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Experimental investigation on heat transfer characteristics of high temperature air in round tube

International Journal of Advanced Nuclear Reactor Design and Technology 2021年 3卷 200-205页

作者： Qin, Hao Wang, Chenglong Tian, Wenxi Qiu, Suizheng Su, Guanghui Department of Nuclear Science and Technology Xi'an Jiaotong University Shaanxi Xi'an710049 China Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology Xi'an Jiaotong University China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

Air is widely utilized as working fluid in heat exchangers with high heat flux and high temperature, and the empirical correlations for predicting local and total heat transfer coefficients are indispensable for thermal design and optimization of the heat exchange applications. Experimental investigation on heat transfer characteristics of high temperature air in round tube is conducted. The experimental system is designed and constructed. The data processing method for obtaining wall temperature and heat transfer coefficient is introduced. The measured local and total heat transfer coefficients are compared with the widely adopted correlations, including Taylor's correlation and Gnielinski's correlation. The suggested empirical correlations obtained from the experimental data are presented, which may contribute to the design of heat exchangers concerning with high temperature air. © 2021 Xi'an Jiaotong University

关键词： Heat transfer coefficients

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A direct polymeric carbon nitride/tungsten oxide Z-scheme heterostructure for efficient photocatalytic hydrogen generation via reforming of plastics into value-added chemicals

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Rare Metals 2024年第8期43卷 3771-3783页

作者： Rui-Zhe Wang Zhi Lin Yi-Qing Wang Kai-Ni Zhang Ge-Hong Zhang Jie Zhang Samuel S.Mao Shao-Hua Shen International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power EngineeringXi'an Jiaotong UniversityXi'an 710049China School of Civil and Architecture Engineering Xi'an Technological UniversityXi'an 710021China Department of Mechanical Engineering University of California at BerkeleyBerkeleyCA94720USA

To promote charge transfer and separation for efficient photocatalysis,a direct Z-scheme heterostructure was constructed by coupling polymeric carbon nitride(PCN) and WO_(3).Interestingly,the obtained PCN/WO_(3)Z-scheme heterostructure could photocataly tic ally produce hydrogen and value-added chemicals(e.g.,formate and acetate) by reforming of plastic polylactic acid(PLA) in alkaline aqueous *** optimizing WO_(3) contents and reaction conditions,the obtained PCN/WO_(3)heterostructure exhibits much increased photocatalytic activity for PLA photoreforming under visible light,with hydrogen evolution rate reaching 402.90 μmol·g~(-1)·h~(-1),which is 3.5 times that of *** is revealed that the Z-scheme charge transfer between PCN and WO_(3) mainly contributes to the promoted charge separation and thus the improved photocatalytic ***,with h+and·OH experimentally evidenced as the predominant active species,a possible reaction pathway for the reforming of PLA into value-added chemicals(e.g.,formate and acetate)over PCN/WO_(3) Z-scheme heterostructure is cleared by monitoring the reaction intermediates and *** work paves a carbon neutrality and scalable route toward the synergistical production of hydrogen and value-added chemicals by utilizing and recycling plastic waste.

关键词： Carbon nitride Z-scheme heterojunction Plastic waste conversion Photocatalytic H_(2)production Value-added chemicals

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ZnS/ZnO heterojunction as photoelectrode: Type II band alignment towards enhanced photoelectrochemical performance

ZnS/ZnO heterojunction as photoelectrode: Type II band align...

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作者： Guo, Penghui Jiang, Jiangang Shen, Shaohua Guo, Liejin International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Shaanxi 710049 China

Heterojunction structures are attracting lots of attention for enhancing the electron injection across the interface. The ZnS/ZnO one-dimensional heterojunction film was firstly prepared via a chemical sulfidization following hydrothermal reaction. The heterostructure was characterized as ZnS(blende)/ZnO(wurtzite) shell-core nanorods via XRD, SEM and TEM. A type II band alignment structure of ZnS/ZnO composite was synthesized via a temperate condition proved by PLS and XPS. The values for valence band offset (VBO) and conduction band offset (CBO) were calculated to be 0.96 eV and 1.25 eV, respectively. The special electron structure in the heterojunction helped reduce the energy barrier height at the interface and enhance the separation of photo-generated carriers. Thus, the photoelectrochemical performance was highly improved, and a photocurrent density of 380 μA/cm2 at 0.9 V (vs. Ag/AgCl) was obtained. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Heterojunctions

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Fabricating CdS/BiVO4 and BiVO4/CdS heterostructured film photoelectrodes for photoelectrochemical applications

Fabricating CdS/BiVO4 and BiVO4/CdS heterostructured film ph...

