Bubble Stability Research Articles

On the scalability of helium-filled soap bubbles for volumetric PIV

The scalability of experiments using PIV relies upon several parameters, namely illumination power, camera sensor and primarily the tracers light scattering capability. Given their larger cross section, helium-filled soap bubbles (HFSB) allow measurements in air flows over a significantly large domain compared to traditional oil or fog droplets. Controlling their diameter translates into scalability of the experiment. This work presents a technique to extend the control of HFSB diameter by geometrical variations of the generator. The latter expands the more limited range allowed by varying the relative helium-air mass flow rates. A theoretical model predicts the bubble size and production rate, which is verified experimentally by high-speed shadow visualization. The overall range of HFSB produced in a stable (bubbling) regime varies from 0.16 to 2.7 mm. Imaging by light scattering of such tracers is also investigated, in view of controversies in the literature on whether diffraction or geometrical imaging dominate the imaging regime. The light scattered by scaled HFSB tracers is imaged with a high-speed camera orthogonal to the illumination. Both the total energy collected on the sensor for a single tracer, as well as its peak intensity, are found to preserve scaling with the square of the diameter at object magnification of 10–1 or below, typical of PIV experiments. For large-scale volumetric applications, it is shown that varying the bubble diameter allows increasing both the measurement domain as well as the working distance of the imagers at 10 m and beyond. A scaling rule is proposed for the latter.Graphical abstract

Reclamation of iron and copper from BCL slag in Botswana

High-grade copper ores have been depleted over the years, making it a challenge in the mining industry. This investigation focused on a methodology to recover iron (Fe) and copper (Cu) from a copper/nickel slag obtained from the Bamangwato Concession Limited (BCL) mine in Botswana. In this modified flotation approach, the Response Surface Methodology (RSM) was used in conjunction with the Central Composite Design (CCD) and Analysis of Variance (ANOVA) to obtain the best optimal flotation conditions for the recovery of iron and copper. Using the RSM – CCD methodology, the optimal predicted responses were illustrated by a coefficient of determination R2 = 0. 9839 for recovery for Fe and 0.9655 for recovery for Cu. The recovery of copper increased with the increasing dosage of Na2S and collector dosage, while the increase of pH, had a decrease in recovery of copper due to the decline in the stability of the froth, which led to the resistance to form stable bubbles for efficient recovery of copper. Selective flotation of copper and iron was achieved by varying the Na2S dosage to achieve maximum recovery. Under these flotation conditions of PAX (800 g/t), pH (8), −75 μm, sulfurizing agent (Na2S, 1000 g/t), flotation time of 8 min, pH regulator of NaOH and H2SO4 and Methyl Isobutyl Carbinol (MIBC) from the experimental runs merited a grade upgrade of Cu in froth concentrate from 0.581 mass% to 0.884 mass%. An enrichment ratio of 2 was realised, with the recovery of Cu being 62%, whereas Fe in the froth concentrate increased from 69.8 mass% to 71.8 mass%. The main aim was to upgrade the grade and recovery of copper and iron to enhance the recovery for copper and iron in the next experimental stage of leaching.

Raman Shifts in Two-Dimensional van der Waals Magnets Reveal Magnetic Texture Evolution.

Two-dimensional (2D) van der Waals magnets comprise rich physics that can be exploited for spintronic applications. We investigate the interplay between spin-phonon coupling and spin textures in a 2D van der Waals magnet by combining magneto-Raman spectroscopy with cryogenic Lorentz transmission electron microscopy. We find that when stable skyrmion bubbles are formed in the 2D magnet, a field-dependent Raman shift can be observed, and this shift is absent for the 2D magnet prepared in its ferromagnetic state. Correlating these observations with numerical simulations that take into account field-dependent magnetic textures and spin--phonon coupling in the 2D magnet, we associate the Raman shift to field-induced modulations of the skyrmion bubbles and derive the existence of inhomogeneity in the skyrmion textures over the film thickness.

