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Wake of a stationary sphere near a wall

Huagong Xuebao/CIESC Journal 2019年第9期70卷 3300-3306页

作者： Li, Xing Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'anShaanxi710049 China

The flow characteristics of the sphere under uniform flow in a large space have been extensively studied, but the influence of the wall on the flow characteristics of the sphere is not clear. The wake of the particle is focused. Results show that there are three regimes of the sphere wake, which are steady wake, unsteady symmetric wake and unsteady asymmetric wake. If Re400, the vortex shedding is not symmetric and becomes chaotic as Reynolds number increases. © All Right Reserved.

关键词： Wakes

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Heat transfer enhancement of plate heat exchangers with symmetrically distributed capsules to generate counter-rotating vortices

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2020年第0期151卷 119455-000页

作者： Jiang, Chen Bai, Bofeng Wang, Haibo Shi, Jiqing Tang, Xiaoying Zhou, Wenxue Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Shanghai Lanbin Petrochem Equipment CO LTD Shanghai 201518 Peoples R China Machinery Ind Shanghai Lanya Petrochem Equipment Shanghai 201518 Peoples R China Shanghai Inst Equipments Inspect & Tech Res Shanghai 200062 Peoples R China Lanzhou Res Ctr Heat Transfer & Energy Conservat Lanzhou 730050 Peoples R China

Capsule-type plate heat exchanger takes advantages of low flow resistance and high overall performance. To obtain greater energy efficiency, a new type named symmetrical capsule plate heat exchanger (SCPHE) is constructed based on the idea of counter-rotating vortices. For SCPHEs, the adjacent capsules distribute symmetrically at the same-side of the plate, and the capsules keep an angle of 45 degrees with the main flow direction. The heat transfer enhancement and the influences of capsule geometries were studied numerically. Counter-rotating vortices generating in the channels promote the swirl flow and disturb the boundary layer. Both fluid impinging and the vortices dominate the heat transfer enhancement, which become much stronger under smaller capsule, resulting in higher heat transfer coefficient. The correlations of Nu and f considering the effects of the capsule geometries are developed. SCPHEs show higher energy efficiency than capsule-type plate heat exchangers and chevron-type plate heat exchangers in the view of PEC and EEL. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Plate heat exchanger Symmetrical capsule Counter-rotating vortices Fluid impingement Energy efficiency

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Study on melt stratification and migration in debris bed using the moving particle semi-implicit method

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NUCLEAR engineering AND DESIGN 2020年 360卷 110459-110459页

作者： Li, Gen Wen, Panpan Feng, Haobo Zhang, Jun Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China China Tianchen Engn Corp 1 Jingjin Rd Tianjin 300400 Peoples R China

In the severe accident of nuclear reactors, the melt stratification and migration in debris bed directly affect the melt heat transfer characteristics and the heat flux distribution on the lower head wall, which in turn affect the follow-up accident progressions including the pressure vessel failure mode, melt leakage, and molten corium concrete interaction. They are the key issues in nuclear reactor severe accident research. In the present study, the MPS method was applied to analyze melt stratification and migration in debris bed by including the models of radiation heat transfer among debris, melt phase change and surface tension. To validate the numerical method, the experiment was performed using the metal fin and ternary nitrate as the core melt simulant. Then, the stratification behavior of oxide and metallic core melt was investigated under varied parameters and conditions. The results indicated that the crust formed at the oxide and metal melt interface could block the stratification, which had important influence to the layered configuration. The melt contact area increased in the conditions of crust formation prior to the stratification completion. The high melt and debris temperatures and surface tension could contribute to the stratification, but the high viscous melt when undergoing phase transition needed a long time. Moreover, the comparison of melt stratification under adiabatic and isothermal boundary conditions showed that the oxide melt solidification trapped some metal melt in the voids. The penetration distance of metal melt in the oxide debris bed increased rapidly in the initial moment and gradually in the following moment and finally the migration was terminated by melt crust. The melt penetration distance increased as the increase of debris bed porosity and melt and debris temperatures.

关键词： MPS method Melt stratification Melt migration Debris bed

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Experimental and numerical study on impinging fuel spray under high-pressure cross-flow condition 14

Experimental and numerical study on impinging fuel spray und...

