a bubble bursts at a viscoelastic surface of a bovine serum albumin solution, a secondary (daughter) bubble is entrapped with no subsequent jet drop ejection, contrary to the counterpart experimentally observed at a Newtonian surface. We show that the strong surface dilatational elastic stress from the viscoelastic surface retards the cavity collapse and efficiently damps out the precursor waves, thus facilitating the dominant wave focusing above the cavity nadir. The onset of daughter bubble entrainment is well predicted by an interfacial elastocapillary number comparing the effects of surface dilatational elasticity and surface tension. Our Letter highlights the important role of surface rheology on free surface flows and may find important implications in bubble dynamics with a contaminated interface exhibiting complex surface rheology.

The catchment area of groomed jets at NNLL

Groomed jet observables have a dynamical catchment area which plays a key role in determining the leading nonperturbative power corrections and the impact of the underlying event. Based on field-theoretic arguments, certain moments of the groomed jet radius Rg capture the entirety of the kinematic and grooming parameter dependence of these effects. These moments can be computed perturbatively in the soft drop operator expansion region where these corrections are small, but yet significant to be relevant for precision physics. A precise determination of these moments is thus crucial to faithfully isolate the universal contributions of hadronization and the underlying event. Building on a previously developed effective field theory framework for the doubly differential soft drop groomed jet mass and groomed jet radius measurement, we present here a calculation of these moments at next-to-next-to-leading-logarithmic (NNLL) accuracy including matching into the plain jet mass region. We compare our predictions for these moments against parton-shower Monte Carlo simulations and find good agreement. These results have applications for precision physics with soft drop jet mass such as determination of the strong coupling constant and the top quark mass and for improving hadronization models.

Mass Transfer of Hydrogen Sulfide at Turbulent Water Surface by Falling Drops or a Single Jet

Hydrogen sulfide (H2S) is a primary cause of odor and corrosion in sewer systems. In drop structures, falling wastewater impinges the surface of bottom water pool as a jet or numerous drops, triggering a high level of turbulence and thus enhancing the emission of H2S and the absorption of oxygen (O2) at the pool surface. In this study, laboratory experiments were conducted to study the mass transfer at the pool surface with falling water drops or a single jet of water. In the test range of falling flow rate of 49–223 mm/h and falling velocity of 3.1–5.2 m/s [kinetic energy flux (KEF)=0.11–0.80 J/(m2·s)], the mass transfer coefficient KL for the pool surface was found to be 2.6–14.8×10−5 m/s for H2S. In addition, KL was found to be 76% larger when the pool surface was impinged by water drops than by a single jet. KL was 27%−47% larger in the half of the water surface directly receiving the drops or jet than the other half. The increase of water depth in the pool promoted the mass transfer, especially for the scenario of falling jet. Equations were proposed to predict KL under drops or jet. Moreover, KL for H2S and for O2 was found almost the same, indicating O2 can be a safe surrogate gas for H2S. Finally, the research results were applied to estimate H2S emissions at the pool surface of a prototype drop structure with a falling height of up to 10 m, which showed that turbulent wastewater surface can enhance mass transfer over 100 times compared with a quiescent surface.

Enhanced singular jet formation in oil-coated bubble bursting

Bubble-bursting aerosols have a key role in mass and momentum transfer across interfaces. Previous studies report that the bursting of a millimetre-sized bare bubble at an aqueous surface produces jet drops with a typical size on the order of 100 μm. Here we show that jet drops can be as small as a few micrometres when the bursting bubble is coated by a thin oil layer. The faster and smaller jet drops result from the singular dynamics of the oil-coated cavity collapse. The air–oil–water compound interface offers a distinct damping mechanism to smooth out the precursor capillary waves during cavity collapse, leading to a more efficient focusing of the dominant wave and thus allowing singular jets over a much wider parameter space than that of a bare bubble. We develop a theoretical explanation for the parameter limits of the singular jet regime by considering the interplay between inertia, surface tension and viscous effects. Contaminated bubbles are widely observed, therefore previously unrecognized fast and small contaminant-laden jet drops may contribute to the aerosolization and airborne transmission of bulk substances.

Enrichment of Scavenged Particles in Jet Drops Determined by Bubble Size and Particle Position

When small bubbles rupture in a contaminated water source, the resulting liquid jet breaks up into droplets that can aerosolize solid particulates such as bacteria, viruses, and microplastics. Particles collected on the bubble surface have the potential to become highly concentrated in the jet drops, dramatically increasing their impact. It has been assumed that only particles small enough to fit within a thin microlayer surrounding the bubble can be transported into its influential top jet drop. Yet here, we demonstrate that not only can larger particles be transported into this jet drop, but also that these particles can exceed previous enrichment measurements. Through experiments and simulations, we identify the prerupture location of the liquid that develops into the top jet drop and model how interfacial rearrangement combines with the bubble size, particle size, and the angular distribution of particles on the bubble surface to set the particle enrichment.

