A study of improvement of a micro-orifice cascade impactor and its particle classification characteristics
|關鍵字:||多階衝擊器;新型噴嘴;截取氣動直徑;cascade impactor;new nozzle plate;cut-off diameter|
|摘要:||本研究以微孔均勻沉積衝擊器(Micro-Orifice Uniform Deposit Impactor, MOUDI) (Marple et al. 1991)為基礎進行外殼上的改良，使得噴嘴至衝擊板的距離可以量測的更精準，並且將Liu et al. (2013)研發的新型多微孔噴嘴裝置於此衝擊器中，此微孔多階衝擊器在本研究中稱為NMCI (NCTU Micro-Orifice Cascade Impactor)。
本研究首先對NMCI第七、八、九及第十階衝擊器的微粒收集效率曲線進行校正，以確保這些具有新型噴嘴片之衝擊器的截取氣動直徑(dpa50)與MOUDI相同。在校正前，本研究先以光學式電子顯微鏡量測自製噴嘴片的噴嘴大小。量測結果顯示NMCI第七至十階噴的噴嘴大小分別為135.8 ± 0.9、108.1 ± 0.8、54.1 ± 0.6及53.8 ± 0.6 m。由於這些多微孔噴嘴的噴孔數量相當龐大(如第九階噴孔數量為2000)，以光學式電子顯微鏡量測相當耗時，因此為了能夠快速的量測新型噴嘴的孔徑大小，本研究建立了壓損與噴嘴孔徑大小的關係式以量測壓損的方式推估噴嘴孔徑大小，驗證結果顯示，以光學電子式顯微鏡量測的結果與推估的孔徑大小誤差皆小於1%。
校正結果顯示，當NMCI第七至十階衝擊器的S與噴嘴孔徑(W)之比值(S/W)分別調整至4.04、2.63、14.27及12.64時，其dpa50分別為318.6 ± 0.5、180.4 ± 0.5、101.7 ± 0.9及56.4 ± 0.8 nm，與MOUDI第七至第十階的dpa50相近，此外衝擊器的dpa50也相當容易受到噴嘴至衝擊板的距離(S)所影響。因此本研究也以可壓縮流體公式探討NMCI第八至十階的微粒分徑特性並以實驗結果建立S/W值與Stk50, isen1/2的關係式，作為未來多微孔衝擊器的設計參數。|
In this study, to make sure the jet-to-plate distance of micro-orifice cascade impactor can be measured more accurate, a new micro-orifice cascade impactor (NMCI) was designed and improved base on the cases of Micro-Orifice Uniform Deposit Impactor (MOUDI) (Marple et al. 1991). Besides the improvement of the cases, the new nozzles with more smooth and stronger structure which was designed by Liu et al. (2013) were also placed on it. The particle collection efficiencies of the 7th, 8th, 9th and 10th stage impactors of the NMCI were calibrated first. Before calibration, the nozzle diameter of these nozzle were measured by optical microscope, and result show that the nozzle diameter of 7th -10th stages imapactor were 135.8 ± 0.9、108.1 ± 0.8、54.1 ± 0.6 and 53.8 ± 0.6 m, respectively. Due to the number of these nozzle plate are very large, the relationship between the pressure drop through the nozzle plate and the average nozzle diameter was established. Validation result shows that the different of nozzle diameter measured by optical microscope and estimated by the relationship are less than 1%. The calibration result shows that when S/W ratio (S: jet-to-plate distance, W: nozzle diameter) of 7th -10th stages of NMCI were adjusted to 4.04, 2.63, 14.27 and 12.64, respectively, the corresponding dpa50 were changed to 318.6 ± 0.5, 180.4 ± 0.5, 101.7 ± 0.9 and 56.4 ± 0.8 nm, respectively, which were very closed to the dpa50 of 7th -10th stages of MOUDI. Due to the dpa50 of impactor are very sensitive to the variation of jet-to-plate distance, the particle classification characteristic of 8th -10th stages of NMCI was investigated by compressible flow equation and the relationship between S/W ratio and Stk50, isen1/2 was also established based on experimental results as the design parameter of micro-orifice cascade impactor in the future.
|Appears in Collections:||Thesis|