Gas Nucleation Research Articles

On the theory of the nucleation of gas bubbles at grain boundaries and incoherent inclusions

On the base of the critical analysis of two-dimensional models of the nucleation of gas filled bubbles at grain boundaries of helium-implanted specimens under the action of tensile stresses, a new model is developed within the framework of the Reiss theory of homogeneous nucleation in binary systems. This approach considers that gas bubbles are formed as a result of agglomeration in a binary system of vacancies and gas atoms at grain boundaries, avoiding significant simplifications of previous models based on the classical nucleation theory for single-component (unary) systems. The new model is extended to consider the nucleation of Xe bubbles at grain boundaries in UO2 under irradiation conditions and can be used for numerical analysis of experimental observations after the foreseen implementation in a fuel performance code. A similar approach can be applied to the nucleation and growth of gas bubbles on incoherent inclusions, such as those observed in irradiated ODS steels.

Efficient evolution mechanism of electrolytic gas products from laser-assisted electrolyte jet machining

Efficient evolution of electrolytic gas products is one of the mechanisms for increased material removal rate in laser-assisted electrolyte jet machining. However, the evolution mechanism of electrolytic gas products with multiple energy fields in laser-assisted electrolyte jet machining is not clear. In order to quantitatively characterize the laser-assisted facilitation of the evolution of electrolytic gas products, a gas quantification and detection device was designed and built in this paper. Compared to traditional electrolyte jet machining, laser-assisted electrolyte jet machining of 2024-T3 aluminum alloy increased the gas production by 52 % in 180 s. For the anode, the surface modification induced by laser texturing reduces the oxygen evolution potential and surface free energy and promotes gas nucleation and detachment. In addition, laser-induced conductive plasma can enhance transient currents for electrolyte jet machining and cause machining vibrations. The cathodic gas discharge phenomenon was characterized in conjunction with interelectrode gap visualization experiments and cathodic nozzle damage. Experimental results show that cathodic gas discharge depends on strong electric field and high laser pulse fluence. In summary, laser temperature rise, anode surface modification, laser-induced plasma, plasma recoil and cathode gas discharge can all contribute to the evolution of electrolytic gas products.

Nucleation mechanism of methane heterogeneous condensation under different driving forces

Clarifying alkane gas condensation characteristics is crucial to designing and optimizing liquefaction heat exchangers, which imposes higher demands on the microscopic understanding of alkane heterogeneous condensation. Thus, in this study, the condensation process of methane nucleation under different driving forces is investigated by molecular dynamics (MD) simulations. The dynamics characteristics of nucleation in methane heterogeneous condensation are analyzed by varying initial gas-phase pressure, cold wall temperature, and ethane content. The results showed that increasing the initial gas-phase pressure enhances intermolecular interactions, which alter the cluster formation path and significantly increase the methane gas nucleation rate from 1.997 × 1033/(m3·s) to 1.068 × 1034/(m3·s). While lowering the cold wall temperature promotes condensation by weakening the thermal motion of the gas molecules. Once condensation nuclei form in the system, the lower temperature conditions from lowering the cold wall temperature result in a higher growth rate of the clusters. Additionally, the addition of easily condensable component ethane can improve the condensation nucleation characteristics of low-saturated methane gas, facilitating the liquefaction of methane. This study aims to provide a microscopic understanding of the advancement of gas liquefaction technology by investigating the heterogeneous nucleation of alkane under different conditions from a microscopic perspective.

Fabrication of Cross‐Linked Polyimide Hollow Microspheres With Lightweight, Thermal Resistance and Controllable Size

AbstractPolyimide (PI) hollow microspheres possess lightweight and excellent thermal resistance, which are widely used in microreactors, catalysis, adsorption separation, high‐temperature insulation, and so on. In this manuscript, PI hollow microspheres are fabricated by constructing a crosslinked structure combined with gradient heating. The formation of PI hollow microspheres includes gas nucleation, expansion, and imidization. The PI hollow microspheres size is controlled by adjusting polyester ammonium salts size, and microspheres size is distributed in 309–956 µm. PI hollow microspheres have lightweight, excellent heat resistance and carbonization performance, bulk density, initial decomposition temperature, and weight residue at 800 °C is 87.3–178.6 kg m−3, 533.6 °C and 59.8%. The PI hollow microspheres have potential applications in high‐temperature resistant and multifunctional composite materials preparation. Moreover, this method is simple, efficient, and highly operable, which can be used for large‐scale production of PI hollow microspheres.

