Decrease In Diffusion Coefficient Research Articles

High-performance of Mg2+ additive for addressing NH3 escape in inorganic ammonia carbon capture

The urgency to reduce the energy consumption of organic amine carbon capture, while the inorganic ammonia carbon capture (IACC) and co-production of ammonium fertilizer eliminates the desorption energy consumption. Inhabiting NH3 escape at the end of IACC process requires a large amount of water consumption, and there is a lack of corresponding process parameters and technical routes. In this paper, Mg2+, one of major components in desulfurization wastewater, was used as an NH3 inhibitor. It’s found that the addition of MgCl2 can increase the total NH3 absorption rate by 13.02 % and reduce the total NH3 escape rate by 87.02 %. Furthermore, the effects of six process parameters in the forward and reverse NH3 mass transfer experiments could be distinctly quantified by the normalization method to determine the differentiation between priority and others. It’s concluded that NH3 can enter the first solvent shell of Mg2+ to replace some H2O based on the first-principles calculations, which is the main cause for the decrease of NH3 diffusion coefficient. Finally, simulation with Aspen Plus was applied to construct the complete process route, and the Arrhenius formula for the Mg(OH)2 nucleation was used to refine the reaction kinetic parameters of the simulation. The heat and water balance of IACC could achieve within this system, and the excellent NH3 inhibition effect of added Mg2+ was verified, which could effectively keep from the NH3 escape within 3 ppm.

Compressive strength and chloride permeability of cement-based materials with high-volume compound mineral admixtures

Ground granulated blast-furnace slag (GGBFS) is well known to be capable of improving the performance of cement-based materials, but few studies focus on the impact of its large dosage on concrete containing basalt powder. In this study, the compressive strength and chloride permeability of cement-based materials with compound mineral admixtures (CMAs) containing high-volume GGBFS, basalt powder and desulfurisation gypsum were investigated. The results showed that the mortar strengths at 3, 7 and 28 days decreased with increasing GGBFS content, but that at 56 and 84 days increased with the addition of 45 wt% GGBFS. This is because the activity of GGBFS at an early stage has not been stimulated and the pozzolanic effect is exerted at a later stage. Moreover, cement replacement with up to 55 wt% GGBFS caused a significant decrease in the chloride diffusion coefficient of the mortar and concrete. Furthermore, the incorporation of GGBFS led to a remarkable refinement in pore structure of the hardened paste due to pozzolanic and filler effects. Therefore, the partial replacement of cement with high CMA contents (≥70 wt%) in concrete is desirable for ocean projects requiring low chloride permeability, and significantly reduces carbon dioxide emissions.

Grand canonical Monte Carlo and molecular dynamics investigation of hydrogen solubility and diffusivity in nonmetallic polyvinyl chloride, polyethylene and polyvinylidene fluoride pipes materials

To choose appropriate nonmetallic pipe materials for reducing hydrogen permeation, the hydrogen permeability in polyvinyl chloride, polyethylene, and polyvinylidene fluoride are studied and compared by molecular dynamics simulations. The findings demonstrate the solubility coefficient of hydrogen in polyvinyl chloride rises as the temperature decreases. However, in polyethylene and polyvinylidene fluoride, the trend is reversed. With the decrease of temperature, the diffusion and permeability coefficients decrease. The diffusion of hydrogen molecules follows the jumping mechanism. Among the materials studied, polyvinylidene fluoride is the most suitable material for hydrogen pipes due to its superior resistance to hydrogen permeation.

Mitigating chloride attack in cementitious materials without compromising other properties via the use of viscosity modifying admixture

To mitigate the harmful chemicals ingression into cementitious materials, traditional methods often aim to densify the pore structure, posing challenges for concrete dead-load or crack control. This paper proposes a facile method to mitigate chloride attack via increasing the pore solution viscosity in cementitious material without changing the matrix density or compromising other properties. The results indicate that the addition of viscosity modifying admixtures (VMAs) to the mortar, as an equivalent mass replacement of mixing water, can mitigate chloride ingress. Although it reduces the early age hydration heat, the mechanical strength at full age (3 d–28 d) and the porosity at 28 d remain unchanged when using an effective VMA (PEG1000). In addition, the matrix resistance to leaching is improved as well. These results may be attributed to the enhanced pore solution viscosity and the coexistence of VMA and C–S–H with decreased interlayer distance and shortened mean chain length. After 28 d of exposure, the most effective experimental group (PEG1000) showed approximately a 28 % decrease in chloride diffusion coefficient compared to the control group. This paper may inspire new technology to mitigate ions diffusion and promote its practical application.

