Bubble Nucleation Research Articles

Charged Nariai black holes on the dark bubble

Abstract In this paper, we realise the charged Nariai black hole on a braneworld from a
nucleated bubble in AdS5, known as the dark bubble model. Geometrically, the black hole
takes the form of a cylindrical spacetime pulling on the dark bubble. This is realised by a
brane embedding in an AdS5 black string background. Identifying the brane with a D3-brane
in string theory allows us to determine a relation between the fine structure constant and the
string coupling, αEM = 3 gs/2, which was previously obtained for a microscopic black hole. We
also speculate on the consequences for the Festina Lente bound and neutrino masses.

Microstructure Evolution of the Interface in SiCf/TiC-Ti3SiC2 Composite under Sequential Xe-He-H Ion Irradiation and Annealing Process.

A new type of SiCf/TiC-Ti3SiC2 composite was prepared by the Spark Plasma Sintering (SPS) method in this work. The phase transformation and interface cracking of this composite under ion irradiation (single Xe, Xe + He, and Xe + He + H ions) and subsequent annealing were analyzed using transmission electron microscopy (TEM), mainly focusing on the interface regions. Xe ion irradiation resulted in the formation of high-density stacking faults in the TiC coatings and the complete amorphization of SiC fibers. The implanted H ions exacerbated interface coarsening. After annealing at 900 °C for 2 h, the interface in the Xe + He + H ion-irradiated samples was seriously damaged, resulting in the formation of large bubbles and cracks. This damage occurred because the H atoms reduced the surface free energy, thereby promoting the nucleation and growth of bubbles. Due to the absorption effect of the SiCf/TiC interface on defects, the SiC fiber areas near the interface recovered back to the initial nano-polycrystalline structure after annealing.

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.

Numerical study of flow boiling on microcavity surface under the action of an electric field using lattice Boltzmann method

The microcavity setting promotes bubble nucleation, and the presence of an electric field enables bubble detachment. In this study, the synergistic effect of electric field and microcavity in improved flow boiling heat transfer was analyzed based on the pseudopotential lattice Boltzmann method. The investigation was focused on the influence of wall superheat, Reynolds (Re) number, electric field intensity, liquid subcooling, and gravitational acceleration on the flow boiling performance under two forms of electric field distributions for uniform conducting microcavity surface (MC–UCS) and conducting–insulating microcavity surface (MC–CIS). Compared with the MC–UCS, the MC–CIS maintained a stable wetting state in the microcavity through inhibition of sliding and merging of bubbles. The increase in electric field intensity and Re number improved convective heat transfer in the microcavity but at the expense of a larger frictional pressure drop. The boiling phenomenon on the microcavity surface weakened with the increase in liquid subcooling, which caused difficulty for the electric field to improve the heat transfer performance by improving bubble behavior. Electrical force can replace buoyancy force to perturb the vapor–liquid interface under low gravitational acceleration. This condition allows the fluid shear force to drive bubbles away from the microcavity surface quickly. The results can provide theoretical and technical guidance for the realization of the enhanced synergistic heat transfer between electric fields and microstructures.

Excellent radiation resistance via enforced local non-directional He diffusion in a WTaCrV multicomponent alloy containing coherent ordered nanoprecipitates

We design and investigate a W15Ta15Cr35V35 (at.%) multicomponent alloy (MCA) with exceptional radiation resistance. The sintered WTaCrV alloy exhibits a body-centered cubic (BCC) matrix with dispersed coherent ordered nanoprecipitates. After ∼3-hour irradiation under 400 keV He+ at room temperature (RT) and 450°C with a fluence of 2 × 1017 ions/cm2, the irradiation hardening values of the MCA are about a quarter of those of pure tungsten counterparts irradiated at identical conditions. Besides, helium bubbles generated in the irradiated matrix of the MCA are much smaller, compared with those in the pure tungsten and other tungsten-rich alloys previously reported. The exceptional radiation resistance of the present WTaCrV alloy can be mainly attributed to two synergistic mechanisms. First, the high lattice distortion of the solid solution matrix promotes the local non-directional diffusion of irradiation defects, effectively suppressing the aggregation of irradiation defects and helium atoms along specific orientations. This facilitates more uniform nucleation of helium bubbles in the alloy matrix. Second, carbon was introduced during fast hot pressing sintering as interstitial solute to form carbon-rich coherent ordered nanoprecipitates. The carbon-vacancy complexes generated in the nanoprecipitates inhibit the nucleation and aggregation of helium atoms at the vacancies during He+ irradiation. The above two mechanisms synergistically enhance the resistance against He+ irradiation. This work thus demonstrates a design strategy for high radiation resistance alloys by introducing well-tuned ordered coherent nanoprecipitates in multicomponent alloy systems.

