Thermodynamic Coupling Research Articles

Effect of C content on the surface gradient structure of (Ti, Mo)(C, N) and Ti(C, N)-based cermets

The C content has a significant effect on the microstructure especially surface gradient structure of nitrogen-containing cermets. In the literature, how the C content affects the gradient structure of nitrogen-containing cermets is unclear. Combining thermodynamic calculations and experimental techniques, a series of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets with different carbon contents were investigated experimentally. When sintering in a denitrification atmosphere, the C content in the binder phase of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets shows the trend of high surface concentration and low core concentration, the thickness of Ni-rich gradient layer of cermets decreases with the increase of C content, and the (Mo, Ti)C phase precipitates in the gradient layer of Ti(C, N)–Mo2C–Ni cermet. The results of XRD and specific saturation magnetization data indicate a decrease of the solubility of alloy elements Ti and Mo in the Ni binder phase with the increase of C content. The formation mechanism of the gradient layer of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets at different C contents was discussed. Due to the thermodynamic coupling of Ti–C, the high concentration of C on the cermets surface inhibits the local activity of Ti atoms, weakens the driving force for migration of Ti to the core, and results in a thinner Ni-rich gradient layer. Moreover, the amalgamation and growth of hard particles in the alloy and the number of bright inclusions in (Ti, Mo)(C, N)-based cermets can also be reduced with the increase of C content.

Directly fabricated Al2O3/GdAlO3 eutectic ceramic with large smooth surface by selective laser melting: Rapid solidification behavior and thermal field simulation

Selective laser melting (SLM), a novel approach for one-step melting and solidifying ceramic powder beds layer by layer without post-process of degreasing and sintering, has been developed to directly prepare highly dense (>95 %) Al2O3/GdAlO3(GAP) eutectic composite ceramics with large smooth surfaces. Compact net-shaped plates with the maximum size of 73 × 24 × 5 mm3 are obtained by different strategies of laser pre-heating and multi-tracks’ deposition without any binders. Combined with the finite element thermodynamic coupling simulation results, it is proved that the stress between the substrate and depositions during SLM can be greatly reduced by the step-up preheating, and thus effectively improving the ceramic forming quality. The macro-morphology, microstructure evolution, rapid solidification behavior and mechanical properties of the SLM-ed eutectic ceramics are systematically investigated at different laser processing parameters. The microstructure transforms from ultra-fine irregular eutectic to complex regular eutectic with the increase of the scanning rate. The average eutectic spacing, and solidification rate has an approximately linear relationship consistent with the Jackson-Hunt (JH) model. The microhardness and fracture toughness can reach 17.1 ± 0.2 GPa and 4.5 ± 0.1 MPa·m1/2, respectively. The results indicate that SLM method is a highly effective technique for fabricating high-performance net-shaped structural composite ceramics.

Thermodynamic Coupling Simulation of CrN/Cr Composite Coating Barrel Bore

The barrel is the core component of the artillery, and its inner coating is the key material to effectively protect the barrel and improve its service lifetime. Due to its good properties, CrN/Cr composite is a potential alternative to the currently used Cr coating. In this study, finite element simulation has been performed using the software Ansys Workbench to analyze the temperature field and coupled stress field of the Cr coating barrel and the CrN/Cr composite coating barrel, respectively, during the firing. The results showed that compared with Cr coating barrel, the CrN/Cr coating can reduce the temperature and significantly mitigate the stress in the coating/steel matrix interface; thus, it is expected the CrN/Cr coating can better protect the artillery barrel.

Surface integrity during rail grinding under wet conditions: Full-scale experiment and multi-grain grinding simulation

Rail grinding will cause poor surface integrity when the critical grinding temperature is exceeded. To improve the grinding quality and explore the feasibility of grinding operations in rainy days, this study first investigated the surface integrity during rail grinding under wet conditions, including surface roughness, grinding burn, phase transition, residual stress, etc. Moreover, a grinding wheel finite element model was established considering abrasive grains' actual geometry and distribution, providing a novel thermodynamic coupling analysis method. As a result, it is revealed that the surface integrity is significantly improved under wet conditions, especially the grinding burn and white etching layer can be avoided, and residual tensile stress can be reduced by up to 45% since the thermodynamic coupling becomes less apparent.

