垂直U型沸腾管传热恶化特性的研究

本文阐述垂直U型管弯管段中,沸腾传热恶化特性的试验结果,试验在高压电加热水回路装置上进行.管子内径21mm,弯管半径700mm,压力P=45—144bar,质量流速G=800—2000 kg/m~2s,热负荷q=80—330 kw/m~2,试验得出了沿弯管段周界壁温分布特性。管子内侧与外侧之间的壁温差随质量流速、热负荷、含汽率和压力而变.△t的变化反映了两相流流型转变的影响,根据本文结果,为确保U型管内外侧壁温均匀,应避免在层状流与间歇状流动工况下工作。     

U型管传热量影响因素的数值模拟研究

地下换热器是地源热泵的重要组成部分,竖直U型管是最常见的地下换热器形式. U型管与土壤间的传热受诸多因素的影响.为分析这些因素对于U型管传热的影响,本文建立了地源热泵竖直U型管地下换热器的三维全尺寸数值模型,在此基础上采用CFD软件FLUENT对U型管的埋管深度、进口水温、管内流速等一系列因素在冬夏不同工况下对U型管传热量的影响进行了数值模拟研究.经过整理分析得出的各种因素对传热量影响可以为优化工程设计提供依据.     

自然循环蒸汽发生器倒U型管内倒流特性研究

以自然循环压水反应堆一回路系统的蒸汽发生器为对象,对蒸汽发生器并联倒U型管内单相水发生的倒流机理及其特性进行了分析,确定了倒流发生的条件和范围,以及发生倒流的倒U型管结构等.在此基础上,建立了分析自然循环系统蒸汽发生器倒U型管内单相水倒流的数学模型,并进行了计算,得出了蒸汽发生器倒U型管内正流和倒流流量、正流和倒流管分布等,并使用实验结果对计算结果进行了检验.研究结果表明,倒流对系统的自然循环能力有重要影响.     

T型三通水管路噪声特性数值研究

水管路系统工作运行中会产生较大的管路振动和流噪声.作为偶极子声源,充液管路内湍流激发的脉动压力会形成流噪声,且激励管壁产生流激振动噪声.为了揭示水管道系统的流激振动噪声与流噪声特性的区别,基于有限元方法对不同厚度的充液管路声学模态、结构模态以及耦合模态进行计算;基于计算流体力学联合声学边界元的混合计算方法探讨变流速下流...     

综述180°回转型弯头对U型管内的气液两相流流型压降与传热的影响

从流型,压降和传热三个方面综述了以前研究者在U型管中所做的研究。指出了180°弯头对整个U型管的流型及其流型转变,压降损失及其预测方法和增强换热的影响。同时提出了今后关于U型管可能的研究方向:(1)细化曲率比等几何因素对流型压降传热的影响;(2)关注低温介质的U型管中的流动与传热;(3)以180°弯头加上距其一定距离的上下游为一个单元考虑其整体的压降损失;(4)量化气液两相流在U型管中的传热。     

自然循环蒸汽发生器倒U型管内单相水流动及传热特性分析

本文以模拟压水反应堆一回路系统在自然循环条件下运行时的蒸汽发生器为对象,提出了分析蒸汽发生器并联倒U型管内单相水的流动及传热流特性的数学模型及相应的数值计算方法,计算结果表明,在一定的回路系统自然循环流动条件下,并联倒U型管内会同时发生正流和倒流。并发现,蒸汽发生器倒U型管内的倒流对一回路系统的自然循环流量有重要影响。     

测定不同形状物体空气阻力系数的实验

设计空气流速连续可调的小型风洞,对圆形平板、圆柱体、流线体的空气阻力系数进行测量.利用U型管中水柱的高度差表达孔板法中空气的流速,通过悬臂梁力传感器测量测试物受到的空气阻力,根据空气阻力和U型管中水柱的高度差的关系测定空气阻力系数.     

