Velocity Of Air Bubbles Research Articles

Effect of bubble volume on the sweeping velocity of air bubbles in horizontal pipelines in water supply system

Trapped air bubbles in pipelines significantly affect the safety and efficiency of water supply systems, potentially inducing water hammer and leading to pipeline explosions and interruptions. This study investigates the sweeping velocity of air bubbles in horizontal pipelines by analyzing the forces acting on a single air bubble and deriving a theoretical expression for calculating the sweeping velocity. Physical model experiments and numerical simulations are conducted to examine the variations in sweeping velocity with respect to bubble volume and dimensionless bubble volume. Results indicate that the sweeping velocity increases with bubble volume, and the diameter of the pipeline significantly affects the movement of air bubbles. These findings contribute to a better understanding of air bubble behavior in horizontal pipelines and can inform strategies for mitigating risks associated with trapped air bubbles, ultimately improving the safety and reliability of water supply systems.

Hydrodynamics of single bubble rising through water column using volume of fluid (VOF) method

The importance of air bubble dynamics in liquid is in some phenomena like chemical and biochemical processes in refinery units. The 2D Volume of Fluid (VOF) method together with the CFD technique were employed for simulating. The dynamic meshing technique is used to simulate the hydrodynamics of rising air bubble in liquid water column via the User Defined Function (UDF) code in the C++ environment was developed to evaluate bubble rising through the water column. The rising of air bubble through a stagnant water column has been considered and the influence of column dimension, bubble size, and aspect ratio on the rising velocity characterized is investigated. The obtained results showed that the bubble rising velocity increase with the bubble size and its shapes was transformed from ellipsoidalto-ellipsoidal cap shape. The rising velocity of air bubbles was affected by the column diameter. It was observed that the air bubble moving toward the top of the water column with oscillation for all cases. A good agreement was obtained between the rising velocity predicted in the simulation with that obtained from the literature.

Shapes and Rise Velocities of Single Bubbles in a Confined Annular Channel: Experiments and Numerical Simulations

Shapes and rise velocities of single air bubbles rising through stagnant water confined inside an annular channel were investigated by means of experiments and numerical simulations. Fast video imaging and image processing were used for the experiments, whilst the numerical simulations were carried out using the volume of fluid method and the open-source package OpenFOAM. The confinement of the annular channel did not affect the qualitative behavior of the bubbles, which exhibited a wobbling rise dynamic similar to that observed in bubbles rising through unconfined liquids. The effect of the confinement on the shape and rise velocity was evident; the bubbles were less deformed and rose slower in comparison with bubbles rising through unconfined liquids. The present data and numerical simulations, as well as the data collected from the literature for use here, indicate that the size, shape, and rise velocity of single bubbles are closely linked together, and prediction methods that fail to recognize this perform poorly. This study and the limited evidence documented in the literature indicate that the confinement effects observed in non-circular channels of complex shape are more complicated than those observed with circular tubes, and much less well understood.

Измерение пробивного напряжения вязких жидкостей

The national standards on measuring the breakdown voltage of liquid dielectrics are considered, in particular, the measurement procedure and the measuring cell main parameters. The breakdown voltage of PDMS-1000, PDMS-12500 and PDMS-30000 liquids produced by various manufacturers was measured, and the main problems faced in carrying out measurements were identified. It is shown, using the example of polydimethylsiloxane liquid dielectrics, that after breakdown of viscous liquids, a channel is produced in them, which consists of gas bubbles held by the surface tension force, due to which the channel may in many cases persist for a long time. Theoretical calculations confirmed by an experiment were performed, based on which the velocity of air bubbles in polydimethylsiloxane liquids can be estimated. A conclusion has been drawn about the necessity to increase the time intervals between individual measurements, as well as the time interval before the start of measurements after pouring the test liquid into the measurement cell. It is shown that visual control of the interelectrode region and a special method of mixing the liquid are also necessary. It can be stated based on the accomplished study that the existing standards for breakdown voltage measurements in viscous liquids need to be refined.

