From: Andy Soos, ENN
Published February 2, 2012 03:14 PM

Nano Improved Transformer Oil

Rice University scientists have created a nano-infused oil that could greatly enhance the ability of devices as large as electrical transformers and as small as microelectronic components to shed excess heat. Research in the lab of Rice materials scientist Pulickel Ajayan, which appears in the American Chemical Society journal ACS Nano, could raise the efficiency of such transformer oils by as much as 80 percent in a way that is both cost-effective and environmentally friendly. The Rice team focused their efforts on transformers for energy systems. Transformers are filled with mineral oils that cool and insulate the windings inside, which must remain separated from each other to keep voltage from leaking or shorting.

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Under severe loads, when lubricating fluids are unable to effectively support the load and are squeezed away from the contact area, nanoparticles provide easy shear for the metal surfaces due to their elastic and quasi-spherical nature. The nano particles adhere to the metal surfaces reducing the friction and wear between the surfaces.

The researchers discovered that a very tiny amount of hexagonal boron nitride (h-BN) particles, two-dimensional cousins to carbon-based graphene, suspended in standard transformer oils are highly efficient at removing heat from a system.

"We don't need a large amount of h-BN," Narayanan, one of the authors said. "We found that 0.1 weight percentage of h-BN in transformer oil enhances it by nearly 80 percent."

"And at 0.01 weight percentage, the enhancement was around 9 percent," Taha-Tijerina another author said. "Even with a very low amount of material, we can enhance the fluids without compromising the electrically insulating properties."

Narayanan said the h-BN particles, about 600 nanometers wide and up to five atomic layers thick, disperse well in oil and, unlike highly conductive graphene, are highly resistant to electricity. With help from co-author Matteo Pasquali, a Rice professor of chemical and biomolecular engineering and of chemistry, the team determined that the oil's viscosity — another important quality — is minimally affected by the presence of the nanoparticle fillers.

"Our research shows that with new materials and innovative approaches, we can add enormous value to applications that exist today in industry," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry. "Thermal management is a big issue in industry, but the right choice of materials is important; for transformer cooling, one needs dispersants in oils that take heat away, yet remain electrically insulating."

Transformer oil helps cool the transformer. Because it also provides part of the electrical insulation between internal live parts, transformer oil must remain stable at high temperatures for an extended period. To improve cooling of large power transformers, the oil-filled tank may have external radiators through which the oil circulates by natural convection. Very large or high-power transformers (with capacities of thousands of KVA) may also have cooling fans, oil pumps, and even oil-to-water heat exchangers. So an improved oil with the anticipated properties will provide valuable.

For further information: http://pda.physorg.com/news/2012-02-nanoparticles-thermal-properties-oil.html

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