降膜过程中液膜厚度和温度同步测量系统研制

针对金属圆管外降膜过程中关键参数的高精度测量,研制了基于双波长激光吸收光谱技术的液膜厚度和温度同步测量系统,利用该系统对不同工况下竖直和水平金属圆管外降膜过程液膜厚度和温度进行同步测量,同时结合图像法和热电偶对该系统的测量精度进行验证.结果 表明:不同方法测得的金属圆管外液膜厚度和温度的变化趋势吻合良好,二者最大平均偏差分别为4.3％和3.8％;该系统有望为深入研究液膜形成、流动及蒸发过程提供高精度、高灵敏度和无干扰的测试手段.     

电场对管内凝结液膜厚度的影响

以R123为工质,对圆柱形电极进行了电场强化管内凝结换热的试验研究,提出并计算了当量液膜厚度。试验换热管为垂直套管式,外层为冷却水路,内层为工质回路。电压范围为0～30 kV,热流密度范围为4～6 kW/m2。实验观察到了凝结液膜的减薄,在给定的实验条件下,当电压超过5 kV后,随着电压的增加,凝结换热系数增加,当量液膜厚度减小。实验结果表明,液膜厚度的减薄是电场强化凝结换热的主要原因。     

微波同轴谐振腔测量液膜厚度的理论分析

汽轮机低压缸湿蒸汽区中,静叶片、动叶片及汽缸壁表面存在水膜的沉积、流动,在高速汽流拖拽撕裂下形成的较大水滴,会造成动叶片的严重水蚀,实时监测液膜厚度,对于叶片防护及机组的安全运行具有重要意义。采用开式微波同轴谐振腔作为液膜厚度测量传感器,根据谐振腔等效电路,建立了水膜厚度测量数学模型,推导了液膜厚度的测量关系式。设计了探针耦合同轴谐振腔传感器,仿真分析了谐振频率随水膜厚度的变化关系,确定了测量关系式中的待定系数,计算了不同温度条件下,液膜厚度随谐振频率的变化。     

单液滴撞击球面液膜水花形成特征分析

应用VOF(volume of fluid)方法对液滴撞击球面液膜的飞溅过程进行数值模拟,由计算结果分析了不同液滴撞击速度和液膜厚度对撞击产生的水花形态、高度和直径的影响。结果表明:随着液滴撞击速度和液膜厚度的增加,水花高度增大;随着液滴撞击速度增加,水花直径增大,但当液膜厚度增加时,水花直径减小。     

平行极板式空间电场校准装置电场均匀域的计算分析

为了实现对直流输电线路下方空间电场的精确测量,采用有限元方法分析了平行极板的直径和间隙距离对空间电场校准装置中电场均匀域的影响,仿真得到了不同极板间隙和极板直径下的均匀域的变化情况,提出了最佳校准位置随极板直径和间隙的计算公式,同时计算分析了探头引入均匀域内后的探头周围的电场畸变情况.结果 表明,均匀域随间隙距离d与高...     

人体对工频电场测试仪测量准确度的影响分析

工频电场是交流输电线路的主要环境影响因子,一般采用现场测量对其环境影响进行评价,现场测试经验表明,工频电场探头附近有人经过时会导致测量结果产生较大偏差。为研究人与探头距离对测量结果的影响程度,建立了有限元模型,模拟工频电场探头在人体影响下的测量结果。基于人体对测量过程的影响分析,提出以探头感应电荷量的变化来表征人体对测量结果的影响程度。结果表明,当人与探头间距为0.5m时,电场最大值和探头感应电荷量的测量结果畸变率分别为102.2%、12.4%;当间距为2.5 m时,两者测量值畸变率分别为3.12%、0.5%;因此,分析认为利用探头感应电荷量的变化表征人体对测量结果的影响程度较最大场强值准确度更高。     

应用伽马射线对垂直上升管内环状流液膜及扰动波特性研究

采用单束伽马射线与高速摄像相结合的方法,利用无干扰动态测量技术对垂直上升管内环状流液膜及扰动波进行了系统性的研究,研究结果表明,在液相折算流速不变时,随着气相折算流速的增高,管壁液膜厚度逐渐减小。当扰动波在管中剧烈变化时,射线计数率较低,反映出液相成分较多,结合环状流扰动波的特性,还研究得出了在流体温度变化范围较小时,温度的改变对计数率影响不大的结论。     

单液滴撞击平面液膜飞溅过程的CLSVOF模拟

采用CLSVOF(coupled level set and volume of fluid)方法对单液滴撞击平面液膜初期的飞溅过程进行了数值模拟,探讨了撞击速度和液膜厚度对撞击后形成冠状水花形态及扩展直径的影响.结果显示,扩展直径随撞击速度的增大而增大,随液膜厚度的增大而减小,CLSVOF方法可较好地用于液滴撞击过程的数值计算.     

