A cool innovation from miniscule particles

Engineers in Britain have created a new type of coolant that could dramatically increase the speed of computers‚ improve the efficiency of car engines‚ lower the cost of residential heating and even change the way surgery is performed.

Coolants are liquids that absorb heat and transport it away from the source‚ often through tubes or pipes. They are used for myriad purposes‚ mainly to dissipate heat to prevent machinery from over–heating‚ as in engines; to transfer heat to buildings‚ as with radiators; or to power other processes‚ such as in nuclear generators.

And‚ as in all areas of technology‚ researchers are striving to create more efficient designs.

The most common liquid used for heat–transfer fluids is water‚ because it has the largest capacity to absorb heat. But many solids‚ particularly metals such as copper and aluminum‚ are much better at transferring heat. Logically‚ it would make sense that suspending tiny bits of metals in water would create coolants that can absorb much more heat‚ but still be pumped away.

However‚ when scientists have tried adding millimeter–sized particles of metals to water‚ the metals tended to clump together and damage the walls of their container. Now‚ they have learned to overcome this limitation by using particles that are only a millionth of a millimetre – a nanometre – in size.

One of the more rapidly expanding areas of research today is nanotechnology‚ the science of engineering materials that are 0.1 to 100 nanometres. Researchers can now design molecules atom by atom‚ engineering from the bottom up‚ so to speak. Materials that are constructed at the atomic scale are often considerably stronger and more flexible‚ and can have higher electrical and heat conductance compared with materials composed of the exact same elements but made of larger particles. And often the nanomaterials have new and remarkable properties.

Nano researchers have already produced consumer products‚ such as LCD flat screens and stainless fabrics. Almost daily‚ scientists predict fantastical applications for nanotechnology‚ such as space elevators and invisibility suits.

A number of research teams around the world are now creating superior coolants‚ called “nanofluids.” By suspending nanoparticles in traditional coolant fluids‚ rarely exceeding concentrations of 5 per cent‚ scientists have been able to improve the speed of heat transfer significantly.

Richard Williams and Yulong Ding of the University of Leeds are developing nanofluids by dispersing tubes made entirely of carbon atoms (called nanotubes) in water. “Typically‚ you get a 200–per–cent increase in heat–transfer rate with nanotubes [compared with the base fluid alone]‚ whereas generally for materials of metals or metal oxides you only get about 20 per cent‚” Dr. Williams says.

Nanofluids could make heating homes much more efficient‚ translating into cheaper bills and lower greenhouse–gas emissions to boot. The same goes for vehicle efficiency – engines could use less fuel. Computer chips could become even smaller and faster with small reservoirs of nanofluids connected by thin tubes tracing the circuits.

And some have even speculated that nanofluids could revolutionize surgery. Hot nanofluids could be pumped through tubes around tumours to kill cancerous cells‚ leaving healthy cells intact. Cold nanofluids could be used to transport heat away from the brain during neurosurgery‚ helping to reduce the risk of brain damage.

However‚ before we can see any of these applications‚ nanofluid engineers need to overcome a number of hurdles. “The mechanisms are still not entirely understood‚” Dr. Ding says. As a result‚ there is a huge amount of variability that researchers have reported in the improved speed of their nanofluids‚ and often the results are hard to reproduce.

Moreover‚ little is known about the health and safety risks of most nanomaterials. “There are a small number of groups doing work on safety aspects of carbon nanotubes‚ but there are no standards whatsoever that have been approved‚” Dr. Ding says.

Most troublesome‚ perhaps‚ is the high cost – a great deal of nanotech research is focused on highly specialized‚ extremely expensive devices that cannot be produced on a large scale at this time.

But nanotube coolants are relatively cheap and simple to make‚ and Dr. Williams hopes to see them in use soon. “Most people are focusing on the ‘fantastic science’ side of nanotechnology‚ but not many people are focusing on bringing those innovations into applications that have value to society‚” he says. “As opposed to innovations that are 20 years in the future‚ I think it’s important to focus on what we can do now.”