A dynamic and thermodynamic coupling view of the linkages between Eurasian cooling and Arctic warming

Investigating the contrast between wintertime warming in the Arctic and cooling in Eurasia is of great importance for understanding regional climate change. In this study, we propose a dynamic and thermodynamic coupling view of the linkages between wintertime Arctic warming and Eurasian cooling since 1979. The key factors are the energy budget at the Earth’s surface, the diabatic heating and baroclinicity of the atmosphere, and subsurface ocean heat. A summertime origin of wintertime Arctic warming suggests a partial driving role of the Arctic in wintertime Eurasian cooling. The reasons for this finding are as follows. First, there is a dipole pattern in the diabatic heating change in winter over the Arctic Ocean corresponding to the anticyclonic circulation that links Eurasian cooling and Arctic warming. Second, the change in diabatic heating of the atmosphere is determined by sensible heat at the Earth’s surface through vertical diffusion. Third, the positive sensible heat change in the eastern Arctic sector in winter originates from the summertime enhanced absorption of solar radiation by the subsurface ocean over the sea ice loss region. Meanwhile, the negative sensible heat change in the western Arctic sector and wide Arctic warming can be explained by the circulation development triggered by the change in the east. Additionally, the background strong baroclinicity of the atmosphere in mid-high latitudes and corresponding two-way Arctic and mid-latitude interactions are necessary for circulation development in winter. Furthermore, the seasonality of the changes indicates that Eurasian cooling occurs only in winter because the diabatic heating change in the Arctic is strongest in winter. Overall, the comprehensive mechanisms from the summertime Earth’s surface and subsurface ocean to the wintertime atmosphere suggest a driving role of the Arctic. Note that the situation in interannual variability is more complex than the overall trend because the persistence of the influence of summertime sea ice is weakly established in terms of interannual variability.

Bowl surface laser forming process of stainless steel composite plate

In this paper, the three-dimensional bowl surface was obtained by reasonably planning the radial heating path by taking the laser as the heat source and the stainless steel composite plate (06Cr19Ni10/1Cr17Mn6Ni5N/06Cr19Ni10) as the research object, and the forming process of the three-dimensional bowl surface was studied. It was found that the target surface bending forming obtained by inside-outside symmetric scanning strategy (strategy d) had the highest accuracy. The plate deformation increased with the increase of laser power (P), increased then decreased with the increase of heating line length (L), and decreased with the increase of scanning speed (V). Moreover, the deformation was approximately linear with the number of repeated heating (N), with the optimal process conditions of P = 500 W, V = 10 mm/s, L = 20 mm, N = 7. A three-dimensional thermodynamic coupling model of a three-layer composite plate was established and verified experimentally.

Quantifying the role of ocean coupling in Arctic amplification and sea-ice loss over the 21st century

The enhanced warming of the Arctic, relative to other parts of the Earth, a phenomenon known as Arctic amplification, is one of the most striking features of climate change, and has important climatic impacts for the entire Northern Hemisphere. Several mechanisms are believed to be responsible for Arctic amplification; however, a quantitative understanding of their relative importance is still missing. Here, using ensembles of model integrations, we quantify the contribution of ocean coupling, both its thermodynamic and dynamic components, to Arctic amplification over the 20th and 21st centuries. We show that ocean coupling accounts for ~80% of the amplification by 2100. In particular, we show that thermodynamic coupling is responsible for future amplification and sea-ice loss as it overcomes the effect of dynamic coupling which reduces the amplification and sea-ice loss by ~35%. Our results demonstrate the utility of targeted numerical experiments to quantify the role of specific mechanisms in Arctic amplification, for better constraining climate projections.

