مهدي خطيبي

The aim of this thesis is to investigate and model the electroosmosis flow based on an alternating electric field, so in this thesis, with the help of modeling the transient electroosmosis flow by solving the Poisson-Nernst-Planck, Navier-Stokes and energy equations, we investigate the complex mechanisms of ion transport and fluid dynamics in microchannels. Smart was paid. In the first part, the comparison of DC and AC electric field on ion transport behavior was investigated. In this regard, two types of electric fields - direct current and alternating current with square, sinusoidal, triangular and toothed waveforms - were chosen to understand their effect. In addition, in this section, symmetric (cylindrical) and asymmetric (conical) nanochannel geometries were compared to eva‎luate the effect of electrical bilayers in creating specific electrokinetic behaviors, such as ion current rectification and selectivity. The results of this section showed that conical nanochannels significantly improve the ion transport characteristics compared to cylindrical channels due to the overlap of the electrical double layer. For example, in the same conditions, the electroosmotic speed for conical and cylindrical nanochannels was 0.1 m/s and 0.008 m/s respectively. In the second part, Joule heating and viscosity loss in soft nanochannels under DC and AC electric fields were investigated with the help of the model presented in the first part. The findings show the superior performance of AC fields in reducing thermal effects, for example, in both aligned and non-aligned modes, the amount of Joule heating with the help of AC field was reduced by 59.32% and 52.75% compared to DC field. As a result, the type of transient electric field is very effective for lab-on-chip device applications in temperature-sensitive biomedical applications. In the third part, a cell-inspired nanofluidic membrane array was used for electrodialysis for desalination applications. The results showed that the single nanochannel array configuration showed relatively uniform salt distribution and achieved a removal efficiency of approximately 58%. The introduction of two nanochannel arrays in distinct locations led to a significant increase in removal efficiency, which reached 72%. The presence of three nanochannel arrays, each with different lengths, created complex patterns, with the highest removal efficiency in the "different lengths" condition of 91%. became. In the fourth part, the investigation of electroosmotic mixing in a wavy microchannel under the influence of surface charge density depending on the sliding length under Newtonian and non-Newtonian fluids was done with the help of the Caro model as one of the most basic applications of electroosmosis. The results of this section indicate that, considering the slip length dependent on the surface charge, the mixing efficiency decreases from 95.5% to 91.5%. In the fifth section, the behavior of AC electrokinetic nanopumps was investigated with the help of the transient electroosmosis model. The results of this section showed that the frequency range plays an important role in the performance of AC electrokinetic nanopumps. In other words, the maximum current is not obtained at very high or very low frequencies, but at the intermediate frequencies where resonance occurs.

جريان الكترو اسمزي گذرا , گرمايش ژول , اثر جدايش يوني , اصلاح جريان يوني , پلاريزاسيون غلظتي يوني

Transient electroosmotic flow , Joule heating , Ionic partitioning effect , Ionic current rectification , Ionic concentration polarization

Mahdi Khatibi

Seyed Nezameddin Ashrafizadeh