Bubble Stability Research Articles

Stability of ultra-fine bubbles against temperature, phase change, and shear stress

Most previous studies concerning applications of ultra-fine bubbles have focused on their use at room temperature, and thus there has been little research into their stability at high and low temperatures and during phase changes. Additionally, external forces such as shear are expected to have an effect during application, but very few studies have examined the effects of shear, mainly because particle size distributions have traditionally been measured under static conditions after the generation of ultra-fine bubbles. Therefore, in this study, we measured the particle size distribution of ultra-fine bubbles under more application-like conditions by subjecting a mixture of ultra-fine bubbles to shearing, temperature changes, boiling, freezing, and thawing. We found that stability was maintained at temperatures up to 50 °C, but stability was lost at 60 °C and during boiling. Relative stability was maintained with respect to freeze-thaw and shear. We conclude by comparing these results to a case involving ultrasound irradiation.

Microbubbles preparation by partial vaporization of low boiling condensate for crude oil/water separation

The poor adhesion of oil droplets and bubbles in the flotation process leads to inefficient separation of oil and water. In this paper, condensate bubbles were prepared by partial vaporization of low boiling point condensate to increase the oil removal effect. The purpose of partial vaporization was achieved by bringing emulsified condensate droplets into the produced water at different temperatures. The structure of the bubble is composed of condensate film wrapped around the gas core of the vaporized portion. The contact angle between condensate bubble and oil surface is >150°, which show great similarity-intermiscibility. The average bubble size prepared at 303 K - 318 K is 20 - 100 μm. The stability of bubbles decreased with an increase in temperature, the half-decay time decreased from 340 s to 110 s, and the zeta potential decreased from −31 mV to −12 mV. However, the gas hold-up of the bubbles first increased and then decreased with the increase in temperature, while the highest gas holdup was 21 % at 313 K. The rise of the condensate/water ratio (Rcon-wat) did not increase the stability of the bubbles, but the gas holdup increase. The condensate bubble flotation experiment found that at the optimum temperature 313 K, the oil removal efficiency of 1.5 % Rcon-wat can reach 85 %. In contrast, the oil removal efficiency of the dissolved air flotation experiment is <75 %. Otherwise, with a smaller amount of flocculant (ferric chloride), the oil removal efficiency of condensate bubble flotation can reach >95 %.

A microfluidic study of bubble formation and coalescence tuned by dynamic adsorption of SDS and proteins

During foaming, bubbles are formed at (sub)millisecond time scales, and emulsifier adsorption determines bubble formation and stabilisation against coalescence. Here we introduce a microfluidic device, in which bubbles are formed in two distinct pressure regimes at low versus high pressures, and emulsifier adsorption can be inferred from the easily-monitored dynamics of bubble formation and coalescence, as well as the bubble properties. We studied dynamic adsorption for various types and concentrations of emulsifiers, namely sodium dodecyl sulfate (SDS; 0.05–3% wt.) and various proteins (5% wt.) including whey protein isolate (WPI), β-lactoglobulin (β-lac), and bovine serum albumin (BSA). The results show that as SDS concentration increases up to 3% wt., the bubble formation time decreases in the low-pressure regime due to the enhanced adsorption of SDS, yet increases in the high-pressure regime due to the promoted ‘dripping-jetting’ transition; in both pressure regimes the neck thinning process slows down, leading to longer bubble growth time and thus larger bubble size. To suppress coalescence of bubbles formed at time scales down to 10 μs, SDS is the most efficient, followed by BSA, WPI, and finally, β-lac; this is ascribed to the dynamics of emulsifier adsorption, e.g., the resulting dynamic surface tension. To conclude, our microfluidic study highlights the dynamic effects in the presence of SDS and proteins during bubble formation, even at high concentrations. This means that to explain the properties of a freshly-formed foam product, it is crucial to understand (and thereafter manipulate) emulsifier adsorption at time scales relevant to bubble formation and coalescence.

