Bubble Motion Research Articles

Unravelling the existence of asymmetric bubbles in viscoelastic fluids

We study the motion and deformation of a single bubble rising inside a cylindrical container filled with a viscoelastic material. We solve numerically the mass and momentum balances along with the constitutive equation for the viscoelastic stresses, without assuming axial symmetry to allow the growth of three-dimensional disturbances. Hence, we may predict the emergence of the notorious knife-edge shape of the bubble, which is a result of a purely elastic instability triggered in the locality of the trailing edge. Our results compare well with existing experiments. We visualize, for the first time to the best of our knowledge, the flow kinematics and dynamics that arise downstream of the bubble. We propose two quantities, one kinematical and one geometrical, for the determination of the onset of the instability. We demonstrate that extension-rate thinning in the constitutive law is necessary for the emergence of the instability. Moreover, our results indicate that increasing (a) the deformability of the bubble and (b) the initial extension rate hardening of the viscoelastic material, prior to thinning, triggers the instability earlier. These novel findings help us formulate and propose a mechanism that controls the onset of the instability and explain why the knife-edge shape is not encountered as frequently.

Study on the Dynamic Characteristics of Single Cavitation Bubble Motion near the Wall Based on the Keller–Miksis Model

The dynamic model of cavitation bubbles serves as the foundation for the study of all cavitation phenomena. Solving the cavitation bubble dynamics equation can better elucidate the physical principles of bubble dynamics, assisting with the design of hydraulic machinery and fluid control. This paper employs a fourth-order explicit Runge–Kutta numerical method to solve the translational Keller–Miksis model for cavitation bubbles. It analyzes the collapse time, velocity, as well as the motion and force characteristics of bubbles under different wall distances γ values. The results indicate that as the distance between the cavitation bubble and the wall decreases, the cavitation bubble collapse time increases, the displacement of the center of mass and the amplitude of translational velocity of the cavitation bubble increase, and the minimum radius of the cavitation bubble gradually decreases linearly. During the stage when the cavitation bubble collapses to its minimum radius, the Bjerknes force and resistance experienced by the bubble also increase as the distance to the wall decreases. Especially in the cases where γ = 1.3 and 1.5, during the rebound stage of the bubble, the Bjerknes force and resistance increase, causing the bubble to move away from the wall. Meanwhile, this study proposes a radiation pressure coefficient to characterize the radial vibration behavior of cavitation bubbles when analyzing the radiation sound pressure. It is found that the wall distance has a relatively minor effect on the radiation pressure coefficient, providing an important basis for future research on the effects of different scale bubbles and multiple bubbles. The overall idea of this paper is to numerically solve the bubble dynamics equation, explore the characteristics of bubble dynamics, and elucidate the specific manifestations of physical quantities that affect bubble motion. This provides theoretical references for further engineering applications and flow analysis.

Effect of surfactant on dynamics and gas-liquid mass transfer for single carbon dioxide bubbles

In carbonation reaction, the impact of surfactants on the movement and mass transfer behavior of carbon dioxide bubbles were crucial for the production of high-quality silicon dioxide products. The study employed the Matlab image processing system to investigate the shapes, motion velocities, and rise path of single carbon dioxide bubbles within varying concentrations of cetyltrimethyl ammonium bromide (CTAB) solutions. This exploration aimed to elucidate the effect of CTAB on the movement and mass transfer coefficient (MTRC) of single carbon dioxide bubbles. Alterations in the CTAB solution concentration and bubble sizes significantly influenced the mass transfer and movement characteristics of single carbon dioxide bubbles. The conclusion was drawn through the computation of the MTRC of single carbon dioxide bubbles in deionized water and CTAB solutions: the addition of CTAB significantly reduced the mass transfer efficiency of carbon dioxide in deionized water, with the MTRC of CTAB solutions decreasing as the solution concentration increased. Utilizing the stagnant cap model, it can be concluded that CTAB's reduction of the MTRC of carbon dioxide was attributed to the high viscosity of the medium, low bubble velocity, stable flow conditions, and intensified adsorption degree of CTAB molecules at the gas-liquid interface. According to the significant periodic trajectories of single carbon dioxide bubbles in the stable range, the correlation between the trajectories of compressible bubbles in surfactant solution and mass transfer in liquid phase was established, and the previous method based on rigid sphere model was modified. The paper proposed the mechanism of CTAB's influence on single carbon dioxide bubbles, offering crucial theoretical insights into the industrial application of surfactants in the carbonation process for producing silicon dioxide.

