Validity of kinetic theory for radiative heat transfer in nanoparticle chains

TL;DR

This paper compares fluctuational electrodynamics and kinetic theory approaches to radiative heat transfer in nanoparticle chains, establishing the conditions under which kinetic theory provides accurate results.

Contribution

It clarifies the validity regime of kinetic theory for radiative heat transfer in nanoparticle chains by comparing it with fluctuational electrodynamics results.

Findings

Kinetic theory matches fluctuational electrodynamics when propagation lengths exceed particle spacing.

Kinetic approach accurately predicts diffusive thermal conductivity under specific conditions.

The study explains discrepancies in literature regarding kinetic theory's applicability.

Abstract

In chains of closely-spaced nanoparticles supporting surface polaritons, near-field electromagnetic coupling leads to collective effects and super-Planckian thermal radiation exchange. Researchers have primarily used two analytical approaches to calculate radiative heat transfer in these systems: fluctuational electrodynamics, which directly incorporates fluctuating thermal currents into Maxwell's equations, and a kinetic approach where the dispersion relation provides modes and propagation lengths for the Boltzmann transport equation. Here, we compare results from the two approaches in order to identify regimes in which kinetic theory is valid and to explain differing results in the literature on its validity. Using both methods, we calculate the diffusive radiative thermal conductivity of nanoparticle chains. We show that kinetic theory is valid and matches predictions by fluctuational electrodynamics when the propagation lengths are greater than the particle spacing.