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

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

Nanoengineered Bifunctional Porous Ni5P4 Electrocatalyst with Accelerated Bubble Departure and Reduced Overpotential for Solar-Driven Water Splitting

To achieve the global "carbon neutral" goal and low-carbon economy by 2050-2100, hydrogen has been considered as an ideal renewable and sustainable energy carrier.1,2 The electrochemical conversion of solar energy to energy dense hydrogen fuel ensures a promising approach to generate a clean and sustainable source of energy.3,4 The integrated solar powered water electrolyzers for green hydrogen production completely eliminate all sources of carbon emissions arising from the direct power supply, towards achieving a low-carbon economy.5,6 However, large-scale solar water splitting for green hydrogen production still remains a challenge due to expensive electrocatalyst. As a low-cost, earth-abundant catalyst Nickel phosphide shows enormous potential to effectively reduce water and generate hydrogen. We propose a low-cost and facile approach to fabricate nanoengineered hierarchically porous Ni5P4 as an electrocatalyst (p-Ni5P4) providing high surface area and enabling fast gas diffusion. Nickel phosphide (p-Ni5P4@NF) has pores ranging from 50-500 nm to 200-600 μm and enlarges the electrochemically-active surface area by 5 times. The porous structure of p-Ni5P4@NF offers abundant cavities to gas nucleation and fast growth of H2 bubble, and small bubbles (10-50 µm) depart quickly owing to reduced contact line. By enhancing gas transfer and reducing bubble overpotential by 30%, p-Ni5P4@NF achieves excellent electrocatalytic performance with a low HER (145 mV), OER (197 mV) and overall water splitting potential (1.54 V) at 10 mA cm-2. Powered by multijunction PV cell, the full electrolytic cell records a high solar-to-hydrogen efficiency of 14.5 %. Keywords: Water splitting; Electrocatalysis; Green Hydrogen; Nickel Phosphide.

Numerical Modeling of Shale Oil Considering the Influence of Micro- and Nanoscale Pore Structures

A shale reservoir is a complex system with lots of nanoscale pore throat structures and variable permeability. Even though shale reservoirs contain both organic and inorganic matter, the slip effect and phase behavior complicate the two-phase flow mechanism. As a result, understanding how microscale effects occur is critical to effectively developing shale reservoirs. In order to explain the experimental phenomena that are difficult to describe using classical two-phase flow theory, this paper proposes a new simulation method for two-phase shale oil reservoirs that takes into account the microscale effects, including the phase change properties of oil and gas in shale micro- and nanopores, as well as the processes of dissolved gas escape, nucleation, growth and aggregation. The presented numerical simulation framework, aimed at comprehending the dynamics of the two-phase flow within fractured horizontal wells situated in macroscale shale reservoirs, is subjected to validation against real-world field data. This endeavor serves the purpose of enhancing the theoretical foundation for predicting the production capacity of fractured horizontal wells within shale reservoirs. The impact of capillary forces on the fluid dynamics of shale oil within micro- and nanoscale pores is investigated in this study. The investigation reveals that capillary action within these micro- and nanoscale pores of shale formations results in a reduction in the actual bubble point pressure within the oil and gas system. Consequently, the reservoir fluid persists in a liquid monophasic state, implying a constrained mobility and diminished flow efficiency of shale oil within the reservoir. This constrained mobility is further characterized by a limited spatial extent of pressure perturbation and a decelerated pressure decline rate, which are concurrently associated with a relatively elevated oil saturation level.

