Assessing Capabilities and Limitations of Air- and Liquid-Cooling for Low Profile Servers

As microprocessor power exceeds 100W, adequate heat removal by convective air-flow through a heatsink increasingly becomes more challenging. This is especially true for low-profile servers with very limited volume for air-flow. It is therefore useful to have an idea of the limitations of air-cooling for such servers. In this paper, three case studies serve to illustrate the capability of typical air-cooled solutions for low-profile servers. These studies show the inherent limitations of air-cooled solutions for volume-constrained computer systems. Liquid-cooling has been used in cooling mainframe processors packaged in MCM format. Its use in low-cost servers is extremely limited. This paper will deal with issues that hinder widespread application of liquid-cooling in commercial servers. The most important issue is cost, followed by lack of commodity components suitable for liquid-cooled systems. One method to reduce cost is to use fabricate the cold plate using heatsink manufacturing techniques. Case studies are presented to show liquid-cooling with these lower cost cold plates can provide performance that exceeds air-cooling solutions. Finally, suggestions are offered for facilitating the introduction of liquid-cooling systems for future low-profile servers.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.