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Large eddy simulation on the wake characteristics of linearly stratified flow past a sphere

Scientific Reports 2025年第1期15卷 1-13页

作者： Xia, Tianci Wei, Na Shi, Liuliu School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai 200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai 200093 China Key Laboratory of Power Machinery and Engineering of Ministry of Education Shanghai Jiao Tong University Shanghai 200240 China

In this study, Large Eddy Simulation (LES) has been employed to examine the influence of the Froude number (Fr) on the linearly stratified wake and internal waves behind a sphere at a subcritical Reynolds number of Re = 3700. Six distinct sets of models with varying Fr (Fr = 0.05, 0.25, 0.5, 1, 2, ∞) have been chosen to establish density linear stratification through the use of a User Defined Function (UDF). The analysis focuses on the impact of stratification on wake characteristics, velocity distribution, and the structure of internal waves within stratified flow. It is evident that density stratification plays a pivotal role in shaping wake structure. Notably, in stratified flows, wakes exhibit unique characteristics including the generation of internal waves, suppression of vertical velocity, and the emergence of oscillating wake patterns. The study reveals that a decrease in the Froude number leads to heightened vertical suppression of the wake and increased anisotropy of the velocity distribution. Furthermore, as the Froude number ascends from 0.05 to 2, the wake undergoes a transition from quasi-two-dimensional vortex shedding to three-dimensional turbulence. © The Author(s) 2025.

关键词： Froude number Internal wave Linearly stratified flow Wake

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Low-energy and accelerated hydrogen release from MgH2–5 wt% NaTiOxH catalyzed hydrogen storage reactor by graphite responsive microwave

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Journal of Magnesium and Alloys 2025年

作者： Wang, Bofei Wu, Zhen Liu, Honghao Yang, Fusheng Zhang, Zaoxiao Yao, Jing Li, Qian Cao, Hujun Li, Bo State Key Laboratory of Fluorine & Nitrogen Chemicals School of Chemical Engineering and Technology Xi'an Jiaotong University Xi'an710049 China State Key Laboratory of Multiphase Flow for Power Engineering Xi'an Jiaotong University Xi'an710049 China National Engineering Research Center for Magnesium Alloys Chongqing University Chongqing400044 China Dalian National Laboratory for Clean Energy Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian116023 China Faculty of Engineering Electrical Energy Management Group University of Bristol BristolBS8 1QU United Kingdom

Owing to high thermal stability and large reaction enthalpy, MgH2 has high reaction temperatures and sluggish reaction kinetics in the dehydrogenation process, which consumes lots of energy. To achieve hydrogen release with low energy consumption, accelerated reaction rate, and high heating uniformity, this paper proposes a novel method of graphite responsive microwave-assisted thermal management with NaTiOxH catalyst. A multi-physics model of the 5 wt% NaTiOxH catalyzed MgH2 reactor integrated with a microwave generator is developed to investigate the reaction, heat and mass transfer process of hydrogen release. It is found that the graphite responsive microwave heating method could improve the temperature uniformity of reaction bed, reduce the energy consumption by at least 10.71% and save the hydrogen release time by 53.49% compared with the traditional electric heating method. Moreover, the hydrogen desorption thermodynamics could be improved with the increase of microwave power. The hydrogen release time is shortened by 19.55% with the increase of 20 W microwave power. Meanwhile, it is also concluded that the microwave excitation frequency of 2.1 GHz and the graphite content of 2 wt% have better heating performance. Therefore, it can be verified that the graphite responsive microwave heating helps to low-energy and accelerated hydrogen release from MgH2 hydrogen storage reactor. © 2025

关键词： Reaction rates

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Enhancing the Frequency Control Stability in Large-Scale VPPs with Limited Capacity of Fast-Response Units 19th

Enhancing the Frequency Control Stability in Large-Scale VPP...

