Layer Growth Model Research Articles

Influence of inorganic solid particles on the stability of water-in-crude oil emulsions: Evaluating the role of surface charge

This study examines the effect of inorganic solid particles on the stability of water-in-oil (W/O) emulsions formed during the transportation, refining, and storage of crude oil. The surface properties of inorganic particles, such as kaolinite and calcite, can influence the interface between crude oil and water, affecting the stability of the emulsion. The study evaluates the quantitative effect of these particles on emulsion stability and investigates how surface properties affect the emulsions. Emulsions were prepared using crude oil and synthetic brine, with calcite and kaolinite added as inorganic solid particles. Adding inorganic solids increased the volume of released water and altered the emulsion stability, with high concentrations decreasing the formation of stable emulsions. The dissolution of inorganic solids increased the pH of the solution and promoted demulsification due to the high surface potential of crude oil. The solid particles enhanced the formation of oil-in-water-in-oil (O/W/O) emulsions, generating unstable emulsions. The study also found that increasing temperature and adding inorganic solids decreased the emulsion height over time, which was predicted by the emulsion layer growth model. The coagulation rate constant was a tuning parameter, with a higher value implying higher internal repulsion and stronger coagulation between water droplets, facilitating emulsion instability. It has been observed that elevating the storage temperature and introducing kaolinite accelerates the coagulation rate constant, whereas the addition of calcite decreases this value, ultimately contributing to the stabilisation of the emulsions.

Development and validation of a numerical model for frost growth based on nucleation theory

Cold surface frosting is a complex process involving multi-component phase change heat and mass transfer and variable void structure. It is very challenging to deeply understand the frosting law and mechanism and accurately simulate the frosting process. Existing numerical models of frost growth have many shortcomings, such as a narrow application range, few verification parameters and low reliability. For these reasons, this paper developed a numerical model of frost layer growth based on nucleation theory, modified the phase transition model, and proposed a formula for constraining the picking limit of the frost layer. Additionally, it introduced a formula for calculating the average temperature of the two phases in the frost layer. The simulation results for frost layer thickness, density, temperature, and distribution were extensively verified using experimental data obtained by different scholars under various conditions and compared with simulation results in related literatures. The results show that the simulation results of all parameters under different conditions are in good agreement with the experimental data, with a maximum deviation of less than 15 %. Notably, the simulation results for frost thickness and distribution are more accurate than those found in existing literatures. The model developed in this paper offers a higher number of validation parameters, a wider validation range, and greater accuracy and reliability. This model can provide a solid theoretical foundation for studying frost characteristics under complex conditions and for the optimal design of frost-prone heat exchangers.

On the Physics of High CAPE

Abstract Large values of convective available potential energy (CAPE) are an important ingredient for many severe convective storms, yet there has been comparatively little research on how, physically, such large values arise or why they take on the observed values and climatology. Here we build on recently published observational and theoretical work to construct a simple, one-dimensional coupled soil–atmosphere model of preconvective boundary layer growth, driven by a single diurnal cycle of prescribed net surface radiation. Based on this model and previously published research, we suggest that high CAPE (>∼1000 J kg−1) results when air masses that have been significantly modified by passage over dry, lightly vegetated soils are advected over moist and/or moderately vegetated soils and then exposed to surface solar heating. Several diurnal cycles may be needed to raise the moist static energy of the boundary layer to levels consistent with high CAPE. The production of CAPE and erosion of convective inhibition (CIN) are strongly affected by the potential temperature of the desert-modified air mass, the level of near-surface soil moisture (and root-zone soil moisture if significant vegetation is present), the type of soil, and the characteristics of the vegetation. Consequently, CAPE production and severe convective weather may be significantly affected by regional-scale land-use changes and by climate change. Significance Statement The energy available for severe convective storms depends strongly on the properties of the underlying soil and vegetation and the temperature of air masses formed over dry terrain upstream. This implies that the severity of convective storms can be strongly affected by changes in land use and by climate change.