Electromotive force induced by the moving non-magnetic phase in ferrofluids

This paper presents a mechanical-to-electrical energy conversion concept by using the upward movement of air bubbles in ferrofluids. As ferrofluids are magnetized by a magnetic field, the air bubbles passing through the induction coils will change magnetic flux in the coils and produce electromotive force. Therefore, the kinetic energy of air bubbles converts into electricity. The idea possesses a promising prospect to be applied in the non-contact sensor field, which can monitor the flow states of boiling two-phase flow in a heat exchanger and warn the deterioration of heat transfer. A millivolt-level induced voltage with a waveform like a sine wave can be generated. The induced voltage's peak value is approximately proportional to the air bubble's volume and velocity and tends to saturate as the magnetic field strength increases.

Measurement of the air bubble size and velocity from micro air bubble generation (MBG) in diesel using optical methods

In this paper, we determine the bubble size and velocity from air bubble generation (MBG) in a diesel using optical methods. A KTM Series Pump was used to generate micro air bubbles in diesel. The air bubble radius and velocity measurements can be useful parameters to optimize the bubble generation process. Two optical systems were used for measurement air bubble sizes and their velocities in diesel. First, the optical system without an objective lens was used to determine the velocity of air bubbles in diesel. Another optical system with a 10× objective lens was used to obtain the size distribution of air bubbles generated in diesel. An available optical system with a 10× objective lens can detect a bubble diameter greater than 3.3 µm that air bubble images were processed using the ImageJ program. We measured the size distribution of air bubbles generated using the ImageJ program. The micro air bubble radius measured in diesel was found to be 6.26 µm in the sample after a month from air bubble generation. In addition, the particle image velocimetry (PIV) technique was used to measure the velocity field. Then, we used the OpenPIV program for PIV image processing. The highest velocity distribution was determined to be 90 mm/s for diesel without air bubbles and 20 mm/s for diesel with air bubbles after a month of the bubble generation.

Velocity of a large bubble rising in a stagnant liquid inside an inclined rectangular channel

The velocity of large air bubbles rising in an inclined rectangular channel filled up with stagnant water is investigated within the inertial flow regime. The experiments based on bubble observation by means of a high-speed camera are carried-out in a versatile channel with easily adaptable geometry over a wide range of inclination angles. The results obtained in vertical channels of various aspect ratios are confronted with the previous analytical predictions to confirm bubble velocity scaling based on the channel perimeter. The extrapolation of velocity measurements done at very low inclinations then provides the translation velocities of large bubbles corresponding to horizontal channel placements. These velocities agree well with the results of previous channel emptying experiments and suggest velocity scaling based on the channel height. Markedly different dependences of the bubble rise velocity on the channel inclination are observed in flat and tall channels. The analysis of our experimental data provides a simple model for the prediction of the bubble rise velocity in inclined rectangular channels. The effects of leveling and buoyancy, which are jointly acting on bubbles in inclined channels, are incorporated into the model through two principal parameters: the limiting bubble velocities achieved at the horizontal and vertical channel placement. Considering the inertial regime of large Taylor bubbles, these limiting velocities are predictable with a sufficient accuracy.

Mobile or Immobile? Rise Velocity of Air Bubbles in High-Purity Water

The velocity of bubbles rising in pure liquids is affected by the boundary conditions at the liquid–air interface, with bubbles rising the fastest when the bubble surface is fully mobile. The prese...

Experimental and theoretical investigation of CO2 and air bubble rising velocity through kerosene and distilled water in bubble column

This paper concerns with developing of parameters which influence terminal velocities of air and CO2 bubbles in distilled water and kerosene pools. The objective of this study is to validate and correct the formulas that were developed by previous investigators for prediction of terminal velocities. The investigation revealed that the terminal velocity of a single rigid spherical bubble in Newtonian fluids can be developed by balancing of mechanical forces acting on the bubble. However, for large bubbles, because of deforming of the bubble which is a result of interfacial tension, the effect of surface tension should be considered in the terminal velocity prediction formula. By using PSO algorithm and plotting experimental data of terminal velocity against the size of gas bubbles, the suitable equation for each of systems was chosen. Results showed that Jamialahmadi model is more practical for terminal velocity prediction. Jamialahmadi model requires a modification to be utilized for air-kerosene, CO2-kerosene, air- distilled water and CO2-distilled water systems. The developed PSO algorithm model is accurate for prediction of experimental data with an average R2 value of 0.9722.

