Bubble Detachment Volume Research Articles

Bubble Formation in Yield-Stress Fluids Using a Coupled Level-Set and Volume-of-Fluid Method.

The bubble formation under the influence of orifice diameter submerged in yield-stress fluids was studied numerically using a coupled level-set (LS) and the volume-of-fluid (VOF) method and was in contrast with that seen in Newtonian fluids. The bubble formation process had a good consistency by virtue of comparing numerical simulation and experiment. The process of bubble formation could be divided into two parts, bubble expansion stage and stretch stage. The influence of orifice diameter and liquid rheological characteristics (consistency coefficient, flow index, and yield stress) on the bubble formation parameters (the bubble formation time, detachment volume, and aspect ratio) was investigated. The results revealed that the bubble detachment volume increases with the increase of orifice diameter, consistency coefficient, flow index, and yield stress. In different kinds of fluids, the formation time and detachment volume of bubbles in the shear-thinning fluid were the lowest, followed by the Newtonian fluid, and finally, in yield-stress fluids.

A comparative study of bubble formation characteristics in non-Newtonian and high-viscosity Newtonian fluids by a laser image technique

A laser image measurement system has been established to study the problem of dynamic bubble formation from a submerged orifice in two kinds of high-viscous fluids, namely Newtonian glycerol aqueous solution and non-Newtonian carboxymethylcellulose (CMC) aqueous solutions. The bubble generation process was measured accurately by means of He-Ne laser as light source using the beam expanding and light amplification technology. The whole formation process, including bubble expansion, stretching and detachment three stages, and the dynamic characteristics of each stage, were investigated experimentally by analyzing comparatively the evolution of the instantaneous shape, volume, surface area, and deformation rate in both fluids. The influences of solution mass concentration, gas chamber volume and orifice diameter on bubble detached volume were discussed respectively, and the results reveals that bubble begins to grow spherically due to the predominant role of surface tension, and then is elongated gradually owing to the increasing buoyancy force. Compared with Newtonian fluid, bubble formed in non-Newtonian fluid presents a slim shape as a result of the shear-thinning effect of CMC solution. Bubble detachment volume in both kinds of fluids increases with solution mass concentration and gas chamber volume, but declines with orifice inner diameter, respectively.

Experimental investigation on pair bubble columns under high voltage DC electric filed

The behavior of a pair bubble column rising in an insulating liquid in the presence of a high voltage electric field was investigated. The purpose of this study was to investigate the bubble column flow regime and the possibility of transferring it without changing the basic parameters of the bubble column. The use of the electric field was the main factor in applying this change to the bubble column. The results show that the employment of an external electric field significantly changes the size, detachment frequency and the pattern of the bubble column. With an increase in electrical potential, the bubble growth time and detachment volume (bubble size) decline continuously due to electrical stress on the bubble surface. Moreover, at sufficiently high electric potential, the electric field intensifies the bubble collision and coalescence, which subsequently leads to more enhancements of the heat and mass transfer in the bubble column reactor. The use of the electric field increased the bubble detachment for Db=1.12mm by 250%, and for the largest bubble in range Db=3.32mm, this increase was about 80%.

Experimental study of bubble formation process on the micro-orifice in mini channels

A visualized experimental system is designed and constructed to study the bubble behaviors on the micro-orifice in liquid layer. The test section is performed in a rectangular duct of 0.27 m × 0.006 m × 0.012 m, and the air is injected from an orifice with 0.49 mm in diameter. The gas flow rate is in the range of 0.3–60 ml/min, while the corresponding Reynolds number is ranged from 0.87 to 173.18. The effect of gas flow rate on bubble behaviors and bubble coalescence characteristics are investigated systematically. The results state that the bubble height, the radius of curvature at the apex and the bubble detachment volume show little variation with the gas flow rate when the gas flow rate is less than 24 ml/min. While the bubble contact line diameter increases firstly and then decreases. During the multi-bubble regimes stage, the detachment volume of both leading bubbles and trailing bubbles increase with the Weber number. The time interval between two adjacent bubbles or coalescence cycles is almost 0 when Weber number is above 18.27.

Study on the formation characteristic of microbubbles used in sewage treatment

Microbubble usually has very small volume, and it is difficult to rise in the water, so it can be used to wrap ozone for sewage treatment. In the present study, the experiments of bubble formation in a mechanical microfluidic device are developed. The effect of liquid flow rate and gas pressure on bubble formation characteristic was obtained through experiments. By observing experimental phenomena, it can be concluded that bubble growth process can be divided into three stages, and the law of the detachment volume and formation frequency of microbubbles under single variable factor was investigated by the control variable method. The investigation of bubble formation characteristic can help to control bubble detachment volume and formation frequency precisely.

