Electrical environment surrounding microbes exposed to pulsedelectric fields

Inactivation of microbes by the application of intense pulsed electric fields (≃10 to 40 kV/cm) could result in low-temperature pasteurization of liquid foods. Advantages over conventional heat pasteurization include longer shelf-life, better flavor, and less enzyme damage. Numerical modeling of electrical parameters near the microbe during exposure to these intense electric fields is described. The continuity equation describes movement of positive and negative ions while Gauss's law yields the electric field after movement of the ions. One negative ionic species and one positive ionic species are assumed to be in the suspension fluid and protoplasm of the microbe. The microbe membrane is modeled as a nonconducting dielectric. With application of unidirectional electric fields, free volume and free surface charge densities form along the membrane. Comparison is made with a uniform conductivity model and it is shown that significant differences exist in parameters such as ion concentration, free surface charge density, free volume charge density, heat sources due to conduction current, and ionic injection at membrane surfaces     

Inactivation of microorganisms by pulsed electric fields ofdifferent voltage waveforms

Processing foods with HV pulsed electric fields (PEF) is a new technology to inactivate microorganisms and denature enzymes with only a small increase in temperature. Introduction of this new technology will replace or complement conventional thermal processing methods. It will also provide consumers with safe, nutritious foods with fresh quality. For a given peak value of field intensity and amount of electric energy input, PEF inactivation of microorganisms is closely related to the waveform of applied pulses. Inactivation of microorganisms was studied with different waveshapes including exponential decay, oscillatory decay, square waves, and bipolar pulses. Microbial inactivation was tested in a parallel-plate static treatment chamber. Treatment field intensity ranged from 12 to 40 kV/cm while pulse length ranged from 30 to 180 μs. From the microbial test results, bipolar square-wave pulses are the most efficient in terms of microbial inactivation for commercial PEF pasteurization     

Effect of short HV pulses on bacteria and fungi

The survival of three kinds of microorganisms under strong-pulse electric field conditions was investigated with a possible application of the electric pulse method for sterilization of consumable liquids. The results of the investigations of survival ratio of Gram-negative (Escherichia coli, Yersinia enterocolitica) and Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacteria and yeastlike fungi (Candida albicans) are presented. The HV pulses with peak voltage U=0 to 100 kV and rise time t_n= 0.5 to 1.2 μs were applied. The microorganisms were suspended in an NaCl solution with γ=6 to 13 mS/cm conductivity and pH=7.2. The experimental setup and the dependency of the microorganism survival ratio on the rise time, peak voltage and on the number of pulses applied, are presented. It has been found that the lethal effect on microorganisms caused by HV pulses depends on the pulse parameters as well as on the kind of microorganism being treated     

Distribution of electric field strength around a large-scalecharged particle cloud

To investigate an electrical discharge occurring from or in a space-charge cloud, a large-scale charged particle cloud was formed by using a cloud generator consisting of a blower and corona charger. The distribution of the electric field strength around a charged particle cloud has been investigated to determine the behavior of charged particles. The soil-conditioning particles were charged by corona charging and blown by high-speed air flow in a test room, 5 m wide, 10 m long, and 3 m high. The average charge-to-mass ratio of the particles blown by this method was 170 μC/kg. The space-charge density of the cloud was calculated at the order of 10 μC/m³ from the electric field strength outside of the cloud. While the electric field strength at the outside of the cloud increased up to 52 kV/m within 2 m downstream from the cloud generator, it decreased below 25 kV/m farther than 2 m away from the cloud generator due to dispersion of charged particles. The change in the electric field strength due to dispersion of charged particles can be qualitatively explained by a simple cloud model. The velocity of charged particles transported by air flow and mobility of charged particles are found to be effective factors increasing the electric field strength around the large-scale charged particle cloud     