In-Situ Raman Spectroscopy of Defined Copper Oxide Surfaces Formed by Electrochemically Controlled High-Temperature Oxidation

The oxidation processes of copper are of great importance since its occurrence leads to various problems, both in further processing and in operation of electronic devices and other technical applications. Extensive research on the thermal oxidation of copper has demonstrated that temperature and oxygen partial pressure affect the formation of oxides, oxidation rates and the chemical composition.In this work powerful electrochemical methods for controlled oxidation are presented, where the oxygen partial pressure on the metal surface can be varied over a range of 10-25 to 100 bar in a single experiment. A specific arrangement of the setup extends its capabilities to enable in-situ Raman spectroscopy measurements of the produced oxide. Controllable oxidation states are achieved in a solid-state electrochemical cell by polarizing a copper sample in contact with a single crystal of yttria-stabilized zirconia, which is conductive for oxygen ions at high temperatures. Optical transparency of the single crystal allows the Raman laser to pass through the crystal to measure the copper oxide formed on the copper-electrolyte interface. Cyclic voltammograms contain kinetic and thermodynamic information about the oxidation processes. Thus, the various oxidation reactions are controlled by the potential that corresponds to the oxygen partial pressure, while the current measures the rate of layer growth as well as the thickness of the oxide layer. In situ Raman measurements allow more detailed analyses of the oxides. The combined data will be used to build a model for oxide layer growth, with particular attention to the defect chemistry of the copper oxide.

A novel method of discharge capacity prediction based on simplified electrochemical model-aging mechanism for lithium-ion batteries

Obtaining the State of Health of lithium-ion batteries and mastering its degradation laws are crucial for the utilization of Electric Vehicles. However, the prediction of discharge capacity of lithium-ion batteries requires high accuracy, which is subject to the variation of cells and the uncertainty of operating conditions. In this work, a discharge capacity prognostics method for lithium-ion batteries is developed based on a simplified electrochemical coupled aging mechanism model. Firstly, the solid-phase diffusion process is analyzed by using a simplified electrochemical model, and the particle rupture stress at different C rates is obtained. Then, based on the aging mechanisms in terms of Solid Electrolyte Interphase (SEI) layer growth model and particle volume expansion model, the SEI growth rate and correlated aging kinetics parameters are optimized by using particle swarm optimization algorithm. Finally, combined with the further analysis of aging mechanisms and variation of model parameters at early, middle, and late stage of degradation, the developed discharge capacity prediction method is verified at separate stages for batteries at 1C, 2C and 3C respectively, with the average relative error of full life cycle no more than 4 %.

The effect of alloying elements in Ti-5Mo-5V-8Cr-3Al alloy on growth kinetics of TiB whiskers in boride layer

As one of the important ways to improve surface properties of Ti alloys, the boride layer prepared by the pack boriding is closely related to the growth and morphology of TiB whiskers in the boride layer, whereas the growth and morphology of TiB whiskers are significantly affected by alloying elements in the alloys. This work systematically explored the effect of alloying elements in β-type Ti-5Mo-5V-8Cr-3Al Ti alloy on growth kinetics of TiB whiskers and thickness of the boride layer using experiment and first-principles investigations. After boriding, an outer TiB2 layer and an inner TiB whisker + Ti layer are formed on Ti surface. TiB/β-Ti interface herein is non-coherent with the orientation relationships of (011)TiB//(1¯1¯ 0)β-Ti and [1¯ 00]TiB//[1¯ 11]β-Ti. Alloying elements segregated at the interface can increase diffusion energy barrier and slow down diffusion rate of active [B] atoms, and further reduce growth rate of TiB whiskers. Finally, a theoretical model for the boride layer growth on Ti surface was proposed.

Optimization of dissolved hydrogen concentration for mitigating corrosive conditions of pressurised water reactor primary coolant under irradiation (2) evaluation of electrochemical corrosion potential

ABSTRACT One of the major subjects for evaluating the corrosive conditions in the PWR primary coolant was to determine the optimal hydrogen concentration for mitigating PWSCC without any adverse effects on major structural materials. As suitable procedures for evaluating the corrosive conditions in PWR primary coolant, a couple of procedures, i.e. water radiolysis and ECP analyses, were proposed. The previous article showed the radiolysis calculation in the PWR primary coolant, which was followed by an ECP study here. The ECP analysis based on a couple of a mixed potential model and an oxide layer growth model was developed originally for BWR conditions, which was extended to PWR conditions with adding Li+ (Na+) and H+ effects on the anodic polarization curves. As a result of comparison of the calculated results with INCA in-pile-loop experiment data as well as other experimental data, it was confirmed that the ECPs calculated with the coupled analyses agreed with the measured within ±100 mV discrepancies.

Diffusional Model of Expanded Austenite Layer Growth on AISI 316L Stainless Steel During Low-Temperature Hybrid Thermochemical Treatment

A simultaneous nitrogen and carbon diffusional model in AISI 316L stainless steel is presented in this numerical study to simulate expanded austenite layer growth developed during hybrid thermochem...

