Bubble Rupture Research Articles

Dynamics of partially obstructed breakup of bubbles in microfluidic Y-junctions.

For revealing the dynamics of partially obstructed breakup of bubbles in microfluidic Y-junctions, the combination of dimensionless power-law and geometric model was applied to study the effects of capillary number, bubble length, and channel angle on the bubble rupture process. In the squeezing process, the gas-liquid interface curve follows the parabolic model. For the evolution of the bubble neck during breakup, the increase of the bubble length, the channel angle, and the capillary number leads to the decrease of the focus distance α. The chord m increases with the increase of the capillary number and the decrease of the bubble length, and it would reach the maximum value when the channel angle is 90°. In the fast pinch-off stage during bubble breakup, the bubble's neck curve no longer conforms to the parabolic model so the focus and chord no longer exist. For the evolution of the bubble head during breakup, the value of γ approaches 1 with the increase of the capillary number and the bubble length, and with the close of the channel angle to 90°. It is found that the quadrilateral model can be applied for the partially obstructed rupture of bubbles in the symmetrical microfluidic Y-junction.

TCT-857 A 75% Stenosis Created Turbulent FLow, Ruptured Bubbles (Cavitation Phenomenon), Eroded the Vulnerable Cap and Triggered Acute Myocardial Infarction

Acute myocardial infarction (AMI) was believed to occur in mild to moderate coronary lesion. The question is: At which degree of stenosis begin the process of development of AMI? Based on common hydraulic principle and practice, a new mechanism of cavitation or air bubble formation and rupture in

Elasticity in Bubble Rupture.

When a Newtonian bubble ruptures, the film retraction dynamics is controlled by the interplay of surface, inertial, and viscous forces. In case a viscoelastic liquid is considered, the scenario is enriched by the appearance of a new significant contribution, namely, the elastic force. In this paper, we investigate experimentally the retraction of viscoelastic bubbles inflated at different blowing rates, showing that the amount of elastic energy stored by the liquid film enclosing the bubble depends on the inflation history and in turn affects the velocity of film retraction when the bubble is punctured. Several viscoelastic liquids are considered. We also perform direct numerical simulations to support the experimental findings. Finally, we develop a simple heuristic model able to interpret the physical mechanism underlying the process.

Effect of ambient temperature on the puffing characteristics of single butanol-hexadecane droplet

Puffing characteristics of BUT50 (50% n-butanol and 50% n-hexadecane by mass) were investigated using the droplet suspension technology under 638, 688 and 738 K. Experimental results showed that BUT50 underwent transient heating, fluctuation evaporation and equilibrium evaporation phases under all ambient temperatures. In the fluctuation evaporation phase, the fluctuation frequency of 738 K was higher than that of 638 K. (Dmax/D0)2 of 738 K was lower than that of 638 K. Easy bubble rupture led to high fluctuation frequency and low (Dmax/D0)2 at 738 K. Three turning points were found in transient temperature growth rate at 638 and 738 K. Four characteristic droplet temperatures were analyzed, including droplet temperatures at the start (T1) and end (T2) of transient heating phase, at (Dmax/D0)2 (T3) and at the end of total lifetime (T4). T2 was slightly lower and T3 was slightly higher than the boiling point of n-butanol. T4 was lower than the boiling point of n-hexadecane. Furthermore, the transient heating duration (tTH), fluctuation evaporation duration (tFE) and total lifetime (tTL) decreased with increasing ambient temperature. The reduction of tFE played an important role in the decrease of tTL. The percentages of tTH/tTL and tFE/tTL were stable with increasing ambient temperature.

Numerical simulation of deformation and rupture process of bubble in an oil film impacted by an oil droplet