Bubble Formation Characteristic of Submerged Single-Hole Orifice in Aerosol Suspension

Bubble column is regarded as an effective containment filtration method. A large amount of radioactive aerosol will retain in liquid pool and generate decay heat. And the surface tension, viscosity and other parameters of liquid phase are affected by increasing of the temperature of liquid pool and the presence of aerosol in pool, which in turn affects the formation characteristics of bubbles. Another important factor affecting bubble generation characteristics is the proportion of steam in gas phase, that is, the exchange of mass and energy of gas phase. This paper will investigate the effects of liquid temperature, aerosol and gas phase composition on bubble formation characteristics by analyzing the variation of bubble detachment volume of the orifice in liquid pool.

Investigation of bubble formation and its detachment in shear-thinning liquids at low capillary and Bond numbers

In the present paper, the formation of an air bubble in a shear-thinning non-Newtonian fluid was investigated numerically. For modeling, an algebraic volume of fluid (VOF) solver of $$\hbox {OpenFOAM}^\circledR $$ was improved by applying a Laplacian filter and was evaluated using the experimental results from the literature. The enhanced solver could compute the surface tension force more accurately, and it was important especially at low capillary and Bond numbers due to the dominance of surface tension force relative to the other forces. The adiabatic bubble growth was simulated in an axisymmetric domain for $$\hbox {Bo}=0.05,0.1,0.5$$ and $$\hbox {Ca}=10^{-1},10^{-2},10^{-3},10^{-4}$$ , and the bubble detachment time and volume were examined. According to the results, for Newtonian fluids, there is a critical capillary number for a given Bond number, and for lower values of this critical number, no difference is observed between the bubble detachment volumes and also bubble detachment times. Similarly, the results indicated that for non-Newtonian fluids, if apparent capillary number (obtained by apparent viscosity) is less than the critical capillary number, the detachment volume is the same as the corresponding Newtonian case. The velocity of the bubble during its formation in Newtonian and shear-thinning fluids was also studied. Moreover, the bubble formation and detachment characteristics such as instantaneous contact angle and necking radius were investigated for Newtonian and non-Newtonian liquids, and the shear-thinning effect was examined as well. The results indicated that changing the ambient fluid to a non-Newtonian liquid has no effect on the trend of the contact angle; however, the minimum contact angle has a higher value when the shear-thinning effect increases. Also, the variation of neck radius with the time until detachment was presented by the power relation $${R}_{\mathrm{n}} =\left( {{t}_{\mathrm {det}} -{t}} \right) ^{{\eta }}$$ , and the effect of shear thinning on its exponent $${\eta }$$ was investigated.

Numerical Simulation of Bubble Formation in a Co-Flowing Liquid in Microfluidic Chip

Numerical simulations of microbubble formation in a co-flowing liquid in Polydimethylsiloxane (PDMS) microfluidic chip by COMSOL Multiphysics are carried out based on the Level-Set Method. The growth process of bubbles in a co-flowing focusing environment with different liquid flow rates and gas pressures is successfully described by numerical simulation, and the simulation predictions are compared with the experimental data. By comparison, it is found that the simulation prediction value and experimental value have the same change rule for bubble detachment volume and formation time. The average deviation between the simulation value and experimental value less than 10%, it is proved that the simulation model can well predict the bubble formation.

Microbubble characteristic in a co-flowing liquid in microfluidic chip

An experimental method for the formation characteristics of co-flowing focusing microbubbles based on polydimethylsiloxane (PDMS) microfluidic chip is introduced. An experimental system was set up to investigate the effects of liquid flow rate, gas pressure and gas channel width on bubble detachment volume and formation time. Based on the assumption of ellipsoid theory, the theoretical model for volume prediction of co-flowing focusing microbubbles is established. The numerical solution of the model is obtained by the fourth-order Runge-Kutta method. The results show that the prediction results of theoretical model correlate well with the experimental data.

The effect of multi-orifice plate configuration on bubble detachment volume

Abstract The multi-orifice plate gas sparger, mainly composed of a multi-orifice plate and a gas chamber, is one of the most common sparger facilities. The aeration performance of multi-orifice plate has a close relation with the multi-orifice plate configuration. In addition, the weeping phenomenon has a considerable influence on the gas chamber condition which affects the bubble detachment volume directly. This paper conducts a set of visual experiments to study the influence of multi-orifice configuration and gas chamber condition on the aeration performance of gas sparger. For multi-orifice plate, an improved theoretical model is proposed which considers the wave effect of the previous bubbles generated from adjacent orifices and the variance of the number of active bubbling orifice. A parameter is proposed to evaluate the aeration performance in order to overcome the difficulty caused by the randomness of bubble formation process. The experimental results suggest that the gas chamber filled with water is in favor of large bubble formation. The influence of the pitch of orifice on aeration performance can only be observed in high-restricted case. According to the theoretical model and experimental results, the influences of gas flow rate and the number of open orifices on the aeration performance are analyzed and a design criterion for the number of open orifice is proposed.

