Motion Of Gas Bubbles Research Articles

Hydrodynamic simulation of liquid steel for optimal design of intermediate ladles in continuous-casting machines

Simulation of the metal and slag fluxes, the removal of nonmetallic inclusions, and the motion of gas bubbles in injection is considered. Laboratory simulation of the intermediate ladle is described.

Numerical Study on Gas Bubbles Motion in a Reciprocally Stirred Flow

Numerical Study on Gas Bubbles Motion in a Reciprocally Stirred Flow

Ebullition events monitored from northern peatlands using electrical imaging

[1] Within northern peatlands, ebullition is potentially an important mechanism for the transport of methane (CH4) to the atmosphere. We applied electrical imaging to characterize the buildup and ebullition of biogenic gas bubbles in a spatially explicit manner. Ebullition events were monitored from a range of different peat types, with and without a vascular plant cover, under different meteorological conditions. Weekly changes in bulk electrical conductivity (σ) were analyzed, during which variations in pore water conductivity had only a small effect on σ. Bulk ebullition losses from the peat cores were independently measured using Mariotte regulators. The largest ebullition events were found to be spatially diffuse: the gas was released from a large volume of peat. We used a measure of the roughness of the electrical images to characterize the magnitude of gas bubble movement within each peat core. Our results show that small variations in air temperatures of 3°C and variations in peat type between different microhabitats have a statistically significant influence on gas bubble dynamics.

Observation of acoustic emission from gas bubble inception and burst

This technical note presents an experimental investigation aimed at exploring acoustic emission (AE) from gas bubble formation, motion, and destruction. AE in this particular investigation covers the frequency range between 100 and 1000 kHz. It is shown that AE energy and amplitude are directly correlated to bubble size at inception and burst.

Eulerian–Lagrangian 3-D simulations of unsteady two-phase gas–liquid flow in a rectangular column by considering bubble interactions

This work discusses the development of a three-dimensional Eulerian–Lagrangian CFD model for a gas–liquid flow in a rectangular column. The model resolves the time-dependent, three-dimensional motion of small gas bubbles in a liquid to simulate the dynamic characteristics of the oscillating bubble plume. Our model incorporates drag, gravity, buoyancy, lift, pressure gradient and virtual mass forces acting on a bubble rising in a liquid, and accounts for two-way momentum coupling between the phases. We use MUSIG model that provides a framework in which the population balance method together with the break up and coalescence models can be incorporated into three-dimensional CFD calculations. We use turbulent flow to describe liquid flow field. The standard κ–ε of turbulence is selected for calculating the properties of turbulent flow. The effect of aspect ratio of the column on the flow pattern, liquid velocity and gas hold-up profiles is discussed.

Chaotic characteristics of gas bubble motion in acoustic field

Considering liquid compressibility, the dynamical behaviors of gas bubble in acoustic field are investigated by regarding water as a work medium. The effects of acoustic frequency, acoustic pressure, initial radius of gas bubble, liquid surface tension, and viscosity coefficient on bubble motion state are numerically simulated. The relationship between cavitation treatment effect and gas bubble motion state is analysed.The results show that when the gas bubble motion is in a chaotic state, it is the most important factor for enhancing acoustic cavitation degradation of organic pollutants ability.

VOF Simulations of Gas Bubbles Motion in a Reciprocally Stirred Flow

This paper reports progress in the numerical simulations of movement and the coalescence of two neighbor bubbles (leading and trailing bubble) in a reciprocally stirred liquid flow field. The full Navier-Stokes equations are solved by the volume-of fluid (VOF) method for tracking the interface between the bubble and the liquid flow. A dynamic mesh method was used to predict the gas-liquid flow in a two-dimensional foaming tank. Results indicate that the motion and merge behavior of the bubbles is dominantly influenced by the initial locations and the sizes of the bubbles as well as by the surface tension, while the reciprocating effect is insignificant.

