Distribution Of Nucleation Sites Research Articles

Impact of Substrate upon Morphology, Luminescence, and Wettability of ZnMgO Layers Deposited by Spray Pyrolysis

In this work, we report on a comparative study of the topology, luminescence, and wettability properties of ZnMgO films prepared by a cost-effective spray pyrolysis technology on GaAs substrates with (100), (001), and (111) crystallographic orientations, as well as on Si(100) substrates. Deposition on nanostructured GaAs substrates was also considered. It was found that film growth is not epitaxial or conformal, but rather, it is granular, depending on the nucleating sites for the crystallite growth. The distribution of nucleation sites ensured the preparation of nanostructured films with good uniformity of their topology. The observed difference in columnar growth on Si substrates and pyramidal growth on GaAs ones was explained in terms of the impact of chemical bonding in substrates. The films grown on GaAs substrates with a (001) orientation were found to be made of larger crystallites compared to those deposited on substrates with a (111) orientation. These effects resulted in a difference in roughness of a factor of 1.5, which correlates with the wetting properties of films, with the most hydrophobic surface being found on films deposited on GaAs substrates with a (111) orientation. The prospects for photocatalytic and gas sensor applications of films produced on flat substrates, as well as for plasmonic and other applications of films deposited on nanostructured substrates, are discussed, taking into account the results of the analysis of their photoluminescence properties.

Micropatterning of LaCoO3 thin films through a novel photosensitive sol-gel lithography technique and their magnetic properties

This paper presents a study on the microstructure and magnetic properties of LaCoO3 (LCO) thin films, and also the micropatterning of LCO thin films using a novel photo-sensitive sol-gel lithography method. It is found that higher heat-treatment temperature can promote the healing of cracks and filling of pores, resulting in refining the grains, and improving the density of LCO film. The film treated at 850 °C has a larger nucleation energy, which makes the distribution of nucleation sites more uniform, promoting the healing of cracks and filling of pores, refining the grains, and improving the density of LCO film. LCO precursor sol, metal chelates with UV photosensitivity were synthesized by adding BzAcH photosensitizer. LCO micro-arrays with diameters of 50 μm, as well as other fine patterns with a minimum line width of about 2 μm were successfully prepared by a UV mask lithography technique. In contrast, our novel lithography method eliminates the need for photoresist, as the fine pattern is formed during the preparation of the LCO gel film, which is the advantages of our lithography method over traditional techniques.

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.

Numerical study on 3D nucleate boiling over an oscillating base plate with high wall superheat and multiple nucleation sites

This paper is on 3D numerical study on nucleate boiling at high wall superheat of 13.5 K, over an oscillating base plate, using a sharp interface dual-grid level set method (SI-DGLSM)-based in-house code. These studies are performed for two nucleation sites, with two configurations of the computational domain. A micro-layer evaporation model has been used to enable 3D simulations on a coarser grid and higher wall superheats. The size of the computational domain is chosen based on the nucleation site density, reported in experiments, and the present numerical results compare well with the published experimental results; for a stationary horizontal plate under atmospheric pressure. For nucleate boiling on an oscillating plate, bubbles departing from both the nucleation sites synchronize and lock-on with the plate oscillation. Enhancement in heat transfer coefficient is observed in presence of base plate oscillations, which is attributed to increase in rate of phase change as compared to increase in rate of convective heat transfer. Non-uniform distribution of nucleation sites on the base plate leads to formation of local convergence zones on the plate, which in turn affects the motion of bubbles as they rise within the computational domain. The present work is significant as it presents 3D simulations for nucleate boiling under the effect of base plate oscillations—as a promising technique for heat transfer enhancement.