软X光能谱仪求辐射能流的改进方法

使用多道软X光能谱仪测量黑腔辐射能流时间过程并使用最小二乘法将多道谱仪的响应函数线性组合为等效平响应。针对惯性约束聚变实验中软X光能谱强度分布不均匀、等效平响应局部不平带来的误差,提出了辐射能流求解的加权改进算法。对不同谱形和等效积分温度的能谱进行了计算,比较了不同方法得到的能流还原能力。改进后的方法应用于实验数据的处理,得到了修正后的等效积分温度随时间的演化过程。     

水平矩形小通道内气-液两相流摩擦压降的研究

本文以氮气和水为工质,在水平矩形小通道(dh=0.99 mm)中对两相流摩擦压降进行了实验研究.实验是在大气压力下进行的,氮气的折算流速的范围为0.017～33.3 m/s,水的折算流速的范围为0.1～5 m/s.实验对所得的219个数据点进行了分析,并同 L & M 关系式、L&L关系式、均相流模型以及均相流修正模型进行了比较,得出(1)L & M关系式比均相流模型、均相流修正模型以及 L & L 关系式的偏差都小,能更好地预测两相流压降变化.(2) L & M 关系式中的C在不同的流型(流型是由UGS、ULS以及dh决定)具有不同的值,在同一ULS下,C随X(UGS)的变化呈现一定的规律性,在X=7左右,C出现最大值,而此处恰好是块状流最激烈区域.但是C随ULS没有一定的规律性.     

碳氢燃料在旋转通道中传热的数值模拟

本文利用数值模拟方法,对不同转速下正癸烷在U型管路的传热特性进行了研究。得到以下结论:对于U型管路来说,旋转速度越大,出口温度越高,整体管路换热能力越强;碳氢燃料在准临界温度附近的变物性对换热有比较显著的影响,会使换热恶化;浮升力也会影响旋转管路的换热,相比静止管路影响更为复杂。     

海底沉积物压缩波声速比与物理特性的关系

海底沉积物因组成结构复杂导致声学特性复杂多样,多种理论解释模型存在参数较多且各具适用性现象·通过运用体积平均和等效参数的方法对海底沉积物声波传播机理进行研究,提出一种少参数的海底沉积物与底层海水的压缩波声速比通用模型(General Model of Sound Speed Ratio,GMSSR).GMSSR模型包含弹性结构分布因子、孔隙度、等效密度比、等效弹性模量比4个物理特性参数。分析海底沉积物两相介质结构的串联和并联两种极限情况分析,基于弹性结构分布因子和串并联结构的体积平均分布建立一般情况下海底沉积物的等效弹性模量表达式·应用GMSSR合理地分析各海域测量的海底沉积物声速比经验模型的共性和解释南海实测数据分散的范围,表明:(1)表层海底沉积物主要是以串联结构为主,接近于悬浮液状态或者体积分量很少的并联堆积状态;(2)等效弹性模量比的影响因素大于等效密度比,结构变化往往通过影响弹性结构分布因子而影响等效弹性模量比,从而引起声速比的变化;(3)不同研究海域的声速比-孔隙度经验关系具有相似性,可以通过GMSSR模型分析得出;(4)基于弹性结构分布因子的差异,可以合理解释南海海域测量表层海底沉积物声速比较大的分散性。      

β-PtO2: Phononic,thermodynamic, and elastic properties derived from first-principles calculations

β-PtO₂ is a useful transition metal dioxide, but its fundamental thermodynamic and elastic properties remain unexplored. Using first-principles calculations, we systematically studied the structure, phonon, thermodynamic and elastic properties of β-PtO₂. The lattice dynamics and structural stability of β-PtO₂ under pressure were studied using the phonon spectra and vibrational density of states. The vibrational frequencies of the optical modes of β-PtO₂ increase with elevating pressure; this result is comparable with the available experimental data. Then, the heat capacities and their pressure responses were determined based on the phonon calculations. The pressure dependence of the Debye temperature was studied, and the results were compared in two distinct aspects. The elastic moduli of β-PtO₂ were estimated through the Voigt–Reuss–Hill approximation. The bulk modulus of β-PtO₂ increases linearly with pressure, but the shear modulus is nearly independent of pressure. Our study revealed that the elastic stiffness coefficients C₄₄, C₅₅ and C₆₆ play a primary role in the slow variation of the shear modulus.     

