The CarnotJet from Green Revolution Cooling, Austin, uses a liquid coolant to remove heat from data-center servers, including highdensity and blade servers. The coolant is a nonproprietary odorless, white mineral oil which was chosen for its clarity, low viscosity, high flash point, and high specific heat capacity.

To ensure servers can survive submersion in the coolant, GRC removes the fans and encapsulates the hard drives. Also, servers typically use thermal grease to help heat sinks remove heat. In the CarnotJet, it gets replaced with a covering of indium, a soft metal foil with Liquid cooling for servers high-heat conductivity.

Coolant is pumped through a heat exchanger, where it gives up its heat to a stream of water. A pump module containing variable-speed, digitally controlled pumps and heat exchangers can handle the thermal demands of up to four racks of servers. And the coolant should last 10 years or more, roughly the life of the system.

Using this equipment instead of an arsenal of chassis and power-supply fans cuts a server’s energy use by 5 to 25% and reduces the amount of energy used for cooling by 90 to 95%. It also lets the servers be packaged in a smaller enclosure. The closed-loop liquid cooling and pump are also significantly quieter than the fans they replace. And water comes out of the heat exchanger at 122°F and can be sent to an evaporative cooler or serve as a source of hot waste for a secondary purpose such as heating nearby buildings.

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