Record-high heat transfer performance of spray cooling on 3D-printed hierarchical micro/nano-structured surface

Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence, communications, electric vehicles, defense and aerospace sectors. Spray cooling, which combines forced convection with phase-change latent heat of working fluids, is promising for high flux heat dissipation. Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux (CHF), leading to a low heat transfer coefficient (HTC). Micro/nanostructured surfaces can enhance boiling, but bubbles inside the structures tend to form a vapor blanket, which can deteriorate heat transfer. This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional (3D) ordered hierarchical micro/nano-structured surface. The hierarchical micro/nanostructured surface is designed to coordinate the transport of spray droplets, capillary liquid films, and boiling bubbles to enhance spray cooling performance. Boiling inversion where superheat decreases with increasing heat flux is observed, leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation. Unprecedented CHF is obtained by overcoming the liquid-vapor counterflow, i.e., synergistically facilitating bubble escape and liquid permeation. A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of 1273 W/cm2 and an HTC of 443.7 kW/(m2 K) over a 1 cm2 heating area.

Numerical study on cavitation generation induced by the high-speed jet impact on the water surface

The complex interaction between shock waves and two-phase interfaces can generate cavitation. In this study, the cavitation induced by the high-speed jet impact on the water surface was investigated. The mixture fluid is modeled using the barotropic equation of state under the framework of the two-phase flow model, which can describe the mixture of air, water, and vapor with any proportion. Through constructing a 1D Riemann problem for the impact-induced cavitation phase transition, it indicates that the coupling effect of multiple rarefaction waves emitted from the two-phase interface is responsible for the cavitation phase transition inside the liquid. Then, a 3D (three-dimensional) simulation regarding the impact of a high-speed jet on the water surface was conducted and validated against previous experiments that captured the cavitation phase transition phenomenon in the central region after the jet impact. The 3D simulation results revealed the spatial structure and development process of shock waves in detail. The coupling effects of shock waves and two-phase interfaces generate a ring-shaped rarefaction wave, which develops radially inward and superimposes, resulting in the formation of acorn-shaped cavitation bubble nuclei inside the water. The 3D simulation can provide spatial shock/rarefaction wave structures and internal flow details that have never been obtained in experiments, such as shock generation and propagation, rarefaction wave generation and center convergence, and the internal structure of acorn-shaped cavitation nucleation. Furthermore, the influence of the jet velocity on the cavitation intensity was analyzed, and a quantitative relationship was provided.

Extended quantum molecular dynamics model predicts new breathing modes in $$^{36}$$Ar bubble nuclei

Extended quantum molecular dynamics model predicts new breathing modes in $$^{36}$$Ar bubble nuclei

Constraints on Metastable Dark Energy Decaying into Dark Matter

We revisit the proposal that an energy transfer from dark energy into dark matter can be described in field theory by a first order phase transition. We analyze a metastable dark energy model proposed in the literature, using updated constraints on the decay time of a metastable dark energy from recent data. The results of our analysis show no prospects for potentially observable signals that could distinguish this scenario from the ΛCDM. We analyze, for the first time, the process of bubble nucleation in this model, showing that such model would not drive a complete transition to a dark matter dominated phase even in a distant future. Nevertheless, the model is not excluded by the latest data and we confirm that the mass of the dark matter particle that would result from such a process corresponds to the mass of an axion-like particle, which is currently one of the best motivated dark matter candidates. We argue that extensions to this model, possibly with additional couplings, still deserve further attention as it could provide an interesting and viable description for an interacting dark sector scenario based in a single scalar field.

