关于微光物镜T数系列数值的确定

本文介绍了正确选定微光夜视仪物镜的基本参数－Ｔ数在研制工作中的重大意义；讨论了在夜视仪总体方案设计时，为达到预定条件下对预定目标的观察要求所需的Ｔ数大小的计算方法，简捷的直接计算了Ｔ数的公式，以及有关物镜焦距和物镜有效孔径的计算方法。并讨论了影响所需Ｔ数大小的因素。在此基础上分析了物镜焦距与Ｔ数之间的关系，最后按焦距分段确定了对物镜Ｔ数数值的最低要求。     

不连续切屑特征及形成机理的研究

半不连续切屑的形成过程分为弹性挤压和集中剪切两个阶段。本文推导出这两个阶段的变形能表达式。认为，集中剪切区的塑性变形能与屑段区的弹性能释放有关。每个切屑单元形成后系统能量应保持最低水平。由此得到切屑单元长度Ｌ＿Ｔ与切屑材料机械性能和切削条件和关系。其中，影响半不连续切屑形成的主要因素是切削材料的屈服强度τｓ和弹性模量Ｅ，并用屑形系数ｇ＿ｃ（ｇ＿ｃ＝τ＿ｓ／Ｅ）表达材料的这种切削属性。     

非均匀加热条件下微矩形槽道内的滑移流动换热特性

利用正交函数法对定热流密度加热、壁面温度在周向可任意变化条件下,气体在微矩形槽道内的热充分发展滑移流动的换热特性进行理论分析,获得相应条件下的Nu数计算方法及换热特性,并与大尺度槽道的换热特性进行比较,探讨了Kn数、槽道高宽比及不同加热条件对微矩形槽道内滑移流动换热性能的影响。结果表明,在任何加热条件下,微矩形槽道内的平均Nu数均低于相同加热条件下大尺度矩形槽道中的Nu数,且随Kn数的增加而减小。高宽比越小,平均Nu数下降越大。在相同的高宽比和Kn数下,单边加热条件下的换热性能相比相同加热条件的常规大槽道内的换热性能下降最小。     

对双自转式球体研磨机构V形槽夹角的仿真研究

介绍了用于加工精密球体的双自转式球体研磨机构。其中,V形槽夹角是影响球体加工过程和最终球体精度的重要影响因素。通过应用ADAMS软件对双自转式研磨成球过程进彳亍运动学仿真分析,研究了V形槽夹角对自转角、自转角速度和公转角速度3个参数的影响。研究结果表明,优化后的V形槽夹角可以改善球体研磨轨迹分布的均匀性,有利于提高球体精度;特殊的V形槽夹角会使球体在公转方向上发生倒滚运动。     

接触式机械密封外圆周织构强化换热机理研究

冲洗是强化机械密封换热的主要措施之一，但在一些特殊场合下冲洗量的大小往往是给定的，因此，需要采取一些强制换热措施来改善机械密封的运行环境。通过在密封环的外周面开设织构，针对冲洗量一定的情况，基于SST k-ω湍流模型，采用Ω方法分析了不同转速下织构深径比对端面温度、外周面局部努塞尔数Nu和织构区域流场的影响，对比研究了动环织构和静环织构的换热机理。研究结果表明：在相同工况、冲洗量和织构几何参数条件下，若动静环外周面单独开设织构，则动环的换热效果更佳。在相同转速下，动环外周面开设织构时，减小深径比会使织构内部换热效果差的区域增大，换热效果减弱，但对于静环织构，减小深径比会使织构流体流动下游侧换热效果差的区域减小，换热效果增强；随着转速的增大，较小深径比动环织构内部出现了新的差换热效果区域，单位面积换热强度显著下降。因此，为获取较优的换热效果，在低转速下宜选取小深径比织构，而在高转速下应选取大深径比织构。     

