Molecular Dynamics Study on Heat Wave and Thermal Diffusion in Solid

Abstract

While majority of heat transfer occurs by way of the thermal diffusion mechanism and Fourier′s law, at nanoscale, the heat wave thermal transfer takes place at high energy density heating. In this study, we discuss the mechanisms and relations for these two kinds of heat conduction. The solid model in the shape of nanoribbon heated from one end is assumed to consist of particles with the Lennard-Jones potential. The temperature is considered as projections along longitudinal and transverse directions of calculation region exhibiting two kinds of heat waves with different velocities and amplitude. The separation of the temperature on translational component corresponding only to the heat wave and vibrational one showing both types of heat conduction is done. The heat flux evaluations in molecular dynamics have previously been done only in the study of thermal diffusion, but not for propagation of the heat wave. Two kinds of evaluation equations, the external heat flux that shows the heat wave flowing into and out of a small region and the internal heat flux that shows the heat wave passing inside of a small region, has been compared. The internal and external heat flux values of the heat wave differ from the ones for the thermal diffusion. The heat flux between layers normal to the direction of wave propagation shows the layer to layer motion, as opposed to a small region expansion and contraction at thermal diffusion. Force, velocity and displacement of particles at the heat wave propagation are also studied.