Bubble Displacement Research Articles

A study on enhancing oil recovery efficiency through bubble displacement based on microfluidic technology

A study on enhancing oil recovery efficiency through bubble displacement based on microfluidic technology

Interaction of ultrasonically driven bubble with a soft tissue-like boundary

This study investigates the size-dependent dynamics of bubbles and their interaction with soft boundaries under various ultrasound (US) conditions. We found that bubble behavior is influenced by size, with smaller bubbles displaying reduced inertial motion in similar ultrasound environments. Detailed analyses of three bubble sizes (1.5 µm, 15 µm, and 150 µm) next to a soft 1 kPa boundary revealed distinct patterns in radial oscillation, bubble center displacement, and boundary deflection for different ultrasound frequencies (5 kHz − 4 MHz). The smallest bubble maintained a spherical shape, while the largest experienced significant shape changes, indicative of impending jet formation. Investigating interactions at various frequencies highlighted the collapse tendency of the larger bubbles, showcasing maximum radial amplitude, displacement, and bubble wall velocity around its natural frequency. The presence of a soft boundary minimally affected radial amplitude and velocity, while the bubble displacement was contingent on the soft boundary modulus. Furthermore, boundary responses demonstrated that softer boundaries experienced less stress during bubble oscillations, exhibiting sharper peaks at resonance frequencies for larger bubbles. These findings provide valuable insights into optimizing ultrasound conditions for a variety of applications, highlighting the influence of bubble size and boundary properties on outcomes.

Hydrodynamics of bubble flow through a porous medium with applications to packed bed reactors

AbstractGas‐liquid flows through packed bed reactors (PBRs) are challenging to predict due to the tortuous flow paths that fluid interfaces must traverse. Experiments at the International Space Station showed that bubble and pulse flows are predominately observed under microgravity conditions, while the trickle and spray flows observed under terrestrial conditions are not present in microgravity. To understand the physics behind the former experiments, we simulate bubble flow through a PBR for different packing‐particle‐diameter‐based Weber numbers and under different gravity conditions. We demonstrate different pore‐scale mechanisms, such as capillary entrapment, buoyancy entrapment, and inertia‐induced bubble displacement. Then, we perform a quantitative analysis by introducing new dynamic scales, dependent upon the evolving gas‐liquid interfacial area, to understand the dynamic trade‐offs between the inertia, capillary, and buoyancy forces on a bubble passing through a PBR. This analysis leads us to define new dimensionless Weber‐like numbers that delineate bubble entrapment from bubble displacement.

Optical measurement of the shear stress and velocity distribution in an idealized deglutition process

The rheological properties of food have an impact on physical interaction with various haptic sensors in the mouth during the chewing and swallowing process. Therefore, the investigations on food rheology are dedicated to improving the texture or mouthfeel of a product. It is advantageous to perform such rheological measurements in geometries and under conditions that reflect the flow conditions during the food distortion in the mouth cavity. Such investigations have been limited primarily to viscous or lumpy foodstuffs. Our study is dedicated to the compression of liquid foams in an idealized deglutition process. To reflect the flow conditions in such a process, we developed an experimental setup consisting of a quasi-two-dimensional replica of the palate and a movable tongue. During the idealized deglutition process, the optical measurements of bubble displacement and deformation were performed. The deglutition process was modelled by varying the compression speed of the tongue towards the static palate. The variation in mean bubble size and liquid fraction of foam for two tongue geometries with different roughness are available. It is observed that the velocity distribution of bubble motion during the deglutition corresponds to a rigid body flow, notwithstanding the surface roughness. The resulting wall-shear stress, however, was higher for the rough tongue plate for all foam bubble sizes and liquid fraction. The resulting velocity and wall-shear stress distributions can provide information about the haptic perception in the mouth during the swallowing process.

Characteristics of bubble behavior in petal-shaped fuel rod bundle channels under different flow conditions

The petal-shaped fuel element is a novel type of fuel element suitable for small-scale reactors. The motion of bubbles in the rod bundle channel has a significant impact on the surrounding flow and temperature fields, thereby influencing the two-phase flow and heat transfer characteristics. To investigate the dynamics of bubbles in the rod channel of the petal-shaped fuel rod, we simulated the rising motion of bubbles with different inlet flow rates using the volume of fluid method (VOF). We obtained the trajectory, rising speed, and shape changes of the bubbles with varying initial sizes, and analyzed the flow field around the bubbles. Our results indicate that the transverse displacement of bubbles in the radius range of 0.5 mm–1.25 mm increases gradually with their initial size, and the degree of deformation and maximum rising velocity of the bubbles also increase. However, bubbles with a radius of 1.5 mm experience less transverse displacement due to their larger size and contact with multiple fuel rods during the ascent process. Furthermore, the transverse displacement distance of the bubble increases and then decreases with the increase of fluid flow rate in the channel, while the aspect ratio of the bubble remains unaffected by the inlet flow rate. The study of bubble behavior sheds light on the mechanism of bubble motion in the channel of petal-shaped rod bundles, and provides a foundation for the study of two-phase flow and heat transfer in the channel.

