Air Microbubbles Research Articles

Bioactive Effects by Air Microbubble Bathing

Bioactive Effects by Air Microbubble Bathing

Corrosion aspects of molten nitrate salt-based nanofluids for thermal energy storage applications

Efficient energy storage is a bottleneck for nearly every renewable energy technology. Thermal energy storage (TES) is widely considered as a relatively simple and reliable method, particularly for concentrated solar power (CSP) plants. Currently, considerable scientific effort is focused on the development of new molten salt-based nanofluids as storage materials with enhanced thermophysical properties and lower cost for TES purpose. However, an understanding of the effect of nanoparticles on the corrosivity of such nanofluids is practically absent. In the present work, using nanofluids based on eutectic mixture of NaNO3-KNO3 we demonstrate that nanoparticles doping has complex effects on the corrosion rates of carbon steel. In particular, if the negative effect of microbubbles of air trapped between the nanoparticles is not predominant, one can obtain reduced corrosion rates due to the incorporation of the nanoparticles into the oxidation layer. The obtained results are important both for expanding the very limited knowledge on the corrosion aspects of molten salts-based nanofluids, as well as for comprehensive evaluation of the feasibility of such nanofluids for TES applications.

Air contamination during medical treatment results in deposits of microemboli in the lungs: An autopsy study.

Microbubbles of air may enter into patients during conventional hemodialysis, infusions of fluids, or by injections. The aim of this study was to investigate whether the air that enters the patient during hemodialysis can be detected in the lungs after death, and if so, whether this may be related to tissue damage. The material consisted of lung tissue from five chronic hemodialysis patients who died either during (two) or after hemodialysis (range 10 min from start until 3333 min after the last hemodialysis session); as reference group tissue was taken from seven patients who died due to amyotrophic lateral sclerosis. The lung tissue was investigated by microscopy after autopsy using a fluorescein-marked polyclonal antibody against fibrinogen as a marker for clots preformed before death. All five hemodialysis patients had microbubbles of air in the lung tissue, whereas two of seven amyotrophic lateral sclerosis patients had such findings (Fisher's test p = 0.0278, relative risk = 3.5, confidence interval: 1.08-11.3). There were more microbubbles of air/10 randomly investigated microscopic fields of tissue in the hemodialysis patients than the amyotrophic lateral sclerosis patients (Student's test, p < 0.05). All hemodialysis patients had a medium graded extent of pulmonary fibrosis that was not found in any of the ALS patients. The microbubbles of air were surrounded by fibrin as a sign of development of clots around the air bubbles while the patients were still alive. Exposure to microbubbles of air during various treatments such as hemodialysis may result in microemboli. Future studies should clarify whether microbubbles of air contribute to tissue scarring. We suggest preventive measures against the exposure to microbubbles of air during especially repeated exposures such as hemodialysis.

Mass transfer from freely rising microbubbles in aqueous solutions of surfactant or salt

Microbubbles are used in many applications. One of the major advantages of using microbubbles is to improve the mass transfer of gases to the bulk phase. In this study, mass transfer from single microbubbles that rise in ultrapure water and aqueous solutions of surfactants (SDS, Pluronic F68) or salt (NaCl) was investigated. The rising and dissolution behaviors of single air microbubbles were observed using a high-speed imaging technique by which the rising velocity, UB, and the mass transfer coefficient, kL, were optically evaluated. We found that the rising velocity of microbubbles obeys Stokes’ law, indicating that the surface of the microbubbles used in this study is immobile, despite their rising in ultrapure water. The obtained mass transfer coefficients were in good agreement with those predicted by Ranz and Marshall’s correlation for the Sherwood number, Sh. Using the two correlations for UB and Sh, a theoretical model that describes the mass transfer from a microbubble was constructed. The proposed model can predict the dissolution of single microbubbles rising in ultrapure water and aqueous solutions with an accuracy of ±10% in terms of dissolution time.

