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Microstructure Transition and Grain Refinement Mechanism of Undercooled Alloys

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Journal of Wuhan University of Technology(Materials Science) 2021年第6期36卷 922-926页

作者： LI hongtao Nancy Julius Siambun Bih-Lii Chuab melvin gan jet hong AN hongen College of Mechanical and Electronic Engineering Huanghe Jiaotong UniversityJiaozuo 454950China Faculty of Engineering University Malaysia SabahKota Kinabalu 88400Malaysia Henan Engineering Technology Research Center on Intelligent Manufacturing Technology and Equipment Jiaozuo 454950China

The solidification microstructures of undercooled Ni90Cu10 alloys under different undercoolings were studied systematically by means of melt coating and cyclic *** the obtained undercooling range,the solidification structures of the two undercooled alloys have similar transformation processes,and there are two kinds of grain refinement structures under the conditions of low undercooling and high undercooling,*** microstructures of the two grain refinement processes were analyzed in more detail by electronic backscattering diffraction *** the condition of small undercooling,dendrite remelting is considered to be the main reason of grain ***,under the condition of high undercooling,the existence of annealing twins and obvious migration of grain boundary are important evidences for the occurrence of recrystallization process.

关键词： microstructure transition grain refinement undercoolcd alloys Ni-Cu alloys

Fabrication of 6FDA-HFBAPP Polyimide Asymmetric Hollow Fiber Membranes and Their CO2/CH4 Separation Properties

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Chinese Journal of Polymer Science 2019年第8期37卷 815-826页

作者： Cong-Jun gan Xiao-Chen Xu Xue-Wei Jiang Feng gan Jie Dong Xin Zhao Qing-Hua Zhang State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and Engineering Donghua University

In this work, poly(amide acid) solution, the precursor of polyimide, was synthesized by the reaction of 4,4′-(hexafluoroisopropylidene)diphthalicanhydride and 2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropanane in the solvent of N-methyl-2-pyrrolidone(NMP) and tetrahydrofuran(THF). Then, hollow fiber membranes for high flux gas separation were prepared by dry-jet wet spinning using the precursor solution of poly(amide acid) as the spinning dope and a subsequent imidization process. Silicone rubber was further coated outside the obtained hollow fiber membranes to repair the defects on the denser layer. The effects of internal, external coagulation bath ratios with air gap, and coating solution concentrations on the morphologies, structures, and separation performance of the membranes were studied. Results showed that the sponge-like support layer was formed when the content of NMP was increased from 50% to 90% in the internal coagulation bath. The outer surface of the membrane became denser when the water content in the external coagulation bath increased from 40% to 100%, and the separation coefficient of CO2/CH4 increased by 2 times. This value could reach up to 1.4 when the air gap was 6 cm. With tuning the mass fraction of silicone rubber as 5%, hollow fiber composite membranes with uniform coating layer and an improved separation coefficient of 5.4 could be obtained.

关键词： Polyimide Gas separation Preparation conditions Membrane structure Permeability

Drying characteristics, functional properties and in vitro digestion of purple potato slices dried by different methods

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Journal of Integrative Agriculture 2019年第9期18卷 2162-2172页

作者： QIU gan JIANG Yong-li DENG Yun Department of Food Science and Technology Shanghai Jiao Tong University

The drying characteristics,physico-chemical and functional properties,as well as starch digestibility,of purple potato slices dried using different methods(such as,vacuum freeze-drying,VFD;hot-air drying,HAD;air-impingement jet drying,AIJD;and far-infrared assisted heat-pump drying,FIHPD)were *** rate was the highest(3.0 g 100 g^-1 min^-1)using AIJD,followed by FIHPD and HAD,and the rate of VFD was the lowest one(0.3 g 100 g^-1 min^-1).Drying data were fitted to 12 thin-layer drying models,with the Midilli model giving the best ***,AIJD showed higher diffusivity(5.5×10^-10 m^2 s^–1)and energy efficiency(55 J g^-1)than any other drying method used in this *** reference to the samples dried by VFD,the starch granules of the samples obtained by HAD,FIHPD,and AIJD exhibited different extent of disruption,which significantly increased their water absorption capacity,swelling power,and in vitro digestibility,but decreased the peak *** sample resulting from AIJD had the greatest water absorption capacity(7.9 g g^-1)and solubility(21.6%),but the smallest syneresis rate(48%).Good correlation coefficients(R^2>0.98)implied that the pseudofirst order kinetic model adequately described the rate and extent of starch digestion of dried potato *** from AIJD and FIHPD showed the highest digestibility percentages,reaching to 72.4 and 72.5%.Based on the drying rate,specific energy consumption,functional properties and digestibility,AIJD appeared to be quite effective and suitable to be transferred on the industry scale.

