Bubble Stability Research Articles

Study on the influence of dynamic characteristics of bubbles on electrochemical discharge machining conductive materials

Electrochemical discharge machining (ECDM) is widely used to machine miniaturized products with electrically conductive and non-conductive materials. However, less attention has been focused on the effect of dynamic characteristics of bubbles on machining electrically conductive materials. Therefore, the aim of this study was to investigate the effect of the dynamic properties of bubbles on the characteristics of machining electrically conductive materials in the ECDM process. To clearly distinguish the effect of the dynamic characteristics of bubbles on the machining process, the large viscosity M-type composite electrolyte was applied, and the movement process of the bubbles was captured by high-speed camera. The effect of the dynamic properties of bubbles on the ignition delay time, the material removal rate (MRR) and the discharge gap have been investigated. The results show that there is an ignition delay time phenomenon, and the stable bubbles state can reduce the ignition delay time. Furthermore, the dynamic characteristics of the bubble may affect the energy conversion efficiency during the ECDM process. A higher MRR and a larger discharge gap can be obtained in the state with a stable bubble condition.

Oxide-mediated mechanisms of gallium foam generation and stabilization during shear mixing in air

Foaming of gallium-based liquid metals improves their processability and-seemingly in contrast to processing of other metal foams-can be achieved through shear-mixing in air without addition of solid microparticles. Resolving this discrepancy, systematic processing-structure-property characterization demonstrates that many crumpled oxide particles are generated prior to air bubble accumulation.

Effect of pH and Dodecylamine Concentration on the Properties of Dodecylamine Two-Phase foam

Over-stabilized foam has always been a problem that plagues the dodecylamine (DDA) flotation system. In this study, a new device, “automatic foam analyzer”, was successfully used to characterize the behavior of foam in DDA solution. The effects of pH and DDA dosage on the foam properties were investigated from four aspects: bubble diffusion capacity, Bikerman coefficient, half-life period and solution conductivity, and the mechanism of pH and DDA concentration on foam properties was analyzed by solution chemistry and surface tension of DDA, then the change process of foam structure was deduced. The results showed that the foaming property and stability of DDA bubbles were the best at pH=8. Simultaneously, with the increase of DDA dosage, the foaming property of bubbles was enhanced, the half-life was prolonged, and the foam stability was also improved.

Stability of big surface bubbles: impact of evaporation and bubble size.

Surface bubbles have attracted much interest in the past few decades. In this article, we aim to explore the lifetime and thinning dynamics of centimetric surface bubbles. We study the impact of the bubble size as well as that of the atmospheric humidity through a careful control and systematic variation of the relative humidity in the measuring chamber. We first address the question of the drainage under saturated water vapor conditions and show that a model including both capillary and gravity driven drainage provides the best prediction for this process. Additionally, unprecedented statistics on the bubble lifetimes confirm experimentally that this parameter is set by evaporation to leading order. We make use of a model based on the overall thinning dynamics of the thin film and assume a rupture thickness of the order 10-100 nm to obtain a good representation of these data. For experiments conducted far from saturation, the convective evaporation of the bath is shown to dominate the overall mass loss in the cap film due to evaporation.

Effect of pH and Dodecylamine Concentration on the Properties of Dodecylamine Two-Phase foam

Over-stabilized foam has always been a problem that plagues the dodecylamine (DDA) flotation system. In this study, a new device, “automatic foam analyzer”, was successfully used to characterize the behavior of foam in DDA solution. The effects of pH and DDA dosage on the foam properties were investigated from four aspects: bubble diffusion capacity, Bikerman coefficient, half-life period and solution conductivity, and the mechanism of pH and DDA concentration on foam properties was analyzed by solution chemistry and surface tension of DDA, then the change process of foam structure was deduced. The results showed that the foaming property and stability of DDA bubbles were the best at pH=8. Simultaneously, with the increase of DDA dosage, the foaming property of bubbles was enhanced, the half-life was prolonged, and the foam stability was also improved.

