Microbubble Generation Research Articles

Microbubble generation with rapid dissolution of ammonia (NH3)-hydrogen (H2) mixed gas fed from a nozzle into water

Because of their useful characteristics, microbubbles attracted much interest in industry and medicine. In this study, we developed a novel method of generating microbubbles through the chemical absorption of ammonia (NH3). By using an ultrahigh-speed camera, consecutive images of bubble formation were captured, and the microbubble generation mechanism was investigated. The effects of the gas flow rate and ammonia concentration in the liquid phase on the size of the microbubbles were examined. The hydrogen (H2) gas flow rate was found not to demonstrate a significant effect on the bubble diameter. The diameter of the microbubbles increased as the superficial velocity of the gas mixture (NH3 – H2) decreased.

Controlled generation of single microbubbles

Controlled generation of single microbubbles

Microbubble generation driven by the oscillation in a self‐excited fluidic oscillator

AbstractThe oscillation‐driven microbubble generation in a self‐excited fluidic oscillator is explored in this work. By investigating the behaviors of bubbles, it is noted that for relatively low liquid flow rate, bubbles move upward directly and breakup does not occur inside the chamber region. Interestingly, the existence of bubbles could destroy the structure of flow field and even affect the oscillation. Nevertheless, for relatively high liquid flow rate, the bubbles would not be able to change the flow field structure of liquid phase effectually. Meanwhile, binary, shear‐off‐induced and a kind of dynamic erosive breakup of the bubbles could occur for the effects of oscillations of liquid main jet. Abundant microbubbles could be produced mainly by the dynamic erosive breakup. The oscillation is only induced by the Coanda effect without any moving parts. Nevertheless, it is able to supply a robust oscillating turbulent field to enhance the breakup of bubbles dramatically.

Preparation of microbubbles with the generation of Dean vortices in a porous membrane

A platform based on gas–liquid membrane dispersion with helical internals inserted is developed for microbubble generation. The effects of internals on microbubble size are investigated, including circular, helical, twisted, and polygonal geometries. Parametric studies are conducted by varying the liquid flow velocity, liquid physical properties, geometric shape, helical pitch and thickness. Compared with membranes developed with other internals inserted, the membrane with helical internals has the highest performance for microbubble generation. The size of microbubbles decreases with increasing helical pitch and decreasing helical thickness in different liquid phases. CFD simulation is used to reveal the flow field with internals inserted into the membrane, which indicates that Dean vortices are effectively generated by inserting helical internals. An empirical correlation describing the microbubble size in the metallic membrane is developed considering the contribution of the gas–liquid ratio, capillary force and Dean vortices, showing good agreement with experimental data.

IMPROVEMENT OF THE MICROFLUIDIC DEVICE FOR THE GENERATION OF MONODISPERSE MICROBUBBLES AS DRUG TRANSPORT SYSTEMS

INTRODUCTION: The localized delivery of drugs has been established since the early eighties of the 20th century as a promising alternative for the localized treatment of tumours, based on the mitigation of side effects produced by traditional methods, notably the administration of chemotherapy by systemic route. Countless scientific works have been dealing with this theme in an attempt to make this therapeutic technique viable and accessible. One of the ways to take the drug to the chosen site is through the use of microbubbles as drug carrier units activated through an ultrasonic field with adequate wavelength and frequency. Therefore, these units must have very peculiar characteristics, such as dimensions, homogeneity, echogenicity and structural characteristics, in addition to the ability to take the therapeutic vector intact to the desired location. In the generation of microbubbles, microfluidic devices of different geometries and different configurations are used, according to the state of the art related to this theme. DEVELOPMENT: In this work the technique used is the fabrication of micro fluidic devices using 3D printing. With this technique, it is possible to manufacture the devices in a single step, eliminating time-consuming and more complex intermediate procedures. The devices were manufactured using an Object Eden 250 printer, using the transparent resin VeroClear®. With these devices it was possible to produce microbubbles with diameters of the order of 16-73 µm with degrees of poly dispersion less than 1%. However, there are difficulties to be overcome, notably with regard to the final composition of the devices. Due to the physical characteristics of the microbubble, notably in relation to its lipid coating layer, the search for drug transport systems is an important strategy. CONCLUSION: In this work, an account of these difficulties will be made, in addition to the proposition of alternatives to overcome them. Additionally, compatible drugs will be suggested to be attached to microbubbles according to their structural composition.

