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Science China(Technological Sciences) 2018年第9期61卷 1353-1363页

作者： LI JieJie XIAN YueHui ZHOU HongJian WU RunNi HU GuoMing XIA Re key laboratory of hydraulic machinery transients Ministry of Education Wuhan University Hubei key laboratory of Waterjet Theory and New Technology Wuhan University

A series of large-scale molecular dynamics(MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations indicate that the principal deformation mechanism is a combination of grain boundary sliding, grain rotation and dislocation movement. The results of uniaxial tensile tests reveal the presence of a reverse Hall-Petch relation between strength and nominal grain size, rather than the conventional Hall-Petch relationship in the present range of nominal grain size(7.9–52.7 nm). An increase of flow stress may possibly attribute to the lower total proportion of grain boundary sliding and grain rotation in the deformation of samples with larger grain size. The Young's modulus shows a linear relation with the reciprocal of nominal grain size, which depends largely on the volume fraction of grain boundaries and thus decreasing grain size leads to relatively lower Young's modulus. MD simulations on samples with ligament diameter ranging from 4.07 to 8.10 nm are also carried out and results show that the increasing ligament diameter resulted in decreased flow stress and increased Young's modulus.

关键词： nanocrystalline nanoporous gold grain-size effect ligament-size effect mechanical properties molecular dynamics

Programmable microfluidics for dynamic multiband camouflage

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Microsystems & Nanoengineering 2023年第2期9卷 275-282页

作者： Chunzao Feng Mingran Mao Xiaohui Zhang Yutian Liao Xiaohui Xiao Huidong Liu Kang Liu MOE key laboratory of hydraulic machinery transients School of Power and Mechanical EngineeringWuhan UniversityWuhan 430072 HubeiChina

Achieving multiband camouflage covering both visible and infrared regions is challenging due to the broad bandwidth and differentiated regulation demand in diverse *** this work,we propose a programmable microfluidic strategy that uses dye molecules in layered fluids to manipulate visible light-and infrared-semitransparent solvent to manipulate infrared *** three primary fluid inputs,we achieve 64 chromaticity values and 8 emissivities from 0.42 to *** view of the wide tuning range,we demonstrate that the microfluidic flm can dynamically change its surface reflectance to blend into varying backgrounds in both visible and infrared ***,we fabricate the microfluidic device in a textile form and demonstrate its ability to match exactly with the colors of natural leaves of different seasons in the full hyperspectrum *** the broadband modulation and ease of operation,the programmable microfluidic strategy provides a feasible approach for smart optical surfaces in long-span optical spectra.

关键词： multiband tuning visible

Investigation of the hydrodynamics of slug flow in airlift pumps

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Chinese Journal of Chemical Engineering 2018年第12期26卷 2391-2402页

作者： Zhineng Wang Yong Kang Xiaochuan Wang Shijing Wu Xiaoyong Li key laboratory of hydraulic machinery transients Ministry of Education Wuhan University Hubei key laboratory of Waterjet Theory and New Technology Wuhan University School of Power and Mechanical Engineering Wuhan University

A slug flow model considering the dispersed bubbles entrained from the tail of Taylor bubble(TB) and recoalesced with the successive TB was proposed. Experiment was conducted to test the validity of this model by using a high-speed camcorder and particle image velocimetry(PIV). It was found that the model was valid for predicting the characteristics of slug flow in airlift pump within average error of 14%. Moreover, large pipe diameter was found to accelerate the rise velocity of TB and decreases void fraction in liquid slug by a small margin.

关键词： Airlift pump Flow regimes Bubble Mass transfer Hydrodynamics

A highly active and stable Sr_(2)Fe_(1.5)Mo(0.5)O_(6)‑δ‑Ce_(0.8)Sm_(0.2)O_(1.95)ceramic fuel electrode for efficient hydrogen production via a steam electrolyzer without safe gas

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International Journal of Coal Science & Technology 2022年第1期9卷 217-224页

作者： Yao Wang Tong Liu key laboratory of hydraulic machinery transients Ministry of EducationSchool of Power and Mechanical EngineeringWuhan UniversityHubei 430072 WuhanChina

High temperature steam(H_(2)O)electrolysis via a solid oxide electrolysis cell is an efficient way to produce hydrogen(H_(2))because of its high energy conversion efficiency as well as simple and green process,especially when the electrolysis process is combined with integrated gasification fuel cell technology or derived by renewable ***,about 60%-70%of the electricity input is consumed to overcome the large oxygen potential gradient but not for electrolysis to split H_(2)O to produce H_(2)due to the addition of safe gas such as H_(2)in the fuel *** this work,Sr_(2)Fe_(1.5)Mo_(0.5)O_(6)-δ-Ce_(0.8)Sm_(0.2)O_(1.95)(SFM-SDC)ceramic composite material has been developed as fuel electrode to avoid the use of safe gas,and the open circuit voltage(OCV)has been effectively lowered from 1030 to 78 mV when the feeding gas in the fuel electrode is shifted from 3%H_(2)O-97%H_(2)to 3%H_(2)O-97%N_(2),reasonably resulting in a significantly increased electrolysis *** addition,it is also demonstrated that the electrolysis current density is greatly enhanced by increasing the humidity in the fuel electrode and the working temperature.A considerable electrolysis current density of−0.54 A/cm^(2)is obtained at 800°C and 0.4 V for the symmetrical electrolyzer by exposing SFM-SDC fuel electrode to 23%H_(2)O-77%N_(2),and durability test at 800°C for 35 h demonstrates a relatively stable electrochemical performance for steam electrolysis under the same operation condition without safe gas and a constant electrolysis current density of−0.060 A/*** findings achieved in this work indicate that SFM-SDC is a highly promising fuel electrode for steam electrolysis.