On the thermodynamic stability of bubbles, immiscible droplets, and cavities

Nanobubbles filled with air or a variety of pure gases are observed to persist in bulk water for weeks and months. Nanoemulsions consisting of oil droplets in water are also remarkably stable against coagulation, with lifetimes up to weeks even if not coated with surfactants. The inverse system of nanodroplets of water in oil is also accessible for study and application. Voids on the nanoscale are formed in simulations of water under strong tension and are stable during the time of the simulation. The stability of these nano-entities is ultimately determined by the molecular-level structure of their interfaces. However, a thermodynamic theory might also be capable of providing some insight. We therefore consider spherical gas nanobubbles, immiscible liquid nanodroplets, and nanocavities formed in water under negative pressure on the same footing, and give a unified thermodynamic analysis of these systems. In all cases, mechanical equilibrium (local free energy maximum or minimum) is expressed by the Laplace equation, and thermodynamic stability (local free energy minimum) follows from the radius dependence of surface tension. All of them would be unstable if their surface tensions were constant. Data from the literature allow construction of numerical examples for cavities and gas nanobubbles. Spectroscopic data are cited in support of an interfacial water structure in gas nanobubbles and water droplets in oil that differ from their flat surface counterparts. The observed longevity of nanobubbles in particular has been thought to violate fundamental principles of diffusion and solubility. A close look at the Laplace equation and its derivation shows why this widespread belief is incorrect.

Pulse gas-assisted multi-needle electrospinning of nanofibers

Multi-needle electrospinning is an effective method to increase the productivity of nanofibers. In this paper, the number of single-needle jets was increased to further improve the production efficiency. As the traditional method for increasing the number of single-needle jets has poor controllability and persistence, we proposed a gas-assisted method to increase the yield of nanofibers. A coaxial gas auxiliary needle was designed with an intermediate shaft supplied gas and the outer shaft supplied solution. Innovatively using pulse gas to produce continuous and stable bubbles which are ruptured on the needle. The liquid film is continuously disturbed, which generates jets in the electric field, thereby increasing the number of jets of a single needle. After optimization of the single-needle gas-assisted electrospinning process, the stable spraying process of 16-pin multi-needle electrospinning has been realized. The gas-assisted electrospinning productivity was 4.7 times higher than that of without gas assistance. It provided a new idea for improving the stable production of the multi-needle electrospinning.

Improvement of viscosity-modifying agents on air-void system of vibrated concrete

The influence of viscosity-modifying agent (VMA) on air-void system of self-compacting concrete has attracted considerable attention in recent years. But for conventional concrete with a sharp loss of air content due to vibration operation, the role of VMA on air-void system remains unclear. This paper aims to validate and clarify the positive effects of VMA on air bubbles stability and air voids homogeneity in vibrated concrete. Three typical VMAs with variable dosages were incorporated to prepare twenty air-entrained fresh mixtures. Rheological properties of mortar matrix portion of fresh concrete, surface tension of aqueous solution and time-dependent air content were evaluated for every mix. The air-void system in hardened concrete was inspected at three casting depths of prism specimen. Results showed that the surface tension of VMA solution played a key role in the stabilization effect on air bubbles, which strongly varied with VMA molecules. A higher plastic viscosity induced by the higher VMA dosage was favorable for maintaining the homogeneous distribution of entrained small air bubbles and reducing the formation of large voids in vibrated concrete. Therefore, a proper incorporation of VMA can improve the freeze-thaw resistance of vibrated concrete with lower spacing factor and smaller chord length.

The effects of sodium reduction on the gas phase of bread doughs using synchrotron X-ray microtomography.

Globally, the bakery industry has a target of reducing sodium content in bread products. However, removing salt results in changes in the quality of bread through effects on dough's gas phase during the breadmaking process. Using synchrotron X-ray microtomography, the objective of this study was to investigate how sodium reduction induced changes in the gas phase parameters (i.e., gas volume fraction, bubble size distribution (BSD) and its time evolution) of non-yeasted doughs made from a wide range of formulations (i.e., wheat cultivar and water content) prepared with different mixing times. As salt content was reduced, a lower gas volume was retained in the dough by the end of mixing. Less gas bubbles were also retained if doughs were prepared from a stronger wheat cultivar, higher water content, and/or mixed for a shorter time. Rates of change in the median (R0) and the width (ε) of the fitted lognormal radius dependence of bubble volume fraction [BVF(R)] indicated that reduced sodium content permitted disproportionation to proceed more rapidly. Higher water content or longer mixing time also resulted in faster disproportionation, indicating that water content and mixing time can be manipulated as a means of increasing bubble stability against disproportionation during low-sodium breadmaking. An examination of relative changes in dough's gas phase parameters arising from sodium reduction demonstrated that wheat cultivar, water content and mixing time all affected dough's tolerance to sodium reduction. Therefore, attainment of good bread crumb cell structure in low-sodium bread formulas is a function of salt's effects on dough rheology in addition to its effect on yeast activity, so that dough formulation and mixing conditions also need to be considered.

Selective aggregation by ultrasonic standing waves through gas nuclei on the particle surface.

