Bubble Flow Rate Research Articles

마이크로 액적/기포 유동반응기에서 ZnO 입자의 연속제조 특성

직경이 0.03 m이고 높이가 1.5 m인 마이크로 액적/기포 유동반응기에서 ZnO 입자의 연속제조 특성을 검토하였다. 마이크로 액적을 운반하는 기체의 속도는 6.0 L/min, 전구체 중 Zn이온의 농도는 0.4 mol/L로 유지하였다. ZnO 입자의 합성을 위한 반응의 온도(973 K~1,273 K)와 마이크로 기포의 유속 (0~0.4 L/min)이 합성된 ZnO 입자의 기공 특성에 미치는 영향을 고찰하였다. 본 연구의 실험범위에서 ZnO 입자의 합성온도는 1,073 K가 합성된 ZnO 입자의 기공을 극대화하는데 최적이었다. 또한, 반응기에서 연속 제조되는 ZnO 입자의 평균크기는 반응온도가 증가함에 따라 감소하였으며 입자의 표면은 점점 매끄럽게 단순화되었다. 반응기 내부에 마이크로 기포를 유입함으로써 유입하지 않는 경우와 비교하여 합성된 ZnO 입자 내부에 기공을 효과적으로 형성시킬 수 있었으며, 평균 BET면적을 58%까지 증가시킬 수 있었다. 마이크로 액적/기포 유동반응기를 사용하여 연속 합성한 ZnO 입자의 평균입도는 반응온도에 따라 <TEX>$1.25{\sim}1.75{\mu}m$</TEX>이었다. Characteristics of continuous preparation of ZnO powder were investigated in a micro drop/bubble fluidized reactor of which diameter and height were 0.03 m and 1.5 m, respectively. The flow rate of carrier gas for transportation of precursors to the reactor was 6.0 L/min and the concentration of Zn ion in the precursor solutions was 0.4 mol/L, respectively. Effects of reaction temperature (973 K~1,273 K) and flow rate of micro bubbles (0~0.4 L/min) on the pore characteristics of prepared ZnO powder were examined. The optimum reaction temperature for the maximum porosity in the ZnO powder was 1,073 K within this experimental condition. The mean size of ZnO powder prepared continuously in the reactor decreased but the surface of the powder became smooth, with increasing reaction temperature. The injection of micro bubbles into the reactor could enhance the formation of pores in the powder effectively, and thus the mean BET surface area could be increased by up to 58%. The mean size of prepared ZnO powder was in the range of <TEX>$1.25{\sim}1.75{\mu}m$</TEX> depending on the reaction temperature.

On the bubble rise velocity of a continually released bubble chain in still water and with crossflow

The rise velocities of in-chain bubbles continually released from a single orifice in still water with and without crossflow are investigated in a series of laboratory experiments for wobbling ellipsoidal bubbles with moderate Reynolds number. For the limiting case in still water, that is, crossflow velocity = 0, the theoretical turbulent wake model correctly predicts the in-chain bubble rise velocity. In this case, the bubble rise velocities VB are enhanced compared to the terminal velocities of the isolated bubbles V0 due to wake drafting and are scaled with flow rate Q and bubble diameter D. Here, we also derive an updated wake model with consideration of the superposition of multiple upstream bubble wakes, which removes the nonlinear behavior of the non-distant (i.e., local) wake model. For the cases with crossflow, the enhancement of the in-chain bubble rise velocity can be significantly reduced, and imaging of the experiments shows very organized paring and grouping trajectories of rising bubbles not observed in still water under different crossflow velocities. The in-chain bubble rise velocities in crossflow are described by two models. First, an empirical model is used to correct the still-water equation for the crossflow effect. In addition, a semi-theoretical model considering the turbulent wake flow and the crossflow influence is derived and used to develop a theoretical normalization of bubble rise velocity, crossflow velocity, and the released bubble flow rate. The theoretical model suggests there are two different regimes of bubble-bubble interaction, with strong interaction occurring for the non-dimensional crossflow velocity Uc+=πUc3D3V0/(18gβQ2) less than 0.06 and weaker interaction occurring for Uc+ greater than 0.06, where Uc is the crossflow velocity, g is the acceleration of gravity, and β is the mixing length coefficient.

