Natural-convection cooling of a housed, simulated printed-circuit board

The rate of heat dissipation from a vertical printed-circuit board (PCB) varies with (i) the separation between the PCB and the adjacent wall of the case containing it, as well as with (ii) the locations of the ventilation holes for cooling air to pass through the case. From more than fifty sets of experimental data, it was concluded that the exact positions of the holes employed in the 300 mm x 300 mm x 200 mm cases used in the present investigation had only a relatively marginal effect on the steady-state rate of heat dissipation from the PCB. Nevertheless, these vents should preferably be in the roof and base of the case. The principal geometric parameter influencing the heat-transfer behaviour is the separation between the large PCB surface and the nearest wall of the container. The simulated PCB used in this investigation was of vertical height 120 mm, horizontal length 150 mm and thickness 10 mm. The steady-state temperature of the simulated board's vertical surface (i.e. the one immediately adjacent to the case) rose sharply as the separation between the simulated PCB and the neighbouring case wall was decreased to below 5 mm, because natural convection was then increasingly inhibited. In practice, employing such a small separation would lead to the more rapid failure of the electronic components of the PCB due to their operation at the resulting higher temperatures. Therefore such gaps should preferably be wider than 5 mm.