Non-equilibrium molecular dynamics simulations have been performed to investigate the effect of the cross-section shape on the thermal conductivity of argon nanowires. Some typical cross-section shapes, such as triangle, square, pentagon, hexagon and circle, axe carefully explored. The simulation results show that with the same cross-sectional area of the regular polygons, tim thermal conductivities decrease with the reduction of the sides of the polygons, and the thermal conductivity of the circular nanowire is larger than those of the other polygonal ones. Phonon gas kinetic theory is used to analyse the phonon transport in nanowires, and the concept of equivalent diameter is proposed to illustrate the characteristic dimension of the none-circulax cross-section.
The conservation equations for heat conduction are established based on the concept of thermal mass.We obtain a general heat conduction law which takes into account the spatial and temporal inertia of thermal mass.The general law introduces a damped thermal wave equation.It reduces to the well-known CV model when the spatial inertia of heat flux and temperature and the temporal inertia of temperature are neglected,which indicates that the CV model only considers the temporal inertia of heat flux.Numerical simulations on the propagation and superposition of thermal waves show that for small thermal perturbation the CV model agrees with the thermal wave equation based on the thermal mass theory.For larger thermal perturbation,however,the physically impossible phenomenon pre-dicted by CV model,i.e.the negative temperature induced by the thermal wave superposition,is eliminated by the general heat conduction law,which demonstrates that the present heat conduction law based on the thermal mass theory is more reasonable.