Micro scale laser shock forming of pure copper and titanium sheet with forming/blanking compound die

A new process fabricating micro parts of thin metal foils by laser shock waves with forming/blanking compound die is reported in this article, in which flexible rubber material was used as the soft punch to act on the thin metal sheet. Systematic studies were carried out experimentally on the process with different laser energies and materials. The formed parts were examined in terms of their morphology, surface roughness, forming depth and mechanical properties (including nanohardness, plasticity and elastic modulus) characterized by nanoindentation test. According to the results, the ablation states of confinement medium and the surface roughness of the different regions change with energies. Additionally, the proper energies are necessary to form complex parts and the forming process can be applied to manufacture parts with good surface quality. What׳s more, the nanoindentation test results showed that the nanohardness, plasticity and elastic modulus of material were increased after impact. The increase in nanohardness and plasticity can attribute to higher stiffness of the parts. The enhanced elastic modulus indicates an increased stiffness of the parts, providing an evidence for the reduced spring back of copper during laser shocking.     

铼的弹性剪切参数C44对温度与压力响应的原位拉曼光谱研究

铼具有高体积弹性模量、高熔点、优良的抗蠕变性能,是一种重要科学研究与工程应用材料。铼的弹性剪切系数C₄₄对温度和压力的响应特性对铼及其合金材料的设计与工程应用具有重要意义。激光拉曼散射技术在研究不同温度和压力条件下六方密堆积结构(hcp)金属的弹性剪切系数C₄₄上具有独特的优势。但由于金属的强反射作用和浅的穿透深度,hcp金属的低波数拉曼散射信号往往很难获取,在一定的温度和压力加载下拉曼信号的获取尤为困难。利用侧向激发拉曼散射技术,有效降低了金属强反射对拉曼光谱采集的影响,成功测量到多晶铼在不同压力与温度条件下的E_2g拉曼振动模,获得铼在常温常压条件的弹性剪切系数(C₄₄=133 GPa)以及其弹性剪切系数C₄₄对温度和压力的响应特性。研究结果表明,多晶铼的弹性剪切系数C₄₄模量随压强的增加而增大,随温度的增加而减小。这也为用光散射方法研究金属材料剪切模量提供了良好研究方法。     

Specific features of the determination of the mechanical characteristics of thin films by the nanoindentation technique

The hardness and the elastic modulus of Cu thin films on Si, Ti, Cu, and Al substrates are investigated. It is demonstrated that the use of the Oliver-Pharr method in combination with the technique for evaluating the true hardness makes it possible to determine uniquely the hardness of Cu thin films at different ratios between the hardnesses of the film and the substrate. The elastic modulus of thin films can be correctly measured by the Oliver-Pharr method only in the case where the film and the substrate exhibit identical elastic properties. In order to determine the elastic moduli of films with the use of the parameter P/S ², the film and the substrate should have close values of both the hardness and the elastic modulus.     

金属玻璃流变的扩展弹性模型

玻璃-液体转变现象,简称玻璃转变,被诺贝尔物理学奖获得者安德森教授评为最深奥与重要的凝聚态物理问题之一.金属玻璃作为典型的非晶态物质,具有与液体相似的无序原子结构,因此又称为冻结了的液态金属,是研究玻璃转变问题的理想模型材料.当加热至玻璃转变温度,或者加载到力学屈服点附近时,金属玻璃将会发生流动.由于热或应力导致的流动现象对金属玻璃的应用具有重要意义.本文简要回顾了金属玻璃流变现象,综述了流变扩展弹性模型的研究进展和未来发展趋势.     

