Bubble In Fluid Research Articles

Observing early cavitation damage evolution from repeated laser-induced single bubbles on aluminium, austenitic steel and nickel-aluminium bronze

Cavitation is the formation and collapse of gas bubbles in fluids due to local pressure changes. The implosion of these bubbles in the immediate vicinity of a surface can lead to shock waves and microjets, inducing plastic deformation and erosion of the material. Reproducible single bubbles with a defined diameter can be induced by a focused laser pulse in liquid, causing local evaporation. Combined with in-situ microscopy, this allows a direct correlation of single cavitation bubbles with the damage caused.Here, this method was applied for a detailed investigation of the damage development on pure aluminium (Al99.999%) as a model material, as well as on the technical alloys austenitic steel (316LVM; 1.4441) and NiAl bronze (NAB; CuAl10Ni5Fe5), especially regarding a comparison of the deformation behaviour. The damage evolution on these materials was monitored in-situ with a light microscope. Additionally, the damage was examined ex-situ using light microscopy, confocal microscopy and scanning electron microscopy.The investigated materials show clear differences in their deformation behaviour under cavitation load. Pure aluminium and 316LVM show a high degree of plastic deformation due to the high ductility and multiple slip planes in their fcc lattice structure. With increasing number of bubbles, strain accumulates at grain boundaries, where material removal initiates. This effect is more pronounced for 316LVM and appears in the presence of slip lines in the material. In contrast to this, NiAl bronze shows a different deformation behaviour, mainly due to the more complex microstructure. The soft fcc copper matrix deforms easily, whereas the hard intermetallic precipitates (containing Fe, Al, and Ni) act as an impediment for plastic flow. This leads to a more localized damage than in the other materials.

Effect of the magnetic field configuration on the detachment of gas bubbles in a magnetic fluid

The process of detachment of gas bubbles in a vertical channel filled with a magnetic fluid from a gas cavity in uniform magnetic field is studied. The behavior of the air–magnetic fluid interface now of separation is considered and dependences of the size of the detached bubbles on the configuration of the magnetic field, concentration of the magnetic fluid, and channel thickness are shown.

Effect of the Magnetic Field’s Configuration on the Detachment of Gas Bubbles in a Magnetic Fluid

Effect of the Magnetic Field’s Configuration on the Detachment of Gas Bubbles in a Magnetic Fluid

Numerical Study of Dielectric Fluid Bubble Behavior in Microchannel Evaporator in Presence of Diverging Electric Field

Herein, the diverging dielectrophoretic (DEP) electrode is designed to extract the vapor bubbles generated in a flow-boiling evaporator. The DEP and hydrodynamic forces acting on the undeformable single vapor bubble in the diverging electrode are estimated by the uncoupled flow and electrostatic simulation. The Maxwell stress, static pressure, and viscous shear stress on the bubble surface are considered. The diverging DEP electrode successfully generates a net force that acts on the bubble in the flow direction. The DEP force is dominant against drag at a low imposed mass flux and high applied electric field, where heat transfer enhancement could be expected. A large DEP force pushing the bubble toward the electrode is found when the bubble is close to the electrode.

Noninvasive fluid bubble detection based on capacitive micromachined ultrasonic transducers

Ultrasonic fluid bubble detection is important in industrial controls, aerospace systems and clinical medicine because it can prevent fatal mechanical failures and threats to life. However, current ultrasonic technologies for bubble detection are based on conventional bulk PZT-based transducers, which suffer from large size, high power consumption and poor integration with ICs and thus are unable to implement real-time and long-term monitoring in tight physical spaces, such as in extracorporeal membrane oxygenation (ECMO) systems and dialysis machines or hydraulic systems in aircraft. This work highlights the prospect of capacitive micromachined ultrasonic transducers (CMUTs) in the aforementioned application situations based on the mechanism of received voltage variation caused by bubble-induced acoustic energy attenuation. The corresponding theories are established and well validated using finite element simulations. The fluid bubbles inside a pipe with a diameter as small as 8 mm are successfully measured using our fabricated CMUT chips with a resonant frequency of 1.1 MHz. The received voltage variation increases significantly with increasing bubble radii in the range of 0.5–2.5 mm. Further studies show that other factors, such as bubble positions, flow velocities, fluid medium types, pipe thicknesses and diameters, have negligible effects on fluid bubble measurement, demonstrating the feasibility and robustness of the CMUT-based ultrasonic bubble detection technique.

