高压方波脉冲电场对微生物的致死作用

研究了高压方波脉冲电场对食品中常见的腐败菌枯草芽孢杆菌 ,灰绿青霉的致死作用 ,比较了几种微生物的灭活效果 ,并以酿酒酵母为材料 ,初步探讨了杀菌机理。研究表明 :微生物的致死率随电场强度、脉宽、脉冲个数的增加而增大 ,同一灭菌条件 ,酵母菌 >大肠杆菌 >枯草芽孢杆菌 >灰绿青霉。电场作用后死亡酵母细胞表面出现凹陷 ,局部有孔洞产生。     

脉冲电场非热杀菌效果分析

研究了高压脉冲电场(PEF)对液体食品的非热杀菌效果。杀菌实验中分别采用平板和同轴两种电极形 式处理接种了啤酒酵母和大肠杆菌的胡萝卜汁样品,通过改变脉冲电场的处理时间(即脉冲数)和电场强度,得到 了各种不同情况下两种细菌的残活率最大下降>4.5和3.5个对数,证明了杀菌效果相当可观,并比较分析了影响 杀菌效果的因素,最后初步讨论了杀菌的机理。     

PEF中脉冲上升沿对金黄色葡萄球菌杀菌的影响

方波脉冲因能量集中、能量利用率高、杀菌效果好而被认为是PEF技术的最优选择。但关于其上升时间对杀菌效果影响的研究和报道都比较少。为此,研究了在脉冲电场(PEF)技术中,高压方波脉冲的上升前沿对金黄色葡萄球菌杀菌效果的影响。通过实验分别比较了在上升时间为2μs和200ns的高压方波脉冲作用下,3种不同电导率(1.5、2.0、2.5mS/cm)的苹果汁在有效处理时间75μs、电场强度分别为25、30、35kV/cm下对金葡菌的杀灭效果。实验结果表明:在处理时间和脉冲电场强度等其它因素都相同的条件下,陡前沿的方波脉冲电场比上升时间长的方波脉冲电场对金葡菌的杀灭效果更好,平均能提高0.5个对数;处理后的温升也要低1～6°C。     

陡前沿方波对金黄色葡萄球菌的杀灭效果

为研究方波脉冲前沿陡度对高压脉冲电场技术(PEF)杀菌效果的影响,通过实验研究了前沿陡化的方波脉冲对金黄色葡萄球菌的杀灭效果。考察并比较了在不同电场强度、等效处理时间、电导率条件下,陡前沿方波和普通方波的杀菌效果。结果表明,脉冲电场的杀菌效果随着电场强度、溶液电导率、等效处理时间的增大而增强,且方波脉冲的上升时间对金葡菌的杀灭效果具有显著影响。上升时间为200 ns的脉冲电场处理后的细菌残存率比上升时间为2μs的脉冲电场的残存率大,且前者的温升比后者小。当杀菌效果相同时,陡前沿方波脉冲所需的等效处理时间比普通方波脉冲更短。此外,陡前沿方波脉冲杀菌效果的提升并非通过改变细胞形貌结构来实现,而是直接作用于细胞内部。     

高压脉冲放电在水处理中的应用及发展

综合论述了高压脉冲水处理技术的应用和研究状况 ,从较为成熟的臭氧水处理和静电水处理技术 ,到长期以来国内外在脉冲杀菌方面的研究进程 ,以及在脉冲电场食品杀菌和脉冲放电废水处理方面的最新探索和发展。指出高压脉冲放电水处理技术大有应用前景 ,但仍需克服多方面的困难 ,进行更系统和深入的研究     

间歇式HPEF的高压脉冲电源及其杀菌实验

高压脉冲电场非热处理应用到食品杀菌可代替传统的热处理方法灭活液体中的病菌,高强度电脉冲能迅速杀死细胞但并不破坏食品的自然风味如色泽和营养,为此研制了高功率脉冲电源,其输出最高电压15 kV,最大电流40 A。在详细介绍了高功率电力电子器件IGBT使用过程中的过流和过压保护等问题和在输出端串联无感小电阻来修正波形实现了输出波形更陡峭的良好效果后,进行了两种相对难杀的典型微生物(枯草芽孢杆菌和黑曲霉菌)在间歇式处理室中的杀菌实验。结果表明,脉冲电场强度为13 kV/cm、脉冲宽度为15μs时,连续作用200个脉冲后,黑曲霉菌灭菌率能达99.64%,1000个脉冲后,所有的黑曲霉菌都被杀死;枯草芽孢杆菌相对难灭,在13kV/cm、15μs作用下灭菌率仅达87.08%;应在提高电场强度的同时避免放电,这对下一步的连续式杀菌实验有技术指导作用。     

