2014 Volume 55 Issue 11 Pages 1770-1776
The present study aims to investigate numerically the effective thermal conductivity for different radial nanowire heterostructures (RNWHSs), such as core–shell, tubular–shell, and core–shell–shell types, which are used for resolving thermal dissipation problem. The influence of core radius and shell thickness on the effective thermal conductivity was examined by using the boundary/interfacial scattering (BS) method derived from the Casimir theory. It was found that the effective thermal conductivity of the RNWHSs was smaller than the bulk thermal conductivity of multi-walled carbon nanotubes (MWCNTs) because of the diffusive interfacial scattering effect. When the shell thickness was much thinner than the core radius, the thermal conductivity of the core MWCNT was relatively higher than that of the shell material. Comparing MWCNT/Al2O3 and MWCNT/SiO2 core–shell RNWHSs, the effective thermal conductivities were similar when the core radius was greater than 100 nm or the core porosity was above 0.4, owing to the effect of MWCNT bulk thermal conductivity. Besides, the effective thermal conductivity of the tubular–shell RNWHS with the same cross-sectional area was always lower than that of the core–shell RWNHSs because of additional interfacial scattering at the pores inside the tubular-shell RNWHSs. When the Al2O3 thickness in the core–shell–shell RNWHS of MWCNT/Al2O3/W was less than 135 nm at a fixed MWCNT radius of 100 nm, the effective thermal conductivity increased with core porosity. When the Al2O3 thickness was 1.0 nm, the effective thermal conductivity rapidly decreased with the increase in porosity.