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研究生:林琮禧
研究生(外文):Tsung-Shi Lin
論文名稱:奈米微粒穿透海綿濾材與旋風分離器特性研究
論文名稱(外文):Nanoparticle Filtration Characteristics of Foams and Cyclones
指導教授:陳志傑陳志傑引用關係
指導教授(外文):Chih-Chieh Chen
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:職業醫學與工業衛生研究所
學門:醫藥衛生學門
學類:公共衛生學類
論文出版年:2004
畢業學年度:92
語文別:中文
論文頁數:69
中文關鍵詞:過濾奈米微粒旋風分離器海綿濾材
外文關鍵詞:nanoparticlesfiltrationcyclonefilter foams
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無論從理論或實驗中均可發現:在某些情況之下,粒徑小的微粒,尤其是粒徑小於1 μm的微粒,在靜電集塵器之中常會有充電不足的現象。不帶電的微粒在電場中並不會受到庫侖力的作用而被收集,以致於當微粒小至某一程度之後,靜電集塵器的收集效率反而會有下降趨勢。換句話說,從質量濃度的觀點,靜電集塵器雖然有相當高的效率,不過卻無法有效地收集奈米粒徑的微粒。本實驗的目的即在於尋找適合的海綿濾材,以期有效收集從靜電集塵器脫逃的奈米微粒。實驗中使用定流量噴霧器 (Constant Output Atomizer) 產生粒徑100-7 nm的固體測試微粒並利用掃瞄式電移動度微粒分徑儀 (Scanning Mobility Particle Sizer, Model 3085) 分別量測海綿及靜電集塵器上、下游的微粒濃度與分佈,藉此探討海綿濾材對於奈米微粒的收集效率如何受到孔隙度、表面風速及填充密度等條件所影響。
實驗的結果顯示,在相同厚度、填充密度之下,孔隙度較大的海綿具有較小的纖維直徑,較多的纖維表面積,奈米微粒的穿透率會隨海綿孔隙度的增加而降低 (15 nm的微粒在60 ppi海綿其穿透率為62 %,且隨著孔隙度增加為100 ppi穿透率減少至9 %)。另外,由於停留在海綿濾材時間長短不同,因此奈米微粒對於海綿的穿透率會隨著表面風速的減小而降低 (15 nm的微粒表面風速由9.5 cm/s增加至66 cm/s時,所得到穿透率由10.5 %上升至62.5 %)。海綿填充密度的影響與孔隙度類似,較高填充密度意味著有較多濾材表面積,因此填充密度愈大其奈米微粒穿透率愈小。從研究中可發現,低孔隙度、低填充密度且低過濾風速可以得到較高的過濾品質。在實驗中靜電集塵器處理風量設計為100 L/min。微粒粒徑小於最易穿透粒徑 (大約0.3�n �慆) 其穿透率隨著粒徑減少而降低。不過在15 nm (穿透率為19 %) 以下,微粒因為部分充電的原因使得微粒穿透率上升。利用海綿濾材 (110 ppi,填充密度0.04,厚度25.4 mm) 串接於靜電集塵器之後可以有效控制奈米微粒 (穿透率由 19 % 降低至2.5 %)。由於靜電集塵器所造成的壓降幾乎可以忽略,即使奈米微粒經過靜電集塵器時有部分充電而無法完全收集的情形,從過濾品質而言靜電集塵器仍是優於海綿濾材。
由於旋風離心裝置無活動式機件,且有建造價格便宜、維修容易、且可以回收製成物料等優點,因此在工業上應用極為廣泛。然而,針對旋風分離器各種設計參數對微米微粒收集效率的影響卻依然不清楚,甚至極少部分提及奈米微粒在旋風分離器中的過濾特性。無論從理論或是實驗均可以發現在接近真空狀態之下,超細微粒在旋風分離器中的的收集效率會提高,且可觀察到奈米微粒會因擴散作用而被收集,不過在常壓之下,奈米微粒的過濾特性卻甚少著墨。本實驗的目的即在於探討切線式旋風分離器中不同構型及操作條件之下之奈米微粒及微米微粒收集效率,其中包括旋風集塵器處理風量、排出管長度、旋風分離器本體長度,及不同構型及操作條件之下壓降變化。實驗中使用定流量噴霧器 (Constant Output Atomizer) 與超音波霧化器 (ultrasonic atomizing nozzle) 產生粒徑100-7 nm及1 �慆以上的固體測試微粒,並利用掃瞄式電移動度微粒分徑儀 (Scanning Mobility Particle Sizer, Model 3085) 與氣動微粒分徑器 (aerodynamic particle sizer, Model 3321A) 來測量奈米及微米粒徑範圍的氣懸微粒數目濃度大小。利用量測旋風分離器上、下游的微粒濃度與分佈,藉此探討旋風分離器對於奈米微粒與微米微粒的收集效率及壓降如何受到處理風量、排出管長度及旋風分離器本體長度等條件所影響。
Stairmand高效率旋風分離器Q=10 L/min擷取粒徑為698 nm,而處理流量愈低,微粒所受到的慣性衝擊愈低,得到較大擷取粒徑 (Q=5、0.6 L/min,dp50分別為1.44、9.7 �慆)。處理風量愈小,奈米微粒停留在旋風分離器內部時間增加,擴散沈積在管壁機會愈大,且粒徑愈小受到擴散沈積作用愈大。在相同Q與h之下,S愈長微粒的收集效率會愈大,不過就過濾品質而言,由於S=12 cm,造成較高的壓降,因此其過濾品質比S=3 cm要低。不同旋風分離器的處理風量,只要奈米微粒的佩雷數相同,則有相同的微粒穿透率。
