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Void fractions in a rod bundle geometry at high pressure-Part.: Drift-flux model assessment and development

INTERNATIONAL JOURNAL OF multiphase flow 2020年第0期125卷 103231-000页

作者： Gui, Miao Liu, Zhaohui Wang, Teng Sui, Zhiqiang Bi, Qincheng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ Sch Nucl Sci & Technol Xian 710049 Peoples R China

The present paper is Part. of an investigation into void fraction measurement and modeling in a triangular-array rod bundle geometry under high-pressure conditions (P = 5-9 MPa and G = 100-350 kg m(-2) s(-1)). In Part I of the study, the experimental facility and measurement techniques were described, and the measured local, chordal, and area-averaged void fractions were presented and analyzed. In this paper, six existing drift-flux models for rod bundles are assessed using the present data. Results show that most of the models are inconsistent with the measured void fraction under low void fraction conditions. This is because the effects of pressure and mass flux on drift-flux parameters are not considered. Hence, a new drift-flux model is developed with flow parameters and flow regime transition being considered. Additionally, the general applicability of this new model is verified by both the present data and existing data in the literatures. Results show that the new drift-flux model agrees well with the experimental data, with the relative deviations of void fraction less than 20%, indicating that the new model is applicable under a wide range of mass-flux conditions. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Void fractions High pressure Rod bundle geometry Drift-flux model Model assessment Model development

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Flocculation of suspended cohesive particles in homogeneous isotropic turbulence

arXiv

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arXiv 2021年

作者： Zhao, K. Pomes, F. Vowinckel, Bernhard Hsu, T.-J. Bai, B. Meiburg, E. Department of Mechanical Engineering UC Santa Barbara Santa BarbaraCA93106 United States State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Leichtweiß-Institute for Hydraulic Engineering and Water Resources Technische Universität Braunschweig Braunschweig38106 Germany Center for Applied Coastal Research Department of Civil & Environmental Engineering University of Delaware NewarkDE19716 United States

We investigate the dynamics of cohesive particles in homogeneous isotropic turbulence, based on one-way coupled simulations that include Stokes drag, lubrication, cohesive and direct contact forces. We observe a transient flocculation phase characterized by a growing average floc size, followed by a statistically steady equilibrium phase. We analyze the temporal evolution of floc size and shape due to aggregation, breakage, and deformation. Larger turbulent shear and weaker cohesive forces yield elongated flocs that are smaller in size. Flocculation proceeds most rapidly when the fluid and particle time scales are balanced and a suitably defined Stokes number is O(1). During the transient stage, cohesive forces of intermediate strength produce flocs of the largest size, as they are strong enough to cause aggregation, but not so strong as to pull the floc into a compact shape. Small Stokes numbers and weak turbulence delay the onset of the equilibrium stage. During equilibrium, stronger cohesive forces yield flocs of larger size. The equilibrium floc size distribution exhibits a preferred size that depends on the cohesive number. We observe that flocs are generally elongated by turbulent stresses before breakage. Flocs of size close to the Kolmogorov length scale preferentially align themselves with the intermediate strain direction and the vorticity vector. Flocs of smaller size tend to align themselves with the extensional strain direction. More generally, flocs are aligned with the strongest Lagrangian stretching direction. The Kolmogorov scale is seen to limit floc growth. We propose a new flocculation model with a variable fractal dimension that predicts the temporal evolution of the floc size and shape. © 2021, CC BY.