Boiling heat flux partitioning model with bubble tracking method considering bubble merger and stochastic characteristics

This study presents the development and validation of a numerical tool of heat partitioning model for boiling heat transfer using a bubble tracking method. It was aimed to account for the effect of stochastic phenomena in the boiling process by simulating individual bubbles. Saturated pool boiling conditions on a horizontal plate heater were analyzed to demonstrate the effectiveness of the proposed model. The model was devised based on the observations from high-resolution pool boiling experiments, assuming a truncated sphere for bubble shape and using simplified microlayer size and thickness models. The developed heat partitioning model was verified by comparisons with the conventional heat partitioning model. Afterward, the validation of the model was conducted by comparing the result of the simulation with the experimental data of the saturated pool boiling. In this validation, measured values of nucleation site density, departure diameter, single-phase heat transfer coefficients, etc. were applied. Additionally, the effect of stochastic phenomena on boiling heat transfer was evaluated using the bubble tracking method, focusing on nucleation timing and nucleation site distribution. Stochastic nucleation was found to reduce the bubble merger probability compared to simultaneous nucleation, leading to increased microlayer evaporation. Stochastic site distribution, on the other hand, decreased active nucleation sites due to the site suppression effect, resulting in reduced microlayer evaporation compared to uniform site distribution.

A layered multifunctional framework based on polyacrylonitrile and MOF derivatives for stable lithium metal anode

Composite Li metal anodes based on three-dimensional (3D) porous frameworks have been considered as an effective material for achieving stable Li metal batteries with high energy density. However, uneven Li deposition behavior still occurs at the top of 3D frameworks owing to the local accumulation of Li ions. To promote uniform Li deposition without top dendrite growth, herein, a layered multifunctional framework based on oxidation-treated polyacrylonitrile (OPAN) and metal-organic framework (MOF) derivatives was proposed for rationally regulating the distribution of Li ions flux, nucleation sites, and electrical conductivity. Profiting from these merits, the OPAN/carbon nano fiber-MOF (CMOF) composite framework demonstrated a reversible Li plating/stripping behavior for 500 cycles with a stable Coulombic efficiency of around 99.0% at the current density of 2 mA/cm2. Besides, such a Li composite anode exhibited a superior cycle lifespan of over 1300 h under a low polarized voltage of 18 mV in symmetrical cells. When the Li composite anode was paired with LiFePO4 (LFP) cathode, the obtained full cell exhibited a stable cycling over 500 cycles. Moreover, the COMSOL Multiphysics simulation was conducted to reveal the effects on homogeneous Li ions distribution derived from the above-mentioned OPAN/CMOF framework and electrical insulation/conduction design. These electrochemical and simulated results shed light on the difficulties of designing stable and safe Li metal anode via optimizing the 3D frameworks.

Unified description over time of heterogeneous condensation with quenched disorder.

We report experimental results on breath figures(BFs) observed on substrates with quenched disorder. The evolution of BFs is found to be primarily influenced by global parameters associated with boundary conditions. We investigate classical statistical measures and explore topological properties using persistent homology techniques based on a modified Vietoris-Rips complex. Our findings reveal that the evolution of the number surface density of condensed droplets plays a crucial role in determining various condensation stages previously considered distinct. This evolution is significantly influenced by the distribution of nucleation sites and the individual growth law governing water droplets when coalescence does not occur. Ultimately, we demonstrate the capability to predict coalescence events based on the topological characteristics of BFs at a given point in time.

Eliminating concentration polarization with gradient lithiophilic sites towards high performance lithium metal anodes under low N/P ratio