Differences in ultrasonic cavitation damage between new and used engine coolants with varying time in operation

This study investigates the cavitation erosion performance of heavy-duty engine coolants before and after operation in trucks using an ultrasonic test rig based on ASTM G32. Fresh coolants with 35% and 50% v/v glycol were compared with used coolants. One coolant was obtained from a gasoline-fueled vehicle with a mileage of 27000 km, and two from diesel-fueled vehicles with mileages of 16000 and 180 000 km, respectively. Surface tension and boiling point at atmospheric pressure were measured, a chemical analysis was carried out, and suspended particles were quantified by dynamic image analysis. The results showed that the used coolants caused a lower mass loss in ultrasonic cavitation testing than the fresh ones, and that they had higher boiling points, lower pH and a higher number of suspended particles, especially of those smaller than 30μm. Surface tension was higher for the used coolants from Diesel engines.The lower mass loss caused by all three used coolants can be attributed mainly to their high boiling point and high particle count. The presence of particles is believed to promote the heterogeneous nucleation of smaller, more stable bubbles, which may protect the exposed surface by shockwave absorption and microjet deflection. Some dissolved ions in the used coolants may help reduce their aggressivity by inhibiting bubble coalescence, reducing bubble collapse energy, despite increasing surface tension. Surface tension has complex interactions with the solutes, particles and bubble formation and cannot, in isolation, explain the differences in performance of the coolants.

Generation, control, and application of stable bubbles in a hypersonic acoustic system.

Bubble-based microfluidics has been applied in many fields. However, there remains a need for a facile and flexible method for stable bubble generation and control in a microchannel. This paper reports a hypersonic acoustic system that can generate and release functional stable bubbles in a microchannel in an on-demand manner. It was found that the hypersonic frequency in this system played a vital role in the generation and control of bubbles. Specifically, a nanostructurally enhanced acoustic resonator was used to generate highly localized ultrahigh-frequency acoustic waves that ensured the feasibility and rapidity of bubble generation. Simultaneously, the acoustothermal effect of hypersound was harnessed to effectuate precise control over the bubble size. In addition, high-throughput droplet splitting was performed to confirm the stability of bubbles and their functionality in micromanipulation. The results showed that a mother droplet could be split controllably into a desired number of daughter droplets with specific volume ratios. In summary, the hypersonic acoustic system was demonstrated to be capable of on-demand-generation of stable bubbles in a microfluidic context and thus may extend the bubble-based applications.

Exploring h-BN as a hydrogen conductor and depository.

The use of hexagonal boron nitride (h-BN) as a material for hydrogen storage is attributed to its ability to accommodate atomic and molecular hydrogen. However, the low diffusion barrier of molecular hydrogen within the h-BN structure does not fully explain the long-term stability of hydrogen bubbles observed in experimental work [L. He, H. Wang, L. Chen, X. Wang, H. Xie, C. Jiang, C. Li, K. Elibol, J. Meyer, K. Watanabe, T. Taniguchi, Z. Wu, W. Wang, Z. Ni, X. Miao, C. Zhang, D. Zhang, H. Wang and X. Xie, Nat. Commun., 2019, 10, 2815, https://doi.org/10.1038/s41467-019-10660-9]. Another unresolved inquiry is the method by which hydrogen infiltrates the h-BN layer in a perpendicular direction. In this study, we conducted a comprehensive examination of several aspects that can impact the permeation of hydrogen in the h-BN structure. We employed DFT within the rPBE (DFT-D3(0)) functional to suggest a process for the penetration of atomic hydrogen through the h-BN sheet along the normal direction by sequential hydrogen passivation.

The role of cavitation and gas bubbles in the non-photochemical laser-induced nucleation of sodium acetate

Laser pulse nucleates anhydrous sodium acetate and stable gas bubbles from solution.

New insights into suspended drops: When soft matter meets acoustic levitation

AbstractAcoustic levitation has developed into a popular but elegant tool for the study of drops as well as soft matter due to its exceptional levitation capabilities to a variety of liquid samples. The acoustically levitated drops offer opportunities for the investigation of a wide range of fundamental issues related to liquid drops. In this review, the unique physics/chemical processes involved in acoustically levitated drops are dealt with. We first introduce the dynamics of the acoustically levitated drops, including drop oscillation, coalescence, and the associated capillary phenomena. The bubble formation and stability are also discussed. Depending on the inhibition of solid surfaces and the nonlinear effects of ultrasound, the self‐assembly of colloidal particles at the air–liquid interface as well as granular matter in air is reviewed. In particular, the exploration of biological drops by using acoustic levitation is also highlighted. In the end, the concept of acoustic‐levitation‐fluidics and possible potential topics are proposed.