Investigation of surfactant effect on ozone bubble motion and mass transfer characteristics

The low solubility and low mass transfer efficiency of ozone (O3) in water are important reasons for limiting the application of ozone oxidation technology and advanced ozone oxidation technology. Low-dose surfactants were introduced to affect the behavior of ozone bubbles, influencing the ozone mass transfer efficiency. The motion of ozone bubbles in three different types of surfactant solutions (polyoxyethylene lauryl ether (Brij35), sodium dodecylsulfate (SDS), and cetyltrimethylammonium bromide (CTAB)) was observed. The decrease in surface tension led to a decrease in bubble size, a tendency to spherical shape, an increase in gas content and residence time, a decrease in lateral displacement of a single bubble, and a more stable trajectory. The effect of surfactants on ozone mass transfer was further investigated. The addition of surfactant was found to increase the gas-liquid interface area but decrease the liquid phase mass transfer coefficient, and the extent of the two opposite effects varied for different surfactants. The analysis combined with the removal of pollutant p-Nitrophenol (PNP) showed that the addition of the nonionic surfactant Brij35 and the anionic surfactant SDS inhibited ozone mass transfer, while low concentrations of the cationic surfactant CTAB enhanced ozone mass transfer. When the CTAB concentration was 3 mg L−1, the ozone volume mass transfer coefficient reached a maximum of 0.2902 min−1.

Cavitation bubble induced wall shear stress on an elastic boundary

A cavitation bubble imposes shear stresses onto a nearby structure during its expansion and collapse. Experimentally, we probe the tangential stresses on an elastic surface by measuring the displacement of embedded particles and the deformation of an elastic structure. Corresponding numerical simulations are done using a fluid–structure interaction Volume-of-Fluid solver in OpenFOAM, where a linear elastic solid is coupled to two viscous, immiscible, and compressible fluids. We find good agreement in terms of bubble dynamics and displacement motions. During the initial bubble expansion and its first collapse, the experiment agrees with the simulation that the strain of the elastic sheet at a distance of 1.25 Rmax from the stagnation point center is larger than at 0.51 Rmax. The maximum lateral strain occurs at a non-dimensionalized bubble stand-off distance of γ≈1.1. The highest calculated wall shear stress is 250 kPa (for position y = 0). However, the largest overall shear stress of 1.9 MPa is found within the elastic sheet at y=24 μm that corresponds to a maximum displacement of Dx=44.5μm. Thus, fracture may start from within the elastic material rather than from the surface. To further examine the fluid–structure interaction, we construct a simple axisymmetrical elastic ring and analyze its deformation. In this case, we find strong deformations not only during the bubble collapse but also during the bubble's initial expansion.

Vertically neutral collapse of a pulsating bubble at the corner of a free surface and a rigid wall

Vertically neutral collapse of a pulsating bubble occurs when the boundaries above or below the bubble balance the buoyancy effect over a pulsation. In this study, the vertically neutral collapse of a bubble near a vertical rigid wall below the free surface is investigated. The boundary integral method (BIM) is employed to model the bubble dynamics with an open-domain free surface. Moreover, this method is validated against several buoyant bubble experiments. Bubble dynamics in such conditions are associated with three dimensionless parameters: the bubble-free surface distance $\gamma _{{f}}$ , bubble–wall distance $\gamma _{{w}}$ and buoyancy parameter $\delta$ . We derive the Kelvin impulse of a spherical bubble and the algebraic relationship for vertically neutral collapse, which proves to be accurate for predicting vertically neutral collapse when the bubble is relatively far from the boundaries. Four patterns of the vertically neutral collapse of the bubble for different $\gamma _{{w}}$ and $\gamma _{{f}}$ are identified: (i) formally downward jet; (ii) annular collapse; (iii) horizontal jet; and (iv) weak jet. Despite the downward jet shape, the ‘formally downward jet’ is in the vertically neutral collapse state in terms of the profile of toroidal bubbles and the orientation of local high-pressure zones around the bubble at jet impact. A bulge with a high curvature above the bubble in the ‘annular collapse’ pattern is formed during bubble collapse under two local high-pressure zones at the left and right extremities of the bubble. The ‘horizontal jet’ pattern has the greatest potential to attack the wall, and the power laws of the moment of the jet impact, jet velocity and bubble displacement with respect to the theoretical Kelvin impulse are discussed. In particular, we quantitatively illustrate the role of the free surface on bubble migration towards the wall through the variational power-law exponents of the bubble displacement with respect to $\gamma _{{w}}$ .

