Thermal diffusion and phase transition of n-octadecane as thermal energy storage material on nanoscale copper surface: A molecular dynamics study

Abstract High thermal conductivity metal materials such as metal foams, metal particles and even metal fins can effectively improve the thermal conduction of alkanes as phase change energy storage materials. For investigating the microscopic behaviors of alkanes interacted with nanoscale copper surface, the molecular system composed of copper surface and amorphous n-octadecane (denoted by system A) was initially constructed. Simultaneously, the single wall carbon nanotubes were added into the previous system (denoted by system B) to understand their effect on the alkane. By performing molecular dynamics simulations, the potential energy components, diffusion coefficient, structural evolution, spatial orientation correlation function, relative concentration and thermal conductivity were calculated, respectively. The results showed that the crystallization of alkane induced by copper contributing to the enhancement of thermal conductivity of alkane/copper compound phase change materials. And the additive of carbon nanotubes can significantly promote the ordered alignment of alkane molecules. The results also showed that the phase transition temperature of n-octadecane in system B was more than that in system A by about 10 K owing to the further crystallization of n-octadecane induced by single wall carbon nanotubes as illustrated from the diffusion coefficient trends and potential energy component analysis.