Behavior Of Gas Bubbles Research Articles

Gas bubble dynamics in airlift photo-bioreactors for microalgae cultivation by level set methods

Coupled level set and CFD (computational fluid dynamics) methods are adopted in this work to track the moving gas–liquid interfaces in the riser of an external loop airlift photobioreactor (ALR) in which microalgae are used to produce biofuels and capture CO2 from flue-gas. Modeling the behavior of gas bubbles is a crucial aspect for the fine-tuning of the operation of the reactor when inserted into a closed-loop biorefinery at the pilot-scale. The experimental data used for simulation were completely acquired or calculated from hydrodynamic experimental campaigns carried out on the ALRs. The rise, coalescence, and shape dynamics of the bubbles of the flue-gas are simulated in a rectangular domain representing the vertical section of the ALR riser. Different correction approaches, such as the conservative level set method (CLSM), are proposed to face the volume loss characteristic of LSM. Computational results evidenced strong agreement with the experimental data (bubble shapes and trajectories). The physically-based CLSM model was then effectively used for the fine-tuning of the multiphase flow regime inside the ALRs, suggesting operating conditions for the outdoor cultivation with Reynolds number = 10000 – 11000, Sherwood number between 1400 and 1800, and spherical-caps bubbles in the upper half of the riser, mildly churning the microalgae while avoiding damages to their cells.

Dynamic Equilibrium Model for Surface Nanobubbles in Electrochemistry.

Gas bubbles are ubiquitous in electrochemical processes, particularly in water electrolysis. Due to the development of gas-evolving electrocatalysis and energy conversion technology, a deep understanding of gas bubble behaviors at the electrode surface is highly desirable. In this work, by combining theoretical analysis and molecular simulations, we study the behaviors of a single nanobubble electrogenerated at a nanoelectrode. With the dynamic equilibrium model, the stability criteria for stationary surface nanobubbles are established. We show theoretically that a slight change in either the gas solubility or solute concentration results in various nanobubble dynamic states at a nanoelectrode: contact line pinning in aqueous and ethylene glycol solutions, oscillation of pinning states in dimethyl sulfoxide, and mobile nanobubbles in methanol. The above complex nanobubble behavior at the electrode/electrolyte interface is explained by the competition between gas influx into the nanobubble and outflux from the nanobubble.

In Situ Tuning Underwater Bubble Movement on Slippery Lubricant-Infused Anisotropic Microgrooved Surface by Unidirectional Mechanical Strain.

Numerous studies have focused on designing and fabricating functional interfaces that control movement behavior of underwater gas bubbles, which are ubiquitous in a variety of natural and industrial settings. Nevertheless, developing surfaces with in situ tunable bubble movement remain elusive because of current complicated tuning strategies on the specific materials. Inspired by natural pitcher plant and rice leaves, here we report a kind of slippery lubricant-infused anisotropic microgrooved surface (SLI-AMGS) fabricated by femtosecond laser direct writing technology and realize the in situ reversible switching between underwater bubble sliding and pinning by unidirectional mechanical tensile strain. Different experimental parameters including lubricant oil film thickness, bubble volumes and laser power have been researched to manifest the relationship with bubble sliding behaviors. The underlying mechanism of in situ reversible switching mainly lies on the decrease of the lubricant oil film thickness during the process of mechanical stretching in which the uniform and stable oil film layer becomes uneven. This uneven lubricant oil film results in an extraordinary increase of contact angle hysteresis and resistance. At last, we demonstrate a real-time dynamic modulation of the underwater bubble on the SLI-AMGS with a changing mechanical tensile strain for several repeatable times in different acid-based environments. Our work manifests great potential applications in widespread fields including underwater bubble microfluidics and microbubble robots.