Bubble collapse near porous plates

The collapse of a gas or vapour bubble near a non-porous boundary is directed at the boundary due to the asymmetry induced by the nearby boundary. High surface pressure and shear stress from this collapse can damage, or clean, the surface. A porous boundary, such as a filter, would act similarly to a non-porous boundary but with reduced asymmetry and thus reduced effect. Prior research has measured the cleaning effect of bubbles on filters using ultrasonic cleaning, but it is not known how the bubble dynamics are fundamentally affected by the porosity of the surface. We address this question experimentally by investigating how the standoff distance, porosity, pore size and pore shape affect two collapse properties: bubble displacement and bubble rebound size. We show that these properties depend primarily on the standoff distance and porosity of the boundary and extend a previously developed numerical model that approximates this behaviour. Using the numerical model in combination with experimental data, we show that bubble displacement and bubble rebound size each collapse onto respective single curves.

Experimental Study on Three-Dimensional Bubble Rising Behaviours by Virtual Stereo Vision

This study addresses the measurement of three-dimensional (3D) bubble rising behaviour in still water with bubble equivalent diameters ranging from 2.61 mm to 5.11 mm using high-speed imaging and virtual stereo vision technology. The bubble shape, 3D trajectory/velocity, displacement angular frequency and terminal velocity of bubbles are analysed. The bubble equivalent diameter is obtained by the elliptic volume method. The bubbles are divided into small and large bubbles with a critical equivalent diameter of 4.49 mm, according to whether they are accompanied by deformation. The small bubbles (deq<4.49 mm) are spherical or ellipsoid, while the large bubbles (deq≥4.49 mm) exhibit ellipsoid, mushroom and hat shapes. The 3D trajectory is obtained by 3D reconstruction of bubble centroid coordinates. The rising trajectory of small bubbles shows 3D spiral motion, while the pitch increases gradually with the increase in the equivalent diameter. The trajectory of large bubbles is a two-dimensional (2D) zigzag. The bubble displacement curves in x- and z-directions are evaluated with third-order Fourier fitting. The results show that the bubble displacement frequency in the x and z-directions decreases with the increasing bubble diameter, and the displacement frequency in the xdirection is larger than that in the z-direction. The relative proportions of the viscous force, buoyancy, surface tension and inertial force on bubbles with different equivalent diameters are different, which leads to three trends in the vertical velocity of bubbles within the diameter range of this study. Finally, the bubble terminal velocity in still water is investigated. The terminal velocity first decreases and then increases with the increase in the equivalent diameter. The minimum value is 16.17 cm/s when the diameter of the bubble equivalent diameter is 4.49 mm. Moreover, the applicability of some classical prediction models is discussed.

Experimental Investigation of Bubble Oscillation and Leaping Driven by Thermocapillary Effects with Non-condensable Gas

Boiling phase-change plays a crucial role in heat transfer as it can dissipate higher heat fluxes than single phase. Bubble nucleation, growth, motion (oscillation or leaping), coalescence and departure, govern the boiling and the heat transfer performance on wires. Many factors affect the bubble mechanisms and interactions taking place, which include the nature of the fluid, experimental conditions, thermocapillary effects, etc. This work investigates the bubble oscillation and leaping phenomena caused by thermocapillary effects in the presence of oxygen and air as non-condensable gases during boiling on a platinum micro-wire. More in particular, the bubble oscillation performance is compared under various bulk temperatures and heat fluxes for two different non-condensable gases. It is observed that for a similar fluid bulk temperature, the lower the heat flux the longer the bubble displacement. Moreover, bubble oscillation phenomenon is influenced by the concentration of non-condensable gas dissolved in the liquid showing larger harmonic periods and shorter waiting times with decrease in the contact line pinning force by approximately 7–44% in the presence of air when compared to nitrogen. Last during oscillations, bubble leaping phenomenon was observed as a consequence of the interaction between the jet flows above the oscillating bubble.

