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An Experimental Study on Sand-dust Particle Concentration Due to the Electric Field

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【Author in Chinese】 周诚

【Supervisor】 谢莉

【Author's Information】 兰州大学, 力学·工程力学, 2020, 硕士

【Abstract in Chinese】 许多大气气溶胶颗粒都会带有一定程度的多余电荷,研究表明沙尘颗粒带电量可达上千微库仑每千克。沙粒在空中运动,由于携带多余电量,在空中产生强风沙电场,从而使带电沙粒受到静电力的作用。已有数值模拟研究表明,带电沙粒在强风沙电场中,由于静电力作用,改变沙粒的运动轨迹,进而可能影响沙粒在空间的浓度分布和空中的滞留时间。电磁波通过沙尘系统后,由于沙尘颗粒对电磁波的吸收、散射使得电磁波信号衰减,衰减值与沙尘颗粒浓度成正比。本论文基于沙尘颗粒系统对电磁波信号衰减与沙尘浓度的关系,通过利用室内风沙流以及沙尘悬浮系统对激光的衰减,展开实验研究,初步探索了沙粒带电和风沙电场对风沙流中沙粒浓度随高度剖面的变化规律以及对沙尘悬浮滞留时间的影响,主要工作和结果如下:首先,通过实验分析沙尘带电极性与粒径的关系,结果显示:当粒径分布范围较窄时,沙粒带电极性与沙粒粒径无关,而与沙尘颗粒的金属氧化物含量相关,带负电荷沙尘颗粒的金属氧化物含量较多;当粒径分布范围较宽时,粒径较大的沙尘带正电荷,粒径较小的沙尘带负电荷。其次,利用激光通过沙尘系统后信号的变化,研究了沙粒带电量和风沙电场对风沙流中沙粒浓度随高度剖面的变化规律以及对沙尘在空中滞留时间的影响。结果表明:向上的电场强度可使风沙流中同一高度处沙粒浓度增大,且随高度的升高沙尘浓度增加程度不同;贴近沙床表面沙粒浓度受电场的影响较小,距沙床表面26cm处,93.75kV/m的电场强度使得沙尘浓度提高约25%;电场会使沙尘颗粒加速沉降,当初始沙尘浓度相同时,80kV/m的电场会使同一高度处沙尘浓度提前降低,与无电场时相比,除初始时刻外,沙尘沉降时间至少缩短75%。

【Abstract】 Many aerosol particles carry a certain amount of excess charge.Studies have indicated that the charges of sand particles carried by a particle can reach to thousands of micro coulombs per kilogram.A strong electric field can be generated by the charges carried by the sand particles flying in air,so that an electrostatic force will be acted upon a charged sand particle to alert the concentration distribution and flying time of a particle in air,to stay longer/short in signals of the electromagnetic waves will be attenuated,even to be faded due to the scattering and absorption by the particles.Usually,when the sand/dust concentration is low,the attenuation of the electromagnetic waves is directly proportional to the sand/dust concentration,based on which,we conducted out studies to investigate what the charges carried by the sand/dust particles and the electrostatic field affect the concentration of sand particles in the wind sand flux and a suspended sand/dust system.Firstly,the factors affecting the charges polarity of sand particles are investigated,and it is found that the metallic oxide in chemical composite of sand particles make the particle carry positive charges when the particle size is much uniform,while the larger particles carry the positive charges,and the smaller particles carry the negative charges when the particle size region is larger.Based on the size-dependent charges carried by sand/dust particles,the experimental studies are conducted out to investigate the particle concentration in the sand flux and the suspended sand/dust system.It is found that the electrostatic field alert the particle concentration in the sand flux,and the upward electrostatic field make the particle concentration increase;the particle concentration close to the sand bed almost be affected by the electrostatic field,while the particle concentration can be enhanced 25% at the height 26 cm above the sand bed.It is also found that the electrostatic field alert the particle concentration and the stay time in a suspended sand/dust system.The results indicated that the upward electric field can speed the sediment of sand/dust particle;when the initial dust concentration is the same,the80kV/m electric field reduces the dust concentration,except for the initial moment makes the sediment time reduced 75% of the one without electric field.

  • 【Contributor】 兰州大学
  • 【Year of Internet Publish】202101
  • 【CLC code】P425.55
  • 【Downloads】36
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