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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 Λ CDM . 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. [ABSTRACT FROM AUTHOR]

In the framework of the Polyakov quark-meson model with two flavors, the bubble dynamics of a first-order phase transition in the region of high density and low temperature are investigated by using the homogeneous thermal nucleation theory. In mean-field approximation, after obtaining the effective potential with the inclusion of the fermionic vacuum term, we build a geometric method to search two existing minima, which can be actually connected by a bounce interpolated between a local minimum to an adjacent global one. For both weak and strong first-order hadron quark phase transitions, as fixing the chemical potentials at  μ = 306 MeV  and  μ = 310 MeV , the bubble profiles, the surface tension, the typical radius of the bounce, and the saddle-point action as a function of temperature are numerically calculated in the presence of a nucleation bubble. It is found that the surface tension remains at a very small value even when the density is high. It is also noticed that the deconfinement phase transition does not change the chiral phase transition dramatically for light quarks and phase boundaries for hadron and quark matter should be resized properly according to the saddle-point action evaluated on the bounce solution. [ABSTRACT FROM AUTHOR]

A detailed study at the microscopic level of the transient behavior of boiling phenomena during quenching of an AISI 304 stainless steel, conical-end, cylindrical probe in flowing water at 60 °C was conducted using high-speed video recordings and cooling curve data acquisition. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950 °C) were investigated. It was complemented by video recordings at 60 fps to calculate the wetting front velocity. Surface heat flux histories at the thermocouple positions were estimated by solving the corresponding Inverse Heat Conduction Problem. As the water velocity increases the duration of the vapor film at each thermocouple position shortens and the difference among cooling curves at the thermocouple positions decreases. Increasing the initial temperature increases the duration of the vapor film stage. The wetting front velocity increased from 4 to 6 m/s. The time to reach the maximum surface heat flux at the position of the thermocouple closest to the probe tip ranged from 9.7 to 18 s. Undulations at the vapor-liquid interface that appear periodically and propagate in the direction of quenchant flow were observed early during the vapor film stage. Later, before the collapse of the vapor film, a kind of a shock wave was generated at the probe tip which modified the appearance of the film. Once the Leidenfrost temperature is reached, a wetting front (which consists of many small bubbles that coalesce rapidly in a very small area) is formed and travels in the direction of quenchant flow while fewer and larger bubbles nucleate and grow upstream. The nucleation, growth and detachment of the larger bubbles was studied; as the free-stream velocity decreases larger values of bubble maximum diameter and half-life time were observed, while the initial temperature has a marginal effect on these quantities. [ABSTRACT FROM AUTHOR]

We document the presence, composition, and number density (TND) of titanomagnetite nanolites and ultra‐nanolites in aphyric rhyolitic pumice, obsidian, and vesicular obsidian from the 1060 CE Glass Mountain volcanic eruption of Medicine Lake Volcano, California, using magnetic methods. Curie temperatures indicate compositions of Fe2.40Ti0.60O4 to Fe3O4. Rock‐magnetic parameters sensitive to domain state, which is dependent on grain volume, indicate a range of particle sizes spanning superparamagnetic (<50–80 nm) to multidomain (>10 μm) particles. Cylindrical cores drilled from the centers of individual pumice clasts display anisotropy of magnetic susceptibility with prolate fabrics, with the highest degree of anisotropy coinciding with the highest vesicularity. Fabrics within a pumice clast require particle alignment within a fluid, and are interpreted to result from the upward transport of magma driven by vesiculation, ensuing bubble growth, and shearing in the conduit. Titanomagnetite number density (TND) is calculated from titanomagnetite volume fraction, which is determined from ferromagnetic susceptibility. TND estimates for monospecific assemblages of 1,000 nm–10 nm cubes predict 1012 to 1020 m−3 of solid material, respectively. TND estimates derived using a power law distribution of grain sizes predict 1018 to 1019 m−3. These ranges agree well with TND determinations of 1018 to 1020 m−3 made by McCartney et al. (2024), and are several orders of magnitude larger than the number density of bubbles in these materials. These observations are consistent with the hypothesis that titanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation. Plain Language Summary: We use magnetism experiments to prove that nanometer‐sized magnetic particles are present in volcanic rocks with low iron content and few visible crystals. Nanolites (particles between 30 and 1,000 nm) and ultra‐nanolites (particles smaller than 30 nm) are extremely difficult to detect in volcanic rocks composed mainly of glass using conventional methods such as optical and electron microscopy. Titanomagnetite nano‐particles may play a role in controlling the explosiveness of volcanic eruptions. The magnetic signatures of minerals can be used to determine their chemical composition, particle size range, and particle abundance. Pumice and obsidian contain the mineral titanomagnetite, with no evidence of prolonged crystallization at high oxygen levels at the Earth's surface. Observed magnetic behaviors are very similar to those of previously published studies of titanomagnetite in the 10–1,000 nm size range, and similar to mathematical models that simulate this size range. We find that pumice clasts have a magnetic fabric, suggesting that the nanolites and ultra‐nanolites were aligned in spatial patterns before the magma solidified, with stronger alignment coinciding with high degrees of vesicularity. Our results indicate that titanomagnetite crystals are highly abundant, and had crystallized in the magma chamber before the eruption. Key Points: Magnetic methods document titanomagnetite nanolites in rhyolitic materials from Glass Mountain, Medicine Lake Volcano, CaliforniaTitanomagnetite number densities for pumice, obsidian, and vesicular obsidian span 1012 to 1020 m−3 of solid materialTitanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation [ABSTRACT FROM AUTHOR]

It is a challenge to study the nucleation of cavitation bubbles, which critically depends on nanoscale morphological features. Our recent advances in synthesizing colloidal negative-curvature nanoparticles (NGC-NPs) offer a rare opportunity, in comparison to the conventional studies of bulk substrates, where it is difficult to obtain consistent and well-defined surface features. In order to quantitatively assess their effects, we exploit the radical-induced color change of [Fe(SCN)6]3−, which turned out to be a more convenient method than the bending of AgNWs and the fluorescence-based methods. We show that the NGC-NPs outperform positive-curvature nanoparticles (PSC-NPs) and homogeneous nucleation, in terms of promoting cavitation. The NGC-NPs provide a higher percentage of gas–solid interface, and thus reduces the activation barrier during the critical stage of bubble nucleation. This leads a higher probability of cavitation and transforms more energy from ultrasonication to radical formation and shockwaves.