Manifestation of site energy landscapes for ion transport in borate glasses.

The potential energy landscape of lithium borate glass of composition Li3B7O12 has been investigated by the charge attachment induced transport (CAIT) technique. Here, native lithium ions have been replaced by foreign alkali ions, M+ = K+, Rb+, Cs+. All experiments exhibit a pronounced decrease of native ion diffusion coefficients over more than 4 orders of magnitude with decreasing local population of Li+. The energy landscape is modelled by a site energy distribution (SED) with a concentration dependent Fermi energy of the native Li+ ions. The width of the populated part of the SED is found to be 250 meV (FWHM). The conclusion is made possible by a combination of a macroscopic ion replacement experiment with a Nernst-Planck-Poisson modelling of concentration depth profiles measured by secondary ion mass spectrometry (SIMS). Possible generalizations of macroscopic transport theory to match an Onsager ansatz are discussed.

Pore‐Scale Modeling of Water and Ion Diffusion in Partially Saturated Clays

AbstractAn accurate mechanistic understanding of solute diffusion in partially saturated clays is critical for assessing the safety of deep geological repositories for radioactive waste. In this study, a pore‐scale numerical framework is developed to simulate water and ion diffusion in partially saturated clays. First, the two‐phase Shan‐Chen Lattice Boltzmann method is employed to establish the liquid‐gas distribution in a reconstructed three‐dimensional pore geometry of a clay. An equivalent solute method is also developed and validated to improve the numerical stability of the solution at the liquid/gas interface corresponding to steep variations of the concentration and diffusion coefficient of the water tracer. By using a mobility‐distance relationship from molecular simulations, Fick's law is numerically solved to simulate water diffusion in nanopores, while the coupled Poisson‐Boltzmann‐Nernst‐Planck equations are solved to simulate ion diffusion under the influence of the electrical double layer (EDL). Our model reveals that the decrease of relative effective diffusion coefficients during the desaturation is more pronounced for ions than for water, due to the additional transport pathway of water tracers in the gas phase. The obtained effective diffusion coefficients of tritiated water and ions agree well with reported data from compacted sedimentary rocks. By comparing the local electric potential and the distribution of ion concentrations in single pores, the simulation results suggest that the EDL in unsaturated clays has a more complex influence on ion distribution than under fully water‐saturated conditions. This study provides critical insights into the coupled transport processes of solutes in partially saturated clays.

Molecular Dynamics Simulation Study of the Diffusion of Carbon Dioxide in Heptane: Application in Natural Gas Cleaning

Using solvents to remove carbon dioxide is an effective way to purify natural gas. Diffusion of solute in solvent is key to natural gas purification. In this study, molecular dynamics (MD) simulations of the diffusion of carbon dioxide in heptane at different temperatures and pressures were performed to simulate the conditions of industrial purification process. The diffusion coefficients were measured in two different configurations; pure solvent and binary solute-solvent systems. The diffusion coefficients of the binary system were observed to be in the order of 10-9 m2/s. An increased temperature was observed to increase the diffusion coefficient of the carbon dioxide in heptane while an increase in pressure reduced the value of the diffusion coefficient. The diffusion coefficient was also observed to follow an Arrhenius-type relationship with respect to temperature. The activation energy of the system increased from 9.228 kJ/mol to 11.139 kJ/mol with pressure increase. A linear relationship was detected between the diffusion coefficient and the viscosity of the system and an increased viscosity of the system results in a decreased diffusion coefficient. The results of the research showed that carbon dioxide behavior in heptane offers the theoretical backing for the development of a new natural gas desulphurization solvent.

