Thermodynamic Simulation Research Articles

Stability and deformation of a vacancy defect in skyrmion crystal under external magnetic and temperature fields

Skyrmion, a local bubble-like topological magnetization structure, can collectively emergent in magnets in a lattice form skyrmion crystal (SkX). SkX has great application potential in functional devices because it can manipulate material properties via coupling with atomic lattices. The lattice defects such as vacancy widely exist in the SkX as well, and they have rich dynamic behaviors and have great implications for the host material. However, although the nature of ideal SkX is well studied, the characteristics of SkX defects are relatively underdeveloped. Here, we deeply studied the structural properties of a vacancy defect in the SkX by a thermodynamic phase-field simulation. We found that the higher external magnetic and temperature fields favor rigid skyrmions (crystal), in which the SkX vacancy is less deformed, while the lower fields favor softer skyrmions where the SkX vacancy structure is considerably deformed. Such unique deformation and stability of the SkX vacancy are mainly the results of the competition between free energies in the view of thermodynamics. Our study demonstrated that the external field-controlled static properties of SkX vacancy highly depend on the quasiparticle nature of skyrmions. This indicates the properties of SkX defects can be controlled by the SkX features under different fields, which should open an avenue for the study and design of smart materials and advanced devices by engineering skyrmion crystals.

Characterization, formation mechanism, and human health risk assessment of fluoride in shallow groundwater of Suzhou city, East China

ABSTRACT Groundwater is a vital water source for human consumption and irrigation. Understanding its fluoride content and health implications is crucial for water resource management. This study investigated the quaternary aquifer in Suzhou, China, collecting and analyzing 49 groundwater samples. Thermodynamic simulation, multivariate statistical analysis, and health risk assessment models were employed to determine fluoride concentration characteristics, hydrochemical controlling mechanisms, and noncarcinogenic risks. Results revealed an average fluoride concentration of 0.89 mg/L, with 26.5% of samples exceeding the Grade III groundwater quality standard. High-fluoride groundwater (>1 mg/L) exhibited spatial heterogeneity and was predominantly of the Na-Mg-HCO3 hydrochemical type. Multivariate analysis and thermodynamics simulations indicated that water–rock interactions (e.g., silicate mineral weathering and fluorite dissolution) governed groundwater hydrochemistry. Fluoride primarily originated from fluoride-bearing mineral dissolution, while negative cation exchange and precipitation of calcite and dolomite enhanced fluoride enrichment. pH had minimal impact on fluoride concentrations under weakly alkaline conditions. Health risk assessment suggested that fluoride in shallow groundwater posed a higher noncarcinogenic risk to children than adults via ingestion. These findings provide valuable insights for regional groundwater resource management.

Phase evolution and heavy metal solidification of cement desulphurized electrolytic manganese residue composite cementitious system under steam curing conditions based on thermodynamic simulation

The mechanical properties and microstructure of desulphurized electrolytic manganese (D-EMR) cement mortar under steam curing at 80 °C for 7 h and 7 days and standard curing for 3 days and 28 days were studied. The hydration products, microstructure and pore distribution were studied by Quantitative X-ray diffraction analysis (QXRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), thermogravimetric-differential thermal analysis (TG-DTA) and backscattered electron (BSE). At the same time, the evolution of hydration products with age and the existence form of heavy metals under different curing conditions were simulated by GEMS thermodynamics. The results show that steam curing can promote the hydration reaction of cement and the secondary hydration of D-EMR. With the extension of steam curing time, the mechanical properties of the early stage are significantly improved. At a D-EMR content of 15 %, the compressive strength of D-EMR cement mortar after steam curing for 7 days is 1.15 times that of the control group under the same conditions, and the content of calcium hydroxide (CH) is 65.91 % of the control group. Steam curing can significantly improve the degree of C3S hydration of cement clinker and the secondary hydration of D-EMR, and increase the degree of polymerization of hydrated calcium silicate (C-S-H) gel. In addition, thermodynamic simulation showed that when the pH value was greater than 7.5, Mn2+ was mainly stable in the form of Mn(OH)2, MnOOH and Mn3O4, and there was no leaching risk. This will provide theoretical support for the use of D-EMR as a new type of supplementary cementitious material (SCM).

