Microbubble Generation Research Articles

Flexible microbubble-based Fabry–Pérot cavity for sensitive ultrasound detection and wide-view photoacoustic imaging

Interaction of acoustic waves and microbubbles occurs in numerous biomedical applications including ultrasound imaging, drug delivery, lithotripsy treatment, and cell manipulation, wherein the acoustically driven microbubbles routinely act as active microscale oscillators or actuators. In contrast, microbubbles were utilized here as passive receivers to detect broadband ultrasound waves in aqueous environments. The microbubble was photothermally generated on a microstructured optical fiber (MOF) tip, forming a flexible Fabry–Pérot cavity whose gas–water interface was sensitive to ultrasound waves. The MOF severed as both a low-loss waveguide and a compact light condenser, allowing high-efficiency generation and stabilization of ultrasmall microbubbles. Integrated with all-fiber interferometry, a 10 μm diameter microbubble exhibited a low noise-equivalent pressure level of ∼ 3.4 mPa / Hz 1 / 2 and a broad bandwidth of ∼ 0.8 MHz , capable of detecting weak ultrasounds emitted from red blood cells irradiated by pulsed laser light. With advantages of high sensitivity, compact size, and low cost, the microbubble-based ultrasound sensor has great potential in biomedical imaging and sensing applications.

Dissolution enhancement of reactive chemical species by plasma-activated microbubbles jet in water

Plasma activated water (PAW) has emerged as a viable technique for sterilization process since it contains some long-lived reactive oxygen and nitrogen species along with some very short-lived but strong oxidation agents such as hydroxyl radical (OH*) and superoxide anion (O2−). However, the concentrations of the reactive species such as nitrite, nitrate, and ozone are often insufficient in water for sterilization, or only a small amount of PAW can be generated. In this study, we developed a state-of-the-art approach by combining microbubbles (MBs) and plasma technology in a water recirculation system to enhance the dissolution of reactive species in a large amount of water. The investigations included plasma absorbing power measurement, visualization of plasma-activated microbubbles (PAMBs) generation, bubble size distribution, and the concentration measurements of various reactive species in water, after the air plasma jet and the PAMBs jet treatments, respectively. The results revealed that the plasma absorbing power efficiency could reach up to 71.7% for both plasma jet and PAMBs jet cases, respectively. For the PAMBs jet, the mean equivalent diameter of the bubble was estimated to be 290 μm. The results of the concentrations of chemical species such as nitrite and ozone in PAMBs water could be increased up to twice as high as compared to PAW using the proposed device. Moreover, the concentration of nitrate in PAMBs water was found to be nearly three times greater than that in PAW. Thus, we found that employing the PAMBs jet can significantly increase the concentrations of chemical species in water, which could considerably widen the application.

Intensification of fine apatite flotation with microbubble generation and inclined plates in the flotation column

Microbubbles have received great interest in the flotation of fine particles. A membrane distributor is developed to generate microbubbles for the flotation of fine apatite particles. Massive microbubbles are continuously formed under the shear flow in the membrane tube. Compared with a Venturi tube the membrane distributor achieves better performance in P2O5 recovery and grade. The effects of superficial gas velocity and collector concentration are investigated. It is found that there exists an optimal superficial gas velocity at which the large P2O5 recovery is obtained. The high P2O5 recovery and grade benefit from large concentration of sodium oleate. To further improve the performance of the flotation column, computational fluid dynamics (CFD) simulation is performed to reveal the gas-liquid flow influenced by inclined plates. The spatial pattern of the bubbles is photographed by a high-speed camera and reasonably characterized by the CFD results. Introducing the inclined plates in the column improves the P2O5 recovery. Both experimental observation and simulated data demonstrate that the inclined plates result in the slow circulating flow below the inclined plate. Good bubble-liquid segregation makes the entrained bubbles move upward into the overflow.

Chemical Microrobots as Self-Propelled Microbrushes against Dental Biofilm

Mouths offer the perfect environments for microbial cell formation, promoting the growth of biofilms, for example, on teeth. Dental biofilm exhibits strong resistance to antibiotics and is a cause of many dental diseases. Common strategies for dental biofilm removal involve the addition of high concentrations of hydrogen peroxide (H 2 O 2 ), which increases tooth sensitivity, or mechanical procedures. Here, we report a different approach based on self-propelled micromachines with high antibacterial activity for the degradation of dental biofilm. Such microrobots use low concentrations of fuel for their propulsion, and they achieve an efficient dental biofilm disruption in only 5 min of treatment. Moreover, these microrobots are biocompatible with epidermal and organ cells and may stimulate the immune system to fight against microbial infection. This approach of exploiting the active motion of bubble-propelled catalytic micromachines for oral biofilm disruption may open the door for more efficient and sophisticated treatments in dentistry. The ability of catalytic microrobots to disrupt dental biofilm is demonstrated 95% killing efficiency is obtained after 5 min of treatment The biocompatibility of these microrobots with epidermal and organ cells is confirmed Autonomous self-propelled tubular microrobots based on titanium dioxide decorated with platinum nanoparticles were developed by Villa et al. for the degradation of dental biofilm strains. The killing ability of these micromachines is attributed to their antibacterial activity and the continuous generation of microbubbles at the biofilm surface.

