Gas Bubble Size Distribution Research Articles

Analyses of bubble dynamics in subcooled boiling flow using Euler-Lagrange method

Subcooled boiling flow is widely used for heat and mass transfer in industries such as nuclear reactor, electronic equipment, and spacecraft, where the bubble dynamics is essential for understanding the gas-liquid flow behavior. Current studies focused on the gas void fraction or bubble size distribution at a global scale, but the dynamics of single bubbles are still obscure, which inhibits the fundamental understanding of gas-liquid flow and the precise prediction of heat transfer. Here, we develop a numerical method that captures the motion and condensation of bubbles in subcooled boiling flow using Euler-Lagrange method, with a proposed model for spatiotemporal lift-off bubble distribution on the heated wall as boundary condition. Our numerical method is validated by the agreement between the calculated gas void fraction distributions with the existing experimental data in vertical subcooled boiling flow. We further investigate the distribution of bubble position and size in the tube and find that the bubble size distribution shows different modes at different radial positions. Analysis of the single bubble dynamics shows that small and large bubbles suffer from centrifugal and centripetal lift forces, and thus tend to accumulate at a radial position near the wall and near the tube center, respectively, which reveals the mechanism of bubble size distribution. Besides, we find that the centripetal wall lubrication force is essential for the path instability of small bubbles near the wall. These findings promote the fundamental understanding of the gas-liquid phase distribution in the subcooled boiling flow and provide a numerical strategy for the precise prediction of mass and heat transfer in subcooled boiling flow.

CAGE20-7 Cruise Report: Sediment and water column analyses around flares at Norskebanken, Hinlopen and offshore Prins Karls Forland

During the cruise CAGE 20-7 (November 2nd to 16th 2020), we observed and investigated a large active methane seepage area south from the Yermak plateau (Northern Svalbard), in particular to characterize the water column and the sediment near known flares in Norskebanken (Geissler et al., 2016). Some flares were targeted for gas composition, DNA and bubble size distribution. The combination of the R/V Kronprins Haakon and the ROV ÆGIR 6000 from the Norwegian Marine Robotics Laboratory at the University of Bergen allowed this investigation to happen in this rough environment, while collecting invaluable data from the ROV. The cruise may be known as: CAGE20_7

EFFECT OF THE ANGLE OF PIPE INCLINATION ON AVERAGE SIZE AND SIZE DISTRIBUTION OF GAS BUBBLES INJECTING FROM A CAPILLARY TO LIQUID

The paper presents an experimental study of the size distribution of gas bubbles in an inclined pipe. The measurements were carried out for gas flow rate 3.3 ml/min, at pipe inclination angles of 30-60 deg. The study of the gas bubble diameters was performed using the shadow photography method. The values of the average size of bubbles and the size distribution of bubbles were obtained depending on the angle of inclination of the pipe and the distance from the location of the gas phase injection the measurement point.

Implementation and verification of a Quasi-Eulerian-Eulerian-IATE model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold

We implement a new gas–liquid two phase model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold. This model shares similarity with the Euler–Lagrange (E-L) method, in which the gas velocity is updated by bubble Lagrangian tracking, and with coupling the phase transport equation in Euler-Euler (E-E) method, thus, it is called the Quasi-Eulerian-Eulerian-IATE (Q-E-E-IATE) model. The local mean bubble size is obtained from solving the interfacial area transport equation (IATE). Various interfacial forces including drag force, lift force, virtual mass force, and turbulent dispersion force are incorporated in this model. This model is verified against published experimental data. Good agreement of gas volume fraction, flow field and bubble size distribution are obtained by adding the virtual mass force and adopting optimized IATE constants. The computational cost of the Q-E-E-IATE model is much lower compared to that of the traditional E-L and E-E models.