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作者： Jiang, Jiangang Wang, Meng Li, Rong Ma, Lijing Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering International Research Center of Renewable Energy Xi'An Jiaotong University Shaanxi 710049 China

The photoelectrochemical (PEC) properties of heterostructured CdS/BiVO 4 and BiVO4/CdS film electrodes on conducting glass for hydrogen production under visible light were investigated. These two types heterostructured film electrodes were prepared using spin coating method and ultrasonic spray pyrolysis method. The structural analyses of the prepared films were determined by using XRD, SEM, EDX and UV-vis. Photoelectrochemical measurements were carried out in a convenient three electrodes cell with 0.5 M Na2SO3 aqueous solution. In order to investigate band gap influence of electrode PEC property, a series ITO/Cd1-xZn xS/BiVO4 and ITO/BiVO4/Cd1-xZn xS (x = 0 ∼ 1) film electrodes were also synthesized. After PEC test, a maximum photocurrent density from ITO/CdS/BiVO4 film electrode was confirmed. The maximum photocurrent density, 3 times and 113 times as that of single CdS film electrode and single BiVO4 film electrode, respectively. Incident photon to current conversion (IPCE) of as prepared film electrodes were measured and the value were 65% (ITO/CdS/BiVO 4), 22% (single CdS film) and 10% (ITO/BiVO4/CdS) at 480 nm with 0.3 V external bias. Comparison with ITO/BiVO4/CdS electrode and single Cd1-xZnxS electrodes, the heterostructured ITO/CdS/BiVO4 electrode can effectively suppress photogenerated electron-hole recombination and enhance light harvesting. Therefore, the ITO/CdS/BiVO4 electrode gave the maximum photocurrent density and IPCE value. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Bismuth compounds

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Flame front evolution and self-acceleration of hydrogen spherically expending flames 11

Flame front evolution and self-acceleration of hydrogen sphe...

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11th Asia-Pacific Conference on Combustion, ASPACC 2017

作者： Cai, Xiao Wang, Jinhua Zhao, Haoran Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University NO.28 Xianning West Road Xi’an710049 China

An experimental study on flame front evolution and self-acceleration of hydrogen spherically expending flames was conducted on a constant volume combustion chamber over a wide range of Lewis number at elevated pressures. Flame morphology, onset of flame acceleration and flame self-similar acceleration were analyzed. The results shows that the critical radius for onset of flame acceleration increases with the increase in effective Lewis number and the decrease in initial pressure. And the critical Peclet number increases nonlinearly with the increasing Markstein length. Thus, the onset of flame acceleration is controlled by the couple effects of hydrodynamic and diffusional-thermal instabilities. Furthermore, the self-similar acceleration exponent increases with the decrease in the effective Lewis number (or Markstein number) and almost keeps constant with initial pressure. It is concluded that the self-similar acceleration exponent is mainly affected by diffusional-thermal instability. © 2018 Combustion Institute. All Rights Reserved.

关键词： Acceleration

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Numerical computation of aerodynamic noise reduction by using ultra-light porous metals

Numerical computation of aerodynamic noise reduction by usin...

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International Conference on Transportation engineering

作者： Liu, Hanru Wei, Jinjia State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an China Xi'An Jiaotong University Xi'an 710049 China

ISBN: (纸本)9780784411841

As the speed of high-speed train (HST) increases continuously, aerodynamic noise has become more important compared with the wheel/rail noise, which affects the inhabited environment around the railway and the comfort of passengers. This paper preliminarily investigates the feasibility of reducing the low Mach number aerodynamic noise by using ultra-light porous metals. The noise generated by the flow around a two-dimensional circular cylinder which is the typical unit of pantographs, was simulated with and without a porous media. The hybrid method that combines large eddy simulation (LES) with Ffowcs Williams-Hawkings (FW-H) equation was employed. The calculated overall sound pressure level (OASPL), vortex shedding frequency and time-average drag coefficient agree well with available experimental data. Then, the effects of porosity and the speed of train on the aerodynamic noise were predicted and explained in view of fluid mechanics. The numerical results indicate that the open cell-type porous media with high porosity can modify and regularize the fluid flow, adjust the vortex shedding frequency, leading to a significant reduction of aerodynamic noise. © 2011 ASCE.

关键词： Porous materials

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Heat Transfer Enhancement of Supercritical Carbon Dioxide and Liquid Lead Bismuth Eutectic Compact Heat Exchanger 20

Heat Transfer Enhancement of Supercritical Carbon Dioxide an...

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20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2023

作者： Liu, Shuhan Liu, Ji'an Liu, Qingjiang Lei, Xianliang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 West Xianning Road Xi'an710049 China

ISBN: (纸本)9780894487934

Lead cooled fast reactor (LFR) is the fourth generation reactor system with great development potential;Supercritical carbon dioxide (S-CO2) Brayton cycle is also considered as the most promising energy system due to its high efficiency and compactness, good flexibility. Their combination is undoubtly considered as one of the most ideal power cycles. In this union system, the intermediate heat exchanger plays a key role in the entire power system. Considering the thermo-physical properties and heat transfer behaviors in both S-CO2 and liquid lead bismuth eutectic (LBE) are significantly different, an asymmetric compact coupled heat exchanger learning from Honeycomb structure is proposed. Then the effect of Reynolds number on the coupling heat transfer is discussed. It is found that the thermal resistance mainly exists in the cold side. In order to enhance the heat transfer in the S-CO2 side, wave channels are used on the cold side. The results show that the wave channels can significantly improve the field synergy of the fluid near the wall;With the increase of wave amplitude, the heat transfer coefficient and the friction factor of the cold side channel increases;The comprehensive heat transfer coefficient PEC is used to evaluate the heat transfer behavior. When the PEC number is the largest, the overall heat transfer coefficient of the heat exchanger is 1.56~1.81 of the straight channel in the range of Re=86700~145000. © 2023 Proceedings of the 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2023. All rights reserved.