Estimating the uncertainty of cosmological first order phase transitions with numerical simulations of bubble nucleation

In order to study the validity of analytical formulas used in the calculation of characteristic physical quantities related to vacuum bubbles, we conduct several numerical simulations of bubble kinematics in the context of cosmological first-order phase transitions to determine potentially existing systematic uncertainties. By comparing with the analytical results, we obtain the following observations: (1) The simulated false vacuum fraction will approach the theoretical one with increasing simulated volume. When the side length of the cubic simulation volume becomes larger than 14.5βth−1, the simulated results do not change significantly. (2) The theoretical expected total number of bubbles do not agree with the simulated ones, which may be caused by the inconsistent use of the false vacuum fraction formula. (3) The different nucleation rate prefactors do not affect the bubble kinetics much. (4) The lifetime distribution in the sound shell model does not obey an exponential distribution, in such a way as to cause a suppression in the gravitational wave spectra. Published by the American Physical Society 2024

Molecular dynamics study of the mechanism of explosive boiling on hybrid wettability surfaces

In this work, molecular dynamics (MD) simulation is applied to study the effect of heating surfaces with different hydrophobicity occupancy ratios (the ratio of the surface area of hydrophobic spots to the total area of the heating surface) on the boiling process of the liquid film explosion. At the same time, the mechanism is revealed from the trajectory of argon atoms. The simulation results showed that the onset of explosive boiling was later for purely hydrophilic surfaces than for hybrid wettability surfaces with a hydrophobicity percentage of <11%. The earliest onset of explosive boiling was observed for the heated surfaces with a hydrophobicity ratio of 6%. In addition, it was found that the superheat required for explosive boiling tended to decrease first and then increase with the gradual increase of the hydrophobicity ratio. Hydrophobic spots arranged on the surface provided bubble nucleation earlier for explosive boiling while enhancing convective heat transfer and thermal perturbation. The critical heat flux (CHF) of the heated surfaces with a hydrophobicity ratio of <11% were all greater than that of the purely hydrophilic surfaces, and all reached the CHF before the purely hydrophilic surfaces.

Experimental study on the pool boiling heat transfer of R134a outside various enhanced tubes

The paper aims to experimentally study the pool boiling heat transfer properties of R134a outside various enhanced tubes under saturation temperatures ranged from 3 to 40 °C and heat fluxes of 5.5∼76.5 kW·m-2. One smooth tube and three micro-fin tubes were selected as the tested tube. Based on the experimental results, it can be found that the pool boiling heat transfer coefficient increases firstly and decreases later with increasing heat flux, but saturation temperature and water velocity have little effect on the heat transfer coefficient. Under the same experimental conditions, refrigerant thermal resistance ratio is greater than 0.5 during the heat transfer process. The micro-fin facilitates the bubble nucleation with the heat transfer enhancement ratio varying in the range of 2.08∼4.59. Moreover, the experimental values are compared with the calculated values of three existing correlations for the pool boiling heat transfer coefficient. The experimental variables, which mainly includes saturation temperature, heat flux and tube structure, have great influences on the correlation accuracy. Finally, to eliminate the influence of the experimental variable, a new correlation was proposed by introducing ratio of fin height to outer diameter of the tested tube. After the further verification, the proposed correlation can predict the heat transfer coefficient with the mean deviation of less than 10%.

Performance of surface structures in enhancing heat transfer rates of miniaturized pulsating heat pipe

Enhancement of the thermal performance by modifying the evaporator surface of a miniaturized pulsating heat pipe (PHP) is the primary target of the present work. Four PHPs having different evaporator surface types i.e., smooth, dimple cavity array, tunnel cavity, and rectangular cavity array were investigated numerically to compare the gas-liquid interfacial behavior and evaluate the role of bubble nucleation, slug-plug movement, and drop-film condensation on the thermal performance. Detailed modeling of evaporating and condensing interfaces shows that activation of nucleation sites at all defined discrete structures and undisturbed liquid flow path at the evaporator promote heat transfer rate. Through thermo fluidic analysis around different surface structures, evaporation dynamics is analyzed to understand the suitability of a structure type for enhancement of heat transfer. Associated slug-plug motion through the adiabatic zone and processes at the condenser have been also discussed to propose the characteristics of an ideal enhanced PHP. The capacity to transfer heat has been also characterized using thermal resistance for different structured PHPs which may be a guiding factor for the design of heat sinks for thermal applications.