Study on dynamic characteristics of cavitation in underwater explosion with large charge

Underwater explosions (UNDEX) generate shock waves that interact with the air–water interface and structures, leading to the occurrence of rarefaction waves and inducing cavitation phenomena. In deep-water explosions, complex coupling relationships exist between shock wave propagation, bubble motion, and cavitation evolution. The shock wave initiates the formation of cavitation, and their growth and collapse are influenced by the pressure field. The collapsing bubbles generate additional shock waves and fluid motion, affecting subsequent shock wave propagation and bubble behavior. This intricate interaction significantly impacts the hydrodynamic characteristics of deep-water explosions, including pressure distribution, density, and phase changes in the surrounding fluid. In this paper, we utilize a two-fluid phase transition model to capture the evolution of cavitation in deep-water explosions. Our numerical results demonstrate that the introduction of a two-phase vapor–liquid phase change model is necessary to accurately capture scenarios involving prominent evaporation or condensation phenomena. Furthermore, we find that the cavitation produced by the same charge under different explosion depths exhibits significant differences, as does the peak value of cavitation collapse pressure. Similarly, the cavitation produced by different charge quantities under the same explosion depth varies, and the relationship between cavitation volume and charge quantity is not a simple linear increase. The research methods and results presented in this paper provide an important reference for studying the dynamic characteristics of deep-water explosions.

Analysis of mechanisms of bubble characteristics and molten pool dynamics in EDM based on a three-phase flow model

Bubble characteristics and bubble volume fraction have significant effects on crater morphology and machining efficiency during electrical discharge machining (EDM) in liquid. Therefore, there is a need to elucidate the mechanism of bubble characteristics in EDM and analyze the mechanism of crater formation based on these bubble characteristics. However, since EDM is a transient multiphysics process, it is extremely difficult to understand bubble characteristics using experimental methods. Therefore, the generation, expansion, explosion, and disappearance of bubbles during EDM were simulated based on a three-phase flow model in this study. The model used the phase field method to track the boundary motion, judged the existence mode of each phase according to the order parameter gradient function, and analyzed the formation of crater morphology by the gradient of surface tension in the molten pool. The motion process of bubbles, the material removal mode, and the formation mechanism of crater morphology during the pulsed discharge were analyzed using the model. The results revealed that the periodic motion of the plasma channel would drive the molten pool to produce the corresponding periodic motion, and the bubbles would grow following the periodic motion of the molten pool. The material was removed in different ways in different periods, among which the removal mode of molten splash was predominant. The surface tension gradient inside the molten pool, the periodic motion of the molten pool, and the hydrostatic pressure in the molten region had a combined effect on bubble motion, the flow of the molten pool, and the formation of the crater morphology.

Research of bubble motion and correction of drag coefficient in viscous oil at low Reynolds number

As the core fundamental components in the field of fluid transmission and control, viscous oil fluid components determine the technological level of fluid machinery and high-end equipment. However, bubbles as effective cavitation nuclei widely exist in the interior of viscous oil fluid components, directly affecting their performance and technological development. In order to reveal the bubble motion characteristics in viscous oil and establish a high-precision prediction method, this paper focuses on No. 110 technical white oil and develops a visualized observation system for studying the motion characteristics and morphological features of bubbles in viscous oil. The bubble motion trajectory, rising rate, and force state are analyzed, and a prediction model for the drag coefficient is proposed and corrected. The research results indicate that during the rising process, the bubble morphologies in viscous oil show an elliptical shape. The oil temperature has a significant influence on the bubble motion characteristics, with the occurrence of oscillations during the rise process after reaching 80 °C. Additionally, a new prediction model for the drag coefficient of bubble is fitted, where the relative error of bubble motion rate can be controlled within 5.5% for 0.3 < Re < 50. This research provides significant theoretical significance and engineering application value.

Numerical simulation of the interaction between a planar shock wave and a backward-facing triangular bubble containing gases with different Atwood numbers

