Gas Bubble Size Research Articles

Enhanced bubble growth near an advancing solidification front

Frozen water might appear opaque since gas bubbles can get trapped in the ice during the freezing process. They nucleate and then grow near the advancing solidification front, due to the formation of a gas supersaturation region in its vicinity. A delicate interplay between the rate of mass transfer and the rate of freezing dictates the final shapes and sizes of the entrapped gas bubbles. In this work, we experimentally and numerically investigate the initial growth of such gas bubbles that nucleate and grow near the advancing ice front. We show that the initial growth of these bubbles is governed by diffusion and is enhanced due to a combination of the presence of the background gas concentration gradient and the motion of the approaching front. Additionally, we recast the problem into that of mass transfer to a moving spherical object in a homogeneous concentration field, finding good agreement between our experimental data and the existing scaling relations for that latter problem. Lastly, we address how fluid flow around the bubble might further affect this growth and qualitatively explore this through numerical simulations.

VOF-DEM study of particle entrainment behaviors in the gas–solid-liquid system with multi-inlet configuration

Enhancing the entrainment capability of particles by bubbles is pivotal for facilitating particle elutriation and augmenting reaction efficiency in gas–liquid-solid systems. The current work utilizes the volume of fluid method in conjunction with discrete element method (VOF-DEM) to study particle entrainment in gas–liquid-solid three-phase reactors featuring different gas inlet layouts. Following model validation, this study delves into the multiphase flow characteristics and particle behaviors in detail. The results reveal that the merging of adjacent channels leads to the formation of larger combined bubbles, thereby increasing particle force, velocity and entrainment height. The average entrainment height during the merging of adjacent bubble channels is 42% higher compared to the four-channel configuration. However, this amalgamation diminishes the channel count and particle entrainment count. Specifically, the highest particle entrainment occurs in the two-channel configuration, which is 26% greater than that in the adjacent-channel merging configuration. Conversely, increasing the channel number decreases bubble size and overall particle entrainment capacity. With consistent bubble sizes, an increase in particle entrainment is associated with reduced entrainment height, indicative of diminished momentum transfer from bubble wakes to individual particles. Additionally, maintaining an optimal number of channels ensures high gas inlet velocity and bubble size, thereby enhancing particle entrainment efficiency. Lastly, appropriately reducing channel distance fosters interaction between adjacent channels, resulting in a meandering bubble path that further promotes particle entrainment and elution efficiency. The results obtained from this study serve as a useful reference for the design and optimization of similar systems.

Performance analysis of a novel gas-liquid separator with industrial application

This paper presents a novel gas-liquid separator characterized by its distinctive geometric design, capable of handling different volume fractions and mass flow rates. The separator's performance is comprehensively assessed across various gas volume fractions, bubble sizes, and mass flow rate fluctuations. The study reveals that variations in vapor volume fraction substantially affect both separation efficiency and pressure loss. An increase in vapor volume fraction from 0.1 to 0.5 leads to a 25% reduction in separation efficiency and a 3.3-fold decrease in pressure loss. In contrast, changes in mass flow rate exert a relatively minor influence on separation efficiency. Specifically, increasing the mass flow rate from 15 to 30 kg/s results in a mere 4% decrease in separation efficiency, whereas pressure loss increases by a factor of 3.2.Additionally, a reduction in bubble size from 1000 µm to 200 µm causes a 33% increase in pressure loss and a 14% decrease in separation efficiency. The incorporation of a meshpad in this design promotes the formation of a forced vortex, thereby enhancing the separation process.

Computational fluid dynamics modeling of gas bubble separation efficiency in downhole separators and vertical / inclined annulus: An experimental validation and analysis

