Suspended Bubbles Research Articles

Enhanced Optical Limiting of Gold Nanoparticles/Porous Carbon Nanocomposites.

With the wide application of laser weapons, the requirements of laser protection technology are becoming more and more strict. Therefore, it is important to find ideal optical limiting (OL) materials to protect human eyes and detectors. In this work, the nonlinear optical responses of gold nanoparticles/porous carbon (Au NPs/PC) nanocomposites prepared by the reduction method were studied using the nanosecond Z-scan technique. Compared with porous carbon, the Au NPs/PC nanocomposites show a lower damage threshold, a bigger optical limiting index and a wider absorption spectrum. The interaction between gold nanoparticles and porous carbon enhances the nonlinear scattering effect of suspended bubbles. These results indicate that Au NPs composites have potential applications in the protection of human eyes and detectors.

Pāhoehoe lava emplacement in Lon Reudle, Mull

The base of the Mull Lava Sequence, part of the Paleogene British Igneous Province, contains a variety of volcanic features; for example, small-scale filled lava tubes and toes that can be interpreted as large-scale inflated sheets from pāhoehoe lava flows. Here, we re-examine a previously reported unique outcrop found along the coastline of Lon Reudle, Mull, which can be better understood under that conceptual model. The outcrop is composed by multiple layers, with repeating porphyritic, poorly columnar jointed and vesicle-free layers, alternating with vesicle-rich layers with individual vesicles measuring up to 1 m. We reinterpret the outcrop as an individual inflated pāhoehoe lobe with an aggregated total thickness of at least 25 m. The estimated thickness of the upper crust of this lobe is 15 m, as the upper crust would account for 40–60% of the total volume of the flow, and the time required for this upper crust to form is c . 4 years. The alternation between vesicle-rich and vesicle-free layers is likely to be caused by instabilities of the suspended bubbles in the basaltic melt, forming a diapir with abundant evidence of bubble coalescence. Typical Hawaiian pāhoehoe lava flows have thickness of 1–3 m, whereas in other flood basalt provinces thickness can reach 75–80 m, suggesting that pāhoehoe structures are scale-independent. This is a key factor to take into account when reinterpreting other lava structures that have been found in the Paleogene British Igneous Province.

Study on the Dynamic Evolution of Bubbles in Oil/Pressboard Insulation

Power transformer may generate bubbles in the transformer oil due to various factors such as internal insulation winding vibration and pressure change. Bubbles distort the spatial electric field, which makes the discharge breakdown along the gas channel, accelerate the discharge breakdown of insulating medium. Therefore, in order to prevent the arc discharge induced by micro bubbles inside the transformer from increasing the risk of transformer combustion damage, it is necessary to conduct in-depth research on the dynamic law of suspended bubbles before insulation breakdown from the source by combining experiments and simulations. In this paper, the bubble dynamic model of needle plate electrode under the multi coupling physical field of transformer is established in terms of the migration and deformation of suspended bubbles in liquid phase. By comparing the migration trajectories of single suspended bubbles obtained from experiments and simulations, the reliability of the model is verified. The variation of velocity component of voltage amplitude and the change of shape stretching of single suspended bubble in power frequency period are simulated, and the fluctuation law of pressure formed by electrostriction force inside and outside the bubble during migration is analyzed. The capacity absorption process of multi bubbles in the strong field region near the needle electrode was simulated. The changes of the surrounding liquid pressure and the spatial electric field distribution during the formation of the gas channel were analyzed, and the internal relationship between the gas channel and the formation of the discharge breakdown was revealed.

Comparative Analysis of Simulation and Analysis of Bubble Motion Characteristics in Transformer Oil Based on Horizontal Set Method and Phase Field Method

Large power transformer is the key equipment for realizing power energy transmission and voltage conversion in the power system, but in actual operation, its internal transformer oil is prone to cause partial discharge of suspended bubbles due to various factors, which endangers the safe operation of the transformer. Therefore, this paper conducts simulation research on the generation mechanism and motion law of suspended bubbles in transformer oil, first of all, based on Comsol simulation software, the motion model of suspended bubbles is constructed, considering the degree of distortion of bubbles and the regular characteristics of motion trajectories under different bubble number, initial position, size, and other influencing factors, and then comparing and analyzing the difference between the simulation results under the horizontal set method and the phase field method two interface tracking methods, and finally obtaining the multi-faceted motion mechanism of suspended bubbles in multiple physics.