A new methodology for quantifying bubble flow rates in deep water using splitbeam echosounders: Examples from the Arctic offshore NW‐Svalbard

AbstractQuantifying marine methane fluxes of free gas (bubbles) from the seafloor into the water column is of importance for climate related studies, for example, in the Arctic, reliable methodologies are also of interest for studying man‐made gas and oil leakage systems at hydrocarbon production sites. Hydroacoustic surveys with singlebeam and nowadays also multibeam systems have been proven to be a successful approach to detect bubble release from the seabed. A number of publications used singlebeam echosounder data to indirectly quantify free gas fluxes via empirical correlations between gas fluxes observed at the seafloor and the hydroacoustic response. Others utilize the hydroacoustic information in an inverse modeling approach to derive bubble fluxes. Here, we present an advanced methodology using data from splitbeam echosounder systems for analyzing gas release water depth (&gt; 100 m). We introduce a new MATLAB‐based software for processing and interactively editing data and we present how bubble‐size distribution, bubble rising speed and the model used for calculating the backscatter response of single bubbles influence the final gas flow rate calculations. As a result, we highlight the need for further investigations on how large, wobbly bubbles, bubble clouds, and multi‐scattering influence target strength. The results emphasize that detailed studies of bubble‐size distributions and rising speeds need to be performed in parallel to hydroacoustic surveys to achieve realistic mediated methane flow rate and flux quantifications.

On the accuracy of wire-mesh sensors in dependence of bubble sizes and liquid flow rates

An experimental study to assess the accuracy of wire-mesh sensors in dependence of bubble sizes and flow rates has been performed in a 50mm×50mm transparent rectangular channel. The liquid superficial velocities were ranging from 0m/s up to 0.62m/s with the obtained bubble size ranging from 3mm to 7mm. A single wire-mesh sensor with 16×16 electrode wires was used with a temporal and spatial resolution of 10kHz and 3.1mm (lateral distance between two wires), respectively. Single bubbles with known bubble size, subsequently called reference bubble size, was injected into the test section via bubble injector approx. 25cm upstream of the wire-mesh sensor. The bubble size measurement by using wire-mesh sensor cannot be obtained directly since it requires the information of bubble velocity which is not available only by installing a single sensor. Therefore, a stereoscopic observation was conducted to obtain the bubble velocity by tracking the successive frames as well as to study the intrusiveness of the sensor. This configuration gave an advantage that the registered bubble will be assigned with its real approach velocity and a better agreement is expected. As the result, a direct comparison of all individual bubbles with the reference bubble size showed an agreement within ±10%. However, a deceleration effect was found for low superficial and observed to disappear as the liquid superficial velocity increased then vanish at observed JL=0.62m/s.

Dynamics of isolated confined air bubbles in liquid flows through circular microchannels: an experimental and numerical study

Experimental and numerical studies are performed to characterise the dynamics of isolated confined air bubbles in laminar fully developed liquid flows within channels of diameters d = 0.5 mm and d = 1 mm. Water and glycerol are used as the continuous liquid phase, and therefore, a large range of flow capillary numbers 10−4 < Ca < 10−1 and Reynolds numbers 10−3 < Re < 103 are covered. An extensive investigation is performed on the effect of bubble size and flow capillary number on different flow parameters, such as the shape and velocity of bubbles, thickness of the liquid film formed between the bubbles and the channel wall, and the development lengths in front and at the back of the bubbles. The micro-particle shadow velocimetry technique (μPSV) is employed in the experimental measurements allowing simultaneous quantification of important flow parameters using a single sequence of high-speed greyscale images recorded at each test condition. Bubble volume and flow rate of the continuous liquid phase are precisely determined in the post-processing stage using the μPSV images. These parameters are then used as initial and boundary conditions to set up CFD simulations reproducing the corresponding two-phase flow. Simulations based on the volume of fluid technique with the aim of capturing the interface dynamics are performed with both ANSYS Fluent v. 14.5, here augmented by implementing self-defined functions to improve the accuracy of the surface tension force estimation, and ESI OpenFOAM v. 2.1.1. The present approach not only results in valuable findings on the underlying physics involved in the problem of interest but also allows us to directly compare and validate results that are currently obtained by the experimental and computational methods. It is believed that similar methodology can be employed to rigorously investigate more complex two-phase flow regimes in micro-geometries.

