Subsequent Bubble Research Articles

Submegahertz Nucleation of Plasmonic Vapor Microbubbles near a Solid Vertical Boundary.

Laser triggered and photothermally induced vapor bubbles have emerged as promising approaches to facilitate optomechanical energy conversion for numerous applications in microfluidics and nanofluidics. Here, we report an observation of spontaneously triggered periodic nucleation of plasmonic vapor bubbles near a rigid sidewall with readily tuned nucleation frequency from 0.8kHz to over 200kHz. The detailed collapsing process of the vapor bubbles was experimentally and numerically investigated. We find that the lateral migration of residual bubbles toward the sidewall refreshes the laser spot area, terminates the subsequent steady bubble growth, and leads to the repeatable bubble nucleation. A mathematic model regarding the Kelvin impulses was derived. It shows that the competition between the rigid boundary induced Bjerknes force and laser irradiation caused thermal Marangoni force on collapsing bubbles governs the process. The model also leads to a criterion of γζ<0.34 for repeatable bubble nucleation, where γ is the normalized distance and ζ thermal Marangoni coefficient. This study demonstrates nucleation of violent vapor bubbles at extreme high frequencies, providing an approach to remotely realize strong localized flows in microfluidics and nanofluidics.

Bubble behavior of single-pulse discharge in EDM

The removal of machining debris in the narrow discharge gap primarily relies on high pressure bubble expansion and fluid agitation induced by the bubble pulsation in electrical discharge machining (EDM). Observing bubble behavior and elucidating the mechanism of bubble behavior is an increasing concern in EDM. The purpose of this study is to investigate the bubble behavior of single pulse discharge in EDM. Using a high-speed camera, this study observed the bubble evolution and measured the discharge duration dependent bubble characteristics. The results show that the bubble experiences rapid expansion, contraction, primary pulsation, intense pulsation in the post-discharge process, and subsequent bubble energy dissipation behavior. Furthermore, the arc plasma persists for a duration even after the discharge ends in positive polarity machining. The findings suggest that bubble behavior in single-pulse discharges is primarily dominated by the discharge energy, with the bubble behavior during the discharge significantly influenced by the jumping and oscillation of the arc plasma. Our research may introduce new ideas for improving the depth-to-diameter ratio of deep micro-holes in EDM and provide fresh perspectives on the mechanism analysis of how machining parameters affect machining performance. For instance, by synchronizing the pulse intervals with the bubble stabilization time, bubble coalescence can be reduced, thus increasing bubble removal in the small machining gap. The stability of deep micro-hole EDM may depend on bubble behavior, which is determined by the electrical parameters.

Numerical study on temperature response of microheater and evolution characteristics of superheated zone under fast transient heating

The nucleate boiling process that occurs on the surface of a microheater immersed in a liquid pool under fast transient heating conditions can be regarded as homogeneous or near-homogeneous nucleation, exhibiting a significant difference when compared to boiling at conventional time scales on large and even micro spatial scales. This paper numerically investigates the boiling process at both small spatial and temporal scale by using a validated model. Results indicate a significant difference between the average microheater temperature and the maximum temperature at the boiling surface, which can reach up to 80 °C within the scope of present study. Consequently, the nucleation temperature, typically determined by the average temperature of the microheater in most references, may not precisely represent the homogeneous (or nearly homogeneous) nucleation temperature. At the initiation of nucleation, the profiles at the boundary of superheated zone are approximately circular in the z-plane and arched in the x-plane, respectively. Meanwhile, the profile of the superheated zone boundary at the onset of nucleation under direct heating mode (DHM) appears approximately trapezoidal, exhibiting a significant difference from that observed under indirect heating mode (IHM). It is also noted that the local temperature distribution in the fluid region can be considerably affected by natural convection, potentially exerting a substantial influence on the bubble dynamic behaviors during the subsequent bubble growing phase. These findings may provide valuable references for future experimental study on the mechanisms involving in microscale boiling heat transfer process under rapid heating conditions.

