Although there definitely are liquid-cooled PCs, there just isn't room for such cooling systems within smartphones – or at least, there hasn't been until now. Fujitsu recently announced development of a loop heat pipe that's less than one millimeter thick, which could help future mobile devices to keep their cool.
Currently, heat is drawn away from hot spots in smartphones using sheets of thermally-conductive solid materials such as graphite. According to Fujitsu, however, those materials won't be sufficient as phones continue to process data faster, and run more integrated devices such as cameras. Not only that, but phones will likely also continue getting slimmer, so they'll be generating more heat which will be concentrated in a smaller space.
That's where the loop heat pipe enters the picture.
Containing an unspecified liquid, it's a closed system that consists of an evaporator located near a hot spot (such as a CPU) and a condenser in a cooler section of the phone. The two are linked together in a loop, by two tiny pipes.
The evaporator contains six 0.1-mm-thick stacked sheets of copper, each one perforated with an array of pores. The liquid climbs up through these pores (which are offset from one another), with the heat from the hot spot causing it to vaporize as it does so.
That vapor then travels along the "vapor line" pipe to the condenser, where the cooler temperature causes it to condense back into liquid, releasing its payload of heat energy in the process. That liquid subsequently travels back along the "liquid line," returning to the evaporator to continue the process.
Because the liquid moves throughout the system via capillary action, it works regardless of the orientation of the phone.
Fujitsu is aiming at introducing the first practical implementations of the loop heat pipe in 2017.