UHV交变电场在人体中感应电流计算分析

为研究1000 kV特高压(UHV)架空线路工频电磁场对人体健康及环境的影响,计算了人体位于UHV线路下方时,交变电场在人体内的感应电流及其影响因素和线路最小对地高度。探讨了设计规程中高压线路最小对地高度应保证线路下方距地1m高处的电场强度<10kV/m的合理性。结果表明,人体的电导率和介电常数的大小对工频电场在人体内感应电流密度的大小并无明显影响;按照线路下方距地1m高处的最大电场强度<10kV/m的原则来确定UHV线路的最小对地高度,感应电流密度不会超过安全值。     

Stratified gas-liquid two-phase electrohydrodynamics in horizontalpipe flow

Stratified gas-liquid two-phase electrohydrodynamics in pipe flow has been studied experimentally and numerically. Experimental studies were conducted using 1.27 and 1.9×10^-2 m-inner diameter horizontal tubes with air-water two-phase flow for the range of gas surface velocity of 10±²-10 m/s, liquid surface velocity of 10^-2-2×10^-1 m/s, and applied voltage of 0-20 kV. Experimental results are analysed by an area-averaged two-fluid one-dimensional model. The results show that the effect of the applied electric field is significantly influenced by the flow regime transition boundaries between stratified smooth-to-wavy and stratified wavy-to-intermittent flow. However, the time-averaged void fraction was not observed to be significantly influenced by applied electric fields     

Intracellular DNA damage induced by non-thermal, intense narrowband electric fields

Intracellular DNA damages caused by intense burst sinusoidal electric fields (IBSEFs) were investigated by means of an alkaline comet assay method. Non-thermal, 200 ?s-long IBSEF with various frequency values (300 kHz-100MHz) and strengths (up to 200 kV/m) was applied to Chinese hamster ovary (CHO) cells in a suspending medium between 1 mm gap parallel electrodes. The comet assay suggests that 100 kV/m IBSEF with frequencies exceeding 1 MHz or 100 MHz IBSEFs with field strengths exceeding 3 kV/m induces significant DNA damage. According to the numerical calculation of the electric field over a simplified cell model under an alternating electric field, the intracellular field strength increases with increasing alternating frequency. The minimum level of the field strength that induces the DNA damage is in the range of 10-30 kV/m. This intracellular strong field might trigger biological processes leading to the DNA damage.     

热导率测量系统的开发及应用

根据一维稳态的导热原理自主研发了一套聚合物材料热导率（λ）的测量系统,适用范围λ=0～2W/（m.K）。该系统由机械子系统和控制子系统组成。机械子系统包含本体、加载模块、加热模块、冷却模块4部分,控制子系统包含温度传感器、热流传感器、PC和基于LabVIEW的图形化软件,实现了温度与热流量信号的采集、温度的控制及热导率等的显示输出。使用该系统实测了5种聚合物材料的热导率,实验测量值高于文献参考值＋2%～＋10%,其主要原因是样品上表面与加热盘下表面之间的存在热阻,略微降低了样品热端温度的测量值。     

NMOSFET ESD self-protection strategy and underlying failuremechanism in advanced 0.13-μm CMOS technology

In this paper, the high current characteristics encountered during electrostatic discharge (ESD) stress using nMOS/L_npn protection devices in a 0.13-μm CMOS technology are investigated for different device parameters: channel length, channel width, gate-oxide thickness, and drain/source contact to gate (DCG/SCG) spacing. From leakage current measurements following ESD stress, it is concluded that the shorter (0.13 μm) devices fail because of source/drain filamentation, whereas longer (0.3 μm) devices with thin (22 Å) oxide gate fail because of oxide breakdown. This conclusion is consistent with and supported by numerical simulations of the electric field. It is also supported by the observed effect of hot carrier stress on I_t2. Hot carrier stress experiments additionally revealed that ESD stress can and does affect subsequent hot carrier degradation of the device     

Inactivating microorganisms using a pulsed electric fieldcontinuous treatment system