Global stability analysis of bubbles rising in a vertical capillary with an external flow

We study the linear stability of bubbles in a capillary tube under external flow. Yu et al. (J. Fluid Mech., vol. 911, 2021, pp. 1–19) showed that a rich variety of bubble dynamics occurs when a downward external flow is applied, opposing the buoyancy-driven ascent of the bubble. They found experimentally and numerically the existence of two branches of solutions that overlap over a finite range of the capillary number of the downward external flow in cases where the Reynolds number is small and the Bond number is larger than the critical value for which the bubble can rise spontaneously (Bretherton, J. Fluid Mech., vol. 10, issue 2, 1961, pp. 166–188). Furthermore, inertialess, symmetry-breaking steady-state shapes were found as the bubble transits near the tipping points of the solution branches. In this work, using steady axisymmetric simulations, we show that the reported multiplicity of solutions can be described using bifurcation diagrams with three branches of steady axisymmetric solutions and two limit points. The linear global stability analysis of the different branches of the stationary axisymmetric solutions demonstrates that the symmetry breaking is due to the development of three-dimensional instabilities with azimuthal wavenumber $|m|=1$ .

The catalytic oxidation process of atrazine by ozone microbubbles: Bubble formation, ozone mass transfer and hydroxyl radical generation

Ozone microbubbles have received increasing attention since they can produce hydroxyl radical (•OH) to decompose ozone-resistant pollutants. Besides, compared with conventional bubbles, microbubbles have a larger specific surface area and higher mass transfer efficiency. However, the research on the micro-interface reaction mechanism of ozone microbubbles is still relatively scarce. Herein, we systematically studied the stability of microbubbles, ozone mass transfer and atrazine (ATZ) degradation through multifactor analysis. The results revealed that bubble size was dominant in the stability of microbubbles, and gas flow rate played a major role in ozone mass transfer and degradation effects. Besides, the bubble stability accounted for the different effects of pH on ozone mass transfer in two aeration systems. Finally, kinetic models were built and employed to simulate the kinetics of ATZ degradation by •OH. The results revealed that conventional bubbles could produce •OH faster compared with microbubbles under alkaline conditions. These findings shed light on the interfacial reaction mechanisms of ozone microbubbles.

Controlled Adsorption of Cellulose Nanofibrils on Fluid–Fluid Interfaces

AbstractAdsorption of particles at fluid–fluid interfaces is of great scientific and industrial importance, encompassing a variety of applications, from the stabilization of bubbles and emulsions to the fabrication of sophisticated materials with micro‐ and nanostructures. The enormous adsorption energy of a particle is believed to be the origin of adsorption, but it cannot fully explain many systems that do not adsorb, even with large adsorption energy. Here, it is systematically shown that the dynamic process of particle adsorption plays a critical role in determining whether particles are adsorbed at interfaces. Using a model system composed of a droplet and solid particle monolayer, the adsorption dynamics of cellulose nanofibrils are studied, focusing on the drainage time of a liquid thin film between the droplet and solid surface. Both the experimental and theoretical results indicate that the drainage time is regulated by the dimensionless capillary number. Controllable particle adsorption in conventional emulsions is further examined, confirming that results from this model system can be extended to large capillary numbers. This study provides important insight that it is not the adsorption energy, but the drainage process that governs particle adsorption, which can be quantitatively controlled by viscosity, interfacial tension, and particle approaching velocity.

How nano-bubble water and nano-silica affect the air-voids characteristics and freeze-thaw resistance of air-entrained cementitious materials at low atmospheric pressure?

With more infrastructures being built in plateau regions, low atmospheric pressure is put forward as a new factor affecting the mechanical properties and durability of cementitious materials, but its influence is inconclusive, and the failure of freeze-thaw has not been effectively solved. This research explored the influences of both nano-bubble water (NBW) and nano-silica (NS) on air-voids characteristics and freeze-thaw resistance of cementitious materials formed and cured at different air pressure (0.4P, 0.7P, P; P=1atm); and investigated the effects and its mechanisms of low air pressure on performances of cementitious materials. The air-voids structure analyser, SEM, XRD and TG-DSC were employed to evaluate the microstructure and cement hydration of hardened cement paste samples. Results show that low-pressure samples have abnormal air-void parameters and poor bubble stability, which lead to a decrease in freeze-thaw resistance. It is proved that both NBW and NS can improve the freeze-thaw resistance and mechanical strength of samples at low atmospheric pressure by accelerating cement hydration, enhancing bubble stability, and optimizing air-voids parameters. The mechanisms of low pressure, NBW and NS on properties of cementitious materials are expounded. This research proposes new perspectives for improving the durability of air-entrained cementitious materials in plateau and enables us to further comprehend the effects and principles of low air pressure on performances of cementitious materials.

