Thermal properties of C17H36/MCM-41 composite phase change materials

Abstract

Phase change materials (PCMs) lie at the heart for energy storage technology. In this paper, we proposed a porous media based composite PCM, consisting of Heptadecane (C17H36) as the core and mesoporous silica (MCM-41) as the shell. Basing on the nanostructures we built and verified, the thermal properties of composite were predicted by molecular dynamics (MD) method, including the melting point, latent heat, specific heat capacity and thermal conductivity. Furthermore, the effects of the filling ratio of C17H36, the pore size or porosity of MCM-41 and the temperature were analyzed. It turns out that the composite C17H36/MCM-41 obtains at least 2-fold increase over bulk C17H36 in the thermal conductivity, due to the introduction of supporting material MCM-41. Owning to the size effect of C17H36 filling in nanopores, both the melting point and latent heat of composite are always lower than bulk values of C17H36, while the specific heat capacity of composite is between values of bulk C17H36 and silica film. The specific heat capacity and thermal conductivity increases with rising temperature. The properties of composite are controllable by tailoring the pore size of supporting material or/and filling ratio of core in the pore. The melting point, latent heat and specific heat capacity would rise with the increase of pore size or/and filling ratio. With respect to the thermal conductivity of composite, it drops when the pore size enlarges or the porosity increases while keeping constant filling ratio; while it first rises almost linearly with the increase of core filling ratio, and then keeps stable after the filling ratio reaches 70%. In addition, increasing filling ratio is more effective than enlarging pore size in improving the latent heat, specific heat capacity and thermal conductivity. On the contrary, the melting point is more sensitive to the change in pore size rather than filling ratio, and it is linearly dependent on the inverse pore size. This work is expected to be helpful in providing some fundamental data for the design of porous media based PCM.