How to adjust bubble’s adhesion on solid in aqueous media: Femtosecond laser-ablated patterned shape-memory polymer surfaces to achieve bubble multi-manipulation

Manipulation of the behaviour of gas bubbles in aqueous environment is of vital significance in medical and microfluidic fields, and has attracted much research attention in the past few years. Making clear the interrelation between underwater bubbles’ wettability and the solid surfaces topography to achieve the bubble adhesion regulation is a crucial factor of realizing the precise bubble manipulation without external stimulation, and a great challenge. Here, by combining the fish-scale-like morphology and rose-petal-like morphology into one sample and changing the proportion of each part, the underwater bubble adhesion could be adjusted from ultralow to low, high, and ultrahigh. The square-patterned array shape-memory polymer (SMP) surfaces with various adhesion forces were fabricated by femtosecond laser ablation and used to realize lossless transportation of a bubble in both horizontal and vertical direction. The high adhesion surface could be used to form programmable microbubble patterns. By taking advantage of the excellent thermal shape-memory character of SMP film, we realized the bubble in-situ release and reversely switch of the bubble adhesion based on the macroscopic and microscopic deforming-recovering of as-prepared SMP sample. The present study will inspire people to develop novel strategies to achieve multi-manipulation of bubbles in practical applications.

Bubbles: The Good, the Bad, and the Ugly

Bubbles are bad news for electrolysis due to undesired overpotentials, though their impact may be even further reaching than previously understood. In a recent report in Energy & Environmental Science, Kempler and researchers control the microstructure of electrodes to minimize overpotentials caused by bubbles in a photoelectrochemical cell.

The Effect of Surface Nano and Microstructures on Hydrogen Gas Evolution Behavior on Ni Patterned Electrodes

Highly efficient water electrolysis process is one of the key technologies for hydrogen economy suppressing global warming. Now, alkaline water electrolysis (AWE) and Proton exchange membrane (PEM) electrolysis are regarded as the representative industrial process. The advanced electrode without precious metal or oxide catalysts for hydrogen evolution reaction (HER) in these processes plays an important role to design HER efficiently and economically. Tremendous efforts focusing to unique characteristic catalysts exploration have been engaged world-widely not only tediously and steadily but also with materials informatic-science utilization driven by AI technology. Roughly speaking based on electrochemical engineering aspects, the energy loss in water electrolysis is composed of electrode reaction kinetics governed by catalytic activity, concentration overpotential and ohmic drop in gas-liquid two phase dispersion layer. The concentration overpotential and ohmic resistance are sometimes result in significant energy loss in large scale industrial process. From the sustainable and economical views toward Hydrogen Economy Society, AWE with less precious catalysts is considered as hydrogen production candidate with cheaper cost and longer durability. Many papers on gas electrode behavior have focused on macroscopic observation, but more fundamental understanding on nucleation and growth behavior of gas bubbles is rather limited due to the experimental difficulties. It is believed that the electrode surface structure tailoring may also provide one of promising methods to improve the catalytic performance as well as advance catalytic HER activity. Especially, nano/micro-scale structures on the electrode surface are suggested to affect the catalyst performance by controlling the nucleation and growth behaviors of bubbles. However, the detailed mechanisms of the effect of surface nano/micro-scale structures on HER and bubble behaviors have not been elucidated. Therefore, to analyze the influence of microstructure and surface wettability of catalytic electrode on bubble behaviors and HER, this study focuses on bubble behaviors on the electrode surface using Ni micro-patterned electrode fabricated by electrodeposition and Pt single crystalline electrodes. Ni micro-patterned electrodes were electrodeposited in the electrolyte containing 0.05 mol dm-3 NiCl2∙6H2O (pH 2.5) on patterned Cu substrate. Pt and Ag/AgCl electrode were employed as CE and RE, respectively. Surface structures and wettability of prepared electrodes were evaluated by scanning electron microscopy (SEM) and contact angle measurement. Water electrolysis was performed in 1 M KOH and Pt mesh and Hg/HgO. The effect of surface roughness on bubble behaviors was additionally examined in 0.1 M H2SO4 with three electrode system; Pt single crystalline electrode prepared by the Clavier method as WE, carbon rod as CE, and reversible hydrogen electrode as RE, respectively. Microdot structures, cylinder-, semisphere- and square-like were prepared. Ni coverage ratio of Ni electrodeposited area to Cu substrate, was calculated to correlate surface wettability measured by sessile drop method and Ni microstructure. It was suggested that electrode surface wettability could be controllable by changing Ni coverage and each Ni microdot structure exhibited an apparent catalytic electrode by surface tailoring. The effect of microstructures and surface wettability on HER performance was then studied during galvanostatic electrolysis at -20 mA cm-2 for 30 min. Total overpotential measured from 200 s to 1800 s seemed to proceed water electrolysis stably. It increased with decreasing surface wettability. This may indicate lower surface wettability derived from Ni microarray structures increases overpotential by accumulating newly evolving H2 bubbles. To further analyze the phenomena, high-speed CCD camera cinematography was applied. The ratio of larger diameter bubble tended to increase with increasing the contact angle. It indicates lower surface wettability would enhance bubble growth behaviors on cathode surface. Moreover, larger diameter bubbles were generated on cylinder-like Ni microdots. These results suggest increasing contact area between bubbles and Ni micropatterned electrode would enhance bubble growth behaviors. The effect of Ni microdot height on bubble nucleation behaviors was also observed. It apparently demonstrated that taller Ni dot height rather increased the nucleation site of bubbles. In order to additionally investigate the effect of nano-scale roughness tailored by single crystalline growth technique on bubble behaviors, H2 bubble evolution behaviors on Pt single crystalline electrode were cinematographically recorded. No H2 bubbles were generated on smooth surface fabricated by Pt (111) microfacet, suggesting lower nano-scale surface roughness considerably suppressed bubble nucleation on Pt electrode surface. These results suggested micro and nano structures and surface wettability influenced on bubble nucleation and growth phenomena frequently encountered in industrial electrolysis. Further unknown room still remains to be challenged even in such a rather matured AWE. This work was partly carried out in Case Western Reserve University. Prof. Daniel Scherson’s supervisions are highly appreciated.