Three-dimensional (3D) skeletons have been extensively explored for effectively inhibiting dendrite growth and mitigating the volume change of lithium (Li). However, the ionic concentration polarization ascribing to the different ionic transmission distance in 3D skeletons inevitably induce the uneven growth of Li, leading to preferential deposition of Li in the top region rather than a spatially ordered manner from bottom-up. This uncontrollable deposition will deviate the original guidance of 3D skeleton. In this study, a gradient lithiophilic carbon fibers (CFs) is designed and constructed by regulating the distribution of ZnO nucleation sites (CFs@GZnO skeleton) to achieve a spatially ordered Li plating/stripping process. Additionally, the top lithiophobic CFs layer acts as a buffer layer to accommodate inactive Li, avoiding the block of Li+ inward migration, the middle and bottom CFs layer decorated with different amounts of lithiophilic ZnO nucleation sites enable lithium preferentially deposits in the bottom layer and further supporting the sequential bottom-up depositing process. Benefiting from this gradient lithiophilic design, the non-uniform ionic polarization within the 3D skeleton is mitigated, effectively inducing Li plating/stripping in a controllable spatially ordered manner and suppressing the volume variation. Full cell with an ultrahigh mass loading NCM811 cathode (38 mg cm−2) and Li-CFs@GZnO (CFs@GZnO skeleton pre-plated with Li) anode under a low negative to positive N/P ratio of 2 achieved a lifespan of 100 cycles with a capacity fading of only 0.083 % per cycle and an average CE of 99.7 %. Thus, the strategy of inducing gradient lithiophilic sites into 3D skeletons may provide a new avenue to construct a dendrite-free and stable metal anode for high energy density LMBs.

Manipulating Li2O2 deposition morphology by surface spin modulation of cobalt-based spinel oxide catalysts in lithium−oxygen batteries

The lithium peroxide (Li2O2) morphology manipulated by the distribution of Li2O2 nucleation sites dramatically affects the electrochemical performance of lithium − oxygen batteries (LOBs). Cathode surface spin modulation engineering is adopted to obtain ideal Li2O2 deposition morphology, as it can effectively manipulate the nucleation site distribution. Herein, Cu1-ZnCo2O4 (Cu0.15Zn0.85Co2O4) electrocatalysts are elaborately constructed by introducing an appropriate amount of Cu2+ into the ZnCo2O4 tetrahedral sites, which successfully regulates the spin state of Co sites under the action of co-top oxygen connection. Density functional theory calculations reveal that the moderate Co dz2 orbital occupancy is obtained via spin regulation, causing the optimum adsorption capability of Cu1-ZnCo2O4 towards oxygen-containing intermediate. On the basis, the distribution of Li2O2 nucleation sites is modulated to promote the uniform deposition of small-size Li2O2 agglomerates, which possess a large contact area with the cathodic surface and a certain void structure, greatly improving reversible deposition and decomposition kinetics. As a result, LOBs catalyzed by Cu1-ZnCo2O4 offer a large specific capacity of 12984.9 mAh/g and an extended cycle stability of over 400 cycles. This work emphasizes that spin regulation engineering efficiently affects the distribution of Li2O2 nucleation sites, achieving the Li2O2 morphology modulation in LOBs.

Microstructural path modeling of primary recrystallization

While the classic KJMA model is frequently used to fit experimental recrystallization kinetics data, the fitted values in most cases are inconsistent with the observed microstructural evolution. In this paper, we review the much more powerful microstructural path modeling (MPM) methodology. A basic assumption in this next generation of recrystallization models is related to the spatial distribution of nucleation sites, which may be uniform in the mathematical sense, i.e. randomly distributed in the sample volume, or clustered either along lines or on planes. For example nuclei are often observed to be linearly aligned because they have formed along original grain boundaries or stringers of second phase particles in the deformed matrix. In this paper, we present a new MPM, which is extending the former idealized linear MPM, allowing the recrystallizing grains to grow with different speeds in different directions, thus becoming prolate spheroid shaped. Finally issues concerning experimental determination and analysis of growth rates, are discussed.

Fluid flow and heat transfer in microchannel devices for cooling applications: Experimental and numerical approaches