Study on bubble column humidification and dehumidification system for coal mine wastewater treatment.

Water is important resource for human survival and development. Coal mine wastewater (CMW) is a byproduct of the process of coal mining, which is about 7.0 × 1010 m3 in China in 2016. Considering coal mine wastewater includes different ingredients, a new bubble column humidification and dehumidification system is proposed for CMW treatment. The system is mainly composed of a bubble column humidification and dehumidification unit, solar collector, fan and water tank, in which air is used as a circulating medium. The system can avoid water treatment component blocking for reverse osmosis (RO) and multi effect distillation (MED) dealing with CMW, and produce water greenly. By analysis of heat and mass transfer, the effects of solar radiation, air bubble velocity and mine water temperature on water treatment production characteristics are studied. Compared with other methods, thermal energy consumption (TEC) of bubble column humidification and dehumidification (BCHD) is moderate, which is about 700 kJ/kg (powered by solar energy). The results would provide a new method for CMW treatment and insights into the efficient coal wastewater treatment, besides, it helps to identify the parameters for the technology development in mine water treatment.

Investigation of breaking and non-breaking solitary waves and measurements of swash zone dynamics on a 5° beach

This study presents an experimental investigation of plunging breakers on a sloping beach with an inclination of 5.1°. The incident waves are solitary waves with various amplitudes from non-breaking waves to plunging breakers, and the area investigated is the swash zone. PIV (Particle Image Velocimetry) is performed on images captured at four different field of views (FOV). Shoreline position and maximum runup are measured, and are repeatable in both time and height, although cross-sectional variations of the shoreline shape are observed at maximum runup. For non-breaking waves the runup and fluid flow is computed by a boundary integral technique combined with a boundary layer model. Then, there is excellent agreement between the experimental and the computed velocity profiles at the lower region of the beach, while the boundary integral technique overpredicts the maximum runup height severely. For breaking waves the experiments indicate that the motion becomes more irregular as we move further up the beach. In addition, there are more irregularities present for waves with larger amplitude. Length and velocity of air bubbles entrapped by the plunging breakers are extracted from an image series captured with a large FOV. The images showed that a large air bubble remains intact for a time period during runup for the breaking waves.

Experimental studies on the terminal velocity of air bubbles in water and glycerol aqueous solution

Terminal rising velocity of a single bubble in stagnant water and glycerol aqueous solution was studied by the techniques of high-speed photography and digital image analysis. The results can be summarized as follows: In water, bubble terminal velocity increases while aspect ratio decreases almost linearly in the region where d<0.83mm. Then, both terminal velocity and aspect ratio begin to show a widely scattered trend with the bubble diameter in the range 0.83–6mm. Finally, the level of scattering tends to be weak and the terminal velocity increases gradually while the aspect ratio remains relatively stable when d>6mm. In the surface-tension-dominated regime, the aspect ratio of a single bubble varies significantly with the value fluctuating from 0.4 to 0.99. The aspect ratio should be taken into account with the bubble diameter when predicting the terminal velocity. In the inertia-dominated regime, the terminal velocity increases gradually with increasing the bubble diameter while their aspect ratios vary between 0.4 and 0.7. In the glycerin aqueous solution, as a whole, the terminal velocity increases with bubble diameter and the trend of the bubble velocity does not show a scattered behavior. In water, the most accurate model for predicting terminal velocity throughout the investigated range is given by Tomiyama et al. (2002), and then followed by Ishii and Chawla (1979).

Bubble entrapment and escape from sprayed paint films

Abstract A model paint consisting of resin dissolved in butanol was sprayed onto horizontal glass substrates to form films varying from 100 μm to 450 μm in thickness. The substrates were photographed at 5 s intervals and image analysis software used to measure the number, diameter and velocity of air bubbles trapped in the paint layer. Painted substrates were weighed to determine the rate of solvent evaporation. Bubbles escaped from the paint in 100–900 s, the time increasing with paint thickness. The Sauter mean diameter of bubbles in films less than 300 μm in thickness decreased with time because larger bubbles escaped faster than small bubbles, while the mean diameter of bubbles in a 450 μm thick layer increased due to bubble coalescence. Bubble velocities due to movement of the liquid increased with paint thickness and reached 30 μm/s. Bubbles were observed to escape from both upward and downwards facing surfaces. Concentration gradients due to solvent evaporation in a paint film create surface tension variations that drive Marangoni flows, which bring bubbles to the paint surface. An analytical one-dimensional model of solvent diffusion was used to calculate solvent concentration variations in the paint film and the Marangoni number.

