磁性顆粒在磁場中之運動軌跡; Magnetic-field-induced collisions of magnetic particles

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Title:	磁性顆粒在磁場中之運動軌跡;Magnetic-field-induced collisions of magnetic particles
Authors:	蕭凱文;kao-wen shou
Contributors:	環境工程研究所
Keywords:	軌跡分析;磁性顆粒;DLVO理論;膠體;trajectory analysis;magnetic particle;colloid;DLVO theory
Date:	2004-10-21
Issue Date:	2009-09-21 12:16:23 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	膠體一般被定義為1?10 μm之微細顆粒，由於尺寸的關係而不易因重力導致沈降，然而當兩顆粒相互接近時，會因彼此作用力的影響，導致碰撞行為的發生。關於膠體間作用力的探討，由科學家Derjaguin and Landau與Verwey and Overbeek分別在同一年時間先後提出的理論最廣為大家所熟知，簡稱為DLVO理論。DLVO理論把膠體間作用力主要分為凡得瓦爾吸引力及靜電斥力。若是顆粒具有磁性時，外加磁場會使得顆粒間產生一額外的磁偶吸引力而相互聚集。本研究係利用影像攝錄系統及處理軟體，觀察及分析磁性顆粒在磁場中運動行為，並與軌跡模式模擬之結果進行比較。結果發現，因為兩顆粒間隔距離隨著顆粒濃度升高而縮短，又兩顆粒間磁偶極吸引力的大小會隨著磁場強度升高而增強，因此，顆粒碰撞的特徵時間會隨著顆粒濃度的升高，或是磁場強度的增強而縮短。就兩顆粒運動軌跡圖來看，雖然兩顆粒中心點連線與磁場方向之夾角的改變，會造成運動軌跡的變化，但大部分都是呈現實驗分析與軌跡模式運算相似的情況。相異情況的發生是因為軌跡模式所模擬的情況並沒有考慮周圍顆粒的影響，所以造成在低磁場時，若兩顆粒中心點連線與磁場方向之初始夾角大於54.7度，實驗分析與模式運算所得之結果會出現截然不同的結果。 Colloid is generally defined as particle between 1 μm and 10 μm. When two particles approach each other, several types of interaction can come into play which may have a major effect on the collision process. The two most familiar colloidal interactions are van der Waals attractions and electrical repulsions, which form the basis of well-known DLVO theory, developed independently by Derjaguin and Landau and Verwey and Overbeek. When a magnetic field is applied to magnetic particles, these particles experience additional attractionse along the direction of the external field and repulsions normal to the external field; as the consequence, chains are formed by magnetic particles. Magnetic-field-induced collisions of magnetic particles areinvestigated via microscopic visualization system and digital image analysis in this work. The observed collision paths of particles were compared with simulation results obtained from trajectory analysis. Results suggest that the characteristic time decreases with increasing particle concentrations and increasing magnetic field strengths.It was also found that the trajectories of the particles in suspension are similar to those obtained numerically from trajectory analysis. Results also suggest that the angle between the particles centerline and the magnetic field direction affects shapes of both experimental and theoretical collision paths significantly.
Appears in Collections:	[Graduate Institute of Environmental Engineering ] Electronic Thesis & Dissertation

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