纳米颗粒物在空气中的阻力特性研究

Investigation of drag force on nanoparticles in air

对于空气中的纳米颗粒，其动力学行为属于自由分子区，并且在阻力计算中需要考虑气体分子与颗粒之间的范德瓦尔斯力。基于气体动力学理论推导得到了纳米颗粒在二元混合气体中所受阻力的计算式。在此基础上，分析了纳米颗粒在空气中所受阻力与空气温度、颗粒粒径、颗粒物质种类等因素的依赖关系。研究发现：纳米颗粒所受空气阻力随温度升高而减小；在颗粒粒径小于30 nm 时，范德瓦尔斯力的作用不能忽略，经典的刚体碰撞模型不再成立；由于势参数的不同，对于不同物质种类的颗粒，其阻力差异比较明显。分析结果表明，提出的计算公式与实验结果吻合较好，而采用经典的 Stokes-Cunningham 公式的计算结果比实验结果偏低了20％～40％。

We theoretically investigate the drag force of a spherical nanoparticle in air,where by the particle is in the free molecule and the van der Waals interaction between the particle and gas molecule has to be taken into account.Within the framework of gas kinetic theory,the drag force of a nanoparticle in air is derived in two limiting collision models,namely,specular and diffuse scat-tering.The effects of air temperature,particle size and material of particles on the drag force for a particle moving in air are stud-ied based on the drag force formulation.It is found that the drag force decreases with increasing air temperature.For particles with radius less than 30 nm,the influence of the van der Waals interaction cannot be neglected.The rigid body collision model employed in previous papers can lead to large errors for nanosized particles,because the drag force is reported to be independent of the particle material upon the rigid body collision between the gas molecule and particle,which is inconsistent with the experi-mental results.If the van der Waals interaction is involved into the collision model,the drag force is found to depend on the mate-rial of the nanoparticle.