Two-Dimensional Physical and CFD Modelling of Large Gas Bubble Behaviour in Bath Smelting Furnaces

The behaviour of large gas bubbles in a liquid bath and the mechanisms of splash generation due to gas bubble rupture in high-intensity bath smelting furnaces were investigated by means of physical and mathematical (CFD) modelling techniques. In the physical modelling work, a two-dimensional Perspex model of the pilot plant furnace at CSIRO Process Science and Engineering was established in the laboratory. An aqueous glycerol solution was used to simulate liquid slag. Air was injected via a submerged lance into the liquid bath and the bubble behaviour and the resultant splashing phenomena were observed and recorded with a high-speed video camera. In the mathematical modelling work, a two-dimensional CFD model was developed to simulate the free surface flows due to motion and deformation of large gas bubbles in the liquid bath and rupture of the bubbles at the bath free surface. It was concluded from these modelling investigations that the splashes generated in high-intensity bath smelting furnaces are mainly caused by the rupture of fast rising large gas bubbles. The acceleration of the bubbles into the preceding bubbles and the rupture of the coalescent bubbles at the bath surface contribute significantly to splash generation.

Surfactant Properties Differentially Influence Intravascular Gas Embolism Mechanics

Gas bubble motion in a blood vessel causes temporal and spatial gradients of shear stress at the cell surface lining the vessel wall as the bubble approaches the cell, moves over it and passes it by. Rapid reversals occur in the sign of the shear stress imparted to the cell surface during this motion. These may result in injury to the cell. The presence of a soluble surfactant in the bulk medium reduces the level of the shear stress gradients imparted to the cell surface as compared to an equivalent surfactant-free system and is an important therapeutic aid. This is particularly true for a very small vessel. In this study, we analyze various physical and chemical properties of any given soluble surfactant to ascertain the relative significance of the property of the surfactant on the reduction in the level of the shear stress gradients imparted to the cell surface in such a vessel. While adsorption, desorption, and maximum possible monolayer interface surfactant concentration significantly impact the shear stress levels, physical properties such as the bulk or surface diffusivity do not appear to have large effects. At a given diameter, surfactants with k(a)/(k(d)d>O(10)⁻⁵ and Γ(∞)/C(0)d>9.5 x 10⁻⁴ are noted to be preferable from the point of view of an increased gap size between the bubble and vessel wall, and a corresponding reduction in the shear stress level imparted to an endothelial cell. The shear stress characteristics of nearly occluding bubbles, in contrast with smaller sized bubbles under identical conditions, are most affected by the introduction of a surfactant in regard to shear stress levels. These observations could form a basis for choosing surfactants in treating gas embolism related illnesses.

The fine scale variability of dissolved methane in surface peat cores

Peat forming wetlands are globally important sources of the greenhouse gas CH 4. The variability of flux recordings from peatlands is however considerable and the distribution of CH 4 below the water table poorly described. Surface peat (0–500 mm below the water table) is responsible for the bulk of emissions and a localised region of intense CH 4 concentration may exist within this region but the structure of peat and presence of gas bubbles make the determination of in situ gas distributions problematic. We report on the in situ distribution and concentrations of CH 4, CO 2 and O 2 in surface bog peat cores using Quadrupole Mass Spectrometry and relate this to peat physical structure. Replicate cores collected in spring and autumn from both hollows and hummocks are used ( n = 10). CH 4 recorded in almost every profile was localised in intense peaks reaching concentrations up to 350 μM at depths where O 2 was absent. Each CH 4 peak had a coincident CO 2 peak with a minimum mean ratio of ∼20:1 (CO 2:CH 4) and we found more CH 4 beneath hollows than hummocks. In statistical comparisons CH 4 concentration and distribution differed significantly between profiles for each depth. We demonstrate that variability found within a single core is at least as great as that between cores collected across the bog. The distribution of CH 4 was negatively correlated with bulk density and in some cases the location of roots matched those of intense CH 4 concentration where bubbles had formed and been trapped. Our comparisons suggest variability in gas distribution is caused by a heterogenous peat structure that controls the movement of gas bubbles and contains localised hotspots of gas production. The small and fine root systems of vascular plants on the peatland surface may cause high levels of methanogenic activity in their vicinity and also represent a physical barrier capable of trapping CH 4 bubbles.

Capillary driven movement of gas bubbles in tapered structures

This article presents a study on the capillary driven movement of gas bubbles confined in tapered channel configurations. These configurations can be used to transport growing gas bubbles in micro fluidic systems in a passive way, i.e. without external actuation. A typical application is the passive degassing of CO2 in micro direct methanol fuel cells (μDMFC). Here, a one-dimensional model for the bubble movement in wide tapered channels is derived and calibrated by experimental observations. The movement of gas bubbles is modelled on straight trajectories based on a balance of forces. The bubble geometry is considered as three dimensional. In the development of the model, the effects of surface tension, inertia, viscosity, dynamic contact angle and thin film deposition are considered. It is found that in addition to viscous dissipation, the dynamics related to the contact line—dynamic contact angle and thin film deposition—are essential to describe the gas bubble’s movement. Nevertheless, it was also found that both of these effects, as modelled within this work, have similar impact and are hard to distinguish. The model was calibrated against experiments in a parameter range relevant for the application of travelling gas bubbles in passive degassing structures for μDMFCs.

