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Effects of Magnetic Fields on Morphology and Nanostructure Evolution of Incipient Soot Particles from n-heptane/2,5-dimethylfuran Inverse Diffusion Flames

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Journal of Thermal Science 2020年第3期29卷 820-839页

作者： JIANG Bo WANG Pengfei LIU Dong MIIT Key Laboratory of Thermal Control of Electronic Equipment School of Energy and Power EngineeringNanjing University of Science and TechnologyNanjing 210094China Advanced Combustion Laboratory School of Energy and Power EngineeringNanjing University of Science and TechnologyNanjing 210094China Jiangsu Province Key Laboratory of Aerospace Power System Nanjing 210016China

Differences of the morphology and nanostructure evolution of incipient soot particles generated in n-heptane/2,5-dimethylfuran(DMF)inverse diffusion flames(IDFs)with/without magnetic fields were *** a high resolution transmission electron spectroscopy,the morphology and nanostructures of soot sampled from spatial locations at different heights in IDFs were *** graphitization and the oxidation reactivity of soot were tested by an X-ray diffraction and a thermogravimetric analyzer,*** demonstrated that the magnetic force on paramagnetic species,such as oxygen molecules,can modify the soot formation and *** incipient soot particles with larger diameters appeared in chains or branches or tufted forms on the flame wing region and the higher position than that on the flame centerline region and the lower *** magnetic fields,greater amounts of clustered soot particles displayed more crowded distribution and larger *** particles with typical structures of the core-shell were promoted to own more orderly bordered lamellae with longer fringe length and smaller fringe tortuosity by the magnetic force acting on oxygen at the same sample *** modifications resulted in relatively larger diffraction angle of the peak,higher graphitization degree and slightly lower oxidation reactivity of soot.

关键词： magnetic fields incipient soot particle n-heptane/DMF morphology nanostructure evolution

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LVRT During-fault-stage Equilibrium Point is Unnecessary for Renewable Grid-tied systems

LVRT During-fault-stage Equilibrium Point is Unnecessary for...

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power system and Green Energy Conference (PSGEC)

作者： Yayao Zhang Min Cheng Meng Zhan Jiawei Yu Yihua Zhu Mingkang Wu State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan China Yunnan Power Grid China State Key Laboratory of HVDC Electric Power Research Institute China Southern Power Grid China National Energy Power Grid Technology R&D Centre Electric Power Research Institute China Southern Power Grid China Guangdong Provincial Key Laboratory of Intelligent Operation and Control for New Energy Power System Electric Power Research Institute China Southern Power Grid China

ISBN: (数字)9798350365573

ISBN: (纸本)9798350365580

Transient synchronous stability of renewable grid- tied systems is of paramount importance. Most of previous studies focused on the grid-tied converter in the low voltage ride through (LVRT) during-fault stage and performed stability analysis based on the belief that if the system has (or has no) a stable equilibrium point in the during-fault stage, the system will be stable (or unstable). Therefore, it has been broadly accepted that the existence and/or stability of equilibrium point in the during-fault stage is necessary. However, the whole LVRT contains four different stages and the during-fault stage is only one among them. The transient synchronous stability of whole system should be determined by the initial state in the late post-fault stage and the attraction basin of its equilibrium point. The late post-fault stage is essential for stability and all four stages are important. Clearly treating the during-fault stage as the whole LVRT stages makes the nonlinear switched dynamics problem be greatly simplified and, certainly, is incomplete. In order to clarify this point, this paper analyzes the influence of existence (or nonexistence) of equilibrium point in the during-fault stage on the transient synchronous stability of permanent magnet synchronous generator grid-tied system. We can find that the existence of an equilibrium point in the during-fault stage is only a sufficient condition, rather than a necessary condition. The theoretical analysis is also verified in the hardware-in-the-loop experiment Therefore, a large number of previous studies and results on the transient synchronous stability of renewable grid-tied systems are incomplete and questionable.