轻质点阵夹芯结构主动换热性能影响因素分析

针对点阵夹芯结构换热性能影响因素问题,采用翅片法推导四面体型点阵结构等热流密度和等壁面温度边界条件下的努塞尔数,以此表征结构的换热性能,并与实验结果进行对比。进而讨论结构支杆长度、支杆直径、导热系数和流动方向单胞个数对结构换热性能的影响,并比较相同孔隙率下四面体型、金字塔型和Kagome型点阵结构的换热性能。结果表明,点阵结构支杆长度和流动方向单胞个数对结构换热性能影响较大,Kagome型结构换热性能明显优于其他两类。     

纵向节距对锯齿螺旋翅片换热管特性影响的试验研究

锯齿螺旋翅片管是在连续螺旋翅片管基础上发展而来的强化换热管型,具有易于制造、翅化比大,换热系数和翅片效率更高等优点,在大型气体换热设备中具有广泛的应用前景.为获得管束布置结构对锯齿螺旋翅片换热管特性的影响,在分析其影响机理的基础上对9个锯齿螺旋翅片管错列管束进行试验研究,获得纵向节距S2对锯齿螺旋翅片管束换热与阻力特性的影响规律,并提出相应的关联式.试验结果表明:在相同雷诺数Re和管束横向相对节距S1/do下存在最优管束纵向相对节距S2/do使得翅侧努塞尔数Nu与综合换热性能j/f(Colburn传热因子与摩擦因子比值)最大;翅侧欧拉数Eu随S2增大而减小;在试验研究的S2/do=2.41～3.07范围,选取较优S2可使管束翅侧Nu数提高6%且Eu数稍有减小,管束j/f可相应提高约7%.     

竖直管内超临界二氧化碳局部对流换热研究

对超临界压力下二氧化碳在竖直管内的对流换热进行了模拟研究,分析了超临界二氧化碳在临界点附近的物性变化,以及二氧化碳进口压力、流动方向和进口Re数对换热系数的影响.结果表明,在临界点附近,物性变化非常剧烈,尤其是比热容的变化最为明显;二氧化碳进口压力对热流体温度的影响较小,换热系数受压力的影响较大;热流体流动方向对传热系数的影响不是太大;Re数的大小对换热系数的影响较为明显.     

微通道内流体流动及换热特性的数值分析

采用Navier—Stokes方程与滑移边界条件联立的理论分析模型，对等壁温、等热流及无温度梯度工况下，气体在微通道中的流速分布、阻力系数变化趋势（Cf·Re）和传热特性（努塞尔数）进行了数值研究。结果表明：气体稀薄效应可显著减小管内的摩擦阻力和努塞尔数，增大气体流速；壁面的速度滑移和温度跳跃对微圆管内换热特性的影响相反，温度跳跃的影响更大；等热流加热与等壁温加热两种情况下，努塞尔数随克努森数的变化趋势明显不同。     

高精度陶瓷球的研磨加工技术研究

在精密球体的制造工艺中,关键技术是最后的精密研磨。本文探讨了球体研磨的成球机理,介绍了国内外精密球体研磨技术的现状,分析了影响陶瓷球研磨质量和效率的工艺因素。     

螺旋槽管内传热及阻力特性的数值研究

为了深入分析螺旋槽管内传热及阻力特性,基于Fluent对16根具有不同结构参数的单头螺旋槽管进行了数值研究。分析了雷诺数Re、槽深e和螺距p对螺旋槽管内传热及阻力特性的影响,结果表明,在研究的雷诺数Re范围内(10000~45000),螺旋槽管的努塞尔数Nu是光管的1.34~2.01倍,且随Re的增加而增加;阻力系数f是光管的2.01~6.40倍,随Re的增加而减小;Nu和f随e的增加而增加,随p的增大而减小。通过回归分析,得到了螺旋槽管传热和阻力的准则关联式,供相关工程设计参考。     

