Evaluation Of Electrical Properties Of Wind-blown Sand And Dust Storms

Dust electrification as a common phenomenon in the dusty phenomena like wind-blown sand,dust devils and dust storms,has a significant effect on the lifting and transport of dust particles.Therefore,the investigation of electrical effects involved in the dusty phenomena is beneficial for the better understanding of its physical process and prediction.However,so far the properties of dust charging and electric field remain poorly understood.To solve some key questions related to the electrical effects,we conducted a series of electrical effects field observations,a comprehensive numerical simulation of wind-blown sand,and a theoretical model of electric field in the dust storms.Firstly,as compared with the previous observations the main innovations of our field observations were: 1)higher precision instruments,i.e.,charge-to-mass ratios measuring system and vibrating-reed electric field mill(VREFM)were adopted;2)wind velocity,ambient temperature,vertical E-field,mass concentration of PM10(dust particles with diameter of <10 mm),number density of saltating particles,and the particle size distribution of airborne dust particles were simultaneously measured in the height of up to 30 m above the ground.Secondly,there were some advantages of our numerical models: 1)the charge transfer process between dust particles during collisions was included,and the effect of the impact speed on the charging of dust particles was explicitly accounted for;2)the ground was regarded as a sand bed contained with sand/dust particles of different size obeying a lognormal distribution.Finally,this thesis proposed a theoretical model of electric field in the dust storms,in which the charge-to-mass ratios of suspended dust particles were determined by calibrating the theoretical model with the measured electric fields.The most important finding of this thesis were: 1)the charge-to-mass ratio of saltating particles could be described by a normal distribution,and the effects of height above the ground,wind speed and particle size distribution of sand sample on the probability distribution function were also investigated;2)the vertical electric field increased first,then decreased,and finally decreased with the height above the ground,reversing its direction at several heights.This suggested that the charge polarity of dust particles changed from negative to positive and back to negative again as the height increased;3)a simple theoretical model of electric fields in the dust storms was proposed,and field measurements and theoretical calculations demonstrated that substantial enhancement in electric field could be observed several hours before the arrival of the dust storms,thus indicating that electric field could be used for the dust storms early warning.Additionally,an early warning scheme based on monitoring the near-ground electric field was proposed.