Experimental Study on the Suspension Amount of Invasion Gas in Drilling Fluid with Yield Stress

The gas suspension phenomenon caused by the yield stress of the drilling fluid affects the accurate calculation of wellbore pressure after gas invasion. At present, most studies on the bubble suspension in the yield stress fluid focus on the single-bubble suspension condition and there are few studies on the gas suspension concentration. This paper carried out the GSC (gas suspension concentration) experiment in the simulated drilling fluid, xanthan solution, with different gas invasion methods. The GSC in the drilling fluid under the conditions of diffuse gas invasion and differential pressure gas invasion was simulated by using two methods of stir-depressurization and continuous ventilation. The results showed that when the size of a single bubble satisfied the single-bubble suspension condition, multiple bubbles can be suspended at the same time. The GSC is affected by the average size of the suspended bubbles, the yield stress of the drilling fluid, and the gas invasion modes. For different gas invasion modes, the empirical models of critical GSC related to the dimensionless number Bi are established. Compared with the experimental data, the relative error of the critical GSC in diffuse gas invasion is less than 6% and the relative error of the critical GSC in differential pressure gas invasion is less than 10%. The results of this work can provide guiding significance for accurate calculation of wellbore pressure.

Detection of Reserve Oxygen Potential in the Present of Fine Bubbles and its Ammonia Removal for Aquaculture Effluent

The availability of oxygen and the minimum amount of ammonia in the water media are crucial in catfish larvae hatchery performance. The condition with a balanced amount of required oxygen and the presence of ammonia resulting from the feces of striped catfish larvae is essential to maintain the health of the aquaculture media. This study aims to remove ammonia by introducing fine bubbles (FBs) into recirculating aquaculture media and investigating reserved dissolved oxygen inside the bubbles in the media. The water media for the striped catfish larvae hatchery was designed and set up with three containers in a recirculating system. Also, a separate container was utilized as bubble storage connected to FBs generator. The water treatment was conducted in three different scenarios using air and pure oxygen as the FBs generator sources. The generated FBs were investigated in terms of their size and zeta potential concerning the dissolved oxygen (DO). The media’s DO was measured using the titration method and digital DO meter. The difference in DO concentration received from titration and DO meter define as potential reserved oxygen. Furthermore, the removal of synthetic effluent (ammonia, NH4Cl) and effluent in the media with FBs resources were investigated and tested at a different duration of FBs applications. The results showed that bubbles size was 518.5 – 607.6 nm independent of gas resource, either pure oxygen or air. However, the gas resources affected the zeta potential value of suspended bubbles, air (-11.5 to -16.7 mV), and pure oxygen (-21.4 to -25.2 mV). When pure oxygen was used as a gas resource, the media reach the oxygen supersaturation DO condition (25.39 ppm) within 45 minutes with reserve oxygen potential (ROP) of 2.95 ppm. Thus, this condition allowed the synthetic effluent removal of 83.33% and effluent removal of 39.93%. It is emphasized that the ammonia removal due to the presence of reactive oxygen species when the FBs collapsed and the information of ROP due to FBs application is important to preserve the fitness of aquaculture media for catfish larvae hatchery.

