微粒於流孔板的損失及其傳輸效率改善研究

Abstract

微粒損失於流孔板的機制有慣性及擴散附著兩種。過去的學者僅對微粒的慣性附著進行研究，本研究則同時針對微粒在流孔板的擴散及慣性損失進行研究，並研究在流孔板前加裝錐狀入口減少微粒損失之方法。本研究所使用之流孔板為O’Keefe公司的E-9流孔板，其臨界流量為0.455slpm。 □研究發現，在臨界流量時，Dpa大於457.7nm之微粒之穿透率會隨Dpa的增加及流孔板下游壓力的降低而下降，而加裝錐狀入口之E-9流孔板之穿透率比E-9流孔板的增加，在Dpa為856.8nm時，穿透率分別為92.5%、83.2%（下游壓力395torr），此穿透率增加主要是因為錐狀進口減少微粒慣性損失之故。 □當E-9流孔板的流量小於臨界流量時，本研究發現Dpa<126.1nm之微粒在E-9流孔板之擴散損失會隨著流量降低及Dpa減小而增加（或穿透率下降），當Dpa=27.6nm時，穿透率分別為80.4%（Q=0.357slpm）及72.4%（Q=0.242slpm）。研究發現加裝錐狀入口之E-9流孔板可減少入口低速迴流區之範圍，微粒之擴散損失因而減少，當Dpa=27.6nm時穿透率分別為93.3%（Q=0.357slpm）及83%（Q=0.242slpm）。而Dpa>126.1nm之微粒穿透率均為100%（Q=0.357或0.242slpm）與原E-9流孔板相同。 □本研究發現在臨界流況下，當流孔板下游壓力愈低，則Dpa愈大的微粒穿透率會降低，如Dpa=856.8nm時，錐狀入口之E-9流孔板之穿透率由92.5%（下游壓力為395torr），降為59%（下游壓力為220torr）。此穿透率降低之現象是因為微粒的慣性隨著下游壓力之降低而加大，導致微粒愈容易在穿過中心線後偏離流線而慣性衝擊於流孔板下游之管壁上。

The inertial impaction and diffusion are two major mechanisms that cause particle loss in the orifice. The impaction loss in the orifice has been studied in the past. In this study, experiment was conducted using orifice with conical inlet to reduce the particle loss to study the effect of inertial impaction and diffusion. The orifice used is O’Keefe E-9, 0.455slpm orifice. The experimental results reveal that when the flow rate through the orifice reach the critical flow rate, the penetration efficiency decreases for the particles with Dpa>457.7nm when the particle size increases more than 457.7nm or the pressure after the orifice decreases. For particle Dpa=856.8nm, the penetration is 83.2% (the pressure after the orifice is 395torr). When the conical inlet is used before orifice, it is found that the penetration efficiency is higher than that to the E-9 orifice for particles with Dpa>457.7nm. The penetration efficiency using conical inlet improves to 92.5% for particle with Dpa=856.8nm. The use of the E-9 orifice with the conical inlet may reduce the inertial impaction of the particle in the inlet of the orifice. Secondly, when the flow rate through the E-9 orifice is smaller than the critical flow rate, the diffusion loss of the particle with Dpa<126.1nm increases with decrease in flow rate and decrease in particle diameter Dpa. The penetration efficiency for particle with Dpa=27.6nm are 80.4 % and 72.4 % with the =Q 0.357slpm and 0.242slpm, respectively. The result reveals that E-9 orifice with conical inlet can sufficiently reduce the range of the ’’recirculating zone’’. So the diffusion loss of the particle is decreases (and penetration efficiency increases). When Dpa=27.6nm, the penetration efficiency are 93.3%(Q=0.357slpm) and 83%(0.242slpm). The result shows that the flow condition is critical flow, the pressure after the orifice reduces, the penetration efficiency of the large particle also reduces. when Dpa=856.8nm, the penetration efficiency to the E-9 orifice with conical inlet is from 92.5%(pressure after the orifice is 395torr) reduces to 59%(pressure after the orifice is 220torr). As the pressure after the orifice is decreased, the inertia of particle is increased. Thus more particles cross the centerline and impacts on the wall.