DISJOINING PRESSURE IN THIN SPHERICAL LIQUID FILMS AND VAPOR LAYERS WITH MOLECULAR CORRELATIONS INCLUDED

Based on the expression for a grand thermodynamic potential as a molecular density functional, disjoining pressures in thin liquid films around nanosized wettable spherical particles and in thin vapor layers around nonwettable particles are calculated depending the degree of lyophilicity, film thickness and particle size. A characteristic feature of the approach is the full consideration of hard-sphere molecular correlations according to the fundamental measure theory in the density functional method and finding the complete dependence of the grand thermodynamic potential of the system on stable droplet or bubble size. Although the obtained results show a qualitative agreement between the new calculated disjoining pressure dependences and those obtained by us earlier in the framework of a simpler gradient method of the molecular density functional, the new results differ significantly quantitatively. It is confirmed that the disjoining pressure in the liquid film around nanosized lyophilic particle grows with the particle radius and lyophilicity.

Aqueous Bubbles Stabilized with Millimeter-Sized Polymer Plates.

(Sub)millimeter-sized hexagonal polymer plates that were monodisperse in shape and size were utilized as stabilizers for aqueous bubbles, and the effects of the hydrophilic-hydrophobic property, size, and solid concentration of the plates on the formability, stability, and shape and structure of aqueous bubbles were investigated. The formability and stability of the bubbles were improved by increasing the hydrophobicity of the plate surface, decreasing the plate size, and increasing the solid concentration of the plates. For plates with suitable water wettability, three-dimensional bubbles with nearly spherical and polyhedral shapes were formed by the adsorption of plates to the bare air bubbles introduced into the continuous water phase by air-water mixing. On the contrary, two-dimensional bubbles with accordion-type structures consisting of alternating layers of plates and entrapped air bubbles were formed by the transfer of multiple plates with poor wettability from the air phase to the water phase by air-water mixing. Furthermore, a correlation was found between the bubble/stabilizer size ratio and bubble shape for plates with the suitable wettability: bubbles with nearly spherical shapes were formed when the bubble/plate size ratios were >2, bubbles with hexahedral, pentahedral, and tetrahedral shapes were formed when the size ratios were approximately 1, and bubbles with triangular and sandwich shapes were formed when the size ratios were <0.8. Additionally, bubbles with similar shapes were formed when the bubble/plate size ratios were close, even when the sizes of the plates and bubbles were different.

The study of functional and technological properties of vegetarian ice cream

The use perspective and expediency of plant-based milk, enriched with fiber when combined with organic products, biobased products, and sugar substitute products, has been substantiated in the manufacturing process of vegetarian ice cream. When combined with pumpkin fiber, stevia, bananas, pistachios, coconut oil, and coffee beans with different functional and technological properties, rice milk has a purposeful influence on organoleptic and Physico-chemical properties of food products. Accordingly, the expediency of added rice milk (62%) has been determined to optimize vegetarian ice cream's vitamin and mineral composition. The optimal component ratio has been determined employing experimental studies and multi-criteria optimization: for ice cream "Banana &amp; Pistachio": rice milk – 62%, pumpkin fiber – 2.5%, – 0.5%, banana – 16%, pistachio – 6.8%, coconut oil – 12.2%; “Coffee and chocolate”: rice milk – 62%, pumpkin fiber – 4.8%, stevia – 4%, cocoa powder – 7%, coffee beans – 8%, coconut oil – 14.2%, It has been found that the main physicochemical parameters of the vegetarian ice cream depend on the chemical composition of the ice cream mixture and its freezing conditions. Thus, when the fat content increases, the stability of air bubbles increases, but their sizes decrease. The study results make it clear that the increase in the fat amount is good for the ice cream structure and consistency, while the distance between the fat balls decreases, which, in turn, helps to obtain the product with the smaller ice crystals.