Recent progress in gas nanobubble electrochemistry

Bubbles are ubiquitous in many natural phenomena and industry processes, particularly in the water electrolysis. Due to the development of gas evolving electrocatalysis and energy conversion technology, a deep understanding of gas bubble behaviors at the electrode surface is highly desirable. This review summarizes the recent methodology and process for the study of gas nanobubbles at the electrode surface. We first introduce the electrochemical measurement of gas bubbles using disk nanoelectrodes and scanning electrochemical cell microscopy, and analyze the dynamic equilibrium for their stability. We then discuss the visualization of gas bubble behaviors from electrogeneration using scanning electrochemical microscopy and optical microscopy. Finally, the main challenges and future research concerning are proposed.

Understanding of Dynamic Contacting Behaviors of Underwater Gas Bubbles on Solid Surfaces.

Understanding of dynamic behaviors of gas bubbles on solid surfaces has significant impacts on gas-involving electrochemical reactions, mineral flotation, and so on in industry. Contact angle (θ) is widely employed to characterize the wetting behaviors of bubbles on solid surfaces; however, it usually fluctuates within the bubble's advancing (θa) and receding (θr) range. Although the term of most-stable contact angle (θms) was defined previously as the closest valuable approximation for thermodynamically meaningful contact angle for a droplet on a solid surface, it has not been widely studied; and the precise θms measurement methods are inadequate to describe bubbles' wetting behaviors on solid surfaces. Herein, we proposed to take θms as the mean value of θa and θr, as a more accurate descriptor of gas bubbles' dynamic behaviors on nonideal solid surfaces, similar to the definition of droplets' θms on solid surfaces. The feasibility and accuracy of the proposed θms have been evidenced by recording the bubbles' contacting behaviors on solid surfaces with varied wettabilities. In addition, it was found that the contact angle hysteresis (δ), as the difference between θa and θr, reached its maximum value when θms approached 90°, regardless of the roughness (r) of the substrates. Finally, built on the above concept, the lateral adhesion force (f) of the gas bubble on the solid interface, which worked on the three-phase contact line (TPCL) of an individual bubble on a solid surface against its lateral motion during the bubble advancing or receding process, was described quantitatively by combining θa, θr, and the liquid-gas interfacial tension (γlg). Experimental and theoretical data jointly confirmed that f reached its maximum value at θms ∼ 90°, namely, a "super-sticky" state, which described the dynamically most sluggish movement of the bubble along the solid surface.