Study of sterilization effects on marine Vibrio sp. using interaction of cavitation with shock wave in a narrow water chamber

Cavitation bubbles could also be called as inertial bubbles because of their oscillation due to the pressure difference between inside and outside. After the passage of an underwater shock wave, the violent collapses of the bubbles are induced and could produce stronger mechanical and biochemical actions so that the marine bacteria around them are inactivated by those productions. In the present study, cavitation inertial bubbles are observed behind multiple waves in a narrow water chamber after an electric discharge is triggered and then interacts with underwater reflected shock waves from the water chamber. The sterilization effects of only these oscillating bubbles and cavitation-shock interaction are investigated by bio-experiments of marine Vibrio sp. The results show that a high sterilization is obtained in the case of the cavitation-shock interaction. Furthermore, the chemical action of free radicals mainly contributes to inactivating the marine bacteria. The generation of the hydroxyl (OH) radicals is clarified by measuring the concentration of H2O2. Subsequently, we focus on a theoretical analysis of the generation condition of the OH radicals by a bubble dynamic model consisting of an oscillation model and an impact model. Finally, the theoretical estimation by the bubble dynamic model is discussed under the conditions of the present experiments. As a result, there is a possibility of effective sterilization by the cavitation-shock interaction without the supply of air microbubbles.

Bubble image velocimetry with a field-deployable acoustic camera

This study explores performing bubble image velocimetry (BIV) analysis on images acquired from an acoustic camera (AC) to obtain measurements of the flow in the wake of a circular cylinder at two flowrates. The AC observes the returns from air micro-bubbles suspended in the flow which are used as tracer particles in PIV-style analysis. The size distribution of the micro-bubbles is measured with an acoustic bubble spectrometer (ABS). The AC BIV measurements of the wake agree well with the comparison measurements made by cross-stream arrays of acoustic Doppler velocimeters (ADVs) for the lower of the two measured flowrates. The AC BIV measurements of cross-stream profiles of the mean downstream velocities and the profiles of characteristics of the velocity fluctuations, such as the standard deviation of the downstream and cross-stream velocity fluctuations, the covariance of the horizontal velocity fluctuations, and the kinetic energy of the horizontal velocity fluctuations, all matched the ADV measurements well. However, the measurement technique is sensitive to bubble size distribution, as the higher flowrate AC BIV measurements struggled to replicate the ADV measurements, particularly the measurements of the velocity fluctuations. The higher flowrate experiment is revealed to have an order of magnitude more bubbles with size exceeding 15 present in the flow than the lower flowrate experiment. The increased bubble density caused increased noise in the AC images and a ‘flickering’ effect, with bubbles further away from the camera being intermittently obscured by those closer to the camera. The ability to make PIV-style measurements with an AC has ramifications for flow measurements in the field. ACs operate in turbid environments, do not require a laser and extensive optics, and do not require calibration with a grid plate to convert pixel space to physical space.

Generation of ultra-stable Pickering microbubbles via poly alkylcyanoacrylates

A range of solution conditions (pH, surfactant concentration and type) have been tested for the polymerization of alkyl cyanoacrylates (ethyl (ECA), butyl (BCA) and octyl (OCA)) into nanoparticles (NPs) potentially capable of stabilizing highly unstable microbubbles (MBs) of air in aqueous solutions. The optimum system was butyl cyanoacrylate (BCA) polymerized into PBCA particles at pH 4 in the presence of 1 wt.% Tyloxapol surfactant. These PBCA particles were highly effective at stabilizing MBs of only a few microns in size for at least 2 months. Microscopy over a range of length scales clearly indicated that these particles were stabilized via a Pickering mechanism. Only a relatively low volume fraction (ca. 1 vol.%) of MBs could be obtained via a single aeration step of a 0.7 wt.% dispersion of PBCA particles in a high shear mixer. Although this could be increased to 2 and 3 vol.% by second and third aerations, this reflects the difficulty of obtaining and maintaining rapid enough particle coverage of small bubbles even under turbulent conditions. Similar sizes and yields of PBCA particles could be obtained in the absence of surfactants, but these particles, with or without addition of surfactant afterwards, could not stabilize MBs. We estimate that approximately one quarter of the Tyloxapol when present during polymerization is incorporated into the particles on polymerization, which somehow imparts the correct surface hydrophobicity and contact angle to the particles at the A/W interface, making such particles so very effective as Pickering MB stabilizers.

