Abstract: In present study a numerical analysis of complex heat transfer (turbulent natural convection, conduction and surface thermal radiation) in a rectangular enclosure with a heat source has been carried out. The finite volume method based on SIMPLEC algorithm has been utilized. The effects of Rayleigh number in a range from 108 to 1011, internal surface emissivity 0≤ε˂1 on the fluid flow and heat transfer have been extensively explored. Detailed results including temperature fields, flow profiles, and average Nusselt numbers have been presented. In this investigation it has been tried to study the shape of heat source influence on heat transfer and fluid field in the considered domain. According to results in low emissivity values usage of circular obstacles is recommended. Although in high emissivity values using rectangular obstacles lead to more efficiency.Abstract: In present study a numerical analysis of complex heat transfer (turbulent natural convection, conduction and surface thermal radiation) in a rectangular enclosure with a heat source has been carried out. The finite volume method based on SIMPLEC algorithm has been utilized. The effects of Rayleigh number in a range from 108 to 1011, internal surfac...Show More