BREAK-UP MECHANISM OF METAL DROPLETS GENERATED BY AN ELECTROHYDRODYNAMIC TECHNIQUE

1.IntroductionNan0meterpowders,whichhavebeenmuchstudiedinrecentyearstarenovelmaterialswithspeciflcpr0perties.Electr0hydrodynamictechniqueisone0ftheimp0rtantmoth0dsusedt0pr0ducenanometerpowders'Theelectrohydr0dynamictechnique,whichhasbeendevelopedt0producenanometerparticles,requiresintenseelectricfieldtogeneratechargedliquiddropletsdirectlyfromtheliquidstate.Thisisachievedbydeliveringamoltenmetaltothetip0fafinecaPillarynozzletowhichvoltageisapplied.Thedropletsaredisruptedagainandacceleratedbyt…     

中心圆柱电极EHD强化垂直管内沸腾换热的实验研究

以R123为工质采用中心圆柱电极对垂直管内沸腾换热的EHD强化进行了实验,得出了沸腾传热系数与电场强度、热流密度等相关参数的关系.测试了外加电场的电流以及击穿电场强度.从外加电场影响气泡的成长、跃离和运动规律的角度对EHD强化垂直管内沸腾换热的机理进行了分析.     

CHARACTERIZATION OF NANOSTRUCTURED MATERIALS BY ANALYTICAL ELECTRON MICROSCOPY

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电场中汽泡行为的变化及对沸腾换热的影响

为进一步探索电场强化沸腾换热的机理,利用高速摄像仪对沸腾汽泡在电场作用下的生长过程进行了可视化实验研究,实验观察到电场作用下汽泡生长的动态图像,并对电场作用下汽泡行为的改变对沸腾换热的影响进行了初步分析。研究结果表明：电场作用下汽泡沿场强方向伸长,随着场强的升高,汽泡的脱离长径比增大,脱离体积减小,脱离频率增大。汽泡变形是由于汽泡受到电应力的作用,电应力在赤道方向压缩汽泡,在极轴方向拉伸汽泡,使得汽泡沿场强方向变细变长。由于在电场作用下汽泡行为的变化使得沸腾传热系数和临界热流密度提高。     

Confectionery coating with an electrohydrodynamic (EHD) system

In the confectionery coating industry, hard butters are frequently used as cocoa butter replacers. An electrohydrodynamic (EHD) system, which forms fine droplets with a relatively narrow size distribution, may be beneficial in confectionery coating to produce more even coverage. The objective of this study was to determine the effect of lecithin content and fat type on electrical resistivity and apparent viscosity, and the effect of these variables under EHD (25kV) and non-EHD coating on droplet size, width of coating area, thickness, and minimum flow rate to produce complete coverage. Total of 3 different types of fat were used: cocoa butter, cocoa butter equivalent, and lauric butter. As lecithin content increased, resistivity and apparent viscosity decreased, except all samples showed a local apparent viscosity minimum at 0.5% lecithin. EHD coating was more efficient than non-EHD as a smaller droplet size and thinner coating was formed. Due to repulsive forces between the like-charges on the droplets during EHD, it spread over wider areas which lead to a higher minimum flow rate to get complete coverage. Under EHD, increasing resistivity significantly increased the droplet size, but only at the highest resistivities. There was no correlation between resistivity and droplet size or width of coating under non-EHD. The width of coating under EHD decreased significantly as resistivity increased. Thickness and minimum flow rate to produce complete coverage, significantly correlated to resistivity, for EHD coating, and to apparent viscosity, for 2 of the 3 fat types during both EHD and non-EHD. PRACTICAL APPLICATION: Electrohydrodynamic (EHD) spraying offers great potential improvement to the food industry especially in the confectionery area. From the quality point of view, EHD offers greater and more complete coverage than non-EHD coating. From the economic point of view, lower cost can be achieved for coated food because during EHD, smaller droplet size and thinner coating is produced.     

用于电流体动力气流控制的等离子体发生器

基于等离子体的电流体动力(EHD)气流控制技术具有良好的发展前景.笔者着重从介质阻挡放电等离子体的电流体动力特性和等离子体发生器的电气特性等方面,综述了此领域取得的研究进展,并指出从放电物理角度解释气流加速和改善等离子体发生器性能为当前研究中的难点和重点问题.最后介绍了等离子体发生器的建模与仿真.     

关于电除尘器内二次流的典型研究

对有关电除尘器内电流体场的理论研究和实验方法作了回顾，并通过对现有资料的分析扼要地对进一步的研究提出了建议。     

电流体动力学技术制备纳米超微粉的液滴破碎机理

分析了电流体动力学技术制备纳米粉的液滴破碎机理结果表明：外加电压、电场强度、液体金属的性质直接影响金属液滴的破碎程度