Phase evolution and performance of sodium sulfate-activated slag cement pastes

This study evaluates the reaction kinetics, phase assemblage, and microstructure evolution of Na2SO4-activated slag cements produced with three commercial slags. The main reaction products identified are ettringite and calcium aluminosilicate hydrates, alongside a poorly crystalline SO42- intercalated Mg-Al-layered double hydroxide (LDH) phase. Results revealed that the Al2O3 slag content alone does not correlate with the cement performance. While pastes made with a higher Al2O3 content slag exhibit faster reaction kinetics, those made with a slag with a higher Mg/Al ratio developed superior compressive strength and reduced porosity over extended curing periods. Thermodynamic modelling simulations indicate that sulfate consumption occurs via ettringite and LDH phase formation, influencing the slag reaction degree, pH value, and porosity reduction in these cements. This research highlights the critical role of slag composition in controlling microstructure and, consequently, performance of sodium sulfate activated slag cement pastes.

Thermodynamic Equilibrium Simulation for Hydrogen-Rich Syngas from Gasification of MSW and Coconut Shells

Thermodynamic Equilibrium Simulation for Hydrogen-Rich Syngas from Gasification of MSW and Coconut Shells

Thermodynamic Simulation of Engine Brake Systems with Decompression

Thermodynamic Simulation of Engine Brake Systems with Decompression

Effect of Quenching Post‐Intercritical Austenitizing on the Microstructure and Tensile Properties of an K55 Grade Steel for Oil and Gas Industry

The API K55 grade steel is widely utilized in seamless pipes for oil and gas exploration, especially as casing pipes for wellbores. Traditionally, this steel is processed using hot rolling followed by quenching and tempering to achieve the desired dimensional and microstructural characteristics, balancing high strength with ductility. This article introduces an alternative method to attaining the required tensile properties for API K55 grade steel by employing a biphasic microstructure (ferrite/martensite) achieved through quenching post‐intercritical austenitizing heat treatment to high‐strength‐low‐alloy steel. Thermodynamic simulations and dilatometric experiments revealed that increasing the austenitizing temperature enhances austenite formation, decreasing significantly its carbon content, which facilitates martensitic transformation and increases the Ms and Mf temperatures. A complete phase transformation mapping was presented, highlighting how the austenitizing temperature influences martensitic transformation kinetics during the quenching heat treatment. It was concluded that austenitizing at 750 °C, followed by quenching and short tempering at 650 °C, produced a biphasic microstructure with 30% ferrite and 70% martensite, providing a favorable balance between mechanical strength and ductility that meets the API K55 grade requirements, surpassing traditional methods in the industry.

The wettability of pure liquid aluminum on oxide substrates

AbstractOxide particles are considered to be one of the reasons for the stability of cellular porous Al foam. Thus, the contact angle (ө) of molten pure aluminum on oxide substrates, including Al2O3, CaO·2Al2O3 (CA2), CaO·6Al2O3 (CA6), mullite (3Al2O3·2SiO2), and SiO2 was measured in a vacuum heating microscope at a temperature of 950°C to determine the value of wettability of molten aluminum on various oxides. Thereafter, the measured contact angles followed the tendency as mullite (155°) > CA6 (152°) > MgAl2O4 (151°) > Al2O3 (149°) > SiO2 (124°) > CA2 (100°). Furthermore, the cross‐sectional area between molten aluminum and substrates was thoroughly analyzed, and the reaction products, such as the Al2O3 layer at the interface, have been detected. Thermo‐Calc, with the combination of available databases, was used to perform thermodynamic simulations and to discuss and predict possible reactions under the current experimental conditions.

Catalytic hydrogenation of magnesite to methane and magnesium oxide using magnesium carbonate hydroxide as model compound

The hydrogenation of magnesite to CH4 and MgO offers a powerful approach for CO2 direct utilization. To deepen the understanding of the reaction mechanisms, (Mg5(CO3)4(OH)2(H2O)4 was selected as a model compound to gain insights into carbonate hydrogenation. A novel Ni/Fe/ZrO2 catalyst with ferromagnetic properties was employed to facilitate the magnetic separation of the catalyst from the solid products. Thermodynamic simulation and experiments were conducted to address key issues such as gas evolution during catalytic hydrogenation, the effects of catalyst on CH4 selectivity, and the separation of solid products and catalyst. The results indicate that lower temperatures favor CH4 formation, whereas higher temperatures favor CO formation. Increasing Ni loading can enhance the CH4 selectivity. With the presence of 10Ni/Fe/ZrO2 catalyst, 100% CH4 selectivity can be achieved at 300 °C. Moreover, 10Ni/Fe/ZrO2 catalyst exhibits high magnetic responsiveness, facilitating the solid separation and the recycle of the catalyst.