基于氢闸流管的高压脉冲电源

针对高压脉冲电场杀菌技术对于系统核心部分高压脉冲电源的要求,设计一种输出脉冲电压峰值可达5～30 kV(100 V步进可调),输出脉冲频率为200~1 000 Hz可调,脉冲宽度为0.2~2μs可调,脉冲前沿<100 ns的高压脉冲电源。该系统利用单片机进行自动控制,通过可调直流高压电源和储能元件作为能源系统,利用氢闸流管作为主放电开关,控制脉冲峰值和频率,最后通过脉冲变压器升压在杀菌腔体的极板上得到所需的脉冲电场。     

基于IGBT的高压脉冲电源研制

高压脉冲电场灭菌技术是近年发展起来的极有潜力的非热灭菌技术,其中高压脉冲电源是系统的核心组成部分.提出了一种基于IGBT的高压脉冲电源,系统由能源系统和脉冲产生回路构成,由单片机来控制IGBT的触发,其设计输出为方波,电压幅值在50～100 kv可调,脉冲宽度在1～10μs可调,频率在1～100Hz可调.所研制的高压脉冲电源可用于间距在2～10 cm之间平行可调的平板电场,满足食品在各种高压脉冲电场强度下非热力灭菌的需要.     

脉冲高电压液体灭菌技术的研究

介绍了脉冲高电压液体灭菌的实验研究工作，研究结果表明，利用脉冲高电压可以在常温条件下１００％地杀灭液体中的细菌，对液体体食品还能保持其色泽，品味不变、维生素、氨基酸等营养成份不受破坏，还对灭菌机理作了分析和探讨。     

高压脉冲电场设备及其在食品非热处理中的应用

为较全面了解高压脉冲电场(PEF)食品非热加工技术,总结了清华大学在PEF上的开发和应用研究,对PEF技术的理论研究和工业化发展现状进行了综述.首先分析了清华大学4代高压脉冲电场系统的电源结构拓扑和性能以及处理室的结构特性,其次对相关系统在液态食品处理领域的应用研究进行了总结介绍.研究结果表明,经过近10 a的努力,清...     

High-efficiency sterilizer by high-voltage pulse usingconcentrated-field electrode system

Recently, a sterilization method of microorganisms in liquid food using pulsed electric fields (PEFs) has been reported by some researchers. Considering the application to the food industry, the energy efficiency of the method becomes important. It is reported that microorganisms suspended in aqueous solution were killed linearly (logarithmic) by the PEF process using a parallel-plate electrode configuration. The PEF is generated by capacitor discharge through a switch (using stationary, rotary, vacuum tube, and semiconductor, etc.). The survivability ratio decreases with increasing operating temperature and increasing capacitance value of the capacitor. Although many kinds of microorganisms suspended in liquid foods were treated by the PEF system, the energy efficiency was still low in the case of high-conductivity liquid. The authors developed a new electrode system for concentrating the electric field in a liquid food medium. The new electrode configuration made it possible to raise the energy efficiency for the pulsed sterilization process compared to that for conventional parallel-plate or concentric-cylinder electrode systems     

Destruction of living cells by pulsed high-voltage application

Destruction of living cells in liquid has been formed by pulsed high-voltage application to the liquid. S. cerevsaie (yeast cell) or Bacillus natto, dispersed in deionized water and one- and three-percent NaCl solution, were used in this experiment. Four different electrodes (plate-plate, needle-plate wire-cylinder, and rod-rod electrode) were tested. The survival rate of cells was measured against peak electric field E_p pulsewidth T _W, and pulse application number N. The experimental results indicate that the survivability roughly follows Weilbull distribution. Yeast cells dispersed in deionized water could be almost completely destroyed when the wire-cylinder electrode was used with E_p=20 kV/cm, T_W=100 μs, and N=200. The energy input to a unit volume of the liquid to complete the cell destruction, however, differed significantly with the electrode type. The wire-cylinder electrode required above 10-30 cal/cm ³ to destroy the yeast cell in deionized water to 10^-6 survivability. This value was less than that required more than 70 cal/cm³. Using the rod-rod electrode contained in a pressure vessel, an arc discharge was generated to produce an intensive shock wave, which also destroyed the cells by its mechanical force. In this case, 5-10 cal/cm³ of energy was required to decrease the survivability of yeast cells in deionized water to 10^-6. Though further studies are necessary, this results indicate a possibility of the cell destruction by pulsed high voltage to be used as an energy-efficient sterilization process     