The interaction between a shock wave and an interface delineating two gases engenders intricate flow physics, with particular attention drawn to the hydrodynamic instability due to its practical significance. Previous studies have primarily focused on elucidating different wave patterns and instabilities evolution at the interface during the initial phase of shock interaction with cylindrical or spherical bubbles. However, scant literature has shifted its focus toward exploring the long-term morphology of bubbles, especially those characterized by polygonal interfaces. Notably, the detailed examination of shock interaction with a polygonal interface, such as a triangular one with a constant incident angle, remains largely unexplored in existing literature. Recently, the longtime evolution of detailed flow structures across the interface of shock-forward-facing triangular bubbles was captured by Kundu et al. [“A study on dynamics of shock-accelerated forward-facing triangular bubbles at different Atwood numbers,” Phys. Fluids 36, 016110 (2024)] through numerical simulation. In this study, the dynamics of a shock-accelerated backward-facing triangular interface containing various gases, namely, Sulfur Hexafluoride, Refrigerant-22, Argon, Neon, and Helium, is studied for a shock Mach number of 1.21. Simulations were performed by solving the two-dimensional Euler equation using low-dissipative advection upwind splitting methods (AUSMD), in conjunction with a derived ninth-order upwind scheme and a four-stage third-order Runge–Kutta scheme for temporal integration. The development of Richtmyer–Meshkov (RM) and Kelvin–Helmholtz (K–H) instabilities at the interface, mixing, and normalized movements of backward-facing triangular bubbles is captured at different Atwood (At) numbers.

Study on flow characteristics and phase holdup in a slurry bubble column coupled with mild agitation

A pilot-scale experimental setup was constructed to investigate the effect of mild agitation on the bubble characteristics and phase holdup in a slurry bubble column. Mild agitation positively impacts the axial uniform distribution of solid holdup, though it shows insignificant influence on the radial distribution. In homogenous regime, mild agitation promotes the coalescence of bubbles, and the effect becomes stronger with increasing agitator speed. The mild agitation contributes to a decrease in bubble size in heterogeneous flow regime. Mild agitation presents a significant effect on the gas holdup by adjusting the bubble size and bubble motion trajectory. The modification was introduced to predict the gas holdup considering the effects of mild agitation, a necessary consideration for applications requiring mild agitation. This adapted model predicts gas holdup with a maximum error of 12.9%.

Air entrainment by a hydrofoil in a high-speed water flow for design of bubbly drag reduction ships

We have investigated the flow behavior around a hydrofoil bubble generator in a high-speed channel flow up to 10 m/s for the first time to understand the air entrainment characteristics of this hydrofoil device caused purely by the inertia effect of water flow. This study is motivated by our previous success in achieving ship drag reduction for full-scale vessels (Kumagai et al., 2015). Depending on the water flow velocity U and the angle of attack of the hydrofoil α, three different major patterns were identified: continuous generation of dispersed bubbles, intermittent formation of an air cavity, and steady formation of a super air cavity that stretched behind the hydrofoil. The transition from the dispersed bubble state to the air cavity formation regime is explained theoretically using the equation of bubble motion coupled with a potential flow analysis. The air volume flow rate increased linearly with U, and its slope was steeper in the dispersed bubble state than in the air cavity formation regime. The highest air flow rate was realized at U = 9 m/s, which corresponds to the nominal air layer thickness at ta = 4.1 mm, and reaches the feasible range for realization of bubbly drag reduction for a long ship hull.

Bubble tracking method based on Kuhn-Munkres algorithm for boiling two-phase flow study

The study of bubble dynamics is important in various engineering applications as it can provide a fundamental understanding of the bubbly flow behavior. This paper presents a novel method for tracking bubble trajectories and classifying bubble behaviors, including formation, extinction, continuous movement, fragmentation, and coalescence. The method is based on the theory of perfect matching in bipartite graphs. By establishing the perfect matching between bubbles identified at adjacent time instants, judging the continuity of bubble motion, and simply calculating the number of bubbles in the neighbor of matching bubbles at adjacent time instants, the method can deal with the challenging situation where the bubble position and volume significantly change between two adjacent time instants. The method is validated in a simulated vertical pipe boiling flow, showing that the tracking accuracy is 100% and classification accuracies for continuous movement, fragmentation, and coalescence events are estimated to be larger than 90% in a wide range of time steps between two adjacent time instants.

Experimental study of the motion and shape of a vapor bubble rising in an annular channel at subatmospheric pressure

Experimental study of the motion and shape of a vapor bubble rising in an annular channel at subatmospheric pressure

Effects of porous transport layer wettability on performance of proton exchange membrane water electrolyzer: Mass transport overvoltage and visualization of oxygen bubble dynamics with high-speed camera

For producing hydrogen from renewable energy, a proton exchange membrane water electrolyzer (PEMWE) is an appealing method offering higher current density and purity of generated hydrogen than other electrolyzers. However, this technique should be further developed to have higher efficiency for utilization. The main issue on reducing the PEMWE performance is the management of generated oxygen bubbles near the reaction site. They persist near the reaction site, inhibit the water supply, and significantly reduce the reaction efficiency. Therefore, how oxygen bubbles are removed from the reaction site should be optimized, however, the mechanism of transport phenomena of oxygen bubbles through the porous transport layer (PTL) has not been clarified. Therefore, in this study, an original cell was developed which allowed us to observe bubble movements inside PTL with a high-speed camera, and the effects of PTL wettability on the oxygen bubble movement were investigated. The PTL wettability drastically affected the PEMWE performance and bubble movement, and hydrophobic PTL reduced the PEMWE performance. The oxygen bubbles tended to stay inside hydrophobic PTL, which might cause lower PEMWE performance.