In search of a Mpemba effect protocol: Some hot water does cool and freeze faster than cold

Zimmerman [Chem.Eng.Sci. 238: 116618, 2021] developed a theory for additional convection of latent heat by microbubbles from regions of hot water to regions of cold water, a modified heat transport equation that incorporates this convective effect, and a scaling analysis that gives a rough prediction for how this additional heat transfer is proportional to the phase fraction of microbubbles. This theory is supported by arguing that Mpemba and Osborne (1969) had such microbubbles dispersed, resulting in a strong correlation between the dissolved gas solubility at saturation, dependent on the sole controlled variable – the initial temperature of the freezing experiment – and the inferred heat transfer coefficient. The argument was made that the source of the microbubbles was exogeneous due to vigorous boiling. In this paper, a range of systematic errors and uncertainties concerning the Mpemba effect is explored. The two largest uncontrolled variables are the level of vigorous boiling and the level of dissolved gases in tap water. Using the same approach for estimation of the heat transfer coefficients, the experiments of Bregovic (2012) which had no boiling are analyzed. The resulting heat transfer coefficients are shown to pass the accepted Mpemba line criteria for the occurrence of a Mpemba effect. Employing the scaling analysis for additional heat transfer shows reasonable agreement with the hypothesis that source of microbubbles in Bregovic’s experiments is endogeneous: the saturation-nucleation mechanism for spontaneous growth of microbubbles in supersaturated water. The parallel analysis applied to the experiments of Mpemba and Osborne show consistency with predictions of endogenous microbubble generation, too.

A classifier design for micro bubble generators based on deep learning technique

This paper aims to study the sizes of bubbles generated by the micro-bubble generator device (MBGs) in the water because of its impact on the dissolved oxygen percentage in the water and we find this in aquaculture where oxygen is important for marine life and in many applications. Where we have designed a classifier for micro-bubbles of different sizes and the effectiveness of the device has been proven in generating bubbles whose size ranges from 20 to 50 and calculating their numbers in the image by converting the image from (RGB) to (HSV), it has proven its effectiveness in maintaining lighting and neglecting color information Which is not important in identifying bubbles in the image, as well as increasing the processing speed, and then finding edges in the image, using canny edge detection, which has proven its great effectiveness in finding weak and strong edges. Where we then used the (Circular Hough Transform) algorithm to identify the tiny bubbles in the image, calculate their average diameter and numbers in the image, and find the overlapping bubbles between them by using (Two Thresholds) one for the edge and the other for the center of the bubble and then making (Segmentation) for these bubbles and inserting them on (Gaussian Normal Distribution) Do not neglect the dark bubbles, because in most cases they are unreal bubbles and may be distortions in the image or reflections in the lighting. And then make (zero paddings) for the extracted images to make them equal in size and avoid the distortion that will happen in the image if another method is used to make all bubbles of equal dimensions to prepare them for classification. And then we calculated the (mean square error) of the resulting bubble images to avoid repeating the same bubble in (datasets). The efficiency of the classifier was calculated by using deep learning technology. Where we built a (Convolution Neural Network) consisting of (15) layers and then we trained these layers on the images resulting from the (CHT), which are individual bubbles, each of them classified according to size. The dataset was divided into two parts, 70% of which is for education and the remaining 30% is for (validation), and the test percentage is 100%.