关键词： Flocculation

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Study on the edge-cooling target structure for transportable accelerator-driven neutron source

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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 2021年 1017卷 165793-165793页

作者： Li, Xiaobo Ikeda, Yujiro Kobayashi, Tomohiro Wang, Sheng Otake, Yoshie Xi An Jiao Tong Univ Sch Energy & Power Engn 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China RIKEN RIKEN Ctr Adv Photon 2-1 Hirosawa Wako Saitama 3510198 Japan J PARC Japan Proton Accelerator Res Complex 2-4 Shirakata Tokai Ibaraki 3191195 Japan Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China

As the Transportable Accelerator-driven Neutron Source (TANS) for the non-destructive testing of outdoor infrastructure requires efficient neutron production with low power, we studied the target structure design based on the Li-7 (p, n) Be-7 reaction under a 2.5 MeV proton beam injection. For practical applications of TANS, the neutron attenuation in the forward direction should be as low as possible, thus we decided to investigate water-cooling target structures, including an edge-cooling type. Relevant parametric simulations of the material thickness of target structures and water flow rates were carried out in both edge-cooling and conventional back-cooling types. The comparison of neutron attenuation and cooling capability shows that the edge-cooling target has a good performance not only in keeping the temperature within a reasonable range but also in providing the necessary intensity of forward-emitting neutrons with less attenuation, which is suitable for practical applications of TANS. And the stress analysis proves the engineering feasibility of edge-cooling target in operation. In addition, the induced radioactivities and associated dose rates were estimated for the edge-cooling structure model.

关键词： Lithium target TANS Edge-cooling Neutron attenuation reduction Cooling effect

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Pd-based catalysts promoted by hierarchical porous Al2O3 and ZnO microsphere supports/coatings for ethyl acetate highly active and stable destruction

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JOURNAL OF HAZARDOUS MATERIALS 2021年 401卷 123281-123281页

作者： Ma, Mudi Yang, Rui He, Chi Jiang, Zeyu Shi, Jian-Wen Albilali, Reem Fayaz, Khaled Liu, Baojun Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Univ Chinese Acad Sci Natl Engn Lab VOCs Pollut Control Mat & Technol Beijing 101408 Peoples R China Xi An Jiao Tong Univ Sch Elect Engn Ctr Nanomat Renewable Energy State Key Lab Elect Insulat & Power Equipment Xian 710049 Shaanxi Peoples R China Imam Abdulrahman Bin Faisal Univ Dept Chem Coll Sci POB 1982 Dammam 31441 Saudi Arabia King Fahd Secur Coll Dept Criminal Justice & Forens Sci POB 2511 Riyadh 11461 Saudi Arabia Guizhou Univ Coll Resource & Environm Engn Guiyang 550025 Peoples R China

Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al2O3 and ZnO microspheres (Al2O3-pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al2O3-pm and flower-like ZnO-pm possess high specific surface area (especially;external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al2O3-pm and Pd/ ZnO-pm, respectively, over 3.4 times higher than those of commercial Al2O3- and ZnO-supported counterparts. Pd/Al2O3-pm possesses excellent activity and CO2 yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 x 10(-3) s(-1) at 160 degrees C under GHSV of 50,000 h4. Moreover, Pd/Al2O3-pm exhibits satisfied performance in EAcontained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Bronsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Bronsted acid sites over Pd/Al2O3-pm promote ethanol formation and C-C

关键词： Hierarchical porous Al2O3/ZnO microsphere Monolithic catalyst Palladium Ethyl acetate Catalytic oxidation

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A bundle CHF mechanism model and its preliminary verification under PWR conditions 18

A bundle CHF mechanism model and its preliminary verificatio...

引用

18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2019

作者： Liu, Yang Shan, Jianqiang Zhang, Bo Liu, Wei State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University No. 28 Xianning West Road Xi'an Shaanxi Province710049 China Nuclear Power Institute of China State Key Laboratory of System Desgin Technology Chengdu Sichuan Province610213 China

A bundle mechanistic model to predict critical heat flux (CHF) over a pressurized water reactor (PWR) operating range in flow boiling has been proposed based on a concept of the bubble crowding in the wall bubbly layer. The new bundle mechanistic model has the following differences with the original tube model proposed by Weisman & Pei. Firstly,the radial velocity distribution within the bundle was used to derive the radial turbulence intensity factor ib instead of the velocity distribution inside the tube. Secondly, a grid enhancement factor was introduced to quantify the effect of grid on CHF enhancement, based on the measurement experiment of the turbulence intensity factor ib with grid. Thirdly, for the turbulence intensity factor ib, the new model considers the influence of pressure and mass flow rate under two phases, and the original ib only considers the influence of mass flow rate. Finally, the new established bundle CHF mechanism model was verified by comparing with the typical PWR CHF data. © 2019 American Nuclear Society. All rights reserved.