Effect of liquid properties on the growth and motion characteristics of micro-bubbles induced by electric fields in confined liquid films

The effect of liquid properties on gas bubble growth and motion characteristics in liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disc under an electric field is reported. Experimental results show that the critical voltage for the appearance of bubbles has insignificant dependence on liquid viscosity and surface tension. The bubble size after detachment increases with liquid viscosity, and bubble instability and coalescence tend to occur when bubbles move some distance away from where they were formed. An increase in liquid surface tension results in larger bubbles at the growth stage. Also, the bubble motion characteristics are greatly influenced by liquid viscosity, and the dielectrophoresis force is demonstrated to be the dominant driving force for bubble movement. Theoretical models and analyses have been used to discuss the bubble formation and describe the bubble movement characteristics.

Bubble flow measurements in pulsed streamer discharge in water using particle image velocimetry

In this paper the flow velocity fields during formation and motion of gas bubbles produced by a high voltage pulsed streamer discharge in water are presented. The discharge reactor was a glass parallelepiped filled with distilled water. In the water one or three stainless steel needles and a brass cylinder were placed. The Particle Image Velocimetry (PIV) measurements of the bubble flow pattern were carried out in six different planes, crossing the reactor. We observed that the bubble flow from the needle tips toward the cylindrical electrode was relatively strong and vortices were formed Owing to it the water was stirred in the whole reactor volume, and the whole reactor volume was filled with bubbles.

Finite-sized gas bubble motion in a blood vessel: non-Newtonian effects.

We have numerically investigated the axisymmetric motion of a finite-sized nearly occluding air bubble through a shear-thinning Casson fluid flowing in blood vessels of circular cross section. The numerical solution entails solving a two-layer fluid model--a cell-free layer and a non-Newtonian core together with the gas bubble. This problem is of interest to the field of rheology and for gas embolism studies in health sciences. The numerical method is based on a modified front-tracking method. The viscosity expression in the Casson model for blood (bulk fluid) includes the hematocrit [the volume fraction of red blood cells (RBCs)] as an explicit parameter. Three different flow Reynolds numbers, Reapp=rholUmaxdmicroapp , in the neighborhood of 0.2, 2, and 200 are investigated. Here, rhol is the density of blood, Umax is the centerline velocity of the inlet Casson profile, d is the diameter of the vessel, and microapp is the apparent viscosity of whole blood. Three different hematocrits have also been considered: 0.45, 0.4, and 0.335. The vessel sizes considered correspond to small arteries, and small and large arterioles in normal humans. The degree of bubble occlusion is characterized by the ratio of bubble to vessel radius (aspect ratio), lambda , in the range 0.9< or =lambda< or =1.05 . For arteriolar flow, where relevant, the Fahraeus-Lindqvist effects are taken into account. Both horizontal and vertical vessel geometries have been investigated. Many significant insights are revealed by our study: (i) bubble motion causes large temporal and spatial gradients of shear stress at the "endothelial cell" (EC) surface lining the blood vessel wall as the bubble approaches the cell, moves over it, and passes it by; (ii) rapid reversals occur in the sign of the shear stress (+ --> - --> +) imparted to the cell surface during bubble motion; (iii) large shear stress gradients together with sign reversals are ascribable to the development of a recirculation vortex at the rear of the bubble; (iv) computed magnitudes of shear stress gradients coupled with their sign reversals may correspond to levels that cause injury to the cell by membrane disruption through impulsive compression and stretching; and (v) for the vessel sizes and flow rates investigated, gravitational effects are negligible.