Preparation and characterization of perfluorocarbon microbubbles using Shirasu Porous Glass (SPG) membranes

Microbubbles are increasingly used in several fields, such as medical imaging for enhanced contrast ultrasound imaging. Theses microbubbles usually consist of a gas core stabilized by surfactant molecules. In this study, a technique using Shirasu Porous Glass (SPG) membranes was used to produce perfluorocarbon microbubbles. The microbubbles obtained were characterized by their size, size distribution, and stability. The effect of several parameters on the microbubble's size was investigated related to the process (transmembrane pressure, ΔP, bubble point pressure, PBP, shear stress, τw), membrane pore size, Dp, and formulation (gas, surfactants in the aqueous phase). The transmembrane pressure nor the shear stress (τw) had influence on the microbubble's size or size distribution for ΔP/PBP <1.5. The decrease of the membrane pore size from 1.1, 0.5, to 0.2 μm led to lower microbubble size 13.3, 6.36, and 4.42 μm, respectively, which was associated with higher size distribution 16%, 24% and 31%, respectively due to the higher Laplace pressure exerted on smaller microbubbles leading to their destabilization. With the 1.1 μm pore size membrane, perfluorocarbon microbubbles were obtained with a diameter of 13.3 μm and coefficient of variation (CV) of 16% when stabilized by sodium dodecyl sulfate (SDS), 15.6 μm with CV% of 23% when stabilized by Tween20, and 16.5 μm with CV% of 26% when stabilized by Polyoxyethylene (40) stearate (PEG40S). These low CV were indication of monodispersity. Perfluorocarbon microbubbles had a smaller size than air microbubbles due to the lower surface tension that decreased the retention force, keeping the microbubbles at the pore opening. The stability study showed that the perfluorocarbon gas greatly increased the lifetime of the microbubbles with a slight increase in size of 1.3 after 90 s compared to 2.2 for air microbubbles. Overall, the membrane technique proved to be an effective, controlled and reproducible method to produce perfluorocarbon microbubbles at a high rate ∼0.6 − 1.5 × 10+10 microbubbles/min. The key factor that determines the microbubbles formation is the adsorption kinetics of the surfactant at the new gas–liquid interface at the pore opening.

Influence of the Distributed Phase of Gas Bubbles on a Pulsed Electrical Discharge in Water

The development of a pulsed electrical discharge in water with vapor–air microbubbles, the volume distribution of which in water is close to uniform, has been studied experimentally. The presence of volumetric microbubbles with an average diameter of ~50 μm and a bulk gas content of no more than 1% does not change the thermal mechanism of the development of the discharge in water with a conductivity of ~300 μS/cm at overvoltages of 1–1.5, the minimum breakdown voltage being ~9 kV. Under these conditions, the determining role is played by the surface bubbles, which change the observed mechanism of the discharge development. The discharge is initiated in the surface bubbles simultaneously on both electrodes. The growth of the cathode channel at a velocity of ~60 m/s leads to the closure of the 1-cm-long gap during a time of ~160 μs.

Deformation of Red Blood Cells, Air Bubbles, and Droplets in Microfluidic Devices: Flow Visualizations and Measurements.

Techniques, such as micropipette aspiration and optical tweezers, are widely used to measure cell mechanical properties, but are generally labor-intensive and time-consuming, typically involving a difficult process of manipulation. In the past two decades, a large number of microfluidic devices have been developed due to the advantages they offer over other techniques, including transparency for direct optical access, lower cost, reduced space and labor, precise control, and easy manipulation of a small volume of blood samples. This review presents recent advances in the development of microfluidic devices to evaluate the mechanical response of individual red blood cells (RBCs) and microbubbles flowing in constriction microchannels. Visualizations and measurements of the deformation of RBCs flowing through hyperbolic, smooth, and sudden-contraction microchannels were evaluated and compared. In particular, we show the potential of using hyperbolic-shaped microchannels to precisely control and assess small changes in RBC deformability in both physiological and pathological situations. Moreover, deformations of air microbubbles and droplets flowing through a microfluidic constriction were also compared with RBCs deformability.

