SilverStone has demonstrated at Computex 2013 a new concept liquid-cooler technology that requires no pump to propel the liquid, making it completely passive.
By harnessing the evaporation properties of a non-water liquid this experimental cooler uses its own coolant as a pump.
Like with heatpipes, the cooler uses the principle of harnessing the evaporation and condensation properties of a non-water liquid to circulate that same liquid. As the liquid is warmed it evaporates and creates pressure. By making one pipe to the radiator narrower than the other and mounting the CPU block vertically the pressure difference forces the liquid to start circulating through the system. As the temperature increases the liquid circulates even faster.
It's an ingenious idea that, assuming the radiator is cooled passively, allows for a system with no moving parts.
There are, however, a few issues. One is that the liquid simply doesn't start pumping itself until it reaches around 30-40 degrees, which means it doesn't actually cool any more effectively than many an air or water cooler. When under load it is also likely the radiator would require fans to keep it dissipating the heat sufficiently. As such the whole passive argument goes somewhat out the window.
All told, although SilverStone is still testing to see whether this can be a viable product, in all likeliness it will never make it to market and is more of a neat trick than anything else. But who doesn't like a neat trick.