帶有不均勻表面電荷之矩形微管中的電滲透模擬

Electroosmosis in a rectangular microchannel with an inhomogeneous charged surface

楊忠瑋(Chung-Wei Yang)

指導教授 ： 徐治平

國立臺灣大學/工學院/化學工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.02225

摘要

本文模擬電解質溶液在帶有不均勻電荷表面之矩形微管中的電滲透流現象。所考慮之微管表面一半帶正電，一半帶負電，且維持固定的表面電位。管壁表面不同電位的分佈導致雙向流動的電滲透流，這個特性可利用在微反應器的設計，使其更具彈性。數值模擬的結果顯示，當離子強度低時，最大滲透流速度發生在微流管中間，然而當離子濃度逐漸變高，最大速度發生的地方就會往角落移動。這個現象將有利於反應器的設計，因為最大的速度發生在管壁角落可以改善反應物在管壁角落流動緩慢所造成的不均勻現象。最大滲透流速度隨離子濃度增加而增加，但是當離子強度大到一定程度之後，即接近一個定值。在固定矩形微管截面積和水利直徑時，隨著微管截面形狀比的改變，電滲透流體積流率會有極大值和極小值出現。若外加壓力場P小於104 N/m3，流場分佈受電動力學主控，當P大於104 N/m3，流場分佈為壓力差主控。

關鍵字

電滲透

並列摘要

The electroosmotic flow of an electrolyte solution in a nonuniformly charged rectangular microchannel is investigated theoretically by considering the case where half of the microchannel wall is positively charged and the other half negatively charged, both are maintained at a constant surface potential. This arrangement leads to a bi-directional electroosmotic flow, which makes design more flexible if the microchannel is used as a microreactor. We show that if the ionic strength is low, the maximal electroosmotic velocity occurs at the center of the microchannel. However, as the ionic strength increases, it shifts towards its corners. This feature is advantageous to reactor design because the nonuniformity problem arising from the slow motion of reactants near corners can be alleviated. The maximal electroosmotic velocity increases with the increase in ionic strength, but reaches a constant value nearly when the ionic strength exceeds a certain level. For a constant cross-sectional area or a constant hydraulic diameter, the electroosmostic volumetric flow as a function of the aspect ratio of the microchannel have a minimum or a maximum. We show that if the pressure gradient is smaller than 104 N/m3, the flow field is dominated by the electrokinetic phenomenon. On the other hand, if the pressure gradient is larger than 104 N/m3, it is dominated by the pressure gradient.

並列關鍵字

Electroosmosis

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