Study on dynamic characteristics of cavitation in underwater explosion with large charge

Underwater explosions (UNDEX) generate shock waves that interact with the air–water interface and structures, leading to the occurrence of rarefaction waves and inducing cavitation phenomena. In deep-water explosions, complex coupling relationships exist between shock wave propagation, bubble motion, and cavitation evolution. The shock wave initiates the formation of cavitation, and their growth and collapse are influenced by the pressure field. The collapsing bubbles generate additional shock waves and fluid motion, affecting subsequent shock wave propagation and bubble behavior. This intricate interaction significantly impacts the hydrodynamic characteristics of deep-water explosions, including pressure distribution, density, and phase changes in the surrounding fluid. In this paper, we utilize a two-fluid phase transition model to capture the evolution of cavitation in deep-water explosions. Our numerical results demonstrate that the introduction of a two-phase vapor–liquid phase change model is necessary to accurately capture scenarios involving prominent evaporation or condensation phenomena. Furthermore, we find that the cavitation produced by the same charge under different explosion depths exhibits significant differences, as does the peak value of cavitation collapse pressure. Similarly, the cavitation produced by different charge quantities under the same explosion depth varies, and the relationship between cavitation volume and charge quantity is not a simple linear increase. The research methods and results presented in this paper provide an important reference for studying the dynamic characteristics of deep-water explosions.

Energy quantification framework for underwater explosive loading into PVC foam cladded composite plates

This paper presents a novel approach for analyzing the effects of near-field underwater blast loading on composite marine structures. The operational requirements of these structures often expose them to blast or shock loading, which can lead to significant damage. The study focuses on the propagation of spherical blast waves and the subsequent secondary bubble collapse pulse that affects the structure under near-field underwater blast loading events. An analytical framework is developed to calculate the blast energies and structural energies during this complex loading event. The study further investigates the effect of applying a sacrificial cladding made of low-density closed-cell foam to the loading face of a composite panel. Experiments were conducted in a specialized facility to characterize the explosive-driven blast-loading and the subsequent interaction between the shock pressure front and the structure. Dynamic pressure measurements and high-speed imaging were utilized to capture the behavior of the composite panel under these extreme conditions. 3D digital image correlation was employed to analyze strain and deformation of the composite panel, while high-speed side view cameras captured the fluid-structure interaction during the blast and bubble collapse loading event. The results strongly indicate that the collapse of the explosion bubble is the dominant failure source in near-field underwater blast loadings. The analytical quantification of energy further corroborates the significant damaging effects of bubble collapse due to the buildup of after-flow energies during the bubble collapse duration. Furthermore, the inclusion of low-impedance elastic-plastic PVC foam cladding is shown to significantly mitigate the effect of blast loading on the composite structure.

Simultaneous plane-wave and ultra high-speed imaging of acoustic droplet vaporization

Super-heated sub-micrometre perfluorocarbon droplets have been shown to offer advantages over microbubbles for ultrasound localization microscopy (ULM). These include better penetration of the microcirculation and enabling higher frame rates using methods such as acoustic wave sparsely activated localization microscopy (AWSALM). The variability of droplet behaviour has however been found to be substantially higher than that of microbubbles and this poses challenges for ULM image construction. The aim of this study was to use simultaneous high speed optical and acoustic imaging to capture the droplet vaporisation process and subsequent bubble dynamics. Droplets composed of octofluoropropane and decafluorobutane were injected into a polyethylene tube submerged in a 37 °C water bath and located at the focus of an ultrasound probe and microscope objective. Optical images were captured at 10 Mfps of the droplet response to ultrasound pulses of varying lengths and amplitude. The results indicate that the number of activated droplets is impacted by increasing either the ultrasound pressure or number of half-cycles as well as by the preceding activation ultrasound pulses; and that different droplet sub-populations can be activated by varying pulse parameters. These data indicate the potential for optimising droplet activation of ULM applications.