Optical Bubble Microflow Meter for Continuous Measurements in a Closed System

This paper describes the design, operation and test results of a simple microprocessor-based device for measuring slow liquid flows. The device uses a module of 30 digital optical sensors to track the movement of a single air bubble inserted into a tube of flowing liquid. During a measurement session, the air bubble remains within the sensor module at all times, allowing the instrument to take measurements for any length of time. The liquid whose flow rate is being measured moves only in the closed tube system, without contact with other components of the device. The test of the device itself was carried out using a tube with an inner diameter of less than 1 mm, where the device is capable of measuring flow rates on the order of microliters per minute. Tests of the device showed good agreement between the measured volumetric flow rate and the reference flow rates of the infusion pump over the entire measurement range. The advantages and limitations of the device are discussed, as well as the prospects for developing the method.

Experimental and numerical simulations of river-crossing pipelines for different water fill patterns

In the process of water filling in long-distance water transfer projects, the transient flow of water and air, along with the fluctuation in pressure, indicates the complexity of the hydraulic transition process, particularly when there are curved pressurized pipes, and the movement of air inside the pipes is not easily determined. This study focuses on pipeline systems with significant changes in elevation, such as those crossing rivers or roads. It employs a combined approach of generalized model experiments and numerical simulations to investigate the formation and transformation of flow patterns in the pipeline system during the filling process. It also analyses the fluctuation of pressure on both sides of the curved pipe under different filling modes and reveals the coupling mechanism between the movement of large-scale air bubbles and turbulent vortex structures within the curved pipe. When the water filling velocity at the pipeline inlet is v = 0.8 m s–1, the size of the bubbles formed by the air is larger, the variety of flow patterns is greater, and the evolution of flow patterns is more complex. When impounded water occurs in the river crossing pipeline due to maintenance, the pipeline system forms slug flow at a filling flow velocity of v = 0.8 m s–1. This leads to an abrupt change in the overall pressure of the pipeline system, with the maximum pressure being 1.36 times that of the filling flow velocity of v = 0.4 m s–1. At a filling flow velocity of v = 0.8 m s–1, bends in the pipe readily foster the formation of large-scale bubbles. The interaction between the buoyancy and drag forces acting on these bubbles and the centrifugal forces provided by the bends results in continuous changes in the hydraulic conditions within the pipe. The research findings not only enrich the study of the hydraulic transition process in pipeline systems but also hold significant importance for expediting the construction pace of long-distance water transfer projects.

Experimental investigation on dynamic characteristics of single bubble near wall in shear flow

The bubble near the wall of shear flow will be subjected to both wall-induced lift and shear-induced lift. The two-lift interaction will markedly change the dynamic behavior of the bubble. In this experiment, the lateral motion of a single bubble (deq=2.33−3.42 mm, Reb=470−680) rising near the vertical wall in a linear shear flow was studied. The positive-synergy and negative-synergy between the wall- and shear-induced lift effects on bubble dynamics were compared. The experiment was carried out in a vertical water tunnel with a curved screen used to generate a stable linear shear flow. Using the shadow method and two charge-coupled device cameras, the movement parameters of the bubble were captured, including the movement trajectory of the bubble, length–diameter ratio, and instantaneous velocity. The lift coefficient CL and drag coefficient CD were obtained by quasi-steady-state analysis and calculation. By fitting the steady lift coefficient, the relation of CL with dimensionless wall distance S* and the Reynolds number Reb was obtained. The results show that there is a critical value of the initial dimensionless distance S* about [S*] = 1.6. When S* > [S*], the bubble is subjected to both wall-induced lift and shear-induced lift. The lift coefficient CL decreases with the increase in S*. When S* < [S*], the bubble receives additional induced lift from the wall. The CL of the smaller bubble was smaller and increases with the increase in S*, while the deformation of the larger bubble will interact with the wall to produce deformation lift away from the wall, presenting larger CL, and decrease with the increase in S*.