Impact of Microstructure on Solar Radiation Transfer Within Sea Ice During Summer in the Arctic: A Model Sensitivity Study

The recent rapid changes in Arctic sea ice have occurred not only in ice thickness and extent, but also in the microstructure of ice. To understand the role of microstructure on partitioning of incident solar shortwave radiation within the ice and upper ocean, this study investigated the sensitivity of the optical properties of summer sea ice on ice microstructures such as the volume fraction, size, and vertical distribution of gas bubbles, brine pockets, and particulate matter (PM). The results show that gas bubbles are the predominant scatterers within sea ice. Their effects on the scattering coefficient and ice albedo are 5 and 20 times stronger respectively than the effect of brine pockets. Albedo and transmittance of ice decrease with higher concentration and larger size of PM particles. A 4-cm top layer of ice with high PM concentration (50 g/m3) results in a 10% increase in radiation absorption. The role of ice microstructure in the partitioning of radiation transfer is more important for seasonal than for multiyear ice, and more important for ponded than for snow-covered ice. Varying ice microstructure can obviously alter solar radiation transfer in the ice-ocean system, even with a constant ice thickness. Our results suggest that numerical models should take the variable microstructure of sea ice into account to improve model accuracy and to understand the interaction between internal variations in Arctic sea ice and the ocean, especially in summer.

Gas phase hydrodynamics in a surface‐aerated tank with a long‐short blades agitator

AbstractThis work aims to study the gas phase hydrodynamics in a stirred tank with a surface‐aerated long‐short blades agitator by the Eulerian–Eulerian approach coupled with population balance model. Predicted local gas holdup and bubble size distribution agree well with those measured by a conductivity probe technique. The predictions demonstrate that the pressure depression in the center is the main driving force for gas suction and the downward flow carries the bubbles down to redistribute in the whole tank. The gas phase has higher gas holdup with large bubble size in the upper part and lower gas holdup but with small bubble size in the lower part of the tank. The predicted liquid‐phase mass transfer coefficients agree well with our previous experimental results and just depend on the power consumption per unit volume when the aspect ratio of the liquid height to the tank diameter varies from 1.1 to 2.0.

Quantification of gas exsolution and preferential diffusion for alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions

The in-situ formation of foamy oil has been found to be a crucial mechanism accounting for the better-than-expected production performance in heavy oil reservoirs under solution gas drive. Not only have the physical laws dominating gas exsolution in foamy oil not yet been well understood, but also the different contributions of each component in a gas mixture to the generation of foamy oil associated with an extremely complicated dynamic process has not been quantified. In this study, a novel and pragmatic technique has been proposed and validated to quantify the gas exsolution and preferential diffusion for alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions by taking gas bubble size distribution and preferential mass transfer of each gas component into account. Experimentally, constant-composition expansion (CCE) tests with various constant-pressure decline rates are utilized to describe gas exsolution behaviour of alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions, during which not only pressure and volume are simultaneously monitored and measured, but also gas samples were respectively collected at the beginning and end of experiments to perform compositional analysis. Theoretically, a mathematical model has been formulated to quantify gas exsolution and preferential mass transfer between each gas component and the liquid phase in alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions. More specifically, quasi-equilibrium boundary conditions, real gas equation, and Rayleigh distribution function are combined with the classical equation of motion, continuity equation, and mass transfer equation to form a novel equation matrix for quantifying gas bubble growth in foamy oil. Considering gas bubble size distribution and preferential diffusion of each component in a gas mixture, the total number of gas bubbles and individual diffusion coefficient of each gas component are determined by minimizing the discrepancy between the measured and calculated volume of alkane solvent(s)–CO2–heavy oil systems. More importantly, the dynamic composition of the gas phase and the amounts of both entrained gas and evolved gas can also be obtained simultaneously during the gas exsolution processes. Excellent agreements between the experimentally measured parameters (i.e., volume of foamy oil, composition of evolved gas, and volume of free gas) and the calculated ones have been respectively achieved. Compared with the individual diffusion coefficient for each component in a gas mixture determined under the traditional equilibrium conditions, a relatively large value has been found during mass transfer processes in a supersaturated oleic phase. Moreover, pseudo-bubblepoint pressure and gas exsolution rate are found to be two main mechanisms dominating the volume-growth rate of the evolved gas.

