當一個管道的尺度接近於一個電荷層的厚度時(典型的厚度定義為10~100 nm)，管道內的分子運動與非平衡效應與一般大尺度下的行為有很大的差別，尤其是針對溶質與溶劑的傳輸行為有顯著的作用，稱之為奈米流體。然而，奈米流體並非是全新領域，此領域的研究隱含在許多的科學研究上，如細胞膜生理學、膠體科學和薄膜科學等等，近年來隨著微流體與奈米科技的進步，針對奈米尺度下的流體運動行為問題已經吸引許多人的關注與興趣。
此論文的第一部份，利用修正後的波以松-波茲曼模型去模擬調查針對電動/壓力驅動具有離子空間效應的電解液傳輸於奈米隙縫與奈米圓管能量轉換上的差異性。其結果顯示當考慮有限離子尺寸大小時在所有不同的電解液濃度下，流動電導值皆會增加，特別是在較高的表面電荷密度下更為明顯。而主要造成流動電導值增加的原因是在於奈米空間內靜電荷密度在有考慮有限離空間時皆被放大。更進一步的比較奈米隙縫與奈米圓管的流動電導值，發現奈米圓管的流動電導值被放大的程度比奈米隙縫更為明顯，其原因是奈米圓管的幾何效應使靜電荷密度被集中放大。最後，發現當考慮有限離子空間時的電解液流動於兩種奈米空間內電滲流的貢獻使得電子電導值增加，特別是在較高的表面電荷密度下。
此論文的第二部份，利用波以松-能斯特-布郎克方程式來模擬調查逆向電透析機制在帶有負的表面電荷密度錐形奈米孔洞內的現象分析。此研究考慮三種不同的電解液，分別是氯化鉀、氯化鈉和氯化鋰，並且去探討不同濃度梯度、表面電荷密度與擴散係數對於逆向電透析系統電流電壓特性曲線與能量轉換係數的效應。結果顯示當擴散方向從奈米孔動的底側到尖端側，此時陽離子的遷移數會增加，其原因為在奈米孔洞的尖端側發生電雙層重疊的現象，使得逆向電透析系統的轉換效率較高於擴散方向從尖端側到底側。換句話說，逆向電透析系統在錐形奈米孔洞內的擴散方向決定轉換效率的優劣。此外，結果還顯示當陽離子與陰離子的擴散係數接近時，系統的轉換效率會增加。然而，針對陽離子的擴散係數小於陰離子的擴散係數時，系統的擴散電流與擴散電壓會發生反向的電流電壓特性曲線表現。而且，結果還顯示在較低的表面電荷密度下轉換效率會隨著濃度梯度增加而增加。最後，此項研究發現最大的轉換效率值可高達45%。

As the channel size approaches the thickness of the charged layer (typically, 10~100 nm), the resulting molecular and non-equilibrium effects are markedly different from those observed in larger channels and have a significant effect on the transport behavior of solutes and solvents. As a result, the problem of modeling fluidic behavior at the nanoscale has attracted increasing interest in recent years.
In the first part of this thesis, simulations based on a Poisson-Boltzmann model, suitably modified to take account of the steric (i.e., finite ion-size) effect, are performed to investigate the ionic transport phenomenon within two nanofluidic confinements, namely a nanoslit and a nanotube, for the case of both electrokinetic and pressure-driven flows. The results show that for all values of the electrolyte concentration, the streaming conductance increases when the steric effect is taken into account; particularly under high surface charge density conditions. In addition, it is shown that the steric effect amplifies the net charge density in both confinements. The enhancement in the streaming conductance is particularly pronounced in the nanotube since the geometry effect of the nanotube results in a greater amplification of the net charge density. Finally, it is shown that for both nanofluidic confinements, the contribution of electroosmotic flow (EOF) to the electrical conductance increases when the finite ion size is taken into account.
In the second part of the thesis, numerical simulations based on the full Poisson-Nernst-Planck (PNP) equations are performed to investigate the reverse electrodialysis (RED) phenomenon in negatively-charged conical nanopores. The simulations consider three different salts, namely KCl, NaCl and LiCl, and examine the effects of the concentration gradient, surface charge density and diffusion coefficient on the current-voltage characteristics and energy conversion efficiency of the RED system. It is shown that when diffusion takes place from the base side of the nanopore to the tip side, the transference number of counter-ions ( ) is enhanced due to an overlapping of the electrical double layer (EDL) in the tip region. As a result, the higher energy conversion efficiency of RED than the salt ion diffusion from the tip side to the base side, i.e., the RED performance of the conical nanopore is dependent on the direction of salt concentration gradient. In addition, the results show that the conversion efficiency also increases as the diffusion coefficient of the positive ions ( ) approaches that of the negative ions ( ). For , the diffusion current and diffusion potential in the negatively-charged conical nanopore show negative on the current-voltage characteristics. Moreover, the conversion efficiency also increases with an increasing concentration gradient given a small surface charge density. For the RED device considered in the present research, the maximum power conversion efficiency is found to be around 45%.

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