Tiny Gas Bubbles Research Articles

Electric-field nanobubbles: A step change in nanobubble engineering, and its “coming of age”

Electric-field nanobubbles: A step change in nanobubble engineering, and its “coming of age” Niall J. English, from Chemical Engineering at University College Dublin, discusses how electric-field nanobubbles have displaced their mechanically-generated counterparts in performance and sustainability. Limited solubility of gases in water, such as oxygen, is a fundamental challenge. In ecosystems and the environment, lack of dissolved oxygen (DO) is a major reason for fish kills and water bodies being blighted by algal blooms, in addition to lack of effectiveness of activated-sludge processes in water treatment or poorer-than-hoped results in irrigation. Nanobubbles (NBs) are tiny gas bubbles on the nanometre (nm) scale. They may be thermodynamically metastable for up to many months, or sometimes even longer, and have enhanced gas-transfer properties and substantial industrial potential. The concept of NBs versus traditional, coarser bubbles – with the latter subject to buoyancy phenomena, while NBs are relatively impervious to rising – in essence, “subverts” Stokes’ Law of bubble rising – and have an excellent area-to-volume ratio. If NBs are generated well – indeed, the art of “nanobubble engineering”, as it were – NBs lead to important and useful applications.

Solutal Marangoni force controls lateral motion of electrolytic gas bubbles.

Electrochemical gas-evolving reactions have been widely used for industrial energy conversion and storage processes. Gas bubbles form frequently at the electrode surface due to a small gas solubility, thereby reducing the effective reaction area and increasing the over-potential and ohmic resistance. However, the growth and motion mechanisms for tiny gas bubbles on the electrode remains elusive. Combining molecular dynamics (MD) and fluid dynamics simulations (CFD), we show that there exists a lateral solutal Marangoni force originating from an asymmetric distribution of dissolved gas near the bubble. Both MD and CFD simulations deliver a similar magnitude of the Marangoni force of ∼0.01 nN acting on the bubble. We demonstrate that this force may lead to lateral bubble oscillations and analyze the phenomenon of dynamic self-pinning of bubbles at the electrode boundary.

Modeling and Simulation of Parametric Nonlinear Focused Ultrasound in Three-Dimensional Bubbly Liquids with Axial Symmetry by a Finite-Element Model

This paper presents the development of a numerical model able to track in time the behavior of nonlinear focused ultrasound when interacting with tiny gas bubbles in a liquid. Our goal here is to analyze the frequency components of the waves by developing a model that can easily be adapted to the geometrical restrictions and complexities that come out in several application frameworks (sonochemistry, medicine, and engineering). We thus model the behavior of nonlinear focused ultrasound propagating in a liquid with gas bubbles by means of the finite-element method in an axisymmetric three-dimensional domain and the generalized-α method in the time domain. The model solves a differential system derived for the nonlinear interaction of acoustic waves and gas bubble oscillations. The high nonlinearity and dispersion of the bubbly medium hugely affect the behavior of the finite-amplitude waves. These characteristics are used here to generate frequency components of the signals that do not exist at the source through nonlinear mixing (parametric antenna). The ability of the model to work with complex geometries, which is the main advantage of the method, is illustrated through the simulation of nonlinear focused ultrasound in a medium excited from two spherical sources in opposite directions.

Modulating Force of Nucleated Hydrogen Bubble Adhesion to Boost Electrochemical Water Splitting

AbstractIn electrochemical hydrogen evolution reaction (HER), the produced hydrogen gas bubbles often adhered to the electrode surface and blocked the active catalytic site. While different catalysts are developed to improve the catalytic performance of HER, the design of a durable and universal approach for minimizing the force of nucleated hydrogen gas‐bubble adhesion to prevent blockage of electrocatalytic sites because of bubbles‐adhesion is unprecedented. Generally, buoyancy should outweigh the capillary force to remove nucleated bubbles, which means these forces ratio, Eötvös number Eo > 1. Herein, a chemically reactive multilayer coating on an electrode is reported to chemically modulate the adhesion force of nucleated gas‐bubble on the electrode. A dual modified coating on Ni‐foam provided a non‐adhesive superaerophobicity with nucleated bubble adhesion force of 4.6 ± 0.3 µN and displayed superior HER performance with lower overpotential (333 to 250 mV) at 100 mA cm−2 with respect to bare Ni‐foam. The chemically‐modulated low bubble‐adhesion facilitates the early removal of nucleated tiny hydrogen gas bubbles with a minimum size of 0.64 mm and Eo = 0.05 to keep catalytic sites available for superior electrochemical HER. Such a positive impact of the prepared coating is also noted for various other electrodes.