Phase-field simulations of intergranular fission gas bubble behavior in U3Si2 nuclear fuel

U3Si2 is a potential accident-tolerant fuel that shows promise due to its high thermal conductivity and higher uranium density relative to UO2. However, its swelling and fission gas release behavior in light water reactor (LWR) conditions is relatively unknown. To provide mechanistic insight and determine parameters for engineering-scale fuel performance modeling of pellet-form U3Si2, phase-field simulations of the growth, interconnection, and venting of intergranular fission gas bubbles were performed. The fractional coverage of the grain boundary and the fraction of bubble area that is vented were calculated as a function of time. From the simulation data, the fractional grain boundary coverage at saturation, an important parameter needed in engineering-scale modeling of swelling and fission gas release, was determined. Multiple simulations were run to determine the uncertainty in the calculated value. The effect of model assumptions and input parameters that are not well known was evaluated. Simulation results are compared to related theoretical and computational work. Based on the simulation results, a value of 0.60 for the fractional grain boundary coverage at saturation is recommended for U3Si2 fuel.

Smart Manipulation of Gas Bubbles in Harsh Environments Via a Fluorinert-Infused Shape-Gradient Slippery Surface

Fundamental research and practical applications have examined the manipulation of gas bubbles on open surfaces in low-surface-tension, high-pressure, and high-acidity, -alkalinity, or -salinity environments. However, to the best of our knowledge, efficient and general approaches to achieve the smart manipulation of gas bubbles in these harsh environments are limited. Herein, a Fluorinert-infused shape-gradient slippery surface (FSSS) that could effectively regulate the behavior of gas bubbles in harsh environments was successfully fabricated. The unique capability of FSSS was mainly attributed to the properties of Fluorinert, which include chemical inertness and incompressibility. The shape-gradient morphology of FSSS could induce asymmetric driving forces to move gas bubbles directionally on open surfaces. Factors influencing gas bubble transport on FSSS, such as the apex angle of the slippery surface and the surface tension of the aqueous environment, were carefully investigated, and large apex angles were found to result in large initial transport velocities and short transport distances. Lowering the surface tension of the aqueous environment is unfavorable to bubble transport. Nevertheless, FSSS could transport gas bubbles in aqueous environments with surface tensions as low as 28.5 ± 0.1 mN/m, which is lower than that of many organic solvents (e.g., formamide, ethylene glycol, and dimethylformamide). In addition, FSSS could also realize the facile manipulation of gas bubbles in various aqueous environments, e.g., high pressure (~ 6.8 atm), high acidity (1 mol/L H2SO4), high alkalinity (1 mol/L NaOH), and high salinity (1 mol/L NaCl). The current findings provide a source of knowledge and inspiration for studies on bubble-related interfacial phenomena and contribute to scientific and technological developments for controllable bubble manipulation in harsh environments.

A Computer Model of the Dynamics of a Heterogeneous Liquid-Solid Medium in a Technological Apparatus with Bubbling

The article is devoted to the development of a computer model of the dynamics of a heterogeneous liquid-solid medium in a technological apparatus with bubbling. In a heterogeneous bubbler medium, the known methods of environmental control are difficult to implement and practically unsuitable for control in the flow of the medium; therefore, new approaches to the implementation of the software and hardware complex of information systems are necessary.
 Existing mathematical not take into account the change in the concentration of the liquid due to the formation of solid suspensions included in the bubbling of the liquid by flue gases and the dyna­mics of the behavior of gas bubbles in the vibration field of the apparatus. Vibration measuring instruments could solve the problem by taking into account changes in the density and viscosity of the components of the medium.
 The developed mathematical model of a heterogeneous liquid-solid medium, which ensures the accuracy of information in information systems, is based on the model of vibration frequency me­thods for monitoring the concentration of the solid fraction of suspensions, based on the use of the behavior of the solid phase of the suspension in a vibration field.
 Based on the equation of motion of a particle in a vibratio­nal field for the case of a spherical shape of the particle, which is in free conditions under a laminar regime of motion, taking into account the dependence of the density of the suspension on the density of the solid phase and liquid, the viscosity of the suspension on the viscosity of the liquid and density of the solid phase, a new differential equation is obtained.
 The obtained equation of dynamics of a heterogeneous li­quid-solid medium in a technological apparatus with bubbling is solved by a software solution in the Python environment, with the introduction of the sympy library using complex Conjugation and simplification.
 Relations are obtained for controlling the concentration of the suspension formed in the technological apparatus after bubbling flue gases through a liquid layer. The presented results of the software implementation of the model confirm that with an increase in the frequency of the vibrational field, the relative amplitude of the solid phase decreases, and therefore its effective mass participating in the vibrations of the medium.