Numerical investigation of the underwater explosion of a cylindrical explosive with the Eulerian finite-element method

The shock wave and bubble dynamics of an underwater explosion are significant in various fields. When the charge is non-spherical, the detonation process will remarkably affect the shock wave formation and the subsequent bubble motion. In this work, the underwater explosion of a cylindrical explosive is investigated numerically with the Eulerian finite-element method combined with the programed burn model treating the detonation process. The present model is validated by comparing the simulated results with the experimental ones. Then, several cases with different slenderness of the explosive charge in various buoyancy environments are simulated and analyzed. The results demonstrate a notable variation of the shock wave in different directions. The shock wave will reach the highest pressure peak and shortest pulse width at a certain angle determined by the ratio between the speeds of the detonation wave and the shock wave. Furthermore, the non-spherical initial expansion of the bubble casts a significant influence on the subsequent bubble evolution. Three typical jet morphologies are identified with different combinations of buoyancy parameter and oblateness ratios of the bubble, featured by a slightly oblique upward jet penetrating the bubble, a laminar jet that failed to penetrate the bubble continuously, and a pair of opposite horizontal jets penetrating the bubble. Meanwhile, the horizontal jets that happen under a weak buoyancy environment will reduce the upward migration.

Nucleation Process in Explosive Boiling Phenomena of Water on Micro-Platinum Wire.

The maximum temperature limit at which liquid boils explosively is referred to as the superheat limit of liquid. Through various experimental studies on the superheating limit of liquids, rapid evaporation of liquids has been observed at the superheating limit. This study explored the water nucleation process at the superheat limit achieved in micro-platinum wires using a molecular interaction model. According to the molecular interaction model, the nucleation rate and time delay at 576.2 K are approximately 2.1 × 1011/(μm3μs) and 5.7 ns, respectively. With an evaporation rate (116.0 m/s) much faster than that of hydrocarbons (14.0 m/s), these readings show that explosive boiling or rapid phase transition from liquid to vapor can occur at the superheat limit of water. Subsequent bubble growth after bubble nucleation was also considered.

Experimental Study on Multi Bubble Ice Breaking Under Layer Ice Boundary Conditions

Under certain conditions of bubble spacing and bubble to ice distance, the motion state and ice breaking effect of horizontal and vertical bubbles under ice plate boundary conditions were studied. Bubbles are generated through underwater discharge, and the generating device is placed horizontally or vertically below the ice plate, and the experimental phenomenon is observed through an ultra-high-speed camera. Firstly, the motion characteristics and ice breaking ability of two horizontal bubbles under an unperforated ice block were demonstrated. Then, the motion characteristics of two horizontal bubbles and two vertical bubbles under a porous ice block, the breaking effect of the ice block, and the water mound phenomenon on the free surface were observed. The experiment observed unique bubble behavior, including bubble fusion, bubble collapse, and oblique jet, as well as the influence of bubble-bubble and bubble-ice interactions on the morphology evolution and ice breaking effect of bubbles. The results indicate that the ice breaking effect of the interaction between bubbles and perforated ice plates is weaker than that of non-perforated ice plates, which may be more helpful for subsequent bubble ice breaking research.

Bubble pulse arrival time calculations to determine SUS charge detonation depths

As part of the New England Seamount Acoustics (NESMA) project in 2023, experiments were conducted over the Atlantis II Seamount. A total of 216 Signal Underwater Sound (SUS) broadband explosives (150 1.1 oz and 66 1.8 lb net explosive weight) were deployed at multiple locations and two different design depths around the seamount. An acoustic recorder (SoundTrap ST4300), with four hydrophone channels of varying sensitivities, was deployed during each of the SUS events to record the signals generated by the explosives. The recorded signals include arrivals corresponding to the shock wave, subsequent bubble pulses and reflections from the sea surface and sea floor. The time between the first arrival and the bubble pulse was used to calculate the depth at which each SUS charge detonated. The resulting SUS detonation depths from the bubble pulse calculation were compared with depths obtained from surface and bottom reflections to assess the accuracy of the bubble pulse method. A comparison of the results from the two methods shows that using the bubble pulse interval to calculate the SUS detonation depth is reasonable and can be used in propagation models. [Work supported by Office of Naval Research Code 322OA and TFO.]