This study presents a comprehensive investigation into gas bubble separation efficiency in a vertical downhole separator using computational fluid dynamics (CFD) modeling, which is validated with experimental data. The research aims to provide detailed insights into the separation mechanisms and the factors affecting them, such as liquid velocity, gas bubble sizes, and positions. Using an Euler-Lagrange multiphase model, the behavior of individual gas bubbles within the liquid-gas mixture was simulated. The results demonstrate that separation efficiency decreases as the liquid flow rate increases. This reduction in efficiency occurs because the increased liquid flow rate drags more bubbles within the stream, making it harder for them to separate. The separation process is primarily driven by the buoyancy force acting on the bubbles and the velocity profile of the liquid flow. Smaller bubbles, which tend to be near the casing wall, separate more efficiently, while larger bubbles are predominantly located between the second and third quarters of the annulus space. The "quarters" refer to radial divisions from the casing wall to the tubing wall, with the first quarter closest to the casing wall and the fourth quarter closest to the tubing wall. The study introduces a nonlinear regression model based on the numerical results to predict liquid slug separation efficiency. This model, validated against experimental data, accurately predicts separation efficiency and offers a robust methodology for estimating the efficiency of gravity-driven gas-liquid separators. This methodology is crucial for refining separator design and improving the operational efficiency of downhole separation systems, which are vital for enhancing the performance of pumping systems in oil and gas wells. The contributions of this study include a deeper understanding of the downhole separation process, the development of a simplified model for assessing bubble separation efficiency, and the potential application of the proposed methodology to different gas-liquid separator designs and inclination angles, thereby informing the design and operation of downhole separation systems.

Bubble Size Characterization in the HydroFloat® Fluidized-Bed Flotation Cell Using Tap Water and Seawater

This research aims to analyze the behavior of bubble size distribution in the HydroFloat® with seawater and tap water. The study characterized bubble size in a two-phase gas–water system in a fluidized-bed flotation cell. The impact of seawater was compared to tap water using two frothers, MIBC and polyglycol F507. The experimental design was used to investigate the influence of various parameters such as superficial air velocity, superficial liquid velocity, frother concentration, and seawater concentration on bubble size. The results indicate that the critical coalescence concentration followed the order of MIBC > F507. Bubble size decreases with increasing superficial liquid velocity, while the superficial gas velocity and frother/seawater concentration have the opposite effect. ANOVA results reveal that all linear factors are significant, the quadratic terms of the frother and seawater concentrations are significant, and the interaction term for the superficial air velocity–superficial liquid velocity is nonsignificant for bubble size. Global sensitivity analysis demonstrates that the variables significantly affecting bubble size are frother concentration and seawater concentration, followed by superficial water velocity. The superficial gas velocity has minimal impact on bubble size under the conditions studied.

Gas and water migration in cement slurries at different curing times

Gas and water migration in the hydrating cement slurry is a major cause of well completion failure. Gas and water migration may occur at different curing times due to varying well conditions and cement slurries. The current study has not been carried out to investigate the gas and water migration at different curing times. In this paper, theoretical calculations and migration experiments are used to investigate the gas and water migration in cement slurry at different curing times. The gas and water migration process can be divided into the formation rock to annular cement slurry (F-A) stage and the bottom to top (B-T) stage. At relatively short curing time, the cement slurry is more like a viscous fluid and there is clear interface between the gas and slurry. The pressure difference required for gas migration in F-A stage is very small. Maximum velocity of gas bubble migration in B-T stage is closely related to gas bubble size and cement viscosity. The smaller the size of gas bubble and the greater the viscosity of the cement slurry, the smaller the maximum velocity of the gas bubble will be. There is no clear interface between the water and slurry at relatively short curing time. The pressure difference of water migration is small. At relatively long curing time, the cement slurry has a certain of gel strength and there is also clear interface between the gas/water and slurry. The water migration is similar to gas migration. The pressure difference required for gas and water migration in F-A stage increases as the static gel strength increases. The size of the gas and water bubbles formed after invasion increases as the static gel strength increases. The critical radius at which gas and water bubbles can move is closely related to the static gel strength of the cement slurry. The greater the static gel strength, the larger the critical radius will be. The channeling path sizes of the gas and water migration are all small at relatively short curing times. The dimensions of the channel are gradually increasing from bottom to top. The pressure difference of gas migration and the dimension of channel increase as curing time increases. When the cement slurry cures for a long enough period, the gas cannot migrate in the cement slurry, but only along the weak cement slurry-wellbore interface.