Kinetic study on the thermal decomposition of iron (II) sulfate using a global optimization approach

The thermal decomposition of sulfates is a major intermediate reaction in oxidizing roasting processes associated with metal sulfides. The optimization of iron (II) sulfate could contribute to lowering processes’ temperatures in complex systems. The present work presents the experimental and modeling results of the thermal decomposition of iron (II) sulfate heptahydrate. The investigation was first based on thermodynamic simulations followed by non-isothermal thermogravimetric analysis. The modeling technique consisted of differential equations formulated to describe each decomposition step individually, with the kinetic parameters estimated using particle swarm optimization (PSO). Using this modeling methodology over a graphical method is advantageous as it can simulate reactions that may occur simultaneously. The modeling succeeded in dehydration and desulfation steps, with an overall R2 value of 0.99. The activation energies and apparent reaction order associated with the dehydration steps were 53.3kJ.mol−1/n=1.65, 88.8kJ.mol−1/n=1.12, and 124kJ.mol−1/n=2.0 for FeSO4.7H2O, FeSO4.4H2O, and FeSO4.H2O, respectively. The desulfation steps were associated with higher activation energy values. In that case, 184kJ.mol−1 and 264kJ.mol−1 for FeSO4 and Fe2(SO4)3, respectively. Regarding the apparent reaction order, both desulfation steps showed to be first-order reactions.

Energy saving of vacuum-based membrane dehumidification with indirect evaporative cooling in a low sensible-heat-ratio building

In hot and humid climates, dehumidification generally consumes more energy than cooling, and conventional mechanical vapor compression system is not efficient for dehumidification. Vacuum-based membrane dehumidification system have been developed as a more environmentally friendly alternative for dehumidification due to non-refrigerant system and isothermal dehumidification process. In this study, a novel hybrid air conditioning system that combines vacuum-based membrane dehumidification with an indirect evaporative cooler for pre-cooling is proposed to achieve efficient air conditioning in building with low sensible heat ratio. The energy performance of the proposed system is investigated by detailed thermodynamic simulations and compared with conventional variable air volume (VAV) system and indirect evaporative pre-coolers combined VAV system. The simulation results show that when the average sensible heat ratio of the space is 0.73 and the COP of the vacuum-based membrane dehumidifier is 1.0, the proposed system can reduce energy consumption by 16.1 % compared to conventional VAV system and by 6.4 % compared to indirect evaporative pre-cooler combined VAV system during the cooling season. The energy performance of the proposed system is significantly affected by the sensible heat ratio of the building and the energy efficiency of the vacuum-based membrane dehumidifier. When the COP of the vacuum-based membrane dehumidifier reaches 2.0, the proposed system can achieve an energy savings of 48.2 % compared to conventional VAV system.

Thermostable nanofiltration membranes enabling superior hot wastewater purification

Emerging nanofiltration (NF) separation technology for precision ionic/molecular separation at the nanoscale, which has the advantages of energy conservation, excellent separation and a small footprint, is promising for obtaining sustainable water resources via efficient water treatment and recycling. However, traditional NF membranes are restricted to applications at approximately room temperature because of the sharp deterioration in stability induced by the fragility of the nanopore structure at higher temperatures. Herein, we synthesized an unparalleled nanofiltration (NF) membrane with superior thermal stability up to 90 °C and finely tailored nanopores with 0.3–1.1 nm, via de novo carbon skeleton-mediated polymerization (CSMP). Molecular thermodynamics simulations and experiments demonstrated that C–C skeletons can manipulate the stability of the intrinsic structure and intermolecular gap size, contributing to exceptionally thermostable and well-tailored nanopores. The synthesized membrane exhibited excellent long-term water permeance and high rejection of (sub)nanoscale contaminant molecules at high temperatures, which is far superior to the performance of currently available NF membranes.