Investigation of submerged membrane photocatalytic reactor (sMPR) operating parameters during oily wastewater treatment process

The performance of a submerged membrane photocatalytic reactor (sMPR) consisted of polyvinylidene fluoride-titanium dioxide (PVDF-TiO2) hollow fiber membranes was evaluated for the separation and degradation of synthetic oily wastewater under UV irradiation. The effects of operating parameters such as TiO2 catalyst loading, membrane module packing density, feed oil concentration and air bubble flow rates (ABFR) on the permeate flux, oil rejection and total organic carbon (TOC) degradation (in the bulk feed solution) were studied. The comparison of TOC degradation based on direct photolysis, neat PVDF membrane and PVDF-TiO2 membrane were determined. It was clearly observed that TOC degradation using PVDF-TiO2 membrane was remarkably higher compared to neat PVDF membrane. Gas chromatography–mass spectrometry (GC-MS) analyses showed that oil components in the wastewater could be efficiently degraded in the presence of TiO2 under UV irradiation. The average flux of membrane was reported to be around 73.04L/m2 h using PVDF membrane embedded with 2wt.% TiO2 at 250ppm oil concentration with module packing density of 35.3% and ABFR of 5L/min. A remarkable TOC degradation and oil rejection as high as 80% and >90%, respectively, could be reached under these optimized conditions. The findings shown in this work provide useful information for the research of simultaneous separation and degradation of oily wastewater and facilitate the development of hybrid sMPR.

Pulsatory rise of microbubble swarm along a vertical wall

Based on the experimental finding that microbubble swarms dramatically promote heat transfer from a vertical heated wall, despite their potentially adiabatic nature, tests of microbubble fluid mechanics in the isothermal state are performed to clarify the unique motion characteristics of microbubble swarms. At constant bubble flow rate, the microbubble swarm shows a significant pulsatory rise along a vertical flat wall, particularly for small bubbles. Particle tracking velocimetry applied to the microbubbles shows that a two-way interaction between the microbubbles and the liquid flow self-excites the pulsation during their co-current rise. The sequence consists of the following processes: (i) increase in the bubble number density close to the wall as a result of the liquid velocity gradient driven by the microbubbles themselves; (ii) wave generation inside the microbubble swarm to induce the pulsatory rise of the swarm; and (iii) amplification of the waves, which results in void-bursting motion in the final stage.

Acoustic monitoring of gas emissions from the seafloor. Part I: quantifying the volumetric flow of bubbles

Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en-route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0–200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance.

Experimental Investigation of the Interaction between Rising Bubbles and Swirling Water Flow

This study experimentally investigates the interaction between rising bubbles and swirling water flow imposed around the central (vertical) axis of a bubble plume in a cylindrical water tank. Small air bubbles are successively released from the bottom of the tank to generate a bubble plume, and a stirring disc at the bottom of the tank is rotated to impose a swirling water flow around the central axis of the bubble plume. The bubbles disperse further with the increasing rotational speedωof the stirring disc. Some bubbles shift toward the central axis of the swirling flow whenωis high. The nondimensional swirling velocity of water reduces with increasing bubble flow rate whenωis lower than a certain value. However, it is less affected by the bubbles whenωis higher. The precessional amplitude for the upper end of the vortex core increases due to the presence of the bubbles. With increasingω, the nondimensional precessional velocity decreases, and the bubble effect also reduces.

