靜電集塵器是一種高效率之微粒收集系統，可以有效移除空氣中之懸浮微粒。其利用電荷的異性相吸原理，在冠狀電極施加高壓電產生電暈放電而使微粒充電，在庫倫力的作用下，微粒充電後受電場影響向收集板移動進而被捕獲。本研究以微粒影像測速儀(Particle Image Velocimetry, PIV)技術，觀察氯化鈉微粒在凹槽型收集電極之二階靜電集塵模型之運動軌跡。測試時上游風速在範圍1.6 m/s〜2.8 m/s和冠狀電極電壓0 kV〜5.5 kV，觀察與測量每個凹槽中帶電微粒的軌跡並量測集塵效率，驗證微粒移動軌跡與集塵效率之相互關係。研究結果表明在凹槽區域使用不同上游風速與電壓情況下，隨著冠狀電極電壓增加，微粒的電荷數提高，氯化鈉微粒容易被接地的收集板吸引。在比較每個凹槽中之微粒變化發現在A part區域微粒經過中心位置才明顯受電場影響，而B、C part區域中，微粒進入凹槽前已受到電場影響，且第三個凹槽後微粒運動軌跡呈現週期性。微粒流經凹槽區，凹槽內x方向速度遠小於主流之速度，而在凹槽內部y方向向下之速度隨上游風速與電壓的增加而變大。在凹槽內壁面處產生較高之渦度，因此再回流機率增加。比較三種不同設置之收集區，上下收集板之距離影響電場甚大。三者之集塵效率大小為平板>凹槽>低平板收集電極，其中集塵效率趨勢會隨風速的增加而降低，最低可達38.8%；隨著冠狀電極電壓的增加而升高，最高可達99.2%。凹槽設計可降低微粒落入凹槽內之x方向速度，減少再回流率，考量上游風速增加導致y方向速度在凹槽內提升以及上下電極距離增加而降低凹槽設計之作用。

Electrostatic precipitator (ESP) is a highly efficient particle collecting device, which effectively removes suspended particles in the air. Because of principle of opposite attraction of charge, corona discharge is generated when high voltage electric field is applied to the corona electrode. Driven by Coulomb force, the particles are charged and moved to the collection plate. In this study, the trajectories and velocities of the charged NaCl particles in a two-stage ESP with cavity-type collector electrode were measured by Particle Image Velocimetry (PIV). Within a range of upstream velocity from 1.6 m/s ~ 2.8 m/s and the corona electrode voltages of 0 ~ 5.5 kV, the trajectories of the charged particles in each cavity were observed and measured, and the collection efficiency is calculated to verify the relationship between the trajectory of particle movement and the collection efficiency. The results show that at various voltage and upstream flow velocity settings, particle with higher charger number due to increasing corona electrode votage will be faster to move towards the collecting electrode. Comparing the results in each cavity, it is found that the particles in the A part are affected by the electric field when they are over the center position, while in the B and C part, the particles are affected by the electric field before entering the cavity, and the results show that after the third cavity, the trajectory of particles in the cavity starts to show periodity. The velocity of the particles pass through the cavity in the x direction will be smaller than the mainstream flow velocity, The downward velocity in the y direction inside the cavity increases as the upstream velocity and voltage increase. Higher vorticity is generated on the inner wall of the cavity, so the probability of re-entrainment increases. Comparing the three different collection areas, the distance between the upper and lower collection plates affects the electric field value, the collection efficiency from large to small are high plate, cavity, low plate. Collecting efficiency results show higher flow velocity makes the particle collecting efficiency lower, the lowest is 38.8%, whereas higher corona electrodes voltage makes the collecting efficiency higher, up to the highest case of 99.2%. The cavity design can reduce the x-direction velocity of particles when falling into the cavity and reduce the re-entrainment rate. Considering that the increase in upstream velocity causes the y-direction velocity to increase in the cavity and the distance increases between the upper and lower electrodes will reduce the effect of the cavity design.

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