Dynamics Of Bubble Formation Research Articles

Investigation of bubble formation dynamics of gas-non-Newtonian liquid two-phase flow in a flow-focusing generator

Investigation of bubble formation dynamics of gas-non-Newtonian liquid two-phase flow in a flow-focusing generator

Dynamics of bubble formation on superhydrophobic surface under a constant gas flow rate at quasi-static regime

Dynamics of bubble formation on superhydrophobic surface under a constant gas flow rate at quasi-static regime

Investigating bubble dynamics on silicon carbide surfaces during flow boiling

Silicon carbide (SiC) is a promising candidate for Accident-Tolerant Fuels (ATFs) in nuclear power plants, critical for maintaining functionality and extending service lifespan due to its superior heat transfer properties. However, the dynamics of bubble formation, size, and distribution on SiC surfaces during flow boiling, especially under the influence of porosity, remain poorly understood. This study aims to elucidate the impact of heat transfer characteristics and bubble distribution properties under flow boiling condition on SiC surface. An experimental was conducted with superheat ranging from 0 to 30K, subcooling ranging from 0 to 12K, and a maximum Reynolds number of 10,400. Videos were recorded and U-net was employed to identify bubble diameters, perimeters, orientations, and positions. Results indicate that the superheat significantly affects bubble size parameters, such as departure diameter and perimeter, but does not influence the distribution categories. Regarding bubble distribution, the aspect ratio and size of bubbles follow a log-normal distribution, while their orientation follows a normal distribution. Under the same experimental conditions, surfaces with higher porosities exhibit increased heat flux, and the Sauter mean diameter of bubbles is larger.

Bubble formation dynamics in aerospace applications

Under microgravity conditions, simulations of bubble formation in a T-junction microchannel with hybrid wettability surfaces allows for more precise control of multiphase flow in space exploration technologies

Influence of the gas–liquid non-equilibrium media structure on the mass transfer dynamics in biophysical processes

Multiphase biophysical media are known to be complex structures with continuous high demand to the scientific community for understanding the relationships and ratios between factors affecting the type, dynamics and nature of its structural changes on their impact degree on the media itself. Among the plentiful list of such factors the following do worth mentioning: the lifetime of a particle, turbulence factors and a number of others, each requiring careful analysis, assessment of the contribution degree and, importantly, correct accounting. The present study is focused on such a factor affecting mass transfer intensity change as surface tension through its relationship with the interfacial area: the latter is the site of mass exchange between the gas and liquid phases, and modifications in surface tension values can significantly impact the characteristics of this area, hence altering the rate of mass transfer. By controlling surface tension, one can effectively modulate the size and stability of particles, namely bubbles or droplets, which in turn changes the interfacial area available for mass transfer. The total interfacial area, which is the cumulative surface area of all bubbles, serves as the site for mass transfer. The impact of the surface tension coefficient variation into gas–liquid mass transfer characteristics is analyzed both for the case of water and model liquid. The latter means the potential contribution of surface-active substances was a part of research scope since it was applied to recreate conditions similar to the cultural liquid when microorganisms that produce surfactants are grown. The proposed new methodology assumes calculating interfacial area through the segmentation of images captured by a high-speed camera, thus we can gain a profoundly enhanced understanding of the relationship between surface tension and mass transfer. The precise visual data and subsequent computation of the interfacial area provide deeper insights into the dynamics of bubble formation and the effects of surface tension on bubble size and distribution. As a result, this method has significantly improved our capacity to investigate and optimize mass transfer processes in multiphase biophysical systems. Both analytical approach and results interpretation not only influence affirmatively on deep understanding of natural mechanisms in biophysical media, but also might serve their best for potential application, e.g. in the context of the development of biotechnological industries based on fermentation processes for protein production.

