Free convection air cooling of the electronic equipment: still a miracle waiting to be explored and explained

An experimental program was carried out to determine the temperature field created by uniform arrays of electronic devices mounted on a printed circuit board. A procedure was developed that allows the taking of infrared pictures of the board under the real flow conditions inside a free-convection-cooled cabinet. The influence of the air drawn in from the unsealed sides, the distance between boards, and the power variation on the temperature profile were studied. The cooling conditions for sealed and unsealed channels were found to be nonuniform in the channel cross-section, with colder regions toward the edges of the board. The unsealed channels showed a slightly more uniform temperature distribution in the vertical direction, and the difference in temperature between different columns was slightly increased when compared with the sealed channels. However, differences cannot be considered important for practical applications. The variation of maximum temperature with the distance between boards and board height was found to be weaker than predicted by existing analytical models. The results cannot be easily explained by the analytical model describing buoyancy-induced flow between two isoflux plates. A possible physical model that explains the observed phenomena is presented.<>