A multiphysics model for analysis of inert gas bubbles in Molten Salt Fast Reactor

Molten salt reactors (MSRs) have gained worldwide interest in recent years due to their appealing safety and resource utilisation characteristics. These reactors have a unique feature, i.e. the presence of nuclear fuel in the form of a molten fluoride or chloride salt containing the fissile and fertile materials. The fuel salt also acts as the coolant, and this dual role results in a complex, highly coupled multiphysics system which poses a challenge in modelling and simulation of MSRs. This paper presents the development of a simulation model for the Molten Salt Fast Reactor (MSFR) to predict the behaviour of inert gas bubbles in the core and to quantify their impact on the reactivity. Inert gas bubbles in MSFR have been modelled using a multiphysics approach coupling computational fluid dynamics for fluid flow and heat transfer with neutron diffusion equation for neutronics and a balance equation with diffusion and advection terms for taking into account the drift of the delayed neutron precursors. The two-phase flow has been modelled using a simplified Euler–Euler model for small volume fraction of the dispersed phase, i.e. for small bubble fraction, which combines the momentum and continuity equation of the liquid and gas phases and adds a gas-phase transport equation to track the void fraction. Simulations reveal that the bubble distribution in the core has a significant impact on reactivity resulting in a difference in the bubbling feedback coefficient compared to studies using a homogeneous distribution.

Hydrothermally degraded carbon fiber / epoxy plates subjected to underwater explosive loading in a fully submerged environment

An experimental and computational investigation was conducted to evaluate the underwater blast response of fully submerged carbon fiber composite plates after prolonged exposure to saline water. The material was a biaxial carbon fiber/epoxy composite with a [±45°] fiber orientation layup. The plates were placed in a saline water bath with a temperature of 65 °C for 35 and 70 days, which simulates approximately 10 and 20 years of operating conditions in accordance to Fick's law of diffusion coupled with Arrhenius's Equation and a reference ocean temperature of 17 °C. Underwater blast experiments were performed in a 2.1 m diameter pressure vessel. The composite plates were placed in the center of the vessel while fully submerged in water, and an RP-85 explosive was detonated at a standoff distance of 102 mm from the center of the plate. Two cases of fluid hydrostatic gage pressures were investigated: 0 MPa, and 3.45 MPa. Two high speed cameras were utilized for three-dimensional Digital Image Correlation, which provided full-field displacements and velocities of the composite plates during underwater blast loading. A third high speed camera captured the behavior of the explosive gas bubble. Moreover, the pressure fields generated by the explosive detonation and resulting gas bubble were recorded with tourmaline pressure transducers. A water diffusion study was completed which showed that the diffusion of water into the composites reached a point of complete saturation after 35 days of exposure. Quasi-static material characterization tests were performed before and after prolonged exposure to saline water. The properties obtained from quasi-static testing also served as material inputs for the numerical models. The quasi-static test results showed that the tensile modulus E1,2 does not change with exposure to saline water, whereas the in-plane shear modulus G12 decreases with saline water exposure. During blast loading, for the case of 0 MPa hydrostatic gage pressure, the gas bubble interacts with the composite plate substantially. In such an event, the out of plane displacement increased for saline water exposed plates when compared to virgin structures. For the case of 3.45 MPa hydrostatic gage pressure, the gas bubble does not visibly interact with the composite plate. In this case, the out of plane displacement for specimens exposed to saline water was similar to the virgin specimen. A fully coupled Eulerian–Lagrangian fluid structure interaction simulation was performed by using the DYSMAS code. The numerical simulations showed that the displacement of fully submerged composite plates is driven by the displacement of fluid, as well as the size of the gas bubble formed by the explosive rather than the peak pressure generated by the explosive. The numerical simulations were in agreement with the experimental findings in terms of pressure history and plate deformation.