(Invited) On the Definition of Velocity in Statistically Accurate, Discrete-Time Simulations of Thermodynamics

One of the most basic struggles in simulations of statistical and dynamical systems is how to appropriately balance the desire for simulation accuracy, obtained in the small time step limit, with simulation efficiency, obtained for large time steps. Obviously, we would like to have the benefits of both limits of accuracy and efficiency. Thus, understanding the influence of discrete time on the behavior of equations of motion is crucial for the understanding and optimization of numerical simulations in physical science and engineering. There are two different types of crucial discretization errors. One is that the simulated, discrete-time trajectory increasingly deviates from the true, continuous-time trajectory as the time step is increased. Another is that the simulated discrete-time velocity increasingly deviates from the expected velocity of the corresponding simulated trajectory as the time step is increased. While the former error is a signature that the simulated trajectory is not exactly the intended one, the simulation may still be representative of the true system. In contrast, the latter error is a signature of a fundamental internal inconsistency in the simulation, which may greatly complicate physical interpretation of the simulation results, especially when both configurational and kinetic measures are required. It is therefore crucially important to understand the relationship between a discrete-time coordinate and its corresponding velocity.It has previously been shown that, unlike in continuous-time, discrete-time configurational dynamics does not need a discrete-time velocity variable. This realization allowed for the derivation of the complete configurational GJ set of stochastic Verlet-type algorithms for simulating the Langevin equation. This set has the key feature of simultaneously giving exact, time-step independent statistical sampling of damped, noisy harmonic oscillators, and giving exact spatial transport values, drift and Einstein diffusion, on flat surfaces. The apparent fact that a discrete-time velocity is not required to simulate a coordinate trajectory implies that discrete-time velocity is an ambiguous concept, which, in turn, implies that multiple velocity definitions can be entertained in order to avoid internal simulation inconsistencies between configurational and kinetic measures. From the derivation of the stochastic GJ methods it was shown that a statistically correct velocity obtained at the same time as the coordinate (an on-site velocity) cannot be obtained. In contrast, a velocity at the half-step between consecutive configurational time steps (a half-step velocity) was identified to produce exact statistical kinetic response for harmonic oscillators regardless of the applied time step. However, only for a single GJ method does this velocity also give the correct drift value.We here derive new, practical velocity definitions that are optimized for statistical kinetic measures, such that, e.g., measures of kinetic energy and correlations with the configurational coordinate are exact for the noisy harmonic oscillator, while also producing the correct kinetic measure of transport on flat surfaces. We identify and analyze three half-step velocity definitions that fulfill these criteria, and we outline simple and practical Verlet-type algorithms that incorporate these velocities within the statistically desirable GJ format that provides the optimized configurational statistics. The application of the methods are demonstrated through characteristic Molecular Dynamics simulations of both simple and complex systems, illustrating how the resulting methods are able to efficiently and simultaneously simulate configurational and kinetic statistical ensembles in different situations using very large time steps.

Pressure-Induced Enhancement in Chemical Looping Reforming of CH4: A Thermodynamic Analysis with Fe-Based Oxygen Carriers.

Chemical looping reforming of methane (CLRM) with Fe-based oxygen carriers is widely acknowledged as an environmentally friendly and cost-effective approach for syngas production, however, sintering-caused deactivate of oxygen carriers at elevated temperatures of above 900 °C is a longstanding issue restricting the development of CLRM. Here, in order to reduce the reaction temperature without compromising the chemical-looping CH4 conversion efficiency, we proposed a novel operation scheme of CLRM by manipulating the reaction pressure to shift the equilibrium of CH4 partial oxidation towards the forward direction based on the Le Chatelier's principle. The results from thermodynamic simulations showed that, at a fixed reaction temperature, the reduction in pressure led to the increase in CH4 conversion, H2 and CO selectivity, as well as carbon deposition rate of all investigated oxygen carriers. The pressure-negative CLRM with Fe3O4, Fe2O3 and MgFe2O4 could reduce the reaction temperature to below 700 °C on the premise of a satisfactory CLRM performance. In a comprehensive consideration of the CLRM performance, energy consumption, and CH4 requirement, NiFe2O4 was the Fe-based OCs best available for pressure-negative CLRM, especially for an excellent syngas yield of 23.08 mmol/gOC. This study offered a new strategy to address sintering-caused deactivation of materials in chemical looping from the reaction thermodynamics point of view.