Experiments and CFD modelling of bubble formation at a lateral hole in a top-submerged nozzle

Top-submerged nozzles with lateral holes find applications as passive mixing devices in radiochemical/hazardous industries. We report the mechanism of bubble formation and detachment at a lateral hole in such a nozzle for the first time. Three distinct phases – a growth phase, an elongation phase and finally a rise/detachment phase – could be observed during bubble formation. Effect of gas flow rate, diameter of lateral hole (1, 2 and 3 mm) and physical properties of liquid-liquid system on bubble detachment time and bubble equivalent diameter are reported. Three different liquid-liquid systems (DM water, 2 N and 4 N nitric acid) have been considered. Bubble diameter first reduced, reached a minimum and then started to increase in an oscillatory manner with increase in air flow rate. Before the onset of oscillatory behaviour an increase in hole diameter was seen to reduce bubble diameter. Such a behaviour is typical to bubble formation at lateral hole and is not seen for top-submerged nozzles with central opening. A detailed analysis of the results was carried out and it was observed that inertial forces played a major role. The work also reports a fundamental criterion which must be achieved for onset of oscillations in bubble diameter with flow rate. We also report a 2D CFD model that can simulate bubble formation dynamics at a lateral hole. The model was validated qualitatively as well as quantitatively against the experimental data.

Insights into the bubble formation dynamics in converging shape microchannels using CLSVOF method

Abstract Bubble formation in a square microchannel having a converging shape merging junction has been studied using the Coupled Level-Set and Volume-of-Fluid (CLSVOF) method. The influence of variations in merging junction angles, fluid properties, and operating conditions on the bubble length and pressure drop has been analyzed. The results show a direct relationship between surface tension, gas-liquid flow ratio, and the inverse relation of continuous phase viscosity with the bubble length. Moreover, opposite variations of these parameters are observed for pressure drop. This work reveals a discerning influence of the angle variations of merging junction on the interplay between inertial, viscous, and surface tension forces in the bubble formation mechanism. We envisage that this numerical work will be of significant interest for the process intensification in various industries that deal with gas-liquid microfluidic systems.

A microfluidic study of bubble formation and coalescence tuned by dynamic adsorption of SDS and proteins

During foaming, bubbles are formed at (sub)millisecond time scales, and emulsifier adsorption determines bubble formation and stabilisation against coalescence. Here we introduce a microfluidic device, in which bubbles are formed in two distinct pressure regimes at low versus high pressures, and emulsifier adsorption can be inferred from the easily-monitored dynamics of bubble formation and coalescence, as well as the bubble properties. We studied dynamic adsorption for various types and concentrations of emulsifiers, namely sodium dodecyl sulfate (SDS; 0.05–3% wt.) and various proteins (5% wt.) including whey protein isolate (WPI), β-lactoglobulin (β-lac), and bovine serum albumin (BSA). The results show that as SDS concentration increases up to 3% wt., the bubble formation time decreases in the low-pressure regime due to the enhanced adsorption of SDS, yet increases in the high-pressure regime due to the promoted ‘dripping-jetting’ transition; in both pressure regimes the neck thinning process slows down, leading to longer bubble growth time and thus larger bubble size. To suppress coalescence of bubbles formed at time scales down to 10 μs, SDS is the most efficient, followed by BSA, WPI, and finally, β-lac; this is ascribed to the dynamics of emulsifier adsorption, e.g., the resulting dynamic surface tension. To conclude, our microfluidic study highlights the dynamic effects in the presence of SDS and proteins during bubble formation, even at high concentrations. This means that to explain the properties of a freshly-formed foam product, it is crucial to understand (and thereafter manipulate) emulsifier adsorption at time scales relevant to bubble formation and coalescence.

Numerical studies of bubble formation dynamics in gas-liquid interaction using Volume of Fluid (VOF) method

Numerical studies of bubble formation dynamics in gas-liquid interaction using Volume of Fluid (VOF) method

Dynamics of bubble formation in yield stress fluids in parallelized microchannels

The bubble formation in yield stress fluids in parallelized microchannels is investigated experimentally. Nitrogen and Carbopol gel are used as the dispersed and continuous phases, respectively. Due to the feedback effect of the downstream microchannels, the uniformity and stability of bubble formation strongly depends on the properties of gels and operating conditions. The effect of yield stress on the interface evolution during bubble formation is investigated under different mass factions of Carbopol (0.2 %, 0.13 %, 0.05 %) and flow rates of gas (0.1–400 mL·min−1) and liquid (0.03–0.2 mL·min−1). The activation rate of parallel microchannels for bubble production increases with the decrease in the concentrations of Carbopol. The increase of liquid flow rate and the decrease of gas flow rate benefit the uniformity of bubble formation frequency. However, under the double-channel bubble-generation flow pattern, reducing the liquid flow rate significantly improves the stability of bubble formation.