几何尺寸对矩形微通道液体流动和传热性能的影响

基于连续介质方法数值研究液体在不同几何结构微通道中的流动和传热性能。在相同热边界条件下,通过比较水力直径、通道长度和宽高比等几何参数对液体微流动的影响,得到各参数对泊肃叶数(Po)和努塞尔数(Nu)的影响关系。研究发现,截面宽高比越大,Po数越小,且雷诺数对泊肃叶数基本无影响;雷诺数(Re)小于500情况下,水力直径小于0.545 mm时,Po数随水力直径减小而减小,水力直径大于0.545 mm时,水力直径变化对Po数基本无影响;Po数不随通道长度变化而变化,但略受流动雷诺数影响;在Re=20～1 800时,Nu数正比于水力直径和宽高比,但是通道长度对Nu数的作用受流动Re数的影响;在通道材料和流动介质相同的条件下,Nu数和Re数之间的关系受通道几何参数的影响,并且拟合得到其关系式。     

横纹槽管内插扭带复合强化传热的试验研究*

不同强化传热方式的复合会产生不同的传热效果,通过试验将不同扭率的扭带与同一规格横纹槽管复合强化传热的效果进行对比。试验以高黏度的导热油为工质,在500<Re<7 000、50<Pr<180的参数范围内,研究复合强化管的Nu数和阻力系数f随着Re数的变化情况,通过多元线性回归得到Nu数和f的关联式,并以强化传热性能评价指标(Performance evaluation criteria,PEC)值为标准评价其综合换热性能。结果表明：相同扭率下,复合强化管的阻力系数是光管内插扭带阻力系数的2~5倍,Nu数是光管内插连续扭带的1~4倍。随着Re数的增加,扭率Y对复合强化管的Nu数值影响越来越小。层流工况下,复合强化管的综合换热性能指标PEC值随Re数的增加而增加,且与扭率Y成负相关;过渡流工况下,复合强化管的PEC值都随Re数的增加而减小,扭率Y为5.21时的复合强化管综合换热效果最好。     

An investigation of heat transfer characteristics of swirling flow in a 180° circular section bend with uniform heat flux

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180° bend for Re=6X 10⁴, 8X 10⁴ and 1 X 10⁵ under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current heat flux of 5.11 kW/m² was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180°. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu_DB values at the 90° station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6X 10⁴ respectively. The values agree well with Said’s results for non-swirling flow.     

A numerical study of impingement heat transfer in a confined circular jet

Heat transfer characteristics of a submerged circular jet impingement with a confined plate was studied numerically. The continuity, momentum and energy equations were solved simultaneously. FIDAP, a finite element code, was used to formulate and solve the matrix equations for fluid elements. The effects of channel height and Reynolds number on the local Nusselt number were considered in the range of H=0.5–1.5 and Re=100–900, respectively. It was found that the channel height influenced strongly on the surface temperature, shear stress and pressure drop. The peak temperature was observed and gradually moved outward to the rim of the heated circular plate with increasing the Reynolds number, which may be related to flow recirculation region in the channel. It is also noted that the pressure drop increased more than the average heat transfer coefficient as the Reynolds number increased. For Pr=7, the Nusselt number was much more dependent on the Reynolds number than the channel height, and the magnitude of the second peak in the Nusselt number distribution increased as the Reynolds number increased. The local Nusselt number calculated based on a mixing-cup temperature was considerably different from that using the inlet nozzle temperature for H=0.5 and Re=100. The present study showed that the local Nusselt number of a confined submerged jet was significantly larger than that of the unconfined free jet which was available in the literature.     

Film condensation on horizontal tube with wall suction effects

This study performs a theoretical investigation into the problem of two-dimensional steady filmwise condensation flow on a horizontal tube with suction effects at the tube surface. An effective suction function is introduced to model the effect of the wall suction on the thickness of the liquid condensate film. The local condensate film thickness and the local Nusselt number are then derived using a simple series numerical method. The results show that the Nusselt number varies as a function of the Jakob number Ja, the Rayleigh number Ra, and the suction parameter Sw. It is found that the wall suction effect has a significant influence on the heat transfer performance. An analytical solution is derived for the mean Nusselt number for the case in which the wall suction effect is ignored. Finally, a closed-form correlation is presented for the mean Nusselt number subject to a wall suction effect.     