Abstract We document the presence, composition, and number density (TND) of titanomagnetite nanolites and ultra‐nanolites in aphyric rhyolitic pumice, obsidian, and vesicular obsidian from the 1060 CE Glass Mountain volcanic eruption of Medicine Lake Volcano, California, using magnetic methods. Curie temperatures indicate compositions of Fe2.40Ti0.60O4 to Fe3O4. Rock‐magnetic parameters sensitive to domain state, which is dependent on grain volume, indicate a range of particle sizes spanning superparamagnetic (10 μm) particles. Cylindrical cores drilled from the centers of individual pumice clasts display anisotropy of magnetic susceptibility with prolate fabrics, with the highest degree of anisotropy coinciding with the highest vesicularity. Fabrics within a pumice clast require particle alignment within a fluid, and are interpreted to result from the upward transport of magma driven by vesiculation, ensuing bubble growth, and shearing in the conduit. Titanomagnetite number density (TND) is calculated from titanomagnetite volume fraction, which is determined from ferromagnetic susceptibility. TND estimates for monospecific assemblages of 1,000 nm–10 nm cubes predict 1012 to 1020 m−3 of solid material, respectively. TND estimates derived using a power law distribution of grain sizes predict 1018 to 1019 m−3. These ranges agree well with TND determinations of 1018 to 1020 m−3 made by McCartney et al. (2024), and are several orders of magnitude larger than the number density of bubbles in these materials. These observations are consistent with the hypothesis that titanomagnetite crystals already existed in extremely high number‐abundance at the time of magma ascent and bubble nucleation.

In this study, the effect of nanostructure morphology on bubble nucleation of liquid argon on a platinum solid surface was explored using molecular dynamics methods. We examined the differences in nucleation behavior on smooth and nanostructured surfaces, including trapezoidal, rectangular, and reentrant cavities. The simulation results demonstrated that nanostructured surfaces outperformed smooth surfaces in terms of bubble nucleation, and the corresponding morphology had a significant effect. The reentrant cavity had the shortest bubble initial nucleation time, followed by the rectangular cavity, and the trapezoidal cavity had the longest bubble initial nucleation time. The mechanism of bubble nucleation on solid surfaces was further investigated from two perspectives: heat transfer through the solid-liquid interface and the potential energy constraint. Compared with other surfaces, surfaces with reentrant cavities exhibited a significantly higher heat transfer efficiency. The liquid atoms on the nanostructured surfaces absorb a large amount of heat within a short time, resulting in rapid accumulation of heat in the cavity. The thermal motions of the liquid atoms are enhanced, and the potential energy constraints from the surrounding atoms are overcome to achieve rapid bubble nucleation. Thus, the nanostructures promote bubble nucleation in the heated liquid. Our results provide novel insights into the design of nanostructures to improve the boiling heat transfer performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Nanostructures have a crucial impact on bubble nucleation. In this paper, different nano-grooved surfaces are constructed using complex trigonometric functions, and the nucleation process of liquid argon on the surfaces is investigated using molecular dynamics simulations. The nanostructures affect the bubble nucleation location, and the results show that the bubble nucleation always occurs in the groove region during the boiling process. In contrast, the bubbles on the flat surface appear randomly. In addition, bubble growth is also affected by the nanostructure. Increasing nanostructure size can reduce the bubble nucleation time and enhance the bubble growth rate. The nanostructure increases the solid-liquid interface area, which enhances the heat transfer between solid and liquid. Finally, the reasons for bubble nucleation on different nanostructured surfaces are analyzed. The heat transfer between solid and liquid is the leading factor for bubble nucleation when the difference in liquid atoms’ potential energy is slight. As the nanostructure size increases, the substrate attracts more argon atoms to form a non-evaporating liquid layer, improving heat transfer and promoting bubble nucleation. [ABSTRACT FROM AUTHOR]

Breadcrust bombs formed during Vulcanian eruptions are assumed to originate from the shallow plug or dome. Their rim to core texture reflects the competition between cooling and degassing timescales, which results in a dense crust with isolated vesicles contrasting with a highly vesicular vesicle network in the interior. Due to relatively fast quenching, the crust can shed light on pre‐ and syn‐eruptive conditions prior to or during fragmentation, whereas the interior allows us to explore post‐fragmentation vesiculation. Investigation of pre‐ to post‐fragmentation processes in breadcrust bombs from the 1999 Vulcanian activity at Guagua Pichincha, Ecuador, via 2D and 3D textural analysis reveals a complex vesiculation history, with multiple, spatially localized nucleation and growth events. Large vesicles (Type 1), present in low number density in the crust, are interpreted as pre‐eruptive bubbles formed by outgassing and collapse of a permeable bubble network during ascent or stalling in the plug. Haloes of small, syn‐fragmentation vesicles (Type 2), distributed about large vesicles, are formed by pressurization and enrichment of volatiles in these haloes. The nature of the pressurization process in the plug is discussed in light of seismicity and ground deformation signals, and previous textural and chemical studies. A third population (Type 3) of post‐fragmentation small vesicles appears in the interior of the bomb, and growth and coalescence of Type 2 and 3 vesicles causes the transition from isolated to interconnected bubble network in the interior. We model the evolution of viscosity, bubble growth rate, diffusion timescales, bubble radius and porosity during fragmentation and cooling. These models reveal that thermal quenching dominates in the crust whereas the interior undergoes a viscosity quench caused by degassing, and that the transition from crust to interior corresponds to the onset of percolation and development of permeability in the bubble network. Plain Language Summary: Breadcrust bombs are volcanic ejecta formed during explosive volcanic eruptions by rapid cooling of the exterior (the crust) and slow cooling of the interior that causes gas loss, bubble growth and cracking of the exterior. The rapidly cooled crust preserves characteristics of the magma prior to explosion. We study here the variations in porosity and vesicle properties from crust to interior in breadcrust bombs from the Guagua Pichincha volcano in Ecuador. Our results shed light on the pre‐eruptive conditions in the magma prior to explosive activity, and on the post‐fragmentation evolution of the bomb interior by bubble formation. Key Points: Vesicle textures in breadcrust bombs correlate with pre‐ to post‐fragmentation degassing processes during Vulcanian eruptionsLarge isolated vesicles preserved in the crust record a pre‐eruptive episode of outgassing and pressurization prior to fragmentationSmall vesicles provide insights into post‐fragmentation onset of permeability from the crust to the interior [ABSTRACT FROM AUTHOR]