An investigation on the bubble transportation of a two-stage series venturi bubble generator

In this paper, we designed a new venturi bubble generator, which mainly consist of two serial rectangular perspex venturi channels with the same geometrical dimension. Visualization experimental method combined with digital image analysis was adopted to study the motion, deformation and breakup process of bubbles when the micro-bubble generator was installed vertically. The bubble foaming frequency which is defined as the amount of forming bubbles within one second from the air injection hole was significantly enhanced with the increase of water flow rate, but was not sensitively affected by the air flow rate. The discrete bubbles moved in a two-stage venturi channel and experienced collapse or breakup in the divergent section. The Sauter mean diameter of bubbles which recorded in each divergent outlet decreased gradually. The Reynolds numbers of water had a significant effect on the breakup characteristics of bubbles. With the increasing of Re, the bubbles experienced binary breakage and multiple breakup successively. Under the effect of complex turbulence vortex, the bubbles presented different breakup patterns in each stage. When Reth>19793, the bubble breakup ratio of the first stage divergent section was larger than that of the second stage, and the difference of the generated bubble Sauter mean diameter in each divergent outlet was minimized accordingly. The surface stability of the daughter bubble was enhanced, and it was difficult to breakup significantly under the effect of recirculation flow. The numerical simulation results by Computational Fluid Dynamics (CFD) indicated that the area of the vortex was increased for larger second stage divergent angle, which intensify the phase interaction and promote the possibility of sub-micron bubble breakup.

IDENTIFIKASI EFEKTIVITAS REAERASI MENGGUNAKAN MICROBUBBLE GENERATOR (MBG) PADA AIR EMBUNG

The retention basin at the Faculty of Engineering Gadjah Mada University was built as a flooding control into the Code river and improving the water quality. The water entering the basin, especially in the dry season, is characterized as greywater due to the dense settlements around the university. The purpose of this study was to determine the effectiveness of reaeration process using a Microbubble Generator (MBG) to increase DO, with the aim of this leading to an improved water quality. The MBG aerator with submersible pumps was installed at a depth of 40 cm from the water surface and placed in the middle of the pond. The aerator was permanently turned on. In situ monitoring of DO was carried out using a seri Lutron WA-2017SD DO meter. The increasing DO correlated with the changes of the surrounding weather which impact on water and air temperature. At the time of DO data collection, the water temperature ranged from 24.5oC - 27oC and the change in DO measured at the inlet and outlet of the reservoir was in the range 0.3 - 1.1 mg/l, with the DO directly surrounding the aerator reaching up to 2.4 mg/l from the inlet. With the DO increased, the concentration of pollutant organic loads can be reduced and the nitritation and nitratation processes has taken place properly so that it has reduced the pollutant load before the water enters the Code river.

Enhancing In Vitro Stability of Albumin Microbubbles Produced Using Microfluidic T-Junction Device.

Microfluidics is an efficient technique for continuous synthesis of monodispersed microbubbles. However, microbubbles produced using microfluidic devices possess lower stability due to quick dissolution of core gas when exposed to an aqueous environment. This work aims at generating highly stable monodispersed albumin microbubbles using microfluidic T-junction devices. Microbubble generation was facilitated by an aqueous phase consisting of bovine serum albumin (BSA) as a model protein and nitrogen (N2) gas. Microbubbles were chemically cross-linked using dilute glutaraldehyde (0.75% v/v) solution and thermally cross-linked by collecting microbubbles in hot water maintained at 368 (±2) K. These microbubbles were then subjected to in vitro dissolution in an air-saturated water. Microbubbles cross-linked with a combined treatment of thermal and chemical cross-linking (TC & CC) had longer dissolution time compared to microbubbles chemically cross-linked (CC) alone, thermally cross-linked (TC) alone, and non-cross-linked microbubbles. Circular dichroism (CD) spectroscopy analysis revealed that percent reduction in alpha-helices of BSA was higher for the combined treatment of TC & CC when compared to other treatments. In contrast to non-cross-linked microbubbles where microbubble shell dissolved completely, a significant shell detachment was observed during the final phase of the dissolution for cross-linked microbubbles captured using high speed camera, depending upon the extent of cross-linking of the microbubble shell. SEM micrographs of the microbubble shell revealed the shell thickness of microbubbles treated with TC & CC to be highest compared to only thermally or only chemically cross-linked microbubbles. Comparison of microbubble dissolution data to a mass transfer model showed that shell resistance to gas permeation was highest for microbubbles subjected to a combined treatment of TC & CC.

