Bubble Nucleation Research Articles

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.

Investigating bubble-induced overpotential, current non-uniformity, and bubble distribution in flow-based water electrolyzers: A numerical study

The transition towards a sustainable energy landscape necessitates efficient and scalable technologies for renewable energy storage. Water electrolysis, a process that converts electrical energy into chemical energy stored in hydrogen, holds immense potential for integration with intermittent renewable sources. However, the performance and efficiency of water electrolyzers are impeded by the complex multiphase flow dynamics involving bubble nucleation, growth, and transport within the electrochemical cell. This study employs state-of-the-art three-dimensional multiphase flow simulations to unravel the intricate interplay between bubbles and the electrochemical processes in a parallel-electrodes flow-based electrolyzer (PE-FBE). By accurately capturing bubble-electrolyte interfaces, the simulations quantify the detrimental effects of bubbles on overpotentials, current density distribution, and bubble distribution. Crucially, the impact of critical parameters, including flow rate, bubble nucleation size, surfactant addition, and applied current, on these performance metrics is systematically investigated. The findings reveal strategies to mitigate bubble-induced losses, enhance current uniformity, and improve hydrogen purity, paving the way for optimized electrolyzer designs and efficient renewable energy storage.

A study on He ion irradiation damage in (Ti0.25Zr0.25Nb0.25Ta0.25)C high-entropy carbide ceramics from room temperature to 700 °C

High-entropy carbide ceramics (Ti0.25Zr0.25Nb0.25Ta0.25)C with a single-phase rock-salt structure were prepared by hot-pressed sintering. These ceramics were irradiated with 500 keV He2+ ions to fluences of 5 × 1016 ions·cm−2 and 1 × 1017 ions·cm−2 at room temperature to 700 °C. The investigation into irradiation-induced lattice swelling was conducted using grazing incident X-ray diffraction, while microstructure evolution was characterized through transmission electron microscopy. Lattice expansion induced by the He ion irradiation was identified, which highly depends on the irradiation temperature and fluence. Notably, the lattice expansion diminishes with rising irradiation temperature primarily as a result of the dynamic annealing effect. Nano-sized He bubbles, with an average diameter of less than 1 nm were uniformly dispersed within the grain interior. Notably, He bubble nucleation does not exhibit a preference for grain boundaries at 700 °C irradiation. Following He ion irradiation at 350 °C and 700 °C, dislocation loops of 1/3<111> and 1/2<110> with sizes in the ranges of several nanometers were observed. The present study provides insights into high-entropy carbide ceramics with potential applications in the field of nuclear energy.

Free Energy Evaluation of Cavity Formation in Metastable Liquid Based on Stochastic Thermodynamics.

Nucleation is a fundamental and general process at the initial stage of first-order phase transition. Although various models based on the classical nucleation theory (CNT) have been proposed to explain the energetics and kinetics of nucleation, detailed understanding at nanoscale is still required. Here, in view of the homogeneous bubble nucleation, we focus on cavity formation, in which evaluation of the size dependence of free energy change is the key issue. We propose the application of a formula in stochastic thermodynamics, the Jarzynski equality, for data analysis of molecular dynamics (MD) simulation to evaluate the free energy of cavity formation. As a test case, we performed a series of MD simulations with a Lennard-Jones (LJ) fluid system. By applying an external spherical force field to equilibrated LJ liquid, we evaluated the free energy change during cavity growth as the Jarzynski's ensemble average of required works. A fairly smooth free energy curve was obtained as a function of bubble radius in metastable liquid of mildly negative pressure conditions.

Molecular insights into vibration-induced phase change dynamics of low-boiling-point refrigerant

Vibration-induced evaporation and boiling has attracted great attention due to its prominent efficiency. However, the understanding of low-boiling-point refrigerant phase change on various vibration and wettability conditions remains to be investigated. In this study, molecular dynamics simulations are performed to explore the vibration-induced phase change performance of R1336mzz(Z) nanofilm over a copper substrate. Results found that the phase change mode of R1336mzz(Z) nanofilm can be divided into diffusive evaporation, nucleate boiling, and film boiling/cavitation. For one thing, the residual ratio of R1336mzz(Z) molecules lies on the vibrational amplitude (A) and frequency (f), with a linear relation to Af3/2 when Af3/2 is less than 150. For another, the molecular motion is originated from joint action of thermal momentum and mechanical tensioning, leading to film boiling or cavitation by tunning the predominant mechanism. In addition, the impacts of interfacial wettability on vibration-induced phase change are discussed in terms of the heat transfer ability and potential barrier for bubble nucleation. Results reveal that hydrophilic surface causes strong attraction at near-wall region to increase heat transfer, while hydrophobic surface shows weak potential barrier, which promotes the occurrence of bubble nucleation. These findings deliver insights to broad the use of high-frequency vibration in industrial applications.

