Microbubble Generation Research Articles

Performance evaluation of micro bubble generator on physiological response of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) farmed at different densities in recirculating aquaculture system

Micro-bubble generator is a device to maintain water quality by producing micron-sized bubbles. This study aims to evaluate the application of micro-bubble generator in different density on production performance and physiological response of nile tilapia reared in recirculating system. An experiment was designated by performing 3 densities, namely 15 , 30, and 45 individuals 60 L-1 with 3 replications. Every single unit of experiment applies a 34×42×41 cm3 maintenance container. The length size of fish used in this study was 7.44±2.89 cm and body weight of 10,96 ± 0,53 g. Fish were reared for 42 days in recirculation water system and fed ad satiation. The results of the evaluation of the physiological response showed that fish kept at density up to 45 60 L-1 did not show any changes, indicating that fish was in stress condition. The best production performance was in treatment A (15 individuals 60 L-1) with a specific growth rate of 1.87 ± 0.15% and a feed conversion ratio of 0.95 ± 0.08.

Effect of Throat Size on Performance of Microbubble Generator and Waste Water Treatment

Microbubble can be widely applied to many fields such as waste water treatment from community, industry and agricultural. This study focus on set up experimental apparatus of microbubble generation to examine the optimum ratio between air to water for generating the best microbubble by using three different sizes of venturi with throat diameters of 3mm, 4mm and 5mm, respectively; and also for apply microbubble to treat community waste water. The venturi with throat diameter of 3mm can generate more microbubble than the other. When applied microbubbles to treat the sampling of the waste water, chemical oxygen demand (COD) of waste water was considered.

마이크로버블 발생을 위한 벤추리 노즐 형상 연구

Microbubble is a part of advanced water treatment technologies, and there are several ways for microbubble generation. A strategy using Venturi (convergent-divergent) nozzle with air-suction holes has advantage of energy and time saving compared with the others. Here, we used 3D printer to make the various nozzle geometries in order to understand two-phase flow in the Venturi nozzle and air-breaking mechanism. It was evaluated the effects of convergent and divergent angles independently on air-suction rate and pressure drop, and the two-phase flow (air bubbles and liquid water) were observed. The convergent angle strongly affect the air-suction rate corresponding with increase of pressure drop. Meanwhile, as the divergent angle increased, it became dominant the minor loss by sudden enlargement of flow area, so that the air-suction rate and pressure drop showed decreased.

Generation of microbubbles in extracorporeal life support and assessment of new elimination strategies.

Occurrence of microbubbles (MB) is a major problem during venoarterial extracorporeal life support (ECLS) with partially severe clinical complications. The aim of this study was to establish an in vitro ECLS setup for the generation and detection of MB. Furthermore, we assessed different MB elimination strategies. Patient and ECLS circuit were simulated using reservoirs, a centrifugal pump, a membrane oxygenator, and an occluder (modified roller pump). The system was primed with a glycerin solution of 44%. Three different revolution speeds (2500, 3000, and 3400rpm) were applied. For MB generation, the inflow line of the pump was either statically or dynamically (15rpm) occluded. A bubble counter was used for MB detection. The effectiveness of the oxygenator and dynamic bubble traps (DBTs) was evaluated in regard to MB elimination capacities. MB generation was highly dependent on negative pressure at the inflow line. Increasing revolution speeds and restriction of the inflow led to increased MB activity. The significant difference between inflow and outflow MB volume identified the centrifugal pump as a main source. We could show that the oxygenator's ability to withhold larger MB is limited. The application of one or multiple DBTs leads to a significant reduction in MB count and overall gas volume. The application of DBT can significantly reduce the overall gas volume, especially at high flow rates. Moreover, large MB can effectively be broken down for faster absorption. In general, the incidence of MBs is significantly dependent on pump speed and restriction of the inflow. The centrifugal pump was identified as a major source of MB generation.

