Understanding Solidification Behavior of Salt Phase Change Material with Added Carbon Nanoparticles Using Computer-Aided Cooling Curve Analysis

In recent years, nanoparticle-dispersed salt-based phase change materials (PCMs) have emerged to be suitable for thermal energy storage applications. In this work, the carbon nanostructures of graphite, multiwall carbon nanotube (MWCNT) and graphene were separately dispersed in potassium nitrate. Solidification of these nanosalt-PCMs was analyzed using a computer-aided cooling curve analysis technique. The technique is much more effective in comparison with other alternatives such as differential scanning calorimetry, as it is simple and low cost and employs large sample sizes. In the present study, PCM sample size of 1kg was fixed with nanoparticle concentration varying from 0.1 to 0.5% by weight of the sample. The solidification time of the PCM was observed to decrease significantly on addition of nanoparticles indicating an enhancement in the heat removal rate. It is beneficial as the same amount of stored thermal energy can then be withdrawn at a much higher rate. Graphite and MWCNT additions decreased the thermal diffusivity property of the base PCM, while the graphene additions resulted in higher thermal diffusivity. However, the benefits of addition of nanoparticles to the salt-PCM reduced on thermal cycling. SEM images show that the deterioration in the observed enhancements occurred due to agglomeration of nanoparticles. This was observed in the initial 3-4 thermal cycles, and the nanosalt-PCM remained stable thereafter. The PCM developed here offers higher heat transfer rates with superior energy density.