Simulation study on the flow behaviors of weak electrolyte solutions in nano-sized and micron-sized pores considering electric double layer interactions

Abstract

ABSTRACT The interactions between the ions in the weak electrolyte solutions and the charged solid wall result in the formation of an electric double layer (EDL) in nano-sized and micron-sized pores. However, in nano-sized pores, EDLs may be overlapping. Herein, a widely applicable Poisson-Nernst-Planck equation combined with the Navier–Stokes equation was adopted for the flow of weak electrolyte solutions under pressure-driven conditions. Meanwhile, the finite element method was utilized to solve the governing equations and investigate the influence of EDL interactions on flow behaviors in different pore radii (25 nm~5 μm). The results showed that as the pore radius increased, the influence of EDL interactions on fluid flow behaviors first increased and then decreased. The influence of EDL interactions on fluid flow behaviors was the most noticeable when the pore radius was close to the EDL thickness. Furthermore, the influence of EDL interactions appeared to be negligible in the pore radius greater than 5 μm. When EDL interactions were ignored, the volume flow in the pores of the circular, square, and equilateral triangle was increased by about 13%. This study provides new insights into the flow behaviors of weak electrolyte solutions in nano-sized and micron-sized pores.