Characteristics Of Bubble Motion Research Articles

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.

Bubble Motion Characteristics in the Transformer Oil Gap at the Top of HV Winding

Bubble Motion Characteristics in the Transformer Oil Gap at the Top of HV Winding

Analysis of Bubble Motion Characteristics in Oil Based on Level Set Method

At present, transformer oil is the primary insulation method for large power transformers, and the dynamic behavior of bubbles in transformer oil can impact the insulation performance of transformer oil. Therefore, based on the level set method in this paper, the motion characteristics of bubbles in two structures, a horizontal oil channel and a vertical oil channel, under various conditions of different bubble numbers, different flow velocities, and different bubble sizes are studied using finite element simulation. The simulation results show that the kinetic behavior of bubbles becomes more complicated as the radius increases, the number of bubbles increases, and the flow velocity increases. At the same time, the bubble expansion and deformation is a cyclic process due to the electric field force, laminar flow and surface tension in the bubble suspension process.

Dynamic behavior of helium bubbles in Fe9Cr1.5W0.4Si F/M steel at elevated temperature

The degradation of mechanical properties caused by transmutation/deuterium-tritium reaction produced helium (He) is directly related to the behavior of He bubbles in nuclear materials. Here, the dynamic behavior of He bubbles was in-situ studied in an annealed Fe9Cr1.5W0.4Si ferrite-martensite (F/M) steel using transmission electron microscopy. The critical temperature at which He bubbles started to appear obvious Brownian motion was ∼1013 K. The mobile spherical bubbles gradually evolved into immobile polyhedral bubbles through migration and coalescence, and the critical size between mobile spherical and immobile polyhedral was ∼4 nm. The macroscopic diffusion coefficients of bubbles at 1023 K were obtained as a function of bubble size by quantifying the bubble motion in the two-dimensional plane. Meanwhile, the motion characteristics of bubbles away from or close to dislocation were compared and analyzed in detail. Due to the attraction of dislocations, the migration path of He bubbles exhibited a similar 1D Brownian motion. This was attributed to the short-range elastic interaction between He bubbles and dislocations. These results provide direct evidence and potential insights for understanding the dynamic behavior of He bubbles in metals.

Study on Bubble Motion Characteristics in Transformer Oil under Non-Uniform Electric Field

Study on Bubble Motion Characteristics in Transformer Oil under Non-Uniform Electric Field

Influence of Aeration Pipe Length on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field.

Improving the gas-liquid mass transfer efficiency in microporous aeration technology is the key to strengthening the restoration effect of black and odorous water bodies. However, the effect of bubble motion characteristics on oxygen mass transfer has not been systematically studied, which limits the efficient and economical application of microporous aeration remediation technology in black and odorous water. The influence under different aeration pipe lengths was analyzed for oxygen mass transfer and bubble movement in microporous aeration technology. The aeration pipe length (0.1-0.5 m) was positively correlated (R = 1.000, R = 0.997) with the number of bubbles and the specific surface area of bubbles and negatively correlated with the time-average velocity of bubbles and Sauter average diameter (R = -0.999, R = -0.997). Moreover, the increase in pipe length weakened the disturbance intensity of plume to water body. The results of oxygen mass transfer showed that the oxygen mass transfer coefficient (K L a) and oxygen utilization rate (E A) increased (K L a from 1.96 to 4.57 h-1, E A from 6.47 to 15.07%) with the increase of pipe length, which was significantly positively correlated (R = 0.985, R = 0.969) with the number of bubbles and bubble specific surface area (S b). This study provided theoretical parameters for the mechanism of oxygen mass transfer during microporous aeration.

Quantification of motion characteristics of vertically ascending bubbles in NaCl solution via image processing

Abstract In this study, the motion characteristics of bubbles in a vertical rectangular glass groove were investigated using image-processing techniques. A new metric (bubble offset) to evaluate the level of solution disturbance was proposed. The motion characteristics, such as the trajectory, bubble diameter, rise velocity, and coalescence, during the bubble rise were studied using different NaCl concentrations and airflow rates. The functional relationship of the bubble diameter and velocity with height was obtained by least-squares fitting (correlation coefficient R2 ≥ 95%), and fits the power-law distribution. The results showed that the bubble motion characteristics were positively correlated with the airflow rate and negatively correlated with the NaCl concentration in the solution. The solution disturbance was closely related to the bubble offset, and the size of the bubble offset can be used to characterize the degree of the solution disturbance. The disturbance of the solution affects the bubble trajectory, rising velocity and coalescence. The bubble offset changed periodically with height, and its functional relationship was obtained. The accuracy of the functional relationship was verified using experimental data. The study of bubble motion characteristics is crucial for understanding phenomena such as heat and mass transfer and multiphase cooling.