Influence of overdriven detonation on the energy release of aluminized explosives in underwater explosion

An underwater explosion experiment was designed for the cyclotrimethylenetrinitramine-based aluminized explosives to study the influence of detonation conditions on the explosion performance and the afterburn reaction of aluminum (Al) particles. The research results showed that the performance of shock wave and bubble pulsation grew stronger under the influence of overdriven detonation (ODD), and the contribution of ODD to the bubble energy was associated with the proportion of the inner core and the outer coat. Considering the propagation characteristics of the detonation wave in the ordinary charge and the inner/outer charge, the attenuation of ODD and its role in the initial pressure of the bubble were investigated, and this relationship was used to establish a numerical model for the bubble dynamic behaviors of aluminized explosives. According to the experimental results, the correctness of the established model for the bubble dynamics under ODD was verified, and the variation laws of the afterburn reaction during the bubble pulsation were investigated. It was found that the initial pressure of the bubble under ODD was higher than that under steady detonation. The improvement on the initial pressure promoted the afterburn reaction during the accelerating expansion and enhanced the bubble expansion capacity to support the formation and propagation of shock waves. In the subsequent bubble pulsation, the duration of the decelerating expansion was significantly longer than that of the accelerating expansion, and the ODD had little effect on the afterburn reaction in this stage.

The response of silicon carbide composites to He ion implantation and ramifications for use as a fusion reactor structural material

Silicon carbide fibre–reinforced silicon carbide matrix (SiCf/SiC) composites are desirable in structural nuclear applications due to their low density, high temperature strength and tolerance to energetic radiation. We have subjected two industrial grades of SiCf/SiC to high energy He²⁺ ion irradiation, up to 10,000 appm implanted He at 700 °C, to determine their suitability for blanket structural applications in nuclear fusion. Minor crystallographic evolution is observed following irradiation, with evidence of phase localised stress, intragranular strain, and lattice swelling. This is attributed to vacancy production and subsequent He bubble formation, both intragranular and at grain boundaries.During post-irradiation annealing up to 1300 °C, varying degrees of He bubble evolution are observed, with the Si phase showing the highest level of instability. The fibres appear stable, with no detectable radiation-induced defects. Meanwhile, bubbles in the fibre coating and matrix grains grow and agglomerate. Despite this, no delamination or microcracking is observed.

Bubbling Phenomena in Liquid-Filled Transformers: Background and Assessment

The degradation of the insulation system in liquid-filled power transformers is a serious concern for electric power utilities. The insulation system’s ageing is accelerated by moisture, acids, oxidation products, and other decay particles (soluble and colloidal). The presence of these ageing by-products is detrimental to the insulation system and may further lead to premature ageing and serious consequences. The ageing mechanisms of oil-paper insulation are complex, highly interrelated, and strongly temperature-dependent. The operating temperature of the transformer insulating system has a direct relationship with the loading profile. The major aspect that is witnessed with the fluctuating temperatures is moisture migration and subsequent bubble evolution. In other words, gas bubbles evolve from the release of water vapor from the cellulosic insulation wrapped around the transformer windings. The models presented in the existing standards, such as the IEC Std. 60076-7:2018 and the IEEE Std. C57.91:2011, are mainly based on the insulation temperature, which acts as a key parameter. Several studies have investigated the moisture dynamics and bubbling phenomenon as a function of the water content in the paper and the state of the insulation system. Some studies have reported different prototypes for the estimation of the bubble inception temperatures under selected conditions. However, there are various attributes of the insulation system that are to be considered, especially when expanding the models for the alternative liquids. This paper reviews various evaluation models reported in the literature that help understand the bubbling phenomenon in transformer insulation. The discussions also keep us in the loop on the estimation of bubbling behavior in alternative dielectric liquids and key attributable factors for use in transformers. In addition, useful tutorial elements focusing on the bubbling issue in transformers as well as some critical analyses are addressed for future research on this topic.