가압펌프와 공기포화탱크를 연계한 하이브리드형 미세기포 발생장치의 운전특성

Dissolved air flotation (DAF) process has been applied to the entire environmental fields. The micro-bubble generator, which is a key facility in DAF process, can be classified according to its generation methodology. In Korea, saturator and DAF-pump types are widely utilized. The feature of saturator type is the application of an air saturation tank (AST), and it has a disadvantage in that operation and maintenance are not easy due to relatively complicated facilities. On the other hand, DAF-pump type uses a micro-bubble generating pump (MGP) alone, so the device configuration is very simple, but the ranges of optimal operating conditions are narrow. In this study, a new hybrid-type microbubble generator has been developed by linking a pressure pump and an AST by converging the advantages of the existing saturator and DAF-pump types. As a result of examining the operation characteristics of this microbubble generator including operating pressure, air flow rate, water flow rate, power consumption, A/W ratio (air/water ratio), DO, and particle size distribution, the appropriate operating conditions could be determined as operating pressure of 4.0 - 6.0 kgf/㎠, air flow rate of 4.0 - 5.0 L/min, water flow rate of 57 - 68 L/min, and A/W ratio of 5.9 - 8.7%. The average diameter of the generated microbubbles showed a stable distribution in the range of 25.0 - 26.7 μm. Based on the above results, it could be verified that the novel hybrid-type microbubble generator had excellent performance at a level that can be applied to the field.

Dual-stimuli-responsive CuS-based micromotors for efficient photo-Fenton degradation of antibiotics

Antibiotics as emerging pollutants in water pose great risks to human health. Due to their persistence in the environment, advanced oxidation processes (AOPs) have been proposed for the degradation of antibiotics. Therefore, developing efficient catalysts for AOPs becomes critical for the removal of antibiotics. Herein, we develop self-propelled CuS-based micromotors (CuS@Fe3O4/Pt) as active heterogenous catalysts for efficient photo-Fenton degradation of antibiotics. Combining the merits of conventional heterogenous and homogenous catalysts, the prepared micromotors are easy to recycle and free of secondary pollution risks, while demonstrating high degradation efficiency due to self-induced intensification of mass transfer via autonomous motion and microbubble generation. The H2O2 in the Fenton reagents can serve as the fuel for the micromotors to drive their self-propulsion by bubbles generated from catalytic decomposition of H2O2 by the platinum layer. The dual-stimuli-responsiveness of the micromotors to magnetic field and light irradiation allows multi-modes of propulsion and guidance in different systems. The efficient photothermal effect of CuS enables the micromotors to achieve collective phototactic motion toward light, whereas magnetic responsiveness facilitates the recovery and collection of the micromotors. The synergistic effect of CuS and Fe3O4 NPs in H2O2 under visible light irradiation generates a large amount of OH· and ·O2– to effectively degrade tetracycline within several minutes. With these advantages, the dual-stimuli-responsive CuS-based micromotors provide a new strategy for enhanced degradation of antibiotics in water purification applications.

Optically Transparent Graphene Flakes as Nanogenerator of Microbubbles for Random Lasing in Weakly Scattering Regime

The minimization of photon loss is one of the significant challenges in designing efficient random lasers (RLs). Herein, the demonstration of a 4‐(dicyanomethylene)‐2‐methyl‐6‐(4‐dimethylaminostyryl)‐4H‐pyran (DCM) dye‐based RL is made by the employment of an innovative adaptive feedback mechanism through the use of a fundamental phenomenon of total internal reflection of light in the microbubbles, generated photothermally in the presence of graphene flakes (GFs). Interestingly, here, GFs have acted simultaneously as passive scatterer and thermocatalyst for in situ generation of microbubbles in the liquid suspension of dye molecules. It is demonstrated by a simple pump‐probe photography experiment that during RL emission, the transport of photons is occurring via weak scattering in GFs followed by total internal reflection on microbubbles. Thus, RL emission at 638.4 nm is achieved with a low lasing threshold, linewidth, and moderately high quality factor of 84 W cm−2, 2 nm, and 1127, respectively. The performances of GFs in RL generation are found to be superior in comparison with those of spherical TiO2 and Ag nanoparticles. The strategy is a contemporary approach for applying a 2D material as a nanogenerator of microbubbles to achieve improved RL emission in the weakly scattering regime using an adaptive feedback approach.

