Bubble Size Evolution Research Articles

Enhancing CO2 Foam Stability with Hexane Vapours: Mitigating Coarsening and Drainage Rates

CO2 foams often suffer from poor stability due to high coarsening and coalescence rates, limiting their effectiveness in various applications. While it is well-established that small amounts of insoluble vapours such as alkane or fluorocarbon vapours can impede coarsening and recent studies have demonstrated their impact on coalescence, their specific effect on the CO2 foams has not been studied. This research provides a comprehensive examination of stabilising effect of hexane on CO2 foams in the presence of sodium dodecylbenzenesulfonate (SDBS). We investigated the foam stability of CO2 foams, benchmarking them against N2 foams by analysing foam lifetime, liquid drainage rate, and the evolution of bubble size. Additionally, we quantified the stabilising impact of hexane by calculating the coarsening rate. To gain insights into the adsorption mechanism of surfactants in the presence of hexane, we conducted surface tension and interfacial dilational rheology measurements, which demonstrated an increased adsorption of surfactant molecules at the interface and increased dilational viscoelasticity of interface when n-hexane was present. The introduction of hexane significantly improved foam stability, reducing coarsening rates by more than an order of magnitude. This improvement in foam stability is attributed to inhibited CO2 diffusion from the bubbles, as well as enhanced surfactant adsorption and surface elasticity, resulting in an approximate 3.6-fold increase in foam half-life.

Simple Method to Assess Foam Structure and Stability using Hydrophobin and BSA as Model Systems.

The properties and arrangement of surface-active molecules at air-water interfaces influence foam stability and bubble shape. Such multiscale-relationships necessitate a well-conducted analysis of mesoscopic foam properties. We introduce a novel automated and precise method to characterize bubble growth, size distribution and shape based on image analysis and using the machine learning algorithm Cellpose. Studying the temporal evolution of bubble size and shape facilitates conclusions on foam stability. The addition of two sets of masks, for tiny bubbles and large bubbles, provides for a high precision of analysis. A python script for analysis of the evolution of bubble diameter, circularity and dispersity is provided in the Supporting Information. Using foams stabilized by bovine serum albumin (BSA), hydrophobin (HP), and blends thereof, we show how this technique can be used to precisely characterize foam structures. Foams stabilized by HP show a significantly increased foam stability and rounder bubble shape than BSA-stabilized foams. These differences are induced by the different molecular structure of the two proteins. Our study shows that the proposed method provides an efficient way to analyze relevant foam properties in detail and at low cost, with higher precision than conventional methods of image analysis.

Power law exponents for single bubbles growth in nucleate pool boiling at zero gravity

Nucleate pool boiling is an important boiling mode used in various fields of application. Bubble detachment and new bubble generation at the nucleation site is an important aspect of the process under terrestrial conditions. This sequence prevents prolonged observation of bubble growth phenomena. The problem can be circumvented by performing single bubble growth experiments under zero gravity conditions. Many experiments of this type are performed in a specially designed cell on board the International Space Station. Several combinations of boiling experimental parameters (pressure, heat flux, waiting time, degrees of subcooling) are tested. The bubble size evolution curve was found to represent the influences off the individual parameters best. Fitting attempts show that the experimental bubble growth curves can be nicely described by power law correlations. An analytical solution is given for the evolution of the liquid temperature field within the experimental test cell, in the absence of boiling incidents. It is shown that the time evolving difference between the solid/liquid interfacial temperature and the liquid saturation temperature is the basic factor that determines the bubble growth exponent. As an outcome, the whole experimental information on the bubble growth curves of 160 different boiling conditions is compressed in the form of tables that include the corresponding power law factors. These tables not only allow the reconstruction of the examined boiling curves but can also generate boiling curves in a dense grid of boiling conditions through interpolation of existing boiling data. The latter offers coherence and continuity in boiling computer codes over a broad range of conditions.