Growth and stability of bubbles in a yield stress fluid

Experiments are reported that explore the onset of motion of bubbles in a model yield stress fluid, Carbopol gel. Starting from a trapped spherical bubble in a gel, the yielding limit for the bubble motion is obtained by gradually expanding the bubble via a stepwise decrease in pressure. Our results show that at the yielding limit bubbles are longer and thinner when they are in a higher concentrated gel. This is suggestive of a link between the shape and size of the bubbles at the onset of motion and the rheology of the material, in particular elastic behaviour below the yielding point. Particular attention has been paid to investigating the dynamic response of gel during the bubble growth. Subjecting the bubble to a periodic change in the pressure confirms the irreversibility of the gel deformation and its hysteresis, which are hallmarks of nonlinear viscoelastic behaviour of the gel before yielding. In this context, the periodic expansion and contraction of the bubbles leave residual deformation (stresses) in the gel which facilitates the liberation of bubbles.

Breakup and coalescence mechanism of high-stability bubbles reinforced by dispersed particle gel particles in the pore-throat micromodel

Bubble breaks up and coalesces continuously during migration in reservoirs, which determines the size distribution of bubbles. As a key parameter of foam technology, the bubble size greatly affects foam stability and plugging performance in the reservoir. Aiming to solve the problem of poor stability of ordinary foam under reservoir conditions, in this study, a high-stability foam for profile control was prepared using dispersed particle gel particles as a foam stabilizer. The characteristics of foam were mainly investigated by the modified Ross-Miles method and microfluidic experiments. The obtained results showed that the foam reinforced by dispersed particle gel particles had a longer half-life under reservoir conditions. It is easier to break up from parent bubbles to daughter bubbles during the migration, which can form foam with higher stability in the porous media. The average size of the daughter bubbles decreased with increasing liquid-phase flow rate, pore-throat ratio and capillary number. The average size varied with the capillary number in a power-law form. Because of the viscoelastic interfacial film and liquid-phase viscous network, the shear effect on the parent bubble in reinforced foam was increased when passing through the pore-throat structure with variable diameter. The large parent bubbles were more likely to break up into more small and stable daughter bubbles. And the interfacial film with higher mechanical strength makes it difficult for the daughter bubbles in reinforced foam to coalesce again. The results indicated that the reinforced foam had stronger dynamic stability and better plugging performance in the reservoir. This work revealed the breakup and coalescence mechanism of bubbles reinforced by dispersed particle gel particles in porous media and provided theoretical guidance for the application of foam technology in high water-cut reservoirs.

Blown film stability for low, medium, and high molecular weight polylactic acid and their tensile properties

Three poly (lactic acid) (PLA) resins with molecular weight (Mw) equal to 55 (3251D), 125 (L105) and 163 (LX175) kg/mol were characterized in terms of capillary viscosity, mechanical and thermal properties and used to produce blown films. The effect of temperature, extrusion rate, stretching (TUR) and blow-up (BUR) ratios were evaluated to determine the optimum processing conditions for blown films based on the bubble stability and to determine their final tensile properties. As expected, the processing temperature was the most critical parameter on the film stability. The lower Mw PLA showed limited processing stability. Stable conditions were found at higher temperature (200°C) for higher Mw. These results correlate with the PLA viscosity (melt strength). Finally, the PLA film tensile strength (TS) strongly depended on their processability. For example, 3251D and L105 required high stretching (TUR = 3.4 and 7) for maximum TS (30 and 64 MPa) with a low blow-up ratio (BUR = 1.02–1.15). However, a moderate increase in BUR (10% at TUR = 3) led to a substantial drop in TS (from 29 MPa to 21 MPa for PLA 3251D and 44 MPa–34 MPa for L105). Overall, LX175 was the most interesting resin with 49 MPa TS which was independent of the BUR and TUR used in this investigation.