Dispersed air flotation of microalgae using venturi tube type microbubble generator

To evaluate biodiesel production from microalgae, a flotation experiment was conducted using the living cell culture fluid of the diatom Chaetoceros gracilis using a venturi tube type microbubble generator. We compared the separation performance of three different culture periods: 1, 2, and 3 weeks from the start of cultivation. After 1 week, the cells were in the logarithmic growth phase, while after 2 and 3 weeks, cell growth had reached the stationary phase. The amounts of triacylglycerol (TAG) in the foam on the surface of the fluid tank were measured. TAG increased during the first 20 min after the start of circulation without additional coagulants and pH adjustment. The disruption of cells was achieved simultaneously. The amounts of TAG in the culture fluids at weeks 2 and 3 were higher than those at week 1. C. gracilis cells in the stationary phase accumulated large amounts of TAG and were easy to disrupt by pressure fluctuation in the venturi tube. These results provide insight into the fracture strength and buoyance of cells for efficiently separating the cells from large volumes of culture fluid.

Ultrasound‐Assisted Drug Delivery: Microneedle‐Based Generation of Microbubbles in Cancer Tumors to Improve Ultrasound‐Assisted Drug Delivery (Adv. Healthcare Mater. 17/2019)

Ultrasound‐Assisted Drug Delivery: Microneedle‐Based Generation of Microbubbles in Cancer Tumors to Improve Ultrasound‐Assisted Drug Delivery (Adv. Healthcare Mater. 17/2019)

T-Shaped Microfluidic Junction Processing of Porous Alginate-Based Films and Their Characteristics.

In this work, highly monodisperse porous alginate films from bubble bursting were formed on a glass substrate at ambient temperature, by a T-shaped microfluidic junction device method using polyethylene glycol (PEG) stearate and phospholipid as precursors in some cases. Various polymer solution concentrations and feeding liquid flow rates were applied for the generation of monodisperse microbubbles, followed by the conversion of the bubbles to porous film structures on glass substrates. In order to compare the physical properties of polymeric solutions, the effects of alginate, PEG stearate (surfactant), and phospholipid concentrations on the flowability of the liquid in a T-shaped microfluidic junction device were studied. To tailor microbubble diameter and size distribution, a method for controlling the thinning process of the bubbles’ shell was also explored. In order to control pore size, shape, and surface as well as internal structure morphologies in the scalable forming of alginate polymeric films, the effect of the feeding liquid’s flow rate and concentrations of PEG-stearate and phospholipid was also studied. Digital microscopy images revealed that the as-formed alginate films at the flow rate of 100 µL·min−1 and the N2 gas pressure of 0.8 bar have highly monodisperse microbubbles with a polydispersity index (PDI) of approximately 6.5%. SEM captures also revealed that the as-formed alginate films with high PDI value have similar monodisperse porous surface and internal structure morphologies, with the exception that the as-formed alginate films with the help of phospholipids were mainly formed under our experimental environment. From the Fourier-transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements, we concluded that no chemical composition changes, thermal influence, and crystal structural modifications were observed due to the T-shaped microfluidic junction device technique. The method used in this work could expand and enhance the use of alginate porous films in a wide range of bioengineering applications, especially in tissue engineering and drug delivery, such as studying release behaviors to different internal and surface morphologies.

Photoacoustic and Ultrasound Dual-Mode Imaging via Functionalization of Recombinant Protein-Stabilized Microbubbles with Methylene Blue.

Contrast-enhanced photoacoustics and ultrasonics are complementary methods of bioimaging. In this study, a flow-focusing junction microfluidic device is used for the generation of uniform microbubbles (<5 μm) for simultaneous enhancement of photoacoustic and ultrasound imaging. Microbubbles stabilized with a mixture of a recombinant protein and a synthetic amphiphilic block copolymer are functionalized with an FDA-approved photoacoustic dye, methylene blue (MetB). These microbubbles are uniform in size and stable. We show that the ultrasound and photoacoustic signals can be independently controlled by changing the concentration of MetB during microbubble preparation and the concentration of MetB-functionalized microbubbles in the probe suspension. We also perform animal tests to demonstrate the enhancement of ultrasound and acoustic signals upon injection of MetB-functionalized microbubbles in mice. The increase in the sonographic and photoacoustic signals is visibly obvious in the images. Taken together, MetB-functionalized microbubbles represent promising dual-mode ultrasound and photoacoustic imaging contrast agents for theranostic applications.

