Liquid cooling or 'thermal spreader': check out the S7 edge heat pipe insides (video)
Back when the Galaxy S7 and S7 edge were announced last week, the first teardowns of the handsets revealed some sort of a heat pipe running around the processor area, presumably a tiny liquid cooling system, like the ones on Sony's high-end Xperias, or the Lumia 950. Samsung then confirmed that the phones do indeed feature this, 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."
There you have it, we definitely don't have liquid nitrogen running in your phone, being pumped by tiny goblins to swoosh elegantly around the CPU in clouds of frozen mist. What we do have, however, is flatter copper piping with a minuscule amount of liquid, often just water, that evaporates when it hits the CPU area, takes the heat away with the gas it forms, and condenses back into liquid when it runs further down the pipe, like on the scheme here:
Samsung itself calls it simply a "thermal spreader," instead of liquid cooling, though technically we likely do have a drop of liquid in there, and it's made on a very, very compact scale. Want to see how it actually looks like from the inside? Well, the video below comes to the rescue, from about 4:30 in, and you also get to see the other set of tiny goblins - the ones that are trying to hold the camera steady when you shoot video, or the so-called optical image stabilization. It's fascinating, check it out.