Impact of oil droplet on oil film usually takes place in the lubrication process of rotating mechanical parts and machinery which can easily lead to bubble entrainment. Bubbles have important influences on the motion process of the oil droplet impacting on the oil film and also on the formation quality of the oil film layer. An oil droplet impacting on the oil film which contains a bubble is simulated numerically based on the coupled level set and the method of determining volume fraction. The bubble deformation process in the oil film during an oil droplet impacting on the oil film is investigated by the simulation method. The influences of the bubble size and the bubble position on the bubble deformation characteristic are also analyzed. The dynamic mechanism of the bubble rupture is discussed. The numerical results show that as the oil droplet impacts on the oil film, the bubble may rupture on the free surface, presenting stable deformation, or rupture in the oil film, which is greatly influenced by the bubble size. When the bubble diameter is in a range between 10 m and 20 m, the bubble deformation becomes more serious with the increase of bubble diameter, and the rupture of bubble on the free surface may occur over time. When the bubble diameters are in a range between 20 m and 30 m, the bubble rupture occurs in a short time after the bubble has reached a maximum deformation, and there is no obvious relationship between the maximum bubble deformation and the bubble diameter. The diameter of 20 m is a critical value for a bubble to rupture on a free surface or inside an oil film, with which a bubble can keep stable in an oil film layer. As the bubble position changes, the bubble deformation process changes correspondingly. Under the same impact conditions, bubbles at the top of the oil film are more likely to deform than those in the center of the oil film. Bubbles at the bottom of the oil film have the smallest total deformation and finally attach to the wall. The bubble rupture is caused by the instability of the gas-liquid interface and the surface tension. The viscous shear force also plays an important role when the bubble rupture takes place in the oil film.

Jet speed in bubble rupture

When a polymer bubble is broken in the bubble electrospinning process, thousands of thousands jets are produced with almost same initial ejecting speed, which plays a very important role on the formation of the nanofiber. In this paper, the nanofiber membranes were prepared by the bubble spinning with different air temperatures. This paper also gives a simple mathematical model to predict the initial speed of jets, and it is as high as 300 m/s.

Toroidal bubble dynamics near a solid wall at different Reynolds number

The bubble dynamics in a viscous liquid have significant applications, but the influence of viscosity on bubble dynamics near a solid wall are still not fully understood, especially for the toroidal bubble. In this paper, a numerical method is presented to study toroidal bubble dynamics near a solid wall in the viscous liquid. The liquid phase is assumed to be incompressible and separated from the gas by a free surface. Based on the finite volume method, the incompressible and viscous Navier–Stokes equations are discretized on the staggered grids, which are solved using the explicit projection method. A Lagrange multiplier method is used to deal with the additional constrain that the tangential stress equals zero, and the bubble surface is advected using a front tracking method. The numerical method is compared with the Rayleigh–Plesset solution for a single bubble with multi-oscillations, and the results between them are favorable with regard to bubble radius history. Finally, the toroidal bubble dynamics near a solid wall with different stand-off parameter (γ = 1.5, 0.95 and 0.6, respectively, where γ = d/Rmax, d is the distance between the solid wall and the bubble center at the moment of formation and Rmax is the maximum bubble radius) at different Reynolds number are studied, including water jet, peak pressure induced by water jet, water layer, bubble rupture, bubble migration, etc, where some important conclusions are obtained.

Before the bubble ruptures

This paper is associated with a video winner of a 2016 APS/DFD Gallery of Fluid Motion Award. The original video is available from the Gallery of Fluid Motion, https://doi.org/10.1103/APS.DFD.2016.GFM.V0092

Modeling shear-sensitive dinoflagellate microalgae growth in bubble column photobioreactors

The shear-sensitive dinoflagellate microalga Karlodinium veneficum was grown in a sparged bubble column photobioreactor. The influence of mass transfer and shear stress on cell growth and physiology (concentration of reactive oxygen species, membrane fluidity and photosynthetic efficiency) was studied, and a model describing cell growth in term of mass transfer and culture parameters (nozzle sparger diameter, air flow rate, and culture height) was developed. The results show that mass transfer limits cell growth at low air-flow rates, whereas the shear stress produced by the presence of bubbles is critically detrimental for air flow rates above 0.1vvm. The model developed in this paper adequately represents the growth of K. veneficum. Moreover, the parameters of the model indicate that bubble rupture is much more harmful for cells than bubble formation.

The effect of different n-butanol-fatty acid methyl esters (FAME) blends on puffing characteristics