Polyelectrolyte multilayer microchamber-arrays for in-situ cargo release: Low frequency vs. medical frequency range ultrasound

An implantable ultrasound triggered controlled release micro-chamber (MC) array based on polylactic acid (PLA) sealed polyelectrolyte multilayers (PEM) is presented. In this work Rhodamine B (RhB) nano-precipitates are loaded as model cargo and sealed water tight within micro-air bubbles. Cargo release at low frequency (LFUS (37 kHz)) and high frequency ultrasound (HFUS (2 MHz, medical range)) is compared. The release speed and mechanism varies significantly between both ultrasound frequencies, allowing for a 60 times faster MC opening at HFUS. LFUS MC opening is based on material fatigue combined with thermo-acoustic effects while strong thermo-acoustic effects are responsible for MC opening at HFUS. The slower MC opening at LFUS allows for controlling the release amount and enables multiple release pulses compared to HFUS. Not PLA coated and no air bubble entrapping PEM thin films are in case of HFUS destroyed, while no interaction is determined at LFUS.

Abstract WP408: Interplay Between Patent Foramen Ovale, Migraine, Stroke and Cerebral Vasomotor Reactivity

Background: The first data on influence of patent foramen ovale (PFO) with high-volume right-to-left shunt (RLS) on cerebral vasomotor reactivity (CVMR) in migraineurs are presented. In addition, immediate effect of air microbubbles (MB), injected for the bubble TCD test, on CVMR has been determined. Methods: Breath holding index (BHI, vasodilatory capacity-vdCVMR) and percent decrease during hyperventilation (vasoconstriction capacity-vcCVMR) tests were performed before and after bubble TCD test in bilateral middle and posterior cerebral arteries (MCA and PCA) in 38 migraine (19 with aura) and 18 control patients; 26 patients had large PFO while others had no RLS. Subjects with mild/moderate RLS were not enrolled. Results: Presence of PFO was related to a significant decrease of BHI recorded in MCA (1.43±0.39 vs. 1.04±0.67, p=0.032) and marginal reduction of PCA BHI (1.01±0.39 vs. 1.25±0.46, p=0.090) in migraineurs. vdCVMR reduction was more prominent in the contralateral side (to pain). PCA BHI significantly decreased after agitated saline injection in the bubble test. Decrease was greater in patients with PFO (from 1.03±0.40 to 0.78±0.38, p=0.007) compared those without PFO (from 1.15±0.42 to 0.91±0.45, p=0.014). The decrease was prominent in subjects with both migraine and PFO (from 1.01±0.40 to 0.76±0.42, p=0.023). No significant difference was seen in BHI with MCA after bubble injection. Bubble passage correlated to occurrence of headache after test. No difference was noted for the parameters of vcCVMR in subjects with/without PFO. Patients with FLAIR-determined silent ischemic lesion(s) had no difference in VMR before bubble test and VMR response to aerated bubble passage. Conclusions: The presence of PFO with high grade RLS is associated with reduced vasodilatory CVMR in migraineurs. Further decrease of vdCVMR of PCA upon MBs passage may support the mechanism of " facilitation with subclinical cerebral ischemia caused by microembolism", one of the hypotheses explaining the onset of migraine.

