當空氣中過多的懸浮微粒經由人體呼吸而沉積在身體體內時，會引發各種疾病，如心血管疾病、呼吸道疾病、以及肺部相關疾病等。隨著工業發展，工廠和燃煤發電廠等所排放出的懸浮微粒越來越多，若不加以控管則會對環境及人體健康造成危害。靜電集塵器是一種適用於具有高微粒濃度以及高溫環境下的微粒收集器。二階靜電集塵器是由充電區以及收集區所組成。當提供充電區適當的強電場時，其所產生的電暈放電現象會將通過充電區的微粒進行充電。隨後，帶電的微粒會受到收集區強電場影響產生感應靜電力而往收集電極移動，最後沉積在收集電極（被收集）。為了維持靜電集塵器的收集效率，會藉由敲擊的方式來清潔電極表面。然而，這些被敲落的微粒有機會受到流場的影響而被帶離整個系統，最終導致所排放出的微粒量增加。此種微粒重新回到流場的現象稱之為再迴流（Re-Entrainment）。本論文提出簡易方波形收集電極（Simple Square-Wave Collecting Electrode, SSCE）與穿孔式方波形收集電極（Perforated Square-Wave Collecting Electrode, PSCE）兩種收集電極來抑制微粒再回流的情形，並且和傳統平板收集電極（Flat Plate Collecting Electrode, FPCE）做交叉比較。結果表示，在氣流速度6.0 m/s 且不具敲擊的情況下，PSCE 和SSCE 相較於FPCE 分別減少了18.3% 和9.8% 的收集效率下降。然而在加入敲擊系統後，隨著流場速度增加至6.0 m/s，PSCE 和SSCE 分別下降了8.9% 和11.6% 的收集效率，FPCE 則下降了28.1%，這代表PSCE 及SSCE 能抑制再迴流並且適用於高流場
速度之環境。從收集電極上進行觀察，由於大微粒所產生的慣性力較大，會衝撞方波結構的迎風面，而小微粒則會隨著流場移動而沉積在方波形結構的背風面。在方波形結構裡亦能觀察到有微粒的沉積現象，當流場流經方波板時，方波形結構裡的速度小於主流場的速度，對剝落的微粒造成較小的拖曳力，最終減少微粒再迴流的機會。此外，使用PSCE 時，部分微粒會穿越PSCE 上的孔洞而進入到介於PSCE 與外殼間的一個空間。此空間裡的流速相當地小，除了有較小的拖曳力之外，還能阻擋微粒再迴流於流場當中。相比SSCE，PSCE 可以在流場速度為6.0 m/s 之情況下多抑制4% 的再迴流率。

Breathing too many aerosol particles can cause various diseases such as ardiovascular
diseases, respiratory diseases, and lung-related diseases. With the development of the industry, more and more particulate matters are emitted from factories and coal-fired power plants. If these particulate matters are not in control, they will harm the environment and human＇s health. Electrostatic precipitator is particle collector, suitable for environments that have high particle concentration or are high temperature. A two-stage electrostatic precipitator consists of a charger and a
collector. When a high-enough electric field is provided to the charger, the corona discharge induced in the charger will charge particles passing through the charger. The charged particles will finally deposit onto the collecting electrode because of
the induced electrostatic forces in the collector. In order to maintain the collection efficiency of the electrostatic precipitator, the collecting electrode is usually cleaned by rapping, to dislodge those collected particles to the hopper underneath the collector. However, these dislodged particles have chances to get away from the entire system due to the nonstop airflow, eventually resulting in an decrease of the collection efficiency. This phenomenon is known as re-entrainment. This thesis compares the ability of suppressing particles re-entrainment by three different collecting electrodes, a perforated square-wave collecting electrode (PSCE), a simple square-wave collecting electrode (SSCE), and a flat plate collecting electrode (FPCE). The results show that, at a gas flow rate of 6.0 m/s without rapping, PSCE and SSCE reduce the decreasing of collection efficiency by 18.3% and 9.8%, respectively, when compared to FPCE. However, at a gas flow rate of 6.0 m/s with rapping, the collection efficiency of PSCE and SSCE decreases by 8.9% and 11.6%,respectively, while that of FPCE decreases by 28.1%. This means that PSCE and SSCE can suppress re-entrainment well. By looking into the collecting electrode, large particles impact the upstream side of the square-wave structure, whereas small
particles tend to follow the flow stream and deposit on the downstream side of the
square-wave structure. Besides, when the airflow goes through the square-wave plate, the velocity in the square-wave structure is small, and thus the drag force on the collected particles, reducing the chance of particles re-entrainment. Additionally,
the space between the PSCE and the enclosure is isolated from the main airstream, the airflow velocity in this space is also small. Particles enter this space through the holes of the PSCE would also experience small drag and thus have low chance to reenter the environment. Compared with the SSCE, the PSCE is able to suppress additional 4% of particle re-entrainment rate at 6.0 m/s airflow velocity.

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