Generation and Influence of Carbon Dioxide Nanobubbles on Physicochemical Properties Including the Surface Tension of Clarified Apple Juice

AbstractThis work aims at examining the impact of generated CO2 nanobubbles (NBs) via the membrane-based method on physicochemical properties and surface tension of commercial clarified apple juice. The gas was injected at 300 kPa pressure for variable liquid circulation times (5, 13 and 26 min) to produce the CO2 NBs. Sets of 13- and 26-min circulation time to mix CO2 and liquid gave the desirably nano-size (~ 80–200 nm) NBs and significantly (p ≤ 0.05) reduced surface tension (by ~ 20–25%) of the juice dispersed with these formed tiny gas bubbles (NB-juice). An increase in circulation time also resulted in more negative zeta potential and higher dissolved CO2 concentration of the NB-juice. Density values of apple juice remained unchanged with and without incorporating CO2 NBs. These experimental outcomes provide the potential use of NBs in controlling the characteristics of liquid food as an environment-friendly approach to minimise chemical usages.

Contemporary application of microbubble technology in water treatment.

Microbubble (MB) technology constitutes a suite of promising low-cost technologies with potential applications in various sectors. Microbubbles (MBs) are tiny gas bubbles with diameters in the micrometre range of 10-100 μm. Along with their small size, they share special characteristics like slow buoyancy, large gas-liquid interfacial area and high mass-transfer efficiency. Initially, the review examines the key dissimilarities among the different types of microbubble generators (MBG) towards economic large-scale production of MBs. The applications of MBs to explore their effectiveness at different stages of wastewater treatment extending from aeration, separation/ flotation, ozonation, disinfection and other processes are investigated. A summary of the recent advances of MBs in real and synthetic wastewater treatment, existing research gaps, and limitations in upscaling of the technology, conclusion and future recommendations is detailed. A critical analysis of the energetics and treatment cost of combined approaches of MB technology with other advanced oxidation processes (AOPs) is carried out highlighting the potential applicability of hybrid technology in large-scale wastewater treatment.

Energetics of a bouncing drop: Coefficient of restitution, bubble entrapment, and escape

Drops bouncing on an ultra-smooth solid surface can either make contact with the surface or be supported on a thin cushion of gas. If the surface is superhydrophobic, either complete or partial rebound usually occurs. Recent experiments have shed light on the lubrication effect of the underlying gas layer at the onset of impact. Using axisymmetric direct numerical simulations, we shed light on the energetics of a drop bouncing from a solid surface. A complete energy budget of the drop and the surrounding gas during one complete bouncing cycle reveals a complex interplay between various energies that occur during impact. Using a parametric study, we calculate the coefficient of restitution as a function of Reynolds and Weber numbers, and the results are in good agreement with the reported experiments. Our simulations reveal that the Weber number, not the Reynolds number, has a stronger effect on energy losses as the former affects the shape of the drop during impact. At higher Weber and Reynolds numbers, a tiny gas bubble gets trapped inside the drop during impact. We show that a large amount of dissipation occurs during the bubble entrapment and escape process. Finally, analysis of the flow field in the underlying gas layer reveals that maximum dissipation occurs in this layer, and a simple scaling law is derived for dissipation that occurs during impact.

Linear energy transfer of fission fragments of 235U and nucleation of gas bubbles in aqueous solutions of uranyl nitrate

Fission fragments emitted in a fissile solution create tiny gas bubbles, the size of which is determined by the linear energy transfer (LET) of the particles. The LET of fission fragments of 235U in aqueous solutions of uranyl nitrate has been determined, and using methods adapted from the literature, the size of gas bubbles generated along the tracks of these particles has been estimated, revealing important variations with respect to particle LET and solution properties. Empirical correlations are presented for the maximum radius of radiolytic gas bubbles in unsaturated solutions of uranyl nitrate as a function of solution temperature and concentration. These can be used to predict the critical concentration of dissolved hydrogen necessary for the appearance of gas voids during nuclear criticality transients. The findings are intended for use in a future model of nuclear criticality transients in aqueous fissile solutions for the purposes of nuclear criticality safety assessment.

