Experimental Validation of Composite Phase Change Material Optimized for Thermal Energy Storage

Thermal energy storage based on phase change materials (PCMs) are advantageous due to their large latent heat storage capacity and favorable melting temperatures. While PCMs have high energy storage by volume, they are limited by low thermal conductivity properties and are often integrated with high thermal conductivity materials to increase the overall power density of phase change/metal composites. The general approach to make such PCM composites consists of dispersing small volume fraction of high thermal conductivity nanomaterials or by implementing micron sized metal foams and flakes, or by using macro scale fins to increase the rate of heat transfer in PCMs. Here, we describe a PCM composite using effective medium properties which are valid for a critical length scale and identify the volume fraction at this scale that is optimized for thermal energy storage. Experimental investigations for cartesian and cylindrical composites made of AlSi12 alloy and octadecane indicate a critical pitch of 1 mm and an optimum metal volume fraction of 0.5 to 0.6. Combined, the optimized composite PCM for thermal energy storage have significantly larger length scale and volume fractions of metal components which is facilitated conveniently using additive manufacturing.