Co-simulation for thermodynamic coupling of crops in buildings. Case study of free-running schools in Quito, Ecuador

Rooftop farms can improve a building's thermal and energy performance, especially for uninsulated free-running buildings. The non-refurbished educational building stock lacks indoor comfort related to temperature and high CO2 concentration, and could benefit from the thermal insulation, food security and social cohesion provided by rooftop farms. However, to assess the adequacy of such strategies, building energy simulations need to include the thermal effect of plants. This study develops a novel co-simulation to leverage the transient flow exchange between crops and buildings by incorporating the plant's heat and mass balances in building simulation. This co-simulation allows an online closed-loop computation using Energy Plus for building energy modelling and MATLAB for crops modelling. The latter solves three agronomical sub-models: 1) crop's growth, 2) energy balance, and 3) net photosynthesis. This dynamic crop's growth function reflects how crops development affects heat, mass and CO2 flows. This co-simulation was first applied to assess the thermal coupling of three rooftop farm systems in two free-running archetype schools in Quito, Ecuador. The assessed rooftop farms were: edible green roofs, hydroponic rooftop greenhouses, and thermally integrated rooftop greenhouses. Results showed that rooftop farms are adequate to improve thermal comfort conditions and air quality in classrooms and diminish thermal demand. Integrated rooftop greenhouses achieve the best overall performance with a 42% decrement in thermal load, a 0.7 °C increment in indoor temperature, and a 40% reduction in hours exceeding CO2 concentration limits, despite a 2.94 kWh/m2 rise in electricity demand.

Coupling properties of thermodynamics and economics of underwater compressed air energy storage systems with flexible heat exchanger model

Underwater compressed air energy (UW-CAES) systems own plentiful merits of high system efficiency, high energy density and stable operation. In terms of research gap of its coupling properties of thermodynamics and economics, along with research lack focusing on detailed design parameters, the comprehensive thermodynamic and economic coupling model of UW-CAES systems are developed in this paper, specifically including more details of heat exchanger structure, thermal storage medium and an improved energy density. In addition, the discharging power capacity is maintained constant in the analysis for practical design. Then, the effect of key parameters on the whole system's thermodynamic and economic performance is deeply investigated in which the coupling characteristics among parameters are focused on. Results show that the studied UW-CAES system has a good thermodynamic performance with a high system efficiency of 0.7074 and an enhanced high energy density of 26.07 MJ/ m3 considering thermal storage tanks. The system investment can be achieved as low as $3.983 million when water is thermal storage medium. Sensitive analysis shows that it is beneficial to improve the whole system performance with larger underwater pipe diameter, and the discharging pressure should not be lower than 30 bar to avoid efficiency and economic deteriorating. The growing discharging power will increase system investment, while decreasing levelized cost of electricity (LCOE) significantly. Generally, the economy of UW-CAES systems with thermal oil is much worse than counterparts with water. As the thermal storage medium is water, there exist optimum economic ranges of discharging pressure, NTU, length-width ratio and part number.

Mathematical Simulation and Experimental Verification of Carburizing Quenching Process Based on Multi-Field Coupling

Based on the multi-field coupling effect of temperature, diffusion, and phase change, the finite element model of carburizing and quenching was established. The 20CrMnTiH steel helical gear as the research object, prediction accuracy of carburizing, and quenching model of complex helical gear was studied. The material properties database of experimental steel was established by JMatPro, and the material thermophysical parameters needed in the calculation process were obtained. The carburizing and quenching process of transmission helical gear was numerically simulated by thermodynamic three-dimensional coupling analysis method combined with actual heat treatment process. The microstructure morphology, macro hardness, and deformation were characterized. The experimental results show that the microstructure of the hardened surface layer was acicular martensite and a small amount of residual austenite. The highest hardness appears at the surface layer of 778.8 HV, the effective hardened layer depth was 0.9 mm, and the maximum deformation of the gear was 0.055 mm. By comparing the experimental measurement results with the simulation results, they were in good agreement, which verifies the accuracy of the finite element model. This indicates that the model has good prediction ability in carburizing and quenching process.

