An investigation on performance of Nano Phase Change Material (NPCM) (water as PCM and 50 nm Al₂O₃) in a spherical capsule is carried out. Both the inlet temperature and volume flow rate of heat transfer fluid (HTF) (Aqua-ethylene glycol solution is used as a HTF) are varied to maintain the capsule wall temperature constant at a temperature range from −4 °C to −10 °C respectively. The volume fraction concentration of the nanoparticles in the used PCM in the experiment ranges from 0.5% to 2%. The results is presented in the form of relations between the solidified mass fraction, percentage of thermal energy storage and the average Nusselt number versus an appropriate combination of Fourier, Stefan, and Rayleigh numbers as well as the volume fraction of nanoparticles. The dimensional analysis that is presented here results a number of useful empirical correlations that can be used in practice.