Bubble Nucleation Rate Research Articles

Supermassive Primordial Black Holes for Nano-Hertz Gravitational Waves and High-redshift JWST Galaxies

Recently, observational hints for supermassive black holes have been accumulating, prompting the question: Can primordial black holes (PBHs) be supermassive, particularly with masses M ≳ 109 M ⊙? A supercritical bubble, containing an inflating baby universe, that nucleated during inflation can evolve into a PBH in our observable universe. We find that when the inflaton slowly transitions past a neighboring vacuum, the nucleation rate of supercritical bubbles inevitably peaks, leading to a mass distribution of multiverse PBHs with a peak mass up to M ≳ 1011 M ⊙. Thus, our mechanism naturally provides a primordial origin for supermassive black holes.

Influence of cavity geometry on the bubble dynamics of nucleate pool boiling

Nucleate pool boiling is known for its exceptional heat transfer coefficients, with the use of cavities further improving bubble nucleation and heat transfer rate. To promote this heat transfer enhancement technique, a thorough understanding of the influence of cavity geometry on single bubble dynamics is required. The influence of depth and radius of cylindrical and conical cavities on the bubble dynamics of nucleate pool boiling of R1234yf were numerically investigated. The cavity radius was varied between 50 and 400 μm and the cavity depth between 100 and 1000 μm at a fixed heat flux of 28 kW/m2. It was found that the maximum equivalent diameter prior to departure was constant for cavities with radii smaller than 120 μm, while it increased linearly when increasing the cavity radius further. Cylindrical cavities exhibited high stability regardless of cavity radius or depth whereas conical cavities showed a decrease in vapor retention with increasing cavity angle. During the necking phase, the bubble interface became pinned at the cavity edge, depending on conical cavity angle, implying that smaller radii allowed for enhanced surface rewetting. Conical cavities could be considered as cylindrical cavities when the cavity angle was less than a quarter of the interface contact angle. When translating the single cavity findings to cavity array design, cylindrical cavities were recommended as they allowed for stable bubble behavior. For increased nucleation zones and rewetting, a sub-critical radius was recommended. Wider cavities were recommended for high superheat conditions as larger bubbles could enhance bubble growth.

Gravitational waves from supercooled phase transitions: dimensional transmutation meets dimensional reduction

Models with radiative symmetry breaking typically feature strongly supercooled first-order phase transitions, which result in an observable stochastic gravitational wave background. In this work, we analyse the role of higher-order thermal corrections for these transitions, applying high-temperature dimensional reduction to a theory with dimensional transmutation. In particular, we study to what extent high-temperature effective field theories (3D EFT) can be used. We find that despite significant supercooling down from the critical temperature, the high-temperature expansion for the bubble nucleation rate can be applied using the 3D EFT framework, and we point out challenges in the EFT description. We compare our findings to previous studies and find that the next-to-leading order corrections obtained in this work have a significant effect on the predictions for GW observables, motivating a further exploration of higher-order thermal effects.

Bubble nucleation and growth on microstructured surfaces under microgravity

Understanding the dynamics of surface bubble formation and growth on heated surfaces holds significant implications for diverse modern technologies. While such investigations are traditionally confined to terrestrial conditions, the expansion of space exploration and economy necessitates insights into thermal bubble phenomena in microgravity. In this work, we conduct experiments in the International Space Station to study surface bubble nucleation and growth in a microgravity environment and compare the results to those on Earth. Our findings reveal significantly accelerated bubble nucleation and growth rates, outpacing the terrestrial rates by up to ~30 times. Our thermofluidic simulations confirm the role of gravity-induced thermal convective flow, which dissipates heat from the substrate surface and thus influences bubble nucleation. In microgravity, the influence of thermal convective flow diminishes, resulting in localized heat at the substrate surface, which leads to faster temperature rise. This unique condition enables quicker bubble nucleation and growth. Moreover, we highlight the influence of surface microstructure geometries on bubble nucleation. Acting as heat-transfer fins, the geometries of the microstructures influence heat transfer from the substrate to the water. Finer microstructures, which have larger specific surface areas, enhance surface-to-liquid heat transfer and thus reduce the rate of surface temperature rise, leading to slower bubble nucleation. Our experimental and simulation results provide insights into thermal bubble dynamics in microgravity, which may help design thermal management solutions and develop bubble-based sensing technologies.