Hydrodynamic Study of a Hybrid Electro-Flotation Column

Bubble columns are used in the mining industry for mineral recovery but are also widely utilized in the chemical and petrochemical industry. The hydrodynamic characteristics of their performance is a field of interest with a number of points, which are nonetheless poorly understood, and a considerable amount of methods have aimed to shed light on the flow regimes that prevail in the columns. The study of the hydrodynamic part of a flotation process should consider characteristics such as air flow, volumetric gas fraction, flow field, and bubble size, along with the mechanical and design factors and pulp properties. The present work aims to elucidate the characteristics of the gas phase of a hybrid flotation system. For this purpose, a hybrid flotation column was designed and constructed and the bubbles size distributions at different radial positions in the flotation column were computed by analyzing high resolution digital images. A patented electrical impedance technique was employed to instantaneously measure the local volumetric gas fraction. Flow dispersion in the column was studied by residence time distributions using conductivity tracers. The experimental results are discussed to comprehend the variation in the gas fraction in the column. In particular, the study showed that the size of the bubbles changed from the center to the walls of the column, and this was observed both radically and vertically. Moreover, the size of the bubbles affected the volume fractions, and no coalescence of the bubbles was observed. Finally, the dispersion of the tracer in the working solution was distributed uniformly in the volume of the column, with a time difference for the four positions of the column.

Electrolyte design for the manipulation of gas bubble detachment during hydrogen evolution reaction

During electrochemical gas evolution reactions, the continuous and vigorous formation of gas bubbles hugely impacts the efficiency of the underlying electrochemical processes. In particular, enhancing the detachment of gas bubbles from the electrode surface has emerged as an effective strategy to improve reaction efficiency. In this study, we demonstrate that the detachment of H2 gas bubbles can be controlled by the electrolyte composition, which can be optimized. We employ a well-defined Pt microelectrode and utilize electrochemical oscillation analysis to elucidate the features of H2 gas bubble detachment. Our investigation explores how the behaviour of H2 gas bubbles responds to variations in electrolyte composition and concentration. The coalescence efficiency of electrochemically generated microbubbles, a critical factor determining the mode of H2 gas bubble detachment (random detachment vs. single H2 gas bubble detachment), is profoundly influenced by the electrolyte composition. Specifically, coalescence efficiency follows the Hofmeister series concerning anions and coalescence is consistently inhibited in the presence of alkali metal cations. Furthermore, we establish a comprehensive model that accounts for both thermal and solutal Marangoni effects, allowing us to rationalize the trend of detachment size and period of single H2 gas bubbles under various conditions.

Influence of ice structure on vitability of frozen sand-water and sand-clay mixtures

Purpose. To establish influence regularity of sand, water and clay preparation conditions on vitability of frozen mixtures made from combinations of these components and to increase the castings quality in foundries, as well as to improve technologies for artificial freezing of soils for underground constructions. Methodology. In this research, sand, clay, and water are used. Ice quality is estimated visually after water freezing at -15 °C in glass tubes. Frozen mixtures’ vitability at -15 °C is studied on beam-type samples. As indicators of survivability, the time to 1 mm bending of samples on supports and the time to their destruction are accepted. The time is recorded with a stopwatch, the temperature with an alcohol thermometer, the mass with electronic scales and the deflection arrow with a clock-type indicator. Findings. The presence and amount of water-soluble impurities in rare water significantly influence the nature, size and distribution of gas bubbles in ice, as well as frozen sand-water mixtures vitability. Frozen mixtures’ survivability increases with water content in them increasing, and, for sand  water mixtures, survivability is maximum if ice has a homogeneous structure. Among mixtures with clays, the mixture with non-swollen kaolin clay has the greatest vitability. Regarding survivability, recommendations for manufacturing products from frozen foundry mixtures have been developed. Originality. For the first time, deformation change kinetics (bending arrows) under the influence of beam-type samples’ self-mass from mixtures of quartz sand and water and quartz sand, clay and water frozen at -15 °C, which have been previously prepared in different ways, have been investigated. Insights into the influence of various factors and ice quality on the vitability of frozen mixtures have been further developed. Practical value. The obtained results can be useful for expanding ideas about natural frozen soils’ behavior during their cyclic temperature changes, soils artificially frozen during mine shafts elaboration, escalators’ and junctions’ tunnels, etc. when constructing subways. In foundries, the developed recommendations will reduce technological losses and will improve casting quality made using frozen casting molds and cores from sand-water or sand-clay-water mixtures, castings’ patterns and their pouring systems from sand-water mixtures.