Experimental investigation of bubble size evolution released from a fine bubble ejector

AbstractThe effects of gas flow rate, liquid flow rate, and liquid properties on the bubble size evolution at the outlet zone of an ejector have been investigated systemically. The liquid properties, including surface tension and viscosity, were changed by adding glycerol, ethanol, or Carbopol 2020 into tap water. It was found that increasing the liquid flow rate is beneficial for producing smaller bubbles with a narrower size distribution in the ejector, while the gas flow rate investigated here shows less influence on the generated fine bubble diameter. An intense bubble coalescence phenomenon, which has a negative effect on mass transfer, was first observed at the small outlet zone of the ejector by exploring the bubble size evolution along the axial height. It was found that the mean diameter of the fine bubbles could increase by 48% ~ 90% when they rose only 25 cm from the ejector outlet, and the bubble coalescence could be effectively suppressed by adding a small amount of glycerol to water. The bubble diameter could be reduced by 32% ~ 43% by using a 2 wt.% glycerol solution under the experimental conditions. A comparative study with tap water, glycerol solution, Carbopol solution, and ethanol solution was taken, and the underlying mechanism of reducing the generated bubble size by changing the liquid properties was revealed.

Viscoelastic coarsening of quasi-2D foam

Foams are unstable jammed materials. They evolve over timescales comparable to their “time of use", which makes the study of their destabilisation mechanisms crucial for applications. In practice, many foams are made from viscoelastic fluids, which are observed to prolong their lifetimes. Despite their importance, we lack understanding of the coarsening mechanism in such systems. We probe the effect of continuous phase viscoelasticity on foam coarsening with foamed emulsions. We show that bubble size evolution is strongly slowed down and foam structure hugely impacted. The main mechanisms responsible are the absence of continuous phase redistribution and a non-trivial link between foam structure and mechanical properties. These combine to give spatially heterogeneous coarsening. Beyond their importance in the design of foamy materials, the results give a macroscopic vision of phase separation in a viscoelastic medium.

Experimental and numerical study on the bubble dynamics and flow field of a swirl flow microbubble generator with baffle internals

Microbubble generators have been widely applied in various fields. This paper explored the bubble generation performance and two-phase flow characteristics of a swirl flow microbubble generator with baffle internals. It showed that the bubble size evolution process in the generator was more sensitive to the liquid flow rate than the gas phase. A semi-empirical expression considering the dimensionless factors of gas-liquid flow rate ratio, Reynolds number, and Weber number predicted the Sauter mean diameter reasonably. Meanwhile, the hydrodynamic simulations were conducted for the generator by using various bubble breakage and aggregation kernels. The Lehr-Liao and Luo & Svendsen-turbulent model combinations were determined to predict the bubble dynamics performance well. The hydrodynamic simulations showed that the larger the liquid flow rate, the higher the turbulent dissipation rate, which resulted in a smaller bubble size. The work is helpful to the design and operation of the swirl flow microbubble generator.

Bubble‐scale observations of polyurethane foam expansion

AbstractWe describe experiments designed to inform computational models of the dynamic filling process of chemically blown, polyurethane foams, especially subgrid models to predict bubble size affecting foam properties. Three experimental methods are used to observe the evolution of bubble sizes during blowing. Magnified views of bubbles at a transparent wall of a channel are recorded during the foaming. The bubble sizes in the final frame after the expansion has stopped are compared to scanning electron microscope images of the interior of the cured samples to determine wall effects. In addition, diffusing wave spectroscopy is used to determine the average bubble sizes across the width of a similar channel during foam expansion. We conclude that the bubble size distribution is dependent on the formulation of foam being tested, temperature, the height in the foam bar, the proximity to a wall, and the degree of overpacking.

Visualization of bubble formation at the wall of beer cans

Visualization experiments are performed to examine nucleation, growth, and detachment of bubbles at hydrophobic surfaces of a beer can. Solutions of our concern are carbonated water and beer. The solution under cooling is poured into a (hydrophilic) glass container; the container is then sealed. A piece of a beer can whose inner coating is hydrophobic is inserted inside the container. To trigger gradual growth of bubbles nucleated preferentially at the piece of the beer can, dissolved gas supersaturation is created by heating the solution (with the container being sealed). From the visualization experiments, we report on the evolution of bubble population and size (from the front view) and the shape of attached bubbles (from the side view) at surface, exploring the role of surface tension and proteins in detachment of the bubbles.

Asymmetric Bubble Formation at Rectangular Orifices.