A model of coupled oscillation of bubble cluster in liquid cavity wrapped by viscoelastic medium

Considering the interactions between bubbles in a multi-bubble system in a liquid micro-cavity, a spherical bubble cluster in a liquid cavity is modeled in order to describe the dynamical effect of the viscoelastic medium outside the liquid cavity on the oscillation of bubbles, and the coupled equations of bubbles are obtained. Subsequently, the acoustic response characteristics of bubbles are investigated by analyzing the radial oscillation, the stability of the non-spherical shape of bubbles and the threshold of inertial cavitation. The results show that the confinement of the cavity and the bubble cluster facilitates the suppression of bubble oscillation, however, it might enhance the nonlinear properties of bubbles to a certain extent. From the acoustic response curve at 1 MHz, it is found that the main resonance peaks shift leftward with the increase of the bubble number, which means a minor resonant radius can be obtained. The nonlinear stability of bubbles in a confined environment is mainly determined by acoustic pressure amplitude and frequency, the initial bubble radius, and bubble number density, while the effect of the cavity radius is enhanced with the increase of the driving pressure. There is a minimum unstable driving acoustic pressure threshold, depending on the initial bubble radius, and the unstable regions are mainly located in a range of less than 4 μm. With the increase in bubble number density, the strip-type stable region scattered of the unstable region in the map is gradually transformed into a random patch-like distribution, which indicates that the bubble oscillation under high acoustic pressure is more sensitive to the parameters, and it is very susceptible to interference, produces unstable oscillation and then collapses. When the bubble equilibrium radius is in a range greater than 4 μm, the influences of frequency and bubble number density on the inertial thresholds are particularly significant.

Structural stability analysis of spherical bubble clusters in acoustic cavitation fields

The upwelling growth and evolution of spherical bubble clusters appearing at one-quarter wavelength from the water surface in ultrasonic cavitation fields at frequencies of 28 kHz and 40 kHz are studied by high-speed photography. Due to the interactions among bubbles, the stable bubble aggregation occurs throughout the rise of the bubble cluster, whose vertical pressure difference leads to a more significant spreading in the upper part of the cluster in the standing-wave field. At 28 kHz, the rising speed is about 0.6 m/s, controlled by the primary acoustic field. After a violent collapse of the bubble clusters, the aggregating structure begins to hover near the water surface. The size and stability of the structure are affected by the frequency and pressure of the primary acoustic field. If two clusters are close to each other, the clusters deviate from the spherical shape, even trailing off, and eventually merge into a single bubble cluster. By considering the influence of water-air boundary, based on the mirror principle, a spherical bubble cluster model is developed to explore the structure stability of the clusters, and the modified dynamics equations are obtained. The effects of driving acoustic pressure amplitude, bubble number density, water depth, and bubble equilibrium radius on the optimal stable radius of the spherical bubble cluster are numerically analyzed by using the equivalent potentials at 28 kHz and 40 kHz. The results show that the optimal stabilizing radius of spherical bubble cluster is in a range of 1–2 mm, and it tends to decrease slightly with the increase of the driving acoustic pressure and bubble number density. It is worth noting that the nonlinearity is enhanced by increasing acoustic pressure, which may promote the stability of the cluster structure. The smaller the unstable equilibrium radius, the easier it is to grow, and the stable size at 40 kHz is slightly smaller than that at 28 kHz. Generally, spherical clusters first appear in a high-pressure region and then move to a low-pressure region. If the acoustic pressure drops below a certain critical value, bubble clusters disappear. The theoretical analysis is in good agreement with the experimental observation. The analysis of the growth and structural stability of spherical bubble cluster is helpful in understanding the behavioral modulation of bubbles.

Investigation on the impact of low atmospheric pressure on bubble stability in cement-based materials

Investigation on the impact of low atmospheric pressure on bubble stability in cement-based materials

Rational fabrication of count film for coliform hypersensitive enumeration based on enzyme-response compound color rendering

A sensitive and portable count film based on dedicated enzyme response combined with a composite chromogenic agent was fabricated for coliform enumeration. Cold-water gel was conjugated with 5-bromo-4-chloro-3-indolyl-β-d-galactoside, crystalline violet, neutral red, and lactose to prepare a composite chromogenic agent. The involvement of MgCl2 and isopropyl-β-D-thiogalactoside appreciably boosted the analytical performance. Compounding with Tween-80 and porous starch, stable bubbles provided corroborative evidence for positive colonies without any further validation. The proposed count film exhibited prominent enumeration performances within the linear range of the relationship varied from 3 CFU/mL to 150 CFU/mL, with an LOD of 3 CFU/mL. The as-obtained coefficient of variation was less than 5%, and recovery rates ranged from 101.30% to 104.47%. In light of its favorable sensitivity and satisfactory feasibility, this reliable analytical pattern provided a novel potential orientation for the evaluation of microorganisms in food-safety detection.

