Hotspot-adapted cold plates to maximize system efficiency

This modeling study is focused on the potential and the limitations of hotspot-adapted liquid heat removal to improve on system pumping power and on the re-usability of output heat, for various packaging schemes at the component level. This is in particular important to improve the power efficiency of datacenters with the consequence to reduce total cost of ownership and their impact on the environment. Inefficient air cooling is responsible for up to 40% of their total power consumption. High-performance liquid cooling has the potential to reduce this number substantially and makes the direct re-use of produced heat in neighborhood-heating networks viable. The application of normal-flow and crossflow cold plate architectures is discussed. Custom-tailored normal-flow cold plates can be produced with high spatial contrast in heat transfer with a granularity of 1 mm². For conventional processor chip packages this results in a flow rate reduction and fluid temperature differential (T_fout-T_fin) increase of 28%. This also translates into a net pumping power decrease of 43% for a server rack with multiple heat sources. Heat flux tailoring with cross-flow heat exchangers is subject to the additional constraint of a fixed volume flow over the length of the channels, which calls for modulation of the heat transfer geometry along the channel in order to address hot spots. In this study the fluid flows through a layered-mesh network, in which the number of mesh layers is modulated. For standard packages employing thermal grease interfaces, we find that for a given flow rate, there is little benefit in terms of maximal junctions temperature at the expense of a significant increase in pressure drop. The parameter improving is the on-chip temperature variation. We conclude the study with recommendations on how to design hotspot-adapted cold plates.