电力系统强迫功率振荡分析

电力系统中持续的周期性小扰动可能引起联络线的大幅度强迫功率振荡。本文通过特征分析方法，阐明了电力系统强迫功率振荡的机理，指出了这类强迫功率振荡与负阻尼低频振荡的不同，并介绍了１９９４年４月２６日南方互联电力系统“４．２６”事故的仿真结果。     

Nitrate ion effect on the passive film breakdown and current oscillations at iron surfaces polarized in chloride-containing sulfuric acid solutions

Current oscillatory phenomena have been used to study the effect of nitrates on pitting corrosion of passive iron surfaces in chloride-containing sulfuric acid solutions. From the quasi steady-state current-potential and potentiostatic current-time curves of the Fe | 0.75 M H₂SO₄+10 mM Cl⁻ system it is deduced that at lower potentials nitrates stimulate pitting acting as activators of the oxide dissolution. At higher potentials nitrates act as passivators causing a sudden passivation of Fe during a mass-transport controlled process across a salt film. Current oscillations appear over a wide potential region. The oscillation period as well as the induction period of time occurring before the onset of oscillation, both decrease by increasing the nitrate concentration. The effect of nitrates at lower and higher potentials is discussed in terms of the electrochemical and redox reactions of nitrate ions.     

ACOUSTIC STUDIES OF INTERFACIAL EFFECTS IN AIRLIFT REACTORS

Rational design of airlift reactors for the culture of plant and animal cells is impeded by a lack of understanding of the causes of loss of viability. Some recent speculations in the literature suggest that gas-liquid interfacial phenomena have played prominent roles in observed instances of loss of viability in both insect and animal cell cultures. The important interfacial events may include bubble formation and detachment at the sparger, bubble coalescence and breakage, and bubble disengagement at the free surface-entailing film thinning, film rupture, and film droplet ejection.

We have carried out an experimental investigation of interfacial phenomena using macrovideography and acoustic signals recorded at both the sparger and the free surface. Data have been collected for several liquid media including distilled water, distilled water with electrolyte (NaCl), and aqueous solutions of glycerol (μ = 3 to 9.5 cP). The studies were conducted in a 3-liter, acrylic plastic, split-column airlift reactor, and air was introduced through interchangeable sieve plates (with hole diameters of 1, 2, and 3 mm). Time-series data collected from the microphone were processed for mean and root-mean-square values, and Fourier transforms were computed to identify important signal energies. A sequence of experiments was also conducted that was designed to relate specific interfacial phenomena to the frequencies of the noises produced.     

电力系统强迫振荡的同心松弛现象分析

为快速准确定位电力系统强迫功率振荡扰动源,提出强迫振荡平均耗散功率分布的同心松弛规律.在强迫振荡等幅振荡阶段,将系统中的频率偏差和功率偏差用相量表示.通过相量运算,推导了耗散能量分布的2条准则:节点注入平均耗散功率和为0,支路首末端平均耗散功率近似相等.再考虑电网相对于故障所具有的放射式结构,得出了平均耗散功率分布的同心松弛规律.10机39节点仿真验证了这一规律.同心松弛规律将有助于制.定大电网强迫振荡扰动源快速定位策略,避免对扰动源的误判.     

横向剪切和旋转惯性影响下管道内流动液体的小振动

当考虑旋转惯性的影响时,流经管道横截面的液体在剪切作用下,会产生小振动.本文推导出无量纲参数表示的系统微分方程.对于某些问题的确定值,使用Galerkin方法,可以得到主振动频率和临界速度.在此基础上,还将研究结果和经典理论值进行了比较.     

Chaos and synchronisation in heterogeneous catalytic systems: CO oxidation over Pd zeolite catalysts

The influence of experimental parameters on the structure of global reaction rate oscillations and the coupling of local oscillators on a catalyst bed in a continuous stirred tank reactor is studied for the oxidation of CO on zeolite supported palladium catalysts. Global coupling can be achieved via mass transfer through the gas phase or via heat transfer in the case of a support of high heat conductivity. Characteristic differences in the activity of catalysts as well as in the period and the amplitude of the oscillations are related to the size of the palladium clusters and can be simulated by adding the state of the oxidation of the metal surface as a parameter to a common kinetic model. The analysis of observed chaotic behaviour leads to the conclusion that diffusional chaos characteristic of a distributed system is observed on the level of the zeolite crystallite that supports the palladium clusters.     

Infrared Evidence for the Existence of Nitrate Species on Cu-ZSM5 During Isothermal Rate Oscillations in the Decomposition of N2O

Isothermal oscillations in the rate of decomposition of N₂O were studied on an over-exchanged Cu-ZSM-5 catalyst by mass spectroscopy and in situ transient FTIR. Oscillations in the production of O₂ and N₂ were observed to occur in a temperature range of 410–490°C at a total pressure of 1.0 Torr pure N₂O. FTIR has provided the first spectroscopic evidence that surface nitrate species are present under oscillatory conditions. This study confirmed a previously proposed model that predicts a slow build-up of surface nitrates, followed by a rapid nitrate decomposition coupled with an increase in the rate of N₂O decomposition. The IR signature of the surface nitrates suggests they are monodentate nitrate species bound to Cu²⁺ ions. Temperature-programmed desorption studies reveal a strong correlation between the stability of the surface nitrate species and the temperature range in which oscillations occur.     

还原炉电极外套强制冷却装置的研究

分析了常用的还原炉电极外套强制冷却装置在技术上的不足,提出了新的强制冷却装置的设计方案。新的冷却装置在实际应用中取得了很好的效果,从而保证了多晶硅的产量和质量。     

Self‐sustained oscillations in opposed impinging jets in an enclosure

The flow of jets in confining enclosures has significant application in many engineering processes. In particular, the impingement of axisymmetric jets in a confined space has been examined using flow visualization, laser Doppler anemometry, and numerical simulations. Several flow regions were found; stable steady, regular oscillatory, and irregular oscillatory. Initially, a steady flow field existed for all arrangements for Re_d < ?90 (based on the nozzle diameter d, the fluid kinematic viscosity v and the volumetric flow rate Q through the nozzle (Q = πd²/4U_avg)) but subsequent increments in the fluid velocity caused a regularly oscillating flow field to emerge. The onset of the oscillations and the upper limit of finite oscillations were found to be a function of the Re_d, and the nozzle diameter to chamber dimension ratio. Steady numerical simulations predicted the steady flow field well and good agreement was obtained in unsteady simulations of the oscillating flow field. The oscillating flow field is considered to be a class of self‐sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances in the impingement region.     

Application of direct fluid flow oscillations to improve mixing in microbioreactors

This article describes an active mixing method for a microbioreactor that was designed, simulated, tested, and successfully implemented. By applying a varying pressure to a microchannel looping tangentially into a cylindrical microreactor an oscillating fluid flow was shown to occur. Such an oscillating fluid flow improved mixing, both by diffusion and convection. The oscillating fluid flow has a large impact on the ratio between the diffusion domain and the convection domain. A good match was obtained between experimental mixing results, computational fluid dynamics simulation results and the results of a simplified mixing model thus demonstrating the potential of simulation on improving the design of microreactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009