The droplet suspension technology was used under the condition of atmospheric pressure and 873K. The n-butanol concentration ranged from 0% to 75% to investigate the effect of n-butanol concentration on the puffing characteristics of a n-butanol-fatty acid methyl esters (FAME) droplet. Experimental results showed that BUT25, BUT50 and BUT75 (BUT’XX’ represented XX% n-butanol by mass fraction in the n-butanol-FAME blend) underwent three phases, namely the transient heating phase, fluctuation evaporation phase and equilibrium evaporation phase. The temperatures of BUT25, BUT50 and BUT75 were similar at the start and end of the transient heating phase. The duration of BUT75’s transient heating phase was much longer than that of BUT25 and BUT50. Therefore, the evaporation cooling of BUT75 was the most prominent because the temperature growth rate of BUT75 was significantly less than that of BUT25 and BUT50. Furthermore, the fluctuation evaporation phase could be divided into the strong and weak fluctuation stages. The violent fluctuation was only observed in the strong fluctuation stage. The weak fluctuation stage was similar as the stable evaporation. The active rupture was found in the strong fluctuation stage and the passive rupture was found in the weak fluctuation stage. The active and passive ruptures were caused by the fast bubble expansion and surface evaporation respectively. In addition, many periodic processes were contained in the strong fluctuation stage. The similarity degree of the periodic process showed a slump and a gradual increase, which were caused by bubble expansion and droplet recovery respectively. The bubble expansion of BUT50 was greater than that of BUT75. Significant bubble expansion led to the violent deformation after bubble rupture. The recovery time of BUT50 was longer than that of BUT75. Therefore, the similarity degree of BUT50 exhibited a wavy structure and BUT75 displayed a comb-like structure in the strong fluctuation stage.

Combustion dynamics of low vapour pressure nanofuel droplets

Multiscale combustion dynamics, shape oscillations, secondary atomization, and precipitate formation have been elucidated for low vapour pressure nanofuel [n-dodecane seeded with alumina nanoparticles (NPs)] droplets. Dilute nanoparticle loading rates (0.1%–1%) have been considered. Contrary to our previous studies of ethanol-water blend (high vapour pressure fuel), pure dodecane droplets do not exhibit internal boiling after ignition. However, variation in surface tension due to temperature causes shape deformations for pure dodecane droplets. In the case of nanofuels, intense heat release from the enveloping flame leads to the formation of micron-size aggregates (of alumina NPS) which serve as nucleation sites promoting heterogeneous boiling. Three boiling regimes (A, B, and C) have been identified with varying bubble dynamics. We have deciphered key mechanisms responsible for the growth, transport, and rupture of the bubbles. Bubble rupture causes ejections of liquid droplets termed as secondary atomization. Ejection of small bubbles (mode 1) resembles the classical vapour bubble collapse mechanism near a flat free surface. However, large bubbles induce severe shape deformations as well as bulk oscillations. Rupture of large bubbles results in high speed liquid jet formation which undergoes Rayleigh-Plateau tip break-up. Both modes contribute towards direct fuel transfer from the droplet surface to flame envelope bypassing diffusion limitations. Combustion lifetime of nanofuel droplets consequently has two stages: stage I (where bubble dynamics are dominant) and stage II (formation of gelatinous mass due to continuous fuel depletion; NP agglomeration). In the present work, variation of flame dynamics and spatio-temporal heat release (HR) have been analysed using high speed OH* chemiluminescence imaging. Fluctuations in droplet shape and flame heat release are found to be well correlated. Droplet flame is bifurcated in two zones (I and II). Flame response is manifested in two frequency ranges: (i) buoyant flame flickering and (ii) auxiliary frequencies arising from high intensity secondary ejections due to bubble ruptures. Addition of alumina NPs enhances the heat absorption rate and ensures the rapid transfer of fuel parcels (detached daughter droplets) from droplet surface to flame front through secondary ejections. Therefore, average HR shows an increasing trend with particle loading rate (PLR). The perikinetic agglomeration model is used to explain the formation of gelatinous sheath during the last phase of droplet burning. Gelatinous mass formed results in bubble entrapment. SEM images of combustion precipitates show entrapped bubble cavities along with surface and sub-surface blowholes. Morphology of combustion precipitate shows a strong variation with PLRs. We have established the coupling mechanisms among heat release, shape oscillations, and secondary atomizations that underline the combustion behaviour of such low vapour pressure nanofuels.

