Bubble Growth Research Articles

Mechanism of pH Effect on Mass Transfer During Bubble Evolution on Photoelectrode Surfaces

This study conducted in-depth research on the limitation problem of mass transfer of gas molecules on the surface of the photoelectrode to the efficiency of photoelectrochemical water splitting. Experimental results reveal significant differences in the dynamic characteristics of bubbles and mass transfer mechanisms during bubble growth under different pH conditions. As the pH deviates from 7.0 (vs RHE), the reaction rate increases, the bubble nucleation voltage decreases, and the terminal rising velocity increases significantly. During the rapid growth phase of bubbles, the mass transfer coefficient reaches its peak, accounting for only 1% of the entire evolution cycle. In a neutral environment (pH = 7.0), the transient mass transfer coefficient reaches a maximum at approximately 1 s of bubble growth, while in an alkaline environment (pH = 12.0), it reaches a maximum at around 0.1 s. In strongly alkaline environments (pH = 13.0), the PEC reaction rate and mass transfer rate increase, resulting in the highest gas production efficiency. The mass transfer coefficients were improved by about 72.4% and 42.8% (vs Ag/AgCl) and by about 22.2% and 33.3% (vs RHE) in the strong alkaline environment relative to the strong acid environment (pH = 1.0) and the neutral environment, respectively.

Foam coarsening in a yield stress fluid.

Foams coarsen because of pressure differences between bubbles of different sizes. We study the coarsening of quasi-2D foams made from model yield stress fluids: concentrated oil-in-water emulsions. We show that increasing the yield stress of the foamed emulsion continuous phase leads to both slower coarsening and irreversible structural change. The impact of the continuous phase rheology is stronger when the foamed emulsion is wetter or more confined. The bubble growth and organisation both become highly heterogeneous with an excess of small bubbles. We present a model that rationalises the impact of these three parameters by taking into account a resisting pressure required to displace the yield stress fluid around the bubbles.

Effect of hydrochemical indicators of Sangzor river water on mollusk population indicators

The article presents information about the influence of hydrochemical parameters of Sangzor river water on mollusk population parameters. The hydrochemical indicators of the water of the Sangzor River are oil and oil products, the level of mineralization is not higher than REM, and the water temperature, flow speed, clarity are favorable for bivalve mollusks of the families Unionidae and Sorbiculidae and bubble growth was determine to be high. Its downstream is in the water after the city of Jizzakh (Khairabad) oil and oil products, mineralization level is higher than REM, pollution of water environment factors, weight, shell length, height, and bubble growth of bivalve mollusks of Unionidae and Sorbiculidae families were determined to be small, affecting the growth of shells to a certain extent as limiting factors.

Bubble dynamics manipulation in polymeric foaming.

The release of pressure from a high-pressure-stable polymer/gas solution is a common method for creating gas bubbles and forming foam with a typical polyhedral cell structure. We propose a new approach to control the foaming process by pausing the bubble growth at intermediate pressure before reaching ambient pressure. This allows us to control the growth of the bubbles and investigate various physical phenomena involved in polymer foaming, such as Ostwald ripening, bubble interactions, coalescence, and different bubble growth regimes. We conducted these studies in a model system PP/N2 by subjecting the solution to non trivial pressure histories. Our method will have an impact on the study of fundamental phenomena involved in foaming and their application in creating new materials.

