| 摘要: | 本研究以有限元素分析法 COMSOL Multiphysics 耦合流場與電場模擬帶電氣懸微粒於靜電集塵式細胞株暴露系統(ALI)中的運動軌跡。過往的文獻提出許多細胞株暴露系統研究呼吸暴露的危害，但這些系統並未實際的定量分析微粒在細胞株沉積的量。特別是在不同的操作參數條件下，微粒的運動軌跡和在系統中的暴露情形皆不相同。因此本研究希冀以數值模擬的方式，輔助靜電集塵式細胞株暴露系統的建構，並以數值模擬結果和實驗結果相互驗證和分析，建構一可信之微粒數值模擬方法。為系統化評估數值模擬結果和實驗結果，以三個評估指標總貫穿率(P)、區域沉積比率(f)和第2區的相對沉積密度(β)分析不同流量、電壓、粒徑大小和電極距離下微粒運動軌跡的變化。
首先，由數值模擬和實驗相互搭配確實改進靜電集塵式ALI系統，改變漸擴角度降低迴流在系統中的產生，並根據使用環境和實驗結果更換材質。本研究中藉由流場流線圖和微粒運動軌跡圖分析流量1.5 lpm和流量0.6 lpm對微粒的影響，並以此改進構型設計。依據Model A和Model B的模擬結果和實驗結果顯示，在電極距離20 mm和流量0.6 lpm下粒徑大小100 nm的微粒於Model B中僅需施加電壓1 kV，即可達到Model A需施加電壓6 kV才達到的完全收集。此一結果顯示改良後的靜電集塵式ALI系統Model B確實較佳，亦突顯施加電壓對於微粒在系統中的暴露量影響是存在的。而微粒的粒徑大小與電壓的關係在研究中也充分展現，例如Model B在電極距離20 mm和流量0.6 lpm的條件下，施加電壓0.5 kV的微粒在粒徑50 nm的總貫穿率約為60 %，而微粒粒徑200 nm的總貫穿率約為80 %，二者的差異代表大粒徑的微粒要達到與小粒徑的微粒相同的總貫穿率需要增加電壓來降低總貫穿率的值。電極距離的變化會造成電場強度和微粒受電場影響時間改變，兩因子的競爭由微粒軌跡線可判斷之。
In the literatures many exposure systems were proposed to study inhalation toxicology, however, the particle deposition flux or the exposed dose had not been well defined in these exposure systems. Moreover, Particle trajectory and deposition were highly depending on operation conditions. Therefore, in this study, we developed a new ESP type air-liquid interface (ALI) cell exposure system and numerically characterized its performance. The commercial CFD software, COMSOL Multiphysics, was coupling the fluid field and the electric field to simulate dynamic trajectory of charged particles in the system and to determine the particle deposition flux. The aim of this study was to establish a numerical simulation scheme to design and to develop an ESP type ALI system. Based on the numerical simulation it was found decreasing expanded degree of the upper exposure chamber would reduce reflux and mitigate unwanted particle loss. Therefore, the new configuration of the exposure chamber was re-designed by considering smoother streamline and particle trajectory to reduce unnecessary spaces and particle loss. The original design, Model A, needs 6 kV to achieve 100% collection of 100 nm particles, but the revised design, Model B, only requires 1 kV. In other words, Model B is more effective than Model A on particle collection.
To further systematically evaluate the performance of the system, three indicators, including total penetration (P), region deposition ratio (f) and relative deposition density in region 2, were introduced. Higher flow rate would case lower total penetration because of more significant re-circulated flow. Although in 0 kV the region deposition ratio was not obviously changing with particle size, the size effect was not negligible when applying voltage. In addition, the applied electric field would increase particle deposition in region 2 and result in more uniform particle depositasion pattern. |