Submerged Ultrafiltration for Minimizing Energy Process of Refinery Wastewater Treatment

Refinery wastewater treatment is needed especially in the oil-producing arid regions such as oil refineries due to water scarcity. One of potentially applicable process to treat refinery wastewater is a submerged membrane technology. However, the application of submerged membrane systems for industrial wastewater treatment is still in its infancy due to significant variety in wastewater composition and high operational costs. Aim of this study was to investigate ultrafiltration (UF) membrane morphology and performance for refinery produced wastewater treatment. Submerged UF bundle was equipped using polyvinylidene fluoride (PVDF) hollow fibers, which added by dispersing lithium chloride monohydrate (LiCl.H2O) and titanium dioxide (TiO2). The comparison of morphological and performance tests was conducted on prepared PVDF ultrafiltration membranes. Distinctive changes were observed in membrane characteristics in term of membrane wettability, tensile testing and roughness measurement. Mean pore size and surface porosity were calculated based on permeate flux. Fouling characteristics for hydrophilic PVDF hollow fibers fouled with suspended solid matter was also investigated. Mixed liquor suspended solid (MLSS) of 3 g/L and 4.5 g/L were assessed by using submerged PVDF membrane with varied air bubble flow rates. Results showed that effect of air bubbles flow rate of 2.4 ml/min increased flux, total suspended solids (TSS) and sulfide removal of 148.82 L/m2h, 99.82 % and 89.2%, respectively due to increase of turbulence around fibers, which exerts shear stress to minimize particles deposited on membrane surface. It was concluded that submerged ultrafiltration is an available option to minimize energy process for treating such wastewater solution.

Passive acoustic mapping of magnetic microbubbles in an in vitro flow model

Magnetic microbubbles can be successfully retained near a vascular target and simultaneously imaged using conventional B-mode ultrasound. When further modified to carry a drug, they could enable significant enhancements in targeted drug delivery for applications such as sonothrombolysis, where stable cavitation has been shown to play a key role. However, the effect of the increased proximity of the microbubbles under the effect of the magnetic field on their acoustic response remains unknown. Passive acoustic mapping is a method that enables real-time spatiotemporal monitoring of cavitation dynamics in an arbitrary plane or volume within the field of view of the ultrasound probe, and classification of the type of cavitation activity on the basis of the spatial distribution of frequency-domain emissions. In the present work, PAM is used to investigate the effect of bubble proximity and flow rate on the type, sustainability, intensity, and spatial distribution of cavitation activity observed for both magnetic and non-magnetic microbubbles excited by 0.5 MHz therapeutic ultrasound in an in vitro flow model. It is hoped that this study will not only yield a new method for real-time monitoring of drug delivery using magnetically trapped microbubbles, but will also help elucidate complex bubble–bubble interactions in therapeutic ultrasound fields.

Feasibility of Generating Peaks of Bioaerosols for Laboratory Experiments

Bioaerosol concentration peaks are frequently encountered in real-life atmospheres (indoor, outdoor, workplace, etc.), where they can be caused by several factors. However, evolution over time and variability of microbiological pollutant concentrations remain under-documented. The contribution of such peaks in the onset or the worsening of respiratory symptoms – in particular immuno-allergic reactions – has yet to be extensively studied. Although experimental bioaerosol generators are increasingly used, the intentional and controlled production of concentration peaks of biological agents has not yet been utilized in laboratory experiments. The main objective of this study was to show that it is possible to produce experimental bioaerosol concentration peaks with defined characteristics. Experiments were performed with a ‘Liquid Sparging Aerosoliser’-type generator. With this system, peaks can be created by increasing the bubbling airflow through a film of bacterial (Escherichia coli) or fungal (Penicillium brevicompactum) liquid culture. The higher the set point value of the bubbling airflow, the greater the maximum bioaerosol concentration during the generated peak. Similarly, longer-lived peaks can be created by maintaining the increased airflow for a longer period of time. For both studied species, the relative size distribution was constant over time, regardless of modifications to the bubbling flow rate. The operator can monitor and control peak formation with this system thanks to real-time measurement of the number concentrations, targeting the appropriate particle size classes corresponding to diameters of the aerosolised microorganisms. This generator, characterized by gentle aerosolisation and a capacity to produce bioaerosol peaks, may contribute to enrich laboratory experiments for numerous applications.