Bubble Coalescence During Pool Boiling with Different Surface Characteristics

This work investigates the bubble dynamics during pool boiling from isolated cavities on a horizontal silicon substrate with three surface coatings, silicon oxide, Perfluorodecyltrichlorosilane, and silica nanoparticles. The experiments were conducted with FC-72 under various superheat degrees. In the case of vertical coalescence, coalescences at the boundary between the departed bubble and the subsequent nucleated bubble were observed and analyzed. Vertical coalescence appears with lower superheat degrees on Perfluorodecyltrichlorosilane coated surfaces due to the faster initial bubble growth than on the other surfaces. However, the vertical coalescence has a limited effect on the bubble departure diameter, which is nearly kept constant at around 0.6 mm. In the case of horizontal coalescence, bubbles growing on the silica nanoparticles coated surface are able to coalesce for small cavity spacing with lower superheat degree than other surfaces. Coalescing bubbles from cavities spaced 0.50 mm apart can detach just after coalescence, while for a shorter spacing of 0.25 mm, bubbles remain attached to the surface and further growth is needed for their detachment. Based on the analysis of energy removal per unit of area, the optimal heat transfer performance may be achieved when the cavities spacing is approximate to the single bubble departure diameter.

Protection mechanism of underwater double-hull coated with UHMW-PE subjected to shaped charge

Shaped charge warhead which is widely utilized for underwater weapons has a severe threat to the survivability of naval ships. Therefore, it is of great significance to improve their anti-destructive capability. Three types of loads - shock wave (SW), shaped charge projectile (SCP) and bubble - are generated during the process of shaped charge associated with underwater explosion, which can cause different damage characteristics into double-hull structure. In this paper, these three loads characteristics and their combined damage into double-hull structure are analyzed. Besides, the protection of fiber metal laminates on this structure are discussed. Firstly, Coupled Eulerian-Lagrangian (CEL) is used to simulate the full physical process of double-hull subjected to shaped charge associated with underwater explosion. Secondly, the damage characteristics of double-hull are obtained under the combined damage of the shock wave, shaped charge projectile and bubble. After that, the steel plate/UHMW-PE laminate (Fiber Metal Laminate, FML) is designed according to the equal surface density theory. The blast and penetration resistance of ultra-high molecular weight polyethylene (UHMW-PE) material is analyzed and the optimized FML models are discussed. The results show that a small plastic deformation and hole of the outer and inner plates of the double-hull are generated by the shock wave and the shaped charge projectile, respectively. A large plastic deformation of the outer plate is caused by the subsequent bubble load, which is torn and pulled off. The hole size of plate coated with PE and the residual velocity of projectile reduced by 26.66% and 69.50% compared with those of the steel plate, respectively. Besides, for the coated cases the outer and inner plates is respectively not pulled off and penetrated by projectile. Additionally, it is worth noting that the bubble collapses and cannot cause the secondary damage into double-hull due to the protection of coated PE. It indicates that the PE has a great protection performance of the double-hull subjected to shock wave, bubble and projectile, which can provide a reference for the naval ships protection design.

Numerical Study of Growth of a Vapor Bubble in Superheated Seawater with Time-Varying Pressure

Flash evaporation is used in a wide range of applications from seawater desalination to nuclear and space applications. The fundamental mechanism in flash evaporation is mechanical and thermal non-equilibrium which results in liquid being superheated and subsequent bubble growth. Therefore, study of bubble growth is essential to accurately predict the vapor generation rate during flashing. Accordingly, this article provides a comprehensive numerical study of growth of a single vapor bubble during flash evaporation in seawater. Effects of system pressure, liquid superheat, salt concentration, and time-varying pressure during flash evaporation on bubble growth behavior are studied. The Rayleigh-Plesset equation with energy and salt concentration equations is solved numerically with 4th-order discretization schemes. Excellent agreement between the results of the present study and reported experimental results is found. It is observed that during bubble growth in seawater, salt continuously accumulates at the vapor-liquid interface which consequently reduces the growth rate and degrades thermal performance characterized by Nusselt number. However, it elongates the inertia-controlled regime during which the bubble radius is directly proportional to time. It is shown that properly handling the non-uniform distribution of solute in the liquid boundary layer is key to modeling bubble growth in seawater and binary solutions.