关键词： purple potato air-impingement jet drying(AIJD) drying characteristics flour properties starch digestibility

Mechanistic Insights into Effects of Outer Stage Flare Angle on Ignition and Flame Propagation of Separated Dual-Swirl Spray Flames

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Journal of Thermal Science 2022年第5期31卷 1642-1662页

作者： YANG Siheng HUI Xin ZHANG Chi QIAN Weijia gan Xiaohua National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power EngineeringBeihang UniversityBeijing102206China Department of Mechanics and Aerospace Engineering Southern University of Science and TechnologyShenzhen518000China

The present work investigates the effects of outer stage flare angle on ignition and kernel propagation in a centrally staged optical model combustor based on the kernel dynamics analysis and laser diagnostics of flow and spray *** outer stage flare angles of 8°,16°,and 25°are researched,*** better ignition performances are found for larger outer stage flare *** properties such as the kernel velocity,kernel trajectory extracted from 6 k Hz high-speed flame images are analyzed in combination with the flow and spray measured via Particle Image Velocimetry(PIV)and Planar Mie Scattering(PMie).Results show that the larger outer stage flare angle imposes a larger opening angle of outer swirl jet(SWJ),shifting the vortex in outer recirculation zone(ORZ)and inner recirculation zone(IRZ)*** spray distribution of a smaller flare angle exhibits a fuel-lean zone near the igniter and this is attributed to the presence of low-angle outer swirl jet that prevents the fuel droplets from arriving at the igniter *** flame kernel propagates along the path where the strain rate and velocity decrease and the spray droplet density is within the flammable limits.A lower outer stage flare angle increases the strain rate and velocity at the early phase of flame propagation,leading to a longer propagation route and thus increasing the risk of ignition failure.

关键词： spray ignition flame propagation spray distribution separated dual-swirl

Optimization of Dimples in Microchannel Heat Sink with Impinging jets Part A： Mathematical Model and the Influence of Dimple Radius

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Journal of Thermal Science 2018年第4期27卷 195-202页

作者： MING Tingzhen CAI Cunjin YANG Wei SHEN Wenqing gan Ting School of Architecture and Urban Planning Huazhong University of Science and Technology Wuhan 430074China China Energy Group Environmental Energy Technologies Division Lawrence Berkeley National Laboratory California 94720 USA. Hubei Institute of Aerospace Chemical Technology Xiangyang 441000 China G. W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta 30332 USA

With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modem advanced cooling technologies. In this work, the combination of dimples, impinging jets and microchannel heat sink was proposed to improve the heat transfer performance on a cooling surface with a constant heat flux 500 W/cm2. A mathematical model was ad- vanced for numerically analyzing the fluid flow and heat transfer characteristics of a microchannel heat sink with impinging jets and dimples （MHSIJD）, and the velocity distribution, pressure drop, and thermal performance of MI-ISIJD were analyzed by varying the radii of dimples. The results showed that the combination of dimples and MHSIJ can achieve excellent heat transfer performance; for the MHSIJD model in this work, the maximum and average temperatures can be as low as 320 K and 305 K, respectively when mass flow rate is 30 g/s; when dimple radius is larger than 0.195 mm, both the heat transfer coefficient and the overall performance h/AP of MHSIJD are higher than those of MHSIJ.

关键词： Microchannel with Impinging jet Dimple Heat Transfer Enhancement Thermal Resistance Numerical Simulation

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Effect of a transverse plasma jet on a shock wave induced by a ramp

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Chinese Journal of Aeronautics 2017年第6期30卷 1854-1876页

作者： hongyu WANG Jun LI Di JIN Hui DAI Tian gan Yun WU Aeronautics and Astronautics Engineering College Air Force Engineering University Xi'an 710038 China

We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.