Bubble formation in liquids is frequently observed in nature and applied in various industrial processes. These include pool and flow boiling for thermal management systems, where bubbles may form asymmetrically at narrow slits and in convective flows. While previous studies have focused on symmetric bubble formation at circular orifices, the dynamics of asymmetric bubble formation remains poorly understood. Here, we experimentally investigate bubble formation at rectangular orifices and examine the effects of the orifice size and aspect ratio and the gas flow rate on the bubble size. The asymmetric bubble shape evolution at the rectangular orifice is analyzed, and we find that the size of the bubble neck is controlled either by the orifice size or by the capillary length. Based on these findings, we develop a static force balance model to predict the bubble size in the quasi-static regime, where the roles of Bond number and aspect ratio are identified. The bubble size evolution in the dynamic regime is further understood by introducing a Weber number that evaluates the effect of the virtual mass force induced by gas flow. Our study provides physical understanding of the dynamics of asymmetric bubble formation and guidance to predict the bubble size at asymmetric orifices.

Notes on the Phenomenological Model of Subcooled Liquid Boiling

It is shown that the Snyder–Bergles model seems to be the best phenomenological one while describing the process of forced boiling of the liquid considerably subcooled relative to the saturation temperature. This model most likely (without contradictions) accounts for the main physical subprocesses that accompany subcooled liquid boiling (liquid microlayer evaporation below the bubble, vapor condensation at the bubble dome, liquid inflow to the microlayer), meets modern concepts on the boiling mechanism, and agrees with the experimental data. Based on experiments at the Joint Institute for High Temperatures, Russian Academy of Sciences (JIHT RAS) using high-speed video recording (at a rate of up to 100 thousand frames per second) and other studies, some subprocceses incorporated into the model are refined. They are as follows: deactivation of the nucleation sites, heat removal from the bubble dome via unsteady heat conduction, and the bubble size evolution in time as the balance of masses of the evaporated and condensed vapor. It is shown that the main mechanism through which heat from the bubble dome is transferred to the surrounding liquid is unsteady heat conduction, the intensity of which is inversely proportional to the square root of the bubble existence time. The evolution of bubble sizes is caused by the balance of masses of the evaporating liquid microlayer and steam condensing on the bubble dome. With high heat flux densities supplied to the heating surface and low liquid subcooling values, the imbalance shifts toward the evaporation side, as a result of which conditions may emerge for a growth of large bubbles and their subsequent merging and occurrence of large vapor agglomerates in the coolant flow.

Subcooled liquid boiling: details of the mechanism and phenomenological description

Using high-speed filming (with a frame frequency up to 100 kHz) the important details of the subcooled liquid boiling mechanism are specified, which allow to conclude that Snyder-Bergles phenomenological model describes the process with the maximal likelihood. This model accounts for the main subprocesses of the subcooled liquid boiling (evaporation of the liquid microlayer located under the bubble near the dry spot boundary, vapor condensation at the bubble dome, liquid inflow to the microlayer). It corresponds to the modern ideas regarding to boiling mechanism and qualitatively well meets the experimental data. On the basis of the conducted experiments the description of several subprocesses of the model is defined more exactly: nucleation sites deactivation, het removal from the bubble dome by means of unsteady heat conduction, bubble size evolution as a result from the balance of masses of the evaporating and condensing vapors. It was shown that large vapor agglomerates appear in the flow due to small vapor bubbles coalescence with a heat flux density increase. Formation of dry patches under the agglomerates was studied. These dry patches are precursors of the boiling crisis. Superheating of the surface under dry patches immediately leads to the heating surface burnout.

The effect of liquid viscosity and modeling of mass transfer in gas–liquid slug flow in a rectangular microchannel

AbstractBoth chemical (by adding 0.05 M NaOH) and physical absorption of CO2 into aqueous glycerol solutions with viscosity up to 45.6 mPa·s in a microchannel are investigated. The concentration distribution pattern, absorption time, and mass transfer coefficient are analyzed and discussed. A new concentration distribution pattern is observed with the lowest concentration locating at the channel center. It is shown for the first time that presents a positive relationship with liquid viscosity, which is explained by the essential role of the mass exchange between the liquid film and bulk liquid slug. This mass exchange may lead to a rise in k L when increasing the liquid viscosity under some cases in chemical absorption. A mass transfer model is successfully applied to predict the bubble size evolution in physical absorption. The model also shows about 10–46% of the mass transfer contribution from liquid films before saturation.