High-voltage pulsed electric fields (PEFs) can be used to inactivate microorganisms in liquids. Applying PEF technology to food pasteurization is a promising nonthermal method, which may radically change food preservation processes and provide consumers with microbiologically safe, minimally processed, fresh-like products. A continuous-flow system in a laboratory-size prototype was constructed for the nonthermal pasteurization of liquid foods with PEF technology. Major components in the prototype include a high-voltage repetitive pulse generator, a coaxial liquid food treatment chamber, a fiber-optic temperature sensing instrument and a data acquisition system. Microbial inactivation tests were conducted in the continuous PEF treatment system. Repetitive high-voltage pulses with an exponential decaying waveshape were applied to the liquid food which was pumped through the treatment chamber. Test microorganisms selected for inactivation were Escherichia coli, Staphylococcus aureus and Saccharomyces cerevisiae. Over 6-order-of-magnitude reductions in the viability of selected microorganisms were achieved while the food temperature was maintained below 40°C     

变电站工频短路时的电磁环境分析

变电站的电磁环境威胁二次系统的安全运行,为分析变电站工频短路时的电磁环境,采用现场测试和数值计算的方法分析了工频短路时产生的空间电磁环境和传导电磁干扰。工频短路时变电站内短时电场强度达到22.6kV/m,短时磁场强度可达到1000A/m,对弱电设备的影响值得关注。500kV变电站站内单相短路接地试验表明,二次电缆如果与母线平行敷设,二者之间的电磁耦合强,二次电缆的芯线对地的骚扰电压可达4.5kV;而与母线非平行布置,二次电缆的芯皮电位差可控制在>1kV,主频率为几~几百kHz。理论分析了电缆结构参数对二次电缆芯皮电位的影响表明,屏蔽层编织角在15°、45°、55°、65°、85°左右将产生较强的电磁干扰。工频短路时二次电缆的芯皮电位差与地电位升有直接的关系,将地电位升限制<5kV时,施加在屏蔽层双端接地的二次电缆上的芯皮电位差最高可控制<2kV绝缘耐受水平。     

考虑配电网容量约束和建筑热惰性的城市换热站电制热补热优化配置方法

北方地区市政供暖普遍存在热源、热网缺口和化石燃料依赖度高的问题,增量建筑的末端供热效果难以保障,而依靠传统配电网增容的方式一定程度上造成了社会资源的浪费。设计了一种面向城市换热站的电制热补热系统,提出了一种配电网“免增容”的城市换热站电制热补热优化配置方法。首先,阐述了电制热补热系统的设计结构,建立了制热设备和蓄热设备的模型与建筑热惰性模型。然后,通过两阶段优化方法,考虑设备投资与运行成本,以经济性为目标,建立了电制热补热优化配置模型。最后,以北京市石景山某居民区为研究对象通过Matlab进行仿真计算,研究结果表明,电制热补热优化配置方法可有效降低配电网负荷峰谷差,保障末端供热效果,并且具有较好的经济性,可为电采暖规划提供参考。     

Ionization and excitation behavior in a microcavity

The excitation and ionization behavior of a 5 μm cavity, subjected to an electric field of 270 kV/cm, has been examined. Data on the production of electrons, ions, dissociated molecules and excited species is presented and the associated charge transfer characteristics are considered. The implications of the ionization and excitation processes, as concerns their effect upon the degradation rate of solid insulation, are discussed     

不同500 kV线路悬式绝缘子电气特性对比试验

遭雷击的、运行中的及新的 3种 5 0 0kV线路悬式绝缘子在昆明 1970m海拔高度的试验室内的有限数量的工频和雷电冲击试验表明 ,不同绝缘状况下的绝缘子的电气特性不尽相同 ;同一杆塔上遭雷击的同一绝缘子串中各绝缘子的绝缘特性并不一样 ;与运行中的及新的绝缘子相比 ,遭雷击的绝缘子表面绝缘特性也不完全劣化。     

Thermal-electric field distribution around a defect in polyethylene

In the presence of a stress enhancement, a lightning surge causes space charge formation and power dissipation which can result in substantial temperature rises in dielectrics. Poisson's equation and the thermal diffusion equation have been solved in 2D with field-dependent material parameters to compute temperature rises of over 80 K during a 100 ns risetime surge which produces a background field of 40 kV/mm applied to a 100 μm protrusion with a 0.5 μm tip radius. Such a temperature rise could play a major role in the lightning-induced conversion of water trees to electrical trees     