Influence of wall elasticity on growth and collapse of bubbles near a wall

Influence of wall elasticity on growth and collapse of bubbles near a wall

Effect of doping on evolution of He<sup>+ </sup>ion irradiation defects and superconductivity in EuBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–δ</sub> superconducting strips

Rare-earth barium copper oxide (REBCO) as a representative of the second-generation high-temperature superconducting materials possesses superior physical advantages such as high critical magnetic field, elevated critical temperature, and superior current density, which has been applied to many domains. Although the introduction of non-superconducting nanoscale particle dopants, as a critical method, can enhance the magnetic flux pinning capability of REBCO strips, the effect of the doping on the performance change and microstructure evolution of the strips under irradiation is ignored. In this work, undoped and 3.5% BaHfO<sub>3</sub> (BHO) doped EuBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–δ</sub> strips are investigated in the room-temperature irradiation experiments (1.4 MeV He<sup>+</sup> ions) with three distinct doses of 5×10<sup>14</sup>, 5×10<sup>15</sup>, and 5×10<sup>16</sup> ions/cm<sup>2</sup>, respectively. Electrical performance tests reveal that the undoped strips exhibit a slight increase in <i>J</i><sub>c</sub> after the low-dose irradiation. However, with dose increasing, <i>J</i><sub>c</sub> decreases by over 60%. In contrast, doped strips experience a significantly smaller decline in <i>J</i><sub>c</sub>, ranging only between 30% and 40% at high-dose irradiation. Raman spectroscopy and transmission electron microscopy characterizations confirm that the defects induced by He<sup>+</sup> ion irradiation lead to amorphization and structural disorder within the superconducting layers, which is the primary reason for the decline in the superconducting properties of the strips. The results show that the introduction of localized strain through BHO nanophase in the superconducting layer changes the migration and aggregation behavior of irradiation-induced defects, repairing the damaged superconductor structure. Furthermore, the field dependence and temperature dependence of <i>J</i><sub>c</sub> of doped strips are irradiation-resistant due to BHO nanocrystals as strong pinning centers. Additionally, unlike the superconducting properties of the REBCO strips that can be repaired through oxygen annealing after neutron or heavy ion irradiation, the electrical properties of the two types of strips irradiated with high doses of He<sup>+</sup> ions in this work are further deteriorated after being annealed. It is worth noting that compared with the undoped strip, the localized strain generated by BHO in the doped strip inhibits the size growth of helium defects in the three-dimensional direction at high temperatures, which changes the magnetic flux pinning characteristics and delays the disorder and amorphization of the superconducting layer structure caused by the severe growth of helium bubbles. This study provides a reference for the application of REBCO superconducting strips in the irradiation environment.

Impact of tracer particles on the electrolytic growth of hydrogen bubbles

The thermocapillary effect at gas bubbles growing at micro-electrodes seems well understood. However, the interfacial flow measured in the upper bubble part decays faster than found in first simulations by Massing et al. [“Thermocapillary convection during hydrogen evolution at microelectrodes,” Electrochim. Acta 297, 929 (2019)]. Recently, Meulenbroek et al. attributed the origin of the difference to the influence of surfactants being present in the electrolyte [“Competing Marangoni effects from a stagnant cap on the interface of a hydrogen bubble attached to a microelectrode,” Electrochim. Acta 385, 138298 (2021)]. Surprisingly, the presence of tracer particles added to the electrolyte for measuring its flow was not yet considered. Our recent experiments reveal that varying the small amount of tracer particles added influences the bubble shape, its dynamics, and also the electrolyte flow nearby. We therefore present a model to describe the particle attraction to and the particle dynamics at the bubble interface, which allows us to quantify the impact. Corresponding simulations are validated against measurements for different bulk particle concentrations and show a good agreement of the tangential velocity profile at the bubble interface caused by thermo- and solutocapillary effects. Depending on the particle concentration, parts of the upper bubble interface are found to become stagnant. The results allow a deeper insight into the complex phenomena of electrolytic gas evolution and further put attention to a careful application of particle-based measurement techniques in gas–liquid systems.

