On 9 September, Apple introduced its newest lineup, including the iPhone 17 series. Much of the attention went to a new ultrathin model and a bright orange color option (a shade not dissimilar to that of the IEEE Spectrum logo). The new smartphones will also ship with the latest operating system and its “Liquid Glass” software design—but the liquid in these phones goes beyond software.
The iPhone 17 Pro and iPhone 17 Pro Max contain thin, hermetically sealed chambers with a drop of water inside that cycles between liquid and gas to help dissipate heat. Known as vapor chambers, the cooling system is becoming more common in smartphones built for sustained high performance. Some high-end Samsung Galaxy and Google Pixel models, among others, have introduced vapor-chamber cooling in the past few years. Now, Apple is following their lead.
“Cooling of smaller portables like phones must focus on spreading heat as widely as possible to the surface of the device, with particular attention to heat-generating components, like the chip,” says Kenneth Goodson, a professor of mechanical engineering at Stanford who specializes in heat transfer and energy conversion. To cool down those hot spots, the industry seems to be moving toward vapor chambers and other phase-change technology.
How vapor chambers keep phones cool
The standard approach to cooling smartphones uses a solid, highly conductive plate made from a material like copper to spread heat. This approach relies on having a surface where heat can spread. Sometimes, fins are added to extend that surface, but this can lead to a thicker device. Most companies, however, are intent on making thinner and thinner phones.
Phase-change technology—which has been used in laptops for decades, Goodson notes—achieves the same goal more effectively with fluid that boils and condenses to dissipate heat. These two-phase solutions include vapor chambers, like those used in the new iPhone, as well as narrow, fingerlike structures called heat pipes.
Phones have limited volume to work with, and “performance per volume is critical,” says Victor Chiriac, the CEO and cofounder of Global Cooling Technology Group, based in Phoenix. Thin and wide vapor chambers have a high heat-removal capacity and offer an effective solution. The cycle between liquid and vapor is “a powerful mechanism for absorbing heat,” he says.
Apple’s vapor chamber efficiently spreads heat across the phone’s body.Apple
In Apple’s version, a small amount of deionized water is sealed in the chamber. The water evaporates when near heat sources, then condenses back into a liquid when the heat dissipates into the phone’s surrounding aluminum body. Water is often used in vapor chambers, though sometimes other materials are mixed in to prevent it from freezing and cracking the seal, Chiriac says.
Vapor-chamber manufacturing faces challenges
As Apple, Samsung, and others push the boundaries of how thin phones can get, manufacturing vapor chambers may become a challenge. While solid materials can easily be shaved down, these chambers need to have enough space for coolant to travel through channels. The chambers have to be perfectly sealed in order to work properly, and “the thinner you make it, the less space you have for that secret sauce to do its thing,” Chiriac says.
It comes down to physics: “A big challenge in small devices like phones is that as you scale down the thickness of a vapor chamber, the fluid physics aggressively scale back their performance relative to copper and other solid heat conductors,” Goodson explains. (This is a problem that researchers, including his students, are working to address with new microstructures.) Plus, vapor chambers tend to be expensive to manufacture.
Still, Apple and other companies have decided to invest in this technology for their most powerful phone models. Goodson suspects part of that decision is to leverage the “wow” factor. But, he says, “with time this approach will likely become an industry standard.”
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