Bubble Population Research Articles

Development and validation of a 1D gas–liquid model for dissolved Mn(II) removal by oxidation process in a square bubble column

Modeling multiphase reactors requires an in-depth multidisciplinary analysis of various phenomena including the chemical kinetics, oxygen mass transfer, as well as the simulation of flows within these contactors. In this study, a 1D model of two-phase flow for Mn(II) removal from drinking water by aeration process is developed and validated. This model is based on the Eulerian description of two-phase gas–liquid flow with the comparison between a one-medium bubble size and a two-bubble class description to represent the bubble population in the heterogeneous flow regime. All the relevant chemical species are simulated by coupling hydrodynamics, gas–liquid mass transfer, and reaction kinetic. A pseudo-first-order model accounting for homogeneous and heterogeneous kinetics is considered for Mn(II) oxidation. The performance of the developed 1D model is compared and validated with experimental data. The 1D model was able to predict quantitatively Mn oxidation as a function of pH, initial Mn(II) and initial Mn(IV) concentrations.

Bubble characterization and bubble population on SiC material surface in subcooled boiling flow

A particularly promising candidate for widespread adopted Accident-Tolerant Fuels(ATF) is Silicon Carbide (SiC), which is deemed significantly advantageous for nuclear energy applications due to its remarkable characteristics. The understanding of bubble behavior on SiC surfaces is critical for the development of improved SiC designs. An experiment study was executed to evaluate the characteristics and population of bubbles on the surface of SiC material in subcooled boiling flow. The experimental setup maintained atmospheric pressure and featured a subcooling range of 0-12 K and a wall superheat from 0K to 30K, and a maximum coolant Reynolds number of 10400. The findings accentuated that the sensitivity of heat to fluid velocity during nucleation boiling is greater on surfaces with small porosity than on those with larger porosity. The Sauter mean diameter displays an upward trend in sync with increasing wall superheat, and the Sauter mean diameter can be represented as a dependence of the maximum and minimum bubble diameters. In terms of bubble distribution properties, it was discovered that bubble size and bubble aspect ratio conform to a lognormal distribution, while bubble orientation adheres to a normal distribution, and bubble circularity validates a Weibull distribution.

Effect of degassing on bubble populations in air-entraining free-surface turbulent flows

Effect of degassing on bubble populations in air-entraining free-surface turbulent flows

Research on factors affecting bubble and particle behavior in a three-phase flotation system based on COMSOL

ABSTRACT To investigate the impact of various parameters on bubble and particle dynamics in a flotation system, COMSOL software was utilized. The “two-phase flow – Level Set” module coupled with the “fluid particle interaction” module was used to explore the behavior of single bubbles and particle groups. The bubbles were set as a discrete phase to represent a group of floating bubbles. By combining the “Single-phase flow” module with dual “fluid-particle interaction” modules, we examined the interactions between bubble populations and particles within the system. The research results show that as the bubble diameter increases, the carrying effect of the bubbles on the particles becomes stronger. When the bubble radii are 1, 1.25, 1.5, 1.75, and 2 mm respectively, the maximum movement speed of the particles in the area increases by 3.0%, 2.3%, 5.1%, and 2.7%. The average speed of the particles increases by 7.9%, 7.3%, 9.0%, and 10.0%. Increasing the mass flow rate can increase the collision probability between particles and bubbles, thus increasing the flotation rate. However, a too high mass flow rate will make the state of bubbles unstable. When the mass flow rate is less than 1.5 kg/s, the bubbles remain stable. When the mass flow rate exceeds 1.5 kg/s, the severity of bubble splitting increases. In the study area, the irregularity of the bubble clusters results in a more chaotic flow field, leading to greater speed and displacement of the particles. Increasing the number of bubbles entering at one time and their initial speed enhances the impact of the bubble clusters on the solid particles. When the number of bubbles entering at one time is 5, 10, 15, and 20 respectively, the maximum movement speed of the particles increases by 6.9%, 8.1%, and 9.0%. When the initial speed of the bubble entering is 0, 0.1, 0.2, and 0.3 m/s respectively, the maximum movement speed of the particles increases by 6.4%, 3.0%, and 8.8%.