Dynamics of an air bubble induced by an adjacent oscillating bubble

This study is concerned with the collapse of an air bubble induced by its adjacent oscillating bubble, including the splitting of the air bubble and the subsequent transitions of the two split sub-bubbles from singly-connected to doubly-connected. The numerical modeling is based on the potential flow theory coupled with the boundary integral method. A two-vortex-rings model is put forward to further simulate the interaction between two toroidal bubbles and a singly-connected one, which is rarely seen in previous studies. To validate the numerical model, experiments are carried out for the dynamics of an air bubble induced by a spark generated bubble captured by a high speed camera. Our numerical results agree qualitatively with the experimental data. It is found that the strength parameter ε of the oscillating bubble greatly affects the jet velocity of air bubble and the length ratio l′ of air bubble determines its collapsing pattern.

Experimental studies and modeling of surface bubble behaviour in froth flotation

Froth flotation is a versatile, widely used beneficiation technique employing air bubbles to selectively pick up certain particles in aqueous medium. The performance of the flotation process is significantly affected by froth stability and mobility, posing the need for precise control of the froth phase. The present paper aims to understand the motion of bubbles entering the froth phase from the pulp phase at different locations. The horizontal velocities of air bubbles across the top surface of the froth containing fine coal particles were measured. The results showed that at the region farthest from the froth discharge lip, no horizontal movement of the surface bubbles could be observed, and when approaching the lip there would be an increase in the horizontal velocity. The measured velocity profile was fitted to a froth model that considers the cumulative air recovery as a function of location. Six different types of cumulative air recovery functions were tested. The coefficient of determination (R2) and the Akaike information criterion were applied to select the cumulative air recovery function with best fit to describe the horizontal velocity profile. The selected cumulative air recovery function was in a simple power-law form.

Influence of β-lactoglobulin and its surfactant mixtures on velocity of the rising bubbles

The rising velocity of air bubbles in surfactant solutions is a sensitive measure for the formation of a dynamic adsorption layer (DAL) at the bubble surface. Due to a certain surface coverage by adsorbed species the bubble surface starts to become immobilized and the rising velocity is retarded. There is a large difference in the retardation effect in presence of the protein β-lactoglobulin (BLG) alone and its mixed solutions with surfactants. In presence of added surfactants BLG forms complexes, which adsorb and retard the bubble rising velocity according to their respective surface activity and adsorption kinetics. While the nonionic surfactant C12DMPO does not show significant increase in retardation effects as compared to BLG alone, the ionic surfactants SDS and DoTAB form highly surface active complexes and change the rising velocity much stronger.

A printed circuit board capacitive sensor for air bubble inside fluidic flow detection

This paper presents a three-electrode capacitive fluidic sensor for detecting an air bubble inside a fluidic channel such as blood vessels, oil or medical liquid channels. The capacitor is designed and fabricated based on a printed circuit board (PCB). The electrodes are fabricated by using copper via structure through top to bottom surface of the PCB. A plastic pipe is layout through the capacitive sensor and perpendicular to the PCB surface. Capacitance of sensor changes when an air bubble inside fluidic flow cross the sensor. The capacitance change can be monitored by using a differential capacitive amplifier, a lock-in amplifier, filter and an NI acquisition card. Signal is processed and calculated on a computer. Air bubble inside the liquid flow are detected by monitor the unbalance signal between the three electrode potential voltages. Output voltage depends on the volume of the air bubble due to dielectric change between capacitor's electrodes. Output voltage is up to 53 mV when an 2.28 mm3 air bubble crosses the sensing channel. Air bubble velocity can be estimated based on the output pulse signal. This proposed fluidic sensor can be used for void fraction detection in medical devices and systems; fluidic characterization; and water---gas, oil---water and oil---water---gas multiphase flows in petroleum technology. That structure also can apply to the micro-size for detecting in microfluidic to monitor and control changes in microfluidic channels.

