Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and s...
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Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and size, nanoporous graphene has been demonstrated as a very high-efficiency separation membrane, due to the ultrafast molecular permeation rate for its one-atom thickness. This review focuses on the recent advances in nanoporous graphene membrane for the applications of gas separation and water purification, with a major emphasis on the molecular permeation mechanisms and the advanced fabrication methods of this state-of-the-art membrane. We highlight the advanced theoretical and experimental works and discuss the gas/water molecular transport mechanisms through the graphene nanopores accompanied with theoretical models. In addition, we summarize some representative membrane fabrication methods, covering the graphene transfer to porous substrates and the pore generation. We anticipate that this review can provide a platform for understanding the current challenges to make the conceptual membrane a reality and attracting more and more attentions from scientists and engineers.
The heat transfer coefficient is a critical parameter for the design and optimization of supercritical carbon dioxide (sCO₂) heat exchange systems. Based on 20723 data points collected from 22 published studies, exist...
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The heat transfer coefficient is a critical parameter for the design and optimization of supercritical carbon dioxide (sCO₂) heat exchange systems. Based on 20723 data points collected from 22 published studies, existing heat transfer correlations are evaluated, and a new model with improved stability and predictive accuracy is developed. Current correlations for upward vertical sCO₂ flow typically include wall-temperature-dependent parameters, which often lead to issues such as non-uniqueness or the absence of solutions during wall temperature prediction, along with limited accuracy. To address these issues, this study integrates the Buckingham Pi theorem and constructs a wall-temperature-independent heat transfer model using a dimensionless neural network. This approach avoids the problems of multiple or no solutions and achieves high predictive performance, with mean absolute relative errors of 2.83 % for wall temperature and 5.81.% for Nusselt number predictions. Furthermore, the active subspace method is employed to identify four dominant dimensionless groups governing the heat transfer process. These groups can be decomposed into products of commonly known dimensionless numbers. During this process, a new dimensionless number—the buoyancy generation ( BG ) number—is proposed and defined. This study leverages data-driven dimensional analysis to explore {1. influencing parameters and dominant dimensionless numbers for supercritical heat transfer, offering new insights into the underlying physical mechanisms.
To conduct the thermal transport characteristics and operational stability of the steam generation system (SGS) under partial load conditions in concentrating solar power (CSP), a real-scale shell-and-tube steam gener...
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To conduct the thermal transport characteristics and operational stability of the steam generation system (SGS) under partial load conditions in concentrating solar power (CSP), a real-scale shell-and-tube steam generator hydrodynamics predictive model is developed. This model integrates lumped parameter methods with the finite volume method to account for heat transfer and phase change. Additionally, in accordance with the prevailing water circulation mode in the CSP plant, a typical model of the natural circulation system is established, while optimal stable operating points of the maximum circulation mass {1. rate under varying operating conditions are determined. The results indicate that the inherent stability of the generator strongly lies in the dynamic compromise between its thermodynamic and hydrodynamic characteristics. Under high load conditions, the natural circulation mode demonstrates excellent {1. stability. Operating at lower operating pressures results in greater circulation {1. and a heightened sensitivity to phase changes. Under system pressures of 1..76, 1..08, 8.39, and 6.71.MPa, the recommended circulation ratios are determined to be 5.38, 7.86, 1..95, and 1..07, respectively. Furthermore, the stability of the circulation curve is optimized by adjusting the structural dimensions of the steam generator. The sensitivity to evaporation capacity and heat exchanger effectiveness is assessed.
The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this *** include the combustion characteristics of direct injection engine fueled with hydrogen en...
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The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this *** include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas,visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel,and the fundamental study of turbulent premixed combustion of hydrogen enriched natural *** effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.
The gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs) is a critical component for the transport of reactants. The efficiency of reactant gas transport remains a major technical challenge in the...
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Underground in-situ pyrolysis of tar-rich coal is an effective approach to expand the supply channels of oil and gas while ensuring energy security, and it has currently aroused wide attention in the academic communit...
Underground in-situ pyrolysis of tar-rich coal is an effective approach to expand the supply channels of oil and gas while ensuring energy security, and it has currently aroused wide attention in the academic community. The coupling of multiple interdependent physical fields causes the in-situ pyrolysis process and related phenomena. However, existing studies usually only have focused on a single process. The study proposed a three-dimensional (3D) model for the in-situ pyrolysis of tar-rich coal employing external high-temperature fluids. Numerical simulation was used to achieve the transient calculation of the coupling model of chemical reaction, fluid flow, and heat transfer. The impacts of medium type, medium temperature, inlet rate, well patterns, and the number of horizontal fractures were investigated by characterizing the temperature and concentration fields. The results indicate that, under the basic working condition, the pyrolysis reaction of tar-rich coal in the formation has been completed after ∼28.5 months of heat injection. Both N 2 and CO 2 are heat carriers with greater advantages in heat transfer as compared to H 2 O (g). The threshold of injection rate is 5 m·s −1.. The heat transfer effect of coal seams with 4 injection wells is obviously better than that of 1.and 2 injection wells. The number of 3 horizontal fractures is superior to 1.and 2 fractures, which can effectively enhance heat transfer and promote the thermal decomposition. The present study has emphatically investigated the evolution of characteristic fields of tar-rich coal seams under thermo-fluid-chemical coupling conditions during the in-situ pyrolysis process, providing substantial reference significance to guide the in-situ conversion mining.