Evaluation of the Performance of CMIP5 and CMIP6 Models in Simulating the Victoria Mode–El Niño Relationship

AbstractThe Victoria mode (VM) is the second dominant sea surface temperature mode in the North Pacific, forced by North Pacific Oscillation–like extratropical atmospheric variability. Observational studies have shown that the boreal spring VM is closely connected to the following winter El Niño, with the VM efficiently acting as a precursor signal to El Niño events. This study evaluates the relationship of the spring VM with subsequent winter El Niño in the preindustrial simulations of phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). We found that most CMIP5 and CMIP6 models can simulate the basic characteristics of the VM reasonably well. The current CMIP6 models simulate the VM–El Niño connections more realistically as compared to the earlier CMIP5 models. The analysis further suggests that the improved capability of the CMIP6 models to simulate the VM–El Niño relationship is because the CMIP6 models are better able to capture the VM-related surface air–sea thermodynamic coupling process over the subtropical/tropical Pacific and the seasonal evolution of VM-related anomalous subsurface ocean temperature in the equatorial Pacific.

Evaluation of the Performance of CMIP5 and CMIP6 Models in Simulating the Victoria Mode–El Niño Relationship

AbstractThe Victoria mode (VM) is the second dominant sea surface temperature mode in the North Pacific, forced by North Pacific Oscillation–like extratropical atmospheric variability. Observational studies have shown that the boreal spring VM is closely connected to the following winter El Niño, with the VM efficiently acting as a precursor signal to El Niño events. This study evaluates the relationship of the spring VM with subsequent winter El Niño in the preindustrial simulations of phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). We found that most CMIP5 and CMIP6 models can simulate the basic characteristics of the VM reasonably well. The current CMIP6 models simulate the VM–El Niño connections more realistically as compared to the earlier CMIP5 models. The analysis further suggests that the improved capability of the CMIP6 models to simulate the VM–El Niño relationship is because the CMIP6 models are better able to capture the VM-related surface air–sea thermodynamic coupling process over the subtropical/tropical Pacific and the seasonal evolution of VM-related anomalous subsurface ocean temperature in the equatorial Pacific.

Variation Law of Infrared Radiation Temperature of Unloading Fracture of Composite Coal-Rock

For composite mining coal-rock dynamic disaster, combining the theory of thermodynamics, damage mechanics, and other disciplines, the thermodynamic coupling mathematical model of composite coal-rock under an unloading condition is deduced, and the simulation model of composite coal-rock is established for numerical simulation. And the variation law of thermal infrared radiation under triaxial loading and unloading of composite coal-rock is analyzed and verified by experiments. The results show the following findings: (1) The distribution of thermal infrared radiation temperature of composite coal-rock is different in different stages of stress. The overall temperature of the temperature field is lower than the initial temperature field in the three-dimensional stress loading stage and the stage of stress-keeping pressure, but the internal temperature of the coal body is the highest. In the first stage of “loading and unloading,” the temperature of a coal seam increases slightly, and the temperature of other parts of the rock layer increases except for the circular low-temperature zone. In the second stage of “loading and unloading,” an alternating zone of high and low temperatures appears in the rock mass, and the temperature field is enhanced, among which the temperature field reaches the strongest after unloading the confining pressure. After jumping over the maximum stress, the temperature field decreases as a whole at the instability and rupture stage. (2) The variation of surface average thermal infrared radiation temperature ( T ave ) of composite coal-rock can be divided into the initial fluctuation stage, the linear heating stage, the local decline stage, the temperature sudden increase stage, and the fracture decline stage. At three different unloading rates of 0.003 MPa/s, 0.03 MPa/s, and 0.05 MPa/s, the T ave of coal body, floor rock, and roof rock reach the maximum before composite coal-rock instability and fracture, and the temperature change of the coal body is the most obvious. (3) Under different confining pressure unloading rates, the T ave of roof rock, coal body, and floor rock shows a strong linear relationship with stress after linear fitting. And the correlation between simulation and experimental results after fitting is above 0.89. The larger the confining pressure unloading rate is, the shorter the peak time of T ave arrives, and the larger the peak value. The comparison between the experimental results and the simulation analysis shows that the two results are consistent, and the research results can provide a theoretical basis for the prevention and control of dynamic disasters in coal and rock mining.

