组合式吸液芯内液汽相变过程的数值模拟

本文对高温热管吸液芯多孔介质内金属钠液的液汽相变过程进行了模拟研究,并采用流体体积分数模型和传质模型对此过程进行了数值分析.研究表明孔隙率和渗透率越大的组合式吸液芯多孔介质,热量在液态金属中的传递速率越快,进而可以增加高温热管的传热量,提高传热效率;但是孔隙率和渗透率越大,组合式吸液芯多孔介质加热壁面的温度分布越不均匀,产生沸腾传热极限的可能性亦越大.     

非饱和多孔介质内毛细驱动流动分析

将非饱和含湿多孔介质层内液体饱和度当量为无量纲的液层厚度,在多孔层内发生相变时其分布规律直观地反映相变传热能力从而预示临界热流(CHF)的发生.计算结果显示,多孔层中心处最容易出现干涸而导致CHF;残余饱和度和孔隙率越大,越不容易出现CHF;饱和度分布形状(液层形状)主要受输入热流密度和孔隙率的影响,热流越小、孔隙率越大就越平缓.     

多孔介质内溶解与沉淀过程的格子Boltzmann方法模拟

本文采用格子Boltzmann方法模拟了多孔介质内的溶解和沉淀现象, 并分析了雷诺数、施密特数、达姆科勒数对多孔介质孔隙结构及浓度分布的影响. 结果表明: 对于多孔介质内的溶解(沉淀)过程, 当雷诺数越大时, 孔隙率越大(小), 平均浓度值越小(大); 当达姆科勒数或施密特数较小时, 溶解和沉淀过程均受反应控制, 此时反应在多孔介质的固体表面较为均匀的发生; 当达姆科勒数或施密特数较大时, 溶解和沉淀过程均受扩散控制, 此时反应主要发生在上游及大孔隙区域.     

颗粒堆积多孔介质干燥多尺度多层结构传热传质模型及模拟

针对骨架颗粒的多层物理结构问题,运用孔道网络方法、热质传递原理和多尺度理论等知识,建立了颗粒堆积多孔介质干燥的多尺度多层结构传热传质模型。以稻谷堆为典型代表进行热风干燥试验验证,模拟分析了颗粒内部不同组织物理特性等因素对干燥过程的影响。结果表明:建立的模型可有效模拟稻谷堆干燥过程;稻谷颗粒内存在较大的水分梯度。胚扩散系数对干燥过程的影响十分显著,其次是壳扩散系数,衣扩散系数影响最小;较小的胚扩散系数可将湿分有效地"囚禁"在胚内。     

具有树形流道双孔隙率多孔介质渗流特性研究

设计具有合适孔道结构的吸附剂能有效提高吸附过程的效率。本文根据构形理论将树形流道嵌入到多孔介质基质中,构建了高渗透率的双孔隙率多孔介质。计算了树形流道内的无量纲压降分布、流道体积分数和渗透率随分叉级数的变化趋势。并利用双孔隙率多孔介质渗流模型计算了该多孔介质的有效渗透率。与并列直管道相比,树形流道在较大的分叉级数下具有更小的压降;树形流道的嵌入能够有效提高多孔介质的有效渗透率。     

考虑吸附效应的多孔介质热风干燥研究

本文基于Whitaker体积平均理论建立了多孔介质热风干燥的理论模型,结合隐式有限差分法对其进行了离散求解,在处理方程的非线性效应时采用了预估-校正算法。模拟得到了湿含量随干燥时间的变化,并与文献中实验结果做了比较,二者吻合较好,验证了模型的可靠性。模拟了干燥过程中温度、液相饱和度等参数随干燥时间的变化,研究分析了固体骨架的吸附效应对干燥过程的影响。     

泡沫陶瓷内火焰分布的ECT可视化研究

本文运用电容层析成像(ECT)方法,以非侵入的方式,对多孔介质燃烧中的火焰分布进行可视化测量.针对高孔隙率泡沫陶瓷(8PPI)的孔隙结构特点,提出了一种"十字架形"几何结构模型,用丁泡沫型多孔介质内甲烷-空气预混燃烧的二维数值模拟.ECT成像结果与数值模拟结果吻合,显示了两个不同学科信息的融合性和互验性.     

基于格子Boltzmann大密度比模型的多孔介质内气泡动力学行为数值模拟

基于格子Boltzmann两相流大密度模型,研究气泡穿过多孔介质的动力学行为.研究发现:当孔隙率较大时,气泡只变形不破裂,能完整地通过多孔介质;而孔隙率较小时,气泡变形更加剧烈且发生破裂,穿过多孔介质所需的时间更长.另外,当障碍物表面接触角(θ)较小时,气泡均能完整地通过多孔介质,随着接触角的增大,气泡开始发生破裂,且...     

多组分气体在多孔介质中扩散过程的数值模拟

通过对已有的多组分气体在多孔介质中的扩散模型与实验结果对比,发现尘气模型(DGM)与实验结果吻合较好,并利用该模型对CH_4/O_2/N_2三元混合气体在不同孔径的多孔介质内扩散过程进行了数值模拟,分析了扩散与对流两种机理在有/无压差下对扩散通量的影响,对比分析了干燥和含水非饱和多孔介质中的扩散过程.结果表明在无压差的扩散过程中也存在对流;气体的扩散速度随孔径的减小先增大后减小;含水非饱和多孔介质中扩散速度减弱。     

纳米多孔氩薄膜热导率的分子动力学模拟

利用经典的Lennard-Jones势能模型,采用分子动力学模拟方法研究纳米多孔氩薄膜热导率.结果表明,纳米多孔氩薄膜热导率明显小于同温度下纯纳米氩薄膜热导率,并且孔隙率越大热导率减小越多.借助基于并联方法的有效热导率模型,对纳米多孔氩薄膜的热导率随孔隙率的变化进行解释.模拟结果还发现,薄膜内的多孔分布对薄膜的热导率有影响.     

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.