On evolving size and shape of gas bubble in marine clay under multi-stage loadings: microcomputed tomography (μCT) characterization and cavity contraction analysis

Discrete bio-gas bubbles commonly form in fine-grained marine sediments and have modified many aspects of the behavior of these sediments, including strength, stiffness, and permeability. Although the level of such modifications is known to govern by bubble shape and size, limited studies have been undertaken, mainly due to difficulty in nondestructively characterizing bubbles within a soil under in situ stresses. In this study, a mini-loading device was developed to perform one-dimensional loading tests on gassy marine clay and gassy silt in a microcomputed tomography (μCT). The evolving bubble shape, size, and pressure during loading were quantified, and the resulting stress fields around the bubble cavities were evaluated via elliptical cavity contraction analysis considering stress anisotropy. As the vertical load increased, bubble cavities were found to compress predominantly along the vertical loading direction, with little horizontal compression, because localized soil failure (LSF) and thus cavity collapse occurred mainly near the roof of the at-rest lateral earth pressure coefficient (K0)-stressed elliptical bubble cavities. The evolution of bubble shape and size under loading is significantly affected by stress anisotropy, which governs the extent and location of the LSF. A Gaussian mixture model is adopted to quantify the evolving distributions of bubble structure parameters, which are essential for developing more physically rigorous gassy soil models.

Investigation of bubble behavior with phase change under the effect of noncondensable gas

An Arbitrary-Lagrangian-Eulerian based numerical method is proposed to study the phase change bubble under the effect of noncondensable gas (NCG). In order to validate the underlying mathematical model, benchmark tests, including the bubble growth in quiescent superheated liquid and the condensation of rising bubble with NCG, are conducted. The numerical results by the phase change model, in which the mass transfer rate is directly determined by interfacial heat flux, is found to agree fairly well with analytical results, and the calculation of fluid flow and heat transfer by the present numerical approach is reasonable. Moreover, the numerical results of free rising bubble condensation with NCG are found to present good agreement with the experimental data on the evolution of bubble size, and the mass balance of the NCGs is proved to be achieved by the model. Finally, the subcooled boiling with NCG on a biphilic surface is numerically investigated, and the bubble behavior and internal distribution of the NCG are studied in detail. In the presence of NCG, the bubbles can even depart from the walls that are negatively superheated. The bubble keeps the bowl-shape for a long time before necking, which is consistent with the experimental observations. The contact line is found to stay at the boundary between the hydrophilic and hydrophobic surfaces. The results also show that the local accumulation of the NCG near the bubble surface decreases the local apparent saturation temperature and inhibits the condensation, and the growth and departure of bubbles is thus promoted. In addition, the amount of NCG in the bubble is found to determine whether the bubble in the subcooled boiling is detached or not.

A mesoscale stress model for irradiated U 10Mo monolithic fuels based on evolution of volume fraction/radius/internal pressure of bubbles

Abstract Fracture near the U 10Mo/cladding material interface impacts fuel service life. In this work, a mesoscale stress model is developed with the fuel foil considered as a porous medium having gas bubbles and bearing bubble pressure and surface tension. The models for the evolution of bubble volume fraction, size and internal pressure are also obtained. For a U 10Mo/Al monolithic fuel plate under location-dependent irradiation, the finite element simulation of the thermo-mechanical coupling behavior is implemented to obtain the bubble distribution and evolution behavior together with their effects on the mesoscale stresses. The numerical simulation results indicate that higher macroscale tensile stresses appear close to the locations with the maximum increments of fuel foil thickness, which is intensively related to irradiation creep deformations. The maximum mesoscale tensile stress is more than 2 times of the macroscale one on the irradiation time of 98 days, which results from the contributions of considerable volume fraction and internal pressure of bubbles. This study lays a foundation for the fracture mechanism analysis and development of a fracture criterion for U 10Mo monolithic fuels.

Observations of Rising Methane Bubbles in Trondheimsfjord and Its Implications to Gas Dissolution

AbstractGas dissolution reduces the release of methane to the atmosphere from subsea sources. Being able to predict and assess the methane flux to the atmosphere requires knowledge on gas dissolution and mass transfer. This can be obtained by studying the size evolution of bubbles rising in water. New data of bubble size evolution have been obtained by releasing, tracking, and filming methane bubbles with an ROV in the Trondheimsfjord from depths varying between 100 and 300 m. Released bubbles had an initial diameter between 5 and 7 mm and were tracked until they reached a diameter of roughly 2 mm. The new data were compared against theory, applying established correlations for the mass transfer coefficient. There was an inconsistency between experiment and theory. Thus, new correlations for the mass transfer are proposed. The new correlations are consistent with both the new experiments and previously published experiments. They indicate that the conditions in the ocean can be labeled as partly contaminated with respect to mass transfer.