Delaminating Metal–Polymer Composites through CO2 Bubble Nucleation and Crystallization for Material Recycle in Electric Vehicles

Delaminating Metal–Polymer Composites through CO₂ Bubble Nucleation and Crystallization for Material Recycle in Electric Vehicles

Primordial black holes from supercooled phase transitions

Cosmological first-order phase transitions (1stOPTs) are said to be strongly supercooled when the nucleation temperature is much smaller than the critical temperature. These are often encountered in theories that admit a nearly scale-invariant potential, for which the bounce action decreases only logarithmically with temperature. During supercooled 1stOPTs the equation of state of the universe undergoes a rapid and drastic change, transitioning from vacuum domination to radiation domination. The statistical variations in bubble nucleation histories imply that distinct causal patches percolate at slightly different times. Patches which percolate the latest undergo the longest vacuum-domination stage and as a consequence develop large overdensities triggering their collapse into primordial black holes (PBHs). We derive an analytical approximation for the probability of a patch to collapse into a PBH as a function of the 1stOPT duration, β−1, and deduce the expected PBH abundance. We find that 1stOPTs which take more than 15% of a Hubble time to complete (β/H≲7) produce observable PBHs. Their abundance is independent of the duration of the supercooling phase, in agreement with the de Sitter no hair conjecture. Published by the American Physical Society 2024

Nucleation-assisted microthermometry: A novel application to fluid inclusions in halite

Halite deposits have long been utilized for interrogating past climate conditions. Microthermometry on halite fluid inclusions has been used to determine ancient water temperatures. One notable obstacle in performing microthermometric measurements, however, is the lack of a vapor bubble in the single-phase liquid inclusions at room temperature. (Pseudo-) isochoric cooling of the inclusions to high negative pressures, far below the homogenization temperature, has commonly been needed to provoke spontaneous vapor bubble nucleation in the liquid. High internal tensile stress in soft host minerals like halite, however, may induce plastic deformation of the inclusion walls, resulting in a wide scatter of measured homogenization temperatures. Nucleation-assisted (NA) microthermometry, in contrast, employs single ultra-short laser pulses provided by a femtosecond laser to stimulate vapor bubble nucleation in metastable liquid inclusions slightly below the expected homogenization temperature. This technique allows for repeated vapor bubble nucleation in selected fluid inclusions without affecting the volumetric properties of the inclusions, and yields highly precise and accurate homogenization temperatures.In this study, we apply, for the first time, NA microthermometry to fluid inclusions in halite and we evaluate the precision and accuracy of this thermometer utilizing (i) synthetic halite crystals precipitated under controlled laboratory conditions, (ii) modern natural halite that precipitated in the 1980s in the Dead Sea, and (iii) Late Pleistocene halite samples from a sediment core from Death Valley, CA. Our results demonstrate an unprecedented accuracy and precision of the method that provides a new opportunity to reconstruct reliable quantitative temperature records from evaporite archives.

Exploiting Non-Classical Nucleation for Improved Gas Bubble Mitigation on Nickel Electrocatalysts for the Oxygen Evolution Reaction

The efficient transport of gas poses a significant challenge in the design of high-performance gas evolving electrocatalysts. Inefficiencies due to mass transport limitations become more pronounced at the high current densities required in industrial electrolyzers, largely as a result of gas bubbles that obstruct a portion of the electrochemically active surface area of the anode and/or cathode, while also hindering electrolyte transport to the electrode surfaces. One promising approach to mitigate these sources of inefficiency is to engineer micro-to-nanoscale surface textures that promote the favorable growth and release of these bubbles. A range of structures have been shown to improve electrocatalyst performance under both stagnant and induced convection conditions, particularly in applications for hydrogen production via electrocatalytic water splitting in alkaline water electrolyzers.1 Trends between surface texture and electrocatalyst performance have been observed for a range of features, such as pillars,2,3 ridges,4 dimples,5 “cracked” structures,6 and electrodeposited crystalline structures,7 however substantial work is still needed to optimize the designs of these materials. These textured surfaces can influence bubble evolution in various ways, such as by altering the wetting properties of a surface, or by providing preferential nucleation sites. Previous studies have noted that surface structures that provide good control over bubble nucleation can often be adversely affected by increased bubble retention.3–5 The present study investigates a method of fabricating patterned electrocatalysts that provides a fine, tunable control over the distribution of bubble nucleation sites on the surfaces of planar Ni electrocatalysts for the oxygen evolution reaction (OER). These textured surfaces are designed to take advantage of so-called “non-classical nucleation” or “type IV nucleation”, a scenario in which gas is trapped at specific surface sites with an effective radius larger than the critical radius for classical nucleation, thereby allowing spontaneous bubble growth without being required to overcome an activation energy barrier.8 The separation between these sites on the surface of the OER active material (i.e., Ni) is then varied to obtain the most favorable distribution of these non-classical nucleation sites. Chronoamperometry is used to compare the current densities achieved by these patterned Ni electrodes to that of a planar Ni electrode. High speed videography is used to directly measure how these textures influence processes such as bubble growth and detachment, and to determine how these processes influence performance. A better understanding of these gas evolution processes can help lower the energy requirements for electrolyzers and may have more general implications for the design of energy efficient gas evolving electrocatalysts relevant to a variety of industrially important reactions.

