2种常用颗粒物粒径表征方法的对比

Comparison of two conventional characterization methods of particle diameter

从理论上推导常用的颗粒物光学散射体积等效直径和空气动力学当量直径之间的相关性,并分别运用马尔文激光粒度分析仪(Mastersizer 2000)和静电低压撞击器测试燃煤电站静电除尘器末级电场中飞灰颗粒物的光学散射体积等效粒径分布特征和空气动力学粒径数目浓度分布特征.通过将2种实验测试的颗粒物粒径分布数据进行对比研究,验证理论推导得出的2种颗粒物粒径表征方法的对应关系.通过扫描电子显微镜观测飞灰颗粒物的微观形貌特征.结果表明:颗粒物的空气动力学当量直径略大于其光学散射体积等效直径;对于外凸近似球形颗粒物,这2种等效直径可以相互转换,其转换关系不仅受到颗粒物和流体密度对颗粒物在流体中运动特性的影响,还受到颗粒物形态对颗粒物在流体中运动特性以及颗粒物光学检测结果的影响;同时,对于粒径大于1μm的颗粒物,2种颗粒物粒径表征方法测得的颗粒物粒径分布之间的相对误差小于3%.

Relationship between optical scattering equivalent volume diameter and aerodynamic equivalent diameter were investigated using theoretical method. The volume distribution of optical scattering equivalent volume diameter and number distribution of aerodynamic equivalent diameter of fly ash particles sampled in an eleetrostatic precipitator＇s last electric field from a coal-fired power plant were investigated using a Mastersizer 2000 and an electrical low pressure impactor （ELPI）, respectively. Experimental data were compared to verify the relationship between two conventional eharacterization methods of particle diameter dedueed by the theoretical method. The fly ash particle mierostruetures were analyzed using a scanning electron microscope （SEM）, and fly ash particle was convex spherical particle according to the SEM photos. Results indicate that aerodynamic equivalent diameter of particulate matter is little bigger than its optical diameter and can transform one to another for convex spherical particles. The transformation between aerodynamic equivalent diameter and optical diameter is affected not only by the density of particles and fluid, but also by the form of particles. For the two particle size distribution measurements, the relative error is less than 3% for the particle with a diameter larger than 1 μm.