Growth and stability of bubbles in a yield stress fluid

Experiments are reported that explore the onset of motion of bubbles in a model yield stress fluid, Carbopol gel. Starting from a trapped spherical bubble in a gel, the yielding limit for the bubble motion is obtained by gradually expanding the bubble via a stepwise decrease in pressure. Our results show that at the yielding limit bubbles are longer and thinner when they are in a higher concentrated gel. This is suggestive of a link between the shape and size of the bubbles at the onset of motion and the rheology of the material, in particular elastic behaviour below the yielding point. Particular attention has been paid to investigating the dynamic response of gel during the bubble growth. Subjecting the bubble to a periodic change in the pressure confirms the irreversibility of the gel deformation and its hysteresis, which are hallmarks of nonlinear viscoelastic behaviour of the gel before yielding. In this context, the periodic expansion and contraction of the bubbles leave residual deformation (stresses) in the gel which facilitates the liberation of bubbles.

Gravitational waves from bubble collisions and fluid motion in strongly supercooled phase transitions

We estimate the gravitational wave spectra generated in strongly supercooled phase transitions by bubble collisions and fluid motion. We derive analytically in the thin-wall approximation the efficiency factor that determines the share of the energy released in the transition between the scalar field and the fluid. We perform numerical simulations including the efficiency factor as a function of bubble radius separately for all points on the bubble surfaces to take into account their different collision times. We find that the efficiency factor does not significantly change the gravitational wave spectra and show that the result can be approximated by multiplying the spectrum obtained without the efficiency factor by its value at the radius R_{textrm{eff}} simeq 5/beta , where beta is the approximate inverse duration of the transition. We also provide updated fits for the gravitational wave spectra produced in strongly supercooled transitions from both bubble collisions and fluid motion depending on the behaviour of the sources after the collision.

Analysis of Fluid-Structure Coupling Vibration Characteristics of Pipeline Transporting Bubbly Fluid Medium: With Application to Luxury Passenger Ship Life Area Pipeline

When pipelines are transporting bubbly fluid medium, due to the coalescence and breakage behaviours of the bubbles, the pressure distribution at the wall is not uniform and the structure response is more complex. The bubbly beverage pipeline in the life area of the luxury passenger ship is a typical scene of the pipeline transporting bubbly fluid medium. In this paper, the two-way fluid-structure coupling analysis is carried out on such a scene with the aid of ANSYS software and the PBM model is introduced to characterize the dynamic properties of bubbles. At the same time, the accuracy of this calculation method is verified by the scaling experiment. On this basis, the response of the pipeline under the excitation of bubbly fluid is calculated for different inlet velocities and gas volume fractions, and the effectiveness of common vibration damping measures is evaluated. The result shows that the addition of bubbles to the fluid medium has a significant effect on the distribution of the flow field in the pipeline during transport, and the vibration acceleration values of the pipe wall also increase significantly. This method enables accurate simulation of the vibration characteristics of bubbly fluid medium pipelines.