关键词： Heat flux

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Correction to: Modification of a first‑generation solid oxide fuel cell cathode with Co3O4 nanocubes having selectively exposed crystal planes

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Materials for Renewable and Sustainable Energy 2022年第3期11卷 299-299页

作者： Xu, Xi Wang, Chao Fronzi, Marco Liu, Xuehua Bi, Lei Institute of Materials for Energy and Environment College of Materials Science and Engineering Qingdao University Qingdao China State Key Laboratory of Multiphase Flow in Power Engineering International Research Centre for Renewable Energy Xi’an Jiaotong University Xi’an China

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Network topology of turbulent premixed Bunsen flame at elevated pressure and turbulence intensity

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AEROSPACE SCIENCE AND TECHNOLOGY 2019年 94卷 105361-000页

作者： Wang, Jinhua Nie, Yaohui Zhang, Weijie Guo, Shilong Zhang, Meng Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

For turbulent premixed flame surface, folded regions will be formed mainly depending on the turbulence-flame interaction and are significant structures which can increase flame surface area at large scale and enhance the local displacement speed. The conventional methods, such as PDF distribution of curvature, may not properly label the folded regions of turbulent flame because these regions intrude deeply into the products, resulting in a small curvature probability. This problem may be aggravated at elevated pressure and turbulence intensity conditions when more folded regions appear at the turbulent flame front. To identify the folded regions, Network topology of turbulent premixed flame front is constructed using the "visibility" method. Results show that this method can convert the spatial signal of turbulent flame to network topology, labeling the folded regions. Compared with curvature PDF, node degree distribution of network can reflect the mechanism of turbulence-flame interaction when the non-dimensional turbulence intensity is increased by different ways. The network structure of turbulent flame will transfer from sparse to condense when the dimensionless turbulence intensity is increased by pressure and perforated plate, as these two methods will extend the turbulence-flame interaction time and promote the interaction intensity, respectively. However, although the dimensionless turbulence intensity will increase with the augment of outlet velocity, the node degree distribution of network structure of turbulent flame front keeps almost constant. This is caused by the reduced turbulence-flame interaction time. It suggests that the turbulence-flame interaction time is an factor as important as the dimensionless turbulence intensity in turbulent premixed combustion. For forced-turbulent premixed flame at elevated turbulence intensity, the "bending phenomenon" will be hidden if the outlet velocity is not taken into account, as the outlet velocity is related t

关键词： Turbulent premixed flame Network topology Turbulence-flame interaction Elevated pressure

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Test of a spectral splitting prototype hybridizing photovoltaic and solar syngas power generation

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APPLIED ENERGY 2021年 304卷 117779-117779页

作者： Xing, Xueli Xin, Yu Sun, Fan Qu, Wanjun Hong, Hui Jin, Hongguang Chinese Acad Sci Inst Engn Thermophys Beijing 100190 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China Xi An Jiao Tong Univ Int Res Ctr Renewable Energy Xian 710049 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Dongguan Univ Technol Sch Chem Engn & Energy Technol Guangdong Prov Key Lab Distributed Energy Syst Dongguan 523808 Peoples R China

