The thermal distribution and fluid flow by natural convection inside a closed cool enclosure is studied. A channel section is placed at the center of the compartment and its temperature is hot. Buoyancy flow is induced inside the enclosure due to the thermal variation. Air is considered as the fluid inside the enclosure and its Prandtl number is 0.71. The fluid is expected to obey Boussinesq approximation. To evaluate the flow, the streamline, isotherms, horizontal and vertical centerline velocity and Nusselt numbers were calculated. The flow is modified by changing the Rayleigh number from 103 to 106. The results show the influence of Rayleigh number on the flow pattern, velocity of fluid flow, and heat transfer rate. Computational fluid dynamics is used as the tool for this study.