Прогнозування ризику розвитку розладів аутистичного спектра в дітей з епілептичними енцефалопатіями

Predicting the risk of developing autism spectrum disorders (ASD) in children with epileptic encephalopathies (EE) is an important task, which makes it possible to identify the most significant risk factors and develop ways of their modification. Purpose - to develop a model for predicting the risk of developing ASD in young children with EE. Materials and methods. 75 children aged 0-3 years with the onset of epileptic seizures in the first year of life, clinical manifestations of EE were examined. The most informative clinical, neurophysiological, and neuroimaging indicators for predicting the risk of clinical manifestations of ASD were determined: age of onset of epileptic seizures, index of spike-wave activity during NREM sleep, frequency and amplitude of alpha rhythm, frequency and amplitude of epileptiform activity, fractional anisotropy and mean diffusion coefficient in the Broca’s center, fractional anisotropy in the Wernicke center and knee of the corpus callosum. The multiple linear regression method was used to predict the risk of developing ASD symptoms. Results. A model for predicting the risk of developing clinical manifestations of ASD in children with EE has been developed. It was established that the risk of developing clinical manifestations of ASD increases with a decrease in the age of onset of epileptic seizures, decrease in the frequency and amplitude of the alpha rhythm according to electroencephalography (EEG) data, increase of the index of spike-wave activity, frequency and amplitude of epileptiform activity, increase in the index of fractional anisotropy in the anterior part of the arcuate tract, decrease in the average diffusion coefficient in the area of the Broca’s center, fractional anisotropy in the Wernicke center and the knee of the corpus callosum according to magnetic resonance tractography. Conclusions. A regression model for predicting the risk of clinical manifestations of ASD in children with EE was developed with an average error of approximation of 13.2% and a coefficient of determination of 0.74, which is recommended for use in clinical practice in order to form groups of children at high risk of ASD. Such children require further dynamic monitoring and early intervention by specialists of a multidisciplinary team for timely identification and correction of ASD symptoms The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of the participating institution. The informed consent of the patient was obtained for conducting the studies. No conflict of interests was declared by the author.

Investigation on interphase mass transfer coefficient of a deformable bubble with density contrast using phase-field lattice Boltzmann method

The gas–liquid mass transfer process with density contrast is modeled in this paper using a phase-field Lattice Boltzmann (LB) method. In this method, the phase-field model used to calculate the flow field and the continuous species transfer model used to calculate the concentration distribution are coupled by introducing the divergence condition of the velocity in the presence of mass transfer into the Allen-Cahn equation. For a deformable bubble rising in stagnant liquid, a two-dimensional parameter dependence study is conducted and the results indicate that an increase in initial diameter, as well as a decrease in liquid diffusion coefficient or liquid viscosity, can improve the steady-state value for the Sherwood number, whereas the distribution coefficient has a little impact on this steady-state value. Furthermore, a correlation originally proposed by Takemura and Yabe (1998) modified with a shape factor can be used to predict the steady-state Sherwood number in the numerical results.

A multi-scale fractal model of gas flow considering the evolution of kerogen microstructure and the multi-physical coupling

Shale is a complex porous medium. The migration mechanism within its different microstructural systems is crucial for the efficient recovery of shale gas. The kerogen microstructure influences the adsorption–desorption effect of the reservoir. This study accounts for the heterogeneity of shale and uses fractal dimension to characterize the fracture and inorganic matrix systems. It also establishes a kerogen fractal diffusion model by integrating fractal diffusion with fractal theory. Furthermore, this study analyzes the effect of evolution of micro structural parameters of kerogen on macro permeability, such as: (1) kerogen fractal dimension; (2) effective diffusion coefficient of kerogen; (3) maximum kerogen aperture. Numerical simulation shows that: The maximum pore size and porosity of kerogen in direct proportion to fractal dimension and effective diffusion coefficient. The fractal dimension and effective diffusion coefficient decrease gradually during shale gas extraction. The fractal effective diffusion has a significant impact on cumulative gas extraction.

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

The addition of nickel oxide (NiO) to 8 mol% yttria-stabilized zirconia (8YSZ) accelerates the phase transformation from cubic phase to tetragonal phase when exposed to a reducing atmosphere at relatively high temperatures such as 900 ℃, resulting in the degradation of oxide ion conductivity.In this study, NiO-related phase transformation of 8YSZ electrolyte is investigated for anode-supported cells (ASCs). 8YSZ electrolyte co-sintered with NiO-YSZ anode at high temperatures exhibited NiO dissolution into the 8YSZ electrolyte during the sintering process and the amount of dissolved NiO increased with increased sintering temperatures. After reducing the cells at 900 ℃, phase transformation is observed in the 8YSZ electrolyte and resulted in a decrease of the oxide ion diffusion coefficient (D*). On the other hand, no phase transformation is observed for the cells reduced at 700 ℃for 5 hours.