Time-resolved alkali release during steam gasification of char in a fixed bed reactor

In this study time-resolved char conversion and alkali release under steam gasification conditions were investigated using a fixed bed reactor. The behaviour of an industrial char and chars produced from straw and furniture waste was investigated. For woody chars, an increase in gasification reactivity is observed together with a notable alkali release as the gasification approaches completion (degree of conversion > 0.8). In contrast, straw char exhibited a decrease in conversion rate and alkali release throughout the gasification process, attributed to the formation of catalytically inactive potassium silicates inhibiting the catalytic role of alkali. Aerosol particles in the 0.01–22 µm size range are emitted during the char conversion. A fraction is formed by nucleation of alkali compounds and other condensable gases. A wide particle distribution that extends over the whole size range is also observed, and the particles are likely to consist of solid char fragments. The study concludes on the importance of alkali release, illustrating the difference in alkali release pattern for high and low ash char.

Eruption dynamics and plumbing system of Shikabe Geyser in southern Hokkaido, Japan, revealed by field observation inside and outside the conduit

The development of observation and data analysis techniques has advanced the understanding of the plumbing systems that contribute to the eruption dynamics of geysers. However, the interrelations between the plumbing system, dynamic and thermal processes inside the conduit, and surface phenomena remain unclear. We recorded video images, pressure, and temperature inside and outside the conduit of the Shikabe Geyser, a geysering well in southern Hokkaido, Japan. Video observations revealed that numerous bubbles are generated in the deep part of the conduit immediately after the eruption begins. However, the water temperature at depth is lower than the boiling point throughout the eruption cycle. The directly measured volume of discharged water indicate that the water supply rate during the eruption phase is significantly higher than that during the recharge phase. At the Shikabe Geyser, there may be void spaces composed of cracks and porous media around the deep part of the conduit, and high-temperature water containing dissolved CO2 gas is likely supplied from the reservoir. Dissolved CO2 plays a critical role in decreasing the boiling point of water. When an eruption occurs, steam with CO2 gas nucleation and expansion owing to decompression drives the vigorous discharge of water at the vent. Simultaneously, bubbles are generated inside the cracks in the aquifer owing to decompression, which may contribute to oversupply during the eruption.

X-ray computed microtomography revealing the effects of volcanic, alteration, and burial processes on the pore structure of rocks from unconventional reservoirs (Songliao Basin, NE China)

The pore structure and storage volume of rocks are crucial parameters to evaluate the favorability of hydrocarbon reservoirs. The unconventional volcanic reservoirs in the Songliao Basin (NE China) include lava and pyroclastics of different composition. Here we apply the X-ray computed microtomography (micro-CT) to reconstruct the 3D pore space of selected samples (basaltic lava, rhyolitic lava and rhyolitic pyroclastics) at depths between 2283 and 3757 m. We reconstruct the morphology and size distribution of the pores. The pore structure records the effects of superimposed volcanic, alteration, and compaction-burial processes. This latter process produces fractures in the rhyolitic pyroclastic rocks. The basaltic lavas have larger, connected pores filled by alteration minerals with a prolate shape, and unconnected, smaller, blade-like, empty pores. The hydrothermal alteration reduces the porosity and the rock is impermeable being the smaller voids unconnected. The basaltic lavas are good cap rocks but very poor reservoir rocks. The rhyolitic lava flows and pyroclastics, some of which placed in the gas zone of the Songliao reservoirs, show prevailing interconnected fractures due to burial processes and minor pores around crystals formed by syn-eruptive heterogeneous gas nucleation. The pore connectivity is ensured by the fractures and the permeability may be high, also depending on the volume, more than on the number, of the pores. Rhyolites may be good reservoir rocks. We search for possible relationships between porosity and permeability and do not find a clear relation between these two parameters as well as between depth and permeability. Although our analysis is valid within a length scale between about 20 μm and 1 cm, the methodological approach used here can be extended to other reservoirs to study the evolution of the pore systems as a function of the different processes affecting the volcanic rocks.