Modeling dynamic behavior of two magnetic microbubbles in ultrasonic and magnetic fields

Magnetic microbubble (microbubble coated with magnetic nanoparticles) has the advantages of hybrid encapsulated shell, non-invasive fields manipulation and drug/gene delivery, which promotes a broad application prospects in both scientific research and clinic communities. In this work, the encapsulated shell coated with magnetic nanoparticles has been translated into the equivalent problem about bubble in the magnetic fluid. Behavior of two bubbles in the magnetic fluid are theoretically studied by using Lagrange formalism. We evaluate the manipulation of acoustic and magnetic fields on two bubbles dynamics. Magnetic pressure generated by magnetic field increases the pulsating amplitude of each bubble, affects bubbles translation and enhances the gas pressure and temperature inside bubble. Besides, bubbles attraction is caused by the competition between viscous drag and attractive secondary Bjerknes force related to bubble pulsation. In addition, the attractive force caused by magnetic field is useful at very close distance between bubbles, and its effect is quite small compared to the attraction driven by ultrasound. These findings may have implications for ultrasound guided drug delivery using microbubbles coated with magnetic nanoparticles, especial their manipulation in magnetic field.

Steady-State Two-Phase Flow of Compressible and Incompressible Fluids in a Capillary Tube of Varying Radius

We study immiscible two-phase flow of a compressible and an incompressible fluid inside a capillary tube of varying radius under steady-state conditions. The incompressible fluid is Newtonian and the compressible fluid is an inviscid ideal gas. The surface tension associated with the interfaces between the two fluids introduces capillary forces that vary along the tube due to the variation in the tube radius. The interplay between effects due to the capillary forces and the compressibility results in a set of properties that are different from incompressible two-phase flow. As the fluids move towards the outlet, the bubbles of the compressible fluid grows in volume due to the decrease in pressure. The volumetric growth of the compressible bubbles makes the volumetric flow rate at the outlet higher than at the inlet. The growth is not only a function of the pressure drop across the tube, but also of the ambient pressure. Furthermore, the capillary forces create an effective threshold below which there is no flow. Above the threshold, the system shows a weak nonlinearity between the flow rates and the effective pressure drop, where the nonlinearity also depends on the absolute pressures across the tube.

Study on Hydrodynamics Characteristics of a Single Bubble in Viscoelastic Fluid at Low Weissenberg Numbers

Study on Hydrodynamics Characteristics of a Single Bubble in Viscoelastic Fluid at Low Weissenberg Numbers

Research on hydraulic actuators that utilize the compressibility of air bubbles in hydraulic fluid as a shock absorbing effect

Research on hydraulic actuators that utilize the compressibility of air bubbles in hydraulic fluid as a shock absorbing effect

Formation and Behaviour of Active Droplets and Bubbles in a Magnetic Fluid in an Inhomogeneous Magnetic Field

This work proposes a new technique for creating active bubbles and droplets with a non-magnetic core and a coating formed by a magnetic fluid. The procedure consists of the injection of a non-magnetic phase into a magnetic one that is supported by the presence of an inhomogeneous magnetic field from the source, which combines an annular magnet and an electromagnet. We explored various modes leading to different active bubbles and drops as well as the influence of the magnetic field on the size, velocity, and acceleration of the formed active droplets. It is shown that active bubbles change their trajectory under the action of a constant magnetic field and also disintegrate under the action of a pulsed one. This provides a new mechanism for controlling the absorption of droplets and bubbles using a magnetic field. Therefore, these results can be applied to create droplet-based microfluidics systems, in which an inhomogeneous magnetic field can be used for focusing droplet and bubble flows in a magnetic fluid.

Memoryless drop breakup in turbulence.

The breakup of drops and bubbles in turbulent fluids is a key mechanism in many environmental and engineering processes. Even in the well-studied dilute case, quantitative descriptions of drop fragmentation remain elusive, and empirical models continue to proliferate. We here investigate drop breakup by leveraging a novel computer code, which enables the generation of ensembles of experiments with thousands of independent, fully resolved simulations. We show that in homogeneous isotropic turbulence breakup is a memoryless process whose rate depends only on the Weber number. A simple model based on the computed breakup rates can accurately predict experimental measurements and demonstrates that dilute emulsions evolve through a continuous fragmentation process with exponentially increasing time scales. Our results suggest a nonvanishing breakup rate below the critical Kolmogorov-Hinze diameter, challenging the current paradigm of inertial drop fragmentation.

