Enhanced melting behavior of carbon based phase change nanocomposites in horizontally oriented latent heat thermal energy storage system

Present study describes the numerical analysis of the melting process of phase change nanocomposites in a horizontally oriented shell-tube latent heat thermal energy storage system. Organic alkane n-eicosane is considered as the pristine phase change material. The influence of different carbon based allotropes in enhancing the thermal conductivity of n-eicosane is considered in this work. To enhance the thermal conductivity of organic alkane, highly conductive carbon nano inclusions of various dimensionalities such as spherical (nanodiamond), one dimensional (single-walled carbon nanotube) and two-dimensional (graphene nanoplatelets) structures were considered. Effective thermal conductivity of such nanocomposites are theoretically modeled based on effective medium formulation considering the influence of interfacial thermal boundary resistance between the nanostructure and the surrounding host matrix into account. Numerical results show that the interfacial thermal boundary resistance and dimensionality of the nano inclusion significantly affects the thermal conductivity enhancement of such nanocomposites. For a fixed nanomaterial loading of 1 vol%, spherical nanoparticle inclusions enhance the melting rate only by ∼2%. The inclusion of 1 vol% loading of single-walled carbon nanotube and graphene nanoplatelets increases the melting rate by 27% and 40% respectively due to significant thermal conductivity enhancement of the nanocomposite compared to that of pure organic alkane.