垂直轴风机叶片覆冰数值模拟及其气动性能研究

研究升力型垂直轴风机叶片的覆冰特性,为风机的防冰、除冰系统研发提供帮助。文章对垂直轴风机叶片的雾凇覆冰物理过程进行了分析,建立了风机叶片覆冰的数值计算模型。通过SST k-ω湍流模型求解旋转叶片周围的空气流场,利用拉格朗日法获得过冷却水滴的运动轨迹及碰撞情况,结合覆冰时间推进法得到叶片表面的覆冰形貌,并通过流场计算分析覆冰对风机气动性能的影响。利用该计算模型研究了不同叶片翼型、叶片数量以及叶尖速比λ对垂直轴风机叶片覆冰的影响。结果表明:当风机的λ增大时,风机叶片表面的覆冰更多的向叶片前缘尖端区域集中,叶片后缘的覆冰量减少;在同一覆冰条件下,不同叶片翼型、叶片数量和λ对垂直轴风机的整体覆冰量、单个叶片的覆冰量以及叶片表面的最大覆冰厚度均产生重要影响;不同叶片翼型、叶片数量和λ的风机的静态扭矩特性受覆冰影响差异大。     

叶片覆冰对抗冰冻机组疲劳载荷的影响研究

风电机组叶片覆冰后叶片质量增加、翼型气动性能变化,引起风轮质量不平衡与气动不平衡。机组的载荷特性发生变化,将对关键部件的疲劳载荷产生影响,进而影响机组的安全性与可靠性。文章依据IEC标准对覆冰工况的要求,在考虑叶片覆冰后叶片质量与气动性能变化的基础上,提出两种不同的寿命周期,来研究叶片覆冰状态及覆冰时间对风电机组关键部件等效疲劳载荷的影响,结果表明叶片不均匀覆冰、覆冰时间及低温环境空气密度对机组关键部件疲劳载荷有较大影响。     

叶片覆冰对风电机组关键结构安全性的影响

为研究低温条件下叶片覆冰对风电机组关键部位振动频率、翼型气动性能、发电功率、极限载荷和疲劳载荷的影响,对某3.XMW风电机组在覆冰、未覆冰条件下,基于IEC61400-1标准、线性疲劳累计损伤理论、雨流循环计数法,通过仿真软件建立该机型覆冰、未覆冰两种模型并进行计算。计算结果表明,叶片覆冰导致叶片和塔筒振动降低,翼型升力系数降低,阻力系数升高,发电功率降低,覆冰条件下的叶根、旋转轮毂中心、固定轮毂中心、偏航中心、塔筒底部极限载荷和等效疲劳载荷增大,最大累计循环次数降低,其中叶片挥舞载荷增幅最大。研究成果可为叶片覆冰时机组优化提供参考。     

基于灰色FTA的风机叶片覆冰对机组运行可靠性影响研究

文章针对风机叶片覆冰影响机组运行可靠性的问题,提出了风电机组灰色FTA模型。根据新疆某风电场风机叶片覆冰期运行数据的统计分析,通过建立灰色矩阵集,对叶片覆冰时风电机组故障数据进行处理;计算覆冰与其它常见故障的灰色关联度,进行灰色FTA分析,并排序绘制FTA故障图。得出叶片覆冰与变桨逆变器ok信号丢失、机舱加速度超限等故障的关联度较大,在覆冰情况发生时需重点排查的结论。研究结论对降低风电机组运维成本,进一步提高运维效率具有重要的意义。     

贵州地区风电机组覆冰原因及甩冰风险分析

正高原寒冷地区气候极易造成风电机组叶片结冰,一方面会影响机组的发电量,另一方面在运行过程中,旋转的风轮在温度升高时,覆冰的粘着力下降,极易发生甩冰、落冰现象,造成人身伤害和运营事故。尤其在"天无三日晴"的贵州,风电机组叶片覆冰发生的频率较高。据不完全统计,贵州地区冬季的凝冻现象造成风电机组的年发电量损失高达15%-20%。资料显示,在特殊天气情况下,比如温度接近零摄氏度又伴有高湿度,如冻雨或雨夹雪,风电机组叶片比较容易覆冰。在重力和风电机组叶片旋转产生的机械力的     

