Solar energy is the most ubiquitous alternate energy source, but has not been harnessed more effectively due to the lack of proper energy storage systems. To address this issue, thermal energy storage systems based on Phase change materials (PCMs) have been extensively researched over the past few years. In many recent works, the efficiency of the potential PCMs were verified using commercial computational fluid dynamics (CFD) software to simulate the experimental conditions with appreciable accuracy. In this numerical analysis, two organic PCMs, the paraffin and D-mannitol having melting temperature of 327 K and 439 K respectively encapsulated in stainless steel enclosures of 40 mm and 80 mm diameter were considered. The enthalpy-porosity model was employed for the analysis. Further the boussinesq approximation and gravity option were included in the numerical procedure to include the buoyancy and natural convection effect during the melting process. Results obtained in terms of liquid fraction contours and energy stored with respect to time were analysed. © 2023 Elsevier B.V., All rights reserved.