FORMATION OF POROUS SILICON ON A HIGHLY DOPED P-TYPE MONOCRYSTALLINE SILICON

Porous silicon layers were formed on a p-type silicon wafers by electrochemical anodisation. Dependencies of thickness and porosity of porous silicon layers as well as effective valence of silicon dissolution versus anodizing time and current density were obtained and analysed. A mathematical model for growth of layers of porous silicon was developed.

VLS Homoepitaxy of Lead Iodide Nanowires for Hybrid Perovskite Conversion.

Controlled fabrication of lead halide-based perovskite (LHP) nanostructures provides a new methodology for exploiting the excellent optoelectronic properties of the material. Here, we report the vapor-liquid-solid (VLS) growth of a highly uniform and dense array of [0001]-oriented PbI2 nanowires using PbI2 thin film as the epitaxial substrate layer. We show that reducing the lattice mismatch of the van der Waals epitaxial PbI2 substrate layer is necessary to accommodate the aligned nanowire growth. Our proposed layer growth model suggests that the nanowire growth is stabilized by maintaining the {0001} liquid-solid interface, which stems from the nucleation on the PbI2 substrate layer. We also demonstrate that the strain-induced nanowire deflection after conversion into CH3NH3PbI3 depends on the transfer sequence and conversion time. These findings provide a general opportunity to design and fabricate nanostructures, such as heterojunctions or superstructures for future device applications, rationally based on lead halide or LHP nanowires.

In-situ synthesis of MgAlB4 whiskers as a promising reinforcement for aluminum matrix composites

Metal boride whiskers were successfully synthesized in Al matrix by ball-milling combining with vacuum hot pressing process. Composition and structural analysis confirm that the metal boride is hexagonal crystal MgAlB4. First-principles calculations indicate that Mg doping can promote the growth of AlB2 in [0001] orientation and inhibit the growth in [213‾0] orientation. Based on the experiment and calculation results, we proposed a layer growth model with tip preferential growing in [0001] direction to obtain MgAlB4 whiskers. Tensile tests show that the in-situ synthesized MgAlB4 whiskers reinforced Al matrix composites have excellent ultimate tensile strength with an acceptable elongation to break. Electron backscatter diffraction results show that the whiskers can significantly refine the grain of the matrix, resulting in more retention of low angle grain boundaries in the matrix. Fracture analysis reveals that strong interface bonding was achieved between the whisker and the Al matrix, which benefits the load transfer between the matrix and the whiskers and results in crack initiation preferentially in whisker.

Equilibrium Versus Paraequilibrium Precipitation of Cementite in Ternary Alloys: Thermodynamic and Kinetic Interpretations

The precipitation of cementite on decomposition of austenite is examined by an edgewise layer growth model of the carbide in Fe–1.2C wt% steels. The interface boundary can migrate into the supersaturated matrix isothermally at 400–600 °C, similar to tempering. The present paper thus explores precipitation mechanisms by two different kinetics. Intitially, an equilibrium growth, by the diffusional transport of atoms is simulated with the Dictra package accessing thermodynamic parameters from Thermo-calc. An extremely slow rate for the growth of the carbide platelet seems to be implausible due to the presence of the ternary [M = Mn, Si, Al] of 2 wt%. To overcome this, the investigation then finds an alternative, bringing diffusion constraints of the substitutional atoms under consideration in a paraequilibrium growth study. The SGTE database of the Thermo-calc however lacks paraequilibrium composition of Al in the carbide, thus Thermo-calc cannot be used thoroughly for this study. A first-principles calculation therefore is necessary which in turn evaluates the time-lag in equilibrium versus paraequilibrium growth kinetics. It reveals that the paraequilibrium precipitation of cementite is decisive due to Si (or Al) as the ternary, whereas, in the case of manganese steel, an opposite trend can be seen that the equilibrium partition of Mn reduces the Gibbs free energy during the interface study.

Modeling of hydrate layer growth in horizontal gas-dominated pipelines with free water

Flow is obstructed as hydrate layer grows on the wall of pipelines. In gas-dominated pipelines with free water, the gas–liquid–solid (hydrate) flow, gas–solid (hydrate) flow, and water-saturated gas flow may coexist at different locations of the pipeline. Current studies on hydrate layer growth largely focus on a single-flow pattern in gas-dominated pipelines. No studies have been conducted considering different flow patterns in pipelines simultaneously. Considering the flow pattern transition due to the variation in the contents of free water and hydrates in the gas phase, an integrated model is developed to quantitatively predict the hydrate layer growth in horizontal gas-dominated pipelines with free water. Based on the proposed model, the hydrate layer thickness distribution in horizontal gas-dominated pipelines is simulated and the sensitivity analysis of different factors is performed. The results show that the distribution of the hydrate layer thickness on the pipe wall along the pipeline is non-uniform. There exists a point in the flow that is most vulnerable to hydrate layer growth at a given point in time in the gas–liquid–solid flow. This study provides a theoretical basis for preventing hydrate blockage in submarine natural gas pipelines.