Taylor bubble formation and flowing in a straight millimetric channel with a cross-junction inlet geometry. Part I: Bubble dynamics

• Taylor bubble formation dynamics were studied at a cross-junction. • Filling and squeezing stage frequencies were not controlled by the same parameters. • Gas finger lengths were measured to identify different bubble pinch-off patterns. • A simple relationship linking relative bubble lengths with j G 0 / j L was established. The investigations of bubble formation dynamics at a cross-junction in a straight milli-channel were reported. The bubble formation process could be divided into the filling and squeezing stages, and their frequencies were compared at various conditions. It was found that the filling and squeezing frequencies were controlled mainly by the gas and liquid superficial velocities, respectively. The bubble formation frequencies could be related to the gas-liquid superficial velocity ratios, the liquid superficial velocities, and the bubble length. The bubble formation process was then analyzed considering the length of the gas finger right after the bubble pinch-off. Two patterns were identified depending on whether the pinch-off occurred inside of the cross-junction or not. The transition between these two patterns was described by a critical liquid Capillary number. Furthermore, the squeezing and dripping patterns were distinguished as the gas finger could fully block the channel or not. The transitions between the bubble formation patterns were determined by the gas Weber number and liquid Capillary number. Finally, the bubble length, the liquid slug length, and the bubble length normalized by the unit cell length could all be predicted based on the gas-liquid superficial velocity ratios η 0 .

Formation characteristics of Taylor bubbles in a T-junction microchannel with chemical absorption

This study focuses on the effect of chemical absorption on the formation dynamic characteristics and initial length of Taylor bubbles. The temporal evolutions of neck width and length of gaseous thread and initial length with and without chemical absorption were investigated with the Capillary number and Hatta number between 0.0010–0.0073 and 1.8–5.8 respectively. The squeezing regime with typical three stages, expansion, squeezing and pinch off is observed for both two processes. Compared with the non-absorption process, the increase of formation time in the chemical absorption process arises mainly from the expansion stage, and the decrease of initial length is from the necking stage. In addition, the temporal length evolution satisfies the power-law scale with the same exponent but a smaller pre-exponential factor. The correlations of neck width for stage transition and initial length with Hatta number demonstrate the enhancement effect of chemical absorption on bubble formation dynamics and initial length at relatively high chemical reaction rates and long formation time. This study provides insight into the bubble formation mechanism and helps to regulate the bubble initial size with chemical absorption.

Effect of Sparger Characteristics on Bubble-Formation Dynamics under Oscillatory Air Pattern

The size of bubbles generated from a porous sparger is at least an order of magnitude larger than the pore diameter under the steady air pattern. Recent studies have shown that the bubble size can be significantly reduced when the steady air flow is replaced by an oscillatory pattern. However, the effectiveness of oscillatory air flow on reducing bubble size under different sparger characteristics is yet to be studied. This work fundamentally investigates the response of bubble size to sparger characteristics under an oscillatory air pattern by segregating the bubble formation subprocesses into bubble detachment and consequent coalescence. The results show that bubble size significantly decreased with hydrophilic plates regardless of contact angle, owing to depressed coalescence, while no impact was observed for a hydrophobic plate. The influence of the oscillatory air pattern on decreasing bubble size was weakened as the chamber volume was increased, and above a critical volume the bubble-formation process became similar with that under a steady air pattern. An optimum plate thickness was obtained for bubble generation by avoiding weeping, and meanwhile taking full advantage of the momentum force by the oscillatory airflow. The outcomes show that the oscillatory air pattern in determining bubble formation closely depends on the sparger characteristics, which should be appropriately determined.