• Two phase flow in microchannels is characterized by numerical and experimental approaches. • Transition from bubbly flow to slug plug flow is numerically predicted but transition from bubbly flow to churn flow is not. • The proposed numerical tool is sensitive enough to capture particular effects of the studied parameters. Microchannel heat sinks are pointed to have a great potential in cooling systems. This paper presents a systematic study to develop a microchannel heat sink to be used in cooling applications. Particular emphasis is given to PV panels cooling. A systematic experimental approach is used to optimize the heat sink geometry. Then the potential advantage of using flow boiling conditions is explored in both numerical and experimental approaches. The two-phase flow is characterized in two different sets of conditions. In the experimental approach, a constrained bubble flow was observed with a stable pattern and bubble frequency in the narrower channel. In the wider channel a bubbly flow was observed with increased bubble diameters. Numerical simulations were also performed in order to examine the first transient stages of the two-phase flow development close to the inlet of the considered microchannels assuming an initial arbitrary distribution of nucleation sites. For this purpose, a previously developed and validated numerical simulation framework was utilised. The proposed customized tool has been developed in the general context of OpenFOAM CFD Toolbox and it accounts for phase-change (boiling/condensation) as well as for Conjugate Heat Transfer between solid and two-phase flow domains. The numerical predictions reveal that the proposed tool is sensitive enough to capture the effects of channel aspect ratio, applied heat flux and applied mass flux on the generated transient bubble dynamics and the associated heat transfer characteristics and it can constitute an important tool for quantifying the underpinned complex physical mechanisms, providing further insight into the experimental observations and measurements.

On the growth and texturing of ultra-thin zinc oxide films in spin coating

The growth and texturing of zinc oxide thin films in sol–gel spin-coating method are re-visited for different rotation speeds of the coater, molarity of the solution and annealing temperature of the films. We report the formation of highly textured ultra-thin films oriented along a-axis on glass substrates and the change in the texture coefficient as a function of the molarity of the sol and the annealing temperature. All the deposited films were found to have a thickness between 15 nm to 70 nm with an optical band-gap of ∼3.33 eV. Highly textured, a-axis oriented films were formed at 400 °C annealing temperature at an angular speed of 4000 rotations per minute by using a 0.4 molar solution and the orientation preference changes to c-axis above 450 °C for a similar thickness of the coating. It appears that the growth of the planes is determined by the annealing temperature and the texture coefficient is determined by the speed of the coater. A phenomenological model is proposed to explain the effect of different parameters on the structure formation and texturing by connecting the properties of the spinning liquid to the ultimate film structure by taking into account the difference in the distribution of nucleation sites at different rotation speeds, the subsequent lattice stress and the formation energy of different planes in the framework of competitive capture of diffusing particles by the growth/nucleation centres.

The Distribution of Nucleation Activities: A New Local Perspective with Scanning Electrochemical Cell Microscopy

Electrodeposition is a convenient strategy for the synthesis of functional nanostructures, for which electrochemical nucleation and growth (EN&G) processes need to be well understood [1]. As a heterogenous process, understanding the distribution of nucleation sites on a substrate is fundamental to relate the microscopic events to the macroscopic properties of the new deposit. In this work, we have explored the EN&G process on a glassy carbon substrate with a local electrochemical approach based on the Scanning Electrochemical Cell Microscopy (SECCM), using copper as a case of study [2]. Since the studies of EN&G are extremely sensitive to the state of the surface, the diversity of the nucleation process is revealed by performing hundreds of spatially resolved experiments on the heterogeneous surface of the glassy carbon [2,3]. The spatially-resolved characterization opens up the opportunity to correlate the electrochemical information to the local surface state, which can be modified with common surface pretreatments (i. e., polishing and preanodization). This unique perspective of the EN&G can help to deconvolute the individual contributions to the overall process, bringing forward information on nucleation sites that is unavailable with the conventional macroscopic approach.[1] J. Ustarroz, Current atomic-level understanding of electrochemical nucleation and growth on low-energy surfaces, Curr. Opin. Electrochem. 19 (2020) 144–152.[2] D.Torres, M. Bernal, J. Ustarroz, distribution of copper nucleation activities on glassy carbon: a new local perspective, to be submitted 2022[3] M. Bernal, D. Torres, S. Semsari, M. Čeh, K. Žužek Rožman, S. Šturm, J. Ustarroz, Diversity matters: Influence of surface heterogeneities in the electrochemical nucleation and dissolution of Au nanoparticles, under revision. Figure 1