Bubbling of Ferrofluid Droplets via Coupled Magnetic and Sound Fields

AbstractBubbles play essential roles in many natural and industrial processes because of the unique effects of their films on heat–mass transfer and their soft confined geometry for interfacial assembly or phase transitions. Here, a technique for noncontact bubbling via coupling of sound and magnetic fields in acoustic levitation is reported. An acoustically levitated ferrofluid droplet can be transformed into a closed bubble in a controlled manner. It has been found that the magnetic field pulls the flattened ferrofluid film downward, and making it deviate from its initial levitation position determined by the balance between acoustic radiation force and gravity. This results in variation in acoustic radiation pressure on the film surface and generates an upwards torque on the levitated film, leading to buckling and subsequent bubble transition via acoustic resonance. Moreover, the levitated ferrofluid bubble can remain unburst in the sound field for minutes to enable its complete evaporation; thus, solid hollow shells form. This work provides insight for understanding the coupled effect of sound and magnetic fields on ferrofluid drops and sheds light on evaporation‐driven self‐assembly of ferrofluid particles into shell structures

Electrochemical Control of the Morphology and Functional Properties of Hierarchically Structured, Dendritic Cu Surfaces

Electrodeposited dendritic copper foams have been extensively studied as an electrocatalyst for CO2 reduction reaction (CO2RR). Many parameters, such as dendrite size, porosity, pore size, and crystal faceting, define the hierarchical properties of these structures and their subsequent bubble evolution and CO2RR capabilities. Herein, the effects the electrodeposition conditions (potential, pH) have on the resulting crystallinity, microstructure, and macroporosity of the copper foam are studied. These morphological differences and the corresponding effects on electrocatalytic activity are characterized. It is shown that the composition of the electrodeposition bath can have significant effects on the mechanics of bubble formation and detachment at the surface during hydrogen evolution reaction in acidic solutions. Similarly, the electrodeposition conditions for the synthesis of the foam affect the product selectivity during CO2RR electrocatalysis. Foams deposited in alkaline electrodeposition solutions show high faradaic efficiency and specificity toward C2H6, an uncommon product of CO2RR, at modest applied potentials (−0.8 V versus reversible hydrogen electrode.

Influence of an external magnetic field on laser-induced plasma and cavitation bubbles in submerged targets

A pulsed Nd:YAG laser is tightly focussed on a metal target immersed in distilled de-ionized water. The resultant laser-induced plasma and subsequent cavitation bubble behavior are studied under the influence of an external magnetic field that is varied from 700 to 1000 Gauss. The study is conducted using a beam deflection probe arrangement. In addition, laser-induced breakdown spectroscopy is also employed to study the plasma spectrum. Furthermore, three different magnetic materials are employed for this investigation: ferromagnetic nickel, paramagnetic gadolinium, and diamagnetic copper. The studies revealed that cavitation bubble radii and collapse durations increased considerably as the magnitude of the external magnetic field was increased. This effect was prominent in the case of nickel and less so in the case of gadolinium and copper. For nickel, collapse times increase when the magnetic field was applied, whereas for gadolinium and copper, significant changes were not observed. The differences observed in collapse times showed that magnetic properties of the targets played a vital role in this phenomenon. The process of pulsed laser ablation in liquid also led to the respective generation of metallic nanoparticles from individual materials. Characterization of the generated nanoparticles revealed size reduction when synthesized under the influence of an external magnetic field. These characterizations were performed using transmission electron microscopy and UV-Vis spectroscopy.

A study on damage characteristics of double-layer cylindrical shells subjected to underwater contact explosion

In this study, the damage characteristics of double-layer cylindrical shells with interlayer water subjected to small charge underwater contact explosion were investigated through experimental and numerical methods. At the same time, the distribution characteristics of the field pressure near the double-layer cylindrical shells and detailed bubble dynamics were revealed. The experimental results showed that there were crevasse and non-crevasse areas in the outer shell of the double-layer cylindrical shells, which form “inrushing bubbles” and “induced bubbles” in the interlayer water, respectively. Their subsequent bubble collapse behavior continued to impact the inner shell. Based on the traced analysis of the field pressure and deformation duration characteristics of the double-layer cylindrical shells, the load characteristics of the shock wave, interlayer bubble (inrushing bubble and induced bubble), and outboard bubble load sequence response to double-layer cylindrical shells were obtained.