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19th Annual Conference of China Electrotechnical Society, ACCES 2024

作者： Liang, Jun Tian, Zeyu Zhang, Penghua Zhang, Mingyue Li, Wei Liu, Huan Chong, Daotong China Nuclear Power Operation Technology Co. Ltd. Hangzhou311215 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China China Nuclear Power Operation Management Co. Ltd. Jiaxing314300 China

ISBN: (纸本)9789819647996

As renewable energy penetration increases, Virtual Power Plants (VPPs) must not only manage energy scheduling but also ensure system security, particularly in response to frequency fluctuations. Existing research focuses on optimizing Primary Frequency Control (PFC) and developing specific control strategies for VPP units. In this study, a dynamic simulation model of a VPP was constructed, and two control systems—Energy Management System (EMS) and Capacity Coordinated Frequency Control (CCFC)—were established and optimized for better control effectiveness. The results demonstrate that the EMS designed for rapid energy storage response is better than traditional methods in responding frequency disturbances caused by rapid power demand changes. Under EMS control, the frequency nadir improved by 17.5%, and the time to reach steady-state was reduced by 77.2% during rapid power increases. Similarly, the nadir improved by 17.1%, and the steady-state time was reduced by 69.5% during power decreases. In addition, the coordinated optimization of EMS and CCFC enhances the VPP’s ability to manage large-scale power fluctuations. The safe power step adaptation range is expanded from 5 MW to 25 MW when the BESS’s dispatchable power is limited. This study highlights the potential of integrated control strategies to significantly enhance the frequency regulation and overall stability of VPPs. © Beijing Paike Culture Commu. Co., Ltd. 2025.

关键词： Frequency stability

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Modeling Study on Anisotropic Transport Properties of Pemfc Gdls Facilitated by Xct

SSRN

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SSRN 2025年

作者： Liu, Hang Li, Yang Huang, Heng Zhou, Zhifu Wu, Wei-Tao Wei, Lei Lyu, Jizu Hu, Chengzhi Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China School of Mechanical Engineering Guangdong Ocean University Zhanjiang524088 China

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 field today. The anisotropic structure of the GDL gives rise to substantial variations of gas diffusion as well as permeability in different directions. The study employs X-CT technology to obtain the actual GDL’s geometry, aiming to investigate a spatial structure at the microscale and its gas transport characteristics. CFD method is used to simulate and study the gas diffusivity and gas permeability of GDL with four different thicknesses. The numerical simulation results show the diffusivity and permeability in the Through-plane (TP) direction are lower than those in the In-plane (IP) direction. Moreover, the effective diffusion coefficient decreases with increasing thickness, but is also dependent on the solid fibre structure of GDL. Horizontal alignment of the carbon fibers and the disc-shaped adhesive contributes to the anisotropy between the TP and IP directions, resulting in anisotropic gas transport. The purpose of the study is to supply critical references for manufacturing techniques and optimization of gas transport in GDLs. © 2025, The Authors. All rights reserved.

关键词： Gas permeability

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Recent advances in nanoporous graphene membrane for gas separation and water purification

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Science Bulletin 2015年第21期60卷 1807-1823页

作者： Chengzhen Sun Boyao Wen Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

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.

关键词： Nanoporous graphene Gas separationWater purification Molecular permeationmechanism Membrane fabrication

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A wall-temperature-independent heat transfer model and dominant dimensionless numbers for supercritical CO2 in vertical upward flow

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Journal of Supercritical Fluids 2025年 224卷

作者： Hou, Zhenghui Liao, Haifan Yang, Kuang Bai, Shaozhe Fan, Xinjiang Yang, Chaofan Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

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 key influencing parameters and dominant dimensionless numbers for supercritical heat transfer, offering new insights into the underlying physical mechanisms. © 2025 Elsevier B.V.