关键词： Flow control Improved delayed detachededdy simulation (IDDES)method Plasma synthetic jet Shock wave/boundary layerinteraction Time resolved schlierensystem

Large-eddy simulation of shock-wave/turbulent boundary layer interaction with and without Spark jet control

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Chinese Journal of Aeronautics 2016年第3期29卷 617-629页

作者： Yang Guang Yao Yufeng Fang Jian gan Tian Li Qiushi Lu Lipeng National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power EngineeringBeihang University Beijing 100083China Faculty.of Environment and Technology University of the West of EnglandBristol BSI6 1Q YUnited Kingdom Computer Scienceand Engineering Department Science&Technology Facilities Council(STFC)Daresbury LaboratoryWarrington WA4 4ADUK

The efficiency and mechanism of an active control device ＂＇Spark jet＂ and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction of an oblique shock-wave generated by 8° wedge and a spatially-developing Ma = 2.3 turbulent boundary layer. The Reynolds number based on the incoming flow property and the boundary layer displacement thickness at the impinging point without shock-wave is 20000. The detailed numerical approaches were presented. The inflow turbulence was generated using the digital filter method to avoid artificial temporal or streamwise periodicity. The , merical results including velocity profile, Reynolds stress profile, skin friction, and wall pressure were sys- tematically validated against the available wind tunnel particle image velocimetry （PIV） measure- ments of the same flow condition. Further study on the control of flow separation due to the strong shock-viscous interaction using an active control actuator ＂＇Spark jet＇＂ was conducted. The single-pulsed characteristic of the device was obtained and compared with the experiment. Both instantaneous and time-averaged flow fields have shown that the jet flow issuing from the actuator cavity enhances the flow mixing inside the boundary layer, making the boundary layer more resis- tant to flow separation. Skin friction coefficient distribution shows that the separation bubble length is reduced by about 35% with control exerted.

关键词： Large-eddy simulation Shock-wave:Turbulent boundary layer Interaction Spark jet control

PARTICLE SIZE DISTRIBUTION IN A PLANAR jet FLOW UNDER-GOING SHEAR-INDUCED COAGULATION AND BREAKAGE

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Journal of Hydrodynamics 2010年第4期22卷 445-455页

作者： gan Fu-jun LIN Jian-zhong YU Ming-zhou State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China China Jiliang University Hangzhou 310018 China State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China China Jiliang University Hangzhou 310018 China

A CFD simulation is performed for a particle-laden planar jet *** Reynolds number is 8300,and the initial particle diameter is 1 μ*** Eddy Simulation（LES） is employed to calculate the flow field,and the Taylor-series expansion moment method（TEMOM） is adopted to deal with the balance equation of particle coagulation and *** shear-induced coagulation kernel,power-law breakage kernel and symmetric fragment distribution function are *** prediction of the distribution of the mean streamwise velocity of the jet is in good agreement with experimental *** evolution of particle number concentration,volume concentration,polydispersity,particle diameter and standard geometric deviation is discussed in *** results show that as the jet travels downstream,the particle number concentration and volume concentration decrease,while their spans become *** polydispersity and particle diameter are very large in the shear layers at the upstream and in the core of vortex structures at the *** particle standard geometric deviation changes within the range of 1.32 ≤σg≤ 1.96,and increases sharply in the shear *** variables approach the steady-state as time progresses.

关键词： Taylor-series expansion moment method shear-induced coagulation breakage planar jet

A possible precessing nozzle and the Lense-Thirring effect in blazar 3C 454.3

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Research in Astronomy and Astrophysics 2014年第3期14卷 249-274页

作者： Shan-Jie Qian S.Britzen A.Witzel T.P.Krichbaum Heng-Qian gan Long Gao National Astronomical Observatories Chinese Academy of Sciences Max-Planck Institt fr Radioastronomie

The kinematics of superluminal components in blazar 3C 454.3 are *** components are included： superluminal knots R1, R2, R3, R4, A, B, C and D（from Britzen et al. 2013） and C4 （from Pauliny-Toth 1998）. We find that their kine-matics derived from VLBI observations can be consistently interpreted in terms of ajet precession scenario with a period of about 14.5 yr. We discuss the model fits oftheir trajectory, distance from the core and apparent velocity. We show that the bulkLorentz factor （in the range 4 to 15） derived for these components does not have anydependence on the phase of the precession （or position angle for ejection）. The Lense-Thirring effect is assumed to interpret the precession of the jet nozzle. The resultsobtained for blazar 3C 454.3 are only suggestive. They are not unique and have yet tobe tested, but they might be useful for understanding the kinematics of superluminalcomponents in blazars and for disentangling different mechanisms and factors.

关键词： radio continuum: galaxies galaxies: jets galaxies: kinematics galaxies: individual (blazar 3C 454.3)