Principles of laser-induced nanobubble formation in water are studied and presented. Nanobubbles were generated by laser light at intensities below threshold for laser-induced breakdown and subsequently expanded by a rarefaction wave to facilitate their observation and analysis. Different methods were used to study nanobubble formation and characteristics. Firstly, probability of nanobubble formation as a function of water sample purity was examined. Secondly, relation between laser fluence at different wavelengths and the number of generated nanobubbles was investigated. Thirdly, measurements of nanobubble lifetime were conducted indicating a contradiction to the Epstein-Plesset equation-based prediction of free bubble dissociation. Accumulated evidence suggests that the presence of physical impurities is a prerequisite for nanobubble formation. Consequently, a lack of impurities results in the absence of nanobubbles in contrast to assumptions by existing studies. The findings presented in this paper provide new insights into the fundamental properties of laser-induced nanobubbles in water.

Surface wettability plays an essential role in bubble nucleation. In this article, the molecular dynamics simulation method is conducted to study the bubble nucleation of liquid argon film on a copper substrate with hybrid wettability. Unlike the constant temperature boundary condition, the variable temperature boundary condition is adopted to simulate the bubble nucleation process. The temperature gradually increases from 86 K to 200 K, so the substrate temperature at the bubble nucleation time can be obtained. The potential energy, kinetic energy, total energy, and temperature during bubble nucleation are analyzed. The results show that bubble nucleation occurs when the kinetic energy exceeds the potential energy barrier. A method is used to capture the bubble nucleation process, described from the perspective of total energy. The initial nucleation time of the hybrid wettability surface gradually reduces with the rise of the proportion of the hydrophilic part. Compared with the pure hydrophilic surface, the hybrid wettability surface can achieve faster initial nucleation time and lower nucleation temperature by altering the proportion of wettability. The potential energy and temperature distribution reveal the microscopic mechanism of bubble nucleation. This study provides theoretical guidance for the design of cooling surfaces of micro/nanoelectronic devices. [ABSTRACT FROM AUTHOR]

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• Bubble dynamics inside droplet in the nucleate boiling regime on two-tier hierarchical micro-pillar array surfaces are systematically studied. • Secondary pillars are most effective at improving heat transfer performance when configured on side of primary pillars and least effective when configured on top of primary pillars. • Configuration of secondary pillars on side of primary pillars enhances heat transfer significantly when triple-phase contact line on pillars dominates evaporation. • Droplet evaporation rate decreases anomalously because evaporation is hindered near primary pillars by wrapping of droplet when secondary pillars are configured on substrate. • Geometrical effects of primary pillar including pillar side length, spacing and height and mechanisms are analyzed. Although hierarchical structured surfaces have shown great potential in improving heat transfer performance of boiling, the mechanisms associated with structure configuration and structure size remain elusive. In this work, the nucleate boiling regime of droplet on single-tier micro-pillar array (SM) surfaces and three types of two-tier hierarchical micro-pillar array (THM) surfaces is investigated comprehensively using the lattice Boltzmann model. Effects brought by the primary pillar size and the secondary pillar configuration on the development of vapor confined in pillar gaps are emphatically discussed from bubble nucleation through vapor coalescence to vapor expansion. Boiling dynamic characteristics concerning droplet morphological evolution, liquid-vapor interfacial deformation and triple-phase contact line (TPCL) motion are elucidated by the distributions of vapor pressure, fluid temperature and substrate heat flux. It is most efficient for the secondary pillar to enhance boiling heat transfer performance when configured on the side of primary pillar and least efficient when configured on the top of primary pillar. [Display omitted] [ABSTRACT FROM AUTHOR]

Surface wettability plays an essential role in bubble nucleation. This paper investigates the phase transition behaviour of argon films placed on inhomogeneous wettability substrates using molecular dynamics simulations. The location of bubble nucleation and initial nucleation time is investigated to reflect the effect of hydrophobic area fraction of inhomogeneous wettability surfaces on bubble nucleation. The results show that the bubbles appear first on the hydrophobic part of the inhomogeneous wettability surface. The relationship between hydrophobic area fraction and initial nucleation time is nonlinear. The initial nucleation time first decreases and then increases as the area of the hydrophobic region increases. In addition, the bubble nucleation process is restricted when the hydrophobic occupation is relatively large on inhomogeneous wettability surfaces. At last, the mechanism of bubble nucleation on inhomogeneous wettability surfaces is discussed in combination with the restrictive relationship between heat absorption and solid–liquid interaction energy. The amount of heat absorption does not directly determine the bubble nucleation. Bubble nucleation can arise in the location with a lower surface energy barrier once the heat absorption can overcome the solid–liquid interaction energy. [ABSTRACT FROM AUTHOR]

