Rising challenges in electric mobility and computing domain to control and condition the temperatures inside circuit boards and motor control drivers call for efficient and effective heat sink designs. Phase change materials come handy and have applications in conditioning temperatures in electronic devices. They prevent failures and increase their efficiencies at different temperatures and conditions. In the present study, the complex flow physics of phase change materials during melting is studied, inside a square enclosure with a heat source mounted at the bottom wall. The walls are assumed to be adiabatic, the material properties of heat source are that of silicon at 330K. The turbulent natural convection flow is modeled by the computational fluid dynamics (CFD) approach using Reynolds averaged Navier-stokes equation (RANS) with Lambremhorst k-ϵ turbulence model. A finite difference method is employed to discretize the governing equations. An in-house CFD code was computed for simulating the convective heat transfer characteristics. The flow physics of three different phase change materials (n-Octadecane, PEG900, and Paraffin (RT60)) have been analysed for a fixed Grashof number value of 103. The transient flow characteristics are examined by plotting the stream function, velocity, and temperature variation with time of the phase change materials. © Published under licence by IOP Publishing Ltd.