微纳通道中物理特性随压力变化的流体的电动能量转化

微纳流控技术是微纳米尺度通道内驱动和操控流体流动的科学和技术，近年来已在药物传输、样本检测和能源获取等领域得到了广泛的应用。通常电解质溶液中的离子与微纳通道壁面的相互作用会产生双电层。当通道两端施加较大的压力差时，双电层内离子的流动会形成与流动方向相同的流向电流。同时，净电荷会聚集到微纳通道的下游，使得下游的电势比上游的高，形成与原流动方向相反的电场，称为流向势。这种有效地将机械能和化学能转化为电能的方法，称为电动能量转化，并已逐渐成为新型绿色能源获取方式之一。但实验得到的转化效率远小于理论预测的结果。本项目通过理论分析和数值模拟，研究在高压驱动下流体的物理特性（如流体的密度、粘性、松弛时间和滑移系数等）随压力变化时的流向势和电动能量转化效率，揭示流体的物性参数对流向势和电动能量转化效率的影响机理，并与已有的将物性参数看作常数时实验结果相比较，对先前实验和理论结果的不一致性给出合理的解释。

Micro nanofluidic is a multidisciplinary cross science and technology by controlling the fluid flow in a micro or nanochannel. Recently, it has wide applications in drug delivery, sample detection and energy harvesting. When an electrolyte comes in contact with a micro or nanochannel wall in which the fluid flows, it will result in the formation of an electric double layer. Under an applied large pressure gradient, the transport of the charge within electric double layer results in an electric current in the direction of the flow, known as the streaming current. The charge polarization due to accumulated ions at the channel downstream creates an electrical potential difference between the channel ends, termed the streaming potential. The streaming current can provide an effective means of transferring mechanical energy of the pressure-driven transport and chemical energy of the EDL to electrical power of the streaming current. This clean energy harvesting in micro or nanochannel via electrokinetic phenomena refers to electrokinetic energy conversion (EKEC) and might open a new avenue in the exploration of new sources for renewable energy. However, EKEC in nanofluidic channels showed the maximum efficiency is only in the tune of 10%, which is largely less than the theoretical result. Therefore, the aim of this proposal is to provide detailed analytical or numerical solutions to the streaming potential and EKEC efficiency under the assumption that the viscosity, relaxation time, density and slip coefficient of the fluid vary with pressure when the applied pressure gradient is very high. The dependence of the streaming potential and EKEC efficiency on the variations of physical parameters of fluid will be determined. Reasonable explanations of the disagreement between theoretical and experimental results in which the physical parameters of fluid are assumed to be constant may be obtained.