Dynamics of bubble formation and ascent motion on submerged orifices under different Mo number of petrol-based random copolymer solutions

The petrol-based random copolymer, e.g., aromatic-hydrocarbon resin, is widely used in industrial production, but the research about its gas–liquid two flow is far from being solved. Herein, the formation, motion, and deformation of a single bubble in six different concentrations of random copolymer solutions were systemically investigated using high-speed photography (1000 fps), combined with digital image processing technology. The departure time of the bubble first decreases and then increases, and maximum of aspect ratio and specific surface area reduce as the proportion of solute increases. The bubble departure time decreases and bubble size increases with viscous force increases in the case of same surface tension. Based on force balance analysis, added mass force is one of the prime reasons to affect bubble oscillation during the acceleration phase after bubble detachment, whereas the effect of added mass force decreases as solute increases or as the bubble reaches stability zone. Also, velocity, drag coefficient and aspect ratio of bubble were discussed in detail by dimensionless analysis. Furthermore, three new shape numerical models (based on We, Ta, and WeEo, respectively) were proposed, which allowed for satisfactory predictions, and new correlations represent well the experimental data in a wider range of Mo numbers from the mentioned literature (−11.6 ≤ logMo ≤ 0.63).

Formation dynamics and size prediction of bubbles for slurry system in T-shape microchannel

The bubble formation dynamics and size manipulation in the slurry of polystyrene microspheres in the microfluidic T-junction were visually investigated by a high-speed camera. Based on the evolution of the bubble neck with time, the formation process of bubbles is divided into three stages: filling, squeezing and pinch-off. The particle concentration has an obvious effect on the squeezing stage, while less impact on the filling and pinch-off stages. In the squeezing stage, the evolution of the dimensionless minimum neck width of bubbles with time could be described by a power-law relationship. The increase of the particle concentration or continuous phase flow rate could lead to the increase of body flow of the continuous phase and the enhancement of the squeezing force acted on the bubble neck, correspondingly, the power-law index α in the squeezing stage enlarges. Moreover, the bubble size increases with the increase of the gas phase flow rate and the decrease of the particle concentration and continuous phase flow rate. However, the effect of the particle concentration on the bubble size weakens with the increase of the continuous phase flow rate. In addition, a new prediction correlation of the bubble size for the slurry system in a T-shape microchannel was proposed with good prediction accuracy.

Dynamics of bubble formation in spontaneous microfluidic devices: Controlling dynamic adsorption via liquid phase properties

HypothesisThe interplay of interface evolution and surfactant adsorption determines the formation and stabilization of bubbles, and can be controlled by the liquid phase properties. ExperimentsWe studied bubble formation in an Edge-based Droplet GEneration (EDGE) microfluidic device at relevant length and time scale, allowing investigation of sub-events in a single bubble formation cycle. We vary the properties of the continuous phase that contains whey proteins and study a range of trans-pore pressures (Pd∗). FindingsThe shallow pores highlight the crucial role of the Laplace pressure and dynamic adsorption of proteins to the meniscus. Bubble formation is divided into two regimes by the Laplace pressure of the bare meniscus inside the pore. At Pd∗<1400 mbar, pre-adsorption of proteins is required to lower the Laplace pressure; the bubble formation frequency f0 increases with increasing protein concentration and is hardly affected by velocity and viscosity. At Pd∗≥1400 mbar, bubble formation immediately occurs upon applying pressure, and f0 mainly decreases with increasing viscosity. In both regimes, the initial bubble size d0 mainly increases with the viscosity (~η1/3). Bubble coalescence is only observed at Pd∗≥1400 mbar and can be effectively suppressed by raising protein concentration and viscosity within certain boundaries, yet ultimately this is at the cost of higher polydispersity of the bubbles. Our insights into the formation dynamics of micrometer-sized bubbles at time scales down to tens of microseconds can be used for effective control of bubble formation and stabilization in practical applications.

On the morphology of elongated bubbles during their formation at submerged orifices

