Direct Air Cooling of Electronic Components: Reducing Component Temperatures by Controlled Thermal Mixing

Abstract

This paper discusses forced convection heat transfer in a channel populated with discrete components similar to those found in electronics cooling situations. The temperature rise of each component is expressed as the sum of two parts; its adiabatic temperature rise, Tad–Tin, due to the thermal wakes of upstream components; and its self-heating temperature rise, Te–Tad due to its own power dissipation. A component’s temperature can be reduced either by reducing the adiabatic temperature rise or the self-heating temperature rise, or both. This investigation concentrates on the former: reducing the adiabatic temperature rise through increased thermal mixing in the coolant flow. The temperature of the air near the components exceeds the mean temperature of the cooling fluid, often by a large amount. In the present work, small scoops were installed in regions of high temperature but low velocity fluid (i.e., in between rows of components rather than in the free stream) to augment thermal mixing and reduce the nonuniformity. This approach does not induce as large a pressure drop as some conventional “turbulators” for a given decrease in operating temperature. In the present work, the scoops reduced the adiabatic temperature rises by 10 to 55 percent, resulting in up to 19 percent reduction in the overall temperature rise. The test section pressure drop increased 11 percent.