Monodispersed microbubble production using modified micro-Venturi bubble generator

This paper presents an innovative method to produce controlled monodispersed bubbles using a modified micro-Venturi channel. The influence of flow control parameters such as liquid pressure and gas flow rate on the controlled generation of micro-bubbles was investigated. Experiments were conducted in a transparent modified micro-Venturi channel, having a depth of 40 μm, in which monodispersed gas bubbles were generated. The proposed design provides a new configuration to produce monodispersed microbubbles. Image analysis focused at the vena-contracta region showed that the geometry of generated microbubbles change suddenly from an ellipsoidal shape to a circular shape having a constant diameter. The dynamics of the bubble breakup mechanism in a modified micro-Venturi channel has been described. It was observed that the velocity and the size of the micro-bubbles were strongly dependent on the flow control parameters. The bubble frequency was linearly increasing with respect to gas mass flow rates.

Optimization of Orifice Shape and Oscillatory Displacement of an Ultrasonic Microbubble Generator to Increase Microbubble Yield

Optimization of Orifice Shape and Oscillatory Displacement of an Ultrasonic Microbubble Generator to Increase Microbubble Yield

Self‐Oscillation of Locally Heated Water Vapor Microbubbles in Degassed Water

AbstractThe self‐oscillation of water vapor microbubbles in degassed water is experimentally investigated by using the photothermal conversion effect of an FeSi2 thin film. A laser spot on the FeSi2 thin film is used as a heat resistant and localized heat source with flexible size and power. The local heating of the degassed water leads to the generation of a water vapor microbubble, which shows self‐oscillation at 0.1–0.7 MHz under continuous heating. The bubble oscillation frequency shows the maximum value when the absorbed power density reaches 1 mW µm−2 ( = 1 × 109 W m−2), regardless of the laser spot size. This value is close to the critical heat flux for highly subcooled boiling of water. The anomalous dependence of the self‐oscillation frequency on the input power density is explained by the transition from nucleate boiling to local film boiling. Additionally, a numerical analysis suggests that the bubble oscillation exceeding 1 mW µm−2 is attributed to the dried region on the laser spot and the periodic contact of the liquid water to the small heater. These results are useful for understanding and enhancing the flow generated around the water vapor bubble, and the design of microscale cooling devices.

Bubble breakup in a swirl-venturi microbubble generator

We present a novel swirl-venturi microbubble generator enabled by tangential inlets in this work, and employ a high-speed camera to obtain breakup phenomena of a single bubble in both the venturi microbubble generator and the swirl-venturi microbubble generator. We observe three different breakup patterns (i.e., tensile breakup, dynamic erosive breakup, and static erosive breakup) in swirl-venturi microbubble generator, while in venturi microbubble generator only tensile breakup exists. Furthermore, both tensile breakup and dynamic erosive breakup appear less frequently with increasing liquid velocity in the swirl-venturi microbubble generator, while static erosive breakup tends to dominate. CFD simulations of liquid flow field show the existence of an apparent vortex region near the wall of the diverging section in the SVMG, which is the essential cause of the erosive breakup of bubbles. Statistical analysis results reveal that the location of bubble initial breakup in the venturi microbubble generator is close to the central axis, while in swirl-venturi microbubble generator it is near the wall and more concentrated. The swirl-venturi microbubble generator performs better than conventional venturi microbubble generators, providing a new idea for strengthening bubble breakup under high gas-liquid ratios.

