一种HCFC-22新型替代制冷剂的实验研究

本文提出采用三元混合工质HFC—161/HFC-125/HFC-32作为HCFC-22替代制冷剂。在空气-水热泵实验台上对该工质及HCFC-22、 R407C进行对比实验,结果表明,在不改动任何系统部件的前提下,该新型制冷剂的COP值大于HCFC-22主要替代制冷剂R407C,在较高的进风温度或较低的进水温度下, COP值接近甚至大于HCFC-22。此外,该三元混合物还具有GWP值小、排气温度低、温度滑移小的优点,是HCFC-22一种有前途的替代物。     

R410A替代R22制冷系统的实验与分析

一个特别设计的高精度实验台,可用于不同制冷剂在同一工况下的性能测试及同一制冷剂在不同工况下的性能测试.本文在此实验台上分别对以R22、R410A为制冷工质的制冷系统在20种工况下进行了系统的实验研究,并建立了该实际循环的稳态模型,对R410A及R22系统在同一工况下的性能进行了比较,给出了R410A系统及R22系统性能上的差异.     

适用于高温工况替代制冷剂系统特性实验研究

以替代传统高温工况(T3)制冷剂R22为背景,选取现阶段最有潜力的替代制冷剂R410A、R290和R32进行灌注式替代测试,发现随着温度升高,R22具有最大能力,R290具有最高能效,而R410A和R32性能将快速衰减。     

饱和液体密度测量装置的研制与可靠性验证

本文研制了一种用于测量制冷剂饱和液体密度的实验装置,该装置主要由恒温系统与测量系统组成,其中密度的测量精度为±0.5 kg/m~3。本文以纯质制冷剂HCFC-22与混合制冷剂HFC-407C为例分别在该实验装置进行了实验测试。结果表明,无论是纯质还是混合制冷剂的液体密度实验测量结果都与文献值具有良好的一致性。在此基础上,本文还用该实验装置对HFC-407C在温度为244～337K范围内的饱和液体密度进行更细致而又精确的测量,并分别采用VDNS型方程与Rackett型方程对HFC-407C实验数据进行了关联,得到各自的方程参数及适用下HFC-407C的预测模型。所有这些研究为纯质与混合工质在实际工程中的应用打下了坚实的基础。     

R134a、R410a和R1234yf双级热泵性能对比

针对一级节流中间完全冷却双级压缩系统,建立了能量方程并编制了程序,对R134a、R410a和R1234yf热泵系统压缩机排气温度、性能COP、压缩机耗功和■损失等进行了对比。结果表明:在环境温度为-25℃时,R1234yf的制热COP可达到1.766,仅比R134a和R410a约低4%和2.9%,低压级压缩机耗功分别比R134a和R410a约低18%和20%;高压级压缩机耗功分别比R134a和R410a约低21%和22%。在一定程度上,R1234yf制冷剂可作为R134a和R410a的替代工质。     

船舶冷库制冷剂替代及性能比较

寻求性能相近且环保的制冷剂取代对臭氧层有破坏作用的制冷剂R22,已成为船舶制冷装置所面临的紧迫、重要课题。文中选择R404A、R407C和R407F作为船舶制冷剂R22的替代品,分析了其制冷特性,并基于船舶冷库制冷装置上,对四种制冷剂进行了特性对比试验,比较了压缩机吸排气温度、压力、制冷性能等。结果显示,在试验工况下,R407F可作为R22的理想制冷剂替代品。文章为船舶制冷剂替代的选择提供技术支持。     

利用P-R方程推算替代制冷剂的绝热指数

应用P-R方程编制了容积绝热指数与温度绝热指数的计算程序,利用该程序计算了HFC-161,HC-290,HC-600a的绝热指数,绘出了三种制冷剂的容积绝热指数与温度绝热指数随对比压力与对比温度变化的图线,并加以对比与分析。结果表明,HC-600a的两种绝热指数值都较小,在压缩机进出口条件一致的状况下,较适于作为替代制冷剂。     

R410A和R22在水平内螺纹管内冷凝性能的实验研究

实验研究了环保替代制冷工质R410A和R22在冷凝温度40℃时在内螺纹强化管(外径为9.52mm)内的冷凝换热特性,对二者的冷凝换热性能进行了对比,并研究了测试管外冷却水流量对换热系数的影响。结果表明:在管外冷却水流量相同时,R22的总换热系数K普遍比R410a小,而管内传热系数hr比R410A大。R22与R410A的总传热系数K均随管外冷却水流量的增加而增加,当制冷剂流量Gm大于300kg.s-1.m-2时,管外冷却水流量对总传热系数K的影响变小。     

HFC32/HFO1234ze二元混合工质的热物性模型

在实验数据基础上,建立了适用于HFC32/HFO1234ze二元混合工质的PR方程模型,并对实验数据、模型计算结果和Refprop 9.0计算结果进行了比较分析;作出了定温度下泡、露点压力随混合比的变化关系图以及定压力下饱和温度随混合比的变化关系图,分析得出HFC32/HFO1234ze二元混合工质属于非共沸工质,存在温度滑移,500 kPa压力下混合物在0.27/0.75处温度滑移达到最大为12.7℃;选取状态参考点后,作出了不同混合比下的混合工质的logP-h图,得出了随混合比变化混合工质的热力学性质的变化趋势,为系统的设计提供基本的热力学数据;最后,以R410A循环性能为基准,对不同混合比下混合工质的"相对循环性能"(COP_(mix)/COP_(R410A))进行了分析,为家用空调制冷剂的替代和系统的优化提供方向。     

北洋2#制冷剂循环性能试验研究

研究了一种双元混合物——北洋2#,它具有优于R22的环保性能和良好的循环性能。在同机型标准空调工况下检测,其性能(COP)较R22低1.7%,但其制冷量较R22高14.6%;其COP较R410A和R32均高8%。在低温区的检测试验证明:其COP稍低于R22,但是其能达到比R22更低的温度。并且北洋2#的制冷速度比R22快35.9%。所以,北洋2#可以作为R22有潜力的替代制冷剂。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.