Gas evolution and the effects on ionic transport inside the lithium-ion battery

PurposeGas evolution within lithium-ion batteries (LIBs) gives rise to safety concerns that question their applicability. The gas evolution is not only the result but also the inducement of performance deterioration of LIBs. In this paper, the growth characteristics and dynamic behavior of gas bubble on the electrode surface are studied, and the interference mechanism of gas evolution on Li-ion diffusion or Li-ion conduction within LIBs is discussed and validated by the numerical simulations.Design/methodology/approachFirst, the mathematical models and simulation method are established. The growth and flow of gas bubble in the serpentine channel on electrode surface, which results from the gas-liquid flow and the effects of surface tension, is modeled by using the multi-phase Navier-Stokes and the volume of fluid method. Integrating Butler–Volmer and Fick’s law, the mathematical model of ions transport in the electrochemical cell is set-up. Second, the motion of gas bubble is tracked, and the variations of bubble shape and characteristic parameters with time are obtained by the computed fluid dynamics (CFD) method.FindingsBased on the CFD results, the battery models and electrochemical simulations are carried out to analyze the ionic transport characteristics. The results show that the microstructural morphology such as the serpentine channel shape and size on electrode surface are important aspects for the gas bubble growth and the local ionic transport. Li ions significantly accumulate at one side of the gas obstacle, hindering the ionic diffusion normally. When the gas bubble blocks the electrolyte, the passage of ions from the positive to the negative is interrupted, and the open circuit zone of the electrochemical cell is formed.Originality/valueThe gas evolution within LIBs is not only a result but also an inducement of its performance deterioration. The primary issues in this study are the growth characteristics and dynamic behavior of gas bubble on the electrode surface, providing the knowledge for the interference mechanism of gas evolution on ionic transport and ultimately leads to significant increase of battery resistance.

Dynamic behavior of gas bubble detached from single orifice in magnetic fluid

A Bubble’s behavior in a magnetic fluid is one of the most critical issues in understanding the characteristics of the gaseous-liquid two-phase flow in basic fluid science. In this study, to understand the dynamic behavior of a gas bubble in a magnetic fluid, a bubble detached from a single orifice in a magnetic fluid is investigated using a near-infrared light source with a long wavelength of 800–1000 nm. The surface tension of a magnetic fluid, which is a crucial factor in determining the bubble’s characteristics, is also investigated by the maximum bubble pressure method. Based on the visualization measured, it is found that the bubble diameter decreases by applying magnetic field. This is caused by a magnetic body force, that enlarges the bubble in the same direction as the buoyancy force. The measurement of the surface tension of the magnetic fluid shows that the surface tension increases as the applied magnetic field increases. From the measurement of the bubble dynamics, the volume of the detached bubble under a magnetic flux density can be evaluated by a force balance equation with an average error of 16.8%.

Influence of Surfactant Additives on the Electrolyte Flow Velocity and Insoluble Gas Bubbles Behavior within a Lead-Acid Battery

Improving the flooded-electrolyte batteries performance in fast charging and discharging processes has attracted many researchers. Due to electrochemical reactions during charging and discharging process in these batteries, many insoluble gas bubbles are produced within the electrolyte. These bubbles have a major effect on the performance of the electrodes and the rate of electrochemical reactions. On the other hand, the electrolyte flow rate plays an important role on the performance of the battery. In the present investigation, the effect of surface tension on the production of insoluble bubbles and velocity of electrolyte flow have been investigated experimentally when different types of surfactants are added to the electrolyte. In addition, a Particle Image Velocimetry setup has been used in order to measure the velocity of electrolyte flow and the behavior of bubbles. The results declared that the capacity of battery enhances about 16% and 10% by adding Triton X100 and SDS surfactants, respectively. Hence, the averaged electrolyte velocities during charging process reduces about 11% and 13% when Triton X100 and SDS, repectively; are used as surfactants. Also, the effect of adding different amounts of SDS surfactant on the mean diameter, rising velocity and production rates of bubbles have been illustrated comprehensively.