Phase-field simulation on fission gas release behavior of large grain UO<sub>2</sub> fuel

In order to predict the release behavior of fission gas in large grain UO<sub>2</sub> fuel and provide support for the development of accident tolerant fuel, a phase-field model is used to simulate the release behavior of fission gas in the microstructure of UO<sub>2</sub> polycrystalline in this work. This model adopts a set of coupled Cahn-Hilliard equations and Allen-Cahn equations, using conserved field variables to represent the distribution of fission gas and vacancies, and distinguishing bubble phase from matrix phase by using order parameters. This model focuses on investigating the effects of different grain sizes, temperature conditions, and diffusion coefficients on the release behavior of fission gas, demonstrating the nucleation, growth, and fusion behavior of bubbles. Simulation results are obtained for fuel porosity, bubble coverage on grain boundaries, and average bubble radius at a certain degree of burnup. The results show that temperature and diffusion coefficient have a significant influence on porosity and bubble coverage on grain boundaries. When the diffusion coefficient is high, grain size also has a significant influence on fission gas release behavior. And when the diffusion coefficient is low, the influence of grain size is not significant. In addition, the distribution of fission gas bubbles under high burnup obtained through this model is also in good agreement with experimental result. The model can predict the behavior of fission gas release in large grain UO<sub>2</sub> fuel.

Mass transfer of microbubble in liquid under multifrequency acoustic excitation - A theoretical study

Microbubble’s mass transfer under external acoustic excitation holds immense potential across various technological fields. However, the current state of acoustic technology faces limitations due to inadequate control over bubble size in liquids under external excitation. Here, we conducted numerical investigations of the mass transfer behavior of microbubbles in liquids under multifrequency acoustic excitations with different frequencies (in the MHz range), pressure amplitudes (in the range of several atmospheric pressures), and amplitude ratios. We identified various pressure threshold regions for the growth of gas bubbles (radii range from a few microns to tens of microns) and observed common intersections between single and multifrequency excitations that enable effective control of the growth intervals and final size of bubbles by adjusting the ratio of pressure amplitude and frequency value. Allocating power to the lower frequency component of multifrequency acoustic excitation is recommended to facilitate mass transfer or diffusion, as small-frequency acoustic excitation has a more significant effect than the higher frequency in the growth region. Our study provides a better understanding of the dynamics of bubbles under complex excitations and has practical implications for developing methods to control and promote bubble-related processes.

Melting and Rapid Solidification of Lunar Regolith Particles Returned by Chang'E-5 Mission.

Melting and solidification of lunar regolith are pivotal for comprehending the evolutionary dynamics of lunar volcanism, geology, and impact history. Additionally, insights gained from these processes can contribute to the advancement of insitu resource utilization technologies, for instance additive manufacturing and resource extraction systems. Herein, we conduct the direct observation of the melting and rapid solidification of lunar particles returned by the Chang'E 5 mission. The melting temperature and melting sequence were obtained. Bubble generation, growth, and release were clearly observed, with a maximum bubble diameter of 5 µm, which is supposed to be according to the release of volatiles that embedded in the particles. During the solidification process, evident crystallization occurred with incremental crystal growth rate approximately of 27 nm/s. Scanning electron microscopy and energy-dispersive x-ray spectroscopy results verified that the Fe-rich mineral crystalizes first. These results would improve the understanding of the evolution of lunar volcanism, geology, and impact history.

Three-dimensional CFD simulation of geyser boiling in high-temperature sodium heat pipe

A deep understanding of the characteristics and mechanism of geyser boiling and capillary pumping is necessary to optimize a high-temperature sodium heat pipe. In this work, the Volume of Fluid (VOF) two-phase model and the capillary force model in the mesh wick were used to model the complex phase change and fluid flow in the heat pipe. Computational Fluid Dynamics (CFD) simulations successfully predicted the process of bubble nucleation, growth, aggregation, and detachment from the wall in the liquid pool of the evaporation section of the heat pipe in horizontal and tilted states, as well as the reflux phenomenon of capillary suction within the wick. The accuracy and stability of the capillary force model within the wick were verified. In addition, the causes of geyser boiling in heat pipes were analyzed by extracting the oscillation distribution of heat pipe wall temperature. The results show that adding the capillary force model within the wick structure can reasonably simulate the liquid backflow phenomenon at the condensation; Under the horizontal and inclined operating conditions of the heat pipe, the phenomenon of local dry-out will occur, resulting in a sharp increase in local temperature. The speed of bubble detachment and the timely reflux of liquid sodium (condensate) replenishment in the wick play a vital role in the geyser temperature oscillation of the tube wall. The numerical simulation method and the results of this study are anticipated to provide a good reference for the investigation of geyser boiling in high-temperature heat pipes.