Spontaneous and unidirectional transportation of underwater bubbles on superhydrophobic dual rails

Superhydrophobic/superhydrophilic surfaces (SBS/SLS) with excellent water repellency/adhesion are important in both academic research and industrial settings owing to their intriguing functions in tiny droplet and gas bubble manipulation. However, most manipulation strategies involving SBS/SLS are limited to their large-area fabrication or sophisticated morphology designs, which distinctly hinders their practical uses. In this paper, we design and fabricate superhydrophobic polydimethylsiloxane narrowing dual rails (SNDRs) beneath a superhydrophilic stainless steel sheet by one-step femtosecond laser ablation. Our SNDR tracks are capable of transporting gas bubbles in various volumes from wide end to narrow end spontaneously and unidirectionally underwater, even when they are bent. The mechanical analysis for diverse geometrical dual-rail configurations in bubble transportation performance is further discussed. Finally, we experimentally demonstrate the intriguing capability of lossless mixing of gas bubbles at a designed volume ratio on a multiple SNDR combination. This approach is facile and flexible, and will find broad potential applications such as intelligent bubble transport, mixing, and controllable chemical reactions in interfacial science and microfluidics.

Wound Healing Efficacy of Re Cell Heal in a Diabetic Foot Infection Patient Diagnosed with Gas Gangrene – A Case Report

Gas gangrene is a rapidly progressive and bacterial infection that produces tissue gas in gangrene. The condition may result from ischemia, infection, or trauma or a combination of these processes. A 72-year-old woman with a 10 years history of type-2 diabetes mellitus (NIDDM) presented to the emergency department with a one-week history of left foot painful, swelling, redness, fever and foul-smelling discharge from wound. Wound infection of the left foot worsening progressing to gas gangrene that remains unhealed after a week to one month. She was diagnosed with Clostridium perfringens and Clostridial myonecrosis. The foot X-ray showed a 13 X 8.5 X 1.75 cm and is surrounded by callus under the 1st to 5th metatarsal heads (Figure 3a & 3b). Computed tomography (CT) scan showed moderate air suggesting deep tissue infection, with multiple tiny gas bubbles within under the first metatarsal heads, concerning for gas gangrene. The patient was treated with Poly Herbal Formulation (PHF), Re Cell Heal 500 mg Capsule (PRANATHI HERBALS; License No. T-2265/Ayur/; Letter No 2884/ DA/2018) (p.o) twice a day, in addition to the (Topical) Wound Check Ointment (Letter No 4964/DA/2018) accompanied with debriment over a five (5) months, foot healed without amputation improved therapeutic outcomes, reduce fatalities caused by gas gangrene. Re Cell Heal helps to provide relief in the symptoms like swelling and pain in tissues. Recent scientific evidences and trials conducted on Re Cell Heal is a traditional and alternative medicine in wound therapy, gas gangrene and diabetic related foot problems holds good promise in the future safety without any side effects.

Testing the injection of air with methane as a new approach to reduce the cost of cold heavy oil recovery: An experimental analysis to determine optimal application conditions

We propose a new approach to reduce the associated cost of CSI (cyclic solvent injection) by using air with methane to pressurize the reservoir and improve the foaminess process. This reduces the cost as the amount of methane injected is curtailed, but the process needs to be optimized by determining the optimal application conditions by maximizing final heavy oil recovery. To study the use of air for a technical and economic improvement of CSI with methane, pressure depletion tests were performed at a pressure depletion rate of −0.51 psi/min in a cylindrical sandpack, placed in a 150 cm long and 5 cm diameter sandpack holder supplied with eight evenly distributed pressure transducers and three thermocouples. Production profiles (pressure at every port, pressure differences, and pressure gradient) and saturation distributions were studied to determine the conditions yielding the best sweep and the highest oil and gas recovery factor with minimal use of gas injected. Different injection/production schemes (alternate or co-injection of an air-methane pair and different injector-producer alignments), depletion rates, and soaking times were tested to determine the conditions to maximize the recovery factor. Furthermore, observational experiments at a macroscopic and microscopic scale after the PVT tests were performed by recombining the heavy oil sample with sole air, sole methane, and a mixture of air and methane at a volume ratio of 1. Using a mixture of air and methane not only expanded the volume of oil (gas bubbles trapped into the oil) by 2.5 but also delayed the defoaming process at both macroscopic and microscopic scales. Numerous tiny gas bubbles were initially observed, which kept its size and number for more time than the methane case, which is an indication of restraining fast bubble growth and subsequent coalescence. The best injection strategy for a single-well injection scheme was the simultaneous injection of air and methane on a soaking period of 2–3 days, whereas for a multi-well injection scheme an alternating injection strategy on a soaking period of 4–5 days offered the best performance. Cumulative oil and gas recovery factors were as high as 27.46% and 76.68%, respectively, when air was accompanied by methane. Using air as a foamy oil ameliorative was observed to save up to 26% on methane use in single-well injection schemes and up to 51% on multi-well injection schemes.