The evolution of H+ implantation induced defects and the different cleavage behaviors under different thermal excitation in 4H-SiC during Crystal-Ion-Slicing technology

The Silicon Carbide (SiC) composite substrate fabricated by crystal-ion-slicing (CIS) technology can be an excellent material platform to realize a variety of microelectronic device functions. The difference in the surface morphology of the exfoliated films under different thermal excitation conditions was found in research. In order to explore the different cleavage behaviors resulting the differences, the basic models of defect evolution during the fabrication of SiC film by CIS technique is established based on AFM, Raman, XRD and TEM material characterizations, which can be divided into detachment, aggregation, growth, and concatenation stages. Combining the molecular dynamics simulation results and defect evolution models, the difference of the cleavage behavior leading to different surface topography under different anneal thermal excitations can be attributed to the different H2 bubble nucleation rate. The work in this paper investigates the fundamental physicochemical phenomena of defect evolution and crystal cleavage in CIS technology, and guides the improvement of heat treatment process, which is beneficial to achieve neat cleavage for the transfer of SiC single crystal film and to realize available heterogeneous integration of SiC single crystal film.

Effect of RIBS/FINS and Aspect Ratio on Flow Boiling Characteristics in Conventional Channels

Abstract In this work, experiments are conducted with conventional rectangular channels of two different aspect ratios (AR = w/d) for the horizontal boiling flow conditions at atmospheric pressure. Distilled water was used as the working substance. The heat transfer coefficients (HTC) were measured for mass fluxes and heat fluxes ranging from 85.94 kg/m2-s to 343.77 kg/m2-s and 10 kW/m2 to 100 kW/m2, respectively, and at inlet subcooled temperatures of 303 K, 313 K, and 323 K. Visualization of the boiling phenomenon was done using a high-speed camera for the two channels under similar conditions. The results show that the AR has a dominant effect on the HTC. At low heat flux values, higher HTC was noticed for the channel of higher AR (AR = 1.25) whereas, at high heat flux conditions, the HTC is higher for the channel of lower AR (AR = 0.2). With an increase in inlet subcooled temperature, the HTC decreased for both channels due to increased thermal boundary layer thickness and reduced bubble formation. Further, the channel of AR = 1.25 with ribs/fins performed better than the smooth channel due to the high bubble nucleation rate.

BubbleDet: a Python package to compute functional determinants for bubble nucleation

We present a Python package BubbleDet for computing one-loop functional determinants around spherically symmetric background fields. This gives the next-to-leading order correction to both the vacuum decay rate, at zero temperature, and to the bubble nucleation rate in first-order phase transitions at finite temperature. For predictions of gravitational wave signals from cosmological phase transitions, this is expected to remove one of the leading sources of theoretical uncertainty. BubbleDet is applicable to arbitrary scalar potentials and in any dimension up to seven. It has methods for fluctuations of scalar fields, including Goldstone bosons, and for gauge fields, but is limited to cases where the determinant factorises into a product of separate determinants, one for each field degree of freedom. To our knowledge, BubbleDet is the first package dedicated to calculating functional determinants in spherically symmetric backgrounds.

Consequences of a stabilizing field’s self-interactions for RS cosmology

It has been argued that the Randall-Sundrum (RS) phase transition rate is suppressed when the holographic theory corresponds to a large N Yang-Mills and when the stabilizing field has a small mass. Here we argue that self-interactions can alleviate the latter suppression. We consider a cubic term in the bulk potential for the Goldberger-Wise (GW) scalar that is responsible for stabilizing the RS geometry. Adding a cubic term suffices to separate the two roles of the GW stabilization: generating a large hierarchy and triggering confinement. We study the resulting radion potential and the dynamics of the early universe phase transition. For a negative coefficient of the cubic term, the effect of the cubic becomes important in the infra-red, and the resulting radion potential is deeper, thereby increasing the radion mass while maintaining a large hierarchy. Staying within the radion effective field theory, we calculate the rate of bubble nucleation from the hot phase to the confined RS phase, both in thin and thick wall limits. The cubic term enhances the rate and allows relaxing the condition on the maximum number of colors Nmax of the dual theory for which the phase transition can be completed. Importantly, this reduces the amount of supercooling that the false vacuum undergoes, increases the peak frequency of the gravitational waves (GW) produced from bubble collisions, and reduces the strength of the GW signal. The reduced GW signal is however still within the reach of proposed space-based GW detectors.