(Dielectric Science and Technology Division Poster Award, 1st Place) Effects of Gas Dissolved Water for Ceria Nanoparticles on the SiO2 Film Surface in Post-CMP Cleaning

In the semiconductor industry, there is a growing trend of using smaller ceria nanoparticles (CNPs) during the Swallow Trench Isolation (STI) CMP process. However, the use of these CNPs has made it more difficult to clean residual particles from the SiO2 film surface after CMP. This study aimed to investigate the effects of gas-dissolved water (GDW) on CNP surfaces and the mechanical cleaning effects of nucleated bubbles applying megasonic conditions. The study found that CNP surface was reduced by H2 GDW and CO2 GDW, but oxidized by O2 GDW. The concentration of Ce3+ ions on CNP surfaces changed from 18.64% to 19.48%, from 20.31% to 21.94%, and from 21.27% to 19.22% when CNPs were respectively immersed in H2 GDW, CO2 GDW, and O2 GDW for 3 to 12 hours. Adhesion energy between CNPs and SiO2 particle surface, following immersion of CNPs in H2 GDW, CO2 GDW, and O2 GDW for 6 hours, was found to be 6.06E-16 J, 6.18E-16 J, and 4.83E-16 J, respectively. After cleaning with GDW and applying megasonic, residual Ce ion concentrations on the SiO2 film surface were found to be 0.06 ppb, 0.41 ppb, and 0.10 ppb for H2 GDW, CO2 GDW, and O2 GDW, respectively.

Wire arc additive manufacturing of ZL205A: Heat input effect on the forming quality, pore defects and mechanical properties

The magnitude of heat input (HI) plays a pivotal role in determining the deposition quality of wire arc additive manufacturing (WAAM) components. This article studies the effects of high and low HI on the forming quality, microstructure, pore defects, and mechanical properties of ZL205A parts, providing a theoretical foundation for choosing optimal HI parameters in the utilization of WAAM technology to fabricate ZL205A structural components. In this study, four thin-walled walls, SP1, SP2, SP3, and SP4, were manufactured with HI of 300.12, 200.08, 163.70, and 138.51 J/mm, respectively. The findings show that the SP4 has the least side forming error, and the maximum deposition efficiency, resulting in the best forming quality. From microstructural studies，SP4 has the lowest average grain size, 72μm. The quantity of θ phases (Al2Cu) on the grain boundary and the quantity and size of θ' phases in the middle and bottom grains both diminish with decreasing HI. As the HI decreases, the porosity of the four samples shows a trend of first decreasing and then increasing, with the highest being 1.41 % of the SP1. This change is explained from the four stages of bubble nucleation, growth, detachment, and escape. Reducing HI can significantly improve the ultimate tensile strength (UTS), and yield strength (YS) of the specimen. The SP4 has the highest UTS and YS, which are 232.99 MPa and 101.20 MPa, respectively.

Submegahertz Nucleation of Plasmonic Vapor Microbubbles near a Solid Vertical Boundary.

Laser triggered and photothermally induced vapor bubbles have emerged as promising approaches to facilitate optomechanical energy conversion for numerous applications in microfluidics and nanofluidics. Here, we report an observation of spontaneously triggered periodic nucleation of plasmonic vapor bubbles near a rigid sidewall with readily tuned nucleation frequency from 0.8kHz to over 200kHz. The detailed collapsing process of the vapor bubbles was experimentally and numerically investigated. We find that the lateral migration of residual bubbles toward the sidewall refreshes the laser spot area, terminates the subsequent steady bubble growth, and leads to the repeatable bubble nucleation. A mathematic model regarding the Kelvin impulses was derived. It shows that the competition between the rigid boundary induced Bjerknes force and laser irradiation caused thermal Marangoni force on collapsing bubbles governs the process. The model also leads to a criterion of γζ<0.34 for repeatable bubble nucleation, where γ is the normalized distance and ζ thermal Marangoni coefficient. This study demonstrates nucleation of violent vapor bubbles at extreme high frequencies, providing an approach to remotely realize strong localized flows in microfluidics and nanofluidics.