Sensitivity analysis and uncertainty quantification based on the analytical solution for nanoparticle-stabilized foam flow in porous media

A model describing nanoparticle-stabilized foam displacement is proposed in this study. Based on literature experimental data, we include nanoparticle dependence in a simplified version of the Stochastic Bubble Population balance model in local equilibrium. To describe the gas–water fractional flow, we utilize quadratic Corey permeabilities. Our model consists of non-strictly hyperbolic conservation laws, and we investigate the existence of a global solution as a sequence of waves. This simpler model maintains the solution structure of classical Corey’s relative permeability model and allows us to obtain algebraic expressions to analyze the solution type and construct the water saturation profiles. We perform uncertainty quantification and sensitivity analysis of the model describing the foam injection assisted by nanoparticles, considering three relevant quantities of interest: breakthrough time, cumulative water production, and pressure drop. The analytical framework developed allows us to obtain these quantities. Our results show that the effect of nanoparticles is greater than the model’s uncertainty (for all quantities), suggesting that measuring it experimentally is statistically feasible. The presence of nanoparticles also significantly reduces the uncertainty propagation due to foam stabilization. From the sensitivity study, the endpoints of water and gas relative permeability are the most significant parameters for the breakthrough time. For the maximum pressure drop, the gas endpoint relative permeability and the concentration of nanoparticles stand out. Otherwise, water production is more sensitive to a foam-related parameter most of the time. We achieve convergence even using the classical Monte Carlo method, showing how analytical solutions drastically reduce computational costs.

Bubbles Counting Using Organic Pollutants Degradation as a Probe

Relying on the fact that both of chemical and physical impacts of sonication are in strong relation to the number of acoustic cavities, the present paper introduces an innovative technique for the estimation of the number of active bubbles using the degradation of nonvolatile pollutants in the bulk liquid as a probe. The internal (gas pages) and external (liquid) bubble sonochemistry were simulated to track the radicals generation and use for nonvolatile pollutants degradation (in the liquid phase). To this end, COPASI® chemical kinetics software has been used for optimizing the acoustic bubble number density by linking the instantaneous bubble gas reaction (described by a bubble dynamic model accounting for the radical dissolution mechanism) and the aqueous free radicals degradation kinetics [i.e. concentration vs. time] of several nonvolatile organics (phenol, 4-chlorophenol, dyes…). Based on this strategy, the number density of active bubbles was determined for different operating circumstances (i.e. acoustic intensity, frequency, liquid temperature and saturation gas type). The performance of our method was evaluated by comparing our findings to those available in the literature, where an excellent agreement was established. Our technique showed that the number density monotonously goes up with increasing ultrasound frequency from 200 to 1140kHz, regardless of the experimental conditions used in this investigation. The opposite behavior has been obtained with the increase of the liquid temperature and acoustic intensity. Additionally, it has been noticed that the variation in the number of cavities with respect to the nature of saturating gas is frequency-dependent. At a frequency of 200kHz, the number of bubbles is in the order: O2>Ar>air. However, over this frequency (>200kHz), the number of acoustic bubbles is in the order: O2>air>Ar. On the other hand, it has been shown that below a frequency of ~860kHz, the variation of void fraction (ε) is synchronized with change in number density (N); nevertheless, over this value (>860kHz), these two parameters (N, ε) are no longer closely connected. As a result, in this case (>860kHz), the evaluation of number density from the total volume fraction of bubbles could not be directly performed without more information regarding the bubbles population, (e.g. size distribution, bubble-bubble interactions, bubbles deformation…etc.). Finally, the current proposed technique is flexible and can determine the number density of active bubbles for a wide range of operating conditions and circumstances.

Instability processes in short and long laminar separation bubbles

This work studies the link between the bursting process of a flat plate laminar separation bubble and the modification of the stability characteristics of the separated shear layer due to changes in the flow parameters. A vast population of short and long laminar separation bubbles was surveyed by means of Particle Image Velocimetry instrumentation for different values of the Reynolds number, the free-stream turbulence intensity and the streamwise pressure gradient. A fine-step variation of the free-stream velocity allowed us to determine the critical Reynolds number at which bursting occurs. Successively, the most amplified wavelength and frequency were computed for both the short and the long bubble regimes. Once scaled with the boundary layer displacement thickness at separation, the average wavenumber of the vortices shed by the bubble was found to be constant and equal to about 0.9 in the short regime, accordingly to previous studies. Differently, this quantity reduces to about 0.6 in the long bubble regime, and a marked change in the Strouhal number of vortex shedding occurs. Also, the temporal growth of spanwise vortices was seen to occur in the recirculation region of long type bubbles, being linked to an absolute instability of disturbances. The currently acquired data demonstrate the existing link between the bursting process of a laminar separation bubble and a marked change in the instability mechanisms driving the transition process of the boundary layer. A simplified correlation for the prediction of bursting is provided in this work as a function of the free-stream turbulence intensity and the streamwise pressure gradient.

