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Optimization of a serpentine flow field with variable channel heights and widths for PEM fuel cells

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science china(Technological sciences) 2010年第2期53卷 453-460页

作者： LIN Lin, ZHANG XinXin, FENG HuTing & WANG XiaoDong Department of Thermal engineering, school of mechanical engineering, university of science and technology Beijing, Bejing 100083, china Department of Thermal engineering School of Mechanical Engineering University of Science and Technology Beijing Bejing China

The present study proposes a modified serpentine flow field design in which the channel heights vary along each straight flow path to enhance reactant transport and liquid water removal. An optimization approach, combining a simplified conjugate-gradient method (inverse solver) and a three-dimensional, two-phase, non-isothermal fuel cell model (direct solver), has been developed to optimize the key geometric parameters. The optimal design has tapered channels for channels 1, 3 and 4 and increasing heights for channels 2 and 5 with the flow widths first increasing and then decreasing. The optimal channel heights and widths enhance the efficiency by 22.51% compared with the basic design having all heights and widths of 1 mm. The diverging channels have a greater impact on cell performance than fine adjustments of the channel widths for the present simulation conditions. The channel heights have more effect on the sub-rib convection, while the channel widths affect the uniformity of the fuel delivery more. The reduced channel heights of channels 2–4 significantly enhance the sub-rib convection to effectively transport oxygen to and liquid water out of the diffusion layer. The final diverging channel prevents significant leakage of fuel to the outlet via sub-rib convection.

关键词： PEM fuel cell simplified conjugate-gradient method optimization sub-rib convection

Effects of silver powder particle size on the microstructure and properties of Ag-Yb_2O_3 electrical contact materials prepared by spark plasma sintering

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Rare Metals 2010年第4期29卷 366-370页

作者： CHEN Xiaohua,JIA Chengchang,and LIU Xiangbing school of Materials science and engineering,university of science and technology Beijing,Beijing 100083,china school of Materials science and engineering University of Science and Technology Beijing Beijing China

mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing （SPS）. The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope （OM）, and the fracture morphologies were observed by scanning electron microscopy （SEM）. The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder （5 ktm）, homogeneous and fme microstmcture was obtained by fine silver powder （_〈0.5-1am）. At the same time, the electrical conductivity, microhardness, and tensile strength of the sin- tered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples （both by free and coarse silver powders） is more than 95%. The fracture characteristics are ductile.

关键词： composites electrical contact materials spark plasma sintering particle size microstructure physical properties mechanical properties

RESEARCH ON A SCANNING NEAR-FIELD MICROSCOPY BASED ON A QUARTZ RESONATOR

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Chinese Journal of mechanical engineering 2001年第4期14卷 319-321页

作者： Wang Xuefang,Zhang Honghai,Zeng Lingdan (school of mechanical engineering, Huazhong university of science and technology) 华中科技大学湖北

A scanning near field acoustic microscopy(SNAM) used in imaging the topography of precise surfaces is presented. As a micro force sensor, a non encapsulated 1 MHz quartz resonator is damped by hydrodynamic forces when approaching an object. Thus the oscillating characteristics of the leg of the quartz resonator change. While measuring the decrease of the amplitude of vibrating, the shape of the object can be obtained. Based on the analyses of the principle and key parameters of SNAM, a SNAM is exploited. A lateral resolution of 0.5 μm and vertical resolution of 2 nm has been achieved in the experiments.

关键词： Scanning near field microscopy Quartz resonator Resolution

Effect of Process Factors on Microstructure of Semisolid Continuous Casting Billets

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International Journal of Minerals,Metallurgy and Materials 2000年第4期14卷 242-245页

作者： Shuming Xing, Qijie Zhai, Hanqi Hu ( Department of mechanical engineering, Tsinghua university, Beijing 100084, china school of Material science and engineering, Shanghai university, Shanghai 200072, china Material science and engineering school, Univer Department of mechanical engineering Tsinghua University Beijing 100084 China school of Material science and engineering Shanghai University Shanghai 200072 China Material science and engineering school University of Science and Technology Beijing Beijing 100083 China

Semisolid continuous casting (SSCC) is a new technology to produce billets for semisolid metal forming (SSMF). The effect of process factors, such as pouring temperature, stirring rate, preheating temperature and thermal conductivity of stirring chamber, on the microstructure of SSCC billets was studied by means of the factorial experimental method. The results show that the microstructure of SSCC billets can be controlled by the above-mentioned four process factors. In order to obtain fine and rounded granular grains in an SSCC billet, the pouring temperature, preheating temperature and stirring rate should be kept in a moderate range, and the thermal conductivity of stirring chamber should be high. The regression equations with the process factors connecting the microstructure was also set up based on experimental data.

关键词： semisolid metal continuous casting process factors microstructure Metallurgy

CALCULATION OF FUZZY RELIABILITY IN THE CASE OF RANDOM STRESS AND FUZZY FATIGUE STRENGTH

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Chinese Journal of mechanical engineering 2000年第3期13卷 197-200,223页

作者： Huang Hongzhong (school of mechanical engineering, Dalian university of technology) 大连理工大学辽宁大连

The fuzzy sets theory is introduced into the fatigue reliability analysis. The concepts of maximizing set and minimizing set are developed to decide the ordering value of each fuzzy number, and these values can be used to determine the order of the fuzzy numbers. On the basis of the works mentioned above, the membership function defining the fuzzy safety event can be calculated, and then the fuzzy reliability in the case of stress and fuzzy fatigue strength is deduced. An example is given to illustrate the method.