Flue gas recirculation and steam injection are employed in hydrogen-rich gas turbines to stabilize fuel reactivity and improve cycle efficiency, introducing high water vapor content into the combustion chamber and the...
Flue gas recirculation and steam injection are employed in hydrogen-rich gas turbines to stabilize fuel reactivity and improve cycle efficiency, introducing high water vapor content into the combustion chamber and thereby necessitating an investigation of water-fuel interactions at elevated temperatures. This study employed UV laser absorption diagnostics behind reflected shock waves to conduct in situ measurements of the ȮH concentration time-histories during the oxidation of CH 4 /H 2 /H 2 O/O 2 /Ar mixtures at pressures of approximately 1.3, 5.0, and 1..2 atm and temperatures ranging from 1.25 to 1.88 K with varying hydrogen blending and water addition ratios. The absorption lineshapes of the ȮH R 1.(5) transition in the A-X(0,0) vibronic band were characterized after broadening and shifting in Ar at different pressures, with diagnostic center wavelengths set at 306.6868 nm (1.3 atm), 306.6874 nm (5.0 atm), and 306.6886 nm (1..2 atm), respectively. The obtained ȮH concentration time-history data were compared in detail with predictions from eight representative reaction kinetic models, and the predictive capability of the models for ȮH behavior was quantitatively assessed using the error function method. NUIGMech1.1.exhibited superior performance in predicting ȮH behavior and was subsequently selected for kinetic analysis to elucidate stage-specific micro-mechanisms and identify key reactions driving the concentration evolution. The activating effect of H 2 on ȮH behavior during CH 4 oxidation was investigated. Results indicate that higher hydrogen levels intensify hydrogen-related reaction pathways, expanding the radical pools (H, ȮH, and Ö), thereby promoting fuel consumption through Ḣ-atom abstraction reactions. Additionally, by introducing weak collision H 2 O* and inert H 2 O**, the thermodynamic and kinetic effects of water were distinguished. The results show that under the current conditions, H 2 O primarily affects ȮH behavior through direct participatio
Supercritical water gasification is a clean technology for biomass conversion and *** supercritical water gasification systems,H_(2)O is often used as the transport *** in the reaction temperature at the gasification ...
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Supercritical water gasification is a clean technology for biomass conversion and *** supercritical water gasification systems,H_(2)O is often used as the transport *** in the reaction temperature at the gasification area and in the heating rate of biomass may limit the gasification rate and *** this paper,CO_(2)is used as the transport medium due to its relatively low critical point and specific heat ***,a corn stalk gasification system with different transport media is established in this paper,and the influences of various operating parameters,such as temperature,pressure and feedstock concentration,are *** results show that the gas yield in the CO_(2)-transport system decreases by no more than 5 wt%.In addition,thermodynamic analysis reveals that a system with CO_(2)as transport medium consumes approximately 25%less electricity than a system with H_(2)O as the transport *** addition,the reaction heat absorption *** results show the superiority of CO_(2)to H_(2)O as a transport medium.
A double reheat ultra-supercritical boiler is an important development direction for high-parameter and large-capacity coal-fired power plants due to its high thermal efficiency and environmental *** has developed a 1...
A double reheat ultra-supercritical boiler is an important development direction for high-parameter and large-capacity coal-fired power plants due to its high thermal efficiency and environmental *** has developed a 1.00 MW double reheat ultra-supercritical boiler with steam parameters of 35 MPa at 605℃/61.℃/61.℃.Reasonable water wall design is one of the {1.s to safe and reliable operation of the *** order to examine the thermal-hydraulic characteristics of the double reheat ultra-supercritical boiler,the water wall system was equivalent to a flow network comprising series-parallel circuits,linking circuits and pressure nodes,and a calculation model was built on account of the conservation equations of energy,momentum and *** the iterative solving of nonlinear equations,the prediction parameters of the water wall at boiler maximum continue rate(BMCR),75%turbine heat-acceptance rate(THA)and 30%THA loads,including total pressure drops,flow distribution,outlet steam temperatures,fluid and metal temperatures were *** results of calculation exhibit excellent thermal-hydraulic characteristics and substantiate the feasibility of the water wall design of the double reheat ultra-supercritical boiler.
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