LTNE条件下界面对流传热系数对部分填充多孔介质通道传热特性的影响

在多孔介质区考虑局部非热平衡,采用Brinkman-extended Darcy模型结合应力跳跃条件对部分填充多孔介质通道内流体传热特性进行分析。获得了各区域温度分布及Nusselt数解析解,并分析了各参数对温度及Nusselt数的影响。结果表明：界面对流传热系数H_s较小时,界面应力跳跃系数β和Darcy数Da的增加会减小流固两相间温差。而在高H_s下,Da减小也会减小两相温差。在Da、H_s和固流两相热导率之比K较大且空心率S（自由流体区高度与通道高度之比）和Biot数Bi较小时,流固两相间会在接近多孔介质区中部出现最大温差,而该最大温差会随着S增加和Da及H_s的减小向界面区移动。对于不同K与Bi,Nusselt数Nu与S的关系曲线存在不同的类型,与模型A（界面处多孔介质固相和流相根据各自温度梯度和热导率划分总热流）不同的是,采用模型C（界面处固相热流分配与自由流体区流相的热交换相关）所获得的Nu曲线类型与H_s有关。在K较小时,β对Nu的影响大于H_s对Nu的影响;而在K较大时,H_s对Nu的影响要远大于β对Nu的影响,且H_s增加会明显提高通道内的Nu。     

定子无磁轭模块化轴向磁通永磁电机研究进展综述

定子无磁轭模块化(yokeless and segmented armature,YASA)轴向磁通永磁电机具有功率密度和转矩密度高、效率高、轴向结构紧凑、易于维修的优点,在电动汽车、风力发电等领域有广阔的应用前景,已有大量文献对YASA电机进行分析研究。该文基于国内外对YASA电机已开展的研究工作,介绍该类电机的典型拓扑结构,并从电机电磁特性计算方法与性能优化、损耗分析与抑制技术、温升与散热研究、齿槽转矩削弱技术、结构强度校核与制造偏差分析,以及定子铁心材料选取等方面进行综述,并对该类电机当前的应用情况进行整理。最后,基于YASA电机的研究现状,对未来研究的发展趋势进行展望。     

Mechanical,thermal, and dielectric properties of SiCf/SiC composites reinforced with electrospun SiC fibers by PIP

Electrospun unidirectional SiC fibers reinforced SiC_f/SiC composites (e-SiC_f/SiC) were prepared with ∼10% volume fraction by polymer infiltration and pyrolysis (PIP) process. Pyrolysis temperature was varied to investigate the changes in microstructures, mechanical, thermal, and dielectric properties of e-SiC_f/SiC composites. The composites prepared at 1100 °C exhibit the highest flexural strength of 286.0 ± 33.9 MPa, then reduced at 1300 °C, mainly due to the degradation of electrospun SiC fibers, increased porosity, and reaction-controlled interfacial bonding. The thermal conductivity of e-SiC_f/SiC prepared at 1300 °C reached 2.663 W/(m∙K). The dielectric properties of e-SiC_f/SiC composites were also investigated and the complex permittivities increase with raising pyrolysis temperature. The e-SiC_f/SiC composites prepared at 1300 °C exhibited EMI shielding effectiveness exceeding 24 dB over the whole X band. The electrospun SiC fibers reinforced SiC_f/SiC composites can serve as a potential material for structural components and EMI shielding applications in the future.     

Deposition of hydroxyapatite coatings by axial plasma spraying: Influence of feedstock characteristics on coating microstructure,phase content and mechanical properties

Axial plasma spray is one of the thermal spray techniques to deposit multifunctional advanced coatings. The present work explores the use of this process to deposit thin, continuous, and adherent Ca₅ (PO₄)₃OH (hydroxyapatite, HAp) coatings and characterize its microstructure, phases, hardness and adhesion strength. Three different suspension-deposited HAp coatings were investigated and compared with powder-deposited HAp coating on a Ti6Al4V substrate. The effect of mean solute particle size and solid-loading in the suspension has been explored on the evolution of microstructure, phase content and mechanical properties of axial suspension plasma sprayed (ASPS) coatings. Phase-characterization has shown retention of hydroxyapatite phase and coating crystallinity in the deposited coatings, whereas the adhesion strength of the HAp coating decreased from ～40 MPa to ～13 MPa when bioglass was added to the feedstock material. The lower solid load content and lower mean solute particle size in the suspension were found to be beneficial in achieving porous, rougher, and well-adhering coatings. This work concludes that ASPS can potentially deposit thin HAp coatings (< 50 μm) with high adhesion strength.     

