AS COMPUTER CHIPS get more compact and run faster, they also run hotter. Attaching radiator fins to their surface and blowing air over them are the usual solutions. But what happens when chips are stacked on top of each other to improve the flow of data between them in parallel processing? The heat-producing volume increases, while the heat-shedding surface gains very little.

The Economist Technology Quarterly, bound into the September 6th edition of the magazine, reports on IBM’s experiments in water-cooling such stacks of chips. Thomas Brunschwiler of IBM’s Zurich laboratory points out that processors stacked in this way generate heat at about two kilowatts per cubic centimetre, a greater density than in a nuclear reactor. Therefore the IBM team has developed a stacked processor through which water is pumped in channels, as thin as a human hair, etched in the process of silicon-chip fabrication. Nor need this heat be wasted: in compact multiple installations such as data centres, the heat can be exploited to warm community housing or other buildings.

Water cooling can also be applied to silicon-based solar cells. Another IBM researcher, Supratik Guha, has increased the efficiency of solar power by using mirrors to concentrate 2,300 times the normal intensity of sunlight onto a solar cell. Without water-cooling, the cell could reach 1,500 degrees Celcius and melt. The cooling system means that the cell is maintained at a safe temperature of 85 degrees C, and generates a record output of 70 watts per square centimetre: a very promising technology for economical electricity generation even in high-latitude countries.