Simultaneous Removal of NO and SO2 with a Novel Oxidation-Absorption Process Based on Air Microbubble Water System

Microbubbles (MBs) can spontaneously generate hydroxyl radicals (·OH) with high oxidizing capacity. In this study, a novel oxidation-absorption process based on a microbubble system in the indirect removal mode was proposed for the simultaneous removal of nitric oxide (NO) and sulfur dioxide (SO2). In this process, an air microbubble water system (AMBW) was produced by a microbubble generator (MBG) inhaling air and tap water and injected into an oxidation-absorption column reactor by the MBG, meanwhile the mixed gas composed of NO and SO2 passed through a micron-sized gas distributor at the bottom of the reactor and flowed into the AMBW. Important parameters including initial pH and temperature of tap water, operation time, NO concentration, SO2 concentration, and NaCl concentration were assessed to investigate the feasibility of the AMBW for the simultaneous removal of NO and SO2. The results showed that ·OH generated from the collapsed MBs played a critical role in the removal and the simultaneous removal of NO and SO2 was successfully achieved with the AMBW. Even with only tap water used as the absorbent, the removal efficiencies of NO and SO2 reached 92.7% and above 99%, respectively, when the experiment conditions were initial water pH 11.5, initial water temperature 298 K, 600 ppm NO, and 3,000 ppm SO2. Compared with the microbubble system in the direct removal mode, this new system is more suitable for the treatment of flue gases with low NO concentration and high volume. Moreover, this novel process should have a good prospect of industrial application in the flue gas treatment due to its high efficiencies of desulfurization and denitration and some advantages such as low usage cost of the reagents, simple system, and small occupation space.

Performance comparison of swirl-venturi bubble generator and conventional venturi bubble generator

The bubble generation performance and liquid volumetric mass transfer coefficient kLa of the venturi microbubble generator and the swirl-venturi microbubble generator were evaluated through the high-speed photography and measurement of dissolved oxygen concentration. The results show that the swirl-venturi microbubble generator generates more bubbles with smaller Sauter mean diameter than the venturi microbubble generator. And the maximum stable bubble size of the swirl-venturi microbubble generator is also smaller than that of the venturi microbubble generator. Moreover, the maximum stable bubble size of the swirl-venturi microbubble generator is not sensitive to the increase of superficial gas velocity, which indicates that the swirl-venturi microbubble generator has a higher probability of breaking bubbles. Eventually, the liquid volumetric mass transfer coefficient kLa of swirl-venturi microbubble generator is measured and higher than that of the venturi microbubble generator at high superficial gas velocity. Based on all above, it can be concluded that the swirl-venturi microbubble generator is a more effective way to generate microbubbles.

Influence of Excess Biological Sludge Disintegration Processes on Pharmaceutical Compounds, Hormones and PAH Concentrations from Anaerobic Stabilized Sludge

This paper shows the influence of certain biological sludge disintegration processes over the concentrations of emerging pollutants, including classes of structurally different compounds such as pharmaceuticals, hormones and polycyclic aromatic hydrocarbons from anaerobic stabilized sludge. Three processes for sludge disintegration were tested: ultrasonic, ultrasonic + electrokinetic and ultrasonic + electrokinetic + microbubble generation. Activated sludge from an urban wastewater treatment plant was used in the experiments. Both pharmaceuticals from the analgesic and antipyretic classes, as well as the identified hormones (estrone) and polycyclic aromatic hydrocarbons (PAHs), were sensitive to the disintegration processes applied, the experimental results showing the decrease of their concentration correlated with the increase of the disintegration energy.

Parameters Optimization of Catalytic Tubular Nanomembrane-Based Oxygen Microbubble Generator.

A controllable generation of oxygen gas during the decomposition of hydrogen peroxide by the microreactors made of tubular catalytic nanomembranes has recently attracted considerable attention. Catalytic microtubes play simultaneous roles of the oxygen bubble producing microreactors and oxygen bubble-driven micropumps. An autonomous pumping of peroxide fuel takes place through the microtubes by the recoiling microbubbles. Due to optimal reaction–diffusion processes, gas supersaturation, leading to favorable bubble nucleation conditions, strain-engineered catalytic microtubes with longer length produce oxygen microbubbles at concentrations of hydrogen peroxide in approximately ×1000 lower in comparison to shorter tubes. Dynamic regimes of tubular nanomembrane-based oxygen microbubble generators reveal that this depends on microtubes’ aspect ratio, hydrogen peroxide fuel concentration and fuel compositions. Different dynamic regimes exist, which produce specific bubble frequencies, bubble size and various amounts of oxygen. In this study, the rolled-up Ti/Cr/Pd microtubes integrated on silicon substrate are used to study oxygen evolution in different concentrations of hydrogen peroxide and surfactants. Addition of Sodium dodecyl sulfate (SDS) surfactants leads to a decrease of bubble diameter and an increase of frequencies of bubble recoil. Moreover, an increase of temperature (from 10 to 35 °C) leads to higher frequencies of oxygen bubbles and larger total volumes of produced oxygen.

Assessing the efficacy of dissolved air and flash-pressurized flotations using low energy for the removal of organic precursors and disinfection byproducts: a pilot-scale study.