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

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

Euler–Lagrange study of cavitating turbulent flow around a hydrofoil

This study presented a multi-scale Eulerian–Lagrangian approach to simulate cavitating turbulent flow around a Clark-Y hydrofoil to study the bubble dynamics. A large eddy simulation was coupled with the volume of fluid method to capture the large vapor volumes in an Eulerian analysis. Micro-scale Lagrangian bubbles were then tracked by solving compressible the Rayleigh–Plesset equation and a bubble motion equation. A Gaussian kernel function was used to model the interactions between the flow field and the vapor bubbles in a coupled two-way algorithm. The predictions give satisfactory agreement with experimental data for the bubble size oscillations, bubble motion, and cavity shedding characteristics. Further investigations analyzed the influence of various parameters on the transformation between the Euler and Lagrange models. The numerical results provide detailed information about the influence of the cavitating turbulent flow on the bubble behavior, especially how the reentrant jet significantly affects the bubble generation and motion. The calculations also capture the bubble size oscillations caused by the surrounding liquid pressure variations and how these generate very high local pressures near the surface. The results show that the pressure wave released as a bubble is compressed reaches 107 Pa, which may cause cavitation erosion of the hydrofoil surface. This research provides a promising method to better investigate the bubble motion characteristics in macroscopic flows and demonstrates that the cavitation erosion caused by bubble size oscillations is significant and deserves attention.

Effect of cavitation bubble on the dispersion of magnetorheological polishing fluid under ultrasonic preparation

In the ultrasonic dispersion process, the ultrasonic cavitation effect can seriously affect the dispersion efficiency of magnetorheological polishing fluid (MRPF), but the mechanism remains unclear now. Through considering the continuity equation and Vand viscosity equation of the suspension, a revised cavitation bubble dynamic model in the MRPF was developed and calculated. The effects of presence or absence of solid particles, the volume fraction of solid particles, and viscosity on the cavitation bubble motion characteristics in the MRPF were discussed. Settlement experiments of the MRPF under ultrasonic and mechanical dispersion were observed. Analysis of particle dispersion is made by trinocular biomicroscope and image processing of the microscopic morphology of the MRPF. The results show that the high volume fraction of carbonyl iron particle (CIP) will significantly weaken the cavitation effect, and the low volume fraction of green silicon carbide (GSC) has a negligible effect on the cavitation effect in the MRPF. When the liquid viscosity is greater than or equal to 0.1 Pa·s, it is inconvenient to produce micro-jets in the MRPF. The sedimentation rate of the MRPF prepared by ultrasonic dispersion is lower than mechanical dispersion when the volume fraction of CIP is between 1% and 25%. The dispersion ratio under ultrasonic dispersion is lower than that under mechanical dispersion. The experimental results fit the simulation well. It offers a theoretical basis for exploring the ultrasonic cavitation effect in the industrial application of the MRPF.

Review of Single Bubble Motion Characteristics Rising in Viscoelastic Liquids

The emphasis of this review is to discuss three peculiar phenomena of bubbles rising in viscoelastic fluids, namely, the formation of a cusp, negative wake, and velocity jump discontinuity, and to highlight the possible future directions of the subject. The mechanism and influencing factors of these three peculiar phenomena have been discussed in detail in this review. The evolution of the bubble shape is mainly related to the viscoelasticity of the fluid. However, the mechanisms of the two-dimensional cusp, tip-streaming, “blade-edge” tip, “fish-bone” tip, and the phenomenon of the tail breaking into two different threads, in some special viscoelastic fluids, are not understood clearly. The origin of the negative wake behind the bubbles rising in a viscoelastic fluid can be attributed to the synergistic effect of the liquid-phase viscoelasticity, and the bubbles are large enough; thus, leading to a very long relaxation time taken by the viscoelastic stresses. For the phenomenon of bubble velocity jump discontinuity, viscoelasticity is the most critical factor, and the cusp of the bubbles and the surface modifications play only ancillary roles. It has also been observed that a negative wake does not cause velocity jump discontinuity.

