Analysis of\nElectroviscous Effect for Flow of Micropolar\nFluids in a Nanochannel with Overlapping Electric Double Layers at\nHigh Zeta Potential

Flows in nanofluidic channels under\nthe influence of pressure gradient\noften lead to the overlapping of the electrical double layers (EDLs)\naugmenting the electroviscous effect. In this work, we analyze the\nelectroviscous effect for the flow of a micropolar fluid in a parallel\nplate nanochannel, considering EDL overlapping and interfacial slip.\nClosed-form expressions of EDL potential, velocity, microrotation,\nyielded streaming potential, and volumetric flow rate are derived\nsemi-analytically for high zeta potential without accounting for the\nBoltzmann distribution. We observe a significant change in streaming\npotential with inverse ionic Peclet number (<i>R</i>) for\nits lower values, and the range of streaming potential is more for\nthicker EDL. The micropolarity parameter does not have any influence\non the streaming potential for weaker EDL overlapping at a lower <i>R</i> value. For thicker EDL, velocity decreases with the micropolarity\nparameter, while it increases drastically with interfacial slip. However,\nvelocity shows a non-monotonic behavior with interfacial slip and\nmicropolarity parameter for thinner EDL. The microrotation remains\ninvariant with interfacial slip for thicker EDL, whereas its magnitude\ndecreases with slip length for thinner EDL. Although the sensitivity\nof the flow rate on slip (<i>Q</i><sub>s</sub><sup>*</sup>) increases with <i>R</i> for\nthicker EDL, the behavior is non-monotonic for thinner EDL. Furthermore, <i>Q</i><sub>s</sub><sup>*</sup> varies non-monotonically with the micropolarity parameter at higher\ncouple stress parameter values and vice versa. In fact, the volumetric\nflow rate is highly sensitive to slip for thicker EDL overlapping.