Mechanical Technology April 2015

⎪ Nota bene ⎪

Metallic grass coating for efficient steam production

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 McCarthy’s team will now look at the performance of dozens of different surface configurations, changing both the spacing of the nanostructures and the shape and the coating metal, so as to find ways of improving the performance of the coating even further. q in critical heat flux, meaning that much more heat can be transferred from the heat source to the liquid before bubbles start sticking to the boiling surface. “Phase-change heat transfer plays an important role in everything from power generation to water purification, HVAC and electronics cooling,” says McCarthy. “Increasing performance of these systems would translate into significant improve- ments in the way we produce, consume and conserve our energy and water resources.” Industry diary

R esearchers at Drexel University have developed a metallic nano coating derived from a virus of the tobacco plant that could lead to more efficient steam production, improving the performance of steam turbines, air condi- tioning and electronics cooling systems. Water’s transition from liquid to gas has plenty of applications beyond the kitchen: water treatment plants; heating and air conditioning systems; and the steam turbines that we use to produce electricity are all heavily dependent on this process. Making this transition even slightly more efficient could have a big impact on energy efficiency. The breakthrough comes from an unexpected source – a virus common to tobacco plants. The tobacco mosaic virus was the very first virus to be identified, back in 1930, and has been studied in detail since then. It’s a simple organ- ism that consists of a single strand of RNA surrounded by a dense network of coating proteins. Today, scientists think that this layout is ideal for building self- assembling nanostructures. Matthew McCarthy and his team at Drexel University are using the virus to create a special coating that uses capil- lary forces to distribute water evenly across a surface. When used to coat

the surface that separates a heat source from the liquid being heated, the scien- tists found that this coating helps boil the liquid more than three times more effectively. As water (or any other liquid) starts to boil, there comes a point where bubbles of vapour form and stick to the surface that separates the liquid from the heat source. This point, known as the ‘critical heat flux’, is problematic because these air bubbles prevent local heating of the liquid, overheating the surface instead. To work around the issue, McCarthy’s team used a mutation of the tobacco mo- saic virus that features molecular ‘hooks’. These hooks let the virus attach to nearly any surface, be it stainless steel, alumin- ium, copper, gold, silicon or a polymer. The virus is then coated with a thin layer of metal to form a solid structure that the researchers called ‘metallic grass’. When liquid comes in contact with this surface, it quickly sticks and spreads due to capillary forces, making it harder for the surface to dry out even while boiling. When air bubbles do form on the surface, they also tend to leave faster, for a much greater heating efficiency. In the team’s preliminary results, ap- plying the metallic grass coating to the boiling surface showed a 240% increase

The virus used is a simple organism that consists of a single strand of RNA sur- rounded by a dense network of coating proteins.

A ‘metallic grass’ nano coating derived from a virus of the tobacco plant has been found to significantly improve heat transfer at the phase-change point, where gas bubbles start to from on the heating surface.

Inaugural Metals and Engineering Indaba 2015 The Southern African Metals and Engineer- ing Indaba (MEIndaba 2015), hosted by the Steel and Engineering Industries Federation of Southern Africa (SEIFSA), will be held at Emperors Palace, Ekurhuleni, Gauteng from May 28-29, 2015. The event, the first of its kind in the sector and will be graced by high profile business, government and civil society leaders. Setting the tone is the first plenary ses-

sion, entitled: ‘Does Manufacturing Have a Future in Southern Africa?’ with contribu- tions from Trade and Industry minister, Rob Davies; ArcelorMittal CEO, Paul O’Flaherty; deputy chairman of the South African Institute of International Affairs (SAIIA), Moeletsi Mbeki; the Democratic Alliance’s Geordin Hill-Lewis; and Bobby Godsell, chairman of Business Leadership South Africa. meindaba.co.za

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Mechanical Technology — April 2015