A novel decoupled triple-fluidized bed reaction system for polyvinyl chloride (PVC) disposal: (I) Thermodynamic simulation and experimental investigation

ABSTRACT In this work, a novel decoupled triple-fluidized bed reaction system was proposed to dispose of polyvinyl chloride (PVC). Thermodynamic simulation and thermogravimetric experiments were conducted to examine the dechlorination feasibility and analyze the effects of CaO and CaCl2 on PVC pyrolysis. Besides, the quantitative removal efficiency of HCl was investigated in a lab-scale bubbling fluidized bed. Results indicated that HCl hardly interacted with the silica−alumina catalyst and Fe2O3 adsorbent, while for Na2O and CaO adsorbents, HCl could convert into corresponding stable chlorides, demonstrating the theoretical feasibility of the system. Next, PVC pyrolysis was a multi-stage process, and CaO spontaneously reacted with the released HCl but simultaneously inhibited its alkylation reaction; moreover, CaCl2 could act as a catalyst to facilitate its HCl release and alkylation reaction. Finally, as the temperature rose, the dechlorination efficiency first increased and then decreased, reaching a peak value of 87.6% at 700°C in the N2 atmosphere. In addition, the dechlorination efficiency in the CO2 atmosphere was higher at 400–900°C.

Revisiting the cost analysis of importing liquefied green hydrogen

Hydrogen emerges as a promising energy carrier in achieving carbon neutrality, especially in countries such as South Korea and Japan, where renewable energy resources are scarce. Consequently, economically importing hydrogen from overseas is paramount to a stable supply. However, previous studies have often oversimplified the estimation of hydrogen import costs with optimistic assumptions, raising doubts about their reliability. This study comprehensively assesses costs incurred from green hydrogen production to liquefaction and transportation. The cost analysis includes detailed design considerations for hydrogen liquefaction and re-conditioning plants, alongside thermodynamic simulations to estimate the boil-off gas rate of liquid hydrogen during transport. Focusing on a case study of importing liquefied green hydrogen from Australia to South Korea, our findings reveal that the levelized cost of hydrogen is approximately 30.2 USD/kgH2 as of 2023. Projections suggest a decrease to around 18.3 USD/kgH2 by 2050, assuming technological advancements, significantly exceeding values reported in the existing literature. Sensitivity analysis highlights the renewable electricity price in Australia and the boil-off rate during shipping as key factors that significantly influence the levelized cost of hydrogen.

Understanding protein adsorption on silica mesoporous materials through thermodynamic simulations

This work presents a molecular thermodynamic theory to study protein interactions within a charge-regulating silica-like nanopore structure. The theory accounts for electrostatic interactions, steric repulsions, finite-size entropic effects, and protonation equilibrium of silanol groups on silica and protein residue side-chains. Coarse-grained representations of proteins based on their 3D crystallographic structures are employed. We evaluate the influence of pH, salt concentration, and pore size on the adsorption of selected proteins (cytochrome c, lysozyme, and myoglobin) in both single- and binary-protein solutions. The surface charge density on the nanopore walls is less negative than on the adjacent planar surface, primarily influenced by pH and salt concentration. Adsorption within the nanopore from single protein solutions exhibits a non-monotonic behavior with pH, increasing with decreasing salt concentration and diminishing pore size. Analysis of the effective interactions between proteins and silica surfaces indicates that adsorption is enhanced when the protein size matches that of the nanopore. Evaluation of various adsorption pathways indicates minimized free energy when the protein enters the nanopore through its edge and contacts its cylindrical walls. In binary solutions, the presence of another protein significantly alters the affinity of a protein for the silica surfaces, potentially preventing its adsorption, and affects its organization on these surfaces upon adsorption.

