Electrostatic actuation of liquid droplets for micro-reactorapplications

A device for the electrostatic transport and manipulation of liquid droplets on a solid surface is described. Arrays of microelectrodes are fabricated on a substrate, which is covered by a hydrophobic layer. Water droplets, typically a microliter in volume, take spherical shape on the surface and are caused to move by switching the voltage applied to the electrode array. The transport of droplets, deflection of a droplet in either of the bifurcating paths, and the mixing of two droplets by coalescence are experimentally demonstrated. The device can be used for microchemical reactors where transport, sorting and mixing of reagents constitute basic unit operation     

Atmospheric pressure discharge plasma decomposition for gaseous aircontaminants-trichlorotrifluoroethane and trichloroethylene

The decomposition performance of gaseous environmental destructive contaminants in air by using atmospheric pressure discharge plasma including the surface discharge induced plasma chemical processing (SPCP) was examined. The main contaminants tested were chlorofluorocarbon (CFC-113) and trichloroethylene, typically. The discharge exciting frequency range studied was wide-50 Hz to 50 kHz. Results showed the low frequency discharge requires high voltage to inject high electric power in the gas and to decompose the contaminants. A gas chromatograph mass spectrometer was used to analyze discharge products of dense CFC-113 or trichloroethylene. Among the detected products were HCl, CCIFO, and CHCl₃. Two different electrode configurations; the silent discharge (coaxial) electrode and the coil-electrode were also tested and compared to each other as a gas reactor     

Charge limits in corona charging of distorted liquid droplets

The efficiency of electrostatic painting depends strongly on the amount of charge on a single paint droplet. The saturation corona charging for a spherical droplet has been theoretically estimated by Pauthenier. However, in many industrial and agricultural applications, the droplets being charged become substantially distorted. The results of numerical estimations of the charge limit, due to a DC corona discharge, on conducting droplets distorted by an electric field are presented. The finite-element method (FEM) and the separation-of-variables method for the Laplace equation have been used as modeling tools. In general it is found that a distorted droplet can exceed the Pauthenier charge limit     

Formation of uniformly sized liquid droplets using spinning diskunder applied electrostatic field

A rotating multinozzle system that utilizes an applied AC potential combined with a DC bias to produce a large number of uniformly sized droplets synchronously with the applied AC frequency is proposed. A three-step experimental investigation is reported. The operational parameters were determined using a stationary single nozzle. Finally, using a rotating multinozzle system with 100 nozzles, a large number of uniform droplets was produced, and the uniformity was checked with a particle analyzer using the immersion sampling method. It was found that the synchronous region of the stationary single nozzle coincided with that of the rotating single nozzle (both nozzles had the same diameter and length). Therefore, one can predict the correct operational parameters for the rotating nozzle system from the results obtained in the stationary nozzle experiment (which are much easier to obtain). Uniformly sized droplets can be produced synchronously with an applied AC frequency using rotating nozzles. The operational parameters for the rotating single and multinozzles are almost the same     

Propagation characteristics of impulse creepage discharge in perfluorocarbon liquid

In this paper, the propagation characteristics of a creepage discharge on the surface of a solid insulator with a back electrode in perfluorocarbon liquid under an impulse voltage application are investigated. The propagation process is observed in detail by means of a high‐speed schlieren optical technique, and simultaneously waveforms of a current and a charge are also measured. Consequently, the polarity effect of the streamer propagation and the positive streamer which propagates stepwise can be seen. The latter is concurrent with the sparse current pulse which corresponds to the charge step‐variation. These results are compared with ones obtained in transformer oil. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 19–28, 2000     

发电厂零排放工艺的新成就

美国 750 MW High Dessert电力工程项目将于 2 0 0 3年 7月投产。这将是南加州 1 0多年来第一个主要发电厂建设项目 ,也是第一个使用微过滤 ( microfiltratin,MF)—反渗透技术的零排放( ZLD,zeroliquid discharge)处理的电厂。水源匮乏以及对用电的急剧需求是采用零排放处理的主要原因。该工程的一次补给水源来自加州水渠( California Aquaduct) ,备用水源为地下水 ,通过一蓄水层筑堤系统送入电厂。1　零排放处理系统该系统包含 5个子系统 :( 1 )预处理系统澄清和过滤除去悬浮物和细菌 ,并对冷却水补充水、蒸汽循环的补给水、燃机冷却…     

Formation of liquid film downstream of an atomizer and its disintegration in gaseous medium

Results from experimental and calculation studies of liquid film downstream of a dual-orifice centrifugal atomizer are presented. It is revealed that film generated downstream of an atomizer with a specified geometry may exist in different forms, which depend only on the liquid flow rate.     

