以迴轉圓盤式靜電測定器量測水溶液流動帶電特性可行性之評估與探討

Abstract

本研究利用旋轉圓盤系統實驗，觀測水溶液流動帶電情況之變化，並將所量測得到之結果進行一系列的討論與比較。在實驗當中，吾人調整旋轉圓盤系統內的參數條件，包括旋轉盤材質(鋁、銅、不銹鋼、壓克力)、旋轉速度(100rpm~600rpm)、旋轉盤尺寸半徑(1cm、1.5cm、2cm、4cm)、實驗流體容量(1600cc、2200cc)，以及旋轉圓盤與法拉第量測容器之垂直間距(1.5cm、6.15cm)，觀測改變各參數條件下，對於水溶液流動帶電所產生之電流有何種影響。由於固體表面與電解質溶液接觸時，固體透過表面解離，以及離子吸附等化學作用影響，將獲得表面電荷，在界面處自然地形成電雙層現象。因為電雙層存在，且旋轉圓盤轉動與水溶液發生相對運動，電雙層遭受一外力作用影響，進而改變電雙層平衡，使靠近旋轉圓盤表面的部分帶電離子，將被轉動中之圓盤離心力與持續流動之水溶液帶離表面而散布至整個溶液中。當增加旋轉盤旋轉速度時，相對運動也隨之更加劇烈，造成電雙層內更多的離子被帶入水溶液中，並藉由法拉第量測容器進行電流訊號之測量。當改變旋轉盤旋轉速度以及轉盤尺寸半徑大小時，將會影響流場之雷諾數。當旋轉圓盤流場之雷諾數約莫超過4000時，量測所得之電流隨雷諾數上升而下降，與前人文獻結果相似。而當改變旋轉盤材質時，因為材料之物理特性不同，造成圓盤上之表面電位差異，而呈現金屬類材質之轉盤轉動下，量測所得之電流明顯較大之情況。

By using the spinning disk system, we can observe the flow electrification in aqueous solutions. Experiments were performed by varying several system parameters such as radius of spinning disk (1cm、1.5cm、2cm、4cm), material of the spinning disk (aluminum、copper、stainless steel、acrylic), spinning angular velocity (100-600 rpm), the vertical distance between the spinning disk and the bottom of the Faraday measuring vessel (1.5cm、6.15cm), and the different volumes of working fluid (1600cc、2200cc). The influences of varying the different system parameters during flow electrification on the streaming current development performances were investigated, documented, and illustrated. The generation of charge was thought to occur when turning on the motor, which caused relative motion between the spinning disk and the aqueous solution. The relative motion between the spinning disk and the liquid strips off the electric charges within the electric double layer at the solid-liquid interface and thus generates free electrostatic charges in the bulk flow which were collected and measured. Results showed that the Reynolds number of the rotating disk flow field depended on several important parameters such as the radius of disk and the angular velocity of rotation. The current increased as the Reynolds number increased when the Reynolds number was roughly below 4000. As the Reynolds number exceeded 4000, the current decreased as the Reynolds number was further increased, which were results likely consistent with those reported in previous literature.