R1270/CO_2复叠式制冷系统热力学分析

针对R1270/CO_2复叠式制冷系统,通过能量及分析的方法,分析了低温级冷凝温度、系统蒸发温度、系统冷凝温度以及冷凝蒸发器传热温差对系统COP、损I和质量流量的影响。分析结果表明,在其他变量一定的条件下,存在确定的低温级冷凝温度使系统COP最大,总损最小;适当的升高系统蒸发温度和降低系统冷凝温度,以及减小冷凝蒸发器传热温差,可以增大系统COP和降低损;R1270高温级部件和冷凝蒸发器的损占总损比例较大,需对其进行重点优化。降低低温级冷凝温度和系统冷凝温度,提高系统蒸发温度可以减少系统中R1270的充注量。     

用于废热回收的开式吸收式热泵性能研究

本文提出了一种用于回收中低温高湿空气潜热的开式吸收式热泵系统,在设计工况下系统COP可达1.632,并能产生温度高于60℃的热水。通过对系统进行理论建模,分析了水蒸气吸收量、湿空气进气温度、换热器效率以及液气比对系统性能的影响。增加水蒸气吸收量、湿空气进气温度和溶液换热器效率均能提高系统COP。最后,讨论了冷却水流向布置对系统运行的影响,提出了防止溶液结晶的系统流程。     

CO2跨临界水-水热泵系统实验研究

对CO2跨临界水-水热泵系统进行研究,并搭建实验台进行测试:系统中添加回热器与否的两种情况下,通过改变蒸发温度、冷冻水的流量和温度、冷却水的流量和温度,测试系统的制热系数COPh和制冷系数COP。结果表明,蒸发温度升高,系统的COPh、COP也随之增加;而冷冻水流量增加,系统的COPh、COP增加不明显;增加回热器后随着冷冻水温度升高,系统COPh和COP上升趋势显著;冷却水流量增加对系统性能的影响很大;随着冷却水温度的升高,系统的换热量降低,导致系统的COPh和COP随之降低。通过以上实验证明在相同的工况下,添加回热器可提高系统的性能。     

带引射器的R744/R717复叠式制冷系统的热力学分析

在R744/R717复叠式制冷系统中加入了引射器来回收膨胀功,并根据热力学第一定律建立分析模型。研究了中间冷凝温度、冷凝温度、蒸发温度和引射器组件效率对COP的影响。发现存在一个最佳中间冷凝温度使得系统COP达到最大值;在给定的条件下,与传统的复叠式制冷系统相比,带引射器的复叠式制冷系统的COP提高了6.4%~7.8%,并且引射器组件的效率越高,制冷系统的COP提升越明显。     

复叠式制冷系统性能的模拟分析

为提高制冷系统运行性能、优化系统结构设计,用EES软件对可实现复叠与双级压缩转换的制冷系统进行模拟分析,分析对比了复叠循环与双级压缩循环、级间容量比及高温级频率对复叠循环的影响。结果表明:蒸发温度对复叠循环和双级压缩循环系统COP的影响都很大,且蒸发温度较低工况下,应选用复叠循环以提高系统COP。对于复叠循环:蒸发温度和冷凝温度一定,随级间容量比的增加,复叠式制冷系统的中间温度降低,级间容量比与冷凝温度一定,蒸发温度每上升1℃,系统的中间温度增加1.5℃;当工况一定时,系统COP随级间容量比的增加呈现出先增大后减小的变化趋势,故对于固定工况下的复叠式制冷系统存在一个使系统COP最优的级间容量比;随高温级频率增大,系统的级间容量比减小,系统的COP先增大后缓慢减小,在达到最佳COP后,系统运行稳定。     

准二级压缩热泵热水机低温工况COP分析

对准二级压缩热泵热水机进行建模,通过计算分析得到系统COP在低温工况下与内压比、水温的关系。得到了只有当水温超过一定温度时,喷气运行才具有较高的COP;而环境温度越低、水温越高时,内压比越高的压缩机具有较高的COP。     

带回热器的跨临界CO2两相流引射制冷系统性能实验研究

对带和不带回热器(IHX)的跨临界二氧化碳两相引射制冷系统进行了实验研究,主要分析了回热器、实验工况、引射器尺寸参数对系统性能的影响。结果表明:对于固定的气冷器出口温度、不同的气冷器压力工况,回热器的使用可使系统制冷量提高0.85%-8.60%,COP提高0.88%-11.7%;对于固定的气冷器压力,在不同的气冷器出口温度条件下,其制冷量可提高1.14%-2.92%,COP可提高0.99%-2.75%;在气冷器压力较低及出口温度较高的工况条件下,回热器对系统性能影响较大,系统COP及制冷量的最大改善均发生在上述工况条件下;喷嘴直径与引射器混合室长度之间存在一个最优匹配,两者的最优匹配能使系统COP大大提高。     

低温空气制冷速冻系统性能的实验研究

对使用空气动压轴承的升压式空气制冷速冻系统进行了实验研究,分析了压气机进口压力、散热器冷边风量及回热器对系统性能的影响。实验结果表明:增大压气机进口压力和散热器冷边空气流量均可降低涡轮出口温度,提高系统制冷量;系统COP随着压气机进口压力的升高而增大,但是增大幅度逐渐减少;系统增加回热器后,涡轮出口温度最多可降低约67%,系统制冷量和COP最多约可增加45.5%,其中涡轮出口温度最低约可降至-50℃,系统COP最大可达0.7左右。     

吸附式制冷的动态特性分析

以非平衡吸附模型为基础,计算了加热流体温度变化时,系统的性能系数COP以及单位质量吸附剂制冷功率SCP随时间的变化,结果表明加热流体温度变化对系统COP和SCP值有很大影响,并且影响相对滞后于加热流体温度的变化.计算结果也表明对于两吸附床的吸附式制冷系统,在稳定运行时,由于吸附床温度、吸附量不断变化、循环周期较长及封闭期影响,其瞬时性能也是不稳定的,如果采用三床交替循环,则可有效改善其瞬时性能的稳定性.     

NH_3/CO_2复叠式制冷循环系统的热力性能分析

为研究NH_3/CO_2复叠式制冷系统的热力性能,寻求最佳的运行参数,建立了NH_3/CO_2复叠式制冷循环数学模型,并对系统的运行参数进行了理论计算。基于计算数据,对低温端蒸发温度、冷凝蒸发器内传热温差、低温端冷凝温度及高低端质量流量与COP的相关性进行了分析,讨论了这些参数对COP的影响。研究结果表明:低温端蒸发温度、冷凝蒸发器内传热温差及高低端质量流量与COP存在显著相关性。     

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.