Microneedle‐Based Generation of Microbubbles in Cancer Tumors to Improve Ultrasound‐Assisted Drug Delivery

Production of local microbubbles (MBs) with dense distribution in tumor environment is achieved by developing an integrated electrochemical stimulator on a microfabricated silicon needle covered by zinc-oxide nanowires (ZnONWs). MBs are then exploded by external ultrasonic actuation, which induce microcavitations in tumor cells followed by direct entrance of anticancer drugs into cancer cells. This system, named ZnO nanowire-based microbubble generator probe (ZnONW-MGP), is tested on tumorized mice models (by MC4L2 breast cell lines). Mice treated by ZnONW-MGP have ≈82% reduction in tumor size within 10 days with just 25% of conventional dose of paclitaxel while in the absence of the system, they have just a 15% reduction in tumor size. Presence of ZnO nanostructures on microneedles strongly reduces the size of MBs and enhances the efficacy of the sonoporation.

Effect of Sodium Dodecyl Sulfate on the Continuous Crystallization in Microfluidic Devices Using Microbubbles

AbstractIntroducing microbubbles in a microreactor for continuous crystallization increases the nucleation rate and also prevents clogging. Adding surfactants affects the microbubble generation as it reduces their size, increases their frequency of formation and consequently also the interfacial area per unit volume of reactor acting as heterogeneous surface for nucleation. Here, the effect of sodium dodecyl sulfate (SDS) on both the microbubble generation and the continuous crystallization of paracetamol is investigated. It is observed that while SDS significantly enlarges the heterogeneous surface available for nucleation, the crystallization itself is inhibited by its presence.

Growth Characteristic of Microbubble in a Co-flowing Liquid in Microfluidic Chip

Experiments of microbubble formation in a co-flowing liquid in polydimethylsiloxane (PDMS) microfluidic chip were developed. The experimental system was set up to investigate the effects of liquid flow rate, gas pressure, gas channel width and concentration of polyvinyl alcohol (PVA) solution on microbubble growth process. Three stages of the bubble growth process were first obtained through experiments. The control variable method was used to explore the growth characteristics of bubbles, such as the volume change rate, the contact angle, the ratio of length to width, and the centroid displacement. This study provides an empirical reference for the growth process of microbubbles in microfluidic chips, which helps to achieve precise control of microbubble volume and generation frequency.

The design of an ejector type microbubble generator for aeration tanks

The ejector type microbubble generator, which is the method to supply air to water by using cavitation in the nozzle, does not require any air supplier so it is an effective and economical. Also, the distribution of the size of bubbles is diverse. Especially, the size of bubbles is smaller than the bubbles from a conventional air diffuser and bigger than the bubbles from a pressurized dissolution type microbubble generator so it could be applied to the aeration tank for wastewater treatment. However, the performance of the ejector type microbubble generator was affected by hydraulic pressure and MLSS(Mixed Liquor Suspended Solid) concentration so many factors should be considered to apply the generator to aeration tank. Therefore, this study was performed to verify effects of hydraulic pressure and MLSS concentration on oxygen transfer of the ejector type microbubble generator. In the tests, the quantity of sucked air in the nozzle, dissolved oxygen(DO) concentration, oxygen uptake rate(OUR), oxygen transfer coefficient were measured and calculated by using experimental results. In case of the MLSS, the experiments were performed in the condition of MLSS concentration of 0, 2,000, 4,000, 8,000 mg/L. The hydraulic pressure was considered up to 2.0 mH2O. In the results of experiments, oxygen transfer coefficient was decreased with the increase of MLSS concentration and hydraulic pressure due to the increased viscosity and density of wastewater and decreased air flow rate. Also, by using statistical analysis, when the ejector type microbubble generator was used to supply air to wasterwater, the model equation of DO concentration was suggested to predict DO concentration in wastewater.