Primordial black holes from strong first-order phase transitions

We study the formation of primordial black holes (PBHs) in strongly super-cooled first-order phase transitions. The mechanism is based on the presence of remnants dominated by the false vacuum that scale slower with the expansion of the Universe than their surroundings where this energy was already converted into radiation. We compute the PBH formation from these remnants including the contribution from the false vacuum and the bubble walls, by estimating the collapse using the hoop conjecture and by considering both regions collapsing immediately when entering the horizon and sub-horizon regions that collapse as their compactness grows. We show that for exponential bubble nucleation rate, Γ ∝ eβt, the primordial black hole formation implies β/H ≳ 3.8, where H denotes the Hubble rate, if the potential energy of the false vacuum is ∆V ≲ (1012 GeV)4, as otherwise a too large abundance of long-lived PBHs forms. The observed dark matter abundance can be formed in asteroid mass PBHs if β/H ≃ 3.8 and 105 GeV ≲ ∆V1/4 ≲ 108 GeV. Finally, we consider also the effect of the second order correction to the exponential nucleation rate showing that the PBH abundance is mainly determined by the average radius of the true vacuum bubbles.

An Overview of Flashing Phenomena in Pressure Hydrometallurgy

Pressure hydrometallurgy has attracted much attention for its characteristics, such as the high adaptability of raw materials and environmental friendliness. Flashing (flash boiling or flash evaporation) refers to the phase change phenomenon from liquid to gas triggered by depressurization, which is an important connection between high-pressure processes and atmospheric ones in pressure hydrometallurgy. This paper takes the flashing process in zinc leaching and alumina Bayer processes as examples, describes the flashing process in pressure hydrometallurgy in detail for the first time, and shows the importance of the flashing process in energy recovery, solution concentration, and liquid balance, as well as increasing equipment life. According to solid holdup (the volume percentage of solid), this paper proposes to divide the flashing process into solution flashing (low solid holdup) and slurry flashing (high solid holdup). A further focus is put on reviewing the state of the art of related studies. The results reveal that the research on the flashing process in pressure hydrometallurgy is scarce and often oversimplified, e.g., ignoring the BPE (boiling point elevation) and NEA (non-equilibrium allowance) in solution flashing and the effect of solid particles in slurry flashing. Computational fluid dynamic (CFD) simulation is a promising tool for investigating the flashing process. Based on the progress made in other fields, e.g., seawater desalination, nuclear safety analysis, and engine fuel atomization, we suggest that solution flashing can be studied using the CFD–PBM (population balance model) coupled two-fluid model, since a wide size range of bubbles will be generated. For slurry flashing, the effect of solid holdup on the bubble nucleation rate and mechanism as well as other bubble dynamics processes should be accounted for additionally, for which a quantitative description is still lacking. Meanwhile, data for validating the numerical method are scarce because of the harsh experimental conditions, and further research is needed. In summary, this work presents an overview of the flashing processes in pressure hydrometallurgy and some guidelines for future numerical studies.

Experimental investigation of pulsating heat pipes with different evaporator roughness values

Three transparent experimental setups of flat-plate pulsating heat pipes were investigated, each with a different channel surface roughness in the evaporator section. Roughness was varied using milling and sand blasting techniques. Experiments were conducted in different orientations with the refrigerant R1233zd(E) with filling ratios of 30%, 50% and 70%. Heat flux values between 5 and 45 W and condenser temperatures of 0 °C, 20 °C and 40 °C were applied. Low filling ratios, high condenser temperatures and high heat flux values were found to achieve the lowest thermal resistances. Increased surface roughness in the evaporator section also reduced the thermal resistance. The effect was especially pronounced for low heat flux values. The surface roughness in the evaporator section was analyzed with a confocal and a novel evaluation method with particular regard to the influence of the surface structure on the bubble nucleation behavior was introduced. The evaluation method yielded estimated bubble radius distribution profiles of the cavities found in the surface structure. The data was then used to calculate a mean bubble nucleation radius for the surface structure of each test setup. Combined with the pool boiling nucleation equation this resulted in a theoretical relative bubble nucleation threshold calculated for each measurement point. It was found that the theoretical bubble nucleation threshold could be directly correlated with the thermal resistance and overall performance of the pulsating heat pipe. In the experiments, bubble nucleation rates were determined by evaluating high-speed camera recordings using a bubble tracking algorithm. For a 70% filling ratio the bubble nucleation rate was found to increase up to a maximum with increasing heat flux. When approaching high heat flux values the bubble nucleation rate dropped again. The quantification of the connection between bubble nucleation threshold and thermal performance is a novelty in this work, as well as the quantification of the bubble nucleation rate in an experimental setup. The work offers meaningful insights into the thermo-hydraulic behavior of a PHP.