Multi-objective optimization of a solid oxide fuel cell-based integrated system to select the optimal closed thermodynamic cycle and heat coupling scheme simultaneously

Integrating thermodynamic cycles with SOFCs is an effective technology to make full use of energy, but the difficulty lies in selecting the optimum thermodynamic cycles and integration scheme. The performance of a thermodynamic cycle is directly determined by the working fluid and operating parameters, and the heat exchange network (HEN) synthesis scheme directly affects the heat coupling degree and the economic performance. Therefore, a multi-objective optimization model is proposed in this paper, where the working fluid and operating parameters of the closed cycle, as well as the HEN synthesis scheme are selected as decision variables, while the total exergy destruction (TED) and the total annual cost (TAC) are adopted as the objectives. To solve this complex problem, a solving strategy based on NSGA-II with two levels is proposed to obtain the Pareto Frontier of TED and TAC. Finally, a case is solved and three Pareto optimality are analyzed and compared.

RETRACTED ARTICLE: Seasonal variation of coastal circulation based on parameter grey estimation and evaluation of residents’ physical exercise behavior

In the past decades, global climate change has greatly changed the natural environment. Due to the lack of measurement data and technical means, there is no consensus on the structure and dynamic mechanism of the b-sea cycle. In this paper, based on ROMs model and grey estimation of parameters, a three-dimensional baroclinic model of thermodynamic coupling in b-ocean region under new background field is established by using high-quality data recently obtained. According to the simulation results and comparative experiments, the seasonal distribution characteristics of b-sea circulation and the water exchange form between b-sea and high seas are analyzed and explained. And many scientific problems of coastal circulation, such as education and mutation mechanism. However, good physical exercise is an important way to improve the physical quality of residents. As the basic requirement of residents’ physical exercise, the community sports environment affects and limits the residents’ physical exercise behavior. Environmental behavior studies show that the relationship between environment and behavior is not directly related to the individual’s response to environmental stimuli. The principle of “applicability” should be emphasized in the construction of sports environment in society. Therefore, the residents’ behavior evaluation of the school sports environment should become an important feedback information in the construction of community sports environment. The purpose of this paper is to analyze the correlation between residents’ sports environment evaluation and sports exercise behavior orientation, and to provide a theoretical basis for improving residents' sports exercise behavior and optimizing and perfecting the sports environment of the community.

Free energy calculations of ALS-causing SOD1 mutants reveal common perturbations to stability and dynamics along the maturation pathway.

With over 150 heritable mutations identified as disease-causative, superoxide dismutase 1 (SOD1) has been a main target of amyotrophic lateral sclerosis (ALS) research and therapeutic efforts. However, recent evidence has suggested that neither loss of function nor protein aggregation is responsible for promoting neurotoxicity. Furthermore, there is no clear pattern to the nature or the location of these mutations that could suggest a molecular mechanism behind SOD1-linked ALS. Here, we utilize reliable and accurate computational techniques to predict the perturbations of 10 such mutations to the free energy changes of SOD1 as it matures from apo monomer to metallated dimer. We find that the free energy perturbations caused by these mutations strongly depend on maturational progress, indicating the need for state-specific therapeutic targeting. We also find that many mutations exhibit similar patterns of perturbation to native and non-native maturation, indicating strong thermodynamic coupling between the dynamics at various sites of maturation within SOD1. These results suggest the presence of an allosteric network in SOD1 which is vulnerable to disruption by these mutations. Analysis of these perturbations may contribute to uncovering a unifying molecular mechanism which explains SOD1-linked ALS and help to guide future therapeutic efforts.