Innovative swirling flow-type microbubble generator for multi-stage DCMD desalination system: Focus on the two-phase flow pattern, bubble size distribution, and its effect on MD performance

In this study, we proposed a novel air-assisted swirling flow-type microbubble generator (MBG) to improve the downstream transmembrane flux of a multistage direct contact membrane distillation (MDCMD) based seawater desalination system, and experimentally demonstrated its performance under various operating conditions. To simulate the downstream operating conditions of the MDCMD system, low temperature and high concentration conditions were implemented on the feed side in the experiments. It was observed that the formation of a gas–liquid two-phase flow in the feed stream demonstrated a positive influence on the performance of the direct contact membrane distillation (DCMD) process; particularly, microbubbles less than 100 μm performed an important role in improving the heat and mass transfer. The DCMD performance using MBG was demonstrated to be more pronounced at lower feed temperatures and higher feed flow rates, where the enhancement in permeation flux was as high as 37%. The optimal air flow rate to achieve maximum DCMD performance was determined to be 50 cc/min at a given feed flow rate, while a further increase in air flow rate incurred a slug flow in the feed channel, which resulted in a decrease in the number of microbubbles and hence a decrease in the DCMD performance. In addition, the process performance was evaluated using highly concentrated brine as the feed solution, and the results demonstrated the feasibility of applying MBG to practical desalination processes.

Oxygen Microbubble Generator Enabled by Tunable Catalytic Microtubes.

Rolled-up catalytic Ti/Cr/Pt microtubes, consisting of inorganic nanomembranes integrated on-chip, are used to generate oxygen microbubbles in solutions of hydrogen peroxide. Oxygen bubble parameters (frequency, radius and volumetric flow rate) are optimized at different concentrations of hydrogen peroxide and common dish soap. Increasing the aspect ratio of the microtube (e.g., tube length/diameter) leads to the formation of smaller bubbles, but at higher frequencies. Longer tubes produce less total oxygen volume in comparison to shorter tubes. We attribute this observation to the specific dynamic behaviours of bubbles in tubes.

Simultaneous removal of NO and SO2 with a micro-bubble gas-liquid dispersion system based on air/H2O2/Na2S2O8

ABSTRACT A novel environment-friendly process was proposed to conduct the simultaneous removal of NO and SO2. In this process, a micro-bubble generator was utilized to generate the micro-bubble gas–liquid dispersion system (MBGLS) by inhaling mixed gas (NO, SO2 and/or air) and absorption liquid. The MBGLS was then sprayed into an oxidation absorption column reactor, in which NO and SO2 were oxidized and absorbed. As the additives, air, H2O2 and/or Na2S2O8 were brought into the MBGLS to investigate their effects on the simultaneous removal of NO and SO2. In addition, the effects of initial pH and temperature of the absorption liquid on the simultaneous removal of NO and SO2 were also explored. The performance of the MBGLS in removing NO and SO2 was excellent. Even if the MBGLS was composed of tap water, NO and SO2, the removal efficiencies of NO and SO2 respectively reached 78% and 94.4%. The additives significantly improved the removal performance of the MBGLS. Under the conditions of pH = 8 and room temperature and the addition of air, SO2 was removed completely and the NO removal efficiency reached 99.5% when Na2S2O8 to H2O2 molar ratio was 0.005/0.05. The effect of the absorbent temperature on the removal of NO and SO2 was insignificant. With the increase in pH, the removal of NO in both H2O2 aqueous solution and Na2S2O8 aqueous solution firstly increased and then decreased, but pH had no effect on the removal of SO2.