Bubbly flow is a widely observed phenomenon in various industrial applications and has remained a topic of sustained interest over decades, owing to the complex multi-physics that govern the multiphase phenomenon. The bubble geometrical morphology and dynamics critically depend on various parameters such as flow rate, orifice diameter, working fluid properties, and height of the fluid above the orifice. Accordingly, experiments are conducted in water, acetone, and Glycerol-water solutions (10% w/w and 20% w/w) using a sub-millimeter submerged orifice of diameter 0.4 mm, 0.6 mm, and 1 mm. The volume flow rate is varied in the range of 100–300 ml per min and experiments are carried out at varying orifice depths of 4 – 12 cm. The dynamics of bubble formation is recorded by high-speed cinematography and is processed using MATLAB script. This paper presents the bubble rise and coalescence morphology and the effect of operating parameters on it. The gas injection and bubble geometrical parameters can be expressed in terms of non-dimensional numbers such as Reynolds number, Weber number, Froude number, and Eotvos number. It is found that simple scaling laws can be established among Reynolds number with Weber number, Froude number, and their ratio, which can effectively predict the bubble geometry. It is found that the relation between the ratio of Weber and Froude number to Reynolds number depends on the height of fluid above the orifice. The present work also quantifies the interconnection between Reynolds number and Eotvos number and demonstrates a relationship that is incumbent on the gas superficial velocity. In particular, it is observed that the slope of the Re-Eo curve decreases with the increase in the gas superficial velocity.

The influence of water hardness perturbations on bubble departure dynamics

The influence of small changes to water hardness on the nonlinear behaviour of liquid penetration into a capillary and the resulting air pressure fluctuations during air bubble formation are examined in this paper. Experiments were undertaken in which bubbles were generated both in water having a surface tensile force of σ = 72.2 mN/m and in an aqueous solution of calcium carbonate having a surface tensile force of σ = 75.4 mN/m, each contained in a glass capillary with an internal diameter of 1 mm. It is shown that both the maximum value of liquid penetration into the capillary and bubble growth time are affected by perturbations to the water hardness. The time it takes for the bubble to depart the capillary was estimated using the following nonlinear data analysis methods: time delay (τ), attractor reconstructions, correlation dimension (D), and largest Lyapunov exponent (λ). All estimates demonstrate that the pressure fluctuations in the c–c aqueous solutions and extent of liquid solution penetration into the capillary during the time between subsequent bubble departures behave chaotically. Furthermore, this work demonstrates that the dynamics of bubble formation along with the bubble waiting time are very sensitive to small perturbation in the physical properties of the liquid, and this sensitivity has a significant effect on the observed chaotic behaviour.

An investigation of the gravity effects on pool boiling heat transfer via high-fidelity simulations

Nucleate pool boiling simulations are carried out to study the effects of gravity on the dynamics of bubble formation, bubble departure, and the mutual bubble interactions. We focus on identifying the dominant trends associated with the flow and thermal behavior at different gravity levels using fixed values of wall superheat and liquid subcooling. This is accomplished by measuring the contributions to heat flux associated with turbulent flow resulting from the dynamics of bubble interaction. The time averaged fluctuations of velocity and temperature indicate that the wall heat flux conditioned by the wetted surface area - the liquid heat flux - provides a useful indication of high heat flux hot spots. Furthermore, despite substantial differences in the dynamics of large scale bubbles at different gravity levels, the average heat flux in the liquid region is found to be dominated by the sliding and merger type events associated with small scale bubbles over a wide range of gravity levels. This significance of near-wall, small scale bubble dynamics is reflected in the transition of vorticity structures from hairpin type vortices in the near-wall region to vortex ring patterns away from the wall. While the maximum value of average turbulent fluctuations occurs away from the wall for earth normal gravity, the near-wall peak is only slightly lower and is similar in magnitude to that in the case of low gravity. These observations reveal the significance of small scale dynamics in affecting the heat transfer which was previously thought to be dominated by large scale bubbles, particularly at low gravity levels.

Bubble formation from sub-millimeter orifices under variable gas flow conditions

We provide an experimental investigation on the mechanism of the bubble formation from sub-millimeter orifices under variable gas flow conditions VGFC. The effect of influential parameters including the volumetric gas flow rate Q, the orifice diameter dor, and the volume of the gas reservoir Vc upstream of the orifice are investigated in detail. We found that, by enlarging Vc,q increases. This affects various aspects of bubble formation dynamics such as the bubble base expansion, the apparent contact angle at the three-phase contact point, and the bubble detachment criterion. The effect of Vc is best presented by its dimensionless group, the capacitance number Nc. The minimum Nc from which the influence of the gas reservoir becomes important depends on the orifice size. Moreover, a significant increase in Vc leads to a change in the bubbling regime towards multiple bubble formation.