Asymmetric thermo-electro-osmotic responses in charged conical nanochannels

Abstract

Nanofluidic thermo-electric and thermo-osmotic responses have attracted increasing attention for their potential in low-grade heat energy recovery. However, the synergistic influence of geometric asymmetry and electrolyte physical properties on these responses is often overlooked. This study investigates asymmetric thermo-electro-osmotic responses by systematically varying parameters such as conicity, Debye length, and surface charge density within conical nanochannels. We employ the numerical model coupling extended Poisson-Nernst-Planck-Navier-Stokes and energy equations to simulate ion transport, fluid flow, and heat transfer. Results demonstrate pronounced asymmetries in thermo-electric and thermo-osmotic responses between forward and backward nanochannel configurations. The short-circuit current strongly depends on conicity, Debye length, and surface charge density, while the Seebeck coefficient is primarily influenced by Debye length, and surface charge density. Thermo-osmotic flow is significantly affected by all parameters, with flow direction reversals observed under specific conditions. The study highlights that Debye length and surface charge density significantly influence both thermo-electric and -osmotic responses, whereas geometric asymmetry predominantly affects thermo-osmotic response. This study provides a valuable framework for understanding fundamental thermal-driven transport phenomena at the nanoscale. The observed synergistic effects between various parameters offer insights for optimizing thermo-electric energy conversion and fluidic control within conical nanochannels, paving the way for innovative applications in nanofluidic technology and energy recovery systems.