Constraining the gravitational-wave spectrum from cosmological first-order phase transitions using data from LIGO-Virgo first three observing runs

We search for a first-order phase transition (PT) gravitational wave (GW) signal from Advanced LIGO and Advanced Virgo's first three observing runs. Due to the large theoretical uncertainties, four shapes of GW energy spectral from bubble and sound wave collisions widely adopted in literature are investigated, separately. Our results indicate that there is no evidence for the existence of such GW signals, and therefore we give the upper limits on the amplitude of GW energy spectrum Ωpt(f *) in the peak frequency range of f * ∈ [5,500] Hz for these four theoretical models, separately. We find that Ωpt(f * ≃ 40 Hz) < 1.3 × 10-8 at 95% credible level, and roughly H */β ≲ 0.1 and α ≲ 1 at 68% credible level in the peak frequency range of 20 ≲ f * ≲ 100 Hz corresponding to the mostsensitive frequency band of Advanced LIGO and Advanced Virgo's first three observing runs, where H * is the Hubble parameter when PT happens, β is the bubble nucleation rate and α is the normalized latent heat.

The Effects of Viscosity and Capillarity on Nonequilibrium Distribution of Gas Bubbles in Swelling Liquid–Gas Solution

A detailed statistical description of the evolution of supersaturated-by-gas solution at degassing has been presented on the basis of finding the time-dependent distribution in radii of overcritical gas bubbles. The influence of solution viscosity and capillarity via internal pressure in the bubbles on this distribution has been considered until the moment when the gas supersaturation drops due to depletion and stops nucleation of new overcritical gas bubbles. This study is based on our previous results for the nonstationary growth rates of overcritical bubbles depending on gas supersaturation, diffusivity and solubility in solution, solution viscosity, and surface tension on bubble surface. Other important factors are linked with the initial rate of homogeneous gas bubble nucleation and coupling between diffusivity and viscosity in the solution. Here, we numerically studied how all these factors affect the time-dependent distribution function of overcritical bubbles in their radii, maximal and mean bubble radii, and the time-dependent swelling ratio of a supersaturated-by-gas solution in a wide range of solution viscosities.

Bubble nucleation in a cold spin 1 gas

Cold atomic gases offer the prospect of simulating the physics of the very early Universe in the laboratory. In the condensate phase, the gas is described by a field theory with key features of high energy particle theory. This paper describes a three level system which undergoes a first order phase transition through the nucleation of bubbles. The theoretical investigation shows bubbles nucleating in two dimensions at non-zero temperature. There is good agreement between the bubble nucleation rates calculated from a stochastic projected Gross–Pitaevskii equation and from a non-perturbative instanton method. When an optical box trap is included in the simulations, the bubbles nucleate preferentially near the walls of the trap.

Stretching-induced foaming of gas-laden thermoplastic elastomers

Stretching-induced foaming of gas-laden thermoplastic elastomer (TPE), styrene-isobutylene-styrene (SIBS), was successfully conducted. CO2-laden TPE plates were prepared by an injection molding process without foaming and later foamed by stretching. The effects of CO2 concentration in the gas-laden elastomer, stretching rate (strain rate), and strain on bubble (cell) diameter and bubble density of the resulting foams were investigated, and a new bubble nucleation rate model was proposed to reflect the stretching effect on bubble nucleation in foam. The model has the stretching rate-dependent elastic strain energy in the bubble nucleation rate to explain why the higher stretching rate and the higher strain produce more bubbles of smaller size. The proposed bubble nucleation model clarifies the effect of the elastic modulus of TPE on the bubble nucleation barrier.