Are monodisperse phospholipid-coated microbubbles “mono-acoustic?”

Phospholipid-coated microbubbles with a uniform acoustic response are a promising avenue for functional ultrasound sensing. A uniform acoustic response requires both a monodisperse size distribution and uniform viscoelastic shell properties. Monodisperse microbubbles can be produced in a microfluidic flow focusing device. Here, we investigate whether such monodisperse microbubbles have uniform viscoelastic shell properties and thereby a uniform “mono-acoustic” response. To this end, we visualized phase separation of the DSPC and DPPE-PEG5000 lipid shell components and measured the resonance curves of nearly 2000 single and freely floating microbubbles using a high-frequency acoustic scattering technique. The results demonstrate inhomogeneous phase-separated shell microdomains across the monodisperse bubble population, which may explain the measured inhomogeneous viscoelastic shell properties. The shell viscosity varied over an order of magnitude and the resonance frequency by a factor of two indicating both a variation in shell elasticity and in initial surface tension despite the relatively narrow size distribution.

Cosmological first-order vacuum phase transitions in an expanding anisotropic universe

We examine the anisotropy originated from a first-order vacuum phase transitions through three-dimensional numerical simulations. We apply Bianchi Type-I metric to our model that has one scalar field minimally coupled to the gravity. We calculate the time evolution of the energy density for the shear scalar and the directional Hubble parameters as well as the power spectra for the scalar field and the gravitational radiation although there are a number of caveats for the tensor perturbations in Bianchi Type-I universe. We run simulations with different mass scales of the scalar field, therefore, in addition to investigation of anisotropy via the shear scalar, we also determine at which mass scale the phase transition completes successfully, hence, neglecting the expansion of the Universe does not significantly affect the results. Finally, we showed that such an event may contribute to the total anisotropy depending on the mass scale of the scalar field and the initial population of nucleated bubbles.

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Mathematical and computational models for simulating transient nuclear criticality excursions within plutonium nitrate systems

This paper presents a novel methodology for the analysis of transient nuclear criticality in aqueous solutions of plutonium nitrate. The transient methodology includes one-dimensional thermal hydraulics and a detailed description of radiolytic gas formation (including aqueous concentrations of radiolysis species and bubble population, nucleation radius and advection velocity). The positive temperature feedback effect in dilute plutonium solutions, due to a low lying resonance (at ≈ 0.3 eV) in the microscopic fission cross section, is investigated. The solutions’ nuclear properties, such as intrinsic neutron source and mean neutron generation time; thermophysical properties and heat transfer coefficients; linear energy transfer and dynamics of radiolytic gas nucleation; and subcritical power, are also investigated. The effect of step and ramp reactivity insertions on transient nuclear criticality behaviour is examined, alongside the effect of fuel solution ingress and egress from the system. For a solution containing 16.0 g L−1 plutonium with an acidity of 0.2 mol L−1, increasing the width of the prescribed step reactivity insertion from 2.25 to 2.50 s increased the magnitude of the initial power peak, and decreased the time to boil, by an order of magnitude. It was observed that the characteristics of the radiolytic gas were dependent on the magnitude of the initial power peak. For example, the transients with the highest initial power peak produced an initially large quantity of radiolytic gas, with defined oscillations in their quantity (and other properties) as the transient progressed. For transients with lower power peaks, the oscillations became less defined, with a reduced period and magnitude, due to the lower quantity of radiolytic gas produced due to the initial power peak. Many of the presented simulations of nuclear criticality transients were terminated when the solution started to boil, a phenomenon which is not included in the presented methodology. Boiling occurred when the initial reactivity input induced a power spike that raised the solution temperature enough for the positive reactivity feedback effect to sustain the transient even when the reactivity input was removed.