Experimental study of the motion characteristics of a bubble near a flexible structure with an attached air bubble

The strong coupling effect between an air bubble attached to a flexible plate and a nearby spark-generated bubble is investigated experimentally while also considering the structural deformation of the plate. Numerous interesting and complex bubble behaviors that depend strongly on the attached air bubble and deformation effect of the structure are observed with a high-speed camera. A multitude of bubble jet behaviors are observed during the two bubble pulsations, such as bubble splitting, jets away from the plate, jets toward the plate, upward and downward movement after splitting, and splitting after the coalescence of the two bubbles. Moreover, the attached air bubble can appear hemispherical, mushroom-shaped, or cup-shaped. To gain a better understanding of the interaction between the bubble and the flexible boundary, the displacement time history curves at the center point of the flexible structure and at the top and bottom vertices of the bubble are obtained. The motion response mode of the flexible plate under bubble loading is explored to summarize the deformation pattern of the flexible structure and the motion characteristics of the bubble. An air bubble attached to the flexible structure can change the motion characteristics of the spark-generated bubble to some extent.

A mechanistic model for wall heat flux partitioning based on bubble dynamics during subcooled flow boiling

This paper aimed to develop a mechanistic model for wall heat flux partitioning based on bubble dynamics in horizontal subcooled flow boiling. The model was established from two dimensions of space and time. In the space dimension, the heating surface was divided into three regions based on the motion characteristics of bubbles, including bubble nucleation region, bubble sliding region, and non-boiling region. In the time dimension, the heat transfer mechanism on the heating surface of the bubble nucleation region and bubble sliding region could be divided into evaporation, condensation, and transient heat transfer. An evaporation model for subcooled boiling was developed based on condensation at the top of the bubble. A transient quench heat transfer model for subcooled flow boiling was modified. The heat flux of each region was obtained by the sum of the time-averaged heat fluxes of these heat transfer mechanisms during a bubble periodic time. The total wall heat flux was obtained by the sum of the area weights of the heat fluxes in these three regions. The new wall heat flux partitioning model and the RPI model were used to predict the experimental values at a variety of flow conditions. The results showed that the new model could well predict the experimental values and the deviation between the predicted heat flux and the experimental results was within 25%. The study also found that it was necessary to consider the condensation at the top of the bubble and the heat transfer mechanism caused by bubble sliding.

Influence of Aeration Microporous Aperture on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field

Microporous aeration has been widely used to restore eutrophic water bodies. The gas–liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.

Numerical Simulation of Hydrogen Bubble Motion Characteristics in Biohydrogen Production by Photofermentation with Corn Stalk

Numerical Simulation of Hydrogen Bubble Motion Characteristics in Biohydrogen Production by Photofermentation with Corn Stalk

Bubble Sweep-Down of Research Vessels Based on the Coupled Eulerian-Lagrangian Method

To explore the reason for the bubble sweep-down phenomenon of research vessels and its effect on the position of the stern sonar of a research vessel, the use of a fairing was investigated as a defoaming appendage. The separation vortex turbulence model was selected for simulation, and the coupled Eulerian-Lagrangian method was adopted to study the characteristics of the bubble sweep-down motion, captured using a discrete element model. The interaction between the bubbles, water, air, and hull was defined via a multiphase interaction method. The bubble point position and bubble layer were calculated separately. The spatial movement characteristics of the bubbles were extracted from bubble trajectories. It was demonstrated that the bubble sweep-down phenomenon is closely related to the distribution of the bow pressure field and that the bubble motion characteristics is related to the speed and initial bubble position. When the initial bubble position is between the water surface and the ship bottom, the impact on the middle of the ship bottom is greater and increases further with increasing speed. A deflector forces the bubbles to both sides through physical shielding, strengthening the local vortex structure and keeping bubbles away from the middle of the ship bottom.

