Liquid Cooling Enters the Mainstream

John Keller, MAE


Until recently, the use of moving liquid to remove excess heat from embedded computing processors was considered an expensive and unreliable luxury, but escalating demand and maturing technologies finally are putting this technology within reach.


The Heat Problem
Despite the relatively mundane nature of electronics thermal management when compared to the latest powerful processors, heat represents an issue that no systems designer can ignore — and the problem grows by the day.


“Heat never sleeps. It’s harder to deal with this year than it was last year,” says Chris Ciufo, chief technology officer at General Micro Systems in Rancho Cucamonga, Calif. “The military wants to apply more processing at the tip of the spear, which means operating in harsher environments that we didn’t do even three years ago.”


As examples, Ciufo cites land vehicles that collect data by driving behind enemy lines, then downloading the data, and later deploying to deal with the problem. “Today there’s more processing in that vehicle,” Ciufo says. “It may link up with the Continental U.S., or with operators in other vehicles looking at actionable intelligence and deciding what to do with it. There are more GPGPUs, more rackmount servers, and more processing required on these sensor platforms. These trends in basic semiconductors are making heat much more difficult to deal with.”



The military embedded computing industry today is seeing explosive growth in liquid cooling — particularly the approach of getting liquid into the cold plate itself with quick disconnects, says Shaun McQuaid, director of product manager at Mercury Systems in Andover, Mass. “It is so much more efficient to cool with liquid — if you have liquid available,” McQuaid says.


Despite the growing popularity, affordability, and reliability of liquid cooling, however, many other thermal management techniques are available to remove the ever-growing amount of heat generated in high-performance embedded computing systems. These techniques range from traditional conduction and convection cooling, to hybrid approaches that blend conduction and convection cooling, new heat-transfer materials, custom approaches, and good old-fashioned engineering to make the most of heat transfer in advanced computing architectures.


The conduction-cooled rugged TITAN 2U rackmount server from General Micro Systems uses Intel second-generation Scalable Xeon processors.


Materials and Architectures
General Micro Systems uses a proprietary thermal-management technology called RuggedCool for high-performance embedded computing applications to cool 300-Watt Intel Xeon processors, which relies on liquid silver not only to move heat away from the processor, but also to cushion the processor from the effects of shock and vibration.


Essentially the RuggedCool approach uses one surface of copper, one surface of aluminum, and sandwiched in-between is a layer of silver. Using materials like liquid silver makes it clear that the RuggedCool technology is expensive, but is intended for applications for which nothing else will suffice.


Extreme Cold Operations
The notion of electronics thermal management typically involves how to cool hot components, but what about electronics that must operate in extremely cold environments? “The opposite of cooling techniques is at the bottom-end of temperature; what do you do when the system gets very, very cold,” asks GMS’s Ciufo. GMS engineers have an architectural approach to speed the warming of electronics to operating parameters.


“We found a way to provide self-heating of electronics such that the non-race-critical parts are not operating in an unreliable state, but other components work and start heating-up the system until the critical components com up to their minimum temperatures,” Ciufo explains. Race conditions involve components that operate at slightly different clock speeds because of low temperatures, which cause them to operate unreliably.


“Our systems can power-up much more quickly, so the time to wake up is much shorter because of the way we have intelligently built the system,” Ciufo says.


Read more on GMS proprietary thermal-management technology called RuggedCool, here.




October 16, 2019

By John Keller
Editor-in-Chief, Military & Aerospace Electronics




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