I was idly browsing some of the new features/technologies that Apple introduced into their new iPhones, and learned that Apple has started using vapor chamber cooling systems for the first time in the iPhone 17 Pro and Pro Max models. Other manufacturers like Samsung, Google, and OnePlus have been using vapor chamber cooling systems for a while now - Samsung since 2016! I was not familiar with this technology, so I read up on it a bit.
A vapor chamber cooling system is a flat, thin, sealed metal container that forms a layer within the technology sandwich of a modern phone. A small amount of water is sealed inside, and the container is depressurized to lower the boiling point of the water to near 30 degrees C. Part of the vapor chamber is in contact with the hot chips in the phone, where the liquid water is boiled into vapor. Turning the water into vapor sucks up a great deal of heat due to the latent heat of evaporation of water. The vapor diffuses through the chamber to the cooler parts of the phone, where it condenses back into liquid water and releases the stored heat. The heat is thus spread out over a larger area, where it can be more easily dissipated. The condensed liquid water is wicked back to the hot parts of the phone, and the cycle repeats.
Note that vapor chamber cooling is different from the liquid cooling systems that may be cooling the CPU in your PC, or the engine in your car. In these systems, the coolant liquid stays in liquid form. The liquid absorbs heat from hot parts and is actively pumped to a location where moving air can remove the heat from the liquid. The liquid never vaporizes, so the latent heat of evaporation never comes into play. Liquid cooling works better than air cooling because the heat capacities of liquids are about 4x larger than that of gases.
Since vaporizing a liquid takes a lot more energy than it takes to just heat it up to its boiling point, vapor chambers can be much more efficient than liquid cooling systems at absorbing and moving heat energy. And a vapor chamber is completely passive, with no pump required to move the coolant. The coolant pump is a critical point of failure for liquid cooling systems in CPUs, cars, and especially nuclear reactors.
Upon first reading about vapor chambers, my thought was “duh, this is not very hi-tech at all, these principles have been understood since the 1800s, why did it take so long to develop this?” (I mean that in the sense of, why did this technology only start appearing in phones in the last decade? Not the different question of why Apple took so long to adopt it relative to other vendors.) The video How One Drop of Water Cools Your Phone (which I highly recommend) answered that question for me, and changed my sentiment to “man, it’s a miracle that these can be made to work at all”. It is tricky to get a thin, flat container that is only about a third of a millimeter thick to reliably hold a partial vacuum without collapsing in on itself. And it takes a lot of engineering to make the inside surfaces better at condensing the vapor back into water, getting the water to the wick, and wicking the water back to the hot parts of the phone. The wick itself is a clever stainless steel or copper mesh that probably took many iterations and redesigns to get it to perform optimally. And there is some chemistry involved with putting additives in the water to promote nucleation or alter its surface tension.
It seems to me that we’ve pretty much mastered the advanced technology to cram incredible amounts of electronics into tiny bits of silicon. So now the relatively unglamorous ‘supporting cast’ technologies like thermal cooling (and batteries!) are getting their share of the attention.