Gas nuclei in water are usually too small to be directly observed. They will grow into bubbles under the negative pressure, which is called cavitation (heterogeneous cavitation). In this study, the gas nuclei in the hydrophilic and hydrophobic silica particle suspension were investigated using the transient cavitation threshold measured by a high-intensity focused ultrasound (HIFU). The transient cavitation bubbles were also observed by a high-speed camera. The results showed that the nuclei only exist on the surface of hydrophobic particles. Furthermore, the aggregation experiments revealed that the aggregates were only formed in the hydrophobic silica suspension by ultrasonic standing waves (USW) at 200kHz. This distinct difference was mainly due to the formation of gas nuclei on hydrophobic silica particles, which grew and coalesced into stable bubbles under the 200kHz USW. The aggregation process in suspension was observed by a CCD camera. Moreover, the cavitation thresholds and acoustic radiation forces were analyzed to explain the mechanism of the acoustic aggregation. This study showed a very promising acoustic method for the selective aggregation of hydrophobic particles, which might be efficiently used in the mineral separation industry.

Combination of egg white protein and microgels to stabilize foams: Impact of processing treatments

The aim of this study was to compare the properties of foams stabilized by egg white protein (EWP) and egg white protein microgels (EWPM), and combinations thereof (EWP + EWPM; 1.0 + 0, 0.7 + 0.3, 0.5 + 0.5, 0.3 + 0.7 or 0 + 1.0, wt%) without or with processing treatments (freezing at −20 °C/30 min, oven-heating at 80 °C/30 min, or microwaving at 700 W/15 s). In order to provide a twofold benefit of high initial foam volume (dictated by rapid adsorption of EWP) and high foam stability (governed by Pickering stabilization by EWPM), various ratios of EWP + EWPM on foam stabilization were investigated. The EWP + EWPM systems generated similar initial foam volumes as compared to those prepared solely with EWP (p > 0.05), and foams generated with increasing ratios of EWPM + EWP showed higher stability to bubble shrinkage and coalescence at longer time scales (9 h). Confocal images revealed that EWPM were preferentially located at the air/water interface with the increasing EWPM + EWP ratio, suggesting pure Pickering stabilization at 1.0 wt% EWPM. Plateauing of bubble size at ca. 75 μm occurred only at EWPM> 0.5 wt% for EWP + EWPM = 1.0 wt% total protein, when stability became EWPM-dominated. Frozen foams showed the most stable bubbles, irrespective of the systems (p > 0.05). The combination of EWP + EWPM significantly improved the stability of the bubbles during oven-heating as compared to the EWP-stabilized counterparts (p < 0.05), whilst the EWPM system was the most stable during microwaving. These results suggest that microgels could be used to formulate food foams with enhanced stability to processing conditions, whereas combination with non-microgel protein can improve the initial foamability.

Contraction of a shear-thinning axisymmetric cavity

We investigate the capillary driven collapse of a small contracting cavity or hole in a shear-thinning fluid. We find that shear-thinning effects accelerate the collapse of the cavity by decreasing the apparent liquid viscosity near the cavity’s moving front. Scaling arguments are used to derive a power-law relationship between the size of the cavity and the rate of collapse. The scaling predictions are then corroborated and fully characterized using high-fidelity simulations. The new findings have implications for natural and technological systems including neck collapse during microbubble pinch-off, the integrity of perforated films and biological membranes, the stability of bubbles and foams in the food industry, and the fabrication of nanopore based biosensors.

The influence of invariant solutions on the transient behaviour of an air bubble in a Hele-Shaw channel.

We hypothesize that dynamical systems concepts used to study the transition to turbulence in shear flows are applicable to other transition phenomena in fluid mechanics. In this paper, we consider a finite air bubble that propagates within a Hele-Shaw channel containing a depth-perturbation. Recent experiments revealed that the bubble shape becomes more complex, quantified by an increasing number of transient bubble tips, with increasing flow rate. Eventually, the bubble changes topology, breaking into multiple distinct entities with non-trivial dynamics. We demonstrate that qualitatively similar behaviour to the experiments is exhibited by a previously established, depth-averaged mathematical model and arises from the model’s intricate solution structure. For the bubble volumes studied, a stable asymmetric bubble exists for all flow rates of interest, while a second stable solution branch develops above a critical flow rate and transitions between symmetric and asymmetric shapes. The region of bistability is bounded by two Hopf bifurcations on the second branch. By developing a method for a numerical weakly nonlinear stability analysis we show that unstable periodic orbits (UPOs) emanate from the first Hopf bifurcation. Moreover, as has been found in shear flows, the UPOs are edge states that influence the transient behaviour of the system.