Effects of surface-active agents on bubble growth and detachment from submerged orifice

Present study deals with the effects of surfactants on the dynamics of bubble growth and detachment from a submerged orifice. Experiments are conducted to study the quasi-static growth of air bubble in de-ionized (DI) water mixed with nonionic surfactant Triton X-100. For comparison, bubble growth in pure DI water is also studied. While high-speed imaging is used for flow visualization, instantaneous velocity field, at different stages of bubble growth, are captured via particle image velocimetry. The study also uses bubble pressure Tensiometer technique and Goniometer for measuring the surface tensions. Present investigation shows that the bubble detachment volume decreases with the increase in the surfactant concentration. Further, for low concentration of surfactant, the surface tension gradient influences the flow field significantly and aid the bubble detachment.

Bubble formation in shear-thinning fluids: Laser image measurement and a novel correlation for detached volume

A laser image system has been established to quantify the characteristics of growing bubbles in quiescent shear-thinning fluids. Bubble formation mechanism was investigated by comparing the evolutions of bubble instantaneous shape, volume and surface area in two shear-thinning liquids with those in Newtonian liquid. The effects of solution mass concentration, gas chamber volume and orifice diameter on bubble detachment volume are discussed. By dimensional analysis, a single bubble volume detached within a moderate gas flowrate range was developed as a function of Reynolds number ,Re, Weber number, We, and gas chamber number, Vc, based on the orifice diameter. The results reveal that the generated bubble presents a slim shape due to the shear-thinning effect of the fluid. Bubble detachment volume increases with the solution mass concentration, gas chamber volume and orifice diameter. The results predicted by the present correlation agree better with the experimental data than the previous ones within the range of this paper.

Application of laser image technique for detection of detached volume of twin-bubble in semitransparent fluids

A laser image measurement has been employed to quantify the volume and shape of twin-bubble generated in semitransparent glycerol aqueous solutions with high viscosity. The bubble generation regime was investigated by analyzing the shape evolution process of captured bubble, and the influences of solution mass concentration, orifice diameter and orifice interval on bubble's detached volume were discussed, respectively. The results show that twin bubbles formation experiences three stages of radial expansion, axial elongation and vertical detachment. Bubble detachment volume increases with the solutions concentration but decreases with orifice diameter. The detached volume climbs with the orifice interval, however smaller than that formed at single orifice.

Experimental and numerical analysis of quasi-static bubble size and shape characteristics at detachment

When investigating the physical mechanisms responsible for pool boiling heat transfer, individual bubbles are commonly assumed to be spherical. This is done in order to ease the computational expense when solving the Navier–Stokes equations. However, bubbles are observed to deviate from spherical depending on fluid properties, cavity sizes and gravitational field strengths. Since it is bubble detachment volume that dictates ebullition frequency, improvements in detachment size and shape predictions would improve nucleate pool boiling heat and mass transfer models.Recent studies have shown that a numerical treatment of the capillary equation’s detachment criterion – which is a result of an interfacial pressure balance analysis – generates profiles corresponding to axis-symmetric quasi-static bubbles for adiabatic conditions. In the present work, this criterion is validated for heat induced bubbles providing the basis for a full analysis of size and shape characteristics of a detaching vapour bubble. A volume detachment correlation is validated for heat induced vapour bubbles and detachment correlations for other size and shape characteristics such as bubble height, width, apex principal radius of curvature, contact angle, and degree of sphericity are developed. Furthermore, a local stress analysis reveals detachment regimes and bubble profile regions.

Laser image measurement of twin bubbles formation in shear-thinning fluids

A laser image system for investigating twin bubbles formation in shear-thinning fluid was established. The process of twin-bubble formation could be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technology. The shape and size of bubbles generating in carboxymethylcellulose (CMC) aqueous solutions were studied experimentally at orifice diameter 1mm, 1.6mm and 2.4mm, the orifices interval 1Do, 2Do and 3Do (Do: orifice diameter) and the gas flow rate from 0.1 to 1.0ml/s, respectively. The effects of solution mass concentration, orifice diameter and orifice interval on bubble detachment volume were investigated. The results reveals that twin bubbles gradually touch each other and then deviate from the vertical axis crossing the middle point of the line joining the two orifice during the formation process. However compared with the perfect teardrop terminal shapes in glycerol solution, the bubbles formed in CMC solutions are stretched vertically due to the shear-thinning effect of fluids. The bubble detachment volume increases with the solution mass concentration, whereas decreases with orifice diameter. The detachment volume generated at twin orifices is less affected by orifices interval, but still smaller than that at single orifice.