Effect of gravity on phase transition for liquid–gas simulations

Direct simulations of phase-change and phase-ordering phenomena are becoming more common. Recently, qualitative simulations of boiling phenomena have been undertaken by a large number of research groups. One seldom discussed limitation is that large values of gravitational forcing are required to simulate the detachment and rise of bubbles formed at the bottom surface. The forces are typically so large that neglecting the effects of varying pressure in the system becomes questionable. In this paper, we examine the effect of large pressure variations induced by gravity using pseudopotential lattice Boltzmann simulations. These pressure variations lead to height dependent conditions for phase coexistence and nucleation of either gas or liquid domains. Because these effects have not previously been studied in the context of these simulation methods, we focus here on the phase stability in a one-dimensional system, rather than the additional complexity of bubble or droplet dynamics. Even in this simple case, we find that the different forms of gravitational forces employed in the literature lead to qualitatively different phenomena, leading to the conclusion that the effects of gravity induced pressure variations on phase-change phenomena should be very carefully considered when trying to advance boiling and cavitation as well as liquefaction simulations to become quantitative tools.

Mechanisms of the memory effect of clathrate hydrates

The memory effect in the nucleation of gas hydrates refers to the phenomenon that gas hydrates nucleate easier or faster in the water that has a history of gas hydrate formation than in fresh water that has no such history. Although several hypotheses have been proposed to explain the cause of the memory effect over the last several decades, it remains the longest-standing mystery in the nucleation of gas hydrates. Supersaturation of the guest gas has been considered to occur in a memory system, however, the extent of its impact on the memory effect has been unclear. In the current research, we used linear cooling ramp experiments under isobaric conditions to determine the nucleation curves of CO2 hydrate in quiescent water in a stainless-steel sample cell and in quiescent quasi-free water droplets supported by a bulk liquid of perfluoromethyldecalin contained in a Teflon sample cell. From systematically comparing the nucleation curves of both freshly prepared samples and samples with a history of CO2 hydrate formation in both the stainless-steel sample cell and the quasi-free water droplets, as well as the nucleation curves of methane – propane mixed gas hydrates previously reported, a coherent picture emerged. The impurity imprinting component, with the interfacial gaseous states as the entity of the “impurity”, and the guest supersaturation component, with or without nanobubbles in the bulk water, are comparable in size, albeit the former is the larger one.

Microstructure and Cavitation Damage Characteristics of GX40CrNiSi25-20 Cast Stainless Steel by TIG Surface Remelting

Cavitation erosion degrades the surface of engineering components when the material is exposed to turbulent fluid flows. Under conditions of local pressure fluctuations, a nucleation of gas or vapor bubbles occurs. If the pressure suddenly drops below the vapor pressure, these bubbles collapse violently when subjected to higher pressure. This collapse is accompanied by the sudden flow of the liquid, which is manifested by stress pulses capable of causing plastic deformations on solid surfaces. Repeating these stress conditions can cause material removal and ultimately failure of the component itself. The present study aims to reduce the negative impact of this phenomenon on the mechanical systems components, using the TIG local surface remelting technique. Cavitation erosion tests were performed in accordance with the ASTM G32-2016 standard on samples taken from a cast high-alloy stainless steel. The alloy response for each melting current value was investigated by measuring mass loss as a function of cavitation attack time and by analyzing the damaged surfaces using optical and scanning electron microscopes. It was highlighted that the TIG remelted layers provide an increase in cavitation erosion resistance of 5-6 times as a consequence of the fine graining and microstructure induced by the technique applied.

