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The Telegraph
Since 1st March, 1999
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Water’s the matter

Complex problems call for innovative solutions. While brightest minds all over the world are exercising their little grey cells to find ways to tackle impending problems associated with climate change, an Indian researcher in the United States has come up with an idea that would help slow down global warming. Kripa Varanasi, professor of materials science at the Massachusetts Institute of Technology, and his team have found a way to improve the efficiency of steam turbines that generate electricity with minimum cost.

Steam turbines are used to generate two-thirds of the electrical energy used worldwide and improving their efficiency can lead to a substantial reduction in the emission of heat-trapping carbon dioxide. A typical steam turbine, used either in a thermal or a nuclear power plant, operates at 85-90 per cent efficiency. These turbines fail to work at full capacity mainly because of the buildup of moisture inside the turbine. Varanasi’s team has developed a water-repelling ceramic material that when applied on the blades of these steam turbines is capable of improving efficiency of power production significantly.

“In a steam turbine, when the steam starts giving out energy, it forms very small (smaller than a millionth of a metre in diameter) droplets. These droplets settle on the turbine blades, forming a thin film of liquid (water),” says Varanasi, who graduated from the Indian Institute of Technology, Madras, before moving to the US for higher studies in 1998.

As the turbine rotates at a very high speed, the blades start shedding these droplets as bigger drops of water. Such water drops rarely get out of the turbine — they usually move from one blade to another, eventually corroding the blades. “In some cases, no blade will be left after a turbine has been in operation for some years, throwing all the aerodynamics that go into designing these blades out of the window,” says Varanasi, who was born to an engineer father and college lecturer mother in Hyderabad.

“It is estimated that 30 per cent of power loss from these turbines is due to moisture related problems. People have been trying to tackle the problems relating to moisture in turbines for nearly a century,” says the MIT scientist.

One way of solving the problem is to design a material that is hydrophobic (water-repelling) so that the water rolls off as soon as it hits the blade. Unfortunately, most hydrophobic materials are made of organic polymers which cannot withstand the high temperatures (500 to 600°Celsius) and other harsh conditions encountered inside a steam turbine. On the other hand metals and ceramics are strong enough to survive such extreme conditions, but they do not repel water.

A steam turbine that is used to generate electricity

So Varanasi and his team, which includes another India-born scientist Rajeev Dhiman, came up with the brilliant plan of designing a hydrophobic ceramic that can survive very high abrasion and temperatures above 1000°C. They have reported about their success in the latest issue of Nature Materials journal. They have devised the new ceramic from rare earth oxides, which unlike other ceramics and metals, is water repelling. When used as a coating on the blades of steam turbines, it can reduce the moisture-induced efficiency loss of the turbines.

“Power gained from improving the efficiency of steam turbines by 1 per cent is equal to the total power generated from nuclear power plants globally,” points out Varanasi. Even this is a conservative number. It is said that if the moisture induced efficiency loss is nullified, the gain could be as much as 5 to 8 per cent, argues Varanasi.

Vikram Jayaram, a materials scientist at the Indian Institute of Science, Bangalore, agrees. “Droplet erosion is a big issue in the lower parts of a steam turbine where the temperature drops to the point of condensation. And loss of steam also lowers efficiency,” he says.

Power generation is not the only industry where the new material may find application. If it is used in desalination plants — where potable water is made from seawater — it is estimated that 5 per cent more water will be recovered. Another potential