Experimental study on puffing characteristics of biodiesel-butanol droplet

In order to research puffing characteristics of biodiesel-butanol blends, single droplet experiments of BUT25 and BUT75 were conducted under the condition of atmospheric pressure and 800°C. Experimental results showed that BUT25 only demonstrated core mode, while BUT75 demonstrated both surface and core mode simultaneously. The core mode was a periodic process including bubble nucleation, bubble expansion and bubble rupture inside the droplet. The surface mode was featured by the appearance of many micron sized child droplets. Two new parameters were proposed to analysis puffing characteristics, namely the similarity degree and the deformation degree. The puffing process usually contained the transient heating phase, fluctuation evaporation phase and equilibrium evaporation phase. Both the transient heating phase and equilibrium evaporation phase were stable evaporation processes. Analysis indicates that the three phases of the puffing process are more appropriately distinguished through the profile of similarity degree than that of the normalized squared diameter. Furthermore, the similarity degree of BUT25 displayed a wavy structure and BUT75 displayed a trapezoid structure in the fluctuation evaporation phase. On the other hand, the deformation degree remained unchanged in stable evaporation processes but exhibited a sharp rise at the instant of bubble expansion or rupture.

Continuous nanofiber coated hybrid yarn produced by multi-nozzle air jet electrospinning

Multi-nozzle air-jet electrospinning was used to produce continuous viscose filament/polyvinylidenefluoride (PVDF) nanofiber hybrid yarns. The production of PVDF nanofibers using this method was based on the principle that the rupture of bubbles results in multiple jet flows. Nanofibers ejected from multiple nozzles were gathered and bundled by conjugate electrospinning and were then twisted on the surface of a filament yarn through the rotation of a metal funnel. The structures and properties of the hybrid yarn were characterized, and spinning mechanism of this novel method was analyzed. The experimental results obtained in this study showed that PVDF nanofibers were perfectly coated on the filament yarn surface with a good orientation and displayed uniform twist distribution with a twist angle of 24.3°, as well as PVDF nanofibers integrated with the core yarn well. After coating with twisted PVDF nanofibers, the mechanical properties of the yarn improved significantly. The stress and strain of the yarn at break increased from 19.39 MPa and 15.83% to 30.82 MPa and 19.81%, respectively. In addition, the hybrid yarn contact angle reached 150° after coating with the twisted PVDF nanofibers, indicating a transformation of the yarn from hydrophilic to hydrophobic. The nanofiber-coated hybrid yarn produced herein can possibly be used as a self-cleaning fabric.

“Immortal” liquid film formed by colliding bubble at oscillating solid substrates

This paper presents an experimental study of the behavior of an ascending air bubble (equivalent radius 0.74 mm) colliding with a solid substrate. The substrate is either motionless or oscillating with a precisely adjusted acceleration, slightly higher than gravity. It is shown that the stability of the liquid film formed between the striking bubble and the solid surface depends not only on the hydrophobic/hydrophilic properties of the solid but also on the energetic interrelations in the system. The results indicate that the rupture of the bubble and its attachment at a smooth hydrophobic solid surface are related to the viscous dissipation of energy, leading to a gradual decrease in the bubble deformation, and in consequence in the radius of the formed separating liquid film. When the film radius is small enough, the bubble ruptures and attaches to the hydrophobic solid surface. Moreover, it is shown that when the bubble deformations are forced to be constant, by applying properly adjusted oscillations of the solid substrate (energy supply conditions), bubble rupture can be prevented and a constant bubble bouncing is observed, irrespective of the hydrophobic/hydrophilic properties of the solid substrate. Under such energy supply conditions, the liquid film can be considered “immortal.” The numerical calculations performed for the respective system, in which constant kinetic energy is induced, confirm that the liquid film can persist indefinitely owing to its constant radius, which is too large to reach the critical thickness for rupture during the collision time.

Vortex-ring-induced large bubble entrainment during drop impact.

For a limited set of impact conditions, a drop impacting onto a pool can entrap an air bubble as large as its own size. The subsequent rise and rupture of this large bubble plays an important role in aerosol formation and gas transport at the air-sea interface. The large bubble is formed when the impact crater closes up near the pool surface and is known to occur only for drops that are prolate at impact. Herein we use experiments and numerical simulations to show that a concentrated vortex ring, produced in the neck between the drop and the pool, controls the crater deformations and pinchoff. However, it is not the strongest vortex rings that are responsible for the large bubbles, as they interact too strongly with the pool surface and self-destruct. Rather, it is somewhat weaker vortices that can deform the deeper craters, which manage to pinch off the large bubbles. These observations also explain why the strongest and most penetrating vortex rings emerging from drop impacts are not produced by oblate drops but by more prolate drop shapes, as had been observed in previous experiments.