Phase-Field Modeling and Simulation of Gas Bubble Coalescence and Detachment in a Gas-Liquid Two-Phase Electrochemical System

Many electrochemical processes involve gas evolution and bubble generation on the electrodes. Understanding the behavior of bubbles on the electrode surface and in the electrolyte is crucial to the design and optimization of the electrochemical process. Gas bubbles tend to coalesce and detach from the electrode surface once they are formed and as they grow, but these processes have not been investigated and understood well. The phase-field modeling method is excellent at tracking the interface between different phases, and the simulation results can give a precise prediction of the interaction between phases. In this research, taking advantage of the phase-field method, a gas-liquid two-phase model has been constructed to investigate the bubble coalescence and detachment in the electrochemical system. Sophisticated, tiny gas bubble coalescence on and off electrode and the detachment of bubbles from the electrode surface were predicted by the model. The results are helpful for the understanding of these transient processes in the electrochemically generated bubble-liquid system.

Numerical modelling for the simulation of nonlinear ultrasound in liquids with gas bubbles

Several numerical models have been developed in different configurations to simulate the behaviour of finite-amplitude ultrasound when interacting with tiny gas bubbles in a liquid. Since this interaction is highly nonlinear, specific models must be developed to understand the propagation of the waves in this kind of dispersive media for which their nonlinear and attenuation coefficients, as well as the sound speed, are extremely dependent on the ratio of the driven frequency to the bubble resonance. The bubble volume variation is mathematically modelled in the time domain through a Rayleigh-Plesset equation with terms up to the second order, whereas the time-dependent acoustic field relies on the wave equation in one or several dimensions. Both differential equations are coupled and auxiliary conditions are imposed. The differential systems are solved by the developed numerical models. In this paper we study in a three-dimensional resonator with axial symmetry how new harmonics obtained by nonlinear distortion can be enhanced by taking the nonlinear resonance effect into account, and we show that the generation of new frequency components by nonlinear frequency mixing exists. We also analyse the stable cavitation phenomenon in a three-dimensional focused field with axial symmetry by considering a nonlinear dependence of bubble generation in the liquid and the existence of primary Bjerknes forces.

Bubble coalescence suppression driven carbon monoxide (CO)-water mass transfer increase by electrolyte addition in a hollow fiber membrane bioreactor (HFMBR) for microbial CO conversion to ethanol

This study investigated the effects of electrolytes (CaCl2, K2HPO4, MgSO4, NaCl, and NH4Cl) on CO mass transfer and ethanol production in a HFMBR. The hollow fiber membranes (HFM) were found to generate tiny gas bubbles; the bubble coalescence was significantly suppressed in electrolyte solution. The volumetric gas-liquid mass transfer coefficients (kLa) increased up to 414% compared to the control. Saturated CO (C∗) decreased as electrolyte concentrations increased. Overall, the maximum mass transfer rate (Rmax) in electrolyte solution ranged from 106% to 339% of the value obtained in water. The electrolyte toxicity on cell growth was tested using Clostridium autoethanogenum. Most electrolytes, except for MgSO4, inhibited cell growth. The HFMBR operation using a medium containing 1% MgSO4 achieved 119% ethanol production compared to that without electrolytes. Finally, a kinetic simulation using the parameters got from the 1% MgSO4 medium predicted a higher ethanol production compared to the control.

Experimental study and numerical optimization on a vane-type separator for bubble separation in TMSR

An axial-flow vane-type bubble separator for TMSR with regard to its working principle and separation efficiency was investigated experimentally and numerically. Experiments study was firstly carried out with air and water as working fluids to demonstrate the feasibility of the vane-type separator in the separation of tiny gas bubbles dispersed in a fluid. On the basis of the experiments, further investigations on the flow field distribution and structure optimization were carried out with numerical method. A vane-type separator with best performance for TMSR was proposed according to the numerical results. Both the experimental and numerical work showed that, the vane-type separator can successfully separate the small bubbles from a liquid flow with a very high separation efficiency, and the RSM model is capable of presenting the flow field in the separator with a good accuracy. The results imply that, it is the radial pressure gradient generated in the separation zone that makes the dispersed bubbles congregate to the center region of the separator, leading to the formation of an air core. The outlet angle of the swirl vanes, volumetric flow rate and the density of the working fluid affect the separation efficiency simultaneously. And for the case with molten salt as working fluid, the outlet angle of the swirl vanes or the volumetric flow rate should be smaller than the case that water is used.

Microbubble in the hole: a rare cause of failed macular hole surgery?

