奈米微粒與次微米微粒在氣膠微粒質量分析儀中的傳輸函數

Abstract

氣膠微粒質量分析儀(APM, Kanomax, Japan)是一部應用離心力與靜電力測量奈米微粒與次微米微粒質量的儀器。過去的文獻指出，微粒在APM內部的擴散損失是造成模擬計算值高估實驗數據(例如:質量分佈)的原因，然而至今仍未有研究能將其差異進行量化(Lall et al., 2009, Tajima et al., 2011)。本研究利用二維數值模式研究奈米微粒與次微米微粒在APM中的傳輸函數，當假設APM中篩選區域的流場為拋物線分佈時，發現本模式的傳輸函數模擬結果與過去採用相同流場的文獻結果相符，但仍舊如過去文獻一樣會高估實驗值。當本研究進一步考慮到因旋轉的篩選區域所引起的強制渦旋及採用更詳細的計算域時，發現旋流出現在APM內部的流場，這些出現旋流的區域增強了奈米微粒在APM儀器裡的對流擴散損失。本研究的研究結果顯著地提高了模式對APM傳輸函數與反應譜的計算準確度。本研究亦根據的數值結果發展出了修正的Ehara模式，該模式可更容易及準確地計算傳輸函數。利用本研究所發展出的模式，預期在未來可發展出準確的即時奈米微粒與次微米微粒的質量分佈量測。

The Aerosol Particle Mass Analyzer (APM, Kanomax, Japan) is one of the popular instruments to measure the mass of nanoparticles and submicron particles. In previous studies, particle diffusion loss in the APM was speculated to be the reason why simulated response functions for the APM overestimated the experimental data. But no models were available to quantify the differences (Lall et al., 2009, Tajima et al., 2011). This thesis studies the transfer function of the APM by using a 2-D numerical model for nanoparticles and submicron particles. At first, the flow field in the annular classifying region of the APM is assumed to be parabolic. It is found that the transfer functions simulated by the present model are in good agreement with previous studies which also considered the parabolic flow profile. But transfer functions are still overestimated just like previous studies. After solving detailed flow and particle concentration fields in the APM by considering the forced vortex due to the rotating classifying region as well as inlet and outlet regions in the calculation domain, recirculation flow regions are found to exist in the APM. These recirculation flow regions lead to enhanced convection-diffusion loss of nanoparticles in the APM. As a result, the present model improves the accuracy of the transfer functions and response spectra of the APM significantly. Based on the numerical results, a modified Ehara model is developed to ease the calculation of the transfer function. Using these models, it is expected that accurate real time mass distribution measurement of both nanoparticles and submicron particles can be realized in the future.