A Multiple Site Type Nucleation Model and Its Application to the Probabilistic Strength of Pd Nanowires

Pristine specimens yield plastically under high loads by nucleating dislocations. Since dislocation nucleation is a thermally activated process, the so-called nucleation-controlled plasticity is probabilistic rather than deterministic, and the distribution of the yield strengths depends on the activation parameters to nucleate. In this work, we develop a model to predict the strength distribution in nucleation-controlled plasticity when there are multiple nucleation site types. We then apply the model to molecular dynamics (MD) simulations of Pd nanowires under tension. We found that in Pd nanowires with a rhombic cross-section, nucleation starts from the edges, either with the acute or the obtuse cross-section angles, with a probability that is temperature-dependent. We show that the distribution of the nucleation strain is approximately normal for tensile loading at a constant strain rate. We apply the proposed model and extract the activation parameters for site types from both site types. With additional nudged elastic bands simulations, we propose that the activation entropy, in this case, has a negligible contribution. Additionally, the free-energy barriers obey a power-law with strain, with different exponents, which corresponds to the non-linear elastic deformation of the nanowires. This multiple site type nucleation model is not subjected only to two site types and can be extended to a more complex scenario like specimen with rough surfaces which has a distribution of nucleation sites with different conditions to nucleate dislocations.

Recrystallization in non-conventional microstructures of 316L stainless steel produced via laser powder-bed fusion: effect of particle coarsening kinetics

Alloys processed by laser powder-bed fusion show distinct microstructures composed of dislocation cells, dispersed nanoparticles, and columnar grains. Upon post-build annealing, such alloys show sluggish recrystallization kinetics compared to the conventionally processed counterpart. To understand this behavior, AISI 316L stainless steel samples were constructed using the island scan strategy. Rhodonite-like (MnSiO3) nanoparticles and dislocation cells are found within weakly-textured grains in the as-built condition. Upon isothermal annealing at 1150 °C (up to 2880 min), the nucleation of recrystallization occurs along the center of the melt pool, where nuclei sites, high stored elastic energy, and local large misorientation are found in the as-built condition. The low value of the Avrami coefficient (n = 1.16) can be explained based on the non-random distribution of nucleation sites. The local interaction of the recrystallization front with nanoparticles speeds up their coarsening causing the decrease of the Zener-Smith pinning force. This allows the progression of recrystallization in LPBF alloys, although sluggish. These results allow us to understand the progress of recrystallization in LPBF 316L stainless steel, shedding light on the nucleation mechanisms and on the competition between driving and dragging pressures in non-conventional microstructures. They also help to understand the most relevant microstructural aspects applicable for tuning microstructures and designing new LPBF alloys.Graphical abstract

Zincophilic Laser‐Scribed Graphene Interlayer for Homogeneous Zinc Deposition and Stable Zinc‐Ion Batteries

Zinc metal is an important anode material for next‐generation energy storage systems. Unfortunately, uncontrollable dendrite growth caused by nonuniform Zn nucleation during the plating process severely restricts their practical applications. Herein, a nitrogen‐doped 3D laser scribed graphene (NLSG) with a large surface area and uniform distribution of nucleation sites is used as the interlayer to control Zn nucleation behavior and suppress Zn dendrite growth. The N‐containing functional groups in the carbon matrix are highly zincophilic, which induces uniform nucleation of Zn and guides homogenous Zn deposition. Meanwhile, the large specific area can effectively decrease the local current density, which is more favorable for highly reversible Zn plating/stripping. Benefiting from superior properties, the NLSG demonstrates improved electrochemical performance with high Coulombic efficiency (99.4%) and enhanced cycling performance (200 h). Compared with the bare Zn anodes, the NLSG‐coated Zn//MnO2 battery demonstrates higher capacity retention (72.3% vs 59.3%) after 1200 cycles.

