The whole cooling system is arranged into layers.Just above the processor is a carbon fiber layer (with very good heat transfer capacity) below a piece of copper.There is a layer of unknown heat transfer material (perhaps a form of silicon) and then a copper heat pipe.Right above the tube is the heat transfer bar to keep the heat concentrated in one place.
Other phones are similar in structure - or simpler but basically the same.Water only works to turn into steam, so it is perhaps more accurate to call it a cooling system.
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