Concentration measurements of bubbles in a water column using an optical tomography system

Optical tomography provides a means for the determination of the spatial distribution of materials with different optical density in a volume by non-intrusive means. This paper presents results of concentration measurements of gas bubbles in a water column using an optical tomography system. A hydraulic flow rig is used to generate vertical air–water two-phase flows with controllable bubble flow rate. Two approaches are investigated. The first aims to obtain an average gas concentration at the measurement section, the second aims to obtain a gas distribution profile by using tomographic imaging. A hybrid back-projection algorithm is used to calculate concentration profiles from measured sensor values to provide a tomographic image of the measurement cross-section. The algorithm combines the characteristic of an optical sensor as a hard field sensor and the linear back projection algorithm

Effect of De-ionized Water Rinse in AlCu Line Post Etch Asher Residue Removal Process Using Fluoride Containing Stripper

Compared with hydroxylamine-based stripper process, De-ionized water rinse becomes more critical due to intermediate solvent rinse elimination in the fluoride containing stripper process. In this paper, an integrated AlCu line photoresist strip de-ionized water rinse process utilizing a fluoride containing stripper is studied systematically in following aspects: a. CO2 bubble flow rate effects to metal galvanic corrosion, metal sidewall roughness and electromigration; b. de-ionized water rinse time effects to metal post-corrosion in wet box and metal electromigration; c. de-ionized water dump time effects to metal resistivity and electromigration. The data show de-ionized water rinse optimization along with CO2 bubble flow rate fine-tuning is essential to provide effective metal corrosion prevention, smooth metal sidewall and good electro-migration.

Effects of process conditions in submerged ultrafiltration for refinery wastewater treatment: Optimization of operating process by response surface methodology

The influence of air bubble flow rate (ABFR), hydraulic retention time (HRT), mixed liquor suspended solid (MLSS) concentration, and pH on the performances of modified polyvinylidene fluoride (PVDF) was investigated in submerged membrane ultrafiltration (SMUF).The refinery wastewater process was conducted using an experimental set-up consisted of an SMUF reservoir, a circulation pump, and an aerator. For SMUF, operated at vacuum pressure, deposition and accumulation of suspended solids on membrane surface were prohibited with continuous aeration. The process performance was measured in terms of the membrane water flux and chemical oxygen demand (COD) removal efficiency. The air bubbles flow rate was controlled at 1.2–3.0mL/min while HRT was manipulated in the range of 120–300min. MLSS and pH solution were controlled at 4.5g/L and 6.5, respectively. Results from response surface methodology (RSM) have demonstrated the improvement in water flux and COD removal, achieving 145.7L/m2h and 90.8%, respectively. By using pH at 6.50, the optimized conditions achieved for refinery wastewater treatment were 2.25mL/min, 276.93min, 4.50g/L for ABFR, HRT and MLSS concentration, respectively.

Experimental study on turbulent natural convection heat transfer in water with sub-millimeter-bubble injection

Using thermocouples and a particle tracking velocimetry technique, temperature and velocity measurements are conducted to investigate flow and heat transfer characteristics of turbulent natural convection from a vertical heated plate in water with sub-millimeter-bubble injection. Hydrogen-bubbles generated by the electrolysis of water are used as the sub-millimeter-bubbles. In the turbulent region, the heat transfer deterioration occurs for a bubble flow rate Q = 33 mm3/s, while the heat transfer enhancement occurs for Q = 56 mm3/s. Temperature and velocity measurements suggest that the former is caused by a delay of the transition due to the bubble-induced upward flow. On the other hand, the latter is mainly due to two factors: one is the enhancement of the rotation of eddies in the outer layer, and the other is the increase in the gradient of the streamwise liquid velocity at the heated wall. These are caused by bubbles, which are located in the inner layer, rising at high speed.

