小颗粒声波团聚中碰撞效率的计算及影响分析

Simulation and analysis of collision efficiency in acoustic agglomeration

碰撞效率指声波团聚中团聚体内能与大颗粒发生碰撞的小颗粒的比例。通过建立碰撞效率模型,研究其变化规律,发现碰撞效率对声波团聚的影响很大。计算结果表明,粒径越小,碰撞效率越低。在PM2.5区域,碰撞效率急剧降低,减弱同向团聚作用。在低频区碰撞效率较高,在高频区(>3000Hz)迅速降低,但同时使最佳团聚频率的范围增大,有利于工程应用。声压级增大不仅使团聚核函数增大,也增大了碰撞效率,使高声压级时的团聚更有效。低温时温度对同向团聚影响不大,但高温时(>600℃)无论碰撞效率和团聚核函数都明显降低。

Classical orthokinetic mechanism assumes that the fine particles near the core particle move straightly until hitting the core particle. Actually, airflow detours the core particles and the trajectories of fine particles will be deflected from straight lines by the airflow. The collision efficiency was introduced to denote the proportion of fine particles that collide with core particles. By modeling the collision efficiency of acoustic agglomeration, the effect on acoustic agglomeration was studied. The results showed that collision efficiency was very low for PM2. s especially for PM1, which meant that the fine particles were hardly collected by orthokinetic agglomeration. Collision efficiency decreased as acoustic frequency increased, but it enlarged the range of optimum frequency of agglomeration. Higher sound pressure level （SPL） favored both collision efficiency and agglomeration kernel, so acoustic agglomeration increased in the higherintensity acoustic field. Acoustic agglomeration was ineffective for SPL less than 140 dB. Temperature produced little influence on orthokinetic agglomeration at a low temperature, but a high temperature reduced both collision efficiency and agglomeration rate.