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14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018

作者： Si, Z. Guo, M. Ashida, Y. Nishida, K. Ogata, Y. Tang, C. Huang, Z. Department of Mechanical System Engineering University of Hiroshima 1-4-1 Kagamiyama Higashi-Hiroshima739-8527 Japan School of Mechanical and Electronic Engineering Wuhan University of Technology 122 Luoshi road Wuhan Hubei430070 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University 28 Xianning west road Xi'an710049 China

It is certified that the fuel spray is strongly affected by both in-cylinder air flow and piston cavity wall impingement in a direct injection engine. In this study, sprays injected by a valve covered orifice nozzle were tested by a high-speed video camera and a continuous wave laser sheet under a wind-tunnel with cross-flow and pressurized ambience, thereby the spray profiles in vertical and horizontal planes were investigated. Moreover, the experiment results were compared with simulations which was calculated by the validated spray models based on the CONVERGE software. With increase in the cross-flow velocity, the spray tip penetration evidently increased, and the increased cross-flow velocity led to an increase in the vortex height because of the enhanced spray dispersion. Furthermore, the high ambient pressure restrains the spray dispersion and leads to smaller spray tip penetration and vortex height. The outlines of spray with same liquid-to-air momentum flux ratio q can agree with each other in the windward side, nevertheless the droplet diffusion under high cross-flow velocity is distinct in the leeside. At the horizontal plane of y=25mm, a complex vortex movement was observed that resulted in a nonuniform distribution of droplets in the upper part of the spray in the leeward side. From the calculations, in the radial region apart from the impingement point (8mm4mm) hardly moved. © 2018 Solar Turbines Incorporated.

关键词： Continuous wave lasers

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An improved DNB-type critical heat flux prediction model for flow boiling at subcritical pressures in vertical rifled tube

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 132卷 209-220页

作者： Xie, Haiyan Yang, Dong Wang, Wenyu Wan, Li Li, Chunmei Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China Nucl Power Inst China Sci & Technol Reactor Syst Design Technol Lab 328 Changshun AveSect 1 Chengdu 610231 Sichuan Peoples R China

Based on the near-wall bubble coalescence model and the structural characteristics of the rifled tube, improvements and optimization of the model for rifled tube were conducted. DNB-type CHF phenomenon in the rifled tube under subcritical and near-critical pressures was investigated by numerical calculation. A new CHF prediction model of flow boiling in rifled tube with low qualities was established and compiled by FORTRAN language. The model used the Staub model which considering the influence of the bubble contact angle to calculate the bubble detachment diameter. The surface friction coefficient of the rifled tube was calculated by the classical Kohler and Kastner formula. And a new critical void fraction of the wall bubbly layer co, correlation was proposed based on a large number of CHF experimental data. The present model was verified by the CHF look-up values and CHF experimental values. Based on the CHF experimental data of the rifled tube, three classic CHF prediction models and the present CHF model were evaluated, and it was found that the present modified CHF model has the highest prediction accuracy for the rifled tube, which is the best agreement with the experimental values, indicating that the present model is appropriate for DNB-type CHF prediction of the rifled tube. In this paper, the effects of pressure, mass flux and inlet fluid subcooled enthalpy on CHF were studied. It was found that, the effect of pressure and mass flux on CHF is obvious in the low quality region, with the increase of vapor quality, the influence of pressure and mass flux on CHF weakens. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Bubble coalescence Rifled tube Departure from nucleate boiling Critical heat flux Numerical computation

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Ion Irradiation Inducing Oxygen Vacancy-Rich NiO/NiFe₂O₄ Heterostructure for Enhanced Electrocatalytic Water Splitting

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SMALL 2021年第40期17卷 2103501-2103501页

作者： Zhong, Huizhou Gao, Guoping Wang, Xuening Wu, Hengyi Shen, Shaohua Zuo, Wenbin Cai, Guangxu Wei, Guo Shi, Ying Fu, Dejun Jiang, Changzhong Wang, Lin-Wang Ren, Feng Wuhan Univ Sch Phys & Technol Ctr Ion Beam Applicat Ctr Electron MicroscopyHubei Key Lab Nucl Solid Wuhan 430072 Peoples R China Wuhan Univ MOE Key Lab Artificial Micro & Nanostruct Wuhan 430072 Peoples R China Lawrence Berkeley Natl Lab Mat Sci Div Berkeley CA 94720 USA Xi An Jiao Tong Univ Int Res Ctr Renewable Energy State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Oxygen evolution reaction (OER) is an obstacle to the electrocatalytic water splitting due to its unique four-proton-and-electron-transfer reaction process. Many methods, such as engineering heterostructure and introducing oxygen vacancy, have been used to improve the catalytic performance of electrocatalysts for OER. Herein, the above two kinds of regulation are simultaneously realized in a catalyst by using unique ion irradiation technology. A nanosheet structured NiO/NiFe2O4 heterostructure with rich oxygen vacancies converted from nickel-iron layered double hydroxides by Ar+ ions irradiation shows significant enhancement in both OER and hydrogen evolution reaction performance. Density functional theory (DFT) calculations reveal that the construction of NiO/NiFe2O4 can optimize the free energy of O* to OOH* process during OER reaction. The oxygen vacancy-rich NiO/NiFe2O4 nanosheets have an overpotential of 279 mV at 10 mA cm(-2) and a low Tafel slope of 42 mV dec(-1). Moreover, this NiO/NiFe2O4 electrode shows an excellent long-term stability at 100 mA cm(-2) for 450 h. The synergetic effects between NiO and NiFe2O4 make NiO/NiFe2O4 heterostructure have high conductivity and fast charge transfer, abundant active sites, and high catalytic reactivity, contributing to its excellent performance.