Investigation of two-phase flow regimes in square minichannels with different mixers created using additive technologies

In this paper, the effect of the junction angle on the Taylor flow regime characteristics was investigated. Using the Direct Light Processing method, minichannel mixers with different liquid and gas junction angles (from 30° to 150°) relative to the minichannel axis were manufactured. An experimental study of the two-phase flow formation was carried out, where Milli-Q® water was used as a working liquid, and high purity nitrogen was used as a working gas. A method of two-phase flow characteristic analysis using a high-speed shadow technique and automatic postprocessing was developed. Two-phase flow regimes were investigated in a wide range of gas and liquid flow rates. Size distribution of gas bubbles and liquid slugs and the distribution of bubble velocities were analyzed. The mechanisms of Taylor bubble formation and their characteristics, depending on the junction angle, were investigated.

Acoustic propagation in gassy intertidal marine sediments: An experimental study.

The need to predict acoustic propagation through marine sediments that contain gas bubbles has become increasingly important for civil engineering and climate studies. There are relatively few in situ acoustic wave propagation studies of muddy intertidal sediments, in which bubbles of biogenic gas (generally methane, a potent greenhouse gas) are commonly found. We used a single experimental rig to conduct two in situ intertidal acoustical experiments to improve understanding of acoustic remote sensing of gassy sediments, eventually including gas bubble size distributions. In the first experiment, we measured sediment sound speed and attenuation between four aligned hydrophones for a quasi-plane wave propagating along the array. The second experiment involved a focused insonified sediment volume created by two transducers emitting coincident sound beams at different frequencies that generated bubble-mediated acoustic signals at combination frequencies. The results from sediment core analyses, and comparison of in situ acoustic velocity and attenuation values with those of water-saturated sediments, together provide ample evidence for the presence of in situ gas bubbles in the insonified volumes of sediments. These datasets are suitable for linear and non-linear inversion studies that estimate in situ greenhouse gas bubble populations, needed for future acoustical remote sensing applications.

Advanced analysis of bubble columns: Comparison of Euler/Lagrange simulations and experiments under CO2 chemisorption conditions

The chemical absorption reaction of CO2 in a circular bubble column reactor was simulated with an Euler/Lagrange CFD method and results were compared with data from a laboratory scale bubble column. The experimental data comprises gas holdup and bubble size distributions obtained with ultrafast X-ray tomography and hydroxide ion conversion obtained with a wire-mesh sensor. Large Eddy Simulation (LES) is used for calculating the fluid flow and modelling the turbulence in the continuous phase, considering the effect of sub-grid-scale (SGS) turbulence on bubble motion, and also SGS turbulence modification by bubbles. Lagrangian bubble tracking is conducted considering all relevant forces, bubble oscillation via stochastic generation of eccentricity and motion angle and consequently non-steady mass transfer via a dynamic Sherwood number. The comparison of experimental and simulation results shows very good agreement for the given data.

Fracturing and healing of basaltic magmas during explosive volcanic eruptions

The eruption of basaltic magmas dominates explosive volcanism on Earth and other planets within the Solar System. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by scanning electron microscopy. We find broken crystals surrounded by intact glass that testify to the brittle fragmentation of basaltic magmas during explosive activity worldwide. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallized basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of fractures that initially fragmented the magma and ultimately indicate that brittle fracturing and viscous healing of magma may underlie basaltic explosive eruptions globally. In explosive basaltic eruptions, brittle fragmentation and subsequent healing by viscous melt are documented by textural analysis of products from ten disparate eruptions, suggesting that grain size may not reflect the initial fracture density of magma.

A mechanistic approach for predicting mass transfer in bioreactors

The biomanufacturing processes that produce biologic drugs has become an extremely important area of study within the pharmaceutical industry. Within such processes, the drug substance is typically produced by living organisms within stirred tank bioreactors that require a continuous supply of sparged oxygen. The overall oxygen transfer rate to the fluid is a nonlinear convolution of the gas bubble size distribution, fluid properties, local fluid energy dissipation rates, and local dissolved oxygen concentrations. The complexity of this process presents challenges to process scale-up and intensification. In this work, we propose, implement, and validate a mechanistic transport model for predicting oxygen transfer rates within stirred tank bioreactors. To begin, we describe the relevant conservation laws and key principles from turbulence theory that govern mass transfer. Next, we present a physics-based modeling approach for solving these equations in tandem and in real-time. We then systematically validate the model against experimental data at operating scales ranging from 5 L to 2000 L. By running the algorithm on graphics processing units (GPUs), the approach is shown to solve at timescales practical for industrial application.