Characterization of Bubble Transport in Porous Media Using a Microfluidic Channel

This study investigates the effect on varying flow rates and bubble sizes on gas–liquid flow through porous media in a horizontal microchannel. A simple bubble generation system was set up to generate bubbles with controllable sizes and frequencies, which directly flowed into microfluidic channels packed with different sizes of glass beads. Bubble flow was visualized using a high-speed camera and analyzed to obtain the change in liquid holdup. Pressure data were measured for estimation of hydraulic conductivity. The bubble displacement pattern in the porous media was viscous fingering based on capillary numbers and visual observation. Larger bubbles resulted in lower normalized frequency of the bubble breakthrough by 20 to 60 percent. Increasing the flow rate increased the change in apparent liquid holdup during bubble breakthrough. Larger bubbles and lower flow rate reduced the relative permeability of each channel by 50 to 57 percent and 30 to 64 percent, respectively.

Acoustophoretic trapping of particles by bubbles in microfluidics

We present in this paper a simple method to produce strategic acoustic particle capture sites in microfluidic channels in a controlled way. Air bubbles are intermittently injected into a micro-capillary with rectangular cross section during a flow motion of liquid suspensions containing micron-sized particles or particles to create bubble-defined “micro-gaps” with size close to 200 µm and spheroidal geometry. The establishment of a 3D standing acoustic wave inside the capillary at a frequency close to 1 MHz produces different radiation forces on solid particles and bubbles, and acoustic streaming around the bubble. While the sample flows, part of the particles collect along the acoustic pressure node established near the central axis and continue circulating aligned through the capillary until reaching the end, where are released enriched. Meanwhile, the bubble travels very fast toward positions of maximum pressure amplitude beside the channel wall, driven by Bjerkness forces, and attach to it, remaining immovable during the acoustic actuation. Some particles adhere to its membrane trapped by the acoustic streaming generated around the oscillating bubble. Changes of frequency were applied to analyze the influence of this parameter on the bubble dynamics, which shows a complete stability once attached to the channel wall. Only increasing the flow motion induces the bubble displacements. Once reached the open air at the end of the capillary, the bubble disappears releasing the trapped particles separated from their initial host suspension with a purity degree. The device presents a very simple geometry and a low-cost fabrication.

Effects of microconvection on bubble displacement during water electrolysis under microgravity

Water electrolysis is the electrochemical process of passing an electrical current through water to separate it into hydrogen and oxygen gases at two electrodes. The hydrogen and oxygen gas bubbles produced during water electrolysis are displaced from the electrodes by two classes of phenomena, which we categorize as either buoyancy or microconvection. Buoyancy is the phenomenon caused by the upward force exerted by a fluid. We define microconvection as the effects of non-buoyant bubble-displacing phenomena, such as Brownian motion. We determined the role of microconvection during water electrolysis by comparing the formation and behavior of gas bubbles under both terrestrial gravity (1G) on Earth and microgravity (μG) aboard the International Space Station. During water electrolysis under 1G, buoyancy-induced macroconvection dominates microconvection attributed to non-buoyant forces. The accumulation of gas bubbles can impede the contact of the buffer solution and platinum electrode, hindering the current flow for further electrolysis. We studied this phenomenon with a camera and current sensor. We hypothesized that microconvection has a weaker effect in displacing bubbles compared to buoyancy and that the current will decrease more over time under μG due to extended contact of the gas bubbles with the electrodes during electrolysis. Our results showed that microconvection plays a non-negligible role in bubble displacement in water electrolysis, a finding which has broad applications, including zero-pollution hydrogen production and hydrogen fuel cells.

Modeling bubble collapse anisotropy in complex geometries

In this work we present an inexpensive model that unifies bubble collapse properties in arbitrary geometries. The model produces a single value that quantifies the asymmetry known as the `anisotropy parameter'. We show that bubble collapse properties, such as bubble displacement, depend primarily on this parameter.

Automated bubble analysis of high-speed subcooled flow boiling images using U-net transfer learning and global optical flow