Rising of asymmetric bubble through milli-tubes: Experimental, theoretical and numerical analysis

Appearance of Taylor bubble is ubiquitous in two-phase fluid flow through millimeter-sized tubes. Precise control over bubble generation and stability in those tubes are instrumental in unit processes in fine chemical industries. In this article, we systematically study the role of wall surface wettability in the structure and dynamics of the gaseous bubble flowing through water across milli-tubes. Specifically, from imaging experiments, we find that in a non-wettable milli-tube, the bubble loses its axial symmetry to reduce contact of the liquid phase with the tube wall. Moreover, we observe that the bubble speed is significantly higher in hydrophobic-coated tubes in comparison to the tubes without coating. Computational simulation balancing the viscous, gravitational, and surface forces recovers the observed effect of surface wettability on bubble shape and velocity. Finally, we establish the observed quantitative correlation between the bubble velocity and the surface wettability using an analytical model. Altogether, integrating experiments, numerical simulation, and theoretical analysis, we demonstrated the significant influence of wall-surface wettability in the shape and velocity of the Taylor bubble through milli-tubes.

Application of Ultra Fine Bubbles for Deoxygenation of Produced Water and Tap Water via Nitrogen Purging Scheme

In this study, we present our findings from examining a gas lift tower for produced and tap water de-oxygenation, applying the nitrogen purging at an ultra-fine bubble scale (18 μm average size). The experiments were conducted for produced water samples grafted with polyacrylamide concentration 300 ppm with a measured bulk viscosity of 5 mPa.s. Upon applying a series of experimental sets, 0 ppm DO was attained in all examined operational schemes (semi batch and once through) within various time limits, depending on the water level in the column. Considering the zero DO level as an objective function, the results showed an improvement of 5.7–14 folds in reaching the 0 ppm DO upon experimenting with the ultra-fine bubble purging in different schemes, compared with of the results obtained from the ordinary bubble size (mm scale). The results show that DO reached < 10 ppb within 23 minutes with nitrogen flowrate 3 L/min while DO reaching < 10 ppb within 28 minutes with nitrogen flowrate 5 L/min. Furthermore, implementing the ultra-fine bubble nitrogen purging was successful in running the de-oxygenation tower in a full continuous mode at a balanced inlet/outlet water flow rate. This has been done after reaching stability in the column operation (lasting around 1 hour for 422 L of examined water sample). The stable fine bubbles cloud in the column was quite efficient in treating water influent stream to be exited directly at 0 ppm DO within the same effluent flow rate. The treatment efficiency has shown an increase with increasing water level in the column, resulting in a denser layer/cloud of fine bubbles. This result suggests a unique approach/solution for the complete removal of DO from produced water, which is accounted effective to be adopted industrially

Cold plasma within a stable supercavitation bubble – A breakthrough technology for efficient inactivation of viruses in water

Water scarcity, one of the most pressing challenges we face today, has developed for many reasons, including the increasing number of waterborne pollutants that affect the safety of the water environment. Waterborne human, animal and plant viruses represent huge health, environmental, and financial burden and thus it is important to efficiently inactivate them. Therefore, the main objective of this study was to construct a unique device combining plasma with supercavitation and to evaluate its efficiency for water decontamination with the emphasis on inactivation of viruses. High inactivation (>5 log10 PFU/mL) of bacteriophage MS2, a human enteric virus surrogate, was achieved after treatment of 0.43 L of recirculating water for up to 4 min. The key factors in the inactivation were short-lived reactive plasma species that damaged viral RNA. Water treated with plasma for a short time required for successful virus inactivation did not cause cytotoxic effects in the in vitro HepG2 cell model system or adverse effects on potato plant physiology. Therefore, the combined plasma-supercavitation device represents an environmentally-friendly technology that could provide contamination-free and safe water.