Effects of porosity in a model of corrosion and passive layer growth

We introduce a stochastic lattice model to investigate the effects of pore formation in a passive layer grown with products of metal corrosion. It considers that an anionic species diffuses across that layer and reacts at the corrosion front (metal-oxide interface), producing a random distribution of compact regions and large pores, respectively represented by O (oxide) and P (pore) sites. O sites are assumed to have very small pores, so that the fraction $\Phi$ of P sites is an estimate of the porosity, and the ratio between anion diffusion coefficients in those regions is $D_{\text r}<1$. Simulation results without the large pores ($\Phi =0$) are similar to those of a formerly studied model of corrosion and passivation and are explained by a scaling approach. If $\Phi >0$ and $D_{\text r}\ll 1$, significant changes are observed in passive layer growth and corrosion front roughness. For small $\Phi$, a slowdown of the growth rate is observed, which is interpreted as a consequence of the confinement of anions in isolated pores for long times. However, the presence of large pores near the corrosion front increases the frequency of reactions at those regions, which leads to an increase in the roughness of that front. This model may be a first step to represent defects in a passive layer which favor pitting corrosion.

Models for predicting TGO growth to rough interface in TBCs

Oxidation is often regarded as a key factor to cause the failure of thermal barrier coating system (TBCs), which arouses uneven growth of thermal grown oxide (TGO) layer. During the process of oxidation, the rough interface between TGO and bond coat (BC) influences the large growth of TGO and the stress concentration in TBCs. However, theoretical models to describe the effect are not many previously. In the present research, firstly, based on the finite deformation analysis, a three-concentric-circle model considering growth effect of TGO layer is presented to characterize stress concentration around the TGO induced by the oxidation of TBCs. Secondly, another growth model for TGO layer growth is presented based on the creep constitutive theory. From two models, the results indicate that the maximum tensile stress in the valley region locates at the interface of top coating (TC)/TGO, while the maximum normal stress locates at the BC/TGO interface in the peak region. Additionally, the thickness of TGO layer in the valley region decreases as roughness increases, while it increases as the roughness increases in the peak region. The theoretical models can be used to explain the uneven growth of TGO.

Semipolar AlN on Si(100): Technology and properties

Initial stages of the semipolar AlN layer formation by chloride-hydride vapor phase epitaxy on a misoriented Si(100) substrate with a thin intermediate nano-SiC layer grown by atomic substitution method are investigated. It is found that once the growth rate of AlN layer on a nano-SiC/Si(100) substrate is about 0.02μm/h, the layer is formed in a polar direction. On the other hand, at the growth rate of 1μm/h the layer is formed in a semipolar direction. We propose the model of the semipolar AlN layer growth based on the formation of the special structure on the SiC layer synthesized by atomic substitution and on the possibility of the matching of the quasi-lattices of Al(20−23) and 3CSiC(100) planes assuming bonding of four atoms from the layer to four atoms of the 3CSiC quasi-lattice consisting of three lattice unit cells in one of the directions.

Albedo changes after fire as an explanation of fire‐induced rainfall suppression

AbstractObservational evidence of rainfall suppression by fire has recently been documented in African drylands, but the underlying mechanism remains poorly understood. Here we investigate the extent to which fire‐induced changes in latent heat flux and albedo may inhibit boundary layer predisposition to convective rainfall. We use Modern‐Era Retrospective analysis for Research and Applications, Version 2 reanalysis data from the Kalahari region of Southern Africa to drive a low‐dimensional boundary layer growth model. We find that both increased albedo and, to a lesser extent, increased latent heat flux could result in less convective rainfall. The sensitivity to land surface feedbacks is higher earlier in the dry season and at drier sites. Finally, using Moderate Resolution Imaging Spectroradiometer fire and albedo data, we present novel evidence that increases in albedo after fire, or brightening, are common in regions receiving less than 850 mm of precipitation annually. This supports the idea that fire‐induced surface brightening is responsible for observed rainfall deficits after fire.