Electrochemically-active carbon nanotube coatings for biofouling mitigation: Cleaning kinetics and energy consumption for cathodic and anodic regimes

Biofouling is a major obstacle in engineered systems exposed to aqueous conditions. Many attempts have been made to engineer the surface properties of materials to render them resistant to biofouling. These modifications typically rely on passive antimicrobial or anti-adhesive surface coatings that prevent the deposition of bacteria or inactivate them once they reach the surface. However, no surface modification strategy completely prevents biofilm formation, and, over time, surfaces will be fouled and require cleaning. In this work, we demonstrate the capacity of electrochemical carbon nanotube coatings in dispersing biofilms formed on the surface. A systematic analysis of the biofilm removal kinetics in function of applied current density is made to identify the optimal current conditions needed for efficient surface cleaning. Operating the electrochemically active surface as a cathode produces superior results compared to when it is operated as an anode. Specifically, the 5.00 A m−2 and 2.50 A m−2 cathodic conditions produced rapid cleaning, with complete biofilm dispersal after 2 min of operation. Surface cleaning is attributed to the generation of microbubbles on the surface that scours the surface to remove the adhered biofilm. Energy consumption analyses indicate that the 2.50 A m−2 cathodic condition offers the best combination of cleaning kinetics and energy consumption achieving 99% biofilm removal at an energy cost of ~$ 0.0318 m−2. This approach can be competitive compared to the current chemical cleaning strategies, while offering an opportunity for a more sustainable and integrated approach for biofouling management in engineered systems.

Laser-induced controllable generation of micro-bubbles on water suspension of absorptive colloid particles

Micrometer-sized bubbles are formed in the water suspension with absorptive pigment particles due to local heating. The heating is performed by moderately focused CW nearinfrared laser radiation with controllable power. Depending on the laser power, regimes of the bubble generation, stable growth of the existing bubbles, stationary bubbles and their shrinkage and collapse are realized. The physical pattern is interpreted based on the temperature conditions in the suspension. We show the possibilities for generation of single bubbles as well as groups of bubbles with controllable sizes and numbers. The bubbles form quasi-ordered structures within the laser-illuminated region. They can be transported together with the focal spot. The results are useful for applications associated with the precise manipulation in nano- and micro-engineering problems.

Microbubble Generation in Organic Solvents by Porous Membranes with Different Membrane Wettabilities

Microbubbles have gained universal interest due to their wide applications in water treatment, cosmetics, and pharmaceutical industry and potential applications in gas–liquid reactions such as hydrogenation and oxidation. However, microbubble formation in organic solvents has been seldom investigated. A controllable and efficient platform is built to investigate microbubble formation in organic solvents using a hydrophilic ceramic membrane and a hydrophobic polytetrafluoroethylene (PTFE) membrane. The effect of membrane wettability on the size of microbubbles is studied with the change of the liquid property and membrane type. Experimental results show that the sizes of microbubbles are in ranges of 130–453 μm and 59–387 μm using the hydrophilic ceramic membrane and the hydrophobic PTFE membrane, respectively. Microbubbles generated in organic solvents using the hydrophilic ceramic membrane are much larger than those in water, and the size of microbubbles formed using the hydrophobic PTFE membrane shows an opposite trend. Furthermore, an equivalent pore is introduced to develop mathematical model to predict the microbubble size, which agrees well with the experimental data.

Oily water treatment in a multistage tower operated under a novel induced pre-saturation process in the presence of a biosurfactant as collector

The increase in water-oil separation efficiency as a function of biosurfactant in a novel process of a continuous induced pre-saturation tower (IPST) with stages was described. The pre-saturation of the effluent in a new IPST prior to its entrance in each stage enabled enhancing the effect of the biosurfactant on the flocculation of oil droplets due to the close contact with the air during the formation of microbubbles inside a centrifuge pump. This change of a conventional dissolved-air flotation device enabled each stage to serve as a final flocculation chamber and flotation separator. The initial flocculation step occurred nearly entirely within the centrifugation pump adapted for the generation of microbubbles. Experimental tests in a bench-scale prototype of an IPST enabled drafting two operation diagrams based on the absence and presence of the biosurfactant produced by the bacterium Pseudomonas cepacia CCT 6659. We used an effluent composed of water and semi-synthetic motor oil at 500 ± 13 mg L−1. The oil removal efficiency was estimated with the aid of Damköhler numbers applied under the analogy of considering the IPST to be a set of perfect-mixture tanks in series. To quantify the increase in efficiency achieved with the addition of the biosurfactant, we identified the kinetic laws corresponding to the addition and non-addition of the biosurfactant. The addition of the biosurfactant led to an increase in the oil removal rate in the IPST from 92.5 % to 97.0 %.