基于运行参数特征的风力机叶片覆冰诊断方法

为更好地解决工程实际中的叶片覆冰问题,通过建立叶片覆冰状态特征参数处理模型,提取出能反映叶片覆冰状态的6种故障特征指标,并将其作为输入,将叶片覆冰状态作为输出,建立风电机组叶片覆冰诊断的BP神经网络模型,利用实际风电机组数据采集与监视控制(SCADA)系统数据构造BP神经网络的训练样本和测试样本。结果表明:所构建的叶片覆冰诊断模型能准确地诊断出叶片覆冰状态。     

玻璃绝缘子超疏水复合涂层的制备及其防冰性能研究

绝缘子是电力系统重要的绝缘控件,输电线路覆冰会对电力系统造成严重的后果。超疏水因其独特的浸润性能在防水、防覆冰和自清洁等方面有着重要的应用前景。本文采用纳米粒子填充法,在玻璃基底上制备出超疏水涂层。采用扫描电子显微镜(SEM)、X-射线光电子能谱仪(XPS)、接触角测量仪等分析手段对涂层的微观形貌、表面元素组成和浸润性能进行表征。同时在人工气候实验室测试了涂覆超疏水涂层绝缘子的覆冰特性及交流闪络电压。结果表明,本文制备的有机树脂/Si O2超疏水涂层的静态接触角达到161.1±1.3°,滚动角低于1°,达到了超疏水效果。纳米粒子的加入增加了涂层的粗糙度,使涂层形成了微纳米交联网状结构。超疏水涂层在雨凇条件下能够有效地延缓覆冰过程,阻止连续水膜的形成,提高了交流闪络电压。该方法制备简单,容易实现大面积制备,在防覆冰领域有着良好的应用前景。     

风力机叶片覆冰状态监测基准值与分级诊断标准研究

以2 MW风力机为研究对象,基于实际风力机状态(SCADA)系统大数据,选取叶片正常状态和覆冰状态下的风速、功率、桨距角和偏航角数据,采用核密度-均值数据处理方法,得到叶片覆冰状态监测基准值及其定量表达式。同时,根据叶片不同覆冰时期桨距角和功率值随风速的变化情况,提出叶片覆冰状态分级诊断标准。应用结果表明,根据桨距角随风速的变化情况可判断在叶片覆冰过程中机组最大功率追踪情况以及气动性能损失情况,根据风速-功率值分布情况可较准确地判别叶片的覆冰状态。     

基于FLUENT的风力机叶片翼型NREL S809覆冰的数值模拟

对经典风力机叶片翼型NREL S809的覆冰过程和翼型覆冰前后的气动性能进行了研究。利用FLUENT软件自带的离散相模型DPM及用户自定义函数UDF,求解出翼型表面的水滴运动轨迹方程、水滴的撞击极限和局部收集系数;选用经典的Messinger积冰传热模型计算积冰厚度,得到积冰形状;并分析在不同的攻角下,洁净翼型与覆冰翼型的气动性能。研究指出,覆冰导致翼型的气动性能发生畸变,升力系数下降,阻力系数上升,升阻比减小,升阻比最大降幅达到85.97%;覆冰后的翼型会提前进入失速区,破坏了翼型原有的流线,会造成翼型空气动力特性恶化。     

贵州省高压输电线路覆冰情况与观冰方法研究

针对近年来贵州省高压输电线路冰灾事故频发已严重危及电网安全可靠运行的问题,以2011年贵州省电网覆冰情况为例,根据贵州省覆冰天气频繁、电网灾害性覆冰过程较多、线路覆冰十分复杂的现状,分析了不同气候及地形中覆冰的特点,在此基础上提出了科学的观冰方法,可准确掌握贵州省高压输电线路覆冰情况,保障了正常、高效地开展防冰工作,为贵州省输电线路防冰提供了科学依据。     