Experimental study of a two-phase surface jet

Results of an experimental study of a two-phase jet are presented, with the jet issued near and below a free surface, parallel to it. The jet under study is isothermal and in fresh water, with air injectors that allow variation of the inlet air volume fraction between 0 and 13 %. Measurements of water velocity have been performed using LDV, and the jet exit conditions measured with PIV. Air volume fraction, bubble velocity and chord length distributions were measured with sapphire optical local phase detection probes. The mean free surface elevation and RMS fluctuations were obtained using local phase detection probes as well. Visualization was performed with laser-induced fluorescence. Measurements reveal that the mean free surface elevation and turbulent fluctuations significantly increase with the injection of air. The water normal Reynolds stresses are damped by the presence of bubbles in the bulk of the liquid, but very close to the free surface the effect is reversed and the normal Reynolds stresses increase slightly for the bubbly flow. The Reynolds shear stresses $$\left\langle {u^{\prime } w^{\prime } } \right\rangle$$ decrease when bubbles are injected, indicating turbulence attenuation, and are negative at deeper locations, as turbulent eddies shed downward carry high axial momentum deeper into the flow. Flow visualization reveals that the two-phase jet is lifted with the presence of bubbles and reaches the free surface sooner. Significant bubble coalescence is observed, leading to an increase in mean bubble size as the jet develops. The coalescence near the free surface is particularly strong, due to the time it takes the bubbles to pierce the free surface, resulting in a considerable increase in the local air volume fraction. In addition to first explore a bubbly surface jet, the comprehensive dataset reported herein can be used to validate two-phase flow models and computational tools.

Direct Numerical Simulation of Bubble Dynamics Using Phase-Field Model and Lattice Boltzmann Method

Knowledge of bubble dynamics provides a microscale or mesoscale basis to further understand the macroscale complex behavior of bubbly flow or extract the constitutive correlations for continuum-based multifluid computational fluid dynamics (CFD) models. This study attempts to investigate the bubble dynamics from a systematic and multiscale perspective, that is, progressively probing the behavior of a single bubble, a bubble pair, and a bubble swarm with a Multiple-Relaxation-Time (MRT) lattice Boltzmann method (LBM). The MRT-LBM method is used to solve the phase-field model and can accurately capture the interface evolution under different flow conditions. This study also incorporates the force term in a different way, and the model is validated by classical numerical tests for a static bubble and capillary wave. Numerical tests show that the model is able to simulate the gas–liquid flows with a large kinematic viscosity ratio (up to 1000) and the bubbles of lower Morton number and higher Reynolds number. The simulation results of the terminal rise velocity of air bubbles are comparable with the classical experimental correlations. Interactions of two bubbles vertically or horizontally aligned are simulated, reproducing the trailing bubble catching up with the leading one for a vertically aligned bubble pair and the repeatedly bouncing and attracting phenomenon for a horizontally aligned bubble pair. The behavior of bubble pairs in a bubble swarm is analyzed with the model to understand the different bubble–bubble interactions and their influence on micromixing.

Effect of turbulence on particle and bubble slip velocity

In multiphase systems involving a dispersed phase, such as fluidized beds, the interphase exchange of mass, heat and momentum transfer can be very different from those from a single particle, droplet or bubble system under terminal conditions. Such differences need to be correctly predicted for proper design of multiphase reactors. However, most existing methodologies still rely heavily on empirical relationships for parameters such as slip velocity, especially for systems operating under turbulent conditions where there is wide difference in the reported results.In this study the hindered settling/rising (slip) velocity of single steel particles (dPD=5–12mm) and single air bubbles (dB=1–4mm) has been measured in a solid–liquid fluidized bed of uniform size borosilicate glass beads (dP=5 and 8mm) as a function of liquid superficial velocity. The homogeneity and intensity of the turbulence within the fluidized bed has been quantified and directly related to the slip velocity of the foreign (steel or bubble) particle. It was found that the turbulence resulted in an increase in the computed drag coefficient for all of the experimental conditions investigated.