Understanding flow and heat transfer characteristics of liquid sodium metal under confined nanochannels of metallic iron: Insights from molecular dynamics simulation and density functional theory

Abstract

Liquid sodium plays a vital role in advanced thermal systems and nuclear reactor applications, necessitating a detailed understanding of its flow and heat transfer behavior in both bulk and confined states. In this study, molecular dynamics (MD) simulations were performed to evaluate the thermophysical properties of sodium metal over a wide range of temperatures. Density functional theory and the Boltzmann transport equation were used to evaluate the electronic thermal conductivity, and MD was used to calculate the phonon thermal conductivity of the sodium metal. Non-equilibrium MD simulations were further performed to investigate flow and heat transfer characteristics of sodium metal under nanoscale confinement of iron walls. The results revealed pronounced interfacial layering of sodium atoms, contributing to increased thermal resistance quantified via Kapitza length. With an increasing temperature gradient, interfacial structuring weakened, resulting in ∼15% reduction in thermal slip length and a 22% increase in heat transfer coefficient (HTC). Under Poiseuille flow, velocity slip increased by 335% with increasing driving force from 1 × 10−4 to 7 × 10−4 eV/Å. The enhanced convective transport and reduced thermal resistance of interfacial sodium atoms lead to a 74.17% increase in HTC for an increase in the sodium Reynolds number from 0.26 to 1.3. Similarly, in Couette flow, increasing wall velocity significantly enhanced HTC owing to distortion of interfacial sodium structure. The multiscale findings demonstrate that interfacial effects dominate heat transfer under nanoscale confinement, yielding HTC values on the order of ∼108 W m−2 K−1, nearly four orders of magnitude higher than macroscale systems.