Elucidation of bubble evolution and defect formation in directed energy deposition based on direct observation

Surface pore defects are always formed during directed energy deposition processes, which may stem from entrapped gas bubbles. Such defects have detrimental effects on the build quality and performance of safety-critical metal parts. Despite previous experimental and theoretical studies devoted to this subject, direct observations of the dynamic behavior of gas bubbles and elucidation of how they form surface pore defects have not yet been achieved. In this work, the relationships between surface pore defects and the bubbles originating on the melt pool surface were carefully studied using high-speed photography at up to 20,000 frames per second. This allowed us to observe the presence of two types of bubble evolution, namely bubble retention and explosion. The appearance of surface pores was a result of dynamic competition between bubble explosion and solidification of the surrounding melt, where the final location of the surface pores is determined by the melt convection and the boundary motion of the melt pool. In the case of single-track deposition, complex thermocapillary convection drives gas bubble diffusion, and pore defects cluster along the lateral edge. In the case of multi-track deposition, surface pore defects were more likely to occur on the last track due to the gravity-driven flow effect that is determined by the track path and overlap.

First-principles study of surface properties of crystalline and amorphous uranium aluminides

Surface energy is a crucial material property required for the modeling of fission gas bubble behavior in nuclear materials. However, there is no information available regarding the surface properties of uranium aluminides. In this work we systematically investigate the surface properties of uranium aluminides (UAl3 and UAl4) by first-principles density functional theory (DFT) calculations. A total of 13 surface orientations with a maximum Miller index (MMI) up to 3 are studied for cubic UAl3, while 19 surfaces with a MMI of 2 for orthorhombic UAl4. Using the surface energies predicted by DFT, the surface properties of equilibrium single crystal UAl3 and UAl4, including surface area weighted surface energy, dominant surface orientations and surface anisotropy, are obtained from Wulff construction. To understand gas bubble behaviors in amorphous uranium aluminides under irradiation, we study the surface properties of amorphous UAl3 and UAl4. Compared to the crystalline phases, the amorphous phases are found to have lower surface energies due to the reduced number of breaking U-Al bonds close to the surface. The currently obtained surface properties of UAl3 and UAl4 can be used for the future modeling of gas bubble behaviors in both crystalline and amorphous uranium aluminide fuels.

Thermally Driven Interfacial Switch between Adhesion and Antiadhesion on Gas Bubbles in Aqueous Media.

It is greatly important to understand the gas bubble behaviors and realize their reliable manipulation. There still remain many challenges in the capture, transport, and release of gas bubbles at a preferred location intelligently. Herein, we provide a simple approach to manufacture a composite film with poly(N-isopropylacrylamide) (PNIPAAM) and polypropylene that exhibits smart, reversible, and reliable regulation of gas bubble adhesive behaviors (high and low adhesion) by controlling the temperature (above or below the lower critical solution temperature). By adjusting the composite surface temperature, thermally driven interface switching between intermolecular and intramolecular hydrogen bonding of the PNIPAAM chains resulted in low and high adhesion of air bubbles in an aqueous medium. Gas bubbles could be precisely captured, directionally transported, and precisely released at any preferred location.

Bubble behavior in gas–solid bubbling fluidized beds based on EMMS model: Comparison of 2D, Q2D, and 3D simulations

In this work, bubbling fluidized beds in two-, quasi-two-, and three-dimensional geometries are simulated by the Eulerian–Eulerian two-fluid model (TFM) coupled with an energy minimization multi-scale model. The parameters bubble diameter, bubble vertical velocity, shape factor, and aspect ratio, as well as bed height, are investigated. Simulation results show that vertical velocities of two- and quasi-two-dimensional bubbles are in good agreement with empirical correlations. Equivalent bubble diameter predicted in all dimensions of beds is also in reasonable agreement with empirical correlations. According to the comparison between simulation results (bubble diameter and vertical velocity) and empirical correlations, two- and quasi-two-dimensional simulations have better performance in predicting bubble behaviors. As for shape factor of three-dimensional bubbles, the peak value of frequency decreases with superficial gas inlet velocity, and the tendency is more significant than that of two- and quasi-two-dimensional bubbles. Slightly positively skewed distributions of aspect ratio are acquired, and the peak value decreases with superficial gas inlet velocity, especially for two- and three-dimensional bubbles. Additionally, bed height of two- and three-dimensional beds shows no major difference and is higher than that of the quasi-two-dimensional bed.