To present a failed macular hole surgery with gas microbubble retention within the hole. A 68-year-old female patient with a Stage 2 macular hole underwent vitrectomy with removal of posterior hyaloid and 12% C3F8 gas injection. Because the macular hole was Stage 2 and posterior hyaloid was observed to be firmly attached over the macular area, no attempt was made for peeling of internal limiting membrane. Postoperatively, the patient was instructed to keep a facedown posture for 1 week. At 1-month visit, ophthalmoscopy revealed a tiny gas bubble filling the macular hole that failed to close. The patient underwent a repeat vitrectomy in which internal limiting membrane was peeled, and the eye was filled with 20% SF6. At 2-week follow-up visit, the hole was observed to be closed. The reason for the macular hole nonclosure in this case may be the lack of internal limiting membrane peeling in the first operation. However, the authors believe that microbubble localized within the hole might have contributed to the failure.

Foreign Body with Gas Gangrene in an Elderly Patient with Diabetes.

A 76-year-old African-American man who lived alone, with an 11year history of poorly controlled diabetes and symptomatic peripheral neuropathy, presented to the Emergency Department with right foot pain and swelling. His initial evaluation included a lower extremity Doppler that ruled out a deep venous thrombosis and the patient was discharged. The patient returned to the Emergency Department after one week for worsening right foot pain and swelling. He was afebrile and hemodynamically stable. The physical exam revealed new unroofed blisters on the dorsal aspect of the right foot. Foot x-ray (Panel 1) showed a 3 cm linear metallic foreign body, which appeared to be a broken sewing needle in the soft tissues between distal first and second metatarsals. Computed Tomography (CT) scan (Panel 2) showed moderate air suggesting deep tissue infection, with multiple tiny gas bubbles within the proximal phalanx of the second digit, concerning for gas gangrene. He received broad-spectrum intravenous antibiotics and underwent a two-stage operation on his right leg. The first stage was a guillotine amputation. The patient remained afebrile and hemodynamically stable. Antibiotics were stopped since now, after removal of the gangrenous tissue, there was adequate source control of the infection. A few days later, he underwent a definitive, below-theknee amputation. The differential diagnoses for gas gangrene includes inflammation

Hydrodynamics of the Aluminium Barbotage Process Conducted in a Continuous Reactor

Today aluminium obtained from ores (primary) and from scrap (secondary) need to be refined. During this process harmful impurities such as hydrogen, sodium, lithium, oxides, borides or carbides can be removed. There are many different ways of aluminium refining process. The most popular seem to be barbotage that means blowing through aluminium many tiny gas bubbles of refining gas. Reactors applying this methods have been working all over the word. They are of different types: bath and continuous, using ceramic porous plugs, special kinds of nozzles or rotary impeller for generating small gas bubbles. At present reactors for continuous refining have become the most popular. In Poland typical representative of such reactors is URC-7000 reactor. The phenomena occurring during this process are rather complicated. Therefore to know them better the modelling research is applied, especially physical modelling. The paper presents the results of such a research. The tests were carried out in the test stand for modelling the babotage process in the URC-7000 reactor. The different modelling agents were tested (water, glycerin and mixture of water and glycerine). The density and viscosity of water and glycerin mixture were determined. Modelling tests were conducted for four different flow rates of refining gas: 6, 10, 15 and 20 dm3/min. Results were registered by digital camera. Pictures for different modelling agents were juxtaposed and discussed.

Precipitation of calcium carbonate by carbon dioxide microbubbles

The microbubble generator (MBG)—an apparatus in which tiny micron-sized gas bubbles are produced in the aqueous phase—has been widely used in water purification systems. In this study, the feasibility of utilizing the MBG to precipitate calcium carbonate along the carbonation route was examined. The effects of the calcium hydroxide concentration and the injection flow rate of carbon dioxide on the precipitation process were evaluated. Changes in pH, temperature of the suspension, and residual calcium ion concentration in the suspension were monitored to evaluate the proposed process. In addition, the process was compared with that based on a conventional bubble generator. This revealed a two-fold improvement in the acquisition time required for calcium carbonate precipitation as well as an increase in the conversion efficiency of carbon dioxide to carbonate minerals. The proposed process should be helpful for practical applications of a carbon sequestration method.

Dihydrogen gas emission of a 250kWth research reactor

The Vienna TRIGA pool-type reactor emits tiny gas bubbles at 250kW. They add up to a total volume of ∼2.4L in 7h of daily operation. The bubbles consist of nitrogen (72.5vol%), hydrogen (17.2%), oxygen plus argon (12.0%) and carbon dioxide (0.23%). The emission of constituents of air is caused by degassing of dissolved air in the hot regions of the reactor. Hydrogen results from neutron-induced radiolysis of the cooling water. This emission should be kept in mind for reasons of fire protection even for low-power reactors.