关键词： heterostructure ions irradiation oxygen vacancies stability water splitting

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Experimental investigation of pressure fluctuation propagation in two orthogonal directions using a clapboard-type internally circulating fluidized bed

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ADVANCED POWDER TECHNOLOGY 2020年第8期31卷 3395-3407页

作者： Wei, Liping Zhang, Bing Lu, Chenfei Lu, Youjun Wang, Chi-Hwa Northwest Univ Sch Chem Engn Xian 710069 Shaanxi Peoples R China Natl Univ Singapore NUS Environm Res Inst 1 Create WayCreate Tower15-02 Singapore 1502 Singapore Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMFPE Xian 710049 Shaanxi Peoples R China Natl Univ Singapore Dept Chem & Biomol Engn 4 Engn Dr 4 Singapore 117585 Singapore

In this work, the pressure wave propagation in the vertical and horizontal directions has been studied using a self-designed clapboard-type internally circulating fluidized bed. The effects of flow regimes and solid mixture on the pressure wave propagation characteristics were analyzed in terms of time averaged pressure, standard deviation, power spectral density, dominant frequency, propagation time delay, and attenuation. The superficial velocity ratio had a remarkable effect on the pressure wave propagation time delay in the vertical direction but had less influence on the pressure wave propagation in the horizontal direction. The particle circulation provided an extra resistance force to the horizontal pressure wave propagation and resulted in an increase in the pressure wave decay factor in the horizontal direction. The addition of glass beads and salt greatly increased the time delay and decay factor both in vertical and horizontal directions. The addition of 15% corn powder (Geldart-C group) reduced the propagation time delay but increased the decay factor. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

关键词： Internally circulating fluidized bed Time domain PSD Pressure wave Propagation velocity Attenuation

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Integrating experimental and theoretical investigations of porous graphite materials with scanning electron microscope image processing

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RESULTS IN engineering 2024年 24卷

作者： Sahto, Muhammad Punhal Wei, Wang Jamil, Muhammad Fawad Mehmood, Awais Sattar, Mariyam Raza, Asif Rahman, Mujib Ur Qaisrani, Mumtaz A. NFC Inst Engn & Technol IET Dept Mech Engn Multan Punjab Pakistan Univ Elect Sci & Technol China Dept Mech & Elect Engn Chengdu 611731 Sichuan Peoples R China Tsinghua Univ Dept Mech Engn Beijing Key Lab Precis Ultraprecis Mfg Equipment & Beijing 100084 Peoples R China Yangzhou Univ Sch Mech Engn Agr Engn Yangzhou Jiangsu Peoples R China Inst Space Technol Dept Aeronaut & Astronaut POB 2750 Islamabad Pakistan Univ Elect Sci & Technol China Sch Automat Engn Chengdu 611731 Sichuan Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Univ Coll Dublin Sch Mech & Mat Engn Dublin Ireland

Accurate determination of fractal dimension (FD) and permeability of porous graphite materials (PGM) is essential for applications like porous aerostatic bearings (PABs). This study addresses the need for improved measurement methods by employing image processing and computer vision (IPCV) techniques to enhance FD and permeability accuracy. We aimed to refine these measurements by analysing the effects of image size and magnification on accuracy. The research developed theoretical models based on fractal theory, Darcy's law, and a modified Hagen-Poiseuille gas equation to evaluate these effects. A dual-path X-ray imaging detection system was used for experimental validation. The gauge pressure was varied across the surface of the PGM and volume flow rate was measured. MATlab was utilized for IPCV, enabling precise FD determination and underscoring the importance of image parameters. Results showed that FD values stabilize at specific image sizes and magnifications, improving accuracy. Linear relationships between pressure gradient and volume flow rate were observed, with permeability stabilizing at high pressures. Porosity values varied among materials: Toyo Carbon (15 %), SGL Graphite (17 %), Super Carbon Graphite (27 %), and poplar porous (30 %). FD obtained through theoretical and scanning electron microscope (SEM) methods had a maximum error of 0.08. The study also found a positive correlation between relative density and image grayscale at the macroscopic level. The findings emphasize the importance of optimizing image size and clarity for accurate PGM analysis, providing crucial insights for PAB design and other advanced applications.