To investigate the falling film evaporation process of R134 a（C2H2F4） on horizontal tube, the volume of fluid (VOF) model and the user-defined functions (UDF) were used to numerically simulate the flow and heat transfer characteristics of the liquid film on tubes, including the flow of liquid film along the axial direction and circumferential direction of cross section of heat exchange tubes (corrugated tubes and smooth tubes), the thickness and distribution of liquid film and the bubbles nucleation and distribution in liquid film. The calculation results show that when the heat flux on the wall is 2×104 W·m-2, both flow and heat transfer of the R134 a liquid film have differences between corrugated tube and smooth tube in the axial and circumferential direction. Along the axial direction, the spreading speed of the liquid film on corrugated tube is 2.0 ms faster than that on smooth tube, while along the circumferential direction, the liquid film spreads more uniformly and slowly than that on smooth tube. The average thickness of the liquid film on corrugated tube is 0.120 mm, which is 7.00% thinner than that on smooth tube. The thickness of liquid film on the front area of tube is 0.119 mm, which is 13.14% thinner than that on smooth tube. Compared with smooth tube, the first bubble nucleation in the liquid film on corrugated tube occurs 2.6 ms earlier, and the number of bubble nucleation is 15.32% more than that on smooth tube, while the range of bubble nucleation is larger with more bubble nucleation occurring at circumferential angles of 55°-135°. The average heat transfer coefficient on corrugated tube is 10.17% higher than that on smooth tube, and the heat transfer coefficient on the front area is 3.53 times bigger than that on the back area. [ABSTRACT FROM AUTHOR]

The nucleation and growth of cavitation bubbles few micrometers in size in water generated by a 60 ps 515 nm fiber laser is observed and visualized near nucleation threshold. The study is performed by monitoring the plasma size, the cavitation bubble size and the emitted shock waves. The latter two aspects are supported by the Gilmore model using a Noble-Abel-stiffened-gas (NASG) equations of state. For the first time, two types of cavitation events are identified and visualized that exhibit a difference of more than two orders of magnitude in the excitation energy converted to mechanical effects with minimal change in excitation laser pulse energy. The result is localized cavitation and reduced mechanical stress on water-based media with potentially positive implications for laser treatments of biological tissue.

In this study, a small visualization device was used to research the dynamic evolution of pressure reactions and bubble nucleation in tanks under rapid decompression. The effect of ethanol impurities on the mechanism of superheated boiling of liquids was investigated. The effect of ethanol impurities on the superheated boiling of liquids under different storage conditions is discussed by studying the pressure characteristic parameters. The experimental results show that ethanol impurities can reduce the bubble nucleation radius, leading to a sharp increase in the number of bubbles and more severe boiling during leakage. Besides, there is a saturation concentration which maximizes the promotion of superheated boiling of the liquid. Under the present experimental conditions, the boiling intensity of ethanol impurities saturates at 3.53%, and this saturation concentration decreases slightly with increasing initial leakage pressure. Ethanol impurities also promote boiling of superheated liquids at different initial liquid levels. This study can provide ideas for the investigation, analysis and prevention of related accidents. [ABSTRACT FROM AUTHOR]

Traditional nucleation theories, designed for uniform surfaces, often fall short in explaining premature nucleation phenomena on non-uniform surfaces. This study employs a novel pressure-controlled approach in molecular dynamics simulations to investigate nucleation dynamics on non-uniform surfaces. Our findings reveal significant insights: hydrophilic surfaces exhibit maximal temperature elevation of the liquid film within the same timeframe, contrasting with the lowest nucleation energy observed on hydrophobic surfaces. Particularly, the 1–0000 surface configuration (combining hydrophilic and conical hydrophobic structures) demonstrates earliest nucleation times. Elevated temperatures consistently accelerate nucleation while reducing surface heterogeneity. Detailed surface analysis elucidates the nuanced nucleation mechanisms on non-uniform surfaces, highlighting the intricate balance between liquid film kinetic energy and surface nucleation energy. Optimizing the ratio and structure of hydrophilic and hydrophobic components emerges as a pivotal strategy to enhance liquid film kinetic energy while minimizing surface nucleation energy, thereby promoting vapor nucleation efficiency. These insights are pivotal for advancing heat transfer performance and operational efficiency in engineering applications. • Pressure control is employed in molecular dynamics simulations. • The nucleation mechanism of surfaces with non-uniform wettability is examined. • Elevated temperatures diminish the distinction between non-uniform surfaces. • Augmenting kinetic energy and minimizing potential energy will enhance nucleation. [ABSTRACT FROM AUTHOR]

Boiling heat transfer has become increasingly importance in a variety of industrial fields, but it involves chaotic nature phenomena that remain experimentally challenging. From the perspective of nucleation, bubble embryos emerge at the early stage on extremely small time and length scales. Therefore, molecular dynamics (MD) simulation is a popular and useful tool to uncover the distinctive boiling mechanisms at microscale. Recently, such method has yielded meaningful achievements, but there is still elusive on the current status and bottlenecks behind complex boiling processes. In this work, the state-of-the-art studies on bubble nucleation and boiling heat transfer that covers 129 papers up to 2024 have been comprehensively reviewed. Meanwhile, fundamental concepts of MD are briefly introduced, including MD principles, force fields, and determination of nucleation-related parameters. In contrast to microscopic boiling, bubble nucleation stems from the competition between potential and kinetic energies on micro/nano scale. Then, the key factors such as interfacial wettability and mixture component are thoroughly elucidated for bubble nucleation. In addition, both passive and active techniques are systematically discussed to unveil the underlaying mechanisms for boiling heat transfer enhancement. Finally, the ongoing trials needed for MD simulation are identified, together with an outlook for how to address these challenges. This review aims to offer an up-to-date summary of boiling mechanisms and draw more attention to the development of advanced MD techniques. [Display omitted] • A review of emerging molecular dynamics simulation on bubble nucleation and boiling heat transfer is presented. • Molecular dynamics simulation generates bubble nucleation spontaneously with no assumption and numerical artifacts. • The mechanism, enhancement methods and future insights of microscale boiling are discussed. [ABSTRACT FROM AUTHOR]