Colloidal bubble propulsion mediated through viscous flows.

Bubble-propelled catalytic colloids stand out as a uniquely efficient design for artificial controllable micromachines, but so far lack a general theoretical framework that explains the physics of their propulsion. Here we develop a combined diffusive and hydrodynamic theory of bubble growth near a spherical catalytic colloid, that allows us to explain the underlying mechanism and the influence of environmental and material parameters. We identify two dimensionless groups, related to colloidal activity and the background fluid, that govern a saddle-node bifurcation of the bubble growth dynamics, and calculate the generated flows analytically for both slip and no slip boundary conditions on the bubble. We finish with a discussion of the assumptions and predictions of our model in the context of existing experimental results, and conclude that some of the observed behaviour, notably the ratchet-like gait, may stem from peculiarities of the experimental setup rather than fundamental physics of the propulsive mechanism.

Enhancing pool boiling heat transfer of modified surface by 3-D Lattice Boltzmann method

In this study, pool boiling from micro-pillar modified surface has been simulated numerically by a 3-D lattice Boltzmann method. Effects of geometries and wettability of micro-pillar on boiling heat transfer performance were also systematically evaluated. Result showed that compared within micro-pillar surface, heat flux of cubic micro-pillar surface was the highest with the lowest wall temperature. In addition, compared to hydrophilic condition, Heat flux of cubic micro-pillar surface with hydrophobic wettability increased by 98.3%. This is because hydrophobic wettability influenced nucleation site density, vapor-liquid-flow field and heat transfer performance much more than cubic shaped geometry. Finally, heat flux of cubic micro-pillar surface with hybrid wettability increased by 430.7% compared to pure hydrophilic wettability. That is due to optimal hybrid wettability surface could control nucleate site location, restrict bubble growth, and increase obviously heat transfer performance.

INFLUENCE OF BUBBLE GROWTH AND LIQUID FILM INSTABILITIES ON DROPLET IMPACT PHENOMENA UNDER SATURATED BOILING REGIMES

Evaporation and boiling are processes that occur in many industrial applications involving multiphase flows. For liquid films, however, studies are scarce regarding heat and mass transfer mechanisms and require further research. The main objective of this work is to evaluate bubble formation and detachment, followed by the impact phenomena. Therefore, an experimental setup was built and adapted for this purpose. A borosilicate glass impact surface is placed over a heat source, which consists of an aluminum block with four embedded cartridge heaters that heat the liquid film by conduction. Water and n-heptane are the fluids adopted for the experimental study, as the differences in thermophysical properties allow for a wider range of experiments. Study cases include dimensionless temperatures of θ > 0.6 for similar impact conditions. In terms of bubble formation, n-heptane displays smaller bubble diameters and higher release rates, whereas water exhibits larger bubbles and lower rates. Qualitatively, liquid film temperatures close to the saturation temperature do not reveal a direct influence on the crown development and posterior secondary atomization. For later stages of the impact, the central jet height and breakup are influenced by the film temperature, which is associated with the variation of thermophysical properties.

Mechanisms of microexplosion-accelerated pyrolysis and oxidation of lithium-containing droplets: an atomistic perspective.

