Keeping a computer cool is a growing problem as microprocessors become more powerful and emit ever increasing quantities of heat. Now, researchers in the US have found that they can increase the rate at which a chip can be cooled by 2.5 times by aiming a stream of ionized air at it. The work, which was funded by the chipmaker Intel, could be used to cool computers within the next three years ( J. Appl. Phys. to be published).
Most portable computers are cooled by a fan which blows air across its hot components. However, this method is reaching the limit of its effectiveness, in part because the air right next to the surface of a chip tends to remain stationary and insulates the hot surface from the cooling breeze of the fan.
Researchers at Purdue University in Indiana and Intel have worked out a way around this problem by using a stream of ions to get this layer of stationary air moving. The team built an “ionic wind engine” that fires ionized air at a hot spot on the surface of a heated glass plate, which was designed to mimic the backside of a computer chip.
The engine consists of two electrodes — with the negative electrode located on the plate and the positive electrode a few millimetres away from the plate. A high voltage across the electrodes creates ions in the air above the hot spot in a process called coronal discharge. A current of positively-charged ions then flows towards the hot spot, causing the normally stationary air to move.
In one experiment, the team found that when the ion engine was turned on, a conventional fan was able to cool the hot spot from about 60 to 35 degrees Celsius. But without the ion engine, the fan could only cool the hot spot to 55 degrees.
According to the researchers, the ions increase the heat transfer coefficient of the cooling system – its ability to transfer heat from a solid to the air — by 2.5 times. According to Purdue’s Suresh Garimella, previous attempts at improving the performance of fan-cooling systems had only managed a 50% improvement.
Although the ionic wind engine is too large (about 4 mm across) and requires too high a voltage (more than 4000 V) to be of any practical use, the team is now working on miniaturizing the generator by a factor of about 1000 so it can be used to cool a real chip. The team have already worked out a way to create a tiny coronal discharge using diamond-coated electrodes separated by about 10 µm and operating at tens of volts. The next step, according to Garimella, is to make the technology rugged enough for use in portable equipment.
The team have applied for patents on the technology, which Garimella claims could be used in computers within three years.
Garimella and colleagues are no the only ones interested in cooling chips using ionic wind. Earlier this year, US-based Kronos Advanced Technologies claimed to have worked out a way to replace the conventional cooling fan in a computer with a coronal discharge generator that uses ionic wind to push air across a microprocessor.