Coupling the VOF and the MHD models for the simulation of bubble rising in a metallic liquid

In the last few decades magnetohy-drodynamic (MHD) effects have attracted growing interest because of its potential impact on numerous industrial technologies such as metallurgy, crystal growth, electron or laser beam melting/evaporation of surfaces, etc… An example of such flow is the Bubble driven flows which have found wide applications in industrial technologies. In metallurgical processes gas bubbles are injected into a bulk liquid metal to drive the liquid into motion, to homogenise the physical and chemical properties of the melt or to refine the melt. For such gas–liquid metal two-phase flows, external magnetic fields provide a possibility to control the bubble motion in a contactless way. Our interest is devoted to the motion of gas bubbles in liquid metals under the influence of a magnetic field. The numerical scheme used in this paper is based on the volume of fluid (VOF) method interFoam of the OpenFoam code, which uses an interface tracking algorithm for the simulation of the two-phase flow coupled with an incompressible laminar magneto-hydrodynamics model mhdFoam of same code. The solver is at its earlier stage and in this paper; we consider the case of a single, isolated bubble rising in a tube of stagnant liquid metal exposed to a longitudinal magnetic field.

Gas Bubble Motion Artifact in MDCT

The purpose of our study was to characterize the imaging features of an MDCT artifact caused by gas bubble motion. For the period 2002-2006, the CT images of 10 patients that revealed a curvilinear artifact thought to be due to a gas bubble moving during CT acquisition were retrospectively identified and reviewed by an attending body radiologist. The clinical images were acquired on MDCT scanners. A phantom containing water and moving air bubbles (gas injection rates of 0.1 and 0.5 mL/s) was designed, built, and scanned using a 16-MDCT scanner. Computer simulation was used to test our hypothesis that these observed artifacts originated from moving gas bubbles. Semicircular tubular CT artifacts with attenuation close to that of air were observed in all 10 clinical cases. The acquired MDCT images from the phantom and the computer simulations showed tubular air-attenuation semicircular artifacts that closely matched the imaging findings on the 10 clinical cases. Increased rates of bubble injection multiplied the artifact. Based on the computer simulation, the precise appearance of the artifact depends on the bubble location and velocity relative to the rotation of the CT scanner. Gas bubble motion during CT generates a semicircular air-attenuation artifact that has not been previously described to our knowledge. The artifact is typically found in bowel and other liquid-containing structures in which a bubble of gas floats up through a liquid medium during CT.

Hydrodynamic aspects of interaction between nucleation sites

The dynamics of twin and triple nucleation sites interaction has been investigated. Nonlinear data analysis techniques such as the dimension spectrum and largest Lyapunov exponent have been used for analysis of data recorded in experiment. It has been shown that properties of dynamics of nucleation sites changes nonlinearly together with changing the spacing between cavities. To explain appearance of such properties of nucleation sites interaction the simulation of gas bubble movement in the liquid in the last stage of bubble departures has been made with using the stabilized finite element method and level set method. It has been shown that the bubble departure velocities and structure of velocity field around the bubbles nonlinearly depend on the initial horizontal spacing between bubbles. The obtained results indicate that one of the reasons for nonlinear changes of properties of dynamics of nucleation sites interaction occurring with changes of initial spacing between them is hydrodynamic interaction between departing bubbles.

MOTION OF GAS BUBBLES, CONSIDERED AS MASSLESS BODIES, AFFORDING DEFORMATIONS WITHIN A PRESCRIBED FAMILY OF SHAPES, IN AN INCOMPRESSIBLE FLUID UNDER THE ACTION OF GRAVITATION AND SURFACE TENSION

A model allowing to describe motion and coalescence of gas bubbles in a liquid under the action of gravitation and surface tension is proposed. The shape of the bubbles is described by a pre-defined family of mappings, for example ellipsoids with a fixed volume and the effects of the gas motions inside the bubbles are neglected. The motion of a bubble is obtained in a Lagrangian form using the D'Alembert principle of virtual works. The set of equations is numerically solved with the help of the fictitious domain technique in which the Navier–Stokes equations in the domain formed by both fluid and gas are considered. The equations governing the bubbles motion are imposed by introducing Lagrange multipliers on the bubbles boundaries. Numerical results in 2D and 3D are presented.

Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate

The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.

Capillary movement of gas inclusions in firing glass coatings

The effect of iron oxides on the physicochemical properties of primer enamels that regulate capillary movement of gas bubbles was investigated. The rates of capillary movement of bubbles in an enamel melt were calculated based on two mechanisms: thermodynamic and Marangoni film flow. The duration of migration of gas bubbles from the enamel layer under the effect of capillary force was determined in approximating the predominant role of the thermodynamic mechanism.