• Systematically explore the geometric effects of nanostructured surfaces on bubble nucleation. • Not all nanostructured surfaces can provide preferential nucleation sites. • When the roughness factor of is below the critical value, bubble nucleation will be delayed, and the CHF will decrease. With the development of nanosurface preparation and nanoscale simulation techniques, the effect of nanostructured surfaces on bubble nucleation and boiling heat transfer capability has received much attention. Many studies have shown that nanostructured surfaces can provide preferential nucleation sites for bubble nucleation and effectively enhance heat transfer, attributing to the increased solid–liquid contact area. However, few studies have systematically compared and assessed the performance of different nanostructured surfaces. The geometric effects and negative impact on heat transfer under certain conditions are still not well understood. In this study, the bubble nucleation process on nanostructured surfaces with different geometries were simulated using molecular dynamics method. The geometric effects of nanostructured surfaces are studied for bubble nucleation and heat transfer enhancement, with mechanisms revealed through surface temperature and energy distribution. The critical roughness factor of nanostructured surfaces with different morphologies is obtained. The critical roughness factor for SCUP is 1.215 and SCOP has the lowest critical roughness factor of 1.062. It can be found that the nanostructured surface will inhibit bubble nucleation and weaken surface heat transfer when the surface roughness factor is less than the critical value. It can delay bubble nucleation time by up to 400 ps and reduce the surface critical heat flux by 6.9 %. We believe that the conclusions of this study can provide some quantitative basis for a more comprehensive understanding of nanostructured surface performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A silicon carbide (SiC) heat sink was fabricated using laser structuring. • Laser structuring enhanced the critical heat flux of SiC by 114 %. • Laser-induced crevices and fins improved the heat transfer coefficient by up to 393 %. • Small bubbles (diameter: ∼0.3 mm) were formed at a high frequency (976 Hz). Silicon carbide (SiC), which has a wide bandgap and superior material properties, offers higher efficiency than conventional silicon in high-power and high-frequency semiconductor applications. In this study, the thermal management of SiC devices was explored through direct liquid cooling with laser-structured heat sinks. Pyramid-structured fin arrays were fabricated directly onto SiC substrates via laser structuring, and their boiling heat transfer performance was investigated through pool boiling experiments in a 5 °C subcooled condition. Laser structuring not only enhanced wettability due to oxidation but also facilitated nucleation through the laser-induced crevices. The oxidized surface created by the laser exhibited increased hydrophilicity, with a significant decrease in contact angle from 57° to 0°. In the pool boiling experiments, these crevices played a crucial role in enhancing the heat-transfer coefficient (HTC) at low heat fluxes (5–40 W/cm2), which promoted nucleation, resulting in the formation of very small and rapid bubbles. At heat fluxes above 180 W/cm2, the large surface area provided by the height of the fin structures further contributed to enhancing the HTC. The sample with the highest performance enhancement exhibited an 114 % increase in critical heat flux and a remarkable 393 % increase in the HTC compared to before laser structuring. [ABSTRACT FROM AUTHOR]

• Vibration-induced phase change dynamics of R1336mzz(Z) nanofilm are studied. • Phase change mode depends on vibrational amplitude and frequency parameters. • Film boiling and cavitation are identified through the predominant mechanism of thermal momentum and mechanism tensioning. • Interfacial wettability affects the heat transfer rate and potential barrier for bubble nucleation. 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 Af 3/2 when Af 3/2 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. [ABSTRACT FROM AUTHOR]

• Two techniques were employed to provide visual insights into the boiling phenomenon in an artificial cavity. • Optical sensor was effectively validated, showcasing its proficiency in analyzing vapor bubble departure frequencies. • Optical flow analysis revealed microconvection as the prevailing heat transfer mode. • Asymmetry in velocity profiles suggested a tendency for horizontal displacement of the bubble interface during growth. • Vorticity fields indicated rotational motion near the bubble's surface and in deformation movement regions. The ongoing quest for methods that enhance the efficiency of heat transfer processes, particularly those involving phase change, underscores the importance of comprehending the dynamics of vapor bubbles during boiling. This study investigates heat transfer mechanisms and the dynamics of vapor bubbles within the nucleate boiling regime. Experimental tests were conducted on a flat copper surface featuring a single cavity, focusing on analyzing vapor bubble growth and departure stages. The working fluid examined was HFE-7100 under saturated conditions. The formation and growth aspects of vapor bubbles, including their diameter (D d) and departure frequency (f), were investigated through experimental data obtained by two different techniques: by an optical sensor of variable resistance capable of generating an analog signal from a voltage change and by a high-speed camera that captures images immediately after the instant that the bubble detached from the surface. Both techniques provide visual insights into the boiling phenomenon. An escalation in heat flux and, consequently, wall superheat resulted in an increased bubble departure frequency. Furthermore, the optical flow analysis successfully identified velocity and vorticity fields induced by micro convection, the prevailing heat transfer mode in nucleated boiling. A slight horizontal displacement trend over time was observed, which may be caused by the asymmetry in the velocity profile, confirmed by velocity peaks tending toward one direction. Vortex analysis reveals rotational motion concentrated in specific regions, with noticeable deformation near the bottom of the bubble and asymmetric movement contributing to vorticity. These findings provide insights into the vapor bubble dynamics, which is important for understanding the cavity rewetting phenomena. [ABSTRACT FROM AUTHOR]