Holographic energy loss near critical temperature in an anisotropic background

We study the energy loss of a quark moving in a strongly coupled quark gluon plasma under the influence of anisotropy. The heavy quark drag force, diffusion coefficient, and jet quenching parameter are calculated using the Einstein–Maxwell-dilaton model, where the anisotropic background is characterized by an arbitrary dynamical parameter A. Our findings indicate that as the anisotropic factor A increases, the drag force and jet quenching parameter both increase, while the diffusion coefficient decreases. Additionally, we observe that the energy loss becomes more significant when the quark moves perpendicular to the anisotropy direction in the transverse plane. The enhancement of the rescaled jet quenching parameters near critical temperature T c , as well as drag forces for a fast-moving heavy quark is observed, which presents one of the typical features of quantum chromodynamics phase transition.

Recyclability of poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBH) for food packaging applications

This study is the first to investigate the recyclability of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), a small chain length PHA, and evaluate the gas barrier properties of the recycled materials. A recycling simulation of PHBH was performed through five twin-screw extrusion cycles. Although the onset degradation temperature and the chemical structure of the processed PHBH remained stable, size exclusion chromatography and melt flow index revealed a drop of 24.3% in the molar mass of the recycled materials. However, the recycled samples showed higher impact strength and, therefore, are less brittle and more elastic. Gas barrier properties of PHBH were found to enhance after the first recycling step. A significant decrease in both permeability and diffusion coefficients was observed after the first extrusion cycle. At the same time, the calculated mean integral diffusion coefficient <D> as well as the plasticization factor (γCeq) demonstrate a weak water plasticization effect for recycled materials.

Molecular dynamics study of the corrosion protection improvement of superhydrophobic dodecyltrimethoxysilane film on mild steel

Recently, superhydrophobic surfaces have received increasing interest in metal corrosion protection due to their excellent waterproofing characteristics. However, little attention has been paid to the related anti-corrosion mechanism at the molecular level. In this work, the protection behaviors provided by the superhydrophobic dodecyltrimethoxysilane for mild steel were first explored using molecular dynamics (MD) simulation in terms of silane absorption orientations and water cluster wetting behaviors. The results show that the conformations of dodecyltrihydroxysilane (DTHS) on the Fe substrate are greatly dependent on the solvent environment. Typically, the DTHS molecule adopts a “standing” orientation with the hydrophilic head attached to the Fe surface and the hydrophobic tail remaining in the polar phase, which is conducting to generate a good repulsive effect on the water droplet. Based on this, the diffusion performance of corrosive species in the superhydrophobic DTHS film was further investigated. The computational results indicate that the corrosive species are confined to specific regions of the film, which results in a decreased diffusion coefficient. Additionally, the weak movement of DTHS molecules also increases the transport resistance of the corrosive medium through the superhydrophobic DTHS film, thereby improving the corrosion protection of the underlying metal substrate. The results obtained in this work will deepen our understanding of the anticorrosion mechanism of superhydrophobic silane films.

Oxygen Ion Conduction Property of Solid Oxide Membrane Based on Multi-scale Analysis