关键词： Electric heating

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Constructing electron transport channel of SnO2/BaSO4 on g-C3N4 for enhanced visible-light-driven photocatalytic H2 production

Materials Today Catalysis

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Materials Today Catalysis 2025年 9卷

作者： Dong, Gongyue Guo, Xiaojuan Cheng, Cheng Chen, Feng Zhang, Jinfeng Du, Yanping Meng, Wei Liu, Maochang Shi, Jinwen International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Guangdong Provincial Key Laboratory of Multi-energy Complementary Distributed Energy Systems Dongguan University of Technology Dongguan523808 China School of Engineering Lancaster University LancasterLA1 4YW United Kingdom Gansu Company PipeChina Lanzhou730060 China Hunan Provincial Key Lab of Dark Tea and Jin-Hua Department of Material & Chemical Engineering Hunan City University Yiyang413000 China

Graphitic carbon nitride (g-C3N4) is confronted with the issue of poor utilization of photogenerated charge carriers, thereby leading to limited performance of photocatalytic hydrogen (H2) production, which restricts its potential application. Herein, the electron transport material SnO2/BaSO4 was synthesized to integrate with g-C3N4 for addressing the above problem. Various characterizations were conducted to investigate the g-C3N4-SnO2/BaSO4 photocatalyst, and it demonstrated that photogenerated electrons from g-C3N4 expeditiously migrate to SnO2/BaSO4 nanoparticles, which markedly hindered photogenerated carriers’ recombination. Subsequently, the g-C3N4-SnO2/BaSO4 photocatalyst demonstrated promoted photocatalytic H2 production at a rate of 14.2 μmol h−1 under visible-light illumination, which was 2.5 times higher than that of pristine g-C3N4. © 2025 The Authors

关键词： Barium sulfate

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Biosorbent silver nanoparticles decorated coffee-ground waste composite for cleaning water and antimicrobial applications

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Environmental Science and Pollution Research 2025年第5期32卷 2280-2297页

作者： Al-Ghamdi, Azza A. Ibrahim, Sherif M. Lu, Xingmei Xin, Jiayu El-Sayed, Ibrahim El-Tantawy Galhoum, Ahmed A. Wageh, Swelm. Department of Chemistry College of Science Imam Abdulrahman Bin Faisal University P.O. Box 1982 Dammam31441 Saudi Arabia Renewable and Sustainable Energy Unit Imam Abdulrahman Bin Faisal University P.O. Box 1982 Dammam31441 Saudi Arabia Nuclear Materials Authority P.O. Box 530 El-Maadi Cairo Egypt Beijing Key Laboratory of Ionic Liquids Clean Process CAS Key Laboratory of Green Process and Engineering State Key Laboratory of Multiphase Complex Systems Innovation Academy for Green Manufacture Institute of Process Engineering Chinese Academy of Sciences Beijing100190 China School of Chemistry and Chemical Engineering University of Chinese Academy of Sciences Beijing100049 China Sino Danish College University of Chinese Academy of Sciences Beijing100049 China Chemistry Department Faculty of Science Menoufia University Shebin El-Kom Egypt Department of Physics Faculty of Science King Abdulaziz University Jeddah21589 Saudi Arabia

A sustainable biosorbent, silver nanoparticles-decorated coffee-ground waste (CWAg), was synthesized through a simple in-situ reduction method. CWAg is extensively characterized via SEM–EDX, PZC, FTIR, XRD, HR-TEM, and XPS analyses. The biosorbent was tested to remove chromium (Cr(VI)) and methylene blue (MB) from wastewater, and its antibacterial properties was evaluated. CWAg demonstrated efficient sorption efficiencies, achieving ⁓149.9 mg/g at 323 K and pH: 2.0 for Cr(VI) and ⁓113.4 mg/g at 293 K and pH: 6.0 for MB, at a biosorbent dose of 1 g/L. The equilibration times were 90 and 120 min for Cr(VI) and MB, with half-sorption times (tHST) of 9.2 and 13.9 min, respectively. The sorption mechanisms were successfully fitted with Sips isotherm and Pseudo-second-order models. Simultaneous sorption of MB and Cr(VI) at pH 2.0 exhibited antagonism, while a synergistic effect was observed at pH 6.0. Desorption and regeneration were achieved using NaOH and HCl solutions for Cr(VI) and MB, respectively. The efficiencies were just reduced by 9–13%. Finally, CWAg exhibited remarkable effectiveness for removing Cr(VI) from complex tannery effluent. Moreover, CWAg demonstrated positive antibacterial effects against both Gram-positive and Gram-negative bacteria, surpassing raw coffee-ground waste, underscoring the significant role of silver nanoparticles in enhancing bacterial inhibition. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.