Modelling of zirconium alloy hydrogenation

Zirconium alloys are the construction materials for critical elements in active zones of nuclear power reactors. During the operation of reactors such materials are subject to hydrogenation. Hydrogenation results in a decrease of alloy plasticity and cracking resistance. The formation of brittle hydrides at crack tips can result in severe embrittlement. One of the most important requirements for the reactor's active zone materials is low hydrogen absorptivity. The mathematical model of hydride layer formation and growth is developed. The problem is to determine the dynamics of the free boundary of phase interface and the distributions of hydrogen concentration in hydride and in solution. Iterative computational algorithm for solving the nonlinear boundary-value problem with the Stefan condition based on implicit difference schemes is developed.

Modeling of Porous Metal Oxide Layer Growth in the Anodization Process

Most of the works on nanotubes growth are oriented on exploring suitable setups for optimal growth for the structures. Substantially less interest is devoted to first principles based mathematical modelling of the growth. We present a simple mathematical model of porous metal oxide layer growth in the anodization process. The mathematical model is essentially the model used by [Sample, Golovin: Formation of porous metal oxides in the anodization process, Phys. Rev. E 74, 2006]. The dynamics of the system is determined by the solution of the continuity equation for the electric current density, while the boundary conditions for the overpotential are given by the Butler-Volmer relation. The arising system of partial differential equations is solved using the finite element method. Unlike in the other works, the continuity equation for the electric current density is solved not only in the oxide layer, but also in the metal and the electrolyte. The positions of the interfaces are not known a priori and must be found in the process of the numerical solution of the problem. The core technical difficulty is the tracking of the metal/oxide and oxide/electrolyte interface. This issue is addresed via the application of the level-set method. The main benefit of using the level-set method is that it can easily handle topology changes and that the computation is done on a fixed mesh. Another important ingredient of the developed numerical scheme is that the problem is solved using the mixed formulation. The mixed formulation allows one to succesfully handle the boundary condition arising from the Butler-Volmer relation even in the level-set setting. It is shown that the chosen methodology correctly captures the discontinuities of the electric potential at the interfaces. The advocated numerical scheme has been implemented in FEniCS (software for the automated solution of differential equations by finite element methods). Results of the simulations with the physical parameters corresponding to the growth of aluminium oxide layer are presented. The computational methodology based on the level-set method and on the mixed formulation can be easily applied in two dimensional as well as in three dimensional setting. The successfully developed method for the interface tracking which is the core technical difficulty in the modelling of oxide layer growth allows one to think about further extensions of the model. In particular the flow in the electrolyte, the deformation inside the oxide layer as well as surface tension effects could be possibly numerically simulated in the future.

A new approach to calculation of flue gas scrubbing efficiency in electrostatic precipitators

The majority of existing approaches to computation of electrostatic precipitator (ESP) efficiency do not take into account particle reentrainment from collecting electrodes. The first attempts to take into consideration particle reentrainment were made only recently. However, the existing reentrainment models for ESP are not sufficiently substantiated. A general model, which takes into account precipitation of particles, entering the ESP inlet (direct precipitation), as well as precipitation of reentrained particles (secondary precipitation), is presented in the paper. The model describes physical processes in an ESP using three integral parameters. These parameters are direct precipitation coefficient, secondary precipitation coefficient, and reentrainment coefficient, which is the ratio of reentrained particle flux to precipitation flux. An improved technique for computation of direct precipitation that takes into account particle charge distribution function is proposed. The influence of gas flow turbulence on charge distribution function parameters, as well as on other parameters of precipitation phenomena, is taken into account. The method has low computational costs. The secondary precipitation coefficient is also computed using this method. The most difficult task is calculation of the reentrainment coefficient. We suggest using data of periodical ESP testing to determine the reentrainment coefficient. The analysis of experimental data indicates that a fly ash layer on collecting electrodes is of paramount importance. It has been shown that the flux per unit length of particles falling into hoppers is proportional to weight (thickness) per unit length of the fly ash layer. Distributions of precipitation flux, flux into hoppers, reentrained particle flux along the ESP duct, and particle penetration through the ESP are computed using experimental data. A novel model that is based on a flux balance equation for each length element of an ESP duct is presented. The model has the form of a connection between physical phenomena that take place on two successive length elements of the collecting electrode. The model qualitatively agrees with experimental data. However, correction of the secondary precipitation coefficient and the reentrainment coefficient is required for quantitative agreement. In this regard, a model of layer growth and determination of functional relations between layer weight, hopper flux, and particle penetration play a key role.