Water-cooled processors, currently the domain of supercomputers, high-end servers and garage hobbyists, may be about to enter the mainstream.

Hitachi has developed a prototype notebook PC that uses a water-based solution to cool down its Pentium 4 processor and is planning to commercialise the product for corporate units in autumn this year, the company said yesterday.

The faster the processing speed of a chip gets, the more heat it generates. This can cause trouble if the heat is not dissipated. On notebook PCs this is usually done with an air-cooling system that makes use of a fan bolted on top of the processor. In the prototype machine, Hitachi has adopted a water-cooling system, which the company says works more efficiently and makes less noise than a fan-based system.

Inside the prototype notebook PC, a stainless steel tube of 1-1.5m in length and 2mm in diameter is placed over the chips. Through the tube runs 50-60ml of a water-based solution at a speed of 10ml per minute, absorbing the heat. As the solution passes along the tube its temperature can reach 60 degrees centigrade, according to Nanako Uchiyama for Hitachi.

The hot water solution is then sent to the display part of the notebook where the heat is released. By repeating this cycle, the system cools down the chips, Uchiyama said. A water tank is placed at back of the display panel and a pump resides in the main body of the machine, she explained.

Although the water-cooling system is more efficient and less noisy, the bottlenecks to commercialisation have been that the water-based solution tends to degrade and evaporate during operation. Hitachi has improved the quality of the water solution for the prototype and enhanced the quality of the stainless tube to prevent corrosion.

The system has been used for the company's supercomputers before, Uchiyama said, but improving the quality of the water-based cooling system was necessary before it could be applied to notebook PCs because, unlike supercomputers, customers demand that they should be maintenance free, she said.

Compared to conventional air-cooled laptops, the price and size of the water-cooled notebook will be about the same. Power consumption will also be approximately equal, Uchiyama said. However, the water cooling system should have a lifecycle that is 1.7 times longer than an air-cooled system, she said.