Distribution and motion characteristics of bubbles in a multiphase rotodynamic pump based on modified non-uniform bubble model

Multiphase rotodynamic pumps are important equipment that transport gas-liquid mixtures in offshore oilfields, suggesting it is necessary to investigate the flow characteristics in such pumps. In this study, the Eulerian two-fluid model is solved to obtain the bubble distribution in the pump, while the non-uniform bubble model is used to predict the break-up and coalescence of bubbles. The gas cavity equation is introduced to capture the rapid coalescence of bubbles near the suction side of the impeller blades, and the interphase forces in the cavities are modified. Compared with the experimental measurements for the gas volume fraction and bubble size, it is found that the simulations with the modification have better accuracies than without it. The effects of the inlet gas volume fraction (IGVF) on the bubble distribution are analyzed. Due to the formation of vortices, a large bubble number density is observed near the shroud of the impeller inlet, which increases with greater IGVF. The gas-liquid separation in the diffuser becomes more significant as the IGVF increases. Bubbles from the impeller inlet are observed to continuously gather near the suction side of the impeller blades. This forms a gas cavity that moves towards the impeller outlet with a low gas volume fraction. The rotor-stator interactions cause the air pockets to discontinuously move along the pressure side of the diffuser blade.

Characteristics of bubble motion and distribution in a multiphase rotodynamic pump

The characteristics of bubble motion and distribution in multiphase pumps are complex and have not yet been clearly described. In this study, high-speed photography technology was used to investigate the gas-liquid flow in detail. A numerical model that considers bubble coalescence and breakup was developed based on Euler two-fluid model, and it was embedded in ANSYS-CFX software with secondary development technology. The reliability of the developed model was validated by comparison with the efficiency and head of the test pump as well as the distribution and size of bubbles. The experimental results revealed that bubbles in the impeller moved from the blade pressure surface to the blade suction surface along a similar path, and accumulated there. Then, the accumulated bubbles decreased in size as they hit the blade wall. The necessary condition for bubble accumulation at the impeller hub was obtained by numerical analysis. The force acting on the bubble, M1, which is caused by the pressure difference from the shroud to hub of the impeller, must be much greater than the sum of the centrifugal force fg and lift force Lg (M1 ≫ fg + Lg). Furthermore, the bubble diameter in the guide vane was significantly greater than that in the impeller due to the strong bubble coalescence. At IGVFs of 3.0%, 9.0%, and 15.0%, the bubble diameters in the guide vane increased by 0.03 mm, 0.21 mm, and 0.24 mm, respectively.

Motion characteristics of bubbles behind a sudden channel expansion

Characteristics of movement of gas bubbles behind a sudden channel expansion were studied experimentally. The data on the distribution of the gas phase and speed of movement of bubbles were obtained. It is shown that at a distance from the sudden channel expansion the bubbles slow down, which relates to the slowing down of liquid due to an increase in the flow cross section. After the reattachment point, the bubbles move along a more curved path than upstream. It is shown that bubble clusters can form in the flow recovery zone. The velocity distribution in the channel was studied by means of laser Doppler anemometry (LDA).

Dynamic control of current and voltage waveforms and droplet transfer for ultrasonic-wave-assisted underwater wet welding

Ultrasonic vibration can change the dynamic behavior of the bubble and improve the process stability in underwater wet welding (UWW); thus, it has been attempted to profitably control metal transfer process. Arc signals about welding current and arc voltage together with the high-speed imaging detected in conventional UWW and ultrasonic-wave-assisted UWW (U-UWW) were used as information source for determining the droplet transfer mode. The results show that the change in the characteristics of bubble motion affects the droplet transfer process in U-UWW. During the short-circuiting transfer process in small arc voltage, the frequency of arc extinction and the peak of short-circuiting current are both decreased. During the droplet repelled transfer process in middle arc voltage, the droplet repulsive phenomenon is weakened, and the transfer frequency is increased from 7.9 Hz to 10.5 Hz at 34 V. Meanwhile, the droplet diameter is reduced and its transfer stability is improved. During the droplet repelled transfer process in high arc voltage, the frequency and duration time of arc extinction are both reduced. The underlying difference of droplet transfer process between conventional UWW and U-UWW was investigated by the two aspects including ultrasonic wave effect and dynamic bubble effect.