Near-field radiative heat transfer between successive nanowires and its effects on thermal conductivity of mesoporous composites

Abstract

Mesoporous silica substrate consists of uniformly distributed, unconnected cylindrical pores, which can be filled with metallic nanowire. Since the separation distance between two consecutive metallic nanowires is less than the characteristic wavelength of thermal radiation, near-field radiative heat transfer between two consecutive nanowires cannot be ignored, which was simulated by employing the fluctuation dissipation theorem and Green function. Such factors as the separation distance, and the temperatures of the nanowires were analyzed. It turned out that when the separation distance is greater than 0.1 nm and less than 100 nm, the radiative heat flux at the mesoscale is 3–5 orders higher than that at the macroscale, and decreases exponentially with the separation distance increasing. Finally, coupling with thermal conductivities of the substrate, the nanowires, the equivalent thermal conductivity of near-field radiation and the confined gas, the effective thermal conductivity of mesoporous composite was obtained. It was concluded that the effective thermal conductivities of mesoporous composites considering near-field radiation can agree with the experimental results properly. It turns out that the effective thermal conductivities of mesoporous composite along the X, the Y and the Z directions show a great anisotropy. And the effective thermal conductivities of mesoporous composites considering near-field radiation can be almost 3–50% higher than non-considering near-field radiation along Z direction.