Thermal analysis of two protruding heaters mounted on a substrate plate suspended in an enclosure

An experimental and numerical investigation was performed to evaluate the relative contributions of thermal radiation, natural convection and conduction-to-substrate heat losses from protruding components mounted on a PCB in a sealed enclosure. The experimental apparatus consisted of an air filled enclosure of rectangular cross section where a substrate plate with two longitudinal protruding heaters mounted on one side was suspended. For a range of electric power dissipation in each heat source, several enclosure temperatures were measured under steady conditions and a global thermal resistance from each heater to the atmospheric air outside the enclosure was obtained. These results were compared with those from a two-dimensional numerical simulation combining the finite volumes and the radiosities methods, assuming gray surfaces behavior. The blockage effects of the substrate plate with both protruding heaters to thermal radiation inside the enclosure were taken into account in the numerical analysis. The resulting favorable comparison allowed confidence to the numerical evaluation of the desired relative contributions of the distinct heat loss mechanisms. Conduction-to-substrate was the major contribution, and contribution in the present experiments. The numerical radiation and natural convection had about the same simulation of an actual PCB with heat sources in a sealed enclosure should include all conjugate heat loss mechanisms.