In recent years, various environmental problems such as rising temperature, droughts, and extreme weather events have become more serious in many parts of the world because of global warming. One of the causes of the global warming is an increase in emissions of greenhouse gases such as CO2, CH4, and N2O, those are emitted during a combustion of fossil fuels such as coal, oil, and natural gas in thermal power generation. As energy consumption accelerates year by year, the depletion of fossil fuels is also becoming an issue. Therefore, hydrogen energy is attracting attention. Hydrogen is known as a clean energy because it reacts with oxygen to produce only water and chemical energy.Fuel cells are attracting attention as a new power generation device that produces electricity from hydrogen energy. Fuel cells generate electricity directly through chemical reactions, resulting in minimal power generation loss from energy conversion. Solid oxide fuel cells (SOFC), in which solid oxide electrolyte membrane (SOEM) is used as the electrolyte membrane, have particularly high-power generation efficiency. On the other hand, the operating temperature of SOFCs is extremely high (over 1000 K), which accelerates degradation of SOEM. Therefore, it is necessary to lower the operating temperature from high to medium (about 700 K) while maintaining high power generation efficiency.To solve this problem, we focus on dual-phasing and nano-structuring of SOEMs. Previous studies of SOEM have shown that dual-phase membranes have better ion transport performance than a single-phase membrane. For example, a dual-phase SOEM is composed of SSC (SrSc0.1Co0.9O3-d) with perovskite structure and SDC (Sm0.2Ce0.8O2-d) with fluorite structure. One the other hand, nano-structuring are nano-thin film and nano-crystalline. Nano-thin film is a method of forming an electrolyte film of several μm by layering nano-films of several nm in size. Nano-crystalline is a method to reduce a crystal size to several tens of nanometers. By these nano structures, the resistance of ion conduction is reduced, and ion conductivity is improved.However, the number of interfaces in dual-phase SOEM and nano structured membrane is expected to increase. Previous studies have reported a decrease in ion conductivity near the interface between different structures of membrane. This decrease in ion conductivity at the interface is caused by an increase in the energy barrier as the conduction path passes through the interface. The correlation between the reduction of ion conductivity and nano structures in membrane has not been clarified clearly.In this study, we analyze the mechanism of oxygen ion conductivity reduction near the interface by numerical simulations. Molecular simulations are performed to build up information by multi-scale analysis. Specifically, density functional theory (DFT), molecular dynamics (MD), and kinetic Monte Carlo (kMC) are performed in a bottom-up manner. First, MD simulations were performed using a potential model constructed from the energy states in the atomic arrangement at the interface obtained by DFT. We analyzed the ion conductivity at the interface and its crystal size dependence. We also create a hopping model of oxygen ions moving from site to site for kMC simulations. Next, kMC simulations are performed to analyze the oxygen ion conductivity in the dual-phase SOEM including interface, on a time and spatial scale similar to that of a real SOEMs.In this presentation, we report on the results of MD simulation. A dual-phase SOEM model consisting of SSC and SDC was used as the simulation model (Fig.1(a)). The diffusion coefficient of oxygen ions was obtained as an indicator of ionic conductivity. Because the ionic conductivity is determined by the balance between the energy barrier of the conduction path and the kinetic energy of the ions involved in ionic conduction. In this study, the activation energy for the diffusion was calculated as the energy barrier. The activation energy was estimated from Arrhenius relation of diffusion coefficient. The number of unit cells in the dual-phase SOEM model was varied to change the crystal size. As a result, both the diffusion coefficient and activation energy increase as the crystal size of SSC increases. On the other hand, as the crystal size of SDC increases, although the diffusion coefficient decreases, the activation energy increases (Fig.1(b)). These results show the dependence of the diffusion coefficient and activation energy on the crystal size in a dual-phase SOEM. Figure 1

Study on aging mechanism of SBS/SBR compound-modified asphalt based on molecular dynamics

Abstract Component ratio change is considered to be the main reason leading to the deterioration of asphalt properties, but there are few studies on the aging mechanism from the perspective of modifier molecules. To reveal the aging mechanism of styrene–butadiene–styrene block copolymer (SBS)/styrene butadiene rubber (SBR) compound-modified asphalt, the micro mechanism in the aging process was studied by combining molecular dynamics (MD) and Fourier transform infrared spectroscopy (FTIR). First, MD was used to establish the micro models of SBS/SBR compound-modified asphalt at different aging stages (non-aging, short-term aging, and long-term aging) and to verify its rationality. Second, the micro characteristics of the SBS/SBR compound-modified asphalt micro model, such as solubility parameters, diffusion coefficient, interface interaction energy, and radial distribution function, were analyzed by calculation. Finally, the FTIR results proved the rationality of the simulation and explained the aging mechanism of SBS/SBR compound-modified asphalt. The results show that the cohesiveness density and solubility parameters of SBS/SBR compound-modified asphalt increase, the diffusion coefficient decreases, and the molecular interface stability increases during the aging process. And, the carbonyl index, sulfoxide index, and aromatic ring index increased in different degrees after aging. The study explains the aging mechanism of SBS/SBR compound-modified asphalt from the perspective of modifier molecules and provides a theoretical basis for the research of asphalt anti-aging.