Experimental investigation on submerged gas-liquid mixture injection into water through a micro-channel

Submerged gas-liquid mixture injection into water through a micro-channel shows unique fluid characteristics by various flow regimes in the micro-channel generating special jetting phenomena which have never been systematically studied. We injected air-water mixtures into water through submerged 1.0 and 1.5mm diameter micro-channels. Bubbly, Taylor, bubble-train Taylor, churn and Taylor-annular flows were observed, and generated respective jetting flow regimes. Overall, two flow regimes namely “unstretched bubbles” and “stretched bubbles” were identified in the jet region. The former consists of three flow patterns, namely discrete bubbles, gathered bubbles and grown irregular bubbles. The latter occured when liquid slugs having strong enough momentum to stretch the bubble interface, from which single-bubble stretched, twin-bubbles stretched and even bubble rupture were further identified. We compared flow regime maps in micro-channels with those of submerged jets, and proposed the correspondence relationship, whose universality was confirmed by the consistency for different sized micro-channels. Transitions between two overall flow regimes of submerged jets, as well as flow patterns of unstretched bubbles were found determined by flow regime transitions in the micro-channel. Besides, transition laws between flow patterns of stretched bubbles were affected by the uniformity of slug length throughout the micro-channel, which were quantitatively analyzed.

Ignition and combustion characteristics of jet fuel liquid film containing graphene powders at meso-scale

At meso-scale, ignition and combustion characteristics of jet fuel liquid film containing graphene powders were investigated. Jet fuel/graphene suspensions were prepared, and sprayed to produce the liquid film. Liquid film was ignited by optical tweezers, five distinctive stages including graphene trap, ignition and combustion of graphene, bubble formation, jet fuel vaporization and bubble growth, bubble rupture and combustion of liquid film were identified. Ignition of graphene is prior to jet fuel. The combustion heat of graphene serves a heat source to accelerate the vaporization of jet fuel. The graphene serves as a nucleation point to form a bubble. Expansion of both combustion products and jet fuel vapor result in the bubble growth. The thickness of bubble boundary layer depends on graphene concentration. As the bubble escaped, liquid film ruptured and micro-explosion occurred. Jet fuel was then ignited, and combusted sustainably till burnt out. During combustion, the flame front fluctuated slightly, indicating good flame stability. Finally, a schematic physical model was presented to analyze the inductive mechanism of graphene for ignition and combustion of jet fuel liquid film by optical tweezers.

Altering Bubble Dynamics via In Situ Vapor Extraction

Spatiotemporal cooling of electronics using latent energy might be achieved by closely spaced, rapid departure of small bubbles. One means to achieve small diameters during boiling is to provide an additional upward force during bubble formation, such as that from vapor extraction. Experiments were conducted of bubble extraction using constant flow rates of both air and vapor that ranged from 30 to 90 mm3/s. Extraction was achieved with a hydrophobic porous membrane sealed to a tube in which a vacuum was drawn. The gap between the extraction and supply surface was varied from 0.5 to 3.25 mm. Only individual bubbles that ruptured at the top surface while still attached to the supply surface were considered. Bubble departure diameters are approximately 80% of the gap height. As with unconfined bubbles in pool boiling, the bubble frequency varies inversely with departure diameter. Correlations for bubble rupture, bubble departure, and bubble frequency are presented as a function of gap height. Using the three distinct regimes identified in the experimental study, namely, growth only, growth with extraction, and extraction only, an effective bubble diameter model and an appropriate static force balance were developed. These were used to predict bubble departure frequencies and diameters, respectively, under confined extraction conditions.

Influence of the Interfacial Tension on the Droplet Formation by Bubble Rupture in Sn(Te) and Salt System

Influence of the Interfacial Tension on the Droplet Formation by Bubble Rupture in Sn(Te) and Salt System

Life and death of not so "bare" bubbles.

In this paper, we investigate how the drainage and rupture of surfactant-stabilised bubbles floating at the surface of a liquid pool depend on the concentration of surface-active molecules in water. Drainage measurements at the apex of bubbles indicate that the flow profile is increasingly plug-like as the surfactant concentration is decreased from several times the critical micellar concentration (cmc) to just below the cmc. High-speed observations of bubble bursting reveal that the position at which a hole nucleates in the bubble cap also depends on the surfactant concentration. On average, the rupture is initiated close to the bubble foot for low concentrations (<cmc) while its locus moves towards the top of the bubble cap as the concentration increases above the cmc. In order to explain this transition, we propose that marginal regeneration may be responsible for bubble rupture at low concentrations but that bursting at the apex for higher concentrations is driven by gravitational drainage.