Compressibility effects in the design of gas-cooled microchannel heat sinks

Thermal management of high power electronic components (chips) with high heat dissipation ratings using air as the cooling fluid clearly demands non-traditional means to be successful. Many different approaches have been attempted in the past with varying degrees of success. One method is by using heat sinks made of microchannels. In particular, Multi-Chip Modules (MCMs) have benefited from the use of microchannels for the effective removal of heat. Thus, microchannel cooling of high power components has made significant progress in the last few years. For gas cooled systems, the push for higher heat transfer rates is making designers opt for higher flowrates. In order to remove relative high amounts of heat, these heat sinks must allow for relatively high fluid flowrates and consequent relative high pressure drops. This paper describes some compressible flow issues for the successful analysis and design of gas microchannel cooling of microchips. It is shown here analytical and computational studies in which the following parameters are changed: channel width and length, pumping power, and power dissipation. Results indicate that there are limits to the performance of microchannel heat sinks. These limits are imposed by the onset of choking (both frictional and thermal) in the system. Its effect is assessed and discussed. Other related compressible flow problems, such as shocks and the inadequacy of using the incompressible convective heat transfer coefficient for compressible flow, are also discussed