Simultaneous nitrification and denitrification by using ejector type microbubble generator in a single reactor

Simultaneous nitrification and denitrification by using ejector type microbubble generator in a single reactor

Bubble characteristics in pressurized bubble column associated with micro-bubble dispersion

Bubble characteristics of air-kerosene system and air-water system in a pressurized bubble column were analyzed. Experiments were carried out at system pressure up to 3.5 MPa on a cylindrical stainless column with an inner diameter of 0.097 m and a height of 1.8 m. Kerosene and tap water were used as liquids while air was used as gas. Bubble characteristics were observed by varying gas velocity up to 98 × 10−3 m/s at 0.1 MPa and up to 31.1 × 10−3 m/s at 3.5 MPa. Bubble chord length and bubble rising velocity were measured with a single tip probe installed at the top of the distributor at 0.5 m. In addition, pressure difference between the top and bottom of the column was measured with a differential pressure transducer to confirm gas holdup. In the air-kerosene system, gas holdup tended to increase with increasing system pressure. From the analysis of drift flux, transition from homogeneous to heterogeneous flow regime was observed only under atmospheric pressure. In the air-kerosene system, drift flux tended to be kept constant as gas holdup increased under pressurized conditions. The system pressure was varied from 0.1 MPa to 3.5 MPa to confirm micro-bubble generation under pressurized conditions. Dynamic gas disengagement (DGD) analysis and image analysis at the same time showed that gas holdup fraction of micro-bubbles was almost constant (εm/εg = 0.4) at atmospheric pressure. However, it was increased from 0.48 at gas velocity of 12.3 × 10−3 m/s to 0.57 with gas velocity of 32.1 × 10−3 m/s at 3.5 MPa.

Experimental investigation of microbubble generation in the venturi nozzle

We studied the effect of varying the entry and exit angles of Venturi nozzles on the formation of microbubbles in Venturi nozzle-type microbubble generators. We 3D-printed nozzles with five entry angles (15, 22, 30, 38 and 45°) and five exit angles (15, 22, 30, 38 and 45°). For the visualization experiment, we inserted the nozzles into a cover case made of aluminum and transparent acrylic. We measured the pressure drop and the air flow rate with respect to the entry and exit angles, determined the diameters of the bubbles using a digital camera, and analyzed bubble breakage by observing the behavior of the bubbles using a high-speed camera. We confirmed that the exit angle (not the entry angle) is dependent on the pressure drop and found that the air flow rate did not vary linearly with the fluid flow rate, as expected according to Bernoulli's theorem. Instead, it tended to remain constant or decrease as the fluid flow rate increased due to the abnormal flow. The sizes of the bubbles decreased as the exit angle increased, except in cases where the outlet angle was greater than 30° at high flow rates (260–300 LPM). We observed a change in bubble size with respect to exit angle. According to our visualization, the bubbles were broken by the flow separation at the beginning of the divergence at the exit.

All-fiber impurity collector based on laser-induced microbubble

Microbubbles have attracted interests in polluted water treatment industry. We proposed and constructed an all-fiber impurity collector based on the laser-induced microbubbles characteristics for polluted water treatment. Without any special pretreatment, such as metallically coating or carbon materials doping, the proposed impurity collector performed microbubbles generation and impurities extraction and collection. We employed the graphite oxide nanoplatelets in an aqueous solution to construct the polluted water environment to show the performance of the all-fiber impurity collector. With the optimal incident laser power of 11 mW, we performed the collection efficiency as high as 16.3×104 /s. The optimal microbubbles diameter was in the range of 80–120 μm. The proposed all-fiber impurity collector extends the potential applications of fiber-based optical manipulation for polluted water treatment.

Tubular catalytic micromotors in transition from unidirectional bubble sequences to more complex bidirectional motion

The generation of oxygen microbubbles in catalytic microtubes has attracted tremendous attention towards the exploration of unidirectional and overloaded bubble ejection regimes, leading to simple and more complex motions of micromotors. While it is widely believed that a bubble's frequency in a unidirectional regime (i.e., a bubble ejected from a single tubular opening) is random, this study shall demonstrate that periodic oxygen bubble frequencies and sequences can be experimentally controlled using various concentrations of hydrogen peroxide fuel and surfactants. When released from a substrate, unidirectional micromotors self-propel in straight, circular, and helical trajectories, leading to a class of well-predictable or simple micromachines. Under overloaded conditions, micromotors generate bubbles at both tubular openings, which influence the trajectories of micromotor motion strongly. A one-dimensional reaction-diffusion equation is formulated to explain the possible mechanisms of mass transport in microtubes and the transition from the unidirectional to the overloaded regime of micromotors.