Numerical investigation of two-phase flow patterns and carbon deposition in a coaxial-type reactor for molten salt electrolysis

The electrodeposition process of carbon in molten lithium carbonate electrolysis and the associated gas-liquid flow hydrodynamics characteristics are for the first time investigated using computational fluid dynamics (CFD). The high-temperature (750 °C) process is challenging for conducting measurements, making CFD a valuable tool for providing insights into the novel coaxial-type cell design. The CFD simulation addresses the electric field distribution, oxygen gas evolution, and electrodeposition of carbon. The effect of gas bubble sizes (1, 0.8, and 0.6 mm) on the electrolysis process was examined at different electrical current densities (0.15 ± 0.01 A cm–2). The CFD results reveal that gas holdup increases by decreasing the bubble size and that the bubble size significantly impacts the current density distribution by affecting the two-phase flow dynamics. The study highlights the potential of CFD for optimization of molten salt processes, while also suggesting the need for further improvements in the model.

Enhancing Oil and Water Separation Vessel Performance: Strategies for Controlling Gas Bubble Size and Understanding Fluid Dynamics

Enhancing Oil and Water Separation Vessel Performance: Strategies for Controlling Gas Bubble Size and Understanding Fluid Dynamics

Harnessing the potential of in-situ, electrically generated microbubbles via nickel foam for enhanced, low energy membrane fouling control

For membrane-based, water treatment technologies, fouling remains a significant challenge for pressure-driven processes. While many antifouling strategies have been proposed, there remains significant room for improved efficiency. Direct application of microbubbles (MBs) at a membrane surface offers a promising approach for managing interfacial fouling through continuous physical interaction(s). Despite such potential, to date, integration and optimization of in-situ generated MBs at the membrane interface that are both highly antifouling with minimal energy inputs and unwanted side reactions remains mostly outstanding. Here we demonstrate the application of conductive, porous nickel foam for electrolysis-based generation of hydrogen microbubbles at an ultra-filtration (UF) membrane interface, which significantly mitigates membrane fouling for a range of model foulants. System characterization and optimization includes comparison of metal foams (Ni, Cu, Ti), faradic efficiencies, hydrogen evolution reaction (HER) curves, cyclic voltammetry, and quantification of hydrogen gas flux and bubble size, as a function of applied current. When optimized, we report rapid (<5 min) and near complete (∼99 %) flux recovery for three classes of foulants, including calcium alginate, humic acid (HA), and SiO2 particles. For all, the described MB-based approach is orders of magnitude more energy efficient when compared to conventional cleaning strategies. Finally, we demonstrate the MB-based regeneration/cleaning process is stable and repeatable for ten cycles and also highly effective for a challenge water (as a model oilfield brine). Taken together, this work presents a novel and efficient approach for the application of in-situ electrically generated MBs to support sustainable pressure-driven membrane processes.

The effect of baffles on the hydrodynamics of a gas-solid fluidized bed studied using real-time magnetic resonance imaging

Understanding and predicting the hydrodynamics of gas bubbles and particle-laden phase in fluidized beds is essential for the successful design and efficient operation of this type of reactor. In this work, we used real-time magnetic resonance imaging (MRI) to investigate the effect of three commonly-used baffle geometries on gas bubble behavior and particle motion in a fluidized bed model with an inner diameter of 190 mm. MRI time series of the local particle density and velocity were acquired and used to study the size, number, and shape of gas bubbles as well as the motion of the particle phase. The superficial gas velocity was varied between 1 and 2 Umf. We found that baffles decreased the average equivalent bubble diameter with a simultaneous increase in the total number of bubbles. Moreover, baffles promoted bubble splitting and the formation of air cushions below the baffles and decreased the average particle velocity and acceleration in the bed. For two of the three baffle types investigated, the spatial variation of the particle velocity became larger compared to the bed without internal.