Cost-effective solar power generation systems are of vital importance. The efficient use of full-spectrum sunlight has drawn widespread attention in solar power generation. Here, a 2 kWe hybrid prototype coupling monocrystalline silicon photovoltaics and solar syngas fuelling a heat engine is proposed and experimentally tested. Using double-layer parabolic trough mirrors as the concentrator, the full-spectrum sunlight is split into different wavebands. Split visible and near-infrared sunlight are provided for the photovoltaics and converted into electricity, while both ultraviolent and far-infrared sunlight are used to drive methanol decomposition and produce solar syngas as a fuel for internal combustion engines. At a given solar irradiance intensity, the testing results show that the net solar-to-electricity efficiency of the hybrid prototype is 20.2%. Furthermore, comparison experiments are carried out between the hybrid prototype and the individual power system. The results show that the efficiency of the hybrid prototype is 5.2% higher than that of individual concentrated solar photovoltaics. This study provides an innovative approach to synergistically couple photovoltaic and solar thermal fuel for the cascading use of full-spectrum sunlight.

关键词： Hybrid prototype Full spectrum utilization Spectral splitting approach Photovoltaics Solar syngas

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Reactivity and Efficiency of Ceria-Based Oxides for Solar CO₂ Splitting via Isothermal and Near-Isothermal Cycles

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ENERGY & FUELS 2018年第1期32卷 736-746页

作者： Zhu, Liya Lu, Youjun Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMF Xian 710049 Shaanxi Peoples R China

In this work, different doping strategies for ceria were investigated in isothermal and near-isothermal cycles for solar fuel production. The system efficiency was evaluated by a more realistic model with the whole oxidation process concerned. In terms of fuel productivity, doping ions with lower valences seems to be a disadvantageous strategy due to formation of inert oxygen vacancies. Zr doped ceria exhibited the highest productivity under all of the reaction conditions investigated. The efficiency comparison of pure and Zr doped ceria is different from theoretical prediction, and the influence of oxidation rate is highlighted. The advantage of higher productivity caused by adding Zr is traded off by its drawbacks in kinetics for isothermal cycles at 1300 and 1400 degrees C. Benefit in efficiency only could be observed in an isothermal cycle at 1500 degrees C. Compared to the isothermal cycle, the near-isothermal cycle with a small temperature swing showed improvement in both fuel productivity and efficiency. Pure ceria showed better performance than 10% Zr doped ceria in 1500 degrees C/1300 degrees C near-isothermal cycles.

关键词： Redox reactions Oxides Oxygen Oxidation Doping

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Experimental study on combustion and NO formation characteristics of semi-coke

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FUEL 2019年 258卷 116108-116108页

作者： Zhang, Jinping Wang, Chang'an Jia, Xiaowei Wang, Pengqian Che, Defu Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Pyrolysis condition is vital to physicochemical properties of semi-coke, influencing the subsequent combustion and NO formation. In this study, the combustion behaviors and NO formation characteristics of semi-cokes obtained from various pyrolysis conditions in a fixed-bed reactor were investigated by thermogravimetric analysis and drop tube furnace experiments. Experimental results indicated that the combustion reactivity of semi-coke lowered as pyrolysis temperature, residence time increased and coal particle size decreased. Addition of CO2 or O-2 in pyrolysis atmosphere improved the reactivity. NO conversion ratio of semi-coke decreased initially and increased afterwards with the elevation of pyrolysis temperature with a turning point at 800 degrees C, arose from the fact that higher surface area was helpful for NO reduction during combustion. For mild pyrolysis semi-coke, a critical particle size range was found corresponding to the lowest NO conversion ratio, and it reduced with increasing residence time. O-2 addition in pyrolysis atmosphere significantly lowered the NO conversion ratio and burnout ratio, because some combustibles in coal had been oxidized during the foregoing pyrolysis. CO2 addition in pyrolysis atmosphere exhibited relatively slight effect on the burnout or NO conversion, since the gasification between CO2 and char was weak at this temperature. Quantitative relationship was established to reflect major factors affecting NO formation, and the surface area was observed to have the most prominent influence.

关键词： Semi-coke Pyrolysis condition Combustion behavior NO formation characteristics

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