Bubble size distributions in gas–liquid–solid systems and their influence on flotation separation in a bubble column

Measurements of bubble size distributions are very important in flotation which is widely used in different chemical industries such as the recovery of valuable minerals, wastewater treatment, deinking of waste paper, and oil recovery from tar sands. Although numerous authors determined bubble size distributions (BSD-s) in gas–liquid systems, BSD-s have been rarely determined in gas–liquid–solid systems. Moreover, the influence of BSD-s on flotation has not been quantified under a wide range of experimental conditions. Thus, this paper is focused on measurements of bubble size distributions by changing surfactant dosage, solid percentage, air velocity and particle size as well as establishing the relationships between bubble size distribution properties and flotation performances. It was found that the experimental bubble size distributions are successfully fitted by using the log-normal distribution model in which the two model parameters (μ and σ) are used. The results showed that the most important factors affecting the Sauter mean diameter (d32), the model parameters and the flotation recoveries are the surfactant dosage and the solid percentage. The increase in the surfactant dosage decreased d32 probably due to the decrease in liquid surface tension. The increase in solid percentage resulted in an increase in d32 perhaps due to the increase in the pulp viscosity at high solid percentage. The lower the d32, the lower the flotation recovery. The results show that d32 and the model parameters represent the true BSD-s. However, a thorough understanding of bubble size distributions is needed to better understand flotation performances.

Influence of the Gas Bubble Size Distribution on the Ladle Stirring Process

This work aims at figuring out the influence of gas bubble size distribution on the ladle stirring process. The work is conducted through three-dimensional (3D) numerical simulation based on the finite volume method. Mesh sensitivity test and the cross-validation are performed to ensure the results are mesh independent and the numerical set-up is correct. Two distributions, uniform and Log-normal function, are investigated under different gas flow rates and number of porous plugs. The results indicate that the results, e.g., the axial velocity and the area of the slag eye, have little difference for low flow rate. The difference becomes dominant whilst the flow rate is increasing, such as 600 NL/min. The Log-normal function bubble size distribution gives a larger axial velocity and a smaller slag eye area compared to the uniform bubble size distribution. This work indicated that, at a higher flow rate, the Log-normal function is a better choice to predict the melt behavior and the slag open eye in the ladle refining process if the bubble interaction is not considered.

Oxygen Mass Transfer in Biopharmaceutical Processes: Numerical and Experimental Approaches

AbstractOxygen supply in aerobic bioprocesses is of crucial importance. For this reason, this paper presents the oxygen demand of different cells and summarizes experimental and numerical possibilities for the determination of oxygen transfer in bioreactors. The focus lies on the volumetric oxygen mass transfer coefficient (kLa) calculation using computational fluid dynamics and state‐of‐the‐art models for surface‐aerated and forced‐aerated bioreactors. In addition, experimental methods for the determination of thekLavalue and the gas bubble size distribution are presented.

Multiphase alternated slug flows: Conditions to avoid coalescence and characterization of mass transfer between droplets

Alternated slug flow in capillaries is an efficient way to separate droplets with different compositions for applications in various fields. This paper describes how to solve the main issue, i.e. droplets coalescence, by using a gas bubble as a separator and demonstrates quantitatively how the mass transfer between resulting liquid-(gas–liquid)-liquid flow is negligibly impacted by the gas bubble size distribution generated. Thus residence time of up to 30 min could be achieved avoiding coalescence. The conditions to generate and maintain the alternated flow such as the superficial velocities, viscosities and surface tensions, are provided. The mechanism for mass transfer between droplets is shown to occur mainly through the film at the wall of the capillaries explaining the negligible impact of the gas. Mastering such alternated slug flow opens the door for many applications requiring compartmentation of several reactions.