Effects of liquid conductivity upon gaseous discharge of droplets

The effect that liquid conductivity has upon gaseous breakdown and conduction between a droplet and a sharp grounded metal point was investigated as a function of the droplet charge level and point-to-droplet gap. A uniform stream of equally spaced 1210 μm droplets was studied in passing the point at 2.05 m/s at a rate of 465/s. The negative droplet charge was set at 24, 40, 55, and 60% of the Rayleigh hydrodynamic instability limit (i.e. 3×10^-10 C) for liquid conductivity values in the 10^-4-10¹ S/m range characterizing electrostatic crop sprays. No significant conductivity effect was found for charges up to the 55% level; the most conductive liquid exhibited a significantly (α<0.10) higher discharge current at the 60% charge level. For close gaps, droplets departed the grounded point region with a reversed charge, indicating they were overneutralized by a positive-ion flux from the grounded point     

基于液态金属的高热流密度电力设备冷却实验研究

大功率电力设备的冷却方式成为制约电力设备集约化紧凑性的重要因素。常规水冷技术难以应对具有高热流密度的工况条件,而新兴的液态金属冷却技术具有解决该难题的潜力。为此,本文建立了基于液态金属的高热流密度电力设备冷却实验平台。在该平台基础上,开展了液态金属和水的对流换热系数和热导率对比实验。实验表明,在相同工况条件下,以液态金属替代水作为冷却介质,系统热阻可由0.033K/W降低至0.019K/W;若进一步以液态金属替代传统导热膏作为界面材料,则散热系统热阻可降低至0.014K/W。     

新型沥青涂覆设备的应用

在110 kV及以上高压电力电缆的生产中,金属护套的防腐层的涂覆工艺是一道重要的工序。老式的沥青涂覆装置存在着生产连续性差,防腐层涂抹不均、对生产机台污染严重等缺点。本文介绍一种新型沥青涂覆装置,它是通过电动装置将加热熔化好的沥青液传送到流槽中,由流槽传送后均匀地涂覆在金属护套上。沥青的加热方式为非接触式的远红外加热,改变了传统的接触式加热,提高了加热效率和安全系数,减少了对生产机台的污染。     

1000kV变电站围墙外的电场模拟试验研究

变电站围墙外的电场是变电站建设时要考虑的主要电磁环境参数之一,对于新建的1000kV级变电站,其围墙外的电场强度是工程环境评价的主要因子。了解1000kV AIS围墙外场强,根据麦克斯韦方程,利用相似理论,采用15:1的缩小尺寸模型进行了相关试验研究。结果表明:1000kV AIS变电站,其围墙外的电场水平<4kV/m,基本与500kV变电站围墙外的电场水平相当;1000kV AIS变电站地面电场最严重的母线和间隔布置情况,考虑电场的影响,变电站围墙与居民间的防护距离应保持5m。     

Self-heating in a coupled thermo-electric circuit-device model

The self-heating of a coupled thermo-electric circuit-semiconductor system is modeled and numerically simulated. The system consists of semiconductor devices, an electric network with resistors, capacitors, inductors, and voltage sources, and a thermal network. The flow of the charge carriers is described by the energy-transport equations coupled to a heat equation for the lattice temperature. The electric circuit is modeled by the network equations from modified nodal analysis coupled to a thermal network describing the evolution of the temperatures in the lumped and distributed circuit elements. The three subsystems are coupled through thermo-electric, electric circuit-device, and thermal network-device interface conditions. The resulting system of nonlinear partial differential-algebraic equations is discretized in time by the 2-stage backward difference formula and in space by a mixed finite-element method. Numerical simulations of a one-dimensional ballistic diode and a frequency multiplier circuit containing a pn-junction diode illustrate the heating of the semiconductor device and circuit resistors.