One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

中文翻译：

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基于浓度和混合熵指数标准差的电渗微混合器异质性影响的数值分析

在最快的时间和尽可能短的长度内在微流体系统中实现均匀混合物的一种方法是采用具有异质表面特性的电渗流动特性。在具有均质壁的微通道内使用电渗流进行混合主要是在分子扩散的影响下进行的，分子扩散的强度不足以彻底混合流体。然而，表面化学技术可以帮助在微通道壁上创建所需的图案，以产生显着的旋转电流并显着提高混合效率。本研究分析了位于微通道壁上的异质 zeta 电位贴片在受电渗流影响的微通道内产生混合的功能，并确定了实现所需混合速率的最佳长度。建议使用近似 Helmholtz-Smoluchowski 模型以降低计算成本并简化求解过程。结果表明，zeta电位贴片的异质性长度和位置会影响最终的混合能力。还观察到壁上的滑移系数比雷诺数变化对提高电渗微混合器的混合效率具有更显着的影响，有利于zeta电位的不均匀分布。此外，使用具有由滑动表面覆盖的异质 zeta 电位补丁的通道不会导致低雷诺数的充分混合。因此，在这样的雷诺数范围内，没有任何异质性的同质通道将是优先事项。然而，增加雷诺数和异质通道壁上滑移系数的存在提高了相对于均质通道的混合效率。但是应该注意的是，增加滑移系数会使混合效率在任何情况下都急剧下降，尤其是在高雷诺数的情况下。