Nonsingular cosmology from nonsupersymmetric AdS instability conjecture

We show that the nonsupersymmetric anti–de Sitter (AdS) instability conjecture can point to how quantum gravity removes the initial big bang singularity, leading to a potential resolution for the past-incomplete inflationary Universe. From the constraints on the dynamics of the Universe realized as the nucleation of a thin-wall bubble mediating the decay of the nonsupersymmetric AdS vacuum, we find the critical temperature Tc and the critical scale factor ac for which the Universe exists. These critical quantities are all finite and determined in terms of the parameters specifying the stringy 10D AdS vacuum solutions. Additionally, we derive the prediction of quantum gravity for Tc and ac relying on the inflationary observations. Published by the American Physical Society 2024

Microstructure evolution mechanism of WB-doped Fe-based amorphous composite coating under proton beam irradiation

Fe-based amorphous coatings exhibit exceptional irradiation resistance attributed to their distinct topologically disordered structure, rendering them highly attractive for advanced nuclear energy applications. The incorporation of WB secondary phase doping can notably alter the coating to enhance its operational safety. In this investigation, three different Fe-based composite coatings, with varying WB doping levels of 5 %, 10 %, and 15 % were fabricated through the High-Velocity Oxy-Fuel (HVOF) spraying technique. Irradiation tests were conducted at room temperature utilizing a proton beam with an energy of 1.52 MeV to simulate neutron irradiation environment in a nuclear reactor. The microstructure evolution before and after irradiation was systematically investigated with XRD, SEM, and TEM techniques. The results demonstrated that proton irradiation induced free volume, crystallization and H bubbles evolution. The doping of WB diminished the proton implantation dose threshold for segregation in irradiation plateaus while enhancing the growth of precipitates around the damage zone by inducing the production of M23C6 carbides and, at the same time, increasing the probability of H bubble nucleation and growth. These findings provide insights for iterative updates in Fe-based amorphous materials, informing their further development and application.

Acoustically controlled bubble nucleation

Fundamental studies of single bubble heat transfer are crucial to improve our understanding of boiling phenomena and develop modeling and simulation tools for the design and optimization of boiling systems. However, conducting these kinds of experiments over a wide range of conditions is challenging and may involve expensive and complicated experimental techniques (e.g., lasers) to isolate and control bubble nucleation. In this work, we introduce a new technique to control nucleation with an ultrasonic beam. A low-cost and widely available piezoelectric disc driven at megahertz frequencies directed at a heated surface can increase the time-averaged pressure and suppress evaporation until the moment the transducer is turned off, allowing us to control the incipience of boiling to within 150 µs. We demonstrate this technique by measuring the physical and thermal footprint of natural and acoustically controlled bubbles with high-resolution infrared thermometry and phase detection diagnostics. We were able to raise the bubble nucleation temperature by over 30 K compared to a reference case with no acoustic control, which significantly changes bubble growth rate, microlayer formation and evaporation and departure diameter. We highlight the potential of this new low-cost and easy-to-use technique in a variety of different boiling heat transfer studies.

Computational fluid dynamics simulation of cryogenic vertical upflow boiling under Earth gravity

This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer phenomena important to space applications. The computational fluid dynamics (CFD) model utilized the coupled level set volume of fluid (CLSVOF) method, incorporating additional source terms for bubble collision dispersion force and shear lift force in the momentum conservation equation to enhance simulation accuracy. The simulations were conducted for two mass velocities (G = 526 and 804 kg/m2s) and three different heat flux levels (approximately 10%, 30%, and 70% of critical heat flux (CHF) under Earth gravity. The model was validated against measured wall temperature data acquired from the authors’ previous experimental studies, demonstrating average deviations of less than 2.8 K across all operating conditions. The simulated two-phase flow contours illustrated various flow patterns, including bubbly, slug, churn, and annular. Both mass velocity and heat flux were observed to impact the onset of nucleate boiling (ONB), bubble nucleation, growth, and coalescence, and overall vapor structure. The simulations also offered insight into axial and radial void fraction and velocity profiles, revealing local flow acceleration trends synchronized with void fraction development. A comparison between predicted and measured bulk fluid temperature profiles showed excellent agreement, further validating the CFD model’s accuracy and practical usefulness for two-phase cryogenic flow boiling simulations in space applications.