Motion of a Taylor bubble in a realistic shear-thinning fluid

<h2>Abstract</h2> This talk will focus on the motion of a gaseous Taylor bubble in a capillary tube. Although the dynamics of a bubble in a Newtonian liquid has been the subject of several studies since the seminal works Taylor and Bretherton, the case where the fluid exhibits a shear-thinning behaviour is much less understood. To fill this gap, we derive a lubrication model in the film region to identify the scaling laws for the bubble speed and the film thickness as a function of the Ellis number and the degree of shear-thinning. Our model identifies a universal scaling law for the effective viscosity that accounts for the interplay of the zero-shear-rate and shear-thinning effects. After discussing the features of the front and rear menisci, we present an analysis of the recirculation vortexes ahead of the bubble. In the final part of the talk, we show the results of recent numerical simulations that validate the proposed theory and suggest a strategy to account for the effect of finite capillary numbers on the scaling law for the film thickness in the case of shear-thinning fluids.

Computational fluid dynamic investigating the reactive species transfer across the interface of a single rising bubble

This study implements a new solver (reactiveInterFoam) to simulate the component mass transfer alongside deformable gas–liquid interfaces. Mass transfer from the rising bubble in a quiescent Newtonian fluid is simulated. An effect of bubble hydrodynamics on the simultaneous diffusion reaction and selectivity of the cyclohexane oxidation process is investigated on a two-dimensional axisymmetric domain. The color function volume of fluid (CF-VoF) technique is applied to capture the deformable interface, and the continuous species transfer method is used to monitor the gas–liquid mass transfer behavior. Several simulations have been conducted to validate the model reliability to forecast component mass transfer from the bubble to the liquid phase, bubble shape, and flow field. Simulation findings approved that the rate of mass transfer is a function of boundary’s concentration, layer thickness, and bubble surface area. Furthermore, the selectivity increases by decreasing bubble diameter in both spherical and ellipsoidal regimes. The small bubbles with a lower Reynolds number have higher average selectivity. Comparing the simulated bubble shape and the grace chart indicates that the suggested numerical method can perfectly predict bubble regimes. The absolute average relative deviation (AARD%) of 14.59% has been observed between the terminal velocities predicted by the numerical simulation and six experimental measurements.

Dispersion of a passive scalar around a Taylor bubble

The motion of Taylor bubbles in capillaries is typical of many engineering and biological systems, ranging from subsurface flows to small-scale reactors. Although the hydrodynamics of elongated bubbles has been the object of several studies, the case where a solute is transported in the surrounding liquid and surface mass-transfer mechanisms act on the solid wall or the bubble–fluid interface is much less understood. To fill this gap, we investigate the transport problem around a confined Taylor bubble to access the competition between advection, diffusion and surface mass transfer in the different regions of the bubble. With this aim, we derive a one-dimensional advection–diffusion–mass-transfer equation where the transport mechanisms are described through an effective velocity, an effective diffusion coefficient and an effective Sherwood number. Our model generalises the Aris–Taylor dispersion to the case of a Taylor bubble and clarifies the impact of surface mass transfer in the advection and diffusion dominated regimes for both the front and rear menisci. The model recovers the typical Pèclet square relationship of the effective diffusion coefficient, which also depends on the film thickness. Also, when the Pèclet number balances with the Sherwood number, there exist conditions that lead to the formation of hot spots of concentration. We show that the typical shape oscillations of the bubble rear locally enhance superficial mass transfer. Finally, we study the transport problem in the uniform film region where the concentration field can be found analytically.