Single Bubble Boiling from an Artificial Cavity

Pool boiling heat transfer is an aggressive and complex phenomenon which needs to be simplified for a better understanding of the mechanism of bubble growth and departure and how boiling heat transfer can be enhanced. Single bubble boiling heat transfer is a simple version of boiling phenomenon which has been used to study the effective elements on pool boiling heat transfer. The purpose of the present review paper is to understand how to produce single bubble pool boiling on a heated substrate and investigate, how single bubble boiling phenomenon can be affected by geometry of cavities, cavity size, wettability, roughness, working fluid, subcooling, wall superheat, heat flux, gravity, etc. It was demonstrated that cylindrical cavities are capable to generate stable and continuous bubbling, small temperature fluctuation, low superheat with short waiting period. The cylindrical cavities can be manufactured very easily in small sizes which can be a good candidate to produce single bubble pool boiling. As heat flux increases, smaller cavities start becoming active. For a given depth, as cavity size increases, the bubble growth rate and departure volume increase. Surface wettability is another complex and important factor to modify the single bubble boiling heat transfer. Wettability depends mainly on force balance at the triple contact line which relies on solid–liquid–gas materials. In case of hydrophobic surfaces, the triple line has tendency to move toward liquid phase and expand the radius of triple line, so the initiation of nucleation is easier, the waiting time is shorter, the downward surface tension force becomes bigger since radius of triple line is larger, the bubble departure volume is higher and bubble growth period is longer. The effects of the rest of main parameters on single bubble boiling are discussed in this paper in details. In addition, a theoretical model is developed to predict the liquid-vapor interface for the single bubble boiling. The theoretical model is compared with single bubble boiling experimental data and good results observed.

Application foam agent to foam cement slurry for geothermal well drilling

One type of light weight cement is foam cement which can be used in cementing operations in weak zones with the possibility of small fractures and reducing the amount of light weigh cement suspension levels. The foam cement suspension can be used to solve lost circulation due to natural vertical fractures or cavernous formations. The purpose of this study was to determine the potential of foam cement slurry to solve the lost circulation in geothermal well. Making slurry cement uses class G cement at 200 mesh and 100 mesh size with the composition of cement. The cements put into the waring blender containing water stirit for 35 second, adding foam agent into cement slurry with variations in foam agent concentration of 0.03%, 0.06%, 0.09%, 0.12% and 0.15%. observations of foam cement above were carried out for 30 minutes to test the stability of bubbles in the mixture. The result this study showed different compressive strength values at variations the concentrations of foam agent. The strength value is strongly influenced by result of sample with 0.03% with Sika-aer concentration have a compressive strength value of 3745 psia, while sample with Sika-aer concentration of 0.15% have compressive strength value of 1701 psia. The value of compressive strength core foam cement can form a linear line according percentage foam agent concentrations. Foam agent between 0.03% - 0.15% with Sika-aer qualified the minimum requirements BHCT compressive strength according API-10B rules to reduce severity lost circulation in the well X-E2 in geothermal drilling well.

Two Phase Flows: Hydrodynamics and Heat-and-Mass Transfer (Based on the Materials of IHTC 16 and RNKT-7 Conferences)

A review of the results from experimental and theoretical studies on fundamental, scientific, technical, and applied orientation are presented for two-phase flows with different structures according to materials of two significant and already traditional scientific forums: the Russian National Conference on Heat Transfer (RNKT-7) and the International Heat Transfer Conference (IHTC 16). Particular attention therein was paid to the classification of gas-liquid and vapor-liquid flows, bubble flows, gas-droplet and gas-dust (gas + solid particles) structures, and plotting flow-pattern diagrams for flowing both in the channels of traditional shape and size and in minichannels of a capillary type. Problems are considered concerning the hydrodynamics and heat-and-mass transfer, increasing heat-transfer efficiency under cooling heated solid surfaces by impact jets. Modern noncontact optical experimental methods for measuring the local characteristics of flows are described in detail, which make it possible to determine, for example, phase slip coefficients, local gas (vapor) content, liquid film thickness, especially in the areas of triple phase contact, etc. Theoretical approaches are also considered wherein analytical and numerical methods are used to describe the stability of bubble and film flows, cavitation phenomena, acoustics, and the gas dynamics of two-phase flows, including gas + solid particles. A significant number of reports are devoted to the urgent problems of power engineering, chemical technologies, studies on heat-and-mass transfer in cooling towers, cryogenic equipment under regasification, absorbers, jet cooling systems for heat-transfer surfaces, snow generators, and ultra-modern and highly efficient capillary-type heat exchangers.