Experimental Investigation of Cavitation Bulk Nanobubbles Characteristics: Effects of pH and Surface-Active Agents

Nanobubbles (NBs) have a widespread application in antimicrobial activity, wastewater treatment, and ecological restoration due to numerous peculiar characteristics, such as small diameter, long-term stability, and ability to produce hydroxyl radicals. Despite significant applications, only limited comprehensive investigations are available on the role of surfactants and pH in NBs characteristics. Therefore, this study examines the effects of different surfactants (i.e., anionic, cationic, and nonionic) and pH medium on bulk NB formation, diameter, concentration, bubble size distribution (BSD), ζ-potential, and stability. The effect of surfactant at concentrations above and below the critical micelle concentration was investigated. NBs were generated in deionized (DI) water using a piezoelectric transducer. The stability of NBs was assessed by tracking the variation in diameter and concentration over time. In a neutral medium, the diameter of NBs is smaller than in other surfactant or pH mediums. The diameter, concentration, BSD, and stability of NBs are strongly influenced by the ζ-potential rather than the solution medium. BSD curve shifts to a smaller bubble diameter when the magnitude of ζ-potential is high in any solution. In pure water, surfactant, and pH mediums, NBs have existed for a long time. NBs have a shorter life span in environments with a pH ≤ 3. Surfactant adsorption on the surface of NBs increases with increasing surfactant concentration up to a certain limit, beyond which it declines substantially. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to interpret the NBs stability, resulting in a total potential energy barrier that is positive and greater than 45.55 kBT for 6 ≤ pH ≤ 11, whereas for pH < 6, the potential energy barrier essentially vanishes. Moreover, an effort has also been made to explicate the plausible prospect of ion distribution and its alignment surrounding NBs in cationic and anionic surfactants. This study will extend the in-depth investigation of NBs for industrial applications involving NBs.

Amide group enhanced self‐assembly and adsorption of thioether‐containing hydroxamic acid on cassiterite surface

AbstractModified surfactants can regulate their adsorption at the target surface and are essential for various separation applications such as froth flotation. Thioether‐containing hydroxamic acid (BTHA) is an excellent oxidized‐ore collector with poor dispersibility. Herein, acylamino, which possesses the ability to improve the surfactants' self‐assembly and dispersion, was introduced to synthesize N‐[6‐(hydroxyamino)‐6‐oxohexyl] benzylthioacetamide (BTAHA); thus, applying it to cassiterite flotation. Surface tension, adsorption capacity, in situ AFM, and surface energy results reveal BTAHA displays strong bubble stability and readily adsorbs onto the mineral's surface, promoting hydrophobic flotation. BTAHA is an effective cassiterite collector and has good separation effects on cassiterite against calcite. It can form Van der Waals forces and five‐membered hydroxamate‐(O,O)‐Sn rings with Sn atoms on cassiterite surfaces via thioether and hydroxamate groups. Meanwhile, the presence of intermolecular hydrogen bond between the amide groups facilitates the self‐assembly of the collectors on the cassiterite surface, and has broad industrial application prospects in various separation processes.

Machining Characteristics of Diamond Grit-Coated Tools in Grinding-Aided ECDM

ABSTRACT This study investigated the machining characteristics of two shapes of diamond grit – coated tools used in grinding-aided electrochemical discharge machining for optical glass drilling. The effects of roundness, machining accuracy, surface roughness, and tool wear under various machining depths and electrode rotating speeds were explored, and the bubble generation mechanism and its effects on the discharge current waveform and electrochemical discharge reaction were observed. This study revealed that the bubbles generated in the gaps between diamond particles combine with each other to form a stable bubble film. Owing to differences in bubble generation mechanisms, the discharging waveform of the diamond grit – coated tool was more stable than that of tools without diamond grit – coated. It is known from the experimental results that the diamond grit – coated ball end mill in this method minimized shape roundness errors, machining time and the fracture of the exit edge.