Hydrodynamic interaction of a bubble pair in viscoelastic shear-thinning fluids

We experimentally investigate the interaction between a pair of bubbles ascending in a stagnant viscoelastic shear-thinning fluid. In particular, we focus on the effect of bubble size, across the velocity discontinuity, on the bubble-bubble interaction. Compared to the drafting–kissing–tumbling (DKT) behavior in Newtonian fluids, bubbles in the viscoelastic shear-thinning fluid exhibit a drafting–kissing–dancing (DKD) phenomenon. In the dancing phase, the bubble pair repeatedly interchange their relative leading and trailing positions as they rise to the free surface. To gain further insights, the flow fields around the bubble pair interaction are obtained using particle image velocimetry (PIV). From the experimental results, we suggest that the elasticity, deformability, and negative wake are responsible for such an interaction between the bubble pair, thus revealing the fundamental physics of bubble clustering often observed in non-Newtonian fluids. • Strikingly different two bubble interactions in viscoelastic shear-thinning fluids. • At critical bubble volume, a discontinuity in the bubble velocity occurs. • For subcritical bubble pairs, the bubbles attract to form chains and coalesce. • Whereas, in supercritical bubble pairs, a ‘dancing’ oscillating behavior is observed. • Negative wake, deformability, and elasticity determine the type of interaction.

The partitioning behavior of Mo during magmatic fluid exsolution and its implications for Mo mineralization

Most of the global Mo resources are derived from porphyry-type ore deposits, the formation of which hinges critically on the ability of an exsolving magmatic fluid to efficiently extract the available Mo from the silicate melt. However, existing data on the extraction efficiency of Mo upon fluid exsolution is inconsistent. In this study, we determine the partition coefficient of Mo between aqueous fluids and granitic melts (DMof/m) at 800 °C, 150 MPa and the oxygen fugacity of the Ni-NiO buffer. To mitigate the problem of disequilibrium resulting from low diffusion of Mo in granitic melts, a new experimental method has been used, which allows the attainment of local equilibrium between silicate melt and microscopic-sized fluid bubbles on reasonable timescales. The results show that DMof/m increases from 2.2 ± 0.6 (1σ) to 33.3 ± 5.4 (1σ) as the total Cl concentration in the magmatic fluid (mCltotal) increases from 1 to 16 mol/kg H2O, with DMof/m = 3.1 ± 0.9 (1σ) for pure water. At a fixed mCltotal = 2 mol/kg H2O, DMof/m is constant at ∼ 3.2 at HCl/total Cl ratios varying between 0.09 and 0.33. The observed partitioning data indicates that Mo was dominantly present as (Na,K,H)MoO3Cl in the aqueous fluid at the experimental conditions. The addition of 4 wt% S to the fluid caused no change in DMof/m at 2 mol/kg H2O total chloride concentration, indicating that S2- does not complex with Mo at the employed experimental P-T conditions. Numerical modeling suggests that Mo concentration in the exsolved magmatic fluid and overall Mo extraction efficiency is favored by delayed fluid saturation during magma crystallization and high initial magmatic Cl concentration, respectively. However, the Mo extraction efficiency by the fluid is low enough to necessitate a large magma chamber to provide enough Mo to form a large-sized Mo deposit.

Methane Pyrolysis in a Liquid Metal Bubble Column Reactor: A Model Approach Combining Bubble Dynamics with Byproduct and Soot Formation

Methane pyrolysis is a promising bridging technology to mitigate the effects of climate change. By decarbonizing natural gas, hydrogen can be produced from fossil fuels without creating CO2 emissions. The focus of future process optimization should not only be on the hydrogen yield and the energy efficiency but also on the carbon products and possible byproduct formation. During methane pyrolysis in a liquid metal (LM) bubble column reactor, at least two very distinct types of carbon are synthesized: soot particles and graphene‐like carbon sheets. A model is presented that couples a description of bubble dynamics in a LM bubble column reactor with a kinetic mechanism, originally developed for the combustion of natural gas that includes byproduct and soot formation. The model is validated by comparing it with an experimental dataset that covers a broad range of process conditions and the implications for carbon and byproduct formation are discussed. The good agreement of model results and experimental data shows that the combustion kinetic mechanism may be applied to methane pyrolysis and that the selected way of modeling bubble fluid dynamics in LM results in a good estimation of the actual bubble residence time in the optically nonaccessible liquid.