脉冲电场灭菌用固态高压开关的研制

针对脉冲电场灭菌技术对开关性能的特殊要求,提出了利用IGBT串联构成高压、大容量固态开关的技术。设计并实际制造出了可供高压脉冲电场灭菌用额定电压10 k V的固态高压开关。该开关采用8个1 700 V、400 A的IGBT串联,以栅极动态RCD为基本均压方式,以FPGA为主控单元,产生8路相对独立的基准控制脉冲,其脉宽、周期、延时均可调节,且以25 ns为步进调节。通过调节各路驱动信号的相对延时,使各单元分压均匀,消除过压影响,从而在负载端得到较为理想的方波脉冲。采用光纤隔离,使隔离电压不受限制。实验结果表明,该装置性能良好,可以满足脉冲电场灭菌的实际需求。     

Streamer discharges in liquids and their applications

Industrial applications using pulsed power technologies have been developed in many fields. One of them is the treatment of exhaust gas by using uniformly produced streamer discharges. Streamer discharges in liquid also generate extremely high electric fields at the tip of streamers, as well as high energy electrons, ozone, other chemically active species, ultraviolet rays and shock waves. All of these may be utilized to sterilize microorganisms and to decompose molecules and materials. Large-volume streamer discharges in water have been produced in order to realize industrial applications. A wire to plane electrode configuration has been used. The discharge in water shows similar optical radiation to that in an atmospheric gas as provided by evidence from still photographs. The influence of polarity, conductivity, electrode geometry and hydrostatic pressure on the streamers in liquid, the mechanism of streamer discharges and possible industrial applications of streamers in liquids, are discussed in the present work     

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     

脉冲电场处理电厂冷却水系统微生物的研究

用脉冲电场处理冷却水系统中的微生物是切实可行的。该法不同于向水中添加杀生剂的方法 ,其基本原理是用脉冲电场处理冷却水 ,使水中的微生物在流过冷却设备时暂时失去活动能力 ,不发生沉积。由实验可知 ,对单脉冲电场来说 ,微生物的抑制时间由脉冲持续时间和脉冲电场幅值或能量密度决定。用重复频率的脉冲处理冷却水中的微生物可在较小的电场强度下获得与较大电场强度单脉冲电场相同的效果。在使用时 ,对处理池中的电极施加脉冲电场 ,可通过改变电极间距改变施加的场强值。     

陡脉冲电场作用下细胞电场力的仿真计算(英文)

The basic characteristic of electric field is that the substance in the field is in operation by the stress. Under external electric fields,there is strong distribution of electric fields on the inside and outside surfaces of cell membrane. In virtue of the difference of the permittivity among membrane,cytoplasm and extracellular medium,there must be electric field stress on the surface of the membrane. The goal of the study is to research the irreversible electrical breakdown (IRE) mechanism of the malignant tumor cells under steep pulsed electric field (SPEF) from the views of mechanics. Electric field stress of plasma membrane under steep pulsed electric field is calculated and simulated both on malignant tumor cells and on the normal cells. The calculation results show that,in addition to a compressive stress normal to the membrane plane,transverse traction stresses are generated in the lateral plane of the membrane. The lateral stress will reduce the membrane tension significantly,leading to electroporation and rupture. At the same electric field strength,the transverse traction stress on malignant cell membrane is greatly larger than the one on normal cell membrane. Therefore,compared with the normal cells,the malignant tumor cells are more sensitive under the steep pulsed electric field. Namely,steep pulsed electric field can selectively destroy the malignant tumor cells,which proved the safety of treating malignant tumors by steep pulsed electric field.     

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     

高压电能计量设备及其检验技术

为更全面地把握高压电能计量技术进步发展脉络,助力新型高压电能计量设备推广应用,文章较系统地梳理了传统以及新型高压电能计量设备的构建原理、实现方案、功能特点及适用范围,且以高压电能表为代表,重点阐述了新型高压电能计量设备的工作原理和技术优势,以及与高压电能计量设备相互促进、不断进步的高压电能计量技术的新变化、新特点及新优势。还总结了高压电能计量设备的各类检验技术,包括综合误差评价、整体检验以及现场/在线检验等;论述了发展高压电能计量设备整体检验技术的必要性,并梳理了相应检验装置的构成、工作原理和技术特点。展望了高压电能计量设备及其检验技术的发展趋势。