Capturing and analyzing the bubble dynamics is crucial to improving the understanding of boiling heat transfer mechanisms and predicting boiling heat transfer coefficient and boiling crisis. High speed video (HSV) imaging has been used for decades towards this end. Still, there is no universal approach to quantitatively analyze bubble dynamics from HSV images.In this study, we propose a data-driven post-processing approach to segment, track, and identify wall-attached vapor bubbles from HSV images of the boiling process in subcooled flow conditions. Firstly, we employ a transfer learning framework with a U-Net-based convolution neural network (CNN) architecture to detect and segment bubbles in HSV images of diverse contrast and surface texture using very little data (e.g., 10 images) for training. Then, we evaluate the trained CNN model with 100 ground-truth images, and the validation results show that the model accuracy and precision in detecting the optical footprint of bubbles are higher than 90%. Finally, we suggest a criterion to identify a condensing bubble based on the divergence of the bubble displacement, which is calculated from sequential segmented bubble images using a global optical flow code. Using this combination of machine learning and optical flow, we can identify nucleation sites and track the growth of bubbles nucleating at each site to quantify nucleation site density, nucleation frequency, and other fundamental boiling parameters. The proposed system is validated using results obtained on a special heater, which enables both infrared (IR) thermometry and HSV imaging on a metallic surface. We compare the fundamental boiling parameters obtained by the two different diagnostics. The results show good agreement. The difference between the measurements of nucleation site density, averaged nucleation frequency, and averaged growth time performed with the two techniques is always within ± 20% and mostly ± 10% of the values measured with IR thermometry.

Jetting and migration of a laser-induced cavitation bubble in a rectangular channel

The jetting behaviour and migratory characteristics of a laser-induced cavitation bubble in a rectangular channel are investigated both experimentally and numerically, for various combinations of the geometric and physical parameters of the system. High-speed photography is used to visualize the temporal development of the bubble shape, the formation of liquid jets during bubble collapse, and the bubble displacement in contact with the sidewalls of the channel during two oscillation cycles of the bubble. The bubble profiles, pressure contours and velocity vectors ambient to the bubble are obtained through numerical simulation results by using an Eulerian finite element method with a compressible liquid impact model. The jetting behaviour of the bubble varies between single jet formation and the formation of three liquid jets directed towards each wall of the channel. The numerical calculations indicate that the liquid jets directed towards the sidewalls of the channel reach maximum velocities of 100 m s−1while the peak velocity of the liquid jet directed towards the channel endwall is about 55 m s−1. A small bubble generated close to a sidewall of the channel develops only a single inclined jet during collapse. Such jets can reach velocities of up to 110 m s−1. A bubble displacement in contact with the sidewalls of the channels of 350 μm was observed during the first two oscillation cycles for a bubble with a maximum diameter slightly smaller than the height of the channel. The results of our investigations are compared to previous results obtained in similar configurations.

CFD simulation and experimental comparison of bubble-induced convection during electrochemical water splitting

The behavior of gas bubbles produced during electrochemical processes is of large interest because of the increase in cell overpotential induced by their production, the electrode surface covering by them and, finally, the detachment of these bubbles and their direct impact on the energy consumption during the reaction. In this work, we used coupled experimental and computational approaches to investigate bubble formation under those conditions where there are important convective effects. We have measured both normal and parallel velocity of the solution and built up a computational fluid dynamics (CFD) model. The results were compared to experimental data. Then, having the computational model validated by experimental data, we have simulated different conditions following bubble displacement. An important change of the surface covering is observed during the electrochemical reaction. Considering just the covering change, for example, there is up to 23 % increase comparing to the electrode edge and center. • Finite element method is suitable to evaluate the bubble-induced convection. • The bubbles create a vortex in the electrolyte. • The induced convection create a non-homogeneous gas covering over electrode surface. • The bubble size has an important effect in the covering variance.

Drift‐flux model for gas–liquid flow subjected to centrifugal fields

AbstractCentrifugal pumps are used in several industrial processes. It is common the operation of this equipment with gas–liquid mixtures, which is the case of the electrical submersible pumping artificial lift method used in the oil industry. The increase of free gas fraction inside the pump may lead to unstable operation and problems such as surging and gas locking phenomena to occur. In this study a drift‐flux model is proposed for the gas–liquid flow subjected to centrifugal fields using the impeller as an example. The model is closed with experimental data of bubble diameter, displacements and velocities acquired via high‐speed camera at several different rotational speeds and gas mass flow rates using water as the continuous medium. From the modeling and the forces balance in the bubbles, quantitative criteria for the start point of surging and gas locking conditions were proposed.

Active motion of contaminated microbubbles

In many natural and technological multi-phase systems, bubbles are exposed to surface-active contaminants (surfactants) that may cover the whole or part of the bubble interface. A partial coverage of the interface may result in a spontaneous self-propulsion mechanism, which is yet not fully characterized. Here, the self-propulsion dynamics of partially contaminated bubbles is examined using high-fidelity simulations. The simulations enable a detailed picture of the flow physics and interfacial mechanisms driving the transient active motion. Results also show that for the case of viscous surrounding and negligible surface diffusion the duration of the active motion is inversely proportional to the contaminated area fraction, and the corresponding bubble displacement is directly proportional to the clean fraction.