螺旋折流板与弓型折流板强化管换热器的传热性能对比

以油-水换热为对象,比较了螺旋折流板与弓型折流板三维翅片管换热器的壳程传热与压降性能.试验结果表明,2台实验换热器的壳程努塞尔特常数和压降都随雷诺常数的增加而增加,但螺旋折流板三维翅片管换热器的努塞尔特常数随雷诺常数的变化更明显.在相同雷诺常数下,螺旋折流板换热器的努塞尔特常数是弓型折流板换热器的1.2～1.5倍,而压...     

Contrastive experimental study on heat transfer and friction characteristics in steam cooled and air cooled rectangular channels with rib turbulators

The present experiment compares the heat transfer and friction characteristics in steam cooled and air cooled rectangular channels (simulating a gas turbine blade cooling passage) with two opposite rib-roughened walls. The Reynolds number (Re) whose length scale is the hydraulic diameter of the passage is set within the range of 10000–60000. The channel length is 1000 mm. The pitch-to-rib height ratio, the channel aspect ratio and the channel blockage ratio is 10, 0.5 and 0.047, respectively. It is found that the average Nu, the average friction coefficient, and the heat transfer performance of both steam and air in the ribbed channels show almost the same change trend with the increase of Re. Under the same test conditions, the average Nu of steam is 30.2% higher than that of air, the average friction coefficient is 18.4% higher, and the heat transfer performances of steam on the ribbed and the smooth walls are 8.4% and 7.3% higher than those of air, respectively. In addition, semi-empirical correlations for the two test channels are developed, which can predict the Nu under the given test condition. The correlations can be used in the design of the internal cooling passage of new generation steamcooled gas turbine blade/vane.     

Numerical study of natural convection and entropy generation of Cu-water nanofluid around an obstacle in a cavity

In this work, natural convection and entropy generation in a square cavity with an obstacle filled with Cu-water nanofluid is numerically studied. Horizontal walls of the cavity are adiabatic and vertical walls are maintained at a different constant temperature. The study has been done for the Rayleigh numbers between 10³ and 10⁶, the obstacle dimensions (W/L) of 0.1?C0.5 and for base fluid as well as nanofluid. It is found that, using the nanofluid overall leads to increase the flow strength, Nusselt number and entropy generation and decrease the Bejan number especially at high Rayleigh numbers. It is observed that by increasing the obstacle dimensions, the entropy generation increases and the Bejan number decreases, but the effect of the obstacle dimensions on Nusselt number depends on Rayleigh number. For the present thermal system, the increasing Nusselt number compared to increasing entropy generation due to increase obstacle dimensions is significant at low Rayleigh numbers.     

Effects of particle entrainment on heat transfer past particles in an oscillating flow

In order to investigate the effect of the particle entrainment on the heat transfer past paricles entrained in an oscillating flow with and without a steady velcoity, the two dimensional, unsteady, laminar conservation equations for mass, momentum and energy transport in the gas phase are solved numerically in spherical coordinates. The particle momentum equation is also solved simultaneously with the gas phase equations. The numerical solution gives the particle velocity variation as well as the gas phase velocity and temperature distribution as a function of time. The local and space-averaged Nusseit number with particle entrainment is compared with that without particle entrainment. In the case of an oscillating flow with a steady velocity, the values of the space-averaged Nusselt number with particle entrainment are lower than those without particle entrainment at frequencies of 50 and 2000 Hz since the moving particle is entrained in the steady velocity. In the case of an oscillating flow without a steady velocity, the space-averaged Nusselt number with entrainment at a frequency of 50 Hz is slightly lower than that without particle entrainment, with a phase lag. At 2000 Hz, the space-averaged Nusselt number with and without particle entrainment is almost the same, due to very small particle entrainment.