Assessment of the Effect of Addition of Nano Particles on Thermal Energy Storage Parameters of Phase Change Materials

Abstract

Molten salts have high prospects of being used in solar power plants as phase change materials (PCMs) for thermal energy storage (TES) on virtue of their superior TES functionalities. The suitability of a simple computer aided cooling curve analysis (CACCA) for characterizing thermal energy storage phase change materials (PCM) was proposed in the present work. In the present work, the effects of addition of various carbon based nanostructures on TES parameters of KNO3 were investigated. The solidification time of the PCM significantly decreased on nano particle addition indicating an enhancement in the heat removal rate. Graphite nanoparticles and MWCNT additions decreased the thermal diffusivity property of the base PCM while the addition of graphene resulted in higher thermal diffusivity. However, the benefits of addition of nanoparticles to the salt-PCM reduced on thermal cycling. The use of dispersants such as carbon black and TiO2 significantly reduced the degradation of the nanosalt-PCM on thermal cycling. Further, solidification of potassium nitrate and zinc-8% aluminium alloy (ZA8) were studied to compare their suitability for TES applications in the concerned temperature range. Metallic PCMs offered higher thermal diffusivity and heat transfer rates while salt PCMs offered higher energy density. These PCMs were chosen to demonstrate the ability of the proposed technique to characterize PCMs freezing at a single temperature as well as over a range of temperatures. Further, suitability of a novel Hot-Cold Probe Technique for assessment of the heat transfer characteristics of nanosalt-PCMs was determined. The probe-PCM control experiment is a stand-in for a container-PCM unit in a TES system. This perspective is different from the conventional PCM characterization studies. The heat flux curves justify the benefits of decrease in solidification time as the nanoparticle added PCMs ensured higher heat flux into the probes.