Degradation of dichloroacetic acid in a novel corona discharge reactor integrated with microbubbles generation

The development of feasible and environmentally friendly technologies to remove dichloroacetic acid (DCAA) from water is needed worldwide to reduce human exposure to this common disinfection byproduct and to minimize cancer risk. In this study, we reported a novel, independently designed water-recirculation-continuous- flow corona discharge reactor (WCD) with integrated microbubble (MB) generation for DCAA treatment. Compared with the performance of WCD or MBs alone, the integrated system (WCD/MBs) showed synergistic effects on DCAA degradation. The functional active species were confirmed to be •OH, •O2–, ONOO–, and e-. The effects of the discharge power, bubble size, and carrier gas were evaluated. At a discharge power of 22.9 W and a bubble size of 34.5 μm, the DCAA removal efficiency reached 76% after treatment for 120 min in the air-WCD/MBs reactor. Based on the intermediates detected by IC, GC–MS, and HPLC-QTOF, several DCAA degradation pathways were proposed, including H-abstraction, dechlorination, carbon–carbon bond cleavage, nitrogen dioxide radical reaction, and ipso attack by amine and azido groups. The WCD/MBs system can be applied to tap water, and its energy yield compares favorably with that of other technologies. The novel non-thermal plasma treatment system provides a sustainable and feasible solution for DCAA removal.

A Hybrid Device for Enhancing Flotation of Fine Particles by Combining Micro-Bubbles with Conventional Bubbles

Flotation in the mining industry is a very significant separation technique. It is known that fine and ultra-fine particles are difficult to float, leading to losses of valuable minerals, mainly due to their low collision efficiency with bubbles. Flotation of fine particles can be enhanced either by increasing the apparent particle size or by decreasing the bubble size. Literature review reveals that electroflotation resulted in higher recoveries of ultrafine particles as compared with dispersed-air flotation, because electrolytic bubbles are smaller in size. To this end, the best practical approach is to combine conventional air bubbles and micro-bubbles from water electrolysis. Therefore, the design, fabrication, and operation of a bench-scale micro-bubble generator through water electrolysis is proposed. Moreover, this electrolysis unit is adapted in a mechanical Denver-type flotation cell. The resulting hybrid flotation device is capable of producing bubbles within a wide range of diameters. The significance of this process is that micro-bubbles, attached tothe surface of fine particles, facilitate the attachment of conventional-sized bubbles and subsequently increase the flotation recovery of particles. Experimental flotation results so far on the hybrid device indicate the enhancement of fine particle recovery by approximately 10% with the addition of micro-bubbles.

The Effectiveness of Microbubble Technology in The Quality Improvement of Raw Water Sample

An experimental study to observe the performance of microbubble generator (MBG) and microbubble-generating nozzle on water is carried out under laboratory conditions. The MBG is used to treat wastewater from water bodies which was impacted by domestic and industrial wastewater. The study uses MBG with a spherical body and a drilled hole, along with a dispersing nozzle placed at the bottom of microbubble reactor tank. The MBG used is considered to be more applicable for water bodies rather than other types. Two types of pressure gauges are installed around the MBG and the nozzle in order to examine and configure the inlet water pressure and the inlet gas pressure based on the best microbubble size produced from a prior experiment. Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Total Suspended Solids (TSS), and Turbidity has been analyzed in the beginning and every 10 minutes of a 60 minute detention time to examine the effectiveness of MBG. The results of study shows the MBG have a high rate of removal percentage in a 60-minute retention time with 60 to 90% for TSS, up to 90% for Turbidity, 74 to 96% for BOD, and 41 to 59% for COD.