Circular motion of submillimeter-sized acoustic bubbles attached to a boundary by high-speed image analysis

The circular motion of submillimeter-sized bubbles attached to a boundary in an 18.5 kHz ultrasonic field are investigated experimentally by high-speed photography and image analysis. It is found that the vibration of gas bubbles with diameters of 0.2–0.4 mm is between spherical radial vibration and regular surface fluctuation. Different from the circular motion of suspended bubbles in water, the circular motion of gas bubbles attached to a boundary presents some new characteristics. These bubbles attached to a boundary (wandering bubbles) will rotate around a fixed bubble array (holding bubbles). Both the wondering bubbles and holding bubbles are “degas” bubbles. The primary Bjerknes force acting on wandering bubbles in the acoustic wave field and the secondary Bjerknes force between the wandering bubbles and the holding bubbles strongly affects the circular motion. The circling and residence behavior of gas bubbles is described and analyzed in detail, which is helpful to understand and improve industrial applications such as ultrasonic cleaning, sonochemical treatment, aeration and cavitation reduction.

From disturbance to measurement: Application of Coriolis meter for two-phase flow with gas bubbles

Entrained gas has been regarded as disturbance to measurements based on Coriolis meters, since measurement accuracy can be degraded because of this disturbance. Recent research from Endress + Hauser has discovered that different types of gas bubbles, namely free bubbles and suspended bubbles, have various impact on the meter measurement performance. It is important to understand the error mechanism for different effects, namely bubble effect and resonator effect, which are introduced by different bubble types, and to take the corresponding measures to cope with the effects. It is also crucial to identify the bubble pattern in the measuring tube of a Coriolis meter to make a diagnosis and reduce the negative influence of the disturbance accordingly. For free bubbles that typically cause inhomogeneity of a medium, the fluctuation of the resonance frequency of the measuring tube in a Coriolis meter is directly correlated to the existence of this type of bubbles, since this medium under a flowing condition causes density fluctuation to the meter as gas density is typically much lower than that of a liquid. For homogenous suspended bubbles that lead to a significantly increased compressibility of a medium, the innovative Multi-Frequency Technology in Promass Q sensor offers the means to qualitatively detect the existence of this type of bubbles and quantitatively calculate the volume fraction of the gas phase, based on its ability to derive the speed of sound in a medium containing such bubbles. Identification of the type of bubbles helps not only for crediting the measurement reliability, but also for obtaining more detailed medium properties, and in turn a better process insight, with which a process optimization can be enabled to improve the quality of production.

High‐Speed 3D Imaging of Multiphase Systems: Applying SCAPE Microscopy to Analog Experiments in Volcanology and Earth Sciences

AbstractMultiphase suspensions are complex systems where microscopic interactions between suspended bubbles, particles, and liquids can significantly alter bulk behavior. Observing the internal mechanics of such suspensions can help constrain the dynamics of natural multiphase flows. To capture these internal processes at high speed and in three dimensions, we propose the use of Swept Confocally Aligned Planar Excitation (SCAPE) microscopy in analog experiments. This imaging technique, developed for neuroscience and biology, uses a sweeping light sheet to illuminate and image fluorophores within a sample. We performed experiments using water and various oils as the liquid phases, glass or PMMA particles for solids, and air or CO2 for gas, which we imaged at rates >50 volumes per second, over a volume size of ∼1 × 1 × 0.4 mm. We focused on three case studies: (1) bubble nucleation, growth, and rise in sparkling water, where we found that bubble detachment from angular PMMA particles left residual bubbles that also grew and detached, generating more bubbles compared to smooth particles; (2) flow of immiscible liquids (water droplets suspended in canola oil) in a porous matrix of PMMA beads, which highlighted the importance of pore and throat sizes on droplet velocities; and (3) injection of air bubbles into concentrated suspensions of glass beads or crushed PMMA particles in a refractive‐index‐matched liquid, which revealed particle motion and strong alterations of the bubble shape. We conclude that SCAPE microscopy is a powerful tool to study the dynamics of multiphase systems.

