转叶孔板螺旋流消能的影响因素试验分析

为解决供水工程中的过剩水头问题,常在有压输水管道中配置合适的消能装置,转叶孔板螺旋流消能是一种新型的内消能方式,通过转叶孔板螺旋流消能装置的水力特性试验,可知影响转叶孔板螺旋流消能效率的主要影响因素有雷诺数Re、转叶孔板开口角度和孔板之间的相互扭转角度,还有试验装置结构的设置。根据试验数据计算分析各个影响因素对消能效率的影响。结果表明,转叶孔板螺旋流消能效率与转叶孔板之间的扭转角成正比,与雷诺数成正比,与转叶板的开口角度成反比。试验装置在进口段和出口段设置管径突变均对消能有利,该装置比与其消能原理类似的孔板消能装置更实用,且消能效率更高,对下游建筑物设施起到良好的保护作用,可推广应用。     

A Mathematical Study for Laminar Boundary‐Layer Flow,Heat, and Mass Transfer of a Jeffrey Non‐Newtonian Fluid Past a Vertical Porous Plate

In this article, we investigate the nonlinear steady‐state boundary‐layer flow, heat and mass transfer of an incompressible Jeffrey non‐Newtonian fluid past a vertical porous plate. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a versatile, implicit finite‐difference technique. The numerical code is validated with previous studies. The influence of a number of emerging non‐dimensional parameters, namely, Deborah number (De), Prandtl number (Pr), ratio of relaxation to retardation times (λ), Schmidt number (Sc), and dimensionless tangential coordinate (ξ) on velocity, temperature, and concentration evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate, mass transfer rate, and local skin friction are also investigated. It is found that the velocity is reduced with increasing Deborah number whereas temperature and concentration are enhanced. Increasing λ enhances the velocity but reduces the temperature and concentration. The heat transfer rate and mass transfer rates are found to be depressed with increasing Deborah number, De, and enhanced with increasing λ. Local skin friction is found to be decreased with a rise in Deborah number whereas it is elevated with increasing λ. And an increasing Schmidt number decreases the velocity and concentration but increases temperature. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21111     

Effect of Newtonian Heating and Thermal Radiation on Heat and Mass Transfer of Nanofluids over a Stretching Sheet in Porous Media

Laminar boundary layer slip flow from a stretching surface in a nanofluid‐saturated homogenous, isotropic porous medium is studied numerically. A Newtonian heating boundary condition in the presence of thermal radiation is incorporated and a Darcy model utilized for the porous medium. The model used for the nanofluids include the effects of Brownian motion and thermophoresis. A group theoretical analysis is conducted to generate similarity transformations. The governing transport equations are nondimensionalized and rendered into a set of coupled similarity ordinary differential equations using similarity transformations. The transformed equations are then solved using the Runge–Kutta–Fehlberg fourth‐fifth order numerical method with shooting technique. It is shown that the physical quantities of interest depend on a number of parameters. The results are presented in tabular and graphical forms. Comparison of the present numerical solutions with published work shows very good agreement. The study finds applications in high‐temperature nanotechnological materials processing.     

Development of a methodology for assessing the adequacy of electric power systems

This study presents the results of a research into the developing a methodology for assessing the adequacy of advanced electric power systems characterized by the integration of various innovative technologies, which complicates their analysis. The methodology development is aimed at solving two main problems: 1) increase the adequacy of modeling the processes that occur in the electric power system and 2) enhance the computational efficiency of the adequacy assessment methodology. This study proposes a new mathematical model to minimize the power shortage and enhance the adequacy of modeling the processes. The model considers quadratic power transmission losses and network coefficients. The computational efficiency of the adequacy assessment methodology is enhanced using efficient random- number generators to form the calculated states of electric power systems and machine learning methods to assess power shortages and other reliability characteristics in the calculated states.     

套管式腔体在盐水淡化过程中的光热及产水性能研究

该文研究一种基于菲涅尔反射镜场和降膜方式相结合的多级套管式淡化系统,分析2种腔体结构,确定了光学性能更好的圆型腔体,并对其内部淡化过程进行仿真计算。建立两级淡化系统的能量流动模型,并进行稳态和瞬态加热实验,由稳态实验数据计算出月牙型有限空间内部自然对流传质经验关系式。瞬态试验结果表明,第1、2级的最高产水量分别为3.79和2.64 kg/h。     

Impact of volume fraction and fluid layer thickness on heat transfer effectiveness of water-based nanofluids

The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al₂O₃ nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al₂O₃–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned.     

双桥墩条件下冰塞发展临界条件试验初步研究

河流中的桥墩改变了附近原有的水流特征,冬季可能对其附近冰塞的形成和演变产生影响。基于水槽模型试验,通过改变墩心距、墩径、墩形、冰水流量比和水流弗劳德数,分析了双桥墩条件下冰塞发展通过桥墩的临界条件。试验表明：冰塞能否发展通过桥墩所在断面存在临界弗劳德数,其值受墩心距、墩径、墩形和冰水流量比等因素控制,随着墩心距的减小或冰水流量比、墩径的增大,冰塞发展通过桥墩所在断面难度增大,方形墩相较于圆柱形墩难度增大;试验范围内,随着墩心距的减小,桥墩所处河道断面输冰能力增强,初始冰塞厚度增加,但冰塞平衡厚度减小。     

结晶器铜管的失效分析

针对结晶器铜管在生产中出现的硬度不均、表面＂桔子皮＂、脱方现象,秦皇岛首钢长白结晶器有限责任公司采用调整加热温度和保温时间的方法,保证硬度符合标准,并解决了铜管裂纹和难以加工问题;控制铜管的变形量〉15%,消除了铜管的＂桔子皮＂现象;采取时效处理使铜管不在出现脱方现象。     

提高曲面铣削编程效率的步骤

数控铣床是模具制造的主导设备,能够完成较为复杂的曲面铣削,编程效率直接决定着生产进度和经济效益。本文以注射模中的虎齿盘工件为例,集中宏程序的优点,介绍曲面编程的思路与步骤。     

第二代催化裂化汽油选择性加氢脱硫（RSDS-Ⅱ）技术的中试研究及工业应用

对催化裂化汽油中硫化物及烃类分布进行详细分析,确立第二代催化裂化汽油选择性加氢脱硫（RSDS-Ⅱ）技术的工艺路线。中试试验结果表明,RSDS-Ⅱ技术对多种原料油具有较好的适应性。工业应用标定结果表明,以烯烃体积分数38.7%～43.3%、硫质量分数250～470 g/g的催化裂化汽油为原料,经过RSDS-Ⅱ技术处理后汽油产品硫质量分数小于50 g/g,满足沪Ⅳ/欧Ⅳ排放标准,RON损失0.3～0.6个单位,说明RSDS-Ⅱ技术具有较好的脱硫活性和较高的选择性,完全可以满足炼油厂汽油质量升级的需要。