两相流中薄层物质分布的ECT测量

介绍利用电容层析成像(ElectricalCapacitanceTomography,简称ECT)对两相流中薄层物质分布进行测量的研究。在对旋流分离器中固体薄层中的浓度分布和热管中液膜厚度的测量中,应用优化的迭代成像方法,取得了良好结果。对旋流分离器的测量结果与CFD计算相互吻合。在对热管中液膜厚度的测量中,在低加热率情况下,ECT测量结果与Nusselt公式计算的吻合良好。但在加热率升高的过程中,ECT测量的液膜厚度高于Nusselt的计算值,并且此偏差随加热率的上升而增加,对此现象做了初步分析。     

外波纹管管外降膜流动过程液膜厚度及速度分布特性

针对外波纹管管外降膜流动过程,采用实验结合数值模拟的方法,考察了液体喷淋密度、管间距和管径变化对液膜厚度周向分布的影响,并与光滑管进行了比较,同时分析了外波纹管管外液膜速度分布特性。结果表明:光滑管外液膜厚度由上至下沿周向呈先减小、后增加的趋势,在90°～120°之间液膜最薄;外波纹管去除波纹间凹槽内的液体后,波纹外的液膜厚度数值及其周向分布规律与相同直径的光滑管相似,周向平均液膜厚度随着液体喷淋密度的增加、管间距及管径的减小而增大;液膜沿周向分布的均匀程度及流动速度大小均与液膜厚度有关,波纹外液膜沿周向分布的不均匀性随着液膜厚度的增加而增加,气液界面处的液体速度沿周向分布规律与液膜厚度分布规律相反;相邻两波峰间凹槽内的液体存在局部循环流动。     

Experimental Study on the Characteristics of Liquid Layer and Disturbance Waves in Horizontal Annular Flow

INTRODUCTIONGas-liquid two-phase annular flow is encountered ina wide range of industrial applications, including nuclear reactors, evaporators and condensers. The studyof annular flow not only because of the need to understand the heat transfer characteristics of such aflow, but also because annular flow may be precursory to liquid dryout in the challnel, which is significant in nuclear reactor safety and in corrosion pre-vention. An important feature of horizontal annularflow is the effe…     

Non-heating simulation of pool-boiling critical heat flux

This paper presents a non-heating experimental method that simulates the critical heat flux (CHF) phenomenon in pool boiling. In the experiments, with providing controlled air flow through the holes on a plate submerged in a pool of water, the liquid sublayer (macrolayer) thickness and bubble departure frequency have been successfully measured by a conductance probe. The CHF is reasonably predicted by applying the measured parameters to a liquid macrolayer dryout model. The measured trends of the macrolayer thickness and bubble departure frequency with air mass flux are also consistent with the present understanding. As a result of this experimental study, it is expected that the non-heating method would be useful to investigate the various parametric effects on pool and flow boiling CHF, with avoiding the difficulty in heating and large electric power requirement even for complex geometries.     

Interfacial friction factor in vertical upward gas-liquid annular two-phase follow

This paper presents new data on the gas-liquid interfacial friction factor in annular two-phase upward co-current flow in a vertical circular pipe. Different from most previous work, the present studies have been performed at relatively high film thickness, taking into consideration the effect of the entrained droplets which occur from the breakup of the disturbance waves. The test section has an inner diameter of 29 mm and the length of 3 m. The porous wall injector is used to introduce the liquid into the test section. The two phase pressure drop is measured by two static pressure tubes connected with a manometer. The film thickness is measured by calibrated stainless ring electrodes mounted flush in the tube wall. The electrode operates on the principle of the variation of electrical resistance with changes in the liquid film thickness between two parallel eletrode rings. The entrained liquid flow rate is measured by using a sampling probe connected with a cyclone separator. The entrainment flow rate in the gas core is calculated from an assumption that the sampling is carried out in an isokinetic manner. The results from the experiments are compared with those calculated from correlations reported in the literature. A new empirical correlation for predicting the interfacial friction factors for practical applications is proposed.     

ITO/metal/ITO multilayer structures based on Ag and Cu metal films for high-performance transparent electrodes

Transparent conductive indium tin oxide (ITO)/metal/ITO multilayer electrodes have been prepared by sputtering at room temperature. Ag and Cu thin films with thickness ranging from 5 to 35 nm have been used as intermediate metal layer, between ITO coatings of about 30 nm thickness. Evolution of the optical and electrical characteristics of the multilayers as a function of each metal film thickness has been analyzed. High-quality transparent electrodes have been obtained, with sheet resistance below 6 Ω/sq for Ag film thickness above 10 nm or Cu film thickness above 16 nm. These multilayers also showed high transmittance in the visible spectral range, above 90% by discounting the glass substrate, with a maximum that is located at lower wavelength for Ag-based electrodes than for the Cu-based ones. After heating at 350 °C in flowing nitrogen, some improvement in the optoelectronical characteristics of the multilayer electrodes has been achieved that is related to the structural improvement of the ITO components.     