关键词： Silver nanoparticles

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Uncertainty and Sensitivity Analysis of Containment Aerosol Removal Under Severe Accident

SSRN

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SSRN 2025年

作者： Ou, Pingwen Chen, Yongzheng Chen, Peng Ouyang, Yong Guo, Chao Su, Guanghui China Nuclear Power Technology Research Institute Co. Ltd. Shenzhen518000 China State Key Laboratory of Nuclear Power Safety Technology and Equipment China Nuclear Power Technology Research Institute Co. Ltd. Shenzhen518000 China School of Nuclear Science and Technology Xi'an Jiaotong University Shaanxi Xi’an710049 China State Key Laboratory of Multiphase Flow in Power Engineering China

This study focuses on the uncertainty and sensitivity analysis of containment aerosol removal under severe accident conditions using the severe accident integral code ASTEC, validated by experiments carried by CNPRI, and the coupled uncertainty and sensitivity tool SUNSET. A "separated" methodology is introduced, which distinguishes between thermal-hydraulic and aerosol boundary conditions to highlight the impact of containment aerosol mechanisms. Eleven uncertainty input parameters related are selected for uncertainty propagation and the Spearman correlation coefficient is utilized to describe sensitivity. The removal factor exhibits significant variation, with peaks due to temporary enhancement of diffusiophoresis deposition caused by corium relocation and subsequent steam generation. Uncertainty in the removal factor is substantial before aerosol release termination and narrows afterward. The gravitational settling and the diffusiophoresis deposition are the most important contributors with approximately 70% and 20% deposited aerosol mass, respectively. The initial mass medium diameter, the gravitational shape factor and the agglomeration shape factor are the most influential input parameters in aerosol removal, including in-containment deposition and environmental release, and they should be considered discreetly with conservatism in source term estimation and radioactive consequence evaluation in nuclear engineering. © 2025, The Authors. All rights reserved.

关键词： Sensitivity analysis

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Efficient One-Step Electrochemical Synthesis of Ammonia-Hydrogen Fuel for Clean Energy Applications

SSRN

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SSRN 2025年

作者： Yang, Zhongmei Wang, Xiaoyang Mu, Xiaojiang Hong, Congjie Miao, Lei Novel Battery Materials Research Center of Engineering Technology State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures School of Physical Science and Technology Guangxi University Nanning530004 China State Key Laboratory of Multiphase Flows in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Ammonia-hydrogen fuel, recognized as a quintessential zero-carbon green energy source, presents significant challenges in storage and transportation due to the inherent safety risks associated with hydrogen fuel handling. Leveraging ammonia's potential as an efficient hydrogen storage medium, we focus on developing a novel technology for on-site ammonia decomposition to produce hydrogen under ambient conditions. Here, we employ a straightforward electrochemical process to catalytically decompose ammonia into hydrogen and nitrogen at standard temperature and pressure, with ammonia in its gaseous form directly volatilized from an aqueous ammonia solution. A CeO2@NiCu₃/NF electrocatalyst capable of efficient ammonia decomposition at an impressively low potential (1.27 V vs. RHE) was synthesized. This catalyst demonstrated a Tafel slope of 41.5 mV dec-1, significantly improving electrolysis efficiency. It also exhibited excellent stability during 21 hours of continuous operation. Density Functional Theory (DFT) analysis revealed that the unique composite structure of CeO2 and NiCu3 features a d-band position similar to platinum, optimizing the adsorption-desorption balance of ammonia. Furthermore, the impact of ammonia on the combustion characteristics of hydrogen under different cracking ratios was investigated from an application perspective. Combustion kinetics simulations were performed to evaluate the effects of ammonia on the ignition delay time (IDT) and laminar flame speed (LFS) of hydrogen. The results indicate that the presence of small amounts of NH3 has a negligible effect on the ignition delay time of hydrogen but significantly reduces its laminar flame *** study provides a valuable experimental foundation for advancing the practical utilization of hydrogen as a sustainable fuel while addressing the challenges associated with ammonia-hydrogen energy systems. © 2025, The Authors. All rights reserved.

关键词： Ammonia

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