Relationship between heat flux and bubble population density in heat transfer enhancement of flow boiling using microstructured surfaces

Relationship between heat flux and bubble population density in heat transfer enhancement of flow boiling using microstructured surfaces

A Numerical Study of the Efficiency of the Sono Galvano-Fenton Process as a Tertiary Treatment Technique for the Wastewater Reuse in Agriculture

In the present study, the Sono-Galvano-Fenton process is studied numerically as a tertiary treatment process for treated wastewater reuse in irrigation, with in situ generation of the Fenton’s reagent and catalyst, i.e., H2O2 and Fe2+. The sonochemical pathway is examined as a source of hydrogen peroxide under the pre-optimized condition of acoustic frequency, 200 kHz. The macroscopic model accounting for the performance of the single acoustic cavitation bubble and the bubble population density is combined with the Fe/Cu galvanic cell operating in acidic conditions (pH 3), following a cumulative and instantaneous production approach in terms of Fenton’s reagent. The combination is optimized based on the rate of hydroxyl radicals generated by the Galvano-Fenton process, as a non-selective powerful oxidant against recalcitrant pollutants, then considering the synergetic effect of the hybrid process in terms of HO● pumped sonochemically and via the Fenton based pathway, treated using simulations of the isolated processes then their combined configuration following both aforementioned approaches.

TEM investigation of helium bubble evolution in tungsten and ZrC-strengthened tungsten at 800 and 1000°C under 40keV He+ irradiation

Helium-induced defect nucleation and accumulation in polycrystalline W and W0.5 wt%ZrC (W0.5ZrC) were studied in-situ using the transmission electron microscopy (TEM) combined with 40 keV He+ irradiation at 800 and 1000°С at the maximum damage level of 1 dpa. Radiation-induced dislocation loops were not observed in the current study. W0.5ZrC was found to be less susceptible to irradiation damage in terms of helium bubble formation and growth, especially at lower temperature (800 °C) when vacancies were less mobile. The ZrC particles present in the W matrix pin the forming helium bubbles via interaction between C atom and neighbouring W atom at vacancies. This reduces the capability of helium to trap a vacancy which is required to form the bubble core and, as a consequence, delays, the bubble nucleation.At 1000 °C, significant bubble growth occurred in both materials and all the present bubbles transitioned from spherical to faceted shape, whereas at 800 °C, the faceted helium bubble population was dominated in W.

Molecular dynamics and experimental study of the effect of pressure on CO2 foam stability and its effect on the sequestration capacity of CO2 in saline aquifer

CO2 foam flooding technology is one of the important methods to improve the efficiency of CO2 sequestration in saline aquifers. This article explores the influence rules of pressure on CO2 foam stability and its micro-mechanisms, and its effect on the efficiency of CO2 foam to enhance CO2 sequestration. Increasing pressure is conducive to delaying the foam drainage and inhibiting CO2 diffusion between the liquid films, micro-mechanisms showed that the binding effect of surfactants on water and CO2 molecules was enhanced due to increased pressure. Then core-nuclear magnetic resonance was used to study the effect of pressure on CO2 sequestration characteristics from core scale, the bubble population accumulation in the macropores increased with the enhanced pressure, promoting the diversion effect of foam to the meso- and micropores. In addition to enhancing the CO2 sequestration potential of the macropores, the utilization of storage space of meso- and micropores was improved.

Ostwald ripening of multi-component bubbles in porous media: A theory and a pore-scale model of how bubble populations equilibrate

Bubbles trapped inside porous materials occur in many applications ranging from geologic CO2 sequestration, underground hydrogen storage (UHS), groundwater remediation, to fuel cells and electrolyzers. If partially miscible in their surrounding wetting phase, bubbles can evolve through a process called Ostwald ripening, in which those with a high interfacial curvature dissolve fastest and feed into bubbles with a low curvature. For single-component bubbles, the physics are relatively well-understood. This work focuses on the ripening of bubbles comprised of multiple components, which remains unexplored. We first present a pore-network model (PNM) to simulate the temporal evolution of a population of partially miscible, multi-component bubbles inside a heterogeneous porous microstructure. We then use the model to identify the different ripening regimes between two adjacent bubbles, some rather counterintuitive. We also show that, under conditions prevalent in the subsurface, multi-component ripening proceeds in two stages separated in timescale: partitioning and coevolution. Based on this insight, we propose a theory to predict the probability density function (PDF) of bubble sizes at the ends of partitioning and coevolution (i.e., equilibrium) from their initial state and the pore-size distribution. The theory is systematically compared against the PNM and very good agreement is found. Limitations of both the PNM and theory are discussed and implications for UHS are outlined.

The "Bubble": What Can Be Learned from the National Basketball Association (NBA)'s 2019-20 Season Restart in Orlando during the COVID-19 Pandemic.