Enhancing flotation separation of fine copper oxide from silica by microbubble assisted hydrophobic aggregation

One of the main challenges facing the flotation of base metal oxide minerals is their fine sizes of particles as a result of fine grinding to achieve a desired degree of liberation for low-grade and finely disseminated complex ores. This study aims at studying hydrophobic aggregation and in situ gas nucleation of fine copper oxides with sodium dodecyl sulfate (SDS) as a selective collector to enhance CuO recovery. Experimental results by in situ and real time particle size measurement using focused beam reflectance measurement (FBRM) coupled with particle vision measurement (PVM) showed an enhanced aggregation of fine CuO by SDS adsorption. Particle aggregation assisted by gas nuclei which were generated in situ on CuO by high intensity agitation (HIA) was visualized by total internal reflection fluorescence microscopy (TIRFM). It is the enhanced aggregation with nanobubbles as bridges that improved its recovery from fine silica. Coupled with the calculation using the extended DLVO theory, contact angle and zeta potential of fine particles were measured to understand the critical role of hydrophobic forces in aggregation of fine CuO particles. The copper ions dissolved from the fine copper oxide were found to inadvertently activate fine silica flotation which could be effectively depressed by ethylene diamine tetraacetic acid (EDTA). A combination of SDS with EDTA was proposed and demonstrated to achieve selective recovery of fine copper oxide from fine silica gangue. The results from this study provide directions for enhancing copper recovery from low grade and finely disseminated copper oxidize ores, in particular from tenorite ores.

Thermoregeneration of Fouling‐Inhibiting Plastrons on Conductive Laser‐Induced Graphene Coatings by Joule Heating

AbstractSuperhydrophobic surfaces are capable to resist the adhesion of organisms through a surface bound air layer, known as a plastron. However, the lifetime of such plastrons is limited and their decay results in the loss of the protective barrier against organism attachment. Here a method is established to replenish the plastron by Joule heating of electrically conductive, superhydrophobic laser‐induced graphene (SLIG) coatings. Local heating with a DC current reduces the water solubility of gases and the growth of an initial microplastron into a macroplastron through gas nucleation at the liquid–air interface is observed. Small temperature differences between the surface and the surrounding water could induce this effect. Different SLIG surfaces are challenged against biofouling by the diatom Navicula perminuta under dynamic conditions and it is shown that surfaces with intact plastron resist diatom accumulation. Surfaces without the protective air layer are found to accumulate high amounts of diatoms. The results underline the promising potential of plastron‐based antifouling approaches because plastrons can be stabilized for extended times. This strategy could be applied to many other materials for an effective protection against fouling organism.

Accelerated bubble departure and reduced overpotential with nanoengineered porous bifunctional Ni5P4 electrocatalyst for PV-driven water splitting

Solar-driven green hydrogen production is a promising sustainable technology though large-scale solar water splitting remains challenging due to expensive electrocatalyst. Herein, we propose a facile and low-cost approach to fabricate nanoengineered hierarchically porous Ni5P4 electrocatalyst (p-Ni5P4), which provides high surface area and enables fast gas diffusion. By coating p-Ni5P4 on Ni foam (NF), p-Ni5P4@NF has pores ranging from 50-500 nm to 200–600 μm and enlarges the electrochemically-active surface area by 5 times. p-Ni5P4@NF offers abundant cavities for gas nucleation and fast growth of H2 bubble, and small bubbles (10–50 μm) depart quickly owing to the reduced contact line. By enhancing gas transfer and reducing bubble overpotential over 29%, p-Ni5P4@NF achieves excellent electrocatalytic performance with a low HER (145 mV), OER (197 mV) and overall water splitting potential (1.54 V) at 10 mA cm−2. Powered by multijunction PV cell, the full electrolytic cell records a high solar-to-hydrogen efficiency of 14.5%.

