Thermodynamic Reversibility Analysis of Electrokinetic Energy Conversion in Nanofluidic Channels

The thermodynamic efficiencies of electrokinetic pumping and electrical power generation are investigated numerically using a two-dimensional axisymmetrical model containing a finite-length nanoscale cylindrical capillary and reservoirs connecting at the capillary ends. The Navier-Stokes, Laplace, Poisson, and Nernst-Planck equations are solved simultaneously to obtain the fluid and electric current flows. The main goal of this study is to justify the reversibility of electrokinetic energy conversion resulting from one-dimensional analysis. Based on our numerical results, it is found that the reversible electrokinetic energy conversion between the pump and electric power generation is valid only when the dimensionless Debye length is greater than 2. Because of the electric double layer (EDL) overlap and current due to the electrostatic potential gradient, significant deviation in maximum efficiencies between the numerical and one-dimensional analysis results are found when the dimensionless Debye length is less than 2.