Broadband Acoustic Inversion for Gas Flux Quantification—Application to a Methane Plume at Scanner Pockmark, Central North Sea

AbstractThe release of greenhouse gases from both natural and man‐made sites has been identified as a major cause of global climate change. Extensive work has addressed quantifying gas seeps in the terrestrial setting while little has been done to refine accurate methods for determining gas flux emerging through the seabed into the water column. This paper investigates large‐scale methane seepage from the Scanner Pockmark in the North Sea with a new methodology that integrates data from both multibeam and single‐beam acoustics, with single‐beam data covering a bandwidth (3.5 to 200 kHz) far wider than that used in previous studies, to quantify the rate of gas release from the seabed into the water column. The multibeam data imaged a distinct fork‐shaped methane plume in the water column, the upper arm of which was consistently visible in the single‐beam data, while the lower arm was only intermittently visible. Using a novel acoustic inversion method, we determine the depth‐dependent gas bubble size distribution and the gas flux for each plume arm. Our results show that the upper plume arm comprises bubbles with radii ranging from 1 to 15 mm, while the lower arm consists of smaller bubbles with radii ranging from 0.01 to 0.15 mm. We extrapolate from these estimates to calculate the gas flux from the Scanner Pockmark as between 1.6 and 2.7 × 106 kg/year (272 to 456 L/min). This range was calculated by considering uncertainties together with Monte Carlo simulation. Our improved methodology allows more accurate quantification of natural and anthropogenic gas plumes in the water column.

SMART‐Reactors: Tailoring Gas Holdup Distribution by Additively Manufactured Lattice Structures

AbstractIn chemical process engineering, fast gas‐liquid reactions often suffer from an inefficient distribution of gas and therefore mixing and mass transfer performance. This study deals with the possibility of influencing the local gas holdup and bubble size distribution in a gas‐liquid process using additively manufactured lattice structures (AMLS). The used measuring technique to study bubble size, velocity, and the local gas holdup is a photo‐optical needle probe. By using AMLS, a significant radial homogenization of the local gas holdup and the mean bubble size is achieved. Furthermore, it can be demonstrated that the bubble size can be tailored by the geometry of the inserted structure. It is illustrated that the mean bubble velocities are lowered within the lattice resulting in a higher residence time of the dispersed phase with an impact on the mass transfer performance within the AMLS.

Numerical simulations of the effect of liquid viscosity on gas-liquid mass transfer of a bubble column with a CFD-PBM coupled model

It is important to understand the gas–liquid mass-transfer performance for the reactor design and scale-up of bubble columns. Air-water bubble columns have been extensively simulated, however the simulation of bubble columns with often used high-viscosity liquids are limited. Here, the CFD-PBM coupled model was developed to simulate the mass transport characteristics in a bubble column with liquid viscosity from 1.0 to 39.6 mPa·s and superficial gas velocity from 0.02 to 0.3 m/s. The gas-liquid interfacial area a was estimated from the simulated local gas holdup and bubble size distribution. Two typical theoretical mass transport models were used to calculate the liquid-side mass transfer coefficient kl. The volumetric mass transfer coefficient kla, calculated from a and kl, significantly decreased with increasing liquid viscosity. Overall, the coupled model accurately predicted the effect of liquid viscosity on mass transport in a wide liquid viscosity.

Hydrodynamics of gas phase under typical industrial gassing rates in a gas-liquid stirred tank using intrusive image-based method

The intrusive image-based method is used to probe local gas hydrodynamics, bubble size (BSD) and holdup distributions (BHD) in a gas-liquid stirred tank reactor (STR). A distinctive scheme combining automatic and manual processes is implemented to identify the object bubbles in the images. This method shows more accurate for judging the flow regime in gas-liquid STRs. Because of high intensity turbulence therein, the instantaneous local gas-liquid flow may present several very different patterns though the time-averaged bulk flow is homogeneous. More small bubbles are detected because of high resolution of the instrument, and consequently d32 obtained is smaller than those by other methods. The BSD and BHD at moderate gassing rates are reported and found closer to the physical reality. The measurements are of significance to understanding the fluid mechanics and provide benchmark data for the validation of the mathematical models in the gas-liquid STRs operating at industrial conditions.