Onset voltage for corona pulses in gaseous Ar under high pressureand in liquid Ar

HV, applied to a point cathode (radius of curvature ~1 to ~8 μm) in a nonpolar liquid, brings about a regular current pulse regime above a threshold value V_s. This regime is similar to the Trichel pulse regime for corona in air. We present results of an investigation of this threshold voltage V_s in argon over a wide range of densities. In gaseous argon, the V_s(P) values increase with pressure. In the liquid, V_s is independent of external pressure. The results show that V_s is mainly a function of fluid density N and cathode tip radius τ_p. The theoretical analysis of the phenomenon is carried out according to the criterion ∫α(x)dx constant, where a(x) is the Townsend ionization coefficient. It is shown that if the dependence of V_s on N for low density gas is extrapolated into the region of liquid densities, it greatly exceeds the experimental values. The dependence of V_s on the fluid number density ~ is derived. Its variation is found to be non-monotonic at very high N values     

Influence of bulk dielectric polarization upon partial discharge transients: effect of void geometry and orientation

The induced charge arising from a partial discharge consists of 2 components. One is associated with the actual space charge in the void. The other is related to changes in the polarization of the bulk dielectric. These changes are a direct consequence of the field produced by the space charge. The influence of the void geometry upon the polarization component of the induced charge is examined for a heterogeneous bulk dielectric system. It is demonstrated that, depending on the ratio of the dielectric permittivities and within which dielectric the void is located, the relative magnitude of this component may increase or decrease. The magnitude of this effect is also strongly dependent upon the prolateness/oblateness of the void geometry, and on the orientation of the void with respect to the detecting electrode.     

肌肉电导率对人体通信信号传输的影响

肌肉组织具有良好的电导率且占据人体较大体积,研究肌肉电导率在人体通信中的作用,有助于掌握电流耦合信号传输特性,提高人体建模的准确性。采用有限元法建立电流耦合信号在肢体传输的准静态场模型,研究不同频率下肌肉电导率的变化引起各组织层总电流密度分布的变化,重点分析肌肉各向异性电导率对耦合电流信号传输的影响,最后通过实验测量验证有限元模型。结果表明,超过64%的电流信号流经肌肉层,并且肌肉电导率越大流经肌肉层的电流越多;在1 kHz~1 MHz范围内,肌肉各向异性电导率对人体信号传输有较大影响;考虑肌肉电导率各向异性的模型更接近人体实验结果。     

Effects of laboratory access modes upon learning outcomes

The Web was first used as a telecontrol medium in 1994. In recent times, Web-based telecontrol is being used as an educational option, providing students with remote access to laboratory hardware. The literature reporting the initial studies into telelaboratories speaks of encouraging responses from students, but very little literature actually addresses the quality of learning outcomes from this alternative access mode. A recent comparative study at the Department of Mechanical and Manufacturing Engineering at the University of Melbourne, Melbourne, Australia, randomly allocated a cohort of third-year students to one of three separate access modes-proximal, Web-based remote, or simulation-to perform the same laboratory class. A range of tools were used to measure the students' learning outcomes and their perceptions of the class. Statistically significant differences were found between the groups in their learning outcomes, students' perceptions of the laboratory class, and the ways in which they engage the learning experience.     

某电厂废水零排放系统污堵分析

某电厂采用“两级软化澄清+介质过滤+超滤+纳滤+反渗透”组合工艺处理循环水排污水,采用“化学软化+管式微滤+纳滤+海水淡化反渗透+电渗析+蒸发结晶”组合工艺处理末端废水,以实现全厂废水“零排放”。工程投运1年后,循环水处理系统出现纳滤出力不足,末端废水处理系统存在微滤膜有机污堵严重、电渗析硅结垢等问题。分析了膜污堵原因,对脱硫工艺用水进行了优化,从源头降低了脱硫废水化学需氧量（COD）;同时优化了微滤运行方式,从而减缓了微滤有机污堵现象;此外,调整了循环水反渗透浓水处理方式,将全硅质量浓度降至1 mg/L以下后再进入电渗析设备,解决了电渗析硅结垢的问题。     

Hot electron phenomena in liquid and gaseous Ar and N2in divergent electric fields

A comparative study of electrical conduction and emitted light in an atomic (Ar) and a molecular liquid (N₂) is presented as a function of various parameters. From the spectroscopic analysis of emitted light (in the range 200 to 850 nm), the energy of the hot electrons in these liquids may be measured. A simultaneous study was carried out on dense gases as a function of the applied pressure. We discuss the electron swarm parameters deduced from these results, in an attempt to explain the behavior of electrons in the gas-liquid phase transition     

Effects of temperature and impurities on the DC conductivity of snow

Several major parameters affecting the electrical behavior of natural snow, namely volume conductivity and density, liquid water content and conductivity of water melted from snow, are crucial for the characterization of the electrical performance of snow-covered HV insulators. However, little study has been devoted to this subject, despite of its importance. These parameters are found to vary significantly with snow composition and purity as well as with other parameters, such as temperature, airborne pollutants, electric field strength and polarity. From laboratory experiments carried out on a large number of snow samples, it was found that DC conductivity of snow shows a peak at about -2degC. This apparently curious behavior near the melting temperature is attributed to important changes to the microstructure of snow. A correlation between DC conductivity and snow temperature was established