ICGAR: producing efficient heat sinks using nanofluids

Tomorrow’s coolants for electronic devices and engines would come from magnetic nanofluids. And scientists at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, have been able to achieve a 300 per cent enhancement in thermal conductivity using such nanofluids, the highest so far.

With the size of electronic chips ever shrinking, there is a great compulsion to find very efficient heat sinks. Scientists at IGCAR have probably been able to produce such efficient heat sinks.

“It will be a big market for magnetic nanofluids as a small amount of fluid can produce great cooling. It is a big thing for NEMS [nanoelectromechanical systems] and MEMS [microelectromechanical systems],” said Dr. John Philip of the Metallurgy and Materials Group, IGCAR who headed the team.

The Dr. Philip also demonstrated the exact mechanism behind the enhanced thermal conductivity of magnetic nanofluids.

The results have been published this year in the reputed international journal, Applied Physics Letters.

Magnetic nanofluids being endowed with excellent thermal conductivity, researchers across the world have been actively involved in preparing nanofluids with greater thermal conductivity. Yet, nobody was certain how the thermal conductivity was produced. At least till recently.

Dr. Philip has now solved the puzzle. He had used Fe304 magnetic nanoparticles (average diameter 6.7 nanometre) in a stable colloidal suspension. “The thermal conductivity was initially 24 per cent. But when we applied a very small magnetic field (10 millitelsa) to the colloidal suspension, we saw a 300 per cent enhancement in thermal conductivity,” he said.

Dr. Philip disproved micro-convection as the possible mechanisms for the enhanced thermal conductivity. Instead he showed that when a magnetic field was applied to the nanofluid, the magnetic particles in the nanofluid tend to align themselves in a linear chain with a magnetic moment seen in one direction. In the absence of an external magnetic field, the magnetic particles are scattered and the magnetic moments are oriented in random directions. “With the increase in magnetic field, the moments of the magnetic particles start to align themselves along the direction of the magnetic field,” states the paper.

And the chains that get aligned in a parallel direction have a “geometric configuration that allows the most efficient means of heat propagation.” So it is only natural to expect very large transfer of heat to take place along these parallel chains.

The alignment and hence its ability to transfer heat is reversible when the external magnetic field is removed.

“It can be used as a smart cooling system,” he said. “By increasing the current, we can produce higher magnetic field to achieve greater thermal conductivity to bring down the temperature drastically.”

Published in The Hindu on May 8, 2008