Enhancing control of air bubbles in water flows through laser-based surface wettability patterning

Air bubble injection has been a widely studied method for reducing frictional drag in fluid flows, especially in the marine industry. However, the lack of control over air bubble stability, size, and shape has hindered its widespread adoption. This study investigates the use of laser-based surface wettability modification techniques to address these challenges by enhancing control over air bubble behavior in water flows. We processed metal plates using nanosecond laser and chemical immersion to create wettability patterns consisting of regions of either superhydrophobicity or superhydrophilicity. Water tunnel experiments were conducted to observe the behavior of air bubbles over these different wettability patterns. The results revealed that surface wettability can be used to control the size and spatial distribution of air bubbles, which can enhance the energy cost-benefit of drag reduction methods in the marine industry. Moreover, this research offers new insights into the potential of laser-based surface wettability modification as a solution for improving the control of air bubble behavior in large-scale applications.

Preparation of cellular SiBOC foams by thermo‐foaming of polymethylvinylborosiloxane–wheat flour dough

AbstractA novel method for the preparation of SiBOC foams from a polymethylvinylborosiloxane (MVBS) solution in ethanol using wheat flour as a foam stabilizer and pore template has been reported. A dough prepared by mixing the MVBS solution and wheat flour undergoes foaming at 180°C due to the stabilization of bubbles created by ethanol vapor by the adsorption of wheat flour particles on their surface. The ceramization of the foamed body at 1500°C followed by burnout of carbon produced from the wheat flour results in SiBOC foams of hierarchical pore structure. The foam density (.68–.44 g cm−3), average cell size (1.81–.58 mm), compressive strength (3.9–1.7 MPa), and thermal conductivity (.33–.21 W m−1 K−1) decrease with an increase in wheat flour to MVBS weight ratio from .25 to 1. The population of smaller pores (∼5–50 μm) created by wheat flour particles on cell walls and struts increases with an increase in wheat flour to MVBS weight ratio. The presence of β‐SiC and turbostratic graphite nanodomains in amorphous SiBOC is evidenced by X‐ray diffraction and transmission electron microscopy analysis.

Stability and dynamics of bubble comprising carbon dioxide and air

The stability and dynamics of a single partial-equilibrium bubble comprising carbon dioxide (CO2) gas and air were theoretically investigated. The partial equilibrium bubbles, which are typically generated by bubbling in CO2 aqueous solutions initiated by pre-existing fine air bubbles, were assumed to be in equilibrium with the surrounding liquids with respect to the pressure and chemical potential of CO2 but not with respect to the chemical potential of air. The stability of the bubble was formulated using thermodynamic inequalities and two types of potential energy that became minimum and maximum at stable and unstable bubble radii, respectively. The dynamics of the bubble were studied by numerically solving the time evolution equation for the bubble radius. In addition, the stability and dynamics of a single complete-equilibrium bubble comprising CO2 gas and air are discussed.

Surface tension of cementitious pore solutions at low atmospheric pressure: An experimental exploration

Currently, it is believed that surface tension increases with the reduction of atmospheric pressure, and the increased surface tension is considered as the primary cause of the decreased bubble stability in cement-based materials at low atmospheric pressure. However, this viewpoint lacks experimental verification due to the difficulty in measuring surface tension at low atmospheric pressure. This study systematically explores the effect of low atmospheric pressure (0∼0.1 MPa) on the surface tension of pore solutions of fresh cement pastes. The surface tension of pore solutions was measured at different atmospheric pressures by using the high-accuracy automatic interface tension meter. Results show that the impact of low atmospheric pressure on the surface tension of deionized water, cement and fly ash pore solutions is insignificant. Therefore, the decrease in bubble stability and air content of concrete at low atmospheric pressure cannot be attributed to the change of surface tension. The effect of low atmospheric pressure on the surface tension of air-liquid interface is explained from the perspective of intermolecular force and density. This research helps to better understand the impact of low atmospheric pressure on surface tension and lays the essential groundwork for improving bubble stability of cement-based materials in high-altitude regions.

Density Functional Theory with Fundamental Measure Theory for Stable Drops and Bubbles on Lyophilic and Lyophobic Nucleation Cores

Density Functional Theory with Fundamental Measure Theory for Stable Drops and Bubbles on Lyophilic and Lyophobic Nucleation Cores