关键词： Maximizing set Minimizing set Total utility value Fatigue strength Fuzzy reliability

A routing algorithm based on clusters and balanced use of energy for wireless sensor networks

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控制理论与应用（英文版） 2010年第1期8卷 81-85页

作者： Liang ZHANG,Xiangdong WANG,Shujiang LI(school of Information science and engineering,Shenyang university of technology,Shenyang liaoning 110178,china) school of Information science and engineering Shenyang University of Technology Shenyang Liaoning China

In a sensor network, data collected by different sensors are often correlated because they are observations of related phenomena. Efficient sensor data fusion is one of the most important issues in building real sensor networks. To balance energy cost, how to select a cluster head is a key problem that must be addressed. In this paper, we use a compression-centric data collection algorithm for use in wireless sensor networks. Also, we propose a balanced cluster head selection algorithm in each cluster. Simulation results are used to investigate the performance of the algorithm. Compared to the exhaustive search solutions, the proposed algorithm shows a significant improvement in power consumption.

关键词： Sensor networks Cluster Sink node Power consumption

Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

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Rare Metals 2010年第1期29卷 86-91页

作者： CHU Ke, JIA Chengchang, LIANG Xuebing, and CHEN Hui school of Materials science and engineering, university of science and technology Beijing, Beijing 100083, china school of Materials science and engineering University of Science and Technology Beijing Beijing China

Two powder mixing processes, mechanical mixing （MM） and mechanical alloying （MA）, were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering （SPS） to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W.m^-1.K^-1, owing to its having few defects and strong inter-facial bonding.

关键词： metal matrix composites thermal properties sintering powder mixing

The Study on the Microstructure and mechanical Properties of 400MPa Grade Bar Prepared by Controlled Cooling After Finish Rolling

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Journal of Iron and Steel Research International 2011年第S1期18卷 610-614页

作者： ZHANG Jun-wei 1,DING Lei 1,XIAO Yi 2,3,HU Xiao-dong 1,HU Lin 1 (1.school of Materials and Metallurgy,university of science and technology liaoning,anshan 114051,liaoning,china 2.Baosteel Nantong Co Ltd.,Nantong 226002,Jiangsu,china 3.school of Electrical engineering,Anhui university of technology,Maanshan 243002,Anhui,china) Univ Sci & Technol liaoning Sch Met & Mat Anshan 114051 Liaoning Peoples R China Baosteel Nantong Co Ltd Nantong 226002 Jiangsu Peoples R China Anhui Univ Technol Sch Elect Engn Maanshan 243002 Anhui Peoples R China

The production process of bars in Baosteel Nantong *** adjusted by both decreasing heating temperature and adding controlling cooling procedure after finish rolling for upgrade of bars.A set of water cooling system was also installed behind the finishing ***-line tests were conducted,and then the microstructure and mechanical properties of the bars with HRB335 composition and φ22mm diameter were *** results showed that the microstructures of the bar cooled by water were ferrite and pearlite with grain sizes of 8.5 to 12 grades,which were finer than that of the bar without water *** the thin outer layer microstructures of the bar cooled by water were mainly tempered sorbite with small amount of tempered *** average yield strength R eL and tensile strength R m of the bars with water cooling increased 105MPa and 73MPa respectively compared with those of the bars without water *** reason of this strengthening was attributed to the synthetic role of fine grains and phase transformation and precipitation *** addition,The ration of R m /R eL could be higher than 1.25,which is the request of earthquake-proof performance for HRB400E,only when the self-tempering temperatures of the bars were higher than 640℃.

关键词： controlled cooling hot rolling bar fine grain strengthening self-tempering

Microstructure Evolution of Semi-solid Processed Hyper-eutectic Al-30%Si Alloy

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International Journal of Minerals,Metallurgy and Materials 1999年第4期13卷 259-261页

作者： Yanjun Li Weimin Mao Xueyou Zhong(Material science and engineering school, university of science and technology Beijing, Beijing 100083, china) Material science and engineering school University of Science and Technology Beijing Beijing 100083 China

An investigation was made on the influences of mechanical stirring on microstructure of hyper-eutectic Al-30%Si alloy (inmass fraction) during solidification. The primary Si crystals formed in the alloy melt were gradually changed from elongated platelets tonear-spherical shapes by mechanical stirring. The spheroidization of primary St crystals occurs by the mechanism of bending and fractureof Si platelets, wear and collision between Si crystals, and coalescence of small Si particles. The influence of under-cooling and coolingrate of the alloy melt on primary Si crystals of semi-solid processed alloys is investigated as well. The increase of under-cooling andcooling rate decreases the size of primary Si crystals.

关键词： semi-solid state process solidification structure mechanical stirring hyper-eutectic Al-Si alloy