High‐pressure high‐temperature fluid displacement by foam injection within a multiblock matrix‐fracture system

AbstractFoam injection has been suggested and demonstrated as a potential gas‐based solution for enhancing oil recovery from underground reservoirs. While the pore‐scale behavior of foam has been investigated for many years, most of those studies were done at room temperature and pressure. A high‐pressure high‐temperature (HPHT) cell was constructed to relax this contributing simplification and evaluate foam behavior under reservoir conditions. The performance of foam injection into a fractured reservoir was investigated experimentally at vertical and horizontal pathways utilizing a 2D microfluidic device. The results showed foam had a higher lamellae density in the fracture network and could direct fluids to the matrix. This was mainly attributed to the created pressure drop in the fractured media dictated by foam self‐tuning ability, which is a higher viscosity in areas with higher conductivity. Generating a viscous crossflow in horizontal tests leads to enhanced recovery relative to gas injection. But the presence of gravity in the vertical tests causes the drainage of the foam film and the segregation of the gas and surfactant solution due to gravity, which ultimately reduces the stability of the foam. Comparing the performance of gas and foam in the vertical injection scenario reveals that foam injection results in a considerably more enhanced oil recovery. The oleic phase had a detrimental impact on foam strength and reduced fluids diversion from fracture to matrix. The sizes of gas bubbles were also larger in the presence of the oleic phase.

Experimental Study of Condensate Vaporization into Bubbles under Different Operating Parameters

Produced water (PW) is a natural by-product of the oil and gas production process, where crude oil is dispersed in the form of micron-sized emulsified droplets in the produced water due to mixing between crude oil and water caused by equipment, piping and valve shear action. Flotation is the main method for treating emulsified oil droplets in oilfield produced water. The conventional flotation technology suffers from a series of problems such as large reflux ratio and poor flotation effect, thus limiting its further application. In this paper, bubbles are prepared by vaporization of low boiling point condensate through theoretical analysis and experimental study. In this paper, the law of bubble generation from condensate solution at different temperatures after decompression and release is investigated. The results demonstrate that the median particle size of gas bubbles generated from condensate is related to the condensate content, mixing pressure, release pressure, and temperature. The median particle size can reach 9.65 μm when mixed at 2.0% condensate content, 0.2 MPa mixing pressure, and 35°C, and released at atmospheric pressure, which is much smaller than the size of gas bubbles generated by dissolved air flotation. The condensate bubbles as alkane congeners are more likely to adhere to the oil droplets in the extracted water, which is conducive to improving the air flotation oil removal efficiency of oily wastewater.

Hydrogen Gas Bubble Evolution on Electrocatalytic Nanostructures in Microgravity Environment

Photoelectrochemical (PEC) monolithic devices for oxygen and chemical production are attractive for space applications due to predominant weight and volume constraints as well as a high system tunability. Here, advanced semiconductor-electrocatalyst systems integrate the processes of light absorption, charge separation and catalysis in one device - processes, which are usually carried out e.g., on the International Space Station (ISS) by an electrolyser coupled to external PV cells. Due to the near absence of buoyancy and buoyancy-induced convection in micro gravity, all (photo)electrolyser systems in space naturally have lower efficiencies, as gas bubble desorption and phase separation are severely hindered. We report on a new approach to design the electrocatalyst morphology on a nanoscale in order to modify the physicochemical properties of the photoelectrode and thus allow for continuous gas bubbles desorption and efficient operation of the PEC device in microgravity. Using a rhodium-coated p-InP model photoelectrochemical system, we discuss different Rh electrocatalyst nanotopographies fabricated by shadow nanosphere lithography and report on their characterisation as well as performance in photoelectrochemical measurements realised during 9.2 s of free fall at the Bremen Drop Tower, Center of Applied Space Technology and Microgravity (ZARM). In particular, we elucidate on how the electrocatalyst nanostructures affect the gas bubble size during growth and at detachment from the electrode and conclude on an efficient (photo-)electrode design for hydrogen evolution in microgravity.

Computational studies of airlift and stirred airlift bioreactors with non-Newtonian fluid: A comparison of hydrodynamics and gas-liquid mass transfer

In this work, the hydrodynamics and gas-liquid mass transfer in airlift and stirred airlift bioreactors with non-Newtonian fluid were investigated by computational fluid dynamics (CFD) modeling. The hydrodynamics in stirred airlift bioreactor is quite different from that of conventional airlift reactor. The gas-liquid mass transfer was comprehensively assessed using five mass transfer models, such as penetration model, slip velocity model, eddy cell model, rigid model and surface renewal stretch model. The predicted averaged quantities of gas holdup, bubble size and volumetric mass transfer coefficient were in good correspondence with the experimental data. This study highlights the need for selecting suitable mass transfer models in gas-liquid flow systems.

