Three-dimensional study of convection-radiation heat transfer of a discrete heat source (chip) inside an enclosure cooled by rectangular finned heat sink is studied. Conduction heat transfer through the enclosure walls and radiation exchange between these walls are considered. Convection heat transfer on the outer surfaces of the enclosure to the ambient is considered. A complete three-dimensional mathematical model of the physical system is presented and solved numerically by using finite difference method and programmed inside MATLAB software and validated by using an experimental work. Results show good agreement between the numerical and experimental results in case of considering radiation. The impact of the enclosure aspect ratio and chip power on
its cooling and heat transfer and fluid flow inside the enclosure is investigated. The results indicate that in an enclosed electronic device, the impact of the radiation is important in the thermal analysis when the natural convection cooling is presented. At chip heat flux of 5 kW/m2 , neglecting radiation impact rises chip temperature by about 20%. The minimum chip temperature is obtained at an aspect ratio of 1.25. Increasing the chip heat flux
and aspect ratio reduces the airflow eddies inside the enclosure. At chip heat flux of 1.25 and 5 kW/m , radiation Nusselt number represents about 17.8 and 19.7% of the total Nusselt number, respectively.