Due to the partial charging effect, the collection efficiency of an ESP tends to decrease with decreasing particle size. In other words, the collection efficiencies in terms of number density for nanoparticles of an ESP may be relatively low, although high mass collection efficiency is well achieved by a conventional ESP. The main objective of this study was to search the right types of filter foams that could efficiently collect those fugitive uncharged nanoparticles. In order to conduct the aerosol penetration tests of filter foams, a constant-output aerosol atomizer was used to generate challenge aerosol particles in the size range of 7 to 100 nm. A scanning mobility particle sizer (SMPS 3085) was used to measure the aerosol concentrations upstream and downstream of the ESP unit and/or the filter foams. Among the operation parameters were the foam porosity, foam solidity, foam thickness and filtration velocity.
The results showed that aerosol penetration through filter foams decreased with increasing foam porosity, apparently due shorter interstitial distance and the more surface area for aerosol deposition by diffusion. Aerosol penetration increased with increasing filtration velocity due to shorter retention time within the filter foam. The effect of foam packing density on aerosol penetration was very similar to foam porosity (fiber diameter) because higher packing density means more filter materials and therefore, more surface area for aerosol deposition. To take into account the air resistance together with aerosol penetration, we found that low porosity, low packing and low filtration velocity resulted in higher filter quality factor. The ESP unit tested in this work had a designed flow rate of 100 L/min. For particles smaller than the most penetrating size (about 0.3 �慆), the aerosol penetration through ESP decreased with decreasing aerosol size until the size reached about 15 nm (19%). Aerosol penetration of particles smaller than 15 nm increased due to partial charging. Filter foam (110 ppi, packing density of 0.04 and thickness of 25.4 mm) removed most of the fugitive ESP nanoparticles (penetration from 19% down to 2.5%). The air resistance induced by the ESP was almost negligible. Therefore, ESP is superior to the filter foams from the perspective of filter quality, even for small particles with partial charging effect.
論文大綱 i
Abstract iii
目錄 iv
圖目錄 v
表目錄 vii
符號表 viii
第一篇 奈米微粒海綿濾材過濾特性 1
第一章 前言 2
第二章 文獻探討 5
第三章 實驗方法 12
第四章 實驗結果 16
第五章 結論與建議 19
參考文獻 21
第二篇 奈米微粒海綿濾材過濾特性 36
第一章 前言 37
第二章 文獻探討 40
第三章 實驗方法 46
第四章 實驗結果 50
第五章 結論與建議 53
參考文獻 55
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