生物基底材料上纳米金薄膜导电、传热性能研究

利用瞬态电热技术测量了不同生物基底材料的热扩散率。通过增加镀层数目,采用微分测量法进行实验,根据实验结果计算了相应基底材料上厚度为5.00～20.00nm金薄膜的洛伦兹数、导热系数以及导电系数。研究结果表明,由于晶格边界散射大大减小了薄膜的导电和导热系数,所有基底上金薄膜的导热和导电系数均小于体材料金的导热和导电系数。由于蚕丝中的蛋白晶体可促进电子跳跃并产生隧道效应,蚕丝基底上金薄膜的导电系数大于其他几种基底上金薄膜的导电系数,因此蚕丝更适合作为柔性电子器件中的基底材料。     

Development of ZnO-based transparent conductive coatings

We have developed a range of single and multilayer transparent conducting coatings consisting of three to five alternating layers of Al-doped ZnO (AZO) and metals using E-beam evaporation method. The prepared optimized coatings show excellent optical and electrical properties, improved thermal and long-term stability. Optimum thickness of metal and AZO layers was determined for high optical transmittance and good electrical conductivity. X-ray diffraction, spectrophotometer, atomic-force microscopy, scanning electron microscopy and four-point probe were used to explore the possible changes in electrical and optical properties. It was found that the multilayer coatings consisting of Al-doped ZnO and Ag metal show satisfactory properties of low resistance of 5 Ω/sq, high transmittance of 90% and thermal stability up to 500 °C.     

Examination of minimum-heat-flux-point condition for film boiling on a sphere in terms of the limiting liquid superheat and the critical vapor film thickness

Previously proposed theories of the minimum-heat-flux-point (MHF-point) condition were examined using available experimental data obtained from the immersion cooling of spheres in water. The sphere diameter ranged from 9.5 to 30 mm and the liquid subcooling from 0 to 85 K. The limiting liquid superheat predicted by the Lienhard equation was compared with the liquid–solid interface superheat at the instant of liquid–solid contact at the MHF-point. The results showed that the liquid–solid interface superheat was not limited by the limiting liquid superheat and its value was connected with the collapse mode of vapor film. The collapse mode was a coherent collapse at a low interface superheat and the mode changed to a propagative collapse as the interface superheat increased. The critical vapor film thickness obtained from the linear stability analysis of vapor film was compared with the calculated value of average vapor film thickness at the MHF-point. For all data, the ratio of the average vapor film thickness to the critical vapor film thickness was correlated well as a function of liquid subcooling. The ratio decreased with increasing liquid subcooling and tended to about 0.8 to 1 depending on the experiments. This indicated that the MHF-point at a high liquid subcooling was determined by the critical vapor film thickness. A physical consideration was given to the effect of liquid–solid contact that occurred in the film boiling region on the calculated value of the vapor film thickness and the stability of vapor film.     

薄膜厚度对ZnO:Ti透明导电薄膜光电性能的影响

利用直流磁控溅射法在室温水冷玻璃衬底上制备出可见光透过率高、电阻率低的掺钛氧化锌(ZnO∶Ti)透明导电薄膜。SEM和XRD研究结果表明,ZnO∶Ti薄膜为六角纤锌矿结构的多晶薄膜,且具有c轴择优取向。讨论了薄膜厚度对掺钛氧化锌透明导电薄膜光学、电学性能的影响。当薄膜厚度为835nm时,薄膜具有最低电阻率3.34×10-4Ω.cm。所制备薄膜附着性能良好,在波长为500～800nm的可见光中平均透过率均超过91%,ZnO∶Ti薄膜可用作薄膜太阳电池和液晶显示器的透明电极。     

An experimental study of rupture dynamics of evaporating liquid films on different heater surfaces

Experimental data were obtained to reveal the complex dynamics of thin liquid films evaporating on heated horizontal surfaces, including formation and expansion of dry spots that occur after the liquid films decreased below critical thicknesses. The critical thickness of water film evaporating on various material surfaces is measured in the range of 60–150 μm, increasing with contact angle and heat flux while decreasing with thermal conductivity of the heater material. In the case of hexane evaporating on a titanium surface, the liquid film is found resilient to rupture, but starts oscillating as the averaged film thickness decreases below 15 μm.     

单缸机主轴承轴心轨迹的测量

介绍了采用电涡流传感器组成轴心轨迹测试系统。该系统可测量内燃机主轴承的油膜厚度、油膜温度、曲轴转角、转速、轴心轨迹和最小油膜厚度。在S195柴油机上进行了多工况的实测，分析了负荷对油膜厚度和轴心轨迹的影响。为了提高测量精度，采取了一系列有效的措施，并对测量结果进行了误差分析。