First-order electroweak phase transitions: A nonperturbative update

We study first-order electroweak phase transitions nonperturbatively, assuming any particles beyond the Standard Model are sufficiently heavy to be integrated out at the phase transition. Utilising high temperature dimensional reduction, we perform lattice Monte-Carlo simulations to calculate the main quantities characterising the transition: the critical temperature, the latent heat, the surface tension and the bubble nucleation rate, updating and extending previous lattice studies. We focus on the region where the theory gives first-order phase transitions due to an effective reduction in the Higgs self-coupling and give a detailed comparison with perturbation theory.

Bubble Formation in Magma

Volcanic eruptions are driven by bubbles that form when volatile species exsolve from magma. The conditions under which bubbles form depend mainly on magma composition, volatile concentration, presence of crystals, and magma decompression rate. These are all predicated on the mechanism by which volatiles exsolve from the melt to form bubbles. We critically review the known or inferred mechanisms of bubble formation in magmas: homogeneous nucleation, heterogeneous nucleation on crystal surfaces, and spontaneous phase separation (spinodal decomposition). We propose a general approach for calculating bubble nucleation rates as the sum of the contributions from homogeneous and heterogeneous nucleation, suggesting that nucleation may not be limited to a single mechanism prior to eruption. We identify three major challenges in which further experimental, analytical, and theoretical work is required to permit the development of a general model for bubble formation under natural eruption conditions. ▪ We review the mechanisms of bubble formation in magma and summarize the conditions under which the various mechanisms are understood to operate. ▪ Bubble formation mechanisms may evolve throughout magma ascent as conditions change such that bubbles may form simultaneously and sequentially via more than one mechanism. ▪ Contributions from both homogeneous nucleation and heterogeneous nucleation on multiphase crystal phases can be captured via a single equation. ▪ Future work should focus on constraining macroscopic surface tension, characterizing the microphysics, and developing a general framework for modeling bubble formation, via all mechanisms, over natural magma ascent pathways.

Convergence of the nucleation rate for first-order phase transitions

This paper investigates the importance of radiative corrections for first-order phase transitions, with particular focus on the bubble-nucleation rate. All calculations are done with a strict power-counting, and observables are consistently calculated at every order. This ensures that physical quantities are gauge and renormalization-scale invariant. Furthermore, to avoid large logarithms at high-temperatures, an effective three-dimensional theory is used. This effective theory automatically incorporates higher-order thermal masses. The results of this paper indicate that sub-leading corrections to the rate can be large. This is partly because radiative corrections are enhanced for large bubbles. To illustrate the calculations, three models are considered: a real-scalar model, a radiative-barrier model, and a model with an effective dimension $6$ operator. Relevant observables are calculated for each model, and the reliability of perturbation theory is discussed.

Extending and validating bubble nucleation rate predictions in a Lennard-Jones fluid with enhanced sampling methods and transition state theory.

We calculate bubble nucleation rates in a Lennard-Jones fluid through explicit molecular dynamics simulations. Our approach-based on a recent free energy method (dubbed reweighted Jarzynski sampling), transition state theory, and a simple recrossing correction-allows us to probe a fairly wide range of rates in several superheated and cavitation regimes in a consistent manner. Rate predictions from this approach bridge disparate independent literature studies on the same model system. As such, we find that rate predictions based on classical nucleation theory, direct brute force molecular dynamics simulations, and seeding are consistent with our approach and one another. Published rates derived from forward flux sampling simulations are, however, found to be outliers. This study serves two purposes: First, we validate the reliability of common modeling techniques and extrapolation approaches on a paradigmatic problem in materials science and chemical physics. Second, we further test our highly generic recipe for rate calculations, and establish its applicability to nucleation processes.

Variations on vacuum decay: The scaling Ising and tricritical Ising field theories

We study the decay of the false vacuum in the scaling Ising and tricritical Ising field theories using the Truncated Conformal Space Approach and compare the numerical results to theoretical predictions in the thin wall limit. In the Ising case, the results are consistent with previous studies on the quantum spin chain and the $\varphi^4$ quantum field theory; in particular we confirm that while the theoretical predictions get the dependence of the bubble nucleation rate on the latent heat right, they are off by a model dependent overall coefficient. The tricritical Ising model allows us on the other hand to examine more exotic vacuum degeneracy structures, such as three vacua or two asymmetric vacua, which leads us to study several novel scenarios of false vacuum decay by lifting the vacuum degeneracy using different perturbations.