Molecular simulation study of liquid sulfur adsorption and diffusion in calcite nanoscale slits under varying temperature and pressure conditions

In the late stages of extensive development of high-sulfur carbonate gas reservoirs, pressure decline leads to sulfur enrichment, and when the temperature exceeds sulfur's melting point, sulfur precipitates in a liquid form, severely restricting the exploitation of high-sulfur carbonate gas reservoirs. However, the adsorption mechanism of sulfur deposition remains poorly understood. In this study, we investigated the microscopic adsorption mechanism of liquid sulfur in calcite nanopores using molecular simulation methods. Our research revealed that liquid sulfur adsorption in calcite nanopores is primarily influenced by pore size. When the pore size is less than 160 Å, multilayer adsorption dominates, with a single-layer sulfur film thickness of approximately 5 Å. At the nanoscale, 1 g of calcite with a 40 Å nanopore structure exhibits excess adsorption of liquid sulfur ranging from 0.00734 to 0.0279 g. As pressure increases, the adsorption of two or more layers intensifies, while the diffusion coefficient decreases. Conversely, as temperature rises, the density of each layer decreases, and the diffusion coefficient increases. Simultaneously, the diffusion coefficient of liquid sulfur in calcite slits exhibits a power function increase as the pore size enlarges. Under a pressure of 15 MPa, when the temperature increases from 420 K to 480 K, the diffusion coefficient increases from 6.96 × 10−11 m²/s to 3.51 × 10−10 m²/s. This study provides valuable insights into the adsorption and diffusion behavior of liquid sulfur in calcite nanopores, which can inform the development of high-sulfur carbonate reservoirs.

Evaluation of the in-vitro antifungal activity of Holoptelea Integrifolia ethanolic extract loaded in microemulsion

Microemulsions improve the transdermal delivery of several drugs over conventional topical preparations such as emulsions and gels: enhanced drug solubilization, increased skin flux, and decreased diffusion coefficient. Microemulsion-based systems find significant improvement in the topical delivery of antifungals. We believe that drug-loaded microemulsion will show better antifungal activity by better penetration into the skin and fungal cells. Antifungal agents are mostly lipophilic and easily formulated in topical vehicles. Microemulsions were prepared by the phase titration method. Formulations of the same drug and Excipient ratio and different concentrations were optimized with selected parameters like pseudo ternary phase diagram, particle analysis size, zeta potential validation, entrapment efficiency, and drug release studies performed by dialysis bag diffusion techniques at a temperature (37ºC). The study continued for 24 hours. The maximum amount of drug Holoptelea integrifolia release is 90% within 8hr. The study was monitored at 37ºC. Successfully done preparation, characterization, and drug release study of Microemulsion drug loaded.

Asteroseismic Investigation on KIC 10526294 to Probe Convective Core Overshoot Mixing

In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass slowly pulsating B-type star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations, and a quick decrease with 4 orders of magnitude shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals.

Molecular-level evaluation of thermal field confinement effects on moisture distribution at the interface of natural ester oil-paper insulation: An investigation of electric field correlation

Oil-paper insulation is commonly used in transformers and is subject to dynamic changes in moisture content and distribution due to the influence of multiple physical fields such as temperature and electric fields. Moisture at the interface of oil-paper insulation can distort the interfacial electric field and cause insulation failure, but it is difficult to measure and characterize. In this study, molecular dynamics was used to simulate the diffusion behavior of water molecules at the interface of natural ester oil-paper insulation at temperatures ranging from 298 to 373 K, and the effect of electric fields on water diffusion was also analyzed. The results showed that without an electric field, water molecules in natural ester insulating oil tend to cluster at 298 K. Water molecules gradually diffuse towards the interface of the natural ester oil-paper insulation, but most remain at the interface and are difficult to penetrate into the cellulose insulating paper. In addition, normal diffusion is gradually enhanced at 298–328 K, reaching a minimum at 343 K. The interaction energy between water molecules and natural ester insulating oil decreases with increasing temperature, while the interaction energy with cellulose insulating paper decreases and then increases, reaching a minimum at 343 K. The combined influence of temperature and electric fields leads to an increase in the number of water clusters at the oil-paper interface. The interaction energy between water molecules and both natural ester insulating oil and cellulose insulating paper is enhanced, inhibiting the diffusion of water into the insulating paper. It was also found that the ability of water to diffuse differs significantly when the electric field direction is normal to the interface compared to when it is tangential to the interface. This is due to the fact that the water molecules when subjected to electric field action turn to polarize, and their electric field direction diffusion coefficient decreases, but still much higher than the non-electric field action direction. Further, the study found that the natural ester oil-paper insulation interface polarization is directional, and water molecules polarized in the direction normal to the insulation interface require a higher electric field strength.