He bubble growth in nickel simulated by object kinetic Monte Carlo

When Ni-based alloys are exposed to neutron irradiation, (n,α) transmutation introduces helium to the metal, leading to the formation of bubbles, which can severely affect the properties of the material. Identifying the key parameters controlling bubble growth can help us design materials with improved radiation tolerance. In this study, we parameterized an object kinetic Monte Carlo (OkMC) framework able to simulate the coalescence and growth of helium bubbles in pure Ni during and after helium ion implantation. The simulated bubbles size is consistent with phenomenological models based on past experimental studies. Our simulations indicate that the mean He bubble size is strongly correlated with temperature and inversely correlated with the implantation dose rate. The interactions between irradiation-induced defects and interfaces (sinks) are shown to play a key role in determining the size and stability of bubbles. Furthermore, our simulations suggest that the controlling reaction in swelling is the annihilation of self-interstitial defects at sinks, not the presence of He.

Atomistic simulations of He bubbles in Beryllium

Formation of He bubbles can have a significant effect on the microstructural evolution and properties of irradiated materials. Here, we use atomistic simulations based on machine learning potentials to investigate the fundamental behavior of He bubbles in Be, with a specific focus on the shape, stability, and diffusivity of bubbles. Stability of He bubbles is quantified in terms of formation energies, which are determined as a function of the ratio of He/V. We find that He bubbles become unstable with respect to plastic deformation through punch-out dislocations around the bubble when the He/V ratio is larger than ∼1.25, and the punch-out process induces the change of the regular bubble shape. In general, the bubble shape of He in Be is found to be ellipsoid-like. It is also found that for a fixed He/V ratio, the bubble attracts vacancies to become larger in size. If the bubble size is constant, the bubble attracts additional He atoms until the punch-out reaction occurs. The dominant diffusion mechanism of He bubbles changes from surface diffusion to volume diffusion as the temperature is increased, with a crossover occurring at about 900 K.

Investigation on physical properties of nanobubbled water using gas water circulation method: Environmental perspective

AbstractThe objective of this present study is to examine the effect of nanobubbles on the physical properties improvement in the chosen water sample. So far, the research outcomes stated that the physical properties could be enhanced by addition of nanoparticles, but very few studies were performed with nanobubbles. The unique properties of nanobubbles (70–120 nanometers) explain their use in a wide range of engineering fields. Simple method for producing nanobubbles in a variety of aqueous solutions along with examples of their use is outlined in this work. Global environmental issues, including the deterioration and depletion of water supply are driving today's need for water treatment technology. As a solution, the use of micro‐ and nano‐bubble (MNB) technologies in wastewater treatment has evolved. This page discuss the fundamentals of water treatment research, including their stability of bubbles, manufacturing processes, and chemical and physical features.

Fluid flow and heat transfer in microchannel devices for cooling applications: Experimental and numerical approaches

• Two phase flow in microchannels is characterized by numerical and experimental approaches. • Transition from bubbly flow to slug plug flow is numerically predicted but transition from bubbly flow to churn flow is not. • The proposed numerical tool is sensitive enough to capture particular effects of the studied parameters. Microchannel heat sinks are pointed to have a great potential in cooling systems. This paper presents a systematic study to develop a microchannel heat sink to be used in cooling applications. Particular emphasis is given to PV panels cooling. A systematic experimental approach is used to optimize the heat sink geometry. Then the potential advantage of using flow boiling conditions is explored in both numerical and experimental approaches. The two-phase flow is characterized in two different sets of conditions. In the experimental approach, a constrained bubble flow was observed with a stable pattern and bubble frequency in the narrower channel. In the wider channel a bubbly flow was observed with increased bubble diameters. Numerical simulations were also performed in order to examine the first transient stages of the two-phase flow development close to the inlet of the considered microchannels assuming an initial arbitrary distribution of nucleation sites. For this purpose, a previously developed and validated numerical simulation framework was utilised. The proposed customized tool has been developed in the general context of OpenFOAM CFD Toolbox and it accounts for phase-change (boiling/condensation) as well as for Conjugate Heat Transfer between solid and two-phase flow domains. The numerical predictions reveal that the proposed tool is sensitive enough to capture the effects of channel aspect ratio, applied heat flux and applied mass flux on the generated transient bubble dynamics and the associated heat transfer characteristics and it can constitute an important tool for quantifying the underpinned complex physical mechanisms, providing further insight into the experimental observations and measurements.