High-speed photography and image analysis of orbital motion of gas bubbles in ultrasonic field

Bubbles in the fluid have a great influence on the macroscopic physical properties and flow state of the fluid. The study of bubble motion in fluid is of great significance to ultrasonic cleaning, sonochemistry, flood discharge and energy dissipation, aeration and cavitation reduction. Bubbles in the fluid may also exhibit a special translational motion in an ultrasonic field—orbital motion. The orbital motions of gas bubbles attached to a boundary in ultrasonic field are investigated experimentally by high-speed photography and image analysis. The present study focuses on the trajectories of wandering bubbles, the arrangement of gas bubble array, the source of gas bubbles and the surface fluctuation details of gas bubbles. It is found that the circular trajectory of the wandering gas bubble is unstable, irregular and unsmooth. The holding gas bubbles in the bubble array originate from wandering bubbles. The transformation of wandering bubbles into array bubbles is mainly realized by merging and increasing the volume, thereby reducing the Bjerknes force. The wandering bubbles are produced by the merging of a large number of cavitation bubbles in the ALF (acoustic lichtenberg figure) structure, which makes the radial vibration bubbles gradually transform into the surface fluctuating bubbles. Under the action of Bjerknes force, the array bubbles show regular surface fluctuations, while the smaller ones are completely unstable, showing extremely irregular morphology, and have an influence on the surface fluctuation of nearby array bubbles. The array bubbles show a very regular arrangement, and the adjacent array bubbles have opposite vibration phases and repel each other. The orbital motion of gas bubbles attached to a boundary is significantly different from that of the bubbles suspended in liquid. First of all, the attached bubbles move along the solid wall, while the suspended bubbles move completely away from the vessel wall in the liquid. Secondly, the attached bubbles move around a regular array of bubbles, while the suspended bubbles move orbitally alone. In addition, the attached bubble is nearly hemispherical, and its surface fluctuates violently, and its motion track is extremely unsmooth, which is different from the circular motion of spherical suspended bubble. Finally, there is a strong interaction between the attached wandering bubble and the array bubble, which has a great influence on the vibration and trajectory of the attached bubble. In contrast, the circular motion of the suspended bubble does not have such a complex effect.

Experimental and modeling investigations into hydrate shell growth on suspended bubbles considering pore updating and surface collapse

Modeling of hydrate behaviors on the bubble surface is important for accurately evaluating the global budgets of greenhouse gas released from the deep ocean. Current mass-transfer models for hydrate shell growth mainly consider the inward and outward hydrate growth. However, the pore updating inside the hydrate shell and hydrate surface collapse may also play a significant role in hydrate growth. In this work, sustained visual observations on the morphological variation of hydrate shell on suspended methane bubbles in supersaturated water were conducted. The observed new insights and data processing results indicate that the dynamic growth of hydrate shell has successively experienced three stages: rapid development, continuous collapse and growth stagnation. Based on the surface characteristics of hydrated bubbles at different stages, a new mechanistic model of hydrate shell growth on bubble surface is developed, which considers the intercoupling of multiple hydrate-forming reactions, multiphase mass transfer processes, and hydrate collapse mechanical properties. This model not only characterizes the hydrate growth on both sides of hydrate shell, but also first presents a quantitative description of capillary pore updating inside the hydrate shell. Moreover, the relationship between the critical collapse pressure of hydrate shell and the dynamic pressure inside the hydrated bubble was investigated. Combining with experimental measurements from the literature, the efficiency of gas diffusion through the hydrate shell was determined, and correspondingly the time evolution of intergranular pore structure at different supercoolings was also performed. Using the proposed model, the variation rules of hydrate growth characterization parameters in different initial conditions were simulated and analyzed. Furthermore, the influence of the surface collapse behavior on hydrate shell thickening growth was also discussed. This work provides further insights into the growth characteristics of hydrated bubble accompanied with interphase mass transfer and surface morphological change.

Analysis of the fire-extinguishing effect and the weakening of flame intensification of nonionic liquid water mist*

