Advances in immersion cooling can help servers chill out

New materials have revived the concept of immersion cooling, and data center servers may soon take the plunge.

What is immersion cooling? What coolants work safely with motherboards and other electronics?

The concept of immersion cooling is easy to understand. Rather than using loud, power-hungry fans to push air across hot electronic components, simply dunk the electronic device in a bath of cold liquid and let the liquid absorb the heat instead. Liquids are much denser than air and can absorb heat very quickly. In addition, dense liquids have a large thermal mass, meaning that the liquid can continue absorbing heat for a long time, even when pumps circulating the liquid (or the power that drives the pumps) fail.

It's long been understood that cooling by conduction -- passing heat energy from one material to another -- is far more efficient with more heat-conductive materials. Consequently, water is a much better conductor of heat than air. But electricity and electronic components cannot function in conductive materials like water. Even the adoption of water-based heat sinks or rack doors has met serious resistance from data center professionals who fear the potential for system damage from liquid spills. However, new materials have revived the concept of immersion cooling, and data center servers may soon take the plunge.

In order to safely submerge an electronic device in a liquid, the liquid must meet several important characteristics. First, the cooling liquid must be nonconductive. That is, it cannot short-circuit electronic signals or change the signal characteristics of sensitive, high-speed electronic devices, such as CPUs and memory modules. The liquid must also be completely noncorrosive and avoid any sort of damage to electronic packaging, contacts, or printed wet or dry circuit layouts. The liquid must be nonflammable, nontoxic and easy to clean up if there is a spill.

Ordinary water is completely inappropriate for immersion cooling because it is conductive and corrosive. However, immersion cooling has been demonstrated to work in baths of mineral oil, and companies such as 3M have developed liquids such as Novec, which meet the criteria for electronic immersion cooling.

This was first published in April 2013

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