Microexplosion has been extensively studied in the context of fuel spray and droplet evaporation in engines, while its existence, impact and atomistic insight have rarely been explored in the context of flame synthesis of nanoparticles. In this study, reactive force-field molecular dynamics simulations are performed to elucidate the mechanisms of pyrolysis and oxidation of an isolated lithium nitrate nanodroplet. During the pyrolysis process, the nucleation and growth of a bubble are observed inside the droplet, which should be ascribed to the release of nitrogen and oxygen gases from the decomposition of lithium nitrate, ultimately leading to rapid droplet fragmentation (microexplosion). To demonstrate the role of microexplosion with various intensities, via altering ambient temperature and addition of oxygen gas into the environment, thorough analyses of bond reactions, droplet morphology and compounds of the synthesized lithium nanoparticles are carried out. With elevated ambient temperature, the droplet substantially expands due to bubble growth and the time required for droplet disruption is shortened, which implies the enhanced strength of microexplosion. Simultaneously, the connection between the lithium and other atoms becomes weak, as evidenced by a decrease in the number of lithium bonds. These give rise to a reduction in the quantity of large-sized lithium agglomerates and simultaneously an increase in the amount of fine lithium nanoparticles. To further clarify the reaction mechanism for a lithium-containing droplet under various ambient conditions, three reaction modes, i.e., core-shell diffusion-controlled, microexplosion-accelerated and microexplosion-dominated, are distinguished based on the intensity of microexplosion and the quality of synthesized lithium nanoparticles. Fine lithium-containing nanoparticles are expected to be produced in the microexplosion-dominated mode under high temperature conditions.

Clustering, coalescing and bursting processes in surface bubbles of surfactant water flows

Breaking waves aerate seawater surfaces and form whitecaps in the open ocean. The aerated surface area, or whitecap coverage, has been used to macroscopically parametrize air–sea momentum and gas exchange. However, the microscopic mechanisms of the generation, evolution and attenuation of surface bubbles in whitecaps remain poorly understood. In this study, we examined the size distributions and size-dependent lifetimes of surface bubbles generated by water sheet entry and air injection on a porous plate during the clustering, coalescing and bursting processes, depending on surfactant concentrations and bubble mobility. Mechanisms of coalescence through film thinning of adjacent bubble walls owing to the inter-bubble attraction and Marangoni forces experimentally described the surfactant-dependent bubble growth, finally achieving bubble bursting, which were statistically characterized in a population balance analysis. Lagrangian bubble lifetimes were described by the Weibull distribution, providing that surfactant in seawater extended the probabilistic survival periods of surface bubbles two times longer than those of clean bubbles.

Hydrodynamic analysis of liquid microlayer formation in nucleate boiling of water

This paper presents analyses of the formation of "microlayers" i.e., very thin (∼ 1μm) liquid films often found beneath steam bubbles growing on a solid surface in low-pressure boiling. The hydrodynamics of bubble growth on a surface in pool boiling of water at atmospheric pressure have been modelled with interface-capturing Computational Fluid Dynamics (CFD) in a range of conditions that include a recent set of experiments, and transcend the remit of extant computational studies. Numerical predictions of bubble and microlayer behaviour were found in broad agreement with experimental measurements, and consistent with the current theoretical understanding of the microlayer hydrodynamic formation process. From recently reported direct measurements of microlayer thickness, a range of values of the likely thickness of the liquid film as formed on the solid surface have been inferred, and used to validate the current simulations, which clearly indicated the formation, beneath a growing steam bubble, of a liquid film of thickness comparable to values inferred from measurements. Notably, CFD simulations revealed the formation of a characteristic "dewetting ridge" i.e., an area where the film surface is markedly convex, in a microlayer region close to the triple contact line not accessible to any present-day optical measurement technique, and indicate that, in an otherwise flat microlayer, a noticeably curved region should be expected to form near the contact line. This paper provides enhanced insight into micro-scale features, such as the shape and thickness of microlayers, that typically evolve over extremely small time scales, and are therefore challenging to measure, and at present not amenable to any observation technique. A parametric study, covering a range of values of the capillary number between 7.86 × 10−4 and 7.86 × 10−2, and surface contact angles between 15˚ and 90˚, typical of wetting or partially wetting fluids on common engineering surfaces, confirmed the trends in microlayer behaviour predicted for the case of atmospheric-pressure water-boiling in laboratory conditions.