Phase change and fluid transport in porous evaporators

Porous evaporators have become the core component of energy systems such as thermal management of electronic equipment, solar steam power generation, and wet power generation by the advantages of their large specific surface area, high-efficiency heat transfer, and liquid self-transportation. How direct observation of the heat and mass transfer process inside the porous evaporator has always puzzled researchers, resulting in a lack of a theoretical foundation for the optimization of the porous structure. This limitation has significantly hindered improvements in the performance of energy systems. To address this challenge, this study proposes a novel visualization approach that integrates three-dimensional (3D) printing and Indium-Tin Oxide (ITO) glass observation of the phase change region in the evaporator. The key novel findings are that: (1) By controlling the pore size to match the bubble nucleation size, the phase change mode can transition from boiling to thin film evaporation, forming a continuous easy vapor escape channel and enhancing heat transfer. (2) The larger the capillary force of the porous structure, the stronger the locking force at the vapor–liquid interface, which ensured the stability of vapor escape and liquid transport at higher heat flux. (3) An ideal porous evaporator should possess strong liquid locking ability, feature pore structures at the phase change point within the size range of vapor nucleation, and simultaneously exhibit large pore size conducive to vapor escape. This investigation casts a new light on the fluid transport and phase change characteristics of porous evaporators, laying a theoretical foundation for the design of porous evaporators.

Modeling the chaotic dynamics of bubble growth under hydrodynamic interactions in pool boiling

This study seeks to understand the origins of intermittency in quantities of interest in pool boiling, such as bubble departure diameter and growth time. The intermittency of nucleation site activity due to hydrodynamic and thermal interactions with nearby nucleation sites is well-established; however, few mechanistic models have been developed that predict such intermittency. Here we assume a fluctuating pressure field at a nucleation site due to an adjacent bubble which alters bubble growth depending on the phase of the pressure oscillation with respect to the instant of bubble nucleation. The results suggest that even when a single departure frequency is assumed for nearby bubbles, its effect on the nucleation site being considered causes aperiodicity and intermittency in bubble departure quantities. The effects of pressure field phase angle, degree of superheat, and choice of force balance model on the bubble departure quantities are examined. The phase angle is shown to play a major role in determining bubble departure diameter and growth time. The departure diameter is observed to have a broad distribution, belying the assumption of a unique value. Period doubling of the ebullition cycle is observed for some conditions, a phenomenon documented by other investigators. A multifractal analysis of the time series of departure events indicates the presence of long term temporal correlations, which become weaker with increasing superheat. The second order Hurst exponent of the structure functions of departure events appears to have a universal behavior with Jakob number, independent of the choice of liquid. The Hurst exponent rises from zero to a value close to 0.5 at large superheats, suggesting a continuous transition from an ordered state to a disordered state along the boiling curve.

Analysis of pool boiling heat transfer characteristics on copper-based structured surfaces modified with superhydrophilic, hydrophobic, superhydrophobic and hybrid biphilic properties

This study involves the fabrication and characterization of original, hydrophobic, superhydrophilic, superhydrophobic and hybrid biphilic pattern coupled with the flat and pillar-structured surfaces. The boiling performance of the seven wettability structured surfaces is experimentally and numerically investigated, aiming at analyzing the boiling mechanism of wetting pattern coupled with structures. The findings indicate that coupling superhydrophobicity pillar structure surface (SHO-PS) result in an excellent boiling performance, the superhydrophilicity have difficulty in improving the heat transfer coefficient and critical heat flux. Analysis of the bubble dynamics behaviors reveals a strong positive correlation between the bubble nucleation sites and bubble departure diameter, except for hydrophobic flat structured surface (HO-FS) and superhydrophobicity pillar structured surface (SHO-PS), which exhibit the negative correlation. The bubble departure frequency shows a linear correlation with the contact angle of all the modified surfaces. In the simulation, it is observed that the similar bubble dynamic behaviors in experiment.