Electronics are slated to consume over a fifth of the world’s electricity use by 2030. Much of that energy is wasted as heat, requiring cooling that also consumes power, and often copious amounts of water.
To put a dent in that energy and water use, researchers have now shown that hydrogels—used in contact lenses, wound dressings, and diapers—could cool high-power electronics using moisture absorbed from the air.
The idea is simple: coat a 0.5- to 1-millimeter-thick hydrogel layer on an aluminum heat sink. Used commonly in laptops and CPUs, heat sinks are metallic structures with fins and ridges to increase their surface area for more efficient heat transfer. The hydrogel coating absorbs moisture from the air and swells up when a processor is not running full tilt. During peak hours, when the processor heats up, the water evaporates and cools the electronics.
“This passive cooling device works autonomously without human intervention, with no power consumption and low maintenance cost and simple system design,” says Renkun Chen, a professor of mechanical and aerospace engineering at the University of California, San Diego. “The method is like human skin. When we get overheated, we sweat, and that evaporates and provides cooling.”
Overheating is a performance and safety concern for high-power electronics, and regulating temperatures in computers keeps getting more complicated as electronics shrink and power goes up. Then there’s the energy and water use. The world’s data centers alone use over 200 billion kilowatt-hours of energy and almost 1.6 trillion tons of water a year.
There are various ways to cool electronics today. In computers, thermal materials transfer heat from microprocessor chips to heat sinks that are air-cooled using fans. Liquid cooling, in which circulating water siphons heat away to a radiator, is also popular for CPUs. Data centers, meanwhile, are housed in air-conditioned spaces and also rely on liquid cooling. All these active cooling systems use energy to run fans, HVAC systems, and water pumps.
Researchers have been developing new ways to cool electronics for years. Microchannel cooling, for instance, brings down the energy use of liquid cooling by putting tiny liquid-cooling channels right next to, or even into, computer chips.
But the concept Chen and colleagues recently presented in the journal Cell Reports Physical Science is relatively straightforward and fully passive, needing no energy input. And it could be low cost, considering that the sodium acrylate–based hydrogel they use is cheap, costing only US $10 per kilogram. Others have demonstrated cooling EV batteries and solar panels before with flat hydrogel films.
At top left is a schematic of the testing setup. The Infrared images are of a field-effect transistor (FET) without a heat sink [top right], with a traditional heat sink [bottom left] and with hydrogel [bottom right]. Renkun Chen
As a demonstration, they placed both a regular heat sink and a hydrogel-coated sink on top of a field-effect transistor to cool it. The heat sink brought the temperature of the chip down by 8 °C, while the hydrogel-coated sink brought it down by 20 °C.
Once the water in the hydrogel depleted, its evaporative cooling effect goes away. Chen says the team is now looking at hydrogels that can absorb and hold more water. The idea could be combined with other active cooling technologies like fans and liquid cooling to reduce energy use. And its use does not have to be limited to electronics. “We also envision using it for applications like cooling buildings or even personal cooling.”
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Prachi Patel is a freelance journalist based in Pittsburgh. She writes about energy, biotechnology, materials science, nanotechnology, and computing.