| The study of thermal rectifiers has attracted a rapidly growing interest from researchers due to the enormous potential for their application in thermal control,information processing,energy conversion.Numerous theoretical and experimental studies have demonstrated that the thermal rectification effect can be achieved by graded mass density,bi-material systems,shape asymmetric structures,thermal radiation,phase change materials or through controlling the defects.Although the thermal rectification properties of many structures have been studied,the thermal rectification ratios of nanostructures that have been studied are still relatively low.Whether the thermal rectification performance of pillared nanostructure materials can be improved by applying axial strain in the direction of heat conduction or by changing the chirality of nanotubes has not been studied.Exploring nanostructures with better thermal rectification properties and designing more efficient thermal rectifiers are of great significance for the realization of "thermal computers" for thermal control and information processing.In this paper,the thermal rectification properties of graphene-boron nitride nanotube junctions,GN-SWCNT(12,12)junctions and DGN-DWCNT junctions are studied by molecular dynamics method.The mechanism of the thermal rectification effect of the studied structures is analyzed.The main contents of this paper include:(1)The effects of size parameters(boron nanotube nanotube length,square graphene sheet length)on the thermal rectification properties of graphene-boron nitride nanotube junctions are investigated.It is found that the thermal rectification properties of graphene-boron nitride nanotube junctions are significantly size dependent.At an average temperature of 300K(Δ=±0.5),the thermal rectification ratio of the graphene-boron nitride nanotube junctions can reach 71.38%.(2)Under the optimized size parameters,the effect of axial strain on the thermal rectification properties of graphene-boron nitride nanotubes junctions is studied.It is found that the thermal rectification properties change significantly with the increase of strain,and applying the appropriate axial strain can increases the strength of the standing wave and significantly increases the thermal rectification ratio.When the strain is 10% and the average temperature is 300K(Δ=±0.5),the thermal rectification ratio of the graphene-boron nitride nanotube junctions can reach 188.80%.(3)At the average temperature of 300 K and 200 K(Δ = ± 0.5),the thermal rectification ratios of GN-SWCNT(12,12)junctions can reach 1487% and 2586.4%,respectively,which is much higher than previously studied that thermal rectification ratio of GN-SWCNT(6,6)junctions.We find that the thermal rectification ratio of GN-SWCNT junctions can be further adjusted by changing the chirality of carbon nanotubes in GN-SWCNT junctions.(4)At an average temperature of 300 K,the DGN-DWCNT junctions can obtain high thermal rectification ratio under higher and smaller thermal bias,and the thermal rectification ratio can achieve up to 300.6% even when the thermal bias |Δ| = 0.1.In fact,due to the abundance of low-grade waste heat,high efficient thermal rectifier under small temperature differences should be more important than those under high temperature bias for real applications. |