Study on the hydrogen barrier performance of the SiOC coating

SiOC coatings were prepared on X70 pipeline steel substrate by a simple dipping method at low temperatures, and their performance of hindering hydrogen penetration was studied through electrochemical hydrogen permeation experiment. The sample thermal-treated at 120 °C achieved a low diffusion coefficient of hydrogen of 8.20 × 10^?9 cm² s^?1, which was nearly three orders of magnitude lower than 3.58 × 10^?6 cm² s^?1 for the X70 steel. This was due to that the amorphous coating did not provide a stable hydrogen diffusion channel, thus limiting hydrogen diffusion. Density functional theory (DFT) calculation further proved that hydrogen moleculars were difficult to be adsorbed at different sites on the surface of the coating.     

Further study on the influence of particle coating on fluidized bed heat transfer

Heat transfer to an immersed sphere from fluidized uncoated sand particles of different mean size and size distribution is compared with that from coated sand particles of equal size extracted from two full-scale fluidized bed boilers for different superficial gas velocities and mean particle diameters from 350 to 646 μm. The thin coating on the sand bed particles from full-scale boilers was found to have a significant effect on the heat transfer coefficient, while the particle size distributions, as well as coating thickness, had little or no influence on the heat transfer coefficients for the conditions investigated.     

On the effect of electrode coating on the breakdown probability ofparticle-contaminated GITL systems

In this letter the dynamics of wire particles in a coaxial gas insulated transmission line (GITL) system with coated electrodes under AC voltage are studied using a computational algorithm. The possibility of the SF₆ gas insulation breakdown due to the presence of metallic contaminants was computed at different applied voltages and gas pressures     

Graphite coating on alumina substrate for the fabrication of hydrogen selective membranes

Development of composite membranes is a suitable alternative to improve the hydrogen flux through palladium membranes. The porous substrate should not represent a barrier to gas permeation, but the roughness of its surface should be sufficiently smooth for the deposition of a thin and defect-free metal layer. In this study, the performances of the modification of the outer surface of an asymmetric alumina hollow fibre substrate by the deposition of a graphite layer were evaluated. The roughness of the substrate outer surface was reduced from 120 to 37 nm after graphite coating. After graphite coating, the hydrogen permeance through the composite membrane produced with 2 Pd plating cycles was of 1.02 × 10^?3 mol s^?1 m^?2 kPa^?1 at 450 °C and with infinite H₂/N₂ selectivity. Similar hydrogen permeance was obtained with the composite membrane without graphite coating, also at infinite H₂/N₂ selectivity, but 3 Pd plating cycles were necessary. Thus, graphite coating on asymmetric alumina hollow fibres is a suitable alternative to reduce the required palladium amount to produce hydrogen selective membranes.     

低辐射镀膜玻璃

传统的窗户有许多卓越的功能，但其隔热性能不尽人意，射入的阳光不是过多，就是不足。为此，人们曾作过许多尝试，试图克服窗户的上述缺点，例如采用遮阳蓬、着色玻璃、隔热百叶窗等，但这些措施都不十分理想。近来，人们开发成功一种无色低辐射玻璃，可提高玻璃窗的热阻...     

Evaluation of the coating layer formed on the substrate of C/C composites

Carbon-fiber-reinforced carbon matrix composites (C/C) are one of the promising candidates for heat-resistant materials because they have high strength and good creep resistance at high temperatures. Their application as a material for the turbine blades of a proposed chemical gas turbine system would increase the thermal efficiency. In this study, the time changes in weight loss of C/C composites have been measured in the combustion field at several equivalence ratios. It was found that the degradation of C/C composites was much less at a high equivalence ratio. Even in a fuel-rich combustion field, however, C/C composites cannot perfectly be free from the degradation. To enable this material to be used at higher temperatures, C/C composites were coated with SiC. The effects of coating layers on oxidation resistance have been investigated experimentally. The surfaces of some specimens before and after the exposure in a combustion gas stream of methane–air were observed by SEM and were also evaluated by Raman spectroscopy. The layer coated by the CVD method was easily peeled off from a substrate. The layer of specimens coated by the pack cementation method has been found to be stable. However, the substrate was degraded because of oxygen penetration through the pores in the coating layer. In order to cover the pores, the specimens were additionally coated with glass materials. This double-coating technique seems to be promising to improve the oxidation resistance of C/C composites in the combustion field.     

