Stop calling Note 9's heat dissipation a 'liquid cooling' system
Way back when the Galaxy S7 and S7 edge were announced, the first teardowns of the handsets revealed some sort of a thin flat heat pipe running away from the processor area, presumably a cooling effort. The same ones were spotted before on Sony's high-end Xperias, starting with the Z2, or even the Lumia 950XL.
At the time, Samsung did confirm that its phones indeed feature this pipe setup when talking about its new Game Launcher setup: "the cooling system in these phones, with a very thin thermal spreader, keeps devices cool, so gamers can focus on winning." You see, Samsung itself doesn't dare to call this system "liquid cooling," as it has nothing to do with those gaming rig setups with coolant flowing through pipes and radiators, pumped by tiny goblins to swoosh elegantly around the CPU in clouds of frozen mist. On the Note 9, the system is called Water Carbon Cooling.
The tiny amount of water is weaved around the CPU/GPU combo to take away the heat that the Exynos and Snapdragon chipsets would generate under, say, gaming stress. The drop evaporates when it hits the chipset area, lowers the temperature there, then condenses back to run down the metal mesh inside and repeat the process, spreading the heat in a more equal manner.
So, thermal spreader, vapor chamber, heatsink, call the system's elements what you will, but tests show that it is only slightly more efficient than what we already have on, say, the Note 8. On hot summer days, it performs much better than phones without, though. In a recent Tom's Guide test, the Note 9 and Note 8 lasted more minutes of sunlight gaming than the iPhone X before overheating, for instance. Still, the heat dissipation system inside the Note 9 is not as fancy as a "liquid cooling" moniker would lead us to believe.