Multidisciplinary approach for investigating the hot corrosion behavior of thermal barrier coatings

Herein, we propose a new multidisciplinary approach for investigating the corrosion behavior of thermal barrier coatings, combining the thermal-gradient mechanical fatigue method with hot corrosion tests. Corrosive salts (Na₂SO₄; V₂O₅) of varying concentrations (10−20 mg/cm²) were deposited on the surface of yttria-stabilized zirconia (YSZ) coatings to evaluate the microstructural changes occurring during the reaction, via thermal graded mechanical fatigue tests. The tests were conducted at a surface temperature of 1150 °C in 10 min cycles and underwent applied uniaxial tensile loads. The corrosion tests show that the ZrV₂O₇ plays an important role as an intermediate in the collapse of the lamellar structures during the reaction, which results from the repetitive precipitation of V₂O₅ and m-ZrO₂ from the ZrV₂O₇. The microstructure of corroded YSZ coatings exhibited a different degradation mechanism under a thermomechanical environment, compared with the testing under isothermal atmospheric conditions.     

单翼迷宫式滴灌带抗热氧老化性能的影响研究

单翼迷宫式滴灌带产品新国家标准中增加了氧化诱导时间（OIT）,这对产品的抗热氧老化性能提出了要求。本文从滴灌带配方出发,讨论了产品原料与其OIT的料效关系,结果表明,防老化母料的加入比例对滴灌带的OIT影响最大,增加其比例可增大滴灌带的OIT;高密度聚乙烯（PE?HD）的加入比例对滴灌带的OIT影响大于线性低密度聚乙烯（PE?LLD）和低密度聚乙烯（PE?LD）的加入比例,增加PE?HD比例、减小PE?LLD和PE?LD比例可增大滴灌带的OIT;PE?LD的加入比例对滴灌带OIT的影响最小,在配方设计时应综合使用比例合理的PE?HD、PE?LLD、PE?LD以满足滴灌带良好的加工和其他性能要求;防老化母料中稳定剂比例不应随成本而减少,稳定剂比例增大时,滴灌带的OIT增大;通过对滴灌带的熔体质量流动速率（MFR）、炭黑含量及OIT指标测试,得出滴灌带MFR和炭黑含量与其OIT无明显的相互变化关系。     

热膨胀法判定建窑黑瓷烧成温度的应用研究

以热膨胀仪判定建窑黑瓷烧成温度的研究为例,综合运用多种测试方法对建窑黑瓷标本进行了系统研究,探讨如何从建窑黑瓷胎体重烧热膨胀曲线中筛选有效转折点的问题及其转折点的形成原因。研究表明:(1)建窑黑瓷胎体重烧热膨胀曲线上有三个转折点,分别为收缩转折点、膨胀转折点和急剧收缩点。其中第一个收缩转折点是判定其古代烧成温度的关键点。(2)建窑黑瓷胎体重烧热膨胀曲线上膨胀转折点和急剧收缩点的形成皆与其胎体中大量Fe_2O_3在高温下发生分解反应有关。该研究不仅为热膨胀仪测定建窑黑瓷烧成温度的应用研究提供判定依据,也将为科学认识古陶瓷胎体重烧热膨胀曲线上多个转折点的形成机理提供数据支持。     

Preparation and properties of TiC-Ni cermets using Ni-plated TiC

TiC powders were coated with Ni by a chemical plating technique and the pressed compacts sintered at 1623K. The density of the sintered bodies was 98–99%. Compared with mechanically-mixed powder, Ni-plated TiC powders gave a more uniform microstructure in which TiC particles were well dispersed in the Ni matrix. The cermets exhibited ductile fracture for TiC-70 vol.% Ni and brittle fracture for TiC-30 vol.% Ni. The flexural strength was improved by the homogeneous dispersion of TiC. The thermal expansion coefficient increased with a decrease in Ni content, following a nearly linear law of mixtures on the basis of volume fractions of pure TiC and Ni.     

提高6063铝合金导热性能的途径探讨

采用试验的方法探讨了镁硅质量比、微量稀土及热处理制度对6063铝合金导热性能的影响。研究结果表明：6063铝合金采用1．73的Mg、Si质量比，加入0．3％稀土，经挤压后在250℃进行退火，然后随炉冷却，热导率比原来提高了9．5％。     

The characterization and corrosion resistance of cerium chemical conversion coatings for 304 stainless steel

A golden yellow-colored cerium conversion coating was obtained on 304 stainless steel surface by immersing the steel into a solution containing cerium (III), KMnO₄ and sulfuric acid. The corrosion resistance of the coatings was evaluated by electrochemical methods, potentiodynamic polarization experiments and electrochemical impedance spectrum. The experimental results indicated that the corrosion resistance for the conversion coated 304SS in 3.5% NaCl solution increased markedly. The corrosion potential of the treated steel increased to a more noble level, the pitting corrosion potential increased also, the passive potential range was enlarged markedly and the passive current density decreased about one order compared to that of the untreated steel. The cathodic and anodic reaction were both inhibited to some extent. The chemical state of the elements in the coatings was investigated by XPS. The cerium element was in the form of tetravalent state. And AES depth profile analysis suggested that the thickness of the conversion coatings was less than 66 nm. The mechanisms of coatings formation and corrosion resistance are discussed.