ABSTRACTThe determination of a water mist additive is important to weaken the flame enhanced by water mist, which affects the safety and applicability of the water mist fire-fighting technology to a certain extent. Based on the theory of physical chemistry, in this study, a water mist additive, that is, a nonionic liquid alkyl phenol epoxide (APE) condensate to weaken the flame intensification and systematically perform an experimental study on extinguishing the fire in oil pool with nonionic liquid water mist. The results show that the nonionic liquid water mist has better atomization parameters. The extinguishing time and the maximum temperature are all decreased with the increase of nonionic liquid mass fraction under the action of nonionic liquid water mist. The maximum CO volume fraction and the time to maintain a high CO volume fraction in fire flue gas decreases with the increasing nonionic liquid mass fraction. The minimum O2 volume fraction and the recovery rate from this minimum value to the normal value increases with increasing nonionic liquid mass fraction. The nonionic liquid water mist can weaken the flame intensification and extinguish the oil pool fire better than pure water mist. This is because the suspended air and water bubbles formed after the spraying of the nonionic liquid water mist can block heat radiation, cutting off the oxygen supply and isolating the contact of combustibles with oxygen. In addition, owing to high temperature, surfactant and water molecules linked by hydrogen bond ether group rupture, resulting in reduced HLB, thus enhancing the ability to trap hydrocarbon molecules and capture H• and OH• radicals in the chain reaction.

Investigation of fluctuation behavior in viscosity of coal slags used in entrained-flow gasifiers

Entrained-flow gasification has attracted extensive attention because of its clean and efficient utilization of coal as well as flexible application in industry for power generation and chemical production. Numerous theoretical and experimental investigations on slag flow in entrained-flow gasifiers have been performed to ensure a smooth operation, but an unscheduled shutdown due to slag tap blockage remains an ongoing challenge. A fluctuation phenomenon of slag viscosity gives a rise in the risk of slag tap blockage. In this work, three Chinese coal slags with low silicon content and high iron content were used to investigate the viscosity fluctuation phenomenon. It was found that the crystalline phases and suspended bubbles can cause the fluctuation phenomenon. The fluctuation degree is related to the volume fraction of crystalline phases and the crystallization rate. In the search for the mechanism of the viscosity fluctuation, an in-situ observation using a high temperature stage microscope system (HTSM) in combination with XRD and SEM analyses was carried out. In addition, the viscosity of investigated slags with the suppression of solid phases as well as the phase distribution at high temperatures was calculated. Based on a comprehensive analysis of the results, a possible mechanism has been proposed that the viscosity fluctuation is attributed to an instant local change in the macrostructure such as the deformation of suspended bubbles, the change of the orientation of acicular crystals and the interaction of the acicular crystals and suspended bubbles.

Acoustic Behaviors of a Continuous Inkjet Multi-Nozzle Printhead Driven by a Traveling Wave

A traveling wave was used to ultrasonically drive the pressurized aqueous jet of a continuous inkjet multi-nozzle type printhead, resulting in remarkable uniformity in the break-off length due to non-resonant perturbation at each jet. Acoustic behaviors of the traveling wave were studied according to the jetting conditions. Propagation of the traveling wave was confirmed by decreasing the terminator length and observing unevenness in the break-off. Measurement of the shift in the phase angle at the drop break-off points allowed estimation of the velocity of the traveling wave, which is equivalent to the velocity of sound in water. Superposition of a harmonic wave onto the driving waveform verified that the measured sound velocity was appropriate by observing periodicities in satellite conditions and break-off length along with the sound propagation. A singular point in the velocity curve, believed to be due to the presence of suspended bubbles, appeared where the drop generation was irregular. The ink was degassed and the drop generation was observed to normalize; the drop generation became irregular again with the addition of non-degassed ink.

Direct numerical simulation of a bubble suspension in small amplitude oscillatory shear flow

Bubble suspensions can be found in many different fields and studying their rheology is crucial in order to improve manufacturing processes. When bubbles are added to a liquid, the magnitude of the viscosity changes and the behavior of the material is modified, giving it viscoelastic properties. For the purpose of this work, the suspended bubbles are considered to be monodisperse. It is assumed that Brownian motion and inertia can be neglected and that the fluid of the matrix is Newtonian and incompressible. The suspension is subject to an oscillatory strain while remaining in the linear regime. The resulting equations are solved in 3D with direct numerical simulation using a finite element discretization. Results of an ordered and random distribution of bubbles of volume fractions up to 40% are presented. The presence of bubbles has an opposite effect on the rheology of the suspension depending on the applied frequency. When the frequency is low, bubbles act as rigid fillers giving a rise to viscosity. On the contrary, when the frequency is high, the strain rate is being accommodated by the gaseous phase. Hence, bubbles deform, leading to a decrease of the viscosity.