Experimental investigation on bubble dynamic behaviors in pool boiling of surfactant solutions

In this study, pool boiling experiments on copper surfaces with different roughness levels (Ra = 0.61 μm and Ra = 0.15 μm) using sodium dodecyl sulfate (SDS) solutions at various concentrations (0.1 CMC, 1 CMC, 5 CMC, and 10 CMC) are investigated. Our study focuses on the impact of SDS concentration, wall superheat, surface roughness, and bubble behavior on boiling heat transfer. The results show that an increase in SDS concentration could improve the heat transfer. However, when the SDS concentration reaches 10 CMC, there is a deterioration in heat transfer. Additionally, rough surfaces show better heat transfer performance compared to smooth surfaces. The presence of surfactant not only promotes bubble nucleation but also reduces the bubble departure diameter and inhibits bubble coalescence. Multiple bubbles are formed from the same nucleation site in surfactant solutions with high concentrations (5 CMC, 10 CMC). Various bubble dynamic parameters, including instantaneous size, departure diameter, growth time, waiting time, and departure frequency are obtained and compared with existing empirical correlations in the literature. It is found that the bubble growth in both deionized water (DI water) and surfactant solutions is mainly influenced by the near-wall thermal conditions, aligning with the thermal diffusion mechanism. In addition, the bubble departure diameters in both DI water and surfactant solutions gradually increase with increasing Jakob number (Ja). The growth time and waiting time in the surfactant solution both decrease with increasing Ja number, leading to a significant rise in the departure frequency. In contrast, the bubble growth time in DI water increased and the waiting time decreased with increasing Ja number, resulting in a relatively stable departure frequency. A new empirical formula is proposed for fDd0.5 based on the surface tension coefficient, surface roughness, and Ja number, which demonstrates good rationality.

Through-Space Electrochemiluminescence Reveals Bubble Forces at Remote Phase Boundaries.

Several groups have reported on the curious chemistry and reaction acceleration in confined volumes. These complex multiphase systems most closely resemble natural processes, and new measurement tools are necessary to probe chemistry in such environments. Generally, electrochemiluminescence (ECL) reports on processes immediately near (within a few micrometers) the electrode surface. Here, we introduce through-space ECL, reporting on dynamics of processes far away (100s of μm) from the electrode surface. We achieved this by collecting reflected ECL light. During the heterogeneous oxidation of C2O42- in an aqueous phase adjacent to a 1,2-dichlorethane droplet, CO2 accumulates in the 1,2-dichloroethane droplet. Upon buildup, we demonstrate that a CO2 bubble forms in the nonaqueous phase and is surprisingly trapped at the water|1,2-dichloroethane interface and continues to grow. The co-oxidation of tris(bipyridine)ruthenium(II) in the aqueous phase lights up the electrode surface and reflects off the edges of the bubble, revealing the bubble growth over time even when the bubble is fractions of a millimeter from the surface. We extend our results to quantifying bubble forces at the water-oil interface at remote distances from the electrode surface.

Nucleation Process in Explosive Boiling Phenomena of Water on Micro-Platinum Wire.

The maximum temperature limit at which liquid boils explosively is referred to as the superheat limit of liquid. Through various experimental studies on the superheating limit of liquids, rapid evaporation of liquids has been observed at the superheating limit. This study explored the water nucleation process at the superheat limit achieved in micro-platinum wires using a molecular interaction model. According to the molecular interaction model, the nucleation rate and time delay at 576.2 K are approximately 2.1 × 1011/(μm3μs) and 5.7 ns, respectively. With an evaporation rate (116.0 m/s) much faster than that of hydrocarbons (14.0 m/s), these readings show that explosive boiling or rapid phase transition from liquid to vapor can occur at the superheat limit of water. Subsequent bubble growth after bubble nucleation was also considered.