The melting and solidification process in enclosures filled with phase change materials has wide applications in metal casting, thermal energy storage, building insulation and battery thermal management. In the current study, the melting and heat transfer characteristics of Nano Enhanced Phase Change Material (NEPCM) are numerically investigated in a differentially heated square cavity. The NEPCM consists of ice as the phase change material (PCM) into which Single Walled Carbon Nano-tubes (SWCNT) particles of uniform size is dispersed. The left and right walls of the enclosed cavity are maintained at a constant wall temperature and considered as hot and cold walls and the remaining walls are treated as adiabatic and the simulation is performed using Ansys Fluent 19.2. The temperature difference between the hot and cold walls are varied and further investigations are performed by considering the effects of nanoparticle volume fraction on the melting behavior of NEPCM. The results are analyzed by plotting the stream function, melting interface temperature and velocity contours. The results indicate that the addition of SWCNT nanoparticles significantly influences the heat transfer characteristics and melting rate of phase change material. It is also found that the increase in nanoparticle volume fraction enhances the average melting and heat transfer rate of phase change material. The present results are validated and are in excellent agreement with the benchmark results available in literature. © Published under licence by IOP Publishing Ltd.