Data centers that underpin the artificial intelligence (AI) boom can be cooled more efficiently and cheaply. A hybrid system for this is being developed at the University of Waterloo (Canada). It targets local overheating - so-called hot spots on computer chips - and uses a single drop of boiling refrigerant to cool them.
The idea combines two approaches. The first is immersion cooling: electronics are placed entirely in a liquid. The second is targeted cooling of especially hot areas with drops of a more expensive refrigerant. The basis is deionized water: it does not conduct electricity and is inexpensive.
"It is a division of labor," explains Dr. Sushanta Mitra, a professor of engineering at the University of Waterloo. "Water handles the constant, everyday heat well, while the drops take on sudden spikes."
Modern data centers generate enormous amounts of heat. Operators increasingly immerse chips and processors in special cooling fluids. But depending on the load, small areas of a chip can heat up much more than the rest within seconds. As a result, the electronics slow down, wear out faster and become less reliable. A conventional flow of coolant reacts too slowly to such sudden hot spots.
The team, which included Dr. Tian-Yu Zhang and graduate student Arnav Banerjee, solved the problem by building on previous work: one liquid is enclosed in a thin shell of another. The study "Hybrid immersion cooling via liquid-liquid encapsulation: a breakthrough in thermal management of transient hot spots" was published in the Journal of Colloid and Interface Science.
The scientists chose a refrigerant with a boiling point much lower than that of water. It is also heavier than water, so it does not mix with it and stays in place when it reaches a hot spot. In laboratory tests, a single drop of refrigerant boiled and lowered the temperature of a simulated chip hot spot immersed in a water tank by up to 17 °C in 15 seconds - several times faster than conventional immersion cooling.
"Boiling absorbs a lot of heat, and the rising bubbles stir the surrounding water, and it carries heat away faster," says Mitra, executive director of the Waterloo Institute for Nanotechnology. "We get the boiling effect, but only where and when it is needed."
The researchers then applied their encapsulation technique to wrap the refrigerant drops in a thin film of silicone oil. Adding tiny heat-conducting ceramic particles to the coating helps control the rate at which the drops boil.
The authors see two possible ways for the system to operate. Either the refrigerant drops circulate in the water and activate when they reach hot spots, or they are delivered directly to areas detected by sensors. Potentially, hybrid cooling could also be useful in electric vehicles, batteries, high-power lasers and LED lighting. For now it is a laboratory development, not a finished product.