关键词： Solid oxide electrolysis cell Steam electrolysis Fuel electrode Molybdenum doped strontium ferrite Safe gas

Thermal Performance of Elliptical Fin-and-Tube Heat Exchangers with Vortex Generator under Various Inclination Angles

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Journal of Thermal Science 2021年第1期30卷 257-270页

作者： WANG Yucheng ZHAO Wensheng WANG Pengfei JIANG Jin LUO Xiangyu key laboratory of hydraulic machinery transients Ministry of EducationWuhan UniversityWuhan 430072China School of Power and Mechanical Engineering Wuhan UniversityWuhan 430072China

Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and *** study numerically investigates the effect of vortex generators on the performance of elliptical fin-and-tube heat exchanger under different inclination *** this study,air flow that is in the transitional regime is selected as the working *** numbers at the inlet are varied in a range of 1300 to 2100,and the shear stress transport k-ωturbulence model is selected to solve the non-closure of basic turbulence *** ellipticity ratios of the tubes which are used for the analysis are between 0.6 and 1.0,and the inclination angles are varied from 15°to 75°.The effects of different inclination angles of vortex generators on the Colburn factor j,friction factor f,and efficiency index j/f are *** friction and Colburn factors are observed to increase with increasing vortex generator inclination *** is found that the efficiency factors for a 15°vortex generator inclination angle at 0.6,0.7,0.8,and 0.9 ellipticity ratios improve compared to the corresponding cases with no vortex ***,the vortex generator cannot improve the efficiency factor of the circular tube heat *** 3 D CFD method employed by this study has great potential for use in optimally designing the arrangement of the vortex generators to enhance the performance of heat exchangers.

关键词： heat exchanger vortex generator Colburn factor friction factor heat exchanger efficiency

Effect of radial heat conduction on effective thermal conductivity of carbon nanotube bundles

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Science China(Technological Sciences) 2018年第12期61卷 1959-1966页

作者： WANG JianLi SONG YaMei ZHANG YuFeng HU YuHan YIN Hang GU YunFeng XIA Re CHEN YunFei Jiangsu key laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments Southeast University College of Electronic and Mechanical Engineering Nanjing Forestry University key laboratory of hydraulic machinery transients (Wuhan University) Ministry of Education

The effect of the radial heat conduction on the effective thermal conductivity of carbon nanotube(CNT) bundles is studied by the nonequilibrium molecular dynamics(NEMD) method. The hexagonal CNT bundle consists of seven(10, 10) single-walled carbon nanotubes(SWCNTs). The radial heat conduction is induced by creating the vacancy defects in some segments of the constituent CNTs. Combined with the temperature differences and the inter-tube thermal resistances at the different segments,the radial heat flow in the CNT bundle is calculated. The maximum percentage of the radial heat flow is less than 7% with the presence of four defective CNTs, while the resultant decrement of the effective thermal conductivity of the bundle is about 18%.The present results indicate that the radial heat flow can significantly diminish the axial heat conduction in the CNT bundles,which probably explains the smaller effective thermal conductivity in the CNT assemblies compared to that of the individual CNTs.

关键词： axial thermal conductivity carbon nanotube bundle inter-tube thermal resistance radial heat flow

Investigating the flow characteristics of air-lift pumps operating in gas-liquid two-phase flow

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Chinese Journal of Chemical Engineering 2018年第2期26卷 219-227页

作者： Zhineng Wang Yong Kang Xiaochuan Wang Deng Li Dong Hu key laboratory of hydraulic machinery transients Ministry of Education Wuhan University Wuhan 430072 China Hubei key laboratory of Waterjet Theory and New Technology Wuhan University Wuhan 430072 China School of Power and Mechanical Engineering Wuhan University Wuhan 430072 China

Experiments were conducted to investigate the flow characteristics in the riser pipe and the suction pipe of airlift pump at a series of air flow rates and submergence ratios by using a high speed camcorder and a Laser Doppler Velocimetvy system （LDV）. A modified model was developed to predict the performance of airlift pump operating in gas-liquid two-phase flow, The results show that an unstable flow structure composed by a water falling film, a bubbly mixture, a water ascending film appearing alternately in riser pipe dominates the performance of airlift pump at large air flow rates. The bubbly mixture with a strongest capacity for pumping water first increases to its maximum and then slightly decreases. In suction pipe, the average velocity shows a flat profile and increases with increasing submergence ratio. Moreover, the predicted results of modified model are in good agreement with the experimental data in a margin of ± 12%.