G232 マイクロバブル注入による自然対流場の伝熱促進(一般講演)

The purpose of this study is to clarify effects of micro-bubble injection on the heat transfer enhancement of natural convection along a vertical heated plate. We use thermocouples for the temperature measurement. We also use an image processing technique for obtaining the diameter of bubbles. The working fluid used is tap water, and hydrogen bubbles generated by electrolysis of the water are used as the micro-bubbles. The temperature measurements show that for all regions, the heat transfer enhancement is caused by the micro-bubble injection and that the maximum heat transfer gain with micro-bubble injection is approximately 24 when the bubble mean diameter and the bubble flow rate are, respectively, 50 μm and 39 mm^3/s.

Characterisation of hydrodynamics induced by air injection related to membrane fouling behaviour

The study focuses on fine bubble and spherical cap bubble injection in case of outside/in fibres immersed in a tank. The objectives are to quantify liquid circulations and shear stresses along the membrane and to understand their effects on the fouling resistance. Thus, both filtration experiments and hydrodynamic characterisation were performed in the same aeration conditions. Only particle cake deposit was studied as fouling mode and the hydrodynamics was characterized experimentally by 2-phase flow particle image velocimetry (PIV) and numerically with the CFD code FLUENT. Results presented in this paper are limited to tight hollow-fibres to well understand hydrodynamics without fibre motion. One important result is that mean values of wall shear stress are very low (maximum 0.25 Pa) eliminating the wall shear stress as a mechanism able to explain filtration performances for a non-confined aeration without fibre displacement. In addition, an analysis has been conducted in terms of horizontal liquid flow toward the membrane. The quantification of this flow allowed to conclude that i) for a given local bubble flow rate, there is no influence of the kind of aeration on this horizontal flow rate; and ii) the filtration performances can be correlated with this horizontal flow. The reason might be an over concentration of particles near the membrane surface induced by this flow.

CFD Modelling and Comparison among Different Configurations of Parallel Plates Iron Electrowinning Cells

Within the ULCOS project, a pilot cell for iron electrowinning is being designed. Electrical energy is used to transform iron ore particles (hematite) suspended in a sodium hydroxide solution into iron metal and oxygen. The work developed by Labein-Tecnalia is focused on the study of the fluid flow for different electrolytic cell configurations to get knowledge of the interaction between the oxygen bubbles generated during the process and the electrolyte flow. The numerical algorithm us ed is the finite volume used in the commercial Computational Fluid Dynamics code FLUENT. The work developed is focused on vertical and horizontal parallel plates configurations, to analyze the removal of oxygen bubbles from the gap between anode and cathode, and the access of iron ore particles to the cathode. A user subroutine has been developed for the CFD code to compute the mass flow rate of oxygen bubbles generated at the anode, as a function of the local current density. A methodology has been developed to analyze the accessibility of the iron ore particles to the cathode. The knowledge obtained from this work has helped for the design of the pilot cell within the ULCOS project.

Effects of bubble size on heat transfer enhancement by sub-millimeter bubbles for laminar natural convection along a vertical plate

Injection of sub-millimeter bubbles is considered a promising technique for enhancing natural convection heat transfer for liquids. So far, we have experimentally investigated heat transfer characteristics of laminar natural convection flows with sub-millimeter bubbles. However, the effects of the bubble size on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of the bubble size on the heat transfer enhancement for the laminar natural convection of water along a vertical heated plate with uniform heat flux. Temperature and velocity measurements, in which thermocouples and a particle tracking velocimetry technique are, respectively used, are conducted to investigate heat transfer and flow characteristics for different bubble sizes. Moreover, two-dimensional numerical simulations are performed to comprehensively understand the effects of bubble injection on the flow near the heated plate. The result shows that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection ranges from 1.3 to 2.2. The result also shows that for a constant bubble flow rate, the heat transfer coefficient ratio increases with a decrease in the mean bubble diameter. It is expected from our estimation based on both experimental data and simulation results that this increase results from an increase in the advection effect due to bubbles.