Li2O-Al2O3-SiO2微晶玻璃表面粗糙度对纳米硬度测试的影响

 介绍了纳米压痕测试技术的基础理论及纳米压痕法常用的Oliver -Pharr方法的计算原理。采用纳米压痕试验测得不同表面粗糙度的Li2O-Al2O3-SiO2微晶玻璃样品的纳米硬度、弹性模量和载荷-位移曲线。结果表明样品表面粗糙度会降低纳米压痕测试结果的稳定性、准确性和可靠性：样品表面粗糙度越小,测得的纳米硬度和弹性模量值波动越小,载荷-位移曲线重合性越高。随着最大载荷的增大,测得的弹性模量逐渐减小,其原因是压痕边缘材料发生了塑形变形。在超光滑表面样品（Ra=0.9 nm）上测得较为准确的Li2O-Al2O3-SiO2微晶玻璃纳米硬度和弹性模量值分别为8.8 GPa和7.79 GPa。纳米压痕测试结果的重合度对于评价超光滑表面完整性研究具有指导意义。     

Effect of porosity on the laser induced damage threshold of porous anodic alumina films

Thermal stress of porous alumina films has been simulated by finite element method based on thermal transfer equation and thermal stress formulas. The influence of equivalent thermal conductivity and elastic modulus on laser induced damage threshold (LIDT) has been studied. It was found that the biggest circumferential tensile stress will be small with the porosity from 15% to 35%, and it effectively improves the LIDT. The equivalent thermal conductivity and LIDT decreases with the increase of porosity. The equivalent elastic modulus decreases and LIDT increase with the increase of porosity.     

Effect of heat treatment on the mechanical and microstructural characterization of Mg-AZ91E/TiC composites

Mg-AZ91E/TiC_p composite was fabricated using a spontaneous infiltration technique at 950 °C under an argon atmosphere. The composites produced have 37 vol.% of metal matrix and 63 vol.% of TiC-like reinforcement. The obtained composites were subsequently solution heat-treated at 413 °C during 24 h, cold water quenched, and subsequently artificially aged at 168 and 216 °C during 16 h in an argon atmosphere. Effect of heat treatment on the microstructure and mechanical properties was evaluated. Microstructural characterization was analyzed using different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Interface between matrix and reinforcement was examined using transmission electron microscopy (TEM), and mechanical properties were evaluated by measuring the elastic modulus and hardness. Mg, TiC, Al, and Mg₁₇Al₁₂ phases through XRD were detected. Meanwhile, using TEM analysis in heat-treated composites MgAl₂O₄, MgO, and Al₂O₃ were identified. The as-fabricated composite have elastic modulus and hardness of 162 GPa and 316 Hv, respectively. After solution heat treatment and aging at 168 °C during 12 h, the composites reaches values of 178 GPa and 362 Hv for the elastic modulus and hardness, respectively. Time of aging was correlated with measures of elastic modulus and hardness.     

基于岩石物理的致密气层识别方法研究

致密储层声波性质受骨架矿物组成及孔隙类型影响较大,为更准确进行气层识别,本文给出了一种综合模型,和利用纵横波速度信息进行致密气层识别的方法:其首先利用Voigt-Reuss-Hill平均模型,求取岩石骨架等效弹性模量,消除岩性影响;根据综合模型和岩石剪切模量计算孔L隙纵横比(或裂隙密度),消除孔隙性质影响;利用DEM和K-T模型计算干燥岩石弹性模量,得到不受孔隙流体性质影响的弹性模量;将实测岩石弹性模量减去干燥岩石弹性模量定义为含气性因子;同时利用最小二乘法和体积模量,进行气层识别。本文含气分析方法考虑因素全面,干燥岩石纵横波速度比非定值,为具有复杂岩性和低孔低渗等特征的致密岩石气层识别提供技术支持。