Direct initiation of detonation in cryogenic gaseous H2-O2 mixtures

Critical conditions for the direct initiation of self-sustained detonation in cryogenic hydrogen-oxygen mixtures are examined experimentally. These initial conditions are expected to depend mainly on four parameters: the equivalence ratio of the mixture, the amount of the initial energy deposition, the initial temperature and pressure of the mixture. These critical conditions are determined by fixing alternatively three of these parameters and varying the fourth one from subcritical to supercritical detonation conditions. Results are presented for initial pressuresP _o and equivalence ratios ranging from 0.3 to 1 bar and from 1 to 2 respectively, for the two initial temperaturesT _o, 123 K and 293 K. These results indicate that for the lowest values of the initial pressure, a decrease of initial temperature may favour the onset of detonation. Whatever the initial conditions, the measured detonation pressures and velocities are in reasonably good agreement with the corresponding Chapman-Jouguet values computed using the ideal-gas equation of state.     

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry

It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K, Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. In this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. The particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. The pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25 J cm⁻²). The plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 μs, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 μm. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity.     

Optical characteristics of one-dimensional photonic crystals composed of high-aspect-ratio Si walls fabricated on V-grooved wafer

We demonstrate optical properties of one-dimensional photonic crystals (PC), which are fabricated using high-aspect-ratio etching on a V-grooved silicon wafer. The measured transmission spectrum has an obvious band gap; the suppression is over 30 dB. The quite small insertion loss of 1.9 dB is achieved by induced coupled plasma (ICP) cryogenic etching and direct coupling to the optical fiber aligned in the V-groove. We also successfully observed peaks originating from a localized cavity mode. Such a microcavity enables control of the light, which qualifies photonic crystal as a fundamental structure of optical functional devices. These results lead to achievement of integrated Si-based photonic circuits.     

扁平绕带式低温高压容器绝热性能分析和计算

扁平绕带式低温高压容器是一种新型低温液体贮存设备 ,由内外两层容器组成 ,内筒体的外壁焊有液氮预冷夹套。平均蒸发率是衡量扁平绕带式低温高压容器绝热性能的重要指标。文中在分析其传热过程和壁厚温差影响因素的基础上 ,提出了一种计算其蒸发率的工程方法 ,并结合1 0 m3液氢储罐设计实例进行了计算。结果表明扁平绕带式低温高压容器具有良好的绝热性能 ,适用于重要介质的低温贮运     

30M-35kV/2000A高温超导电缆制冷系统

本文介绍了我国新研制成的首条并网运行的热绝缘型30M-35KV/2000A高温超导电缆制冷系统。该制冷系统主要有液氮泵箱、过冷箱、高真空输液管道、液氮贮槽、辅助减压抽空系统、泵箱及气动阀门供气系统、监控系统所组成。冷却方式是过冷液氮循环,制冷方式是G-M制冷机和减压抽空(备用)。给出了制冷系统的运行结果。     

空间应用的低温工质

介绍了低温流体在低温低压近临界区以及稀薄状态下的特殊性质,并详细介绍了几种低温工质的特点以及它们在空间技术中的应用。     

EAST低温系统又一新降温模式

EAST氦低温系统是EAST(Experimental Advanced Super-conducting Tokamak)先进超导托卡马克实验装置重要子系统之一;到目前为止,EAST已经成功进行了6次降温实验。第四次降温实验于2008年8月完成,这次降温实验与前几次降温实验很不相同。前3次的降温实验冷却磁体依赖四台透平膨胀机(透平A、B、C和D),透平B、C和D获得LHe去冷却PF和TF磁体、5&8对电流引线和busline到相应的温度。透平A用于制取80K的冷量冷却外冷屏。而此次降温是采用3台透平膨胀机(透平A、B和C),透平B和C与节流阀获得LHe去冷却PF和TF磁体、5&8对电流引线和busline到相应的温度。透平A还是用于制取80K的冷量冷却外冷屏。此次整个降温过程大概用了20天,比以前多耗时25%;文中给出了透平的启动过程、磁体冷却过程和一些操作经验。     

S波段低温低噪声放大器

中介绍了S波段低温低噪声放大器的研制.在15K左右的环境温度下,300MHz带宽内,实测放大器的等效噪声温度≤4.6K,增益≥35dB,增益平坦度≤1.0clB,输入、输出回波损耗≤-20dB.它已经成功运用于射电天文等领域.