Effect of fabrication parameters on coating properties of tubular solid oxide fuel cell electrolyte prepared by vacuum slurry coating

The process of vacuum slurry coating for the fabrication of a dense and thin electrolyte film on a porous anode tube is investigated for application in solid oxide fuel cells. 8 mol% yttria stabilized zirconia is coated on an anode tube by vacuum slurry-coating process as a function of pre-sintering temperature of the anode tube, vacuum pressure, slurry concentration, number of coats, and immersion time. A dense electrolyte layer is formed on the anode tube after final sintering at 1400 °C. With decrease in the pre-sintering temperature of the anode tube, the grain size of the coated electrolyte layer increases and the number of surface pores in the coating layer decreases. This is attributed to a reduced difference in the respective shrinkage of the anode tube and the electrolyte layer. The thickness of the coated electrolyte layer increases with the content of solid powder in the slurry, the number of dip-coats, and the immersion time. Although vacuum pressure has no great influence on the electrolyte thickness, higher vacuum produces a denser coating layer, as confirmed by low gas permeability and a reduced number of defects in the coating layer. A single cell with the vacuum slurry coated electrolyte shows a good performance of 620 mW cm⁻² (0.7 V) at 750 °C. These experimental results indicate that the vacuum slurry-coating process is an effective method to fabricate a dense thin film on a porous anode support.     

The investigation of the effect of thermal barrier coating on the performance of Stirling engine

The shuttle heat transfer is one of the reasons reducing the performance of Stirling engines. This study is concerned with the reduction in shuttle heat transfer by coating the displacer. The displacer of a gamma type Stirling engine was coated with a layer of yttria‐stabilized zirconia (YSZ), and the effect of the coating on the engine performance was evaluated by comparing speed‐power and speed‐torque characteristics of the engine with coated and uncoated displacers. Characteristics were obtained for 700, 800 and 900°C heater temperatures. At each stage of the heater temperature, the charge pressure ranged from 1 to 3.5 bars with 0.5 bar increments. At 900°C heater temperature and 3 bars charge pressure, the shaft power before coating was 34.9 W, after coating the power increased to 43.8 W, which corresponds to a 25% increment. The temperature applied to the engine did not cause any damage on the coating layer. Copyright © 2008 John Wiley & Sons, Ltd.     

环氧粉末静电喷涂在太阳热水器上的应用

太阳热水器具有节能、清洁、方便和无污染等优点，在生产及生活中得到了广泛应用。目前，平板型太阳热水器的核心部件———铜铝复合集热板芯，其寿命长达１０—１５年，但其外框、压条等金属部件表面的喷漆涂层耐蚀性能较差，从而影响太阳热水器的使用寿命。为改变这一状...     

Influences of the Exhaust Flow on the Boundary Layer Flow on the Wafer Surface in Spin Coating System

Recently, development of high technology has been required for the formation of thin uniform film in manufacturing processes of semiconductor as the semiconductor become more sophisticated. Spin coating is usually used for spreading photoresist on a wafer surface. However, since rotating speed of the disk is very high in spin coating, the dropped resist scatters outward and reattaches to the film surface. So, the scattered resist is removed by the exhaust flow generated at the gap between the wafer edge and the catch cup. It is seriously concerned that the stripes called Ekman spiral vortices appears on the disk in the case of high rotating speed and the film thickness increases near the wafer edge in the case of low rotating speed, because it prevent the formation of uniform film. The purpose of this study is to make clear the generation mechanism of Ekman spiral vortices and the influence of exhaust flow on it Moreover the influence of the catch cup geometry on the wafer surface boundary layer flow is investigated.