亚微米颗粒在汇作用下运动机理的实验研究

当前,城市空气质量的不断恶化,引起了公众的普遍性关注.空气中的悬浮颗粒物,是城市大气环境重要污染源之一,其分布、运动及扩散规律已成为科学领域的研究热点.与连续流体不同,大气中的悬浮颗粒物是离散的,确定颗粒运动的模型是研究大气细微颗粒污染问题的关键.本文拟研究小空间静稳空气中亚微米级颗粒在汇作用下的运动规律,并构建其运动模型.在密闭实验空间中通过燃烧生成亚微米颗粒,利用静电吸附装置模拟颗粒汇,并通过粒子图像测速(particle image velocimetry,PIV)实验和激光多普勒测速仪(lasser Doppler velocimeter,LDV)实验技术测量分析不同空间内亚微米颗粒在大气中的热运动速度和在汇作用下的运动规律,并推导出颗粒物的速度分布经验公式.结果显示:粒子在汇作用下的运动与连续流体汇运动规律类似,但在小空间内颗粒的运动不满足流体连续方程;说明在无气流夹带输运情况下,利用汇作用及颗粒的扩散而发展的颗粒净化技术是可行的.

EXPERIMENTAL STUDY OF SUBMICRON PARTICLES' MOTION IN THE EFFECT OF PARTICLE-SINK

As particulate air pollution has aroused the universal concern of the public, the motion and diffusion law as well as the distribution rule of suspended particles have become research focuses. The suspended particles in air are discrete which are different from continuum medium,and thus the model of particle motion are different from that of continuous fluid. To ascertain the model of particle motion is a critical issue in the research of ambient particulate matter. This paper concentrates on the movement of submicron particles in still air where the particle-sink exists. In this experimental study, submicron particles were generated by combustion, particle-sink was simulated through electrostatic adsorption device, and particles' movements at different intensities of particle-sinks were measured by PIV and LDV. The experimental results show that movements of particles in still air without sink are Brownian motion, and if there is a sink, particles move to the sink at variable velocities which varied inversely as the distance to the sink. It turns out that particles' movements around sink are analogous to that of continuum flow. Also, an empirical formula of particle's two-dimensional velocity distribution is given on the basis of PIV experimental data, which shows the motion of particle in small space does not satisfy the continuity equation. Meanwhile, experiments in a bigger space were performed by LDV technique, and the result is identical with previous experimental outcome. Therefore, according to this study, a hypothesis is presented as follows: a non-pneumatic-conveying air purify technology base on sink's action and particle disperse is feasible.