The kinetics of homogeneous nucleation of the vapour-gas phase was studied by the molecular dynamics (MD) method in Lennard-Jones systems simulating solutions with partial (A) and complete (B) solubility of components. The calculations were carried out at a temperature close to the normal boiling point of the solvent, two concentrations of the solute, and negative pressures. The pressure, as a function of density and concentration, in stable and metastable states, the parameters of phase equilibrium at a flat interface were determined. The ultimate stretching Δpn = ps–pn exceeded than those calculated from the classical nucleation theory at concentrations of solute c > 0.14 and were less theoretical ones at c < 0.2 in solutions A and B, respectively. A qualitative difference in the formation and growth of the vapour-gas nucleus in solutions A and B was established. In solution A, the partial density of the solvent sharply decreases and the density of the volatile component increases at the region of the bubble formation. In solution B, the density of the volatile component inside the bubble remains close to the density in the surrounding phase, and the density of the solvent decreases at the initial stage of bubble formation. [ABSTRACT FROM AUTHOR]

Nucleation is the formation of a new phase that has the ability to irreversibly and spontaneously grow into a large-sized nucleus within the body of a metastable parent phase. In this experimental work, the effect of wettability on the incipiation of vacuum-driven bubble nucleation, boiling, and the consequent rate of evaporative cooling are studied. One hydrophilic (untreated), and three hydrophobic (chlorinated polydimethylsiloxane, chlorinated fluoroalkylmethylsiloxane and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane) glass vials of different wettabilities were filled with degassed deionized water and exposed to a controlled vacuum inside a transparent desiccator. The vacuum was increased by 34 mbar abs. (1 inHg rel.) steps with 15-min waiting period to observe bubble nucleation. The average onset pressures for gas/vapor bubble nucleation in CM, CF, and HT vials were 911 ± 30, 911 ± 34, and 925 ± 17 mbar abs., respectively. Bubble nucleation was not observed in hydrophilic vial even at 65 mbar abs. pressure. During the vacuum boiling at 65 mbar abs., the average temperatures of water in hydrophilic, CM, CF, and HT vials reduced from room temperature (~22.5 °C) to 15.2 ± 0.9, 13.1 ± 0.9, 12.9 ± 0.5, and 11.2 ± 0.3 °C, respectively. The results of this study show that the wettability of the container surface has a strong influence on the onset vacuum for vapor/gas bubble nucleation, rate of vacuum boiling, and evaporative cooling. These findings are expected to be useful to develop wettability-based vacuum boiling technologies. [ABSTRACT FROM AUTHOR]

When the concentration of a gas exceeds the equilibrium concentration in a liquid, the gas–liquid system is referred as a supersaturated system. The supersaturation can be achieved by either changing the pressure and/or temperature of the system. The gas from a supersaturated liquid escapes either through bubble nucleation that usually occurs on solid surface and/or gas diffusion through the gas–liquid interface. The bubble nucleation requires a minimum threshold supersaturation. A waiting time is required to observe whether the applied supersaturation is sufficient to initiate bubble nucleation. When the supersaturation is not sufficient to cause bubble nucleation, some or all of the supersaturated gas may diffuse out from the liquid through the gas–liquid interface before further reducing the pressure in order to increase the supersaturation. In this article, using Fick's second law of diffusion and Henry's law, an analytical method is proposed to estimate the level of supersaturations generated in three gas–liquid systems at different step-down pressures. Characteristic times of the gas–liquid systems were estimated to validate whether the waiting times used in this study are in accordance with the semi-infinite diffusion model used to estimate the supersaturations generated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sparkling wine tasting was considered from the physicochemical angle. • Sparkling wines are complex hydro-alcoholic mixtures saturated with dissolved CO 2. • A perspective is proposed, from uncorking the bottle to bubble bursting. • The crucial role of glass shape was revealed through various analytical methods. From uncorking the bottle to the bursting of bubbles in the glass, the science behind the tasting of champagne and other sparkling wine is both traditional and at the forefront of modern developments. The strong interaction between the various parameters at play in a bottle and in a glass of sparkling wine has been the subject of study for around two decades. Indeed, sparkling wine tasting is often seen as the pinnacle of glamor and frivolity for most people, but it should also be considered as a fantastic playground for chemists and physicists to explore the subtle science behind this centuries-old drink, whose prestige today goes well beyond the borders of Champagne and France. This article offers an overview of the physicochemical processes that mark a tasting of champagne or sparkling wine in the broad sense, from the cork popping out of the bottleneck to the formation and bursting of bubbles in your glass, including the choice of the glass and how to serve and drink the wine correctly. [ABSTRACT FROM AUTHOR]

• Boiling on flat mixed-wettability surface with an increasing temperature is studied. • The condition is consistent with the situation of radiation from photons, plasma, or gas molecules with high temperature. • Compared to hydrophobic surface, it enhances solid/liquid interaction and promotes bubble nucleation. • Compared to hydrophilic surface, it delays vapor film formation. • An appropriate proportion of area favorable for bubble nucleation and heat transfer enhancement was found. This paper introduces a molecular dynamics investigation of the influence of mixed-wettability on the boiling of a water layer over a flat plate surface with nonlinearly increasing wall temperature. The first-type Dirichlet temperature condition, which is considered for the first time in the analysis of the wettability influence on nucleation and boiling at the atomic scale, is consistent with the case of irradiation from photons, plasma, or high-temperature gas molecules. The simulation of the density evolution of water molecules in the nucleation zone shows that the surface with an optimal proportion (60 %∼70 %) of hydrophilic walls is most efficient for nucleation on the studied mixed-wettability substrates, attributing to the increased surface potential energy on the walls. Compared to the hydrophilic or hydrophobic surfaces, the mixed-wettability surfaces transfer more energy from the wall to the liquid. This is because the hydrophobic portion retards the forming of vapor layer and the hydrophilic portion induces an efficient liquid/solid interaction, with a lowered interfacial heat resistance and promoted nucleation. The results also indicate that there exists an appropriate area ratio that is most advantageous for nucleation and boiling intensification under such temperature-increasing boundary conditions. Based on this work, it may be possible to successfully manage boiling at the nanoscale by exploiting the coupled effects of hybrid wettability and irradiation. [ABSTRACT FROM AUTHOR]