A Test of the Equation for Bubble Nucleation in Polymer Solutions

A Test of the Equation for Bubble Nucleation in Polymer Solutions

Comprehensive experimental thermal analysis of single bubble nucleation in vertical flow boiling: Whole field temperature and microlayer dynamics

Nucleate boiling, an important heat transfer phenomenon, holds significance in the thermal management of numerous engineering applications. Understanding and predicting its heat transfer characteristics are vital for system optimization. The formation of a microlayer, resulting from rapid bubble growth on a heater substrate, subsequently facilitates further bubble growth through evaporation playing a critical role in overall bubble dynamics. This study examines the intricate relationship between bubble and microlayer dynamics and their impact on heat transfer rates. Experimental work is conducted for varying heat fluxes using rainbow schlieren deflectometry (RSD) and thin-film interferometry (TFI) in tandem for simultaneous mapping of key parameters: bubble dynamics, microlayer dynamics, and two-dimensional temperature field in vertical flow boiling. The analysis of these parameters has provided significant insights into some fundamental aspects of boiling. Firstly, this study emphasizes that the bubble growth rate models need to take into initial microlayer thickness in accurately predicting bubble growth dynamics. The iteratively obtained constant Ceff (describing the initial microlayer thickness) for bubble growth models matches well the value of Ceff obtained experimentally from thin film interferograms. Additionally, this study also validates the applicability of the kinetic theory-based model in predicting the evaporative heat transfer coefficient during the initial stage of flow boiling, while demonstrating that the accommodation coefficient is ∼0.04 for the investigated range of heat fluxes. Subsequently, using the experimentally obtained evaporative heat transfer coefficient, further insights are provided into the dry patch dynamics. Experimental dry patch dynamics were in good agreement with theoretical predictions up to the rewetting phase. The results also indicate a substantial contribution of microlayer evaporation, constituting approximately 34 % of the total heat flux.

The effect of hydrogen co-injection on the microstructure of triple ion irradiated F82H

The reduced activation ferritic/martensitic steel F82H-IEA was studied through a systematic set of dual (Fe2++He2+) and triple (Fe2++He2++H+) ion irradiations to determine the effect of hydrogen co-injection with helium and radiation damage on the irradiated microstructure and in particular, cavity evolution. Irradiations were conducted in four distinct permutations from a set of nominal irradiation parameters of 50 dpa, 1 × 10–3 dpa/s, 500 °C, and 40/10 appm/dpa of H/He or 10 appm/dpa of He. A temperature series of dual and triple ions ranging from 400 to 600 °C was conducted where swelling values of 1.3–2.4x were obtained with the co-injection of hydrogen. A damage level (50 to 150 dpa) and damage rate (2.5 × 10–4 to 2.5 × 10–3 dpa/s) series were also conducted where hydrogen was again observed to cause a ∼1.2–1.8x increase in swelling in triple ion irradiation versus dual ions. The effect of hydrogen was also observed to increase the overall steady state swelling rate from 0.02%/dpa in dual ions to 0.034%/dpa under triple ions at 500 °C by 150 dpa. A final series of triple ion experiments was conducted at 450 °C and 500 °C at 80 appm/dpa of H where swelling was suppressed by 50% compared to the dual ion irradiated case due to over-nucleation of small bubbles. The effect of hydrogen on bubble nucleation was to stabilize higher densities of smaller helium bubbles possibly through increasing nucleation rates and reduction of the stable bubble radius. The effect on swelling was in the promotion of higher densities of larger voids experiencing bias-driven growth. Hydrogen was shown to have a moderate influence on the nucleation and growth of dislocation loops, although these effects appear to be convoluted by the changes in cavity microstructure dominating sink strength across conditions. Hydrogen co-injection was also loosely correlated with enhanced dissolution of M23C6 precipitates across temperature and damage level regimes.

Bubble 36Ar and its new breathing modes

The bubble nuclei are important components of exotic nuclear structures characterized by special depletions of central densities. Focusing on bubble structures of 36Ar, the characterizations of bubble nuclei were explored with the framework of the extended quantum molecular dynamics model. Three density distribution modes were uncovered for the first time, i.e. micro-bubble, bubble, and cluster resonances, which show unique spectral signature compared to the monopole resonance spectrum as the excitation intensity was increased in bubbles. Of pivotal importance is the revelation that the bubble mode's oscillation frequency closely resembles macroscopic bubble dynamics, building a connection between classical macroscopic phenomena and the quantum complexity of the nuclear structure. The discovery marks a crucial step forward in deciphering the relationship between classical and quantum domains within the enigmatic world of atomic nuclei.