微纳通道中物理特性随压力变化的流体的电动能量转化

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.

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。

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粘性随压力变化时的流向势和电动能量转化效率，研究结果表明，在较小的电动宽度K下，依赖压力的粘性略微提高了流电位和电动功率输出，这意味着更多的输出电能可以用于外部负荷。无量纲压力粘性系数的增加会导致电动能量转换(EKEC)效率的降低。然而，它可能会导致驱动流动所需的压力的增加。研究结果揭示了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。本项目还研究了微流体相关的诸多前沿方向，为实验提供了许多可靠依据。其中在电磁流动方面，证明了广义Maxwell流体对电磁流动的电粘性效应大于牛顿流体。并且对于具有调制的滑移系数的电磁流动，微通道壁上调制的滑移可以诱导横向流动，从而增加微流控装置的混合速率。此外，我们开展了不同几何形状微管道内牛顿/非牛顿流体周期/非定常电渗流动、磁流体流动、粘性随压力变化的流体流动、两层流体的流动对电动能量转化影响的研究。这些研究内容充分体现了将流体力学与物理、化学等多学科交叉的特点。接着我们还开展了对电渗微推进器、微纳流体传热效应、奇粘性效应等方向的研究，并且都获得了不错的研究成果。