• Breakup regime of flashing jet under thermodynamic and mechanical effects is revealed. • Relationship between void fraction (α) and jet angle (k) is revealed. • The inadequacy of the existing criterion (Ja-We, χ*) are identified. • Relationship between flashing regimes and void fraction (α) is revealed. Accident release of superheated liquid could produce a violent phase change and trigger a highly destructive flashing jet. In this work, release experiments are performed using a 20 L tank and transparent nozzles, with water as the fluid throughout. The experimental conditions included storage temperature (T st = 100-160 °C), storage pressure (P st = 6-16 bar), and nozzle sizes (D = 1-6 mm). High-speed image processing and capacitive void fraction sensor are used to quantify the two-phase flow of superheated liquid inside the nozzle and the downstream jet break-up regimes. The experimental results show that void fraction (α) goes through three phases during the release process: growth, stabilization and decay. It is also demonstrated that bubble nucleation, growth and burst determine the breakup of the downstream jet. The T st and D are the main factors affecting the α , while the P st only change the release rate. Moreover, it is verified that none of the existing flashing criteria (Ja-We, χ*) can accurately determine the boundary conditions of the flashing regimes. Instead, the parameters characterizing bubbles nucleation and growth, α, can unify the effects of (T st , P st , and D) to determine the physical mechanism of the flashing process. In this work, a novel method to distinguish between external flashing (α = 0), internal flashing (0 < α ≤ 25) and full flashing (α > 25), and a steady-state model k = f (Ja, We, α) is developed for the flashing jet. [Display omitted] [ABSTRACT FROM AUTHOR]

• The heat transfer characteristics of flow boiling with inlet subcooling have been investigated using a "heat pump model". • The effect of the depth of the groove structure on the heat transfer characteristics at the nanoscale is investigated. • The bubble growth process at different wall temperatures is studied, and the mechanism of bubble nucleation promoted by the nanostructures is analyzed. As a prominent limiting factor in the performance of microelectronic devices, the improvement of heat dissipation is of utmost importance. The enhancement of heat and mass transfer during boiling by nanostructured surfaces has been demonstrated in many studies. In this study, a nanoscale flow-boiling model is developed by molecular dynamics method in order to deeply investigate the microscopic mechanism of nanostructure-enhanced heat transfer. Simple liquid argon is heated by grooved substrate to explore the effect of the depth of the cavities on the boiling heat transfer. The results indicate that the grooved surface improves heat transfer performance through two key mechanisms. Firstly, it induces bubble nucleation, and secondly, it delays the onset of film boiling. The presence of cavities allows the argon atoms within to absorb additional energy from the surrounding walls and be in closer proximity to the heating layer. This reduction in solid thermal resistance results in increased heat transfer efficiency, leading to earlier bubble nucleation and a greater propensity for nucleation within the cavities. The low horizontal velocity of argon atoms within the cavities suggests their ability to retain a significant number of atoms, thereby effectively mitigating the deterioration of heat transfer caused by the formation of a vapor film on the solid wall. The comprehensive performance is observed to improve with increasing depth of the cavities within the range investigated in this study. [ABSTRACT FROM AUTHOR]

Surface properties have a crucial effect on advancing boiling heat transfer (BHT). This study proposes a porous microgroove-structured surface fabricated via copper powder sintering and femtosecond laser processing to enhance pool boiling heat transfer. Copper powder sintering creates a porous layer, and the application of a femtosecond laser subsequently induces the formation of a microgroove structure atop the porous layer. Eight porous microgroove-structured surfaces were fabricated under different laser surface energy densities. Laser surface energy density was controlled by laser power and scanning speed. Pool boiling experiments were conducted for each sample, including smooth, porous, microgroove, and porous microgroove structures. Interestingly, a distinctive displacement was identified within the heat flux curve of porous microgroove-structured surfaces. The wall superheat decreased with increasing heat flux, causing the graph to shift to the left. To elucidate this phenomenon bubble visualization on the boiling surfaces was performed for each sample. It was observed that a porous microgroove-structured surface could effectively activate several bubble nucleation sites. Additionally, secondary pool boiling on the porous microgroove-structured surface was observed leading to the unique "hook back" shift in the boiling curve and the nonlinear increase of HTC. A pool boiling enhancement mechanism was proposed based on experimental data and bubble visualization. This study offers a pathway for advancing heat dissipation efficiency and understanding of surface engineering strategies. • Porous microgroove surface fabricated via copper sintering and femtosecond laser. • These surfaces offer more nucleation sites, better wettability, large boiling area. • They activate several pores and clustered cavities, generating bubbles. • Secondary boiling effect on the surface leads to superior heat transfer coefficient. • Fabricated surfaces have potential for achieving high heat dissipation efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of wettability and step-down pressure on bubble nucleation of sparingly soluble gases in water is studied. • Effective supersaturation is estimated as function of stepdown-pressure and waiting time. • Hydrophilicity discourages bubble nucleation irrespective of step-down pressure. • Hydrophobicity-promoted bubble nucleation depends upon step-down pressure. The liberation of dissolved gas from a liquid typically occurs either by diffusion through the gas–liquid interface and/or by bubble nucleation at the solid–liquid interface. The goal of this research was to study the influences of step-down pressure (degree of supersaturation) and wettability on the onset pressure for bubble nucleation of sparingly soluble gases, methane and nitrogen, in water. Bubble nucleation experiments were carried out with the gas-supersaturated liquids in the hydrophilic (untreated) and hydrophobic (treated) glass vials. The gas-saturated liquids were prepared by saturating water with methane or nitrogen in a glass vial placed in a pressure cell at 6,000 mbar for a minimum of 16 or 15 h, respectively. To initiate the pressure-driven bubble nucleation process, 100-, 500-, or 6,000-mbar step-down pressures were applied to the pressure cell until the bubble nucleation was initiated. Bubble nucleation did not occur in the hydrophilic vial with any of the gas-supersaturated waters, irrespective of the step-down pressures. Unexpectedly, 100-mbar step-down pressure did not cause neither methane nor nitrogen bubble nucleation in the hydrophobic vials. Whereas, both methane and nitrogen bubble nucleations occurred in the hydrophobic vials when the step-down pressure was increased to 500 mbar. The above experimental findings revealed the importance of step-down pressure and surface wetting nature on sparingly soluble gas bubble nucleation. To further understand the experimental findings, an analytical method was developed to estimate the effective supersaturations using Fick's 2nd law of diffusion and Henry' law, which indicated that at any given pressure the 500-mbar step-down pressure creates higher supersaturation compared to 100-mbar step-down pressure. [ABSTRACT FROM AUTHOR]