The National Basketball Association (NBA) suspended operations in response to the COVID-19 pandemic in March 2020. To safely complete the 2019-20 season, the NBA created a closed campus in Orlando, Florida, known as the NBA "Bubble." More than 5000 individuals lived, worked, and played basketball at a time of high local prevalence of SARS-CoV-2. Stringent protocols governed campus life to protect NBA and support personnel from contracting COVID-19. Participants quarantined before departure and upon arrival. Medical and social protocols required that participants remain on campus, test regularly, physically distance, mask, use hand hygiene, and more. Cleaning, disinfection, and air filtration was enhanced. Campus residents were screened daily and confirmed cases of COVID-19 were investigated. In the Bubble population, 148 043 COVID-19 reverse transcriptase PCR (RT-PCR) tests were performed across approximately 5000 individuals; Orlando had a 4% to 15% test positivity rate in this timeframe. There were 44 COVID-19 cases diagnosed either among persons during arrival quarantine or in non-team personnel while working on campus after testing but before receipt of a positive result. No cases of COVID-19 were identified among NBA players or NBA team staff living in the Bubble once cleared from quarantine. Drivers of success included the requirement for players and team staff to reside and remain on campus, well-trained compliance monitors, unified communication, layers of protection between teams and the outside, activation of high-quality laboratory diagnostics, and available mental health services. An emphasis on data management, evidence-based decision-making, and the willingness to evolve protocols were instrumental to successful operations. These lessons hold broad applicability for future pandemic preparedness efforts.

The mathematical model and analysis of the nanoparticle-stabilized foam displacement

This work proposes a mathematical model to study the foam displacement in porous media stabilized by nanoparticles. We consider a simplification of the Stochastic Bubble Population balance model in local equilibrium, with nanoparticle dependence inspired by the experimental data from the literature. It consists of a non-strictly hyperbolic system of conservation laws, which is solved for the generic initial and injection conditions. We investigate the existence of a global solution as a sequence of waves following the Conservation Laws Theory. When the solution is composed of two or more waves, we present necessary and sufficient conditions to guarantee the compatibility of these wave sequences. The analytical solution for the nanoparticle-stabilized foam displacement in porous media allowed us to quantify the effect of nanoparticles on foam displacement, focusing on the breakthrough time and cumulative water production. In agreement with the literature, when only gas is injected, the breakthrough time and the water production increase with the nanoparticle concentration. Although, we also observe that the effect of nanoparticles is less pronounced for high nanoparticle concentration. Counterintuitively, during gas-water co-injection for a certain parameter range, adding nanoparticles changes the mathematical solution qualitatively, yielding a negligible effect on water production. We discuss the most favorable conditions to observe the action of nanoparticles in laboratory experiments.

Large eddy simulations of bubbly flows and breaking waves with smoothed particle hydrodynamics

For turbulent bubbly flows, multi-phase simulations resolving both the liquid and bubbles are prohibitively expensive in the context of different natural phenomena. One example is breaking waves, where bubbles strongly influence wave impact loads, acoustic emissions and atmospheric-ocean transfer, but detailed simulations in all but the simplest settings are infeasible. An alternative approach is to resolve only large scales, and model small-scale bubbles adopting sub-resolution closures. Here, we introduce a large eddy simulation smoothed particle hydrodynamics (SPH) scheme for simulations of bubbly flows. The continuous liquid phase is resolved with a semi-implicit isothermally compressible SPH framework. This is coupled with a discrete Lagrangian bubble model. Bubbles and liquid interact via exchanges of volume and momentum, through turbulent closures, bubble breakup and entrainment, and free-surface interaction models. By representing bubbles as individual particles, they can be tracked over their lifetimes, allowing closure models for sub-resolution fluctuations, bubble deformation, breakup and free-surface interaction in integral form, accounting for the finite time scales over which these events occur. We investigate two flows: bubble plumes and breaking waves, and find close quantitative agreement with published experimental and numerical data. In particular, for plunging breaking waves, our framework accurately predicts the Hinze scale, bubble size distribution, and growth rate of the entrained bubble population. This is the first coupling of an SPH framework with a discrete bubble model, with potential for cost-effective simulations of wave–structure interactions and more accurate predictions of wave impact loads.

Editorial for Special Issue “Hydrodynamics and Gas Dispersion in Flotation”

Gas dispersion, the breakage of a mass of gas into a population of small bubbles, is one of the most important subprocesses occurring in flotation machines [...]