The electroviscous effect in nanochannels with overlapping electric double layers considering the height size effect on surface charge

Abstract

The electroviscous effect has been extensively investigated in micro/nano scale ions transport, fluidic flow and heat transfer, etc. Previous researches often used constant surface charge in theoretic calculation and numerical simulations. However, for thick overlapping electric double layer (EDL) nanochannels, the channel height size effect on surface charge cannot be neglected. In this work, we consider the channel height size effect on surface charge to investigate the related ions transport, fluidic flow and heat transfer in nanochannels. The corresponding results show that the deviation considering the height effect or not is significant, especially in the situation of boundary slip. The relative errors of local ionic concentration and potential can reach 50% and 8%, respectively. The maximum relative errors of induced electrical field strength and the ratio of apparent viscosity to fluidic viscosity reach 10% and 9%, respectively, indicating strong height size effect on the fluidic flow. The deviation of Nu is relatively small and almost not affected by the surface charge. These deviations will decrease to zero when the channel height is large enough or the solution concentration is high enough to reach a non-overlapping EDL situation. The results of this work are meaningful to further understand the electroviscous effect in nanochannels, which may provide useful guidelines for the design and performance optimization of nanofluidic devices.