关键词： Sufficient conditions Stability criteria Switches Voltage power system stability Synchronous generators Permanent magnets Nonlinear dynamical systems Transient analysis Magnetic switching

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Basic reason for the accumulation of charge on the surface of polymer dielectrics

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Science China Materials 2022年第10期65卷 2884-2888页

作者： Tianyu Wang Xiaofen Li Boya Zhang Dayu Li Jianbo Liu Guixin Zhang State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical EngineeringTsinghua UniversityBeijing 100084China Key Laboratory of Advanced Materials(MOE) School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China State Key Laboratory of Electrical Insulation and Power Equipment Xi’an Jiaotong UniversityShaanxi 710049China

Due to their outstanding electrical insulation performance,low energy loss and high reliability,polymer dielectrics are widely used in flexible electronics,capacitors and large-scale power transmission equipment[1–5].However,polymer dielectrics accumulate large amounts of charge on their surface during use,which causes local electric field distortion and induces flashover,explosion,and equipment damage[6–9].Although researchers have attempted to develop methods to reduce the accumulation of surface charge through material modification,such as plasma treatment[10],direct fluorination[11],and coating[7,9,12],each of these methods has drawbacks;thus,the bottleneck has yet to be overcome.

关键词：电荷量第一性原理计算聚合物表面电介质电场畸变深能级缺陷电荷测量电荷特性

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Phonon transport in freestanding SrTiO3 down to the monolayer limit

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Physical Review B 2023年第11期108卷 115435-115435页

作者： Qi Wang Chen Wang Cheng Chi Niuchang Ouyang Ruiqiang Guo Nuo Yang Yue Chen Thermal Science Research Center Shandong Institute of Advanced Technology Jinan Shandong Province 250103 China Department of Mechanical Engineering The University of Hong Kong Pokfulam Road Hong Kong SAR China Key Laboratory of Power Station Energy Transfer Conversion and System of Ministry of Education School of Energy Power and Mechanical Engineering North China Electric Power University Beijing 102206 China State Key Laboratory of Coal Combustion School of Energy and Power Engineering Huazhong University of Science and Technology Wuhan 430074 China

Perovskites down to the monolayer limit have emerged and have attracted increased interest due to their two-dimensional nature with potentially novel physical properties. Here, we investigate the phonon transport in the oxide perovskite SrTiO3 with thicknesses from the monolayer limit to 10 nm by constructing an accurate first-principles machine-learning potential and combining it with the Boltzmann transport equation and homogeneous nonequilibrium molecular dynamics simulations. Compared to its bulk counterpart, the phonon dispersion relation of monolayer SrTiO3 is insensitive to temperature, and the calculated in-plane thermal conductivity of monolayer SrTiO3 is much larger than that of bulk SrTiO3, which mainly results from the unique out-of-plane atomic vibrations in monolayer SrTiO3. The thermal conductivity of SrTiO3 thin film first decreases and then approaches the bulk value as thickness increases from the monolayer limit to 10 nm. The hardening of the out-of-plane acoustic phonon branch and the transition of low-frequency optical phonons can explain the observed trend in thermal conductivity transitions. Our study demonstrates that monolayer SrTiO3 has a higher thermal conductivity than its bulk counterpart with covalent bonds at the first-principles level of accuracy, and dimension reduction has a weak inhibition on phonon transport in freestanding atomically smooth SrTiO3 thin films, which furthers the understanding of phonon transport in two-dimensional perovskite thin films.

关键词： Thermal properties Perovskites Thin films Boltzmann theory Density functional calculations Molecular dynamics

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Numerical Study on Benchmark Analysis of NACIE-UP Facility with Uniform and Non-Uniform power Distribution

SSRN

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SSRN 2024年

作者： Li, Haoyang Zhang, Dalin Zhou, Lei Deng, Jian Tian, Wenxi Su, Guanghui Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China Nuclear Power Institute of China 328 Changshun Avenue Chengdu610213 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China

The NACIE-UP facility is located at the ENEA Brasimone Research Centre and is designed to investigate the thermo-hydraulic properties of LBE within a wire-spaced assembly under uniform and non-uniform power distribution conditions. In this study, the thermo-hydraulic characteristics of FPS are analyzed. ANSYS Fluent solver is applied with the COUPLE algorithm of RANS [[EQUATION]] model. Cheng&Tak correlation and computational conditions are implanted into Fluent in the form of UDFs. The results show that the RMSEs of ADP10SS1 and ADP10SS2 are 2.52 K and 3.69 K, 7.05 K and 8.48 K for ADP06SS1 and ADP06SS2, respectively, which indicate that the adopted models have good prediction ability for the temperature of the experimental conditions. Meanwhile, the heat transfer characteristics are investigated and compared with the correlations of Ushakov, Mikityuk, Kazimi and Carelli. Above all, this study provides quantitative and qualitative analysis for verification and validation of CFD/STH code and stand-alone CFD simulation. © 2024, The Authors. All rights reserved.

关键词： Heat transfer

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Small-Signal Stability of MMC Grid-Tied system under Two Typical Unbalanced Grid Conditions 4

Small-Signal Stability of MMC Grid-Tied System under Two Typ...

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4th IEEE China International Electrical and Energy Conference, CIEEC 2021

作者： Zhu, Jianhang Hu, Jiabing Li, Yingbiao Ma, Shicong Wang, Tiezhu Institute of Artificial Intelligence Huazhong University of Science and Technology State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Wuhan China Electric Power Research Institute Power System Department China Beijing China

ISBN: (纸本)9781728171494

The AC transmission network of Modular Multilevel Converters (MMC) usually adapts the overhead line, so the single-phase grounding faults of the AC side are rather general. At this time, the protection system will cut off the fault line for the first time, so there are two unbalance grid conditions (UGCs), i.e. single-phase grounding (SGUGC) and disconnection (SDUGC) during this process. However, the comparative analysis of small-signal stability under two different UGCs has never been involved. Therefore, when ignoring the transient process of faults and protection actions, and considering the inherent properties of the MMC system, two small-signal models based on the linear time-periodic (LTP) theory are built under SGUGC and SDUGC, respectively. Then, the influence of control parameters on the system stability under the two UGCs is compared in detail, and the results provide theoretical support for the control parameters optimization after protection system action. Finally, the detailed nonlinear MMC grid-connected model verifies the analysis results. © 2021 IEEE.

关键词： Signal analysis

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Dynamic Characteristics of the Subsea Direct Drive Hydraulic Servo Rotary Valve

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China Ocean engineering 2025年第2期 329-339页

作者： SHI You-cheng SHAN Jun-feng ZHANG Hu-cheng LIU Yin-shui College of Energy and Fluid Power Engineering Lanzhou University of Technology Key Laboratory of Advanced Pumps Valves and Fluid Control System of the Ministry of Education Lanzhou University of Technology

Hydraulic technology has the outstanding advantages of easy pressure compensation and high power density. It is an indispensable part of subsea equipment, such as deep-sea operations and submersible propulsion. There are few studies on electrohydraulic servo valves(EHSVs) in the deep sea. In this work, a novel electro-hydraulic servo rotary valve is designed, and its mathematical model is established. The analysis considers the variations in physical parameters such as temperature, ambient pressure, and oil viscosity resulting from changes in sea depth. This study focuses on the deformation of the rotary valve and the consequent alterations in leakage and friction torque. The findings indicate that at a depth of 12000 m, the fit clearance between the valve spool and the valve sleeve is 0.00413 mm, representing a 17% reduction compared with the clearance in a land environment. Then, the response of the rotary valve to depth is analyzed. The results indicate that the bandwidth of the rotary valve decreases with increasing depth. This study provides a reference for the use of the EHSV in the deep sea.

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Concept and Definition of Dynamic Symmetrical Components with Time-Varying Amplitude and Frequency

Concept and Definition of Dynamic Symmetrical Components wit...

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IEEE General Meeting power& Energy Society

作者： Yingbiao Li Jiabing Hu Weizhong Wen Qinghua Wang Shicong Ma Jianbo Guo State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Wuhan China State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing China China Electric Power Research Institute Beijing China

This paper investigates the dynamic symmetrical component method of internal voltage vector with time-varying amplitude and frequency. With the large-scale integration of power electronic devices into the power grid, when there is an asymmetrical fault in the AC network, the voltages and currents present the characteristics of amplitude and frequency time-varying modulation. Hence, the traditional asymmetrical fault analysis method and concept based on phasor models with constant amplitude and frequency are not adaptive enough. In order to supplement the traditional symmetrical component method and concept, the phasor models and vector models with time-varying amplitude and frequency are established. Then, the asymmetrical three-phase phasors with time-varying amplitude and frequency are decomposed into three groups of symmetrical phasors with time-varying amplitude and frequency. Based on the mathematical and physical characteristics of symmetrical components, the applicable concept and definition are reestablished. Lastly, time-domain simulations corroborate the theoretical analysis.

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Physical Optimization and Safety Analysis of Space Thermionic Reactor

SSRN

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SSRN 2023年

作者： Xie, Lin Qiu, Zhifang He, Yuhao Tian, Ruifeng Meng, Tao Tan, Sichao Zhao, Fulong Heilongjiang Provincial Key Laboratory of Nuclear Power System & Equipment Harbin Engineering University Harbin150001 China Key Laboratory of Nuclear Safety and Advanced Nuclear Energy Technology Ministry of Industry and Information Technology Harbin Engineering University Harbin150001 China Nuclear Power Institute of China Sichuan Province Chengdu610000 China Aerospace System Engineering Institute of Shanghai Shanghai201109 China

Thermionic reactor, with its advantages of small size, simple structure and high technical maturity, will become a relatively feasible reactor type in space nuclear reactors in the future. In order to study the application of thermionic reactor in megawatt nuclear spacecraft and the higher technical requirements under high power, a reactor core structure scheme of a megawatt thermionic reactor controlled by control rods is proposed in this paper. The influence of core parameters of fuel element, fuel enrichment, fuel center hole size and radial reflector thickness on reactor miniaturization and radial power flattening is analyzed by Monte Carlo method, and reactor core optimization results based on miniaturization and higher power flattening objectives are obtained. The operation safety characteristics and accident safety characteristics of the optimized thermionic reactor are analyzed. The analysis results show that the reactor has physical safety. The present work provides the foundation and support for the optimization design and thermal safety analysis of megawatt thermionic reactor in the future. © 2023, The Authors. All rights reserved.

关键词： Monte Carlo methods

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Evaluation of a Numerical Model for Predicting Flow and Heat Transfer in a Hexagonal Helical Cruciform Seven-Rods Bundle and Analysis of Rod Bundle Size Independence

SSRN

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SSRN 2024年

作者： Jiang, Dianqiang Deng, Jian Zhang, Dalin Zhou, Xingguang Xiao, Changzhi Tian, Wenxi Qiu, Suizheng Su, Guanghui H. State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China Nuclear Power Institute of China Science and Technology on Reactor System Design Technology Laboratory Chengdu610213 China China Institute of Atomic Energy Beijing611731 China

In this study, the accuracy and applicability of the numerical model are comprehensively evaluated based on the experimental data of a hexagonal helical cruciform (HC) seven-rods bundle. The STAR CCM+ is utilized as a tool to obtain predicted results of flow and heat transfer in different flow regions. The numerical results indicate that it is an improved method to set a negative heat flux on the hexagonal wall in the laminar flow region. The Reynolds stress transport model can accurately predict the experimental results of heat transfer in the transitional flow region, with an average wall temperature deviation of 2.8℃. The SST k-ω model with cubic constitutive option can accurately predict the experimental results of the flow resistance, and a relative error of f is 1.8%. In the turbulent flow region, the SST k-ω model with cubic constitutive option provides an accurate prediction, with an average wall temperature deviation of 3.7℃. The realizable k-Ε two-layer model can accurately predict the flow resistance, and the relative error of f is 0.1%. The preferred numerical model is used to analyze the size independence of the HC rod bundle. This work provides certain guidelines for the accurate simulation in the HC seven-rods bundle. © 2024, The Authors. All rights reserved.

关键词： Computational fluid dynamics

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