Ballistic thermal wave propagation along nanowires modeled using phonon Monte Carlo simulations

The propagation of ballistic thermal waves when the phonon transport is in the ballistic-diffusive regime is markedly affected by the boundary. This work simulates ballistic thermal wave propagation in nanowires with a phonon-traced Monte Carlo method to investigate the effects of the nanowire characteristics including the radial Knudsen number and the specularity parameter, and the effects of the temporal resolution of the measurements. The phonon boundary scattering accelerates the evolution of the phonon transport from ballistic to ballistic-diffusive and finally to diffusive transport and increases the thermal conduction resistance by reducing the effective thermal conductivity. High heat pulse frequencies lead to thermal wave propagation in ballistic regime, moderate heat pulse frequencies lead to thermal wave propagation in ballistic-diffusive regime and very low heat pulse frequencies lead to purely diffusive thermal wave propagation, i.e. the Fourier thermal conduction. The ballistic-diffusive thermal wave propagation relies heavily on the specific type of the dominated phonon scattering mechanism while the purely ballistic and diffusive propagations do not. Thus, ballistic-diffusive thermal wave propagation should be modeled by a new constitutive equation with new characteristic parameters.