Bowl Surface Laser Forming Process of Stainless Steel Composite Plate

In this paper, the three-dimensional bowl surface was obtained by reasonably planning the radial heating path by taking the laser as the heat source and the stainless steel composite plate (06Cr19Ni10/1Cr17Mn6Ni5N/06Cr19Ni10) as the research object, and the forming process of the three-dimensional bowl surface was studied. It was found that the target surface bending forming obtained by inside-outside symmetric scanning strategy (Strategy d) had the highest accuracy. The plate deformation increased with the increase of laser power (P), increased then decreased with the increase of heating line length (L), and decreased with the increase of scanning speed (V). Moreover, the deformation was approximately linear with the number of repeated heating (N), with the optimal process conditions of P = 500W, V = 10 mm/s, L = 20 mm, N = 7. A three-dimensional thermodynamic coupling model of a three-layer composite plate was established and verified experimentally.

Heat-assisted hole-clinching process for joining magnesium alloy and ultra-high-strength steel

Due to the limited formability of magnesium alloy and ultra-high-strength steel, joining by forming of these dissimilar materials is still a big challenge, which requires suitable manufacturing technologies. To join both of the two limited formability materials, a heat-assisted hole-clinching process was investigated using numerical method and experiment test; AZ31B was chosen as the material of the upper sheet, and the numerical model was built in the DEFORM-2D software; isothermal thermo-dynamic coupling method was used to analyze the effect of upper sheet temperature on its formability during hole-clinching using the proposed numerical model and experiment tests. Meanwhile, the stress developing during hole-clinching which causes material fractures were analyzed, and damage distribution and fracture evolution were investigated. The results showed that the heat-assisted hole-clinching process can be predicted by the proposed numerical model; the formability of magnesium increased significantly as upper sheet temperature is raised; AZ31B and 22MnB5 can be joined using a hole-clinching method with the usage of heat. The results point to the applicability of the heat-assisted hole-clinching process to the joining of two limited formability materials.

Swell induced stress in a hydrogel coating

A hydrogel can be coated on various substrates to enable multiple functions. Potential applications include biomedical devices, anti-fouling surfaces and microfluidics. In practical use, hydrogel coatings are often submerged in fluids. The swell of hydrogel coating deteriorates the interfacial bonding with the substrate. This paper presents a stress analysis of a hydrogel coating on a cylindrical metal substrate. We adopt the thermodynamic theory coupling large deformation and water migration and formulate two boundary value problems for the coating–substrate system with and without an interfacial crack. The inhomogeneous stress fields in the hydrogel coating are obtained. The influences of modulus, thickness of the hydrogel coating on the maximum radial stress at the interface are analyzed. These results may guide the design of hydrogel coating to avoid interfacial failure. The swell of a hydrogel coating deteriorates the interfacial bonding with the substrate. This paper presents a stress analysis of a hydrogel coating on a cylindrical metal substrate. We adopt the thermodynamic theory coupling large deformation and water migration, formulate two boundary value problems for the coating–substrate system with and without an interfacial crack, and obtain the inhomogeneous stress fields. These results may guide the design of hydrogel coating in future applications.

Structure formation and properties of WC-(W,Ti)C-Ti(C,N)-TaC-Co gradient cemented carbides with cubic phases free in the surface layer

In this paper, gradient cemented carbides with the cubic-phase free in the surface layer were prepared, and the compositional gradient formation was explored. The relations between the properties of the gradient cemented carbide and the TaC addition were investigated. The results showed that the inward Ta migration during the gradient-structure formation of the cemented carbide WC-Co-(W,Ti)C-Ti(C,N)-TaC-W was mainly driven by the thermodynamic coupling between Ta and Ti. The thickness of the cubic-phase free layer decreased as the total Ta/C ratio is enlarged in the gradient cemented carbide. With TaC added in the gradient cemented carbide, the undissolved Ti(C,N) cores was rarely observed in the bulk owing to the solid solution of Ta. The average sizes of WC phases and (W,Ti)C phases could be reduced by the TaC addition, but hardly refined further when TaC exceeds its solubility in the binder. All of the transverse rupture strength, the hardness and the fracture toughness increased with the low TaC content but decreased with the high TaC content. The coercive force was elevated with TaC added in the gradient cemented carbide, and the magnetic saturation increased when increasing TaC contents. Additionally, the coercive force was raised while the magnetic saturation fell down after the cubic-phase free layer was removed.