关键词： Porous graphite materials (PGM) flow through porous media Permeability Aerostatic bearings Fractals

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Performance of different flocculants for harvesting Chlorella vulgaris by dissolved air flotation and sedimentation

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Bioresource technology 2025年 433卷 132743页

作者： X Wei N R H Rao S Tyagi W Thielemans W Cao L J Guo K Muylaert State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 Shaanxi China Laboratory of Aquatic Biology KU Leuven Campus Kulak Kortrijk 8500 Kortrijk Belgium. Laboratory of Aquatic Biology KU Leuven Campus Kulak Kortrijk 8500 Kortrijk Belgium Sustainable Materials Laboratory Department of Chemical Engineering KU Leuven Campus Kulak Kortrijk 8500 Kortrijk Belgium. Electronic address: n.hanumanthrao@unsw.edu.au. Sustainable Materials Laboratory Department of Chemical Engineering KU Leuven Campus Kulak Kortrijk 8500 Kortrijk Belgium. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 Shaanxi China. Electronic address: caowenxjtu@***. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 Shaanxi China. Electronic address: lj-guo@***. Laboratory of Aquatic Biology KU Leuven Campus Kulak Kortrijk 8500 Kortrijk Belgium. Electronic address: koenraad.muylaert@kuleuven.be.

This study systematically evaluated the performance of dissolved air flotation and sedimentation for harvesting Chlorella vulgaris using eight different flocculants. Significant variation was observed in both the maximum harvesting efficiency and the minimum effective flocculant dose across different flocculant-process combinations. Among the tested flocculants, pyridinium modified cellulose nanocrystals achieved the highest harvesting efficiency of 99 % in both dissolved air flotation and sedimentation, while chitosan required the lowest minimum flocculant dose (∼2 mg·g) to induce flocculation. The impact of floc size formed during the flocculation step on harvesting performance was also investigated, revealing that large flocs significantly favored sedimentation-based microalgae harvesting. A preliminary cost analysis highlighted the importance of integrating economic considerations into the selection of both flocculant and harvesting method. The findings suggest that optimal flocculant and process selection should be based not only on harvesting efficiency but also on cost-effectiveness for microalgal biomass recovery.

关键词： Cationic flocculants Dissolved air flotation optimization Floc size distribution Microalgal recovery Water treatment

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Catalytic supercritical water gasification of glucose with in-situ generated nickel nanoparticles for hydrogen production

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2019年第38期44卷 21020-21029页

作者： Huang, Jianbing Zhu, Chao Lian, Xiaoyan Feng, Huifang Sun, Jingli Wang, Li Jin, Hui Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China State Grid Shaanxi Elect Power Res Inst Xian 710100 Shaanxi Peoples R China Baoji Univ Arts & Sci Coll Chem & Chem Engn Baoji 721013 Peoples R China

Hydrogen production from catalytic supercritical water gasification of glucose with in-situ generated nickel nanoparticles in a quartz tube reactor is demonstrated. The effects of various operating parameters such as the presence of catalyst, resident time, reaction temperature and feed concentration on the gasification performances are studied. The results show that both the carbon gasification efficiency and the hydrogen gasification efficiency of glucose in supercritical water were improved with in-situ generated nickel nanoparticles as catalyst compared to those without catalyst. The catalyst promotes the water-gas shift reaction and CO methanation reaction, resulting in increased yields of H-2, CH4 and CO2 and decreased yield of CO. At the presence of catalyst, 10 wt% glucose solution exhibits the best gasification performances at 500 degrees C. Highly dispersed nickel nanoparticles identified by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) are assumed to be generated via supercritical hydro thermal synthesis through hydrolysis, dehydration and in-situ reduction. However, the in situ generated nano-nickel catalyst underwent an activation to deactivation transition due to carbon deposition on the surface of nickel nanoparticles. Regeneration strategies of the deactivated catalysts need further study for practical application. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Hydrogen production Supercritical water gasification Hydrothermal synthesis Quartz tube reactor Nickel catalyst

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