Abstract:

Cotton threads are employed as flow channels in thread-based microfluidic fuel cells, which eliminates external pumps and benefits for miniaturization, showing a promising power source for portable microfluidic devices. However, the cell performance is limited by the fuel transfer at the anode. To better understand the fuel transfer characteristics coupled with electrochemical reaction at the anode, lattice Boltzmann (LB) method was used for the cotton thread-based microfluidic fuel cell. A three-dimensional numerical model of the cotton thread flow channel was developed and the distributions of velocity and concentration of fuel were calculated. The effects of inlet fuel concentration and flow rate on performance and mass transfer characteristics of anode were also discussed. The results show that LB results agree well with experimental results of the anode polarization curve. The velocity of fuel inside the cotton thread is lower than that in the gaps among threads. The fuel concentration decreases along the flow direction under different anodic over potentials and larger decrement is found at higher anodic over potentials. An increasing average current density is obtained with an increase in the inlet fuel concentration, leading to a better anode performance. Moreover, with an increase in the inlet fuel flow rate, a greater difference in the fuel concentration is observed between the location where the cotton thread contacts with reaction interface and other regions. When the inlet flow is low, the difference in concentration is small and the concentration in the rear part of the flow channel is low.

Key words: microfluidics, fuel cells, lattice kinetic scheme, lattice Boltzmann, mass transfer, flow

摘要：

基于棉线的微流体燃料电池采用棉线作为流道，无须外部泵、易于微型化，是便携式微流体设备非常有前景的电源，但其性能受阳极燃料传质的限制。本文采用格子Boltzmann方法研究基于棉线的微流体燃料电池阳极耦合电化学反应的传质特性，通过构建三维的棉线流道数值模型，计算得到该流道内燃料的速度及浓度分布，并讨论燃料的进口浓度及流量对该电池阳极性能及传质特性的影响。计算结果表明：阳极极化曲线与实验结果吻合较好；燃料在棉线内部的流速较低，在不同阳极过电位下，燃料浓度沿流动方向均降低，且过电位越大降低得越多；进口燃料浓度越高时，平均电流密度越高，阳极性能升高；随着进口燃料流量的增加，棉线与反应界面接触部位的浓度与其他区域浓度之间的差异增大，而进口流量较低时，该浓度的差异较小且流道后段的浓度较低。

关键词: 微流体学, 燃料电池, 格子动理格式, 格子Boltzmann, 传质, 流动