Prediction of grain structure in direct-chill cast Al–Zn–Mg–Cu billets using cellular automaton-finite element method

A cellular automaton-finite element (CA-FE) model was used to predict the solidification grain structure of permanent mold cast A7086 alloy. In this model, a Gaussian distribution of nucleation sites was adopted, and the Kurz-Giovanola-Trivedi model was extended to a multicomponent Al–Zn–Mg–Cu alloy system to determine the growth kinetics of the dendrite tip. For describing the Gaussian distribution of nucleation sites on the mold surface, an empirical relationship between the initial cooling rate of the melt and the nucleation density was proposed. Under various casting conditions, the calculated grain structures agreed well with the experimental results. Subsequently, the model was applied to the direct-chill (DC) cast billets, and the simulated grain structures reproduced well the experimental results. This confirmed that the current CA-FE model can be used practically and effectively in DC casting processes.

Advanced boiling heat transfer model for a horizontal tube with numerical analysis of bubble behaviours

The boiling heat transfer model for a horizontal tube is developed herein, with numerical investigations to realistically simulate bubble nucleation site distributions and bubble behaviours. Accordingly, a new heat partitioning model was proposed to reflect the bubble sliding phenomena more realistically than the extant heat partitioning models for horizontal tubes. The bubble trajectories, merging, lift-off, and distribution of nucleation sites were numerically analysed based on the force balance model, bubble tracking method, and Latin-hypercube sampling. The proposed approach can overcome the limitations of the arithmetic heat partitioning model, which does not reflect bubble mergers and the random nature of the nucleation site distribution. Distinctive bubble behaviours on a horizontal tube can be reproduced by the present model, including bubble sliding, departure, lift-off, and merger. The numerical model presented here considers bubble sliding based on a mechanistic force balance model and bubble merger based on the bubble tracking method. The Monte Carlo method was applied to determine the spatial distribution of the nucleation sites, and statistical information on the wall heat transfer and contribution of each heat transfer mechanism were obtained via extensive calculations. The method developed herein was applied to evaluate the wall heat transfer in horizontal heaters. Further, the proposed numerical boiling heat transfer model was validated against an extant experimental database of horizontal heat exchanger tubes, and the model was observed to predict the wall heat flux with satisfactory accuracy.

Nucleation Site Distribution Probed by Phase-Enhanced Environmental Scanning Electron Microscopy

Summary Nucleation site distribution is ubiquitous in many natural and industrial processes, such as liquid-to-vapor phase change, gas-evolving reactions, and solid-state material growth. However, a comprehensive understanding of nucleation site distribution remains elusive. These limitations are due to the challenge of probing micro/nanoscopic nucleation sites and inadequate statistical interpretation of the nucleation process. Here we report direct experimental observation of nucleation site distribution in droplet condensation using phase-enhanced environmental scanning electron microscopy. We also use statistical theory to demonstrate that the population of nucleation sites is governed by the Poisson distribution, whereas the nearest-neighbor distance follows the Rayleigh distribution instead of the commonly used Poisson distribution. We further show the broad applicability of these insights into nucleation site distribution to hydrogen-evolving reactions and chemical vapor deposition. Our platform, combining precise characterization and theory, advances the fundamental understanding of nucleation phenomena and guides designs from materials to devices.

Macrolayer Formation Model for Prediction of Critical Heat Flux in Saturated and Subcooled Pool Boiling

A macrolayer formation model for predicting the critical heat flux (CHF) in saturated and subcooled pool boiling was proposed. The concept of this model was based on the bubble coalescence process, which was observed using a high-speed camera. In the present model, the thickness of the macrolayer was calculated assuming that the liquid volume remaining under the lower part of the bubble should contribute to the formation of the layer. A Poisson distribution was adopted for the distribution of nucleation sites. The predicted macrolayer thicknesses were used for the prediction of CHFs in saturated and subcooled pool boiling based on the macrolayer dryout model. This model reproduced the CHF values for pool boiling up to subcooling 40 K. The model concept was confirmed using a computational fluid dynamics code, where the assumption was that the liquid was captured and the macrolayer was formed at the coalescence of bubbles.