Influence of boundary conditions on nonequilibrium heat transport
When the characteristic size of the material approaches the mean free path of the phonons or the characteristic time becomes comparable to the phonon relaxation time,the Quasi-equilibrium hypothesis is no longer valid,leading to non-local effects within the system.In this situation,boundary conditions become a key factor affecting non-equilibrium thermal transport.Ultrafast laser heating of nano-thin films is a typical case to reflect non-local effects,as both the heat response duration is extremely short and the interaction region occurs at the nanoscale in the heat transfer process.This study invistigates the influence of various boundary conditions of nano-silicon thin films on the non-equilibrium thermal transport and analyzes the transition of phonon transport from diffusion to ballistic.The results show that the thermal transport process is similar between the specular and the reflective boundary condition,and the difference of energy density is minimal within the film.Under convective boundary condition,the energy density is the lowest due to the continues heat loss to the external environment.In addition,it is found that the forced convection will extract more heat than the natural convection by changing the convection mode.And as the film size decreases,the influence of boundary conditions on thermal transport becomes increasingly pronounced.
non-equilibrium thermal transportboundary conditionsconvection modenano-thin film
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