三種微粒帶電量評估方法之比較與靜電集塵器教具開發

Abstract

環境教育在提升公眾環境意識上扮演無可取代的角色，透過直觀且互動性的教學工具，能顯著提升學習者對污染控制原理的理解。靜電集塵器（Electrostatic precipitator, ESP）為目前最廣泛應用的粒狀污染物控制設備，其性能關鍵取決於帶電微粒與電場間的複雜交互作用。然而，現行微粒帶電量評估方法多仰賴理論模型或間接量測，不同方法常因假設差異而產生不一致的結果。因此，本研究一方面比較擴散充電模型、電流與濃度量測及電移動理論等不同微粒帶電量評估方法之結果，並深入探討造成其結果差異之機制；另一方面，基於流場可視化與靜電集塵技術，開發一套具備可調控氣流與電場之實體教具。 為了觀察微粒的運動軌跡，本實驗系統以透明壓克力板建構兩階段靜電集塵器，配置針狀與平行極板電極，並設有可調控之充電與集塵電壓。微粒產生則使用凝結式單分散微粒產生器（CMAG）產生數目中位數粒徑為1.4 µm之微粒。在帶電量評估方法的對比實驗中，本研究透過雷射與攝影設備捕捉微粒運動軌跡，並結合電移動度理論進行反推；同時輔以氣膠靜電計、氣動粒徑分析儀（APS）與超細凝結核微粒計數器（UCPC），量測離子與帶電微粒之總電流、微粒粒徑與數目濃度，藉此對比其與擴散充電模型及電流與濃度量測之帶電量差異。 實驗結果顯示，提高氣流流量能減少離子停留時間與損失，進而顯著提升下游離子濃度。透過修正管路損失預測初始離子濃度，以充電時間t = 0.45 s代入擴散充電模型計算之理論帶電量介於44–52 e；若考量局部噴流情況（t = 0.03 s），理論帶電量則顯著下降至14–19 e，顯示模型預測值高度取決於充電時間。相較之下，於充電器出口直接量測之電流與濃度法，量測之平均帶電量介於77–110 e。此外，若採樣點位於系統尾端，量測之帶電量則下降至42–62 e。此結果證實高帶電微粒易受沿路管路輸送與靜電損失之干擾，顯示在實務量測上，應避免管路過長而導致量測值低估。然而，利用微粒軌跡結合電移動度理論反推之帶電量範圍最高，介於90–130 e，實驗亦證實微粒濃度與收集電極的電場強度會干擾漂移距離及帶電量之推估。 綜上所述，本研究成功開發一套結合流場可視化與兩階段靜電集塵器之實驗系統，並對比了三種帶電量評估方法之差異。利用微粒軌跡、電移動度理論與可視化技術之結合，能最直觀地呈現微粒在電場中的行為，且能有效避免微粒在管路傳輸中的沉積損失，是評估微粒受力行為最直接且有效的工具；相較之下，擴散充電模型與電流與濃度量測法則易受到離子或帶電微粒沿途損失的干擾而低估帶電量。最後，本研究亦製作出一套具備高度實用價值的可攜式靜電集塵教具，該系統可調控氣流、微粒濃度、充電電壓及集塵電場強度，成功將抽象的靜電集塵原理轉化為直觀的教學模組。

Environmental education plays an irreplaceable role in enhancing public environmental awareness. Through intuitive, interactive tools, it significantly improves learners' understanding of pollution control principles. Electrostatic precipitators（ESP）are widely used for particulate control, yet their performance critically depends on complex particle-electric field interactions. Current particle charge assessments rely heavily on theoretical models or indirect measurements, which often generate inconsistent results due to varying assumptions. Therefore, this study aims to compare the particle charge assessment results obtained from the diffusion charging model, current and concentration measurement, and electrical mobility theory, while elucidating the mechanisms causing these discrepancies. Simultaneously, integrating these flow visualization and electrostatic precipitation techniques, a physical educational apparatus with controllable airflow and electric fields was developed to transform these principles into an intuitive learning module. To observe particle trajectories, a two-stage ESP system was constructed using transparent acrylic plates, featuring needle electrodes for charging and parallel plates for collection, with independently adjustable voltages. A condensation monodisperse aerosol generator（CMAG）produced particles with a count median diameter of 1.4 μm. To compare charge assessment methods, particle trajectories were captured using laser and photographic equipment to back-calculate charge via electrical mobility theory. Simultaneously, an aerosol electrometer, an aerodynamic particle sizer（APS）, and an ultrafine condensation particle counter（UCPC）were employed to measure the total current of ions and charged particles, as well as particle diameter and number concentration, thereby comparing the resulting particle charge with those obtained from the diffusion charging model as well as current and concentration measurements. Experimental results showed that increasing the airflow rate reduced ion residence time and losses, thereby significantly enhancing the downstream ion concentration. By correcting for transport losses to predict the initial ion concentration, the theoretical charge calculated from the diffusion charging model ranged between 44–52 e when utilizing a charging time of t = 0.45 s. However, when considering the local jet flow condition（t = 0.03 s）, the theoretical charge significantly decreased to 14–19 e, demonstrating that the model predictions were highly dependent on the definition of the charging time scale. In comparison, the current and concentration measurement method directly applied at the charger outlet yielded an average particle charge ranging from 77 to 110 e. Furthermore, when the sampling point was located at the system terminus, the measured charge declined to 42–62 e. This outcome confirmed that highly charged particles were susceptible to transport and electrostatic losses along the pathway, indicating that excessive tubing length should be avoided in practical measurements to prevent underestimation of the measured values. Nevertheless, the particle charge range back calculated using the particle trajectory method coupled with electrical mobility theory was the highest, spanning from 90 to 130 e. The experiments also verified that both particle concentration and the electric field strength of the collection electrode dictate the drift distance, thereby affecting the subsequent back-calculation of particle charge. In conclusion, this study successfully develops an experimental system integrating flow visualization with a two-stage ESP. The combination of particle trajectories and electrical mobility theory provides the most intuitive representation of particle dynamics and avoids transport losses, serving as a direct tool for force behavior evaluation. Meanwhile, diffusion charging model and current and concentration measurement tend to underestimate charges due to particle or ion losses. Finally, this study creates a portable, adjustable ESP educational tool that transforms abstract principles into visual modules, demonstrating a dual contribution to aerosol science and environmental education.