Visualizing and Evaluating Microbubbles in Multiphase Flow Applications

Accurate visualization of bubbles in multiphase flow is a crucial aspect of modeling heat transfer, mixing, and turbulence processes. It has many applications, including chemical processes, wastewater treatment, and aquaculture. A new software, Flow_Vis, based on experimental data visualization, has been developed to visualize the movement and size distribution of bubbles within multiphase flow. Images and videos recorded from an experimental rig designed to generate microbubbles were analyzed using the new software. The bubbles in the fluid were examined and found to move with different velocities due to their varying sizes. The software was used to measure bubble size distributions, and the obtained results were compared with experimental measurements, showing reasonable accuracy. The velocity measurements were also compared with literature values and found to be equally accurate.

Dynamics of Taylor bubble under chemical reaction enhanced mass transfer in minichannel

Taylor bubble dynamic characteristics of CO2 chemical absorption into MEA aqueous solution in a vertical minichannel were systematically investigated in this study. The generation, movement, and shrinkage of bubbles in the minichannel were visualized and monitored using a high-speed camera, and their dynamic behaviors were characterized by image analysis method. The effects of gas and liquid Re numbers and absorbent concentration on two-phase flow patterns, bubble generation frequency, initial bubble length, bubble length decrease rate, and bubble velocity were examined and analyzed. Results showed that chemical reaction-enhanced mass transfer hindered the bubble cap penetration into the main channel, and alleviated the bubble neck thinning, both effects inhibiting the bubble generation. A new Damköhler number (Da)-based correlation has been proposed to predict the initial Taylor bubble length, showing good prediction accuracy for experimental data in the literature using different absorbents. Results also showed that before the formation of sphere bubble at the end of absorption, an approximate linear relationship exists between bubble length decrease rate and bubble velocity, with the slop decided by chemical reaction rate that could be characterized by the Da number. Finally, a simple model has been developed to determine the effective channel length at a given operating condition, providing design guidelines for microchannel-based miniaturized CO2 absorbers.

Effect of Nozzle Clogging on Bubble Movements and Slag Behaviors in a Slab Mold

Effect of Nozzle Clogging on Bubble Movements and Slag Behaviors in a Slab Mold

Simulation analysis of bubble coalescence behavior characteristics in non-Newtonian fluids based on the phase field method

Gas-liquid two-phase flow is widely used in various fields of chemical production because of its stability. The bubble coalescence behavior has a significant impact on the size, shape and movement of bubbles. These parameters are important parameters for affecting the interphase mass and heat transfer processes and equipment performance. This paper presents a simulation study of the bubble coalescence behavior of non-Newtonian fluids using the phase field method through simulation software. The relative location of bubbles were divided into three types: vertical, parallel and random; and also the distribution of bubbles can be divided into three cases: symmetric, left-skewed and right-skewed. This paper focuses on the influence of the arrangements of the bubbles on their coalescence behavior in non-Newtonian fluids. The results show that in non-Newtonian fluids, the relative distance of the bubbles and the flow characteristics of the fluid are both key factors in whether bubble coalescence can occur, and they exhibit different patterns of action when the bubbles are in different arrangements. Also bubbles show different patterns of motion in different distributions.

Bubble generation mechanisms in microchannel under microgravity and heterogeneous wettability

Advances in hybrid surfaces have revealed interesting opportunities for multiphase flow control under microgravity, as the surface tension force is dominant in this condition. However, a comprehensive investigation of bubble generation rates and slug flow parameters remains challenging. This research integrates hybrid wettability and modified dynamic contact angle models to address this important knowledge gap. Using the computational capabilities of the IsoAdvector multiphase method, we performed detailed simulations of complex multiphase flow scenarios with the OpenFOAM package. We then validated these simulation results through rigorous comparison with available experimental data, thereby strengthening the accuracy and reliability of our numerical simulations. Our comprehensive research demonstrates the profound effect of altering contact angle distribution patterns on several critical parameters. These results highlight the precise control that can be achieved through the strategic manipulation of these patterns, offering the possibility of adjusting factors such as bubble production rate, slug length, bubble diameter, the relationship of flow residence to bubble movement, bubble movement speed in the channel, and pressure drop. Interestingly, altering these patterns can also induce asymmetric behavior in bubbles under microgravity conditions, a phenomenon that has significant implications for various applications. Such insights are crucial for fields such as heat transfer in energy systems, reaction mechanisms in chemical processes, multiphase flow control in petrochemical industries, fluid dynamics in aerospace engineering, and cooling mechanisms in electronic devices. With the ability to modulate these fundamental parameters, we gain valuable insights into the design and optimization of microchannel systems. Consequently, this research presents a more efficient and innovative approach to multiphase flow control, promising improved operational performance, and efficiency in various engineering applications.