关键词： PumpGas-liquid flowMixturesFlow structureRiser pipe

Large eddy simulation of the transient cavitating vortical flow in a jet pump with special emphasis on the unstable limited operation stage

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Journal of Hydrodynamics 2020年第2期32卷 345-360页

作者： Xin-ping Long Dan Zuo Huai-yu Cheng Bin Ji Hubei key laboratory of Waterjet Theory and New Technology School of Power and Mechanical EngineeringWuhan UniversityWuhan430072China key laboratory of transients in hydraulic machinery Ministry of EducationWuhan UniversityWuhan430072China State key laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan430072China

This paper studies the unsteady three-dimensional cavitating turbulent flow in a jet ***,thefocus is on the unstable limited operation stage,and both the computational and experimental methods are *** the experiments,the distribution of the wall pressure,as well as the evolution of cavitation over time,are obtained for a jet *** is carried out using the large eddy simulation,combined with a mass transfer cavitation *** numerical results are compared with the experimental results,including the fundamental performances(the pressure ratio h and the efficiencyη),as well as the wall pressure *** the experimental and computational results indicate that the evolution of the cavitation over time in a jet pump is a quasi-periodic process during the unstable limited operation *** annular vortex cavitation inception,development and collapse predicted by the large eddy simulation agree fairly well with the experimental ***,the relationship between the cavitation and the vortex structure is discussed based on the numerical results,and it is shown that the development of the vortex structures in the jet pump is closely related to the evolution of the *** cavitation-vortex interaction is thoroughly analyzed based on the vorticity transport *** analysis reveals that the cavitation in a jet pump dramatically influences the distribution and the production of the *** process of the annular cavitation inception,development,and collapse involves a significant increase of the vorticity.

关键词： Cavitation jet pump large eddy simulation vortex structure vorticity transport equation

Stiction of a Nano-Beam with Surface Effect

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Chinese Physics Letters 2011年第11期28卷 186-189页

作者： LIU Jian-Lin XIA Re ZHOU Yue-Ting Department of Engineering Mechanics China University of PetroleumQingdao 266555 key laboratory of transients in hydraulic machinery Ministry of EducationWuhan 430072 School of Mechanical Engineering Yonsei UniversitySeoul 120-749Republic of Korea

Nanowire stiction is a crucial bottleneck for the development of M/NEMS *** present a model of a nano-beam stuck to the substrate in consideration of both surface elasticity and residual surface *** critical detachment length can be derived from the transversality condition using the variational *** effects of the surface parameters on the adhesion of the nano-beam are discussed in *** analyses provide some suggestions for engineers in the design and fabrication of more accurate M/NEMS instruments.

关键词： elasticity beam surface

Fracture toughness and destructive mechanism of ductile nanoporous metallic glass and its crystal-impregnated nanocomposite

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Science China(Technological Sciences) 2023年第11期66卷 3328-3342页

作者： ZHANG YuHang XU JianFei HU YiQun SU Lei DING SuHang WU WenWang XIA Re key laboratory of hydraulic machinery transients(Wuhan University) Ministry of EducationWuhan 430072China Department of Engineering Mechanics School of Naval ArchitectureOcean&Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

Nanoporous metallic glasses(NPMGs)and crystalline/amorphous nanocomposites exhibit superior ductility over bulk macroscopic metallic glasses(MGs).Their fracture behaviors remain a mystery due to experimental technical *** this work,the fracture behaviors of pre-cracked NPMGs and crystal-impregnated nanoporous metallic glasses(CINPMGs)are investigated through large-scale molecular dynamics simulations,and the MG and crystal phases are amorphous Cu_(50)Zr_(50)and crystalline B2CuZr,*** toughness is determined by simultaneously considering the surface energy and plastic dissipated *** results confirm the excellent plasticity of both the pre-cracked NPMGs and *** progressive necking and ductile rupture of ligaments are responsible for generating NPMGs with prominent ductility and fracture ***,secondary cracking is also triggered,which can consume energy without extending the major crack,thus further improving fracture *** is also found that the fracture toughness of NPMGs can be improved by increasing the solid fraction of MG,and linear relation between fracture toughness and solid fraction can be *** impregnation effectively inhibits global failure as the crystal phase shields the individual amorphous *** plastic flow characterized by shear bands is observed in CINPMGs,and this homogeneous global deformation is facilitated by the crystalline/amorphous ***,the fracture toughness of CINPMGs is higher than that of the constituent single phases,regardless of the volume fraction of each *** material charts manifest that these two types of materials demonstrate promising potential in the material selection library for advanced structural design.

关键词： nanoporous metals crack fracture toughness nanocomposites metallic glasses