Binder Jetting Additive Manufacturing: Spreading and Permeation of Multiple Micron Droplets in Porous Media

AbstractThe penetrating behavior of binder droplets has a substantial effect on the dimensional correctness and strength of the manufactured components. In this article, a physical model and a mathematical model of multiphase flow are created, computationally computed, and experimentally validated to predict the spreading and penetration behavior of multi‐drop binder in a powder bed. The findings indicate: 1) The spreading diameter and penetration depth of the binder increase as the number of droplets grows. However, the size of the rise reduces as the number of droplets grows. 2) The binder is spread symmetrically in the powder bed, with greater saturation in the middle area than margins on both sides, and a higher saturation in the upper region than the lower. 3) Repeated drops of binder in various areas may improve the saturation of the peripheral region while ensuring that the core area is not oversaturated. 4) It is discovered that as the number of ink jet drops rises, the size of the sample grows, and the growth in sample size reduces with the number of ink jet drops. This paper's findings provide light on the mechanics behind light‐cured binder jet additive manufacturing.

A Mechanistic Sea Spray Generation Function Based on the Sea State and the Physics of Bubble Bursting

AbstractBubbles bursting at the ocean surface are an important source of ocean‐spray aerosol, with implications on radiative and cloud processes. Yet, very large uncertainties exist on the role of key physical controlling parameters, including wind speed, sea state and water temperature. We propose a mechanistic sea spray generation function that is based on the physics of bubble bursting. The number and mean droplet radius of jet and film drops is described by scaling laws derived from individual bubble bursting laboratory and numerical experiments, as a function of the bubble radius and the water physico‐chemical properties (viscosity, density and surface tension, all functions of temperature), with drops radii at production from 0.1 to 500 µm. Next, we integrate over the bubble size distribution entrained by breaking waves. Finally, the sea spray generation function is obtained by considering the volume flux of entrained bubbles due to breaking waves in the field constrained by the third moment of the breaking distribution (akin to the whitecap coverage). This mechanistic approach naturally integrates the role of wind and waves via the breaking distribution and entrained air flux, and a sensitivity to temperature via individual bubble bursting mechanisms. The resulting sea spray generation function has not been tuned or adjusted to match any existing data sets, in terms of magnitude of sea salt emissions and recently observed temperature dependencies. The remarkable coherence between the model and observations of sea salt emissions therefore strongly supports the mechanistic approach and the resulting sea spray generation function.

The role of geometry on controlled cavity collapse and top jet drop

The contents of this work explore the influence of three geometric parameters on controlled cavity collapse at liquid interface and the subsequent ejected drop; the parameters are the angle of the ejecting nozzle plate (θ), the height (H), and the radius (R) of the vessel used to enclose the liquid within. The conducted computational modeling shows that changing the angle of the nozzle plate from a flat surface to inclined surface in one direction causes the droplet diameter to decrease, whereas an inclination in the opposite direction results in larger droplets. Moreover, changing the height of the fluid vessel does not actually influence the drop size and its velocity as long as the vessel height is much larger than the nozzle radius (R0). Below the limit H = 5R0, the droplet size starts to decrease and its velocity to increase by decreasing the vessel height. Finally, the droplet size decreases by increasing the radius of the fluid vessel even when R ≫ R0. This is attributed to the change in the displaced liquid volume and subsequently the cavity volume at the tip of the nozzle when the vessel radius is changed.

Numerical Study of Free Liquid Jet Primary Breakup Phenomenon in Still Gases

The present paper consists of a numerical investigation carried out for primary break up analysis of a vertical water jet. Many parameters impact the flow development such as velocity, turbulence and nozzle shape. In this work, two types of nozzle geometries have been performed, the first is a capillary circular and the second is conical. The calculations have been performed using the CFD Code Fluent of ANSYS, considering laminar and turbulent flow regimes. While turbulence was modelled using RNG k-ε of RANS approach. The main results show that the jet evolves differently in the two considered nozzle geometries comparing the jet intact lengths, drop sizes and distance between successive drops. It is observed that the turbulence increases substantially the jet intact length and enables the jet breakup at the lower part of the water column. For the conical nozzle case, the jet instabilities grow quickly resulting a drop size in the same order of the jet diameter and an intact length larger in comparison with the circular nozzle case.