API AerosizerTM 計數效率之理論研究

Abstract

本研究主要探討 API Aerosizer 對於微粒的計數效率。首先模擬在噴嘴內的二維流場，利用此流場來計算液體和固體微粒的運動軌跡，然後求得微粒在不同情況的操作條件下之計數效率。本研究指示出微粒的氣動直徑、種類、密度，和用來偵測的雷射光源之光束直徑會明顯地影響計數效率。當微粒的氣動直徑小於幾微米時，計數效率會隨著微粒氣動直徑的增加而增加。由於液體微粒在噴嘴內的慣性衝擊的損失，計數效率會隨著微粒從幾微米附近開始增加時而明顯地降低，而固體微粒的計數效率和粒徑的關係則是比較復雜。當固體微粒的氣動直徑小於幾微米時，固體和液體微粒兩者的計數效率相同，然而當固體微粒大於幾微米時，由於固體微粒的反彈影響，計數效率會隨著氣動直徑的增加而增加，直至微粒增大到發生塑性變形，當此情況發生時，計數效率則隨著固體微粒的氣動直徑的增加而降低。

This study has investigated the particle counting efficiency of the API AerosizerTM numerically. Two-dimensional flow field in the nozzle was first simulated. Particle trajectories for both liquid and solid particles were then calculated to obtain the particle counting efficiency under various conditions. This study shows that particle aerodynamic diameter, particle materials, particle density and laser beam diameter influence counting efficiency significantly. Counting efficiency is found to increase with increasing particle diameter when particle aerodynamic diameter is less than several micrometers. The efficiency for liquid particles drops significantly when particle aerodynamic diameter increases from several micrometers because of impaction loss in the nozzle. For solid particles, the relationship of the efficiency with paricle diameter is found to be more complicated. For particles less than several micrometers in aerodynamic diaeter, solid particles behave similarly to the liquid particles. However, as particles are greater than several micrometrs,effect of solid particle bounce is to increase counting efficiency with increasing aerodynamic diameter until particles become large enough so that plastic deformation occurs in the particles. Then the counting efficiency will decrease with increasing particle aerodynamic diameter.