一种风沙运动的颗粒动力学静电起电模型

An electrostatic dynamic model for wind-blown sand systems

基于水的电离理论和颗粒动力学理论,提出了一种风沙运动颗粒碰撞的静电起电模型:颗粒表面覆盖有水分子薄层,颗粒间的碰撞导致能量转移和颗粒温度变化;水电离生成H3O+和OH-离子,当两个温度不同或水分子薄层正(负)离子浓度不同的颗粒相接触时,H3O+比OH-以更快地速度从浓度高的地方向浓度低的地方迁移.在动力学的模拟计算中采用0.1 mm,0.2 mm和0.4 mm三种粒径的沙粒以示沙粒直径分布特性,并根据沙源地采样分析,沙粒的数量选取750,100和50.模拟结果表明:在三种大小的颗粒系统中,不同大小的颗粒平均带电量随时间的变化规律为大颗粒平均的带电量为正、小颗粒平均的带电量为负,这一结果解释了风沙电场的产生机理,同时定性解释了Guardiola的实验结论——颗粒摩擦静电产生需要一定的湿度环境.颗粒动力学静电起电模型可进一步与气固两相流模型耦合,提高风沙运动颗粒行为的模拟精度.

An electrostatic dynamic model for wind-blown sand systems of dust devils or sand-dust storms was developed based on the electrochemistry of water molecular film on the surface of particles,in which water is ionized as H3O^＋/HO^-and their concentration vary with temperature.The mobility of H3O^＋ from high concentration regime to low concentration regime is greater than that of HO^-.The interaction of particles result in the change of particle kinetic energy and the particle surface temperature.The simulation of a three-sized particle system with diameters of 0.1,0.2,and 0.4mm and particle numbers of 750,100 and 50,respectively,shows that the small particles are charged negatively while the large particles are charged positively,which reasonably explains the electrostatic mechanism of dust devils and sand-dust storms.It was also found that the electrification is relevant to the humidity of granule system,which explains Guardiola＇s experiments.Coupled with gas-particle two-phase flow model,this electrostatic dynamic model will improve the accuracy of numerical simulation of the wind-blown sand system.