Dissolved air flotation (DAF) is a widely used treatment process in drinking water and wastewater treatment plants despite high energy cost associated with operation and maintenance (accounts 50% of the total annual operation cost). In recent years, the focus has been diverted to optimizing or reducing energy, and a microbubble generation without a saturator was developed and used in small treatment facilities because of its simple structure. Thus, in this study, DAF and low-energy flash-pressurized flotation (FPF) efficacies were investigated in a pilot plant based on organic precursors, different molecular weight (MW) fractions, and disinfection byproduct reduction. The organic fractions with different MW was analyzed by liquid chromatography-organic carbon detector. Both DAF (550kPa) and FPF (300kPa) showed similar removal of dissolved organic carbon (DOC) and chromatographic DOC; however, the removal tendency of different MW fractions found was different. There was no significant difference in the removal of biopolymers, building blocks, and low molecular weight (LMW) neutrals for both DAF and FPF. Interestingly, the removal of LMW acids was found to be higher (93.8%) for DAF, whereas only 35.8% removal was observed for FPF. The total trihalomethanes concentration in a DAF-treated water sample was found to be 10% lower than that of FPF. Also, the reduction in haloacetonitriles was found to be slightly higher for a water sample treated by using DAF than by using FPF (1.5 and 1.8μgL-1, respectively). Moreover, the formation of chloral hydrate was observed to be the same (1.9μgL-1) for DAF- and FPF-treated water, with a total reduction of 40.6%. FPF with low pressure enabled a reduction in energy of around 55% when compared with DAF. Thus, FPF with low-pressure energy provides an alternative to DAF by reducing the annual operation cost and carbon footprint.

Effect of Fine Bubbles on Removal of Linear Alkyl Benzene Sulfonate Surfactant during the Rinsing Stage of Laundry Washing

AbstractThe use of fine bubbles is a promising approach to remove surfactant efficiently during the rinsing process of clothing, to fulfill a requirement. Therefore, the influence of fine bubbles on the removal performance of surfactant from cloth during the rinse process of pulsator washing machine (top loading type) was investigated. The test apparatus was assembled by connecting a microbubble generation tank and a small washing machine with tubes and circulating fine bubble water to a small washing machine. Swatches of cloth with a specified amount of linear alkylbenzene sulfonate (LAS) adsorbed from aqueous solution, were rinsed with tap water, and the LAS concentration in the rinse water was examined with an HPLC system equipped with a high‐precision fluorescence detector. The average bubble diameter of the fine bubble water used was 0.13–1.4 μm. In the rinsing experiment, no difference was found in the final LAS removal efficiency between water with and without bubbles; but the former increased the LAS removal rate during the initial stage of rinsing. This tendency was particularly noticeable when the stirring power of the washing machine was weak. Therefore, it was concluded that the fine bubble effect on the removal of the surfactant is mainly a kinetic effect rather than an equilibrium effect.

Effortless separation of transparent adhesive films using phase-change core-shell nanocapsules

Effortless separation without damage to the substrates is highly advantageous for the recovery and recycling of expensive electronic components in display devices. In this study, we present an approach for separating transparent adhesive films from substrates using phase-change core-shell nanocapsules. The nanocapsules are prepared from poly(methyl methacrylate) (PMMA) nanoparticles via the encapsulation of methylcyclohexane (MCH). The evaporated MCHs facilitated the detachment of adhesive films through micro-bubble generation after thermal treatment, leading to the effortless separation of the adhesive layer. The newly fabricated adhesive film with phase-change nanocapsules resulted in high transmittance, with an excellent debonding efficiency after thermal treatment.

Effects of the Microbubble Generation Mode on Hydrodynamic Parameters in Gas–Liquid Bubble Columns

The hydrodynamics parameters of microbubbles in a bubble column were studied in an air–water system with a range of superficial gas velocity from 0.013 to 0.100 m/s using a differential pressure transmitter, double probe optical fiber probe, and electrical resistance tomography (ERT) technique. Two kinds of microbubble generators (foam gun, sintered plate) were used to generate microbubbles in the bubble column with a diameter of 90 mm, and to compare the effects of different foaming methods on the hydrodynamics parameters in the bubble column. The hydrodynamic behavior of the homogeneous regime and the transition regime was also studied. The results show that, by changing the microbubble-generating device, the hydrodynamic parameters in the column are changed, and both microbubble-generating devices can obtain a higher gas holdup and a narrower chord length distribution. When the foam gun is used as the gas distributor, a higher gas holdup and a narrower average bubble chord length can be obtained than when the sintered plate is used as the gas distributor. In addition, under different operating conditions, the relative frequency distribution of the chord length at different radial positions is mainly concentrated in the interval of 0–5 mm, and it is the highest in the center of the column.