Free surface lattice Boltzmann with enhanced bubble model

This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid–gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.

Interaction and ordering of bubbles levitated in vortical flow

Interaction of suspended bubbles with the flow and with other bubbles is encounted in numerous ground-based natural and technological processes and plays essential role in space applications. In experiments conducted on board spacecraft, bubbles remain suspended for a long time while at normal gravity they tend to rise due to buoyancy. However, in intensive flow bubbles may be trapped by vortices and maintain their vertical position, exhibiting the behavior similar to microgravity conditions. This type of behavior was observed e.g. bubble motions in the Couette-Taylor flow. Air bubbles injected to the viscous fluid sheared in a Couette device form a highly ordered structure. In a short time scale, the bubbles are getting entrapped in the secondary rotating flow of the Taylor vortices and are pushed to the center streamline of the vortex defying buoyancy. During a longer time scale the inertial interaction between the bubbles in the primary shear flow drives the bubbles away from each other. Equal size bubbles eventually assume an ordered string with equal separation distances between all neighbors. This phenomenon repeats itself regardless of the number of bubbles in the flow. Hence, doublets will assume opposite positions, triplets will form a triangle, four bubbles will arrange in a square and so on. We present visualizations, measurements and a model inviscid 2D analysis

Synoptic imaging of nearshore bathymetric patterns

A new technique for near real‐time optical imaging of surf zone morphology, synoptic imaging, implemented at Scripps Beach, La Jolla, California, permits simultaneous measurements of the time‐varying position of individual linear and lunate megaripples, fields of bed forms, rocks, cobble patches, beach steps and sandbars, and troughs. A varying threshold filter for brightness is applied to video frames sampled at 1 Hz to remove pixels corresponding to surface foam and suspended bubbles or sediment. Remaining fragments of the video frames are averaged over time intervals generally ranging from 5 to 10 min to produce images of the surf zone sand bed. To facilitate accurate measurement of the position of sand bed features, these images are enhanced to increase feature visibility, transformed to plan view, and corrected for refraction using surveyed bathymetry and tide level. Contrast in the images results from differences in water depth, shading variations from tilted bed surfaces, and changes in bed material. The surveyed positions of megaripples and sandbars correspond to the positions of persistent features in the images. A ray path model quantifying sand bed contrast as a function of water depth, angle of line‐of‐sight, and light attenuation coefficient in water predicts that for the Scripps Beach field site, bed forms with height as small as 0.03–0.2 m can be detected in water depths up to 2.5 m, in accord with observations, and that visibility can be improved by changing the line of sight toward overhead viewing. Bed visibility is reduced by persistent surface foam and water turbidity generated by waves with period <8 s and height exceeding 1.5 m. Example images showing transitions between linear and lunate megaripples, location of megaripple crestlines, and the interaction between sandbars, bed form fields, and cobble patches illustrate the potential of synoptic imaging.

The collapse of vapor bubbles in a spatially non-uniform flow

Pressure gradients act differently on liquid particles and suspended bubbles and are, therefore, capable of inducing a relative motion between the phases even when no relative velocity initially exists. As a consequence of the enhanced heat transfer in the presence of convection, this fact may have a major impact on the evolution of a vapor bubble. The effect is particularly strong in the case of a collapsing bubble for which, due to the conservation of the system?s impulse, the induced relative velocity tends to be magnified when the bubble volume shrinks. A practical application could be, for instance, the enhancement of the condensation rate of bubbles downstream of a heated region, thereby reducing the quality of a flowing liquid?vapor mixture. A simple model of the process, in which the bubble is assumed to be spherical and the flow potential, is developed in the paper.

97/00096 Separation of hydrophilic-hydrophobic particles using a column with suspended air bubbles

97/00096 Separation of hydrophilic-hydrophobic particles using a column with suspended air bubbles