Phase change materials (PCMs) are materials with high latent heat of fusion values which can be used to absorb significant amounts of heat during the melt transition. This absorption of heat occurs at a constant temperature, providing a passive thermal management solution. PCM system work best in transient low power applications such as thermal management of portable electronics, in systems that demand high reliability passive solutions such as aerospace applications, or in systems requiring a significant amount of energy storage such as solar energy applications. The most significant drawback to most PCMs is a low thermal diffusivity, leading to slow progression of the melt front through the system. Slow progression of the melt front often leads to overheat of the liquid phase PCM at the heated surface. Thus, to eliminate superheating, a thermal conductivity enhancer (TCE) is often used in the system to improve thermal diffusivity. The high thermal conductivity of carbon based materials has led to their use as TCEs.
The research investigates the effect of graphite nanofiber addition on the thermal properties of a sub-ambient melt temperature PCM in order to ascertain if the addition of the GNF has a beneficial effect on the thermal conductivity of the material, and if there is any additional possible detrimental effects of the GNF on the melting temperature. While previous studies have reported the benefits of carbon and graphite based TCEs on standard PCM systems, there is little to no work on sub-ambient PCM systems. It is important for thermal designers to understand how all PCM systems respond to carbon/graphite based TCE additions, and the characterization of the thermal properties of these materials is the first step to understanding their behavior.