Separation of chemically modified carbon nanotubes by surfactant free microbubble generation

Bubble separation is a widely used and effective method for separating solids from liquids. In this study, we propose a method to generate roughly ∼104 microbubbles/μl in an ethanol–water solution (surfactant-free) by subjecting the container of the solution to impact. Hydrophobic carbon nanotubes (CNTs) and hydrophilic carboxylated CNTs can be rapidly separated by the process of attachment of CNTs to rising microbubbles. More than 90% of hydrophobic CNTs can be collected on the top layer of the solution by microbubbles generated in the ethanol solution. The proposed mechanism of bubble enhancement material separation in ethanol solution is because of the effect of hydrophobic surfaces of surfactant-free microbubbles, while normal microbubbles in a surfactant solution have hydrophilic surfaces. CNTs can be separated from the solution by microbubbles with hydrophobic surfaces. The results show that the use of surfactant-free microbubbles can achieve high efficiency of recovery of CNTs in a short time, which provides a potential method for the separation of different materials based on their surface properties.

Optothermal generation, trapping, and manipulation of microbubbles.

The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pulsed laser (λ = 532 nm) at silver nanoparticles photodeposited at the distal end of a multimode optical fiber. Light absorbed from each laser pulse quickly heats up the silver-ethanol interface beyond the ethanol critical-point (∼ 243 °C) before the heat diffuses through the liquid. Therefore, the liquid achieves a metastable state and owing to spontaneous nucleation converted to a vapor bubble attached to the optical fiber. The bubble grows with semi-spherical shape producing a counterjet in the final stage of the collapse. This jet reaches the hot nanoparticles vaporizing almost immediately and ejecting a microbubble. This microbubble-generation mechanism takes place with every laser pulse (10 kHz repetition rate) leading to the generation of a microbubbles stream. The microbubbles' velocities decrease as they move away from the optical fiber and eventually coalesce forming a larger bubble. The larger bubble is attracted to the optical fiber by the Marangoni force once it reaches a critical size while being continuously fed with each bubble of the microbubbles stream. The balance of the optothermal forces owing to the laser-pulse drives the 3D manipulation of the main bubble. A complete characterization of the trapping conditions is provided in this paper.

All-Optical Formation and Manipulation of Microbubbles on a Porous Gold Nanofilm.

Microbubble generation and manipulation in aqueous environments are techniques that have attracted considerable attention for their microfluidic and biological applications. Ultrasonic and hydrodynamic methods are commonly used to form and manipulate microbubbles, but these methods are limited by the relatively low precision of the microbubble sizes and locations. Here, we report an all-optical method for generation and manipulation of microbubbles with ~100 nm precision by using “hot spots” on a porous gold nanofilm under the illumination of near-infrared focused laser beam. The microbubble diameter ranged from 700 nm to 100 μm, with a standard deviation of 100 nm. The microbubbles were patterned into two-dimensional arrays, with an average location deviation of 90 nm. By moving the laser beam, the microbubbles could be manipulated to a desired region. This work provides a controllable way to form and manipulate microbubbles with ~100 nm precision, which is expected to have applications in optofluidic and plasmonic devices.

APLIKASI MICROBUBBLE GENERATOR POROUS-VENTURI PADA PENGOLAHAN AIR LIMBAH BUATAN

Abstrak
 Keterbatasan air bersih akibat terjadinya pencemaran air dari limbah rumah tangga dan industri maka perlu mengembangkan sebuah alat teknologi pengolahan air limbah yang ramah lingkungan dan instalasi yang mudah. Microbubble generator (MBG) digunakan untuk menghasilkan oksigen yang diperlukan oleh bakteri untuk melakukan dekomposisi air limbah. Pada penelitian ini didesain MBG porous-venturi dipasang pada kolam air limbah buatan. Parameter yang akan diukur koefisien perpindahan massa (KLa), kadar dissolved oxygen (DO) dan chemical oxygen demand (COD). Nilai KLa diukur dengan menggunakan DO meter yang dipasang sejauh 60 cm dan 180 cm dari MBG. Debit air diatur 30-80 lpm dan debit gas 0,1, 0,4 dan 1 lpm. Berdasarkan hasil penelitian, kenaikan debit air pada semua jarak pengukuran menyebabkan nilai KLa semakin naik, namun kenaikan debit gas tidak mempengaruhi secara signifikan. Nilai DO yang semakin tinggi akan mengurangi kadar COD dalam air limbah buatan dibawah 100 mg/L.
 Kata kunci: Microbubble, venturi, DO, COD, KLa