高质量流速下立式螺旋管内汽液两相传热特性研究

对高质量流速下立式螺旋管内高压汽液两相流沸腾传热特性进行了试验研究,参数范围为:系统压力8.0～15.0MPa;质量流速2500～4000kg/m2s;壁面热流密度200～1000kW/m2;实验段为Φ14的不锈钢管弯制而成的螺旋管直径比为D/d=30.1的管圈,总长为2.335m,考察了热流密度和质量流速对两相传热的影响,分析核态沸腾和两相强制对流沸腾机理在螺旋管内两相传热中所起的作用,得到了局部传热系数的分布特性和平均传热系数计算关联式,首次发现高质量流速区域内螺旋管内汽液两相传热效果亦趋近于相同条件下直管内的换热系数,并对已有的结论进行了分类比较分析.     

螺旋管内高压汽水两相流不稳定性试验研究

本文在3—10MPa压力范围内,对内径为12mm的立式上升流动螺旋管内高压汽水两相流不稳定性进行了试验研究,得到了不稳定性的脉动曲线和各参数的影响以及预报系统稳定性的界限图,给出了依据系统参数预报稳定性的关系式。     

三维微肋螺旋管内流动沸腾流型与传热性能

采用三维微肋螺旋管进行了制冷剂R134a在管内的流动沸腾传热与流型可视化实验。随着流量和干度的变化,流型可划分为泡状流、塞状流、分层波状流、间歇流以及环状流。在Taitel-Dukler流型图上给出了流型的分区及其转变曲线,讨论了螺旋管内两相流动流型转变的特性。传热实验揭示了质量流量、热流密度及蒸汽干度对传热性能的影响,三维微肋螺旋管的强化因子为1.5-2.1。     

自然循环加热段内摩擦阻力及对流传热的实验研究

以常压去离子水为工质,对自然循环工况下上升加热段内单相水的摩擦阻力及对流传热特性进行了实验研究.结果表明,自然循环工况下加热段内由浮升力引起的自由流动对摩擦阻力及对流传热特性有重要影响,自然循环与强制循环二种工况下加热段内的摩阻系数及对流换热系数存在明显差别;并且,自然循环工况下加热段内的摩擦阻力存在滞后现象.通过实验提出了计算自然循环工况下加热段内单相水的摩阻系数及对流换热系数的经验关系式.     

螺旋管内超临界氮的对流换热研究

在内径为2mm曲率为0.057的螺旋管内进行了超临界氮的对流换热实验,研究探讨了螺旋管入口温度、壁面热流密度对沿程壁面温度分布以及平均换热系数的影响,与前人关于螺旋管内常规流体流动换热的平均Nu的经验关系式进行了比较。并基于FLUENT软件进行了数值计算,并与实验结果进行了比较。分析表明,数值计算对壁面温度的预测有一定的适用性。     

螺旋管分离器中液固两相流颗粒相分布研究

螺旋管分离器是一种高效低阻的新型液固/气液固分离装置,研究分离器内部相分布特征及影响因素具有重要意义。本文利用Malvern粒度仪和观察窗技术测量了分离器模型中水-砂两相流动的颗粒浓度和粒度分布,并且对具有相似结构和流动参数的平面组合方管液固两相流动进行了数值模拟。研究表明颗粒相分布是离心力、二次流和紊流扩散的综合结果:离心力使颗粒由内弯侧向外弯侧聚集,是实现分离的根本动力,颗粒越大,分离现象越显著;二次流对分离具有双重作用;紊流扩散不利于分离。液速越高,分离效果越好。颗粒平均浓度对浓度分布没有显著影响。     

垂直环管内紊流同向混合对流放热过程试验研究

带有椭圆端头的插入管式换热元件(图1)广泛地应用在各种高热负荷换热设备中,其内外管尺寸d、D与内管下端口到端头的距离H间的配合,严重地影响端头内工作流体的流动及其放热过程。在环隙中,向上流动的流体因受热而产生的自然对流与强迫对流叠加的现象称为混合对流。此时粘性力、惯性力及重力(热力浮升力)共同起作用,影响环形流道内流速分布、外管内壁面处切应力分布以及紊流迁移特性等,从而影响放热     

同时确定换热器管内介质放热系数和污垢系数的经验方法

本文在实验研究的基础上,提出了一种可以通过实验数据的整理,同时确定煤加压制气废热换热器内含有高压不凝性气体的水蒸汽管内强制对流凝结放热系数及焦油污垢系数的经验方法,方法正确可靠,可应用于工程设计。     

螺旋管内高压汽水两相流动沸腾干涸点的研究

在较宽的实验参数范围内(系统压力P=8～15 MPa,质量流速G=800～1800 kg·m~(-2)·s~(-1),壁面热流密度q_w=200～950 kW·m~(-2))对一立式螺旋管内(管内径为10 mm,螺旋直径为300 mm,节距为50 mm)汽水两相流动沸腾干涸特性进行了实验研究。通过研究,获得了干涸发生时螺旋管圈壁温的分布特征以及压力、质量流速和壁面热流密度这三个参数对临界干度的影响规律。同时在实验数据的基础上,提出了一个适用于计算螺旋管内高压高含汽率工况下汽水两相流临界干度的经验关系式。     

立式螺旋管内气液两相向下流动的流型及转变特性

本文对低压水-空气两相流动在立式螺旋管内向下流动的流型及其转变特性进行了实验和理论研究.流型的判定是用直接观察和电容探针法来进行的.根据实验结果系统地作出了曲率半径为114、228、475mm,管内径为19mm.的三种管圈的流型图;根据力平衡原理,从连续流动介质中不相溶离散相的形状变化及其运动的稳定性出发,建立了分散泡状流转变和环状流转变的理论模型,在实验基础上得到了半经验的转变判别方程.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.