Combining α-Al2O3 Packing Material and a ZnO Nanocatalyst in an Ozonized Bubble Column Reactor to Increase the Phenol Degradation from Wastewater

The ozonation reaction in a bubble column reactor (BCR) has been widely used in the removal of phenol from wastewater, but the phenol removal efficiency in this type of reactor is limited because of low ozone solubility and reactivity in the system. In the present study, the phenol degradation in the BCR was enhanced by using α-Al2O3 as a packing material and a ZnO nanocatalyst. The reactor diameter and height were 8 cm and 180 cm, respectively. The gas distributor was designed to include 52 holes of a 0.5 mm diameter. Also, the gas holdup, pressure drop, and bubble size were measured as a function of the superficial gas velocity (i.e., 0.5, 1, 1.5, 2, 2.5, and 3 cm/s). The evaluation of the hydrodynamic parameters provided a deeper understanding of the ozonation process through which to select the optimal operating parameters in the reactor. It was found that the best superficial gas velocity was 2.5 cm/s. A complete (100%) phenol removal was achieved for phenol concentrations of 15, 20, and 25 ppm at reaction times of 80, 90, and 100 min, respectively; this was achieved by using α-Al2O3 packing material and a ZnO nanocatalyst in the BCR. Additionally, a reaction kinetics study was conducted to describe the ozonation reaction in BCR. The first-order reaction assumption clearly describes the reaction kinetics with an R2 = 0.991. Finally, the applied treatment method can be used to efficiently remove phenol from wastewater at a low cost, with a small consumption of energy and a simple operation.

Bubble-assisted matte transportation into slag phase: A numerical investigation

Copper loss into the slag phase during the smelting process can be minimized by controlling gas bubble size and hydrodynamics. Here, bubble rising characteristics from copper matte to slag phase were investigated using the volume-of-fluid modelling approach, in which the continuous surface force model was adopted to define the surface tension parameters. The simulated results for bubble terminal velocities in bulk water and the literature data showed relative errors up to 4.51 %. The obtained qualitative and quantitative data from simulation at the liquid–liquid interface agreed well with the literature experimental results. The simulation setup was applied to investigate three different sizes of bubble rising dynamics from matte to slag phase with the bubble Reynolds number (Re) up to 1734 and the Eotvos number (Eo) up to 3.2. For low Re and Eo, the bubble rising velocity decreased before the matte film rupture and the bubble required a long time to complete that film drainage due to the balance of interfacial tension force and bubble buoyancy. No matte residue associated with the bubble rise in the slag phase was obtained because of restoring initial, non-deformed shape of bubbles. For the higher Re and Eo, quicker matte film drainage was obtained around the upper bubble surface while the entrained matte contribution to the slag phase was strongly dependent on the bubble-shape deformation, which was discussed with the well-known Grace diagram. The decreasing viscosity and increasing surface tension of the slag phase significantly affected the matte film height more than the film rupture time. The film height and rupture time increased and decreased with increasing Eo, respectively. The outcomes of our studies are useful for the design and operation of smetling furnaces in pyrometallurgical purification of metal concentrates.

Accelerating Gas Escape in Anion Exchange Membrane Water Electrolysis by Gas Diffusion Layers with Hierarchical Grid Gradients.

At high current densities, gas bubble escape is the critical factor affecting the mass transport and performance of the electrolyzer. For tight assembly water electrolysis technologies, the gas diffusion layer (GDL) between the catalyst layer (CL) and the flow field plate plays a critical role in gas bubble removal. Herein, we demonstrate that the electrolyzer's mass transport and performance can be significantly improved by simply manipulating the structure of the GDL. Combined with 3D printing technology, ordered nickel GDLs with straight-through pores and adjustable grid sizes are systematically studied. Using an in situ high-speed camera, the gas bubble releasing size and resident time have been observed and analyzed upon the change of the GDL architecture. The results show that a suitable grid size of the GDL can significantly accelerate mass transport by reducing the gas bubble size and the bubble resident time. An adhesive force measurement has further revealed the underlying mechanism. We then proposed and fabricated a novel hierarchical GDL, reaching a current density of 2 A/cm2 at a cell voltage of 1.95 V and 80 °C, one of the highest single-cell performances in pure-water-fed anion exchange membrane water electrolysis (AEMWE).