Synergism effects of coconut diethanol amide and anionic surfactants for entraining stable air bubbles into concrete

Entraining tiny and stable bubbles into cement and concrete is becoming more and more important with the complex composition of cement and concrete. In this work, multi-component surfactants are compounded to improve the air-void stability in fresh concrete. The surface tensions, foam properties of their solutions, and the air contents and air-void parameters of the fresh and hardened cement mortars were tested. The results show that there are strong interactions on the interface of multi-components by calculating the important parameters of surface activity. When coconut diethanol amide molecules are introduced into the interface for co-assembly, the electrostatic repulsion between the anionic surfactant molecules is effectively diminished, thereby decreasing the interfacial free energy and making the interface more stable. The multi-component surfactants induced smaller bubbles with larger amounts in aqueous solutions, which also have higher stability of air bubbles in both cement mortars and concretes. So it is of great practical significance to compound nonionic and anionic surfactants to improve the air-void stability in concrete.

A Review and Analysis on Recent Advancements in Bubble Electrospinning Technology for Nanofiber Production.

Multiple applications of nanofiber in various segments of science and technology have sparked the interest of innovators to explore the innovative approaches for nanofiber production. The bubble electrospinning technique is the most versatile and simplest approach to scale up the production of nanofiber at the industrial level. Numerous patent applications have been filed with innovations and advancements in the field of bubble electrospinning technique. In present work, different patent applications in the field of bubble electrospinning technique, which represents the advancement in bubble electrospinning technology, are searched and analyzed using various paid and free patent databases. The patent search results are compiled, analyzed and individual innovations are studied in detail to bring all the advancements hitherto in the bubble electrospinning technology under the purview of one review article. The "bubble ws3 electrospin" syntax in the structured search (TAC) facility of the patseer® has revealed most relevant patents on advancement in bubble electrospinning. After applying the family patent filter to the search result (33 patents), ten patents are selected for detailed study. The gist of the invention from each of the patent application or granted patent is recapitulated in this paper, along with their mosaics. Definite number of inventions are available in the field of bubble electrospinning technique. Inventions, which are disclosed, might have their pros and cons with respect to ease of acceptance by the industrial fraternity for large-scale production depending upon simplicity or complexity of the instrument. There is a profound scope of innovation in the bubble electrospinning technology in the areas like bubble stabilization, size and production rate control and much more.

Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles

Skyrmion, a topologically-protected soliton, is known to emerge via electron spin in various magnetic materials. The magnetic skyrmion can be driven by low current density and has a potential to be stabilized in nanoscale, offering new directions of spintronics. However, there remain some fundamental issues in widely-studied ferromagnetic systems, which include a difficulty to realize stable ultrasmall skyrmions at room temperature, presence of the skyrmion Hall effect, and limitation of velocity owing to the topological charge. Here we show skyrmion bubbles in a synthetic antiferromagnetic coupled multilayer that are free from the above issues. Additive Dzyaloshinskii-Moriya interaction and spin-orbit torque (SOT) of the tailored stack allow stable skyrmion bubbles at room temperature, significantly smaller threshold current density or higher speed for motion, and negligible skyrmion Hall effect, with a potential to be scaled down to nanometer dimensions. The results offer a promising pathway toward nanoscale and energy-efficient skyrmion-based devices.

Practical application of nonaqueous foam in the preparation of a novel aerated reduced-fat sauce

This study aims to develop a new formulation of a sauce by incorporation of air in the oil phase. First, the effect of mono- and diglyceride (MDG) concentration (2, 6, and 10wt.%), whipping speed (1100, 3200, and 5400rpm) and time (up to 60min) on foam properties were studied. The desired foam (overrun≥60%) achieved by oil containing 10wt.% MDG at 3200rpm for 10min. Optical micrographs showed stable air bubbles (20–25μm) even after six months of storage. Then this foam was used to produce an aerated reduced-fat sauce. For purposes of comparison, aerated sauce, along with commercial full- and reduced-fat sauces, was analyzed by measuring the rheological properties, stability, and color. The power-law equation was used to model the behavioral features (R2=0.99). Compared with the full-fat sauce, the consistency coefficient (K) of aerated and reduced-fat sauces was more close to each other, and their flow behavior index (n) was higher. Overall samples showed shear-thinning thixotropic flow behavior. Also, aerated sauce showed acceptable stability and lightness (L*). These findings affirm the potential of nonaqueous foam for the production of reduced-fat sauces, which could be meet consumers’ and marketing requirements.