Investigation on the Properties of Aqueous Foams Stabilized by Cetyltrimethylammonium Bromide in Terms of Free Drainage and Bubble Size

AbstractAlthough foams stabilized by surfactants have been the subject of massive investigations and great achievements were made over the past few years, many questions concerning their properties are still not well understood. The aim of this study is to examine the effect of the cetyltrimethylammonium bromide (CTAB) concentration on the foam properties and illustrate the interaction between liquid drainage and bubble size evolution. Experiments were carried out at varying CTAB concentrations ranging from 0.1 to 5.0 times the critical micelle concentration (CMC), where the variation of the liquid content of foam and bubble size was simultaneously determined using a commercially available FoamScan device. The results showed that the foam properties (both foamability and foam stability) of CTAB were largely dependent on the surfactant concentration when concentrations c < CMC but this effect did not scale linearly with concentration. When c ≥ CMC, both foamablity and foam stability were nearly concentration independent, while the latter showed a small decrease due to the formation of micelles. In addition, the correlation between free drainage and bubble size evolution indicated that the increase of bubble size could indeed enhance the foam drainage.

A study of bubble size evolution in Jameson flotation cell

The Sauter mean diameter (d32) of bubbles was characterized for a gas–liquid system in a laboratory Jameson-type flotation cell with focus on the size variation in the uprising path of the bubbles in the riser of the flotation cell. Methyl isobutyl carbinol (MIBC) was used as frother for bubble stability. The effect of MIBC concentration, sampling height in the riser, gas flow rate (Jg) and liquid flow rate (Jl) in the downcomer on d32 was investigated. The d32 significantly decreased with increasing MIBC concentration until the Critical Coalescence Concentration (CCC), above which the d32 was almost constant at 0.645mm. CCC95, CCC90 and CCC85 were calculated to be 0.059, 0.046 and 0.038mmol/L, respectively for a Jg of 1.32cm/s and Jl of 11cm/s. Four frother concentrations covering these three values were selected for detailed studies. The size variation of bubbles was related to the Reynolds number (Re) in the downcomer, where the Re was influenced by Jl and Jg. Bubble size increased with the sampling height in the riser at MIBC concentrations below CCC95. This bubble size decreased with the Re and, for all the MIBC concentrations used in this investigation, it reached a critical value, even at MIBC concentrations below the CCC85.

Mathematical Modeling of the Multiphase Flow and Mixing Phenomena in a Gas-Stirred Ladle: The Effect of Bubble Expansion

A three-dimensional discrete phase model–volume of fluid coupled model has been developed to study the argon/steel/slag/air multiphase flow and mixing phenomena in an industrial gas-stirred ladle taking the coalescence, expansion and breakup of the argon bubbles as well as the fluctuant slag layer into account. The simulated results of the flow rate and bubble size evolution of the water model, as well as the slag eye size, are in good agreement with the experimental results reported in the literature. The modeling results show that the expansion of bubbles has a significant impact on the bubble size evolution and multiphase flow in an industrial ladle. The effects of different plug configurations on the flow characteristics and mixing time in the ladle are also investigated.

Bubble growth in cylindrically-shaped optical absorbers during photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a non-invasive, agent-free technique to shut down microvessels with high precision by promoting cavitation activity precisely in the targeted microvessels. PUT is based on the photoacoustic (PA) cavitation generated through concurrently applied nanosecond laser pulses and ultrasound bursts. In this study, a PA cavitation model is employed to understand the enhanced cavitation activity during PUT, with full consideration of the optical absorption of blood vessels. Bubble size evolution in cylindrically-shaped optical absorbers (vessels) due to rectified diffusion is simulated. Results show that the ultrasound pressure required for bubble growth decreases dramatically with the increased laser fluence. At a relatively low ultrasound driving pressure, bubble equilibrium radius increases rapidly due to concurrently applied nanosecond laser pulses and ultrasound bursts, resulting in a transition from inertial cavitation to stable cavitation. This inertial to stable transition is verified by the experimentally measured results on 0.76 mm silicone tubes filled with human whole blood with 0.5 MHz ultrasound at 0.243 MPa. This study demonstrated the potential to induce stable bubbles in blood vessels by PUT non-invasively.