Study on bubble formation in non-Newtonian fluids by laser image technique

A laser image system for studying bubble formation at the orifice submerged in liquid was established. The process of bubble formation can be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technique. The behaviors of bubble formation in polyacrylamide (PAM) aqueous solutions were investigated at temperature 293.15 K and orifice diameters 1, 1.5 and 2 mm, respectively, the chamber volume was 90 cm 3 and the gas flowrate from 0.1 to 0.6 cm 3/s. The influences of mass concentration of solution and orifice diameter on bubble detachment volume were investigated experimentally and the results show that bubble detachment volume increases with solution concentration and orifice diameter in the experimental range of this work.

Experimental characteristics of steam bubble growth at orifices in sub-cooled liquid

The experimentally determined characteristics of steam bubble growth when generated at a number of 1 mm diameter orifices in sub-cooled water are presented. Three orifices were used with a wide range of flowrates and liquid sub-coolings. Tests were conducted at pressures of 2 and 3 bar absolute and at constant flowrate conditions. A high speed cine camera recordings were used to determine the bubble geometrical characteristics such as volume, surface area, and centroid. This data indicated significant dependencies of flowrate, pressure and liquid sub-cooling as would be expected and these have been used to provide non-dimensional correlation's for bubble detachment volume and bubble formation time. The effect of neighbouring orifices was investigated by imposing combinations of different orifice flowrates adjacent to the orifice under investigation. The results indicated that the effect of neighbouring orifices is small for the conditions tested.

Bubble formation at a submerged orifice in reduced gravity

We consider gas injection through a circular plate orifice into an ideally wetting liquid which results in the successive detachment of bubbles, each of which is regarded as a separate entity. At normal gravity and at relatively low gas flow rates, the growing bubble is modelled as a spherical segment that touches the orifice perimeter during the whole time of its evolution. If the gas flow rate exceeds a certain threshold value, a second stage of the detachment takes place that follows the first spherical segment stage. In this second stage, a nearly cylindrical stem forms at the orifice that lengthens as the bubble rises above the plate, and this stems feeds an almost spherical gas envelope stituated at the stem upper end. At high gas flow rates, bubble shape resembles that of a mushroom, and its upper envelope continues to grow until the gas supplied through the stem is completely cut off. This second stage always develops when gravity is sufficiently low, irrespective of the gas flow rate. There are two major factors that determine the moment of bubble detachment: the buoyancy force and a force due to the momentum flowing into the bubble with the injected gas. The buoyancy force dominates the process at normal gravity whereas the inflowing momentum force plays the key role under negligible gravity conditions. As gravity fluctuates, the interplay of these forces drastically influences bubble growth and detachment. At sufficiently low gravity, the bubble formation frequency is proportional to gas flow rate whereas the bubble detachment volume is independent of gas flow rate. At normal and moderately reduced gravity conditions, when the gas flow rate grows, bubble formation frequency slightly decreases and bubble detachment volume increases almost linearly. Effects of other parameters, such as the orifice radius, gas and liquid densities and surface tension coefficient are discussed.

Formation of ellipsoidal bubbles at a free-standing nozzle

When gas is injected at high velocity into liquid, the bubbles formed at the nozzle are elongated in the direction of gas flow due to the axial momentum of the gas. In this paper, the bubble is modelled as a prolate ellipsoid growing at a nozzle which projects vertically upwards into a body of inviscid liquid. The shape of the bubble is defined in terms of axial ellipticity, as determined by an energy balance on the gas jet enclosed by the expanding envelope. The time of growth and hence the free bubble volume is derived from the familiar inertial model of bubble motion in which the bubble hydrodynamic mass is presented as a function of axial ellipticity. Theoretical predictions of bubble shape and size at the detachment stage are presented in terms of the injection number, N I , a dimensionless representation of the gas dispersion forces. There is good agreement with experimental observation of air and helium injection into water. Over a range of N I from 0.17 to 1.5 which embraces the energetic injection conditions encountered commercially, bubble ellipticity at detachment increases parabolically whereas the dimensionless bubble volume decreases steadily. The bubble detachment volume under these conditions shows a linear relationship with the gas injection rate. The implications of these findings for gas-liquid contacting and for nozzle design are briefly considered.