A study was conducted on whether periodic micro/nano ripple structures generated on metal surfaces using femtosecond laser processing could improve pool boiling heat transfer. Depending on the laser irradiation conditions on the metal surface, a surface structure with different geometrical characteristics is created. Changes in sample surface morphology caused by the laser irradiation intensity are examined using scanning electron microscopy and confocal laser microscopy. Pool boiling tests are conducted to compare three laser irradiation conditions fabricated samples and the bare copper surface. The working fluid is deionized water. The pool boiling curves of each sample surface were compared with each other. Visualization of bubble nucleation is performed using a high-speed camera. The superheat, bubble departure diameter, and bubble growth period of each sample are measured and compared at the onset of nucleate boiling (ONB). The most efficient periodic micro/nano ripple-structured surface reduces the superheat at the ONB by 6.13 °C in comparison with that at the bare Cu surface. The enhanced surface structure reduced the bubble departure diameter and renewal period by 60.5% and 55.6% in comparison with that of the smooth surface. Further, the structured surface showed 178.5% enhancement in heat transfer coefficient and 39.1% in critical heat flux, respectively. Thus, the combination of increased nucleate site density, high nucleation site activation, and a wicking effect in the periodic micro/nano ripple structure significantly improves the pool boiling heat transfer. • Femtosecond laser irradiation create periodic micro/nano-ripple structures. • Bubbles are easily created with high nucleate density on metal surface • Bubbles with a small diameter detach from the laser-treated surface. • Bubble characteristics are confirmed using high-speed camera visualization. • Periodic micro/nano surface structure can enhance HTC by 178.5% and CHF by 39.7%. • Increased nucleation site density and wicking effect enhances HTC and CHF. [ABSTRACT FROM AUTHOR]

• The bubble nucleation and growth in flat microchannels at localized ultra-high heat fluxes were studied. • The time duration of bubble growth was less than 200 μs. • A linear growth rate of about 20 m/s was evidenced at about the first half of bubble growth stage. • The short micro-pin fin arrays lowered the threshold heat flux and onset temperature of bubble nucleation. The two-phase flow boiling in microchannels is an attractive cooling strategy for high-power density electronic/optoelectronic devices, while the exist of sub-millimeter "hot spots" characterized by ultra-high heat fluxes would degrade the reliability and safety for commercial and consumer applications. In this paper, the bubble nucleation and evolution characteristics of subcooled flow boiling in high aspect ratio flat microchannels were experimentally studied with the aid of high-speed visualization and infrared temperature measurement at localized heat fluxes exceeding 1.5 kW/cm2. Dielectric liquid HFE-7100 was used at mass flow rates ranging from 11.1 to 178.2 kg/(m2·s). Results show that the explosive boiling process was accompanied by an approximately linear bubble growth rate of about 20 m/s at about the first half of growth stage, and the time duration for overall bubble growth was less than 200 μs. The bubble nucleation was suppressed dramatically on the smooth bottom surface of the channel even at a localized "hot spot" heat flux above 2.5 kW/cm2. The introduction of staggered short micro-pin fin arrays at the bottom wall significantly lowered the threshold heat flux and onset temperature of bubble nucleation and reinforced the bubble growth to larger sizes. It is attributed to the reduction in the temperature gradient of thermal boundary layer adjacent to the heated wall, and it would be further reduced by increasing the micro-pin fin denseness. Even at quite high superheats on smooth and micro-structured surfaces, the heterogeneous boiling mechanism was proved to still work. [ABSTRACT FROM AUTHOR]

• Modeling of super deep thermosyphons in artificial ground freezing. • Development of a novel cold heterogenous boiling model for thermosyphons. • Bubble nucleation site at thermosyphon wall only. • Formation of three unique zones at deep evaporators. • Observation of a dead-zone at large thermosyphon filling ratios due to hydrostatic pressure. Super-long thermosyphons exceeding 100 m are being employed more frequently in artificial ground freezing (AGF) applications. In this study, we develop a fully-conjugate computational-fluid-dynamics (CFD) model to fundamentally analyze the heat extraction capacity and profile of super-long thermosyphons in AGF. The CFD model couples a heterogeneous condensation/evaporation mass transfer model inside the thermosyphon with thermosyphon-pool hydrostatic pressure distribution and heat diffusion from the ground. The heterogeneous model also considers the kinetic energy required for bubble nucleation and has been validated against experimental studies from the literature. Three main parameters have been investigated: 1) the filling ratio, 2) the charge pressure inside the thermosyphon, and 3) the wind temperature. The results reveal a no-boiling-zone below 10–25 m of pool surface. Further, the charge pressure significantly affect the start-up of the thermosyphon. Lastly, lower wind temperature extracts more heat from the ground in a qualitatively similar manner (similar heat flux profile along thermosyphon wall) to that of higher wind temperature. Overall, the results of this study provide fundamental understanding of the performance of super-long thermosyphons in AGF. [ABSTRACT FROM AUTHOR]