複式旋風集塵器性能特性

Performance characterization of the multi-cyclone

毛嘉儀(Jia-Yi Mao)

指導教授 ： 陳志傑

國立臺灣大學/公共衛生學院/環境與職業健康科學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102259

摘要

旋風集塵器可應用於粒狀物控制設備前端，用以去除較大微粒，以延長下游防制設備的使用壽命。過去的研究指出在相同的入口風速下，並聯小型旋風集塵器比起單一個大型旋風集塵器有更高的微粒收集效率，但少有文獻將壓降與微粒收集效率一起探討。本研究將以定流率及定功率系統，以FOM、CADR與CADRE為指標探討複式旋風集塵器的性能特性。
酒石酸鉀鈉為挑戰氣膠，粒徑分布範圍為1至10 μm，數目中數粒徑為5 μm。使用氣動粒徑分析儀(APS)測量旋風集塵器之上下游粒徑分布及數目濃度，以獲得穿透率曲線，並且以品質因數(FOM)、潔淨空氣輸出率(CADR)及有效潔淨空氣輸出率(CADRE)做為評估工具。實驗中測試的所有旋風集塵器和歧管均採用3D列印製成，其中歧管設計分為雙並聯(M2A、M2C、M2D、M2P)以及四並聯(M4A、M4C、M4D、M4P)，根據旋風集塵器出口與歧管出口面積比例，氣流在管內會產生加速(MC2A、MC4A)、等速(MC2C、MC4C)以及減速(MC2D、MC4D、MC2P、MC4P)八種不同形式的複式旋風集塵器。
本研究透過改變歧管角度、分歧管長度，獲得一具最小壓降的歧管設計參數，但是在穿透率以及品質因數的表現上並沒有明顯改善。定流率(40 L/min)且相同截取粒徑下，單一旋風集塵器比複式旋風集塵器有較高的品質因數，主要是因為無歧管造成的壓降，而且單位體積氣流與旋風集塵器主體內壁的接觸面積比例較低，故整體壓降較低，相較於後者具有較高品質因數。此外，除了M4A之外，歧管存在與否皆對複式旋風集塵器的微粒穿透率沒顯著影響，但皆造成壓降增加，導致品質因數下降6%至80%。1.15瓦特的定功率系統下，大致上結果與定流率系統下相同，由於單一個旋風集塵器有較低的壓降，而有較高操作流率及收集效率，得到較高的CADRE。最後，高功率系統雖然可提升整體的CADR，但CADRE反而變差，特別是針對大微粒的收集。
單一旋風集塵器比起複式旋風集塵器有更低的經濟成本，愈大的旋風集塵器有愈低的能量耗損，通過改變歧管的設計參數並不能有效提升FOM，由於大部分的微粒皆在前端的集塵器中被收集下來，後端的歧管的所佔的收集貢獻不大，卻增加了多餘的能量損失。因此，追求節能則建議採用單一旋風集塵器做為預處理設備，若考慮空間因素選擇複式旋風集塵器，則盡量選擇愈大的旋風集塵器，且愈少並聯數目。最後，當該粒徑範圍的收集效率已超過約80%，則增高功率反而會降低CADRE，此情況下可使用較小功率的系統即可。

關鍵字

複式旋風集塵器 ； 穿透率 ； 有效潔淨空氣輸出率 ； 品質因數 ； 歧管設計

並列摘要

The cyclone is usually used as a pre-separator to reduce the particle loading and prolong the service life of other downstream control devices. Previous studies had pointed out that cyclones installed in parallel had higher particle collection efficiency than a single cyclone, when the flow rate was fixed. Yet, the data considering both collection efficiency and pressure drop across the cyclone were limited. This study aims to investigate the effects of cyclone size, cyclone number, and manifold design on the overall performance of multi-cyclone, from the perspectives of figure of merit (FOM), clean air delivery rate (CADR), and effective CADR (CADR/Watt).
The challenge particles of potassium sodium tartrate (PST), count median diameter of 5 μm, were generated using an ultrasonic atomizer and then neutralized by a radioactive source, Am-241. An aerodynamic particle sizer was used as the major aerosol size spectrometer. The particle size distribution and pressure were measured at the upstream and downstream of the cyclones and manifolds to acquire the particle penetration and pressure drop. The figure of merit, CADR and CADRE were used to evaluate the performance of the multi-cyclone and manifold under constant flow and power. The two-channel (M2A, M2C, M2D, M2P) and four-channel (M4A, M4C, M4D, M4P) manifolds connected to the multi-cyclones composed two and four cyclones respectively. According to the cross-sectional area ratio between the outlet of the cyclone and the outlet of the manifold, the airflow in the manifold pipe of the multi-cyclone will be in the three different states: acceleration (MC2A, MC4A), constant velocity (MC2C, MC4C) and deceleration (MC2D, MC4D, MC2P, MC4P). All the cyclones and manifolds are made of PLA by 3D printing technology.
A single big cyclone always performs better than a small cyclone from the FOM standpoint, because the fraction of air flow dragged by the inner wall of the cyclone increases with decreasing cyclone body diameter. Regarding the manifold design, changing the manifold angle and the length of the branch pipe can obtain a manifold design with the smallest pressure drop, but the performance improvement is not significant. A single cyclone has a higher FOM than the multi-cyclone under the same flow, mainly because there is no pressure drop caused by the manifold. Aerosol penetration results that the two-channel manifolds (M2A, M2C, M2D, M2P) and four-channel manifolds (M4C, M4D, M4P) show about the same penetration rate, except M4A. All manifolds cause an increase in pressure drop, thus, a decrease in FOM. Under the constant power (1.15 W) system, the trend of effective CADR as function of particle size is about the same with the case of constant flow (40 L/min). Due to a single cyclone has a lower pressure drop, and a higher operating flow rate and collection efficiency, causing higher effective CADR. Finally, although the high-power system can increase the overall CADR, the effective CADR becomes worse, especially for the collection of large particles.
The single cyclone always has a higher FOM value and effective CADR, thus, a lower operation cost than the multi-cyclone. Adjusting the design parameters of the manifold cannot effectively improve the quality. Therefore, one large cyclone is advantageous over the multi-cyclone, from the energy conservation standpoint. If choosing multi-cyclone due to space restrictions, the number of parallel cyclones should be minimized. In addition, increasing the power does not increase the effective CADR, when the collection efficiency exceeds around 80%. Under the condition, a low-power system is suitable to be used.

並列關鍵字

Multi-cyclone ； Aerosol penetration ； Figure of Merit ； Effective CADR ； Manifold design

參考文獻

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