Investigation of transition from thermal- to solutal-Marangoni flow in dilute alcohol/water mixtures using nano-plasmonic heaters

We experimentally investigated Marangoni flows around a microbubble in diluted 1-butanol/water, 2-propanol/water, and ethanol/water mixtures using the thermoplasmonic effect of gold nanoisland film. A laser spot on the gold nanoisland film acted as a highly localized heat source that was utilized to generate stable air microbubbles with diameters of 32–48 μm in the fluid and to induce a steep temperature gradient on the bubble surface. The locally heated bubble has a flow along the bubble surface, with the flow direction showing a clear transition depending on the alcohol concentrations. The fluid is driven from the hot to cold regions when the alcohol concentration is lower than the transition concentration, whereas it is driven from the cold to hot regions when the concentration is higher than the transition concentration. In addition, the transition concentration increases as the carbon number of the alcohol decreases. The observed flow direction transition is explained by the balance of the thermal- and solutal-Marangoni forces that are cancelled out for the transition concentration. The selective evaporation of the alcohol at the locally heated surface allows us to generate stable and rapid thermoplasmonic solutal-Marangoni flows in the alcohol/water mixtures.

Effects of initial conditions on the coalescence of micro-bubbles

The effects of initial conditions on the coalescence of two equal-sized air micro-bubbles ( R0) in water are studied using the lattice Boltzmann method. The focus is on effects of two initial set-ups of parent bubbles, separated by a small distance d and connected with a neck bridge radius r0, on the neck bridge growth at the early stage of the bubble coalescence. A sophisticated free energy lattice Boltzmann method model based on the Cahn-Hilliard diffuse interface approach is employed. This lattice Boltzmann method model has been demonstrated suitable for handling a large density ratio of two fluids up to 1000 and capable of minimizing the nonphysical spurious current. In both initial scenarios, the neck bridge evolution exhibits a half power-law scaling, [Formula: see text] after a development time. The half power-law agrees with the recent analytical prediction and experimental results. It has been found that smaller initial separation distance or smaller initial neck bridge radius results in faster growth of neck bridge and bubble coalescence, which is similar to the effects of these two initial scenarios on droplet coalescence. The physical mechanism behind each behavior has been explored. For the initial connected case, faster neck growth and longer development time corresponding to smaller initial neck radius is due to the significant bias between the capillary forces contributed by the meniscus curvature and the neck bridge curvature, whereas in the case of initial separated scenario, faster growth and shorter development time corresponding to shorter separation distance is due to the formation of elongated neck bridge. The prefactor A0 that represents the growth of neck bridge radius at the characteristic time ti captured in each case is in good agreement with the experimental results.

Ultrasound-to-plastic optical fiber coupling as an acoustic source probe.

An integrated ultrasonic detection system that consists of emission and detection has been proposed and demonstrated experimentally. The proposed emission source is based on plastic optical fiber (POF). In order to promote the coupling of ultrasound-to-POF, and the end of the POF is heated to form a circular pedestal. A homemade fiber Fabry-Perot interferometer is employed to evaluate the coupling efficiency of ultrasound-to-POF. The sensing head is spliced with a short section of hollow-core fiber and single-mode fiber, resulting in an air microbubble formation by discharging. The experimental results show that ultrasound can be transmitted effectively in a narrow space using the coupling method, and the compact sensor also presents a considered sensitivity for ultrasonic detection. This all-fiber ultrasonic interrogation can be integrated as a system for the application in the bioimaging field, especially the organism body.

Influence of Physical Treatment on Kaolinite Floccule Microstructure

Microstructure investigation of kaolinite clay suspensions were conducted to understand better the poor settling and dewatering of clay rich mine tailings. The subject of testing was a 5 wt.kaolinite (KGa-2) aqueous suspension treated by pH change, ultrasonic and microwave action, polymeric flocculent and steatite addition. Kaolinite suspensions were investigated using synchrotron powered Transmission X-ray Microscope with subsequent computer 3D reconstruction. Treatment results favour the microwave treatment over ultrasonic for better aggregate dispersion. Surprisingly, after the flocculent addition into the dispersed kaolinite slurry, particles were prevented from coagulation by polymer action. Best aggregation results were recorded at low pH, microwave treated and ultrasonic treated after small amounts of Smectite addition. Significant portion of the voids were found to be filled by air micro-bubbles which add buoyancy to the entire clay network, reinforcing it against gravitational sedimentation along with steric interaction inflicted by scaffolding-like clay platelets space network. Key Wards: Clay suspension structure; Georgia Kaolinite; Kaolinite; Kaolinite flocculation; minerals processing

