Study on the theoretical calculation method for the effective thermal conductivity of carbon nanotube composite molten salt for solar energy application

Abstract

Carbonate salt is a potential heat storage material for solar thermal power. Aimed at calculating the effective thermal conductivity of Li 2 CO 3 -K 2 CO 3 eutectic doped with carbon nanotube (CNT), a theoretical calculation method based on the three-dimensional random curl structure model was developed. Meanwhile, for the purpose of method verification, CNT composite molten salt was prepared by high-energy ball grinding method. The curl degree of carbon nanotube was determined by image identification technique. The effective thermal conductivity of the composite molten salt was measured to validate the calculation model. The comparison showed that, for well-mixed CNT composite molten salt, the error of the theoretical calculation model was less than 8.5%, which indicated that this calculation model can be used to calculate the effective thermal conductivity of CNT composite molten salt. Moreover, the influence of key factors such as the curl degree and aspect ratio of CNT on the effective thermal conductivity of composite molten salt were revealed. The results included that, first, the effective thermal conductivity ( λ eff ) of composite molten salt decreased with increasing CNT curl degree. Second, increasing CNT aspect ratio to 175 could improve λ eff of composite molten salt. Third, the increase of CNT thermal conductivity was the key factor to the improvement of λ eff of composite molten salt. Fourth, λ eff of the composite molten salt could be significantly increased when the order of magnitude of the interfacial thermal resistance (m 2 ·K·W −1 ) was reduced to 10 −7 . • A calculation model on λ of CNT enhanced molten salt for heat storage is given. • Curl phenomenon of carbon nanotube is quantified via image identification. • 3-D random curl structure physical model is established. • Carbon nanotube enhanced salt is prepared by ball milling method and tested. • Effective thermal conductivity calculation is validated with experiments.