Computing Degree-Based Topological Descriptors of Certain Tessellations of Kekulenes Using M-Polynomial and Neighborhood M-Polynomial

Topological indices are well-known molecular descriptors that may be applied to any graph and to model specific molecular structures, utilized for property correlation in quantitative structure activity and property relationship (QSAR and QSPR) analyses. Strong methods for machine learning information and thermodynamic simulations of massive networks and nanomaterials can be facilitated by using topological indices. Kekulenes are a novel type of cycloarenes, arranged in doughnut-shaped cyclic benzene rings with riveting superaromaticity and other significant properties. The main aim of this paper is to ascertain the notable degree and the neighborhood degree sum-based indices through M-polynomials and neighborhood M-polynomials of certain types of tessellations of kekulenes. Then, a graphical comparison of the resulting indices is also performed.

Exploring the efficiency of powder reusing as a sustainable approach for powder bed additive manufacturing of 316L stainless steel

The efficiency and sustainability of Laser Powder Bed Fusion (L-PBF) greatly depends on the ability to recycle the used powder since a large portion of the feedstock remains unsolidified surrounding the printed part. To assess the impact of reusing iterations on the properties of the feedstock and printed part, we employed thermodynamic simulation to study oxidation in the building chamber. We then compared the 5 times reused powder of austenitic steel 316L (SS316L) and the printed part with its virgin counterpart. Our findings revealed that minor residual oxygen in the building atmosphere reacts with the molten pool and hot spatters, leading to the formation of Rhodonite (MnSiO3) inclusions. As sieving cannot remove oxides smaller than steel particles, the repetition of feeding the used powder into the printing process directly increases the fraction of oxides in the printed parts. The increase in inoculated oxygen by reusing, coupled with the dissolution of oxides into the molten pool, facilitates the formation of Spinel (MnCr2O4) and Tridymite (SiO2) oxides, as well as clustered inclusions. While small oxides anchor cellular structures, stress concentration on the coarse fragile inclusions leads to sudden rupture and weaker tensile strength of the printed part with reused SS316L powder.

Deciphering ore-forming fluid evolution processes of the Yuerya gold deposit, eastern Hebei, China: Insights from pyrite texture, trace element and sulfur isotope compositions

The Yuerya gold deposit, a representative gold deposit associated with Mesozoic granites in the eastern Hebei region, is located in the eastern Hebei-western Liaoning gold ore-concentrated area, the northern margin of the North China Plate. The orebody is mainly preserved in the Yanshanian granite and its contact zone with the carbonate rocks of the Gaoyuzhuang Formation, and the main ore mineral is pyrite. Based on the pyrite texture, geochemical characteristics of the in-situ trace element analysis, and sulfur isotope, the pyrite in the mining area is classified into five generations (Py1, Py2, Py3, Py4a, and Py4b). Five generations of pyrite all have an average Te/Se ratio > 1, and their average Co/Ni ratios are 1087.27, 43.97, 4.17, 12.62, and 4.99, respectively, indicating that the ore-forming fluid predominantly originates from magmatic-hydrothermal. In-situ sulfur isotopic analysis using LA–MC–ICP–MS shows that the δ34S values of the five generations of pyrites ranged from 0.3 ‰ to 9.6 ‰; the mean values are 3.8 ‰ (Py1, n = 4), 4.2 ‰ (Py2, n = 10), 2.6 ‰ (Py3, n = 18), 4.0 ‰ (Py4a, n = 20) and 4.6 ‰ (Py4b, n = 29), respectively. Approximately 32 % of the results exceed 5.0 ‰, surpassing the values indicative of a magmatic-hydrothermal source. Thermodynamic simulations reveal that the fluctuations in the oxidation state of the ore-forming fluid is not the predominant cause of δ34S enrichment in the pyrite. Our studies suggest that sulfur is primarily derived from mantle-crust mixtures, with some contributions from the wallrock of the Gaoyuzhuang Formation. The results from LA–ICP–MS trace element analysis of pyrites reveal a significant enrichment of As-Bi-Te-Tl alongside Au in the ore-forming fluid. Additionally, the results of ore-forming elements in three typical cross sections of different wallrocks in the mining area also show that Au, Ag, As, and Pb are closely related. Therefore, it is considered that the over-enrichment of As could be an important factor leading to the precipitation of Au. Pyrite undergoes expansion of the mineral lattice parameters or lattice dislocation due to the substitution of S with As, creating space for the growth of solid-solution Au. Subsequently, some of the solid-solution Au within pyrite is liberated through internal oscillations, forming the visible gold particles.