Combination of microbubbles with oxidizing sanitizers to eliminate Escherichia coli and Salmonella Typhimurium on Thai leafy vegetables

Microbubbles (MB) technology was applied in a washing process a few studies have been done with food materials, particularly to reduce the microbial contamination on leafy vegetables. This study determined the effectiveness of MB (Ø ∼ 50–70 μm) combined with three sanitizers acidic electrolyte water (AEO, 20 and 40 mg/L, ORP 910–1010 mV, pH 2.7–3.1), chlorine dioxide (ClO2, 3 and 5 mg/L, ORP 550–680 mV, pH 7.1–7.5), and sodium hypochlorite (NaOCl, 40 and 80 mg/L, ORP 900–990 mV, pH 6.5–6.7) in order to inactivate Escherichia coli and Salmonella Typhimurium on artificially contaminated sweet basil (Ocimum basilicum Linh) and Thai mint (Mentha cordifolia Opiz.). Although air MB alone did not possess antimicrobial activity, washing with MB combined with the two oxidizing sanitizers (NaOCl and AEO) for 5 min resulted in an effective reduction in S. Typhimurium and E. coli on sweet basil and Thai mint with 2–3 log reductions (99.2–99.8%). Washing vegetables with MB and NaOCl at a concentration of free chlorine of 40 mg/L NaOCl or 20 mg/L AEO yielded the best results in killing S. Typhimurium with 1.21–1.90 and 0.67–2.25 log reductions, respectively. In addition, the reduction of E. coli and S. Typhimurium on sweet basil appeared to be higher than on Thai mint. Differences in surface roughness may assist the bubbles and sanitizers to detach bacterial cells and therefore increase the washing efficacy. Furthermore, applying sanitizers in washing solution was a powerful means of killing planktonic E. coli and S. Typhimurium in the wash water and preventing cross-contamination in the washing process.

Miniaturized fiber-taper-based Fabry-Perot interferometer for high-temperature sensing.

A microminiaturized all-fiber Fabry-Perot interferometer (FPI) for high-temperature sensing has been proposed and experimentally demonstrated. The FPI is composed of a micro-air bubble and a taper probe with a tip less than 2 μm in diameter as reflected interfaces. A temperature sensitivity of 14.68 pm/°C near the wavelength of 1550 nm is obtained. The sensor, with its miniature size, can work in an ultra-small space with a large range of temperature variation.

Purification of Bioethanol Using Microbubbles Generated by Fluidic Oscillation: A Dynamical Evaporation Model

A computational model of a single gas microbubble immersed in a liquid of ethanol–water mixture is developed and solved numerically. This complements earlier binary distillation experiments in which the ethanol–water mixture is stripped by hot air microbubbles achieving around 98% vol. ethanol from the azeotropic mixture. The proposed model has been developed using Galerkin finite element methods to predict the temperature and vapor content of the gas microbubble as a function of its residence time in the liquid phase. This model incorporates a novel rate law that evolves on a time scale related to the internal mixing of microbubbles of 10–3s. The model predictions of a single bubble were shown to be in very good agreement with the existing experimental data, demonstrating that the ratio of ethanol to water in the microbubble regime are higher than the expected ratios that would be consistent with equilibrium theory for all initial bubble temperatures and all liquid ethanol mole fractions considered and w...

Spark discharge in conductive liquid with microbubbles

Pulse electrical breakdown in 15% water solution of Isopropyl alcohol with air microbubbles from a pointed anode has been studied experimentally. It is shown, that the breakdown is always initiated from the bright region near the anode (anode “spot”). Detailed investigation into dynamic current-voltage characteristics and synchronized images reveals that it is thermal instability in the near anode region that causes spark channel initiation and development. The breakdown voltage, spark channel propagation speed and short-circuit current increase when the microbubbles are presented in the solution. The spark channel propagation speed is about 4-12 m/s and grows along with microbubbles concentration.