On the theory of void nucleation in irradiated crystals

The theory of void nucleation in irradiated materials is critically analysed and further developed. It is shown that the existing theory overestimates the rate of empty void nucleation in ion-irradiated steels by several orders of magnitude and therefore requires revision for an adequate interpretation of ion bombardment tests. To extend the nucleation model to the conditions of reactor neutron irradiation, it is modified to take into account the effect of void stabilisation by transmutation gas (He) in steels or by fission gases (Xe, Kr) in fuels. It is shown that the presence of gas atoms in a solid solution strongly reduces the free energy of void formation, but does not affect the number of void nucleation sites, which is determined by the concentration of vacancies in the irradiated material. The model developed for nucleation of small gas filled voids (bubbles) is further modified to adequately consider their further growth, stabilisation (due to athermal resolution of gas atoms) and generation of a new population of larger bubbles. The obtained analytical expression for the nucleation rate is applied to a simplified analysis of experimental data on neutron irradiation of stainless steel in PWRs and FRs. For a more accurate analysis of these tests, it is recommended to implement the new model in a fuel performance code, additionally taking into consideration the migration and coalescence of small bubbles.

Influence of MIBC on the surface-air nucleation and bubble-particle loading in graphite froth flotation

This paper investigates one aspect of surface air nucleation in froth flotation, namely the impact of frother-type surfactants like Methyl isobutyl carbinol (MIBC). During this study, tap water was pressurized in an autoclave to produce air-oversaturated water for air nucleation precondition in flotation. Various experiments were carried out with graphite particles to investigate the influences of gas nucleation and MIBC on flotation: micro-flotation, single bubble collision experiments in hydrodynamic conditions and pick-up experiments in static conditions. In addition, microscopic observations were combined with agglomeration analysis to clarify the effects of the frother MIBC on the air nucleation and agglomerate formation. The experimental results show the combination of MIBC and air nucleation can significantly increase the graphite recovery compared to using air-oversaturated water or normal tap water with MIBC alone, respectively. The analysis indicates that MIBC can improve the air nucleation probability on graphite surfaces by enhancing the stability of the air nuclei to form more microbubbles on the surface. Meanwhile, the surface microbubbles can collide with other particles forming coarser aggregates, improving their collision probability and with this increasing the recovery of fine particles. Furthermore, the results show that MIBC can reduce the detachment of particles from the surface of nucleation bubbles, leading to an increase in particle load of the bubble-particle aggregates in hydrodynamic conditions, improving the graphite recovery significantly.

Homogeneous nucleation and condensation mechanism of methane gas: A molecular simulation perspective

Liquefied natural gas (LNG) occupies an increasing proportion in global natural gas industry. However, there is a lack of microscopic understanding of methane condensation mechanism. Furthermore, the accuracy of existing nucleation theories for alkane gases remains unclear. Herein, methane nucleation and growth pathways are elucidated and the influence mechanisms of initial conditions on nucleation thermodynamics and kinetics are analyzed using molecular dynamics (MD) simulations. It is discovered that a system with a controlled carrier gas temperature is more consistent with the actual condensation process. For such a system, the heat transfer processes between monomers and clusters make the condensed molecules easier to vaporize and its nucleation and growth stages last longer. Besides, the condensation processes end earlier with higher nucleation rates and liquefaction degrees at high initial pressures and low cooling temperatures. Higher pressures lead to higher temperatures of monomers and clusters during nucleation, while avoiding secondary evaporation. Furthermore, as initial pressures and cooling temperatures increase, the effects of system quenching on pressure relieve, and the fall in pressure mainly depends on the liquefaction degree. Compared with Classical Nucleation Theory (CNT), Internally Consistent Classical Theory (ICCT) has higher accuracy for the nucleation calculation of methane under high-pressure and low-temperature conditions.

Coupling between nucleation and chemical reactions and its importance in understanding the oxidation of iodine by hydrogen peroxide.

We have investigated the reaction of iodine with hydrogen peroxide coupled to gas nucleation. A step-like increase in the nucleation rate with increasing amounts of dissolved oxygen can act as a trigger for the formation of highly reactive components and complete oxidation of iodine to iodate despite the large thermodynamic barrier for the whole process. Energetic coupling of nucleation with chemical reactions is based on local redistribution of energy by collapsing unstable nuclei. The developed model correctly describes the evolution of the measured reaction parameters. It offers a conceptual improvement of formal-kinetic models by drawing attention to important contributions of physical effects to the reaction mechanism.