Diffuser cooling technology for electronic high-density packaging

The original airflow on the VAX 9000 prototype system was well below the rate required to achieve the established cooling and reliability goals. An investigation of the pressure losses through the system established that the exit grille was a major contributor to the overall pressure loss. It was also noted that a large portion of the energy introduced into the airflow at the exit of the fan was in the form of dynamic head. These two facts are related; a high-velocity flow has high dynamic head and causes large pressure drops. A diffuser was designed to decelerate the high-velocity flow and convert this dynamic head to a rise in static pressure. The exit plenum was redesigned to have a lower pressure loss. The original airflow in a prototype model was only 450 ft³ per minute where the goal was at least 600 ft³ per minute. The final rate, using the same fan with a diffuser, was increased to 850 ft³ per minute