Solidification characteristics of water based graphene nanofluid PCM in a spherical capsule for cool thermal energy storage applications

• Addition of graphene nanoplatelets greatly reduced degree of subcooling.
• Thermal conductivity enhancement of ~12% and 56% was observed in liquid and solid of NFPCM.
• Higher cooling rate was achieved in NFPCM for a given driving potential.
• Innermost 9% of total volume solidified during 22% of total solidification time.

This study aimed to investigate the solidification behavior of water dispersed with graphene nanoplatelets (GNPs) in a spherical container during solidification. The nanofluid phase change materials (NFPCMs) with GNP mass concentrations of 0.3%, 0.6%, 0.9% and 1.2% were prepared and their corresponding thermal conductivity was measured both in liquid and solid states. The thermal conductivity data showed the linear and nonlinear enhancement in liquid and solid state, respectively. The addition of GNPs resulted to an appreciable reduction in the subcooling of water from −7 °C to −2.5 °C along with reduction of 25% in solidification time owing to its high thermal conductivity and larger specific surface area. The onset of solidification got advanced in the case of NFPCM due to higher cooling rate in the subcooling region for any given driving potential. The accelerated mode of energy charging occurred during 78% of total solidification time.