关键词： Brayton cycle

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Synthesis of uniform ZnO/ZnS/CdS nanorod films with ion-exchange approach and photoelectrochemical performances

Synthesis of uniform ZnO/ZnS/CdS nanorod films with ion-exch...

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作者： Jiang, Jiangang Wang, Meng Ma, Lijing Chen, Qingyun Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering International Research Center of Renewable Energy Xi'An Jiaotong University Shaanxi 710049 China

The uniform ZnO/ZnS/CdS core-shell nanorod film was synthesized by a two-step ion-exchange method. The crystal structure, morphology, composition and optical property of as-prepared films were characterized by X-ray diffraction (XRD), Raman, Scanning electron microscope (SEM), Transmission electron microscope (TEM), Energy dispersive X-ray Detector (EDX) and UV-vis techniques. The results showed that the ZnO nanorod arrays can be used as sacrificial templates to synthesize uniform ZnS layer and further transform into CdS by simple ion-exchange approach. The CdS content in the films can be adjusted easily by changing the reaction temperature. The intimate contact between core and shell can be observed by high-resolution TEM image, which decrease the crystal boundary potential barrier and then facilitate the photogenerated charges transfer between the different phases. In this experiment, the ZnO/ZnS/CdS nanorod films were used in the photoelectrochemical (PEC) hydrogen production. And it is found that the film prepared at 70 C (first step) and 100 C (second step) gives a maximum photocurrent density and photo conversion efficiency. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Cadmium sulfide

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NUMERICAL SIMULATION OF SINGLE/TWO-PHASE flow IN A STRATIFIED POROUS BED 31

NUMERICAL SIMULATION OF SINGLE/TWO-PHASE FLOW IN A STRATIFIE...

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2024 31st International Conference on Nuclear engineering, ICONE 2024

作者： Bouloudenine, Aimad Li, Liangxing Xiang, Zutao Shi, Shang Bakar, Muhammad Abu Xi’an Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xianning West Road 28 Xi’an City710049 China

ISBN: (纸本)9780791888292

This study investigates the coolability of debris beds formed from Fuel-Coolant Interactions (FCI) within nuclear reactors, a critical safety concern when cooling systems fail, leading to significant core melting in light-water reactors. The research focuses on understanding the flow dynamics within two-layer stratified porous beds, which develop from the mixture of corium and coolant, particularly around the interface between layers. Using ANSYS Fluent software, numerical simulations were conducted to estimate velocity profiles and pressure drops across a stratified porous structure. The Euler-Euler two-fluid model was employed alongside the k-ω-based Shear Stress Transport (SST) turbulence model to separately model turbulence for each phase. The results reveal that lateral flow dynamics are significant as fluids traverse through the porous media, affecting pressure drops across layers with varying permeabilities. Specifically, the pressure drops across the lower-permeability layer decrease while that across the higher-permeability layer increases, highlighting the influence of lateral flows between layers of different particle sizes due to variations in porosity. This lateral flow is most likely formed during the initial stages of fluid movement through the bed. The study underscores the importance of understanding these flow characteristics for both single/two-phase flow to enhance the safety and design of nuclear reactors by improving debris bed coolability predictions. Copyright © 2024 by ASME.

关键词： Computational fluid dynamics

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Energy and exergy analyses of a novel recirculated regenerative rotary desiccant wheelassisted dehumidification system 33

Energy and exergy analyses of a novel recirculated regenerat...

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33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2020

作者： Han, Xiaoqu Wu, Wenxiang Chong, Daotong Su, Minqi Zhang, Dan Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an China MOE Key Laboratory of Thermal Fluid Science and Engineering Xi'An Jiaotong University Xi'an China

The indoor air humidity and temperature in the marine cabins could be as high as 80% and 40 °C - 50 °C, respectively, which may cause security risks to crews and devices. The incorporation of solid desiccant wheel for improved dehumidification and air quality control would contribute to energy saving in air conditioning system through waste heat recovery for regeneration. In the present work, a novel recirculated regenerative rotary desiccant wheel-assisted dehumidification system was proposed. The energy and exergy performances of the system under variable working conditions were quantitatively studied based on experimental tests. The dehumidification effectiveness, dehumidification performance coefficient (DCOP), sensible energy ratio and coefficient of performance (COP) were introduced as key energetic indicators. The effects of air bypass ratio (50% - 85%), process air temperature (28 °C - 40 °C), relative humidity of process air (60%RH - 80%RH) and regeneration air temperature (130 °C - 150 °C) on the system performances were obtained. It was found the COP of the system ranged between 0.4 and 1.8, while the exergy efficiency was only 4% - 11%. An optimal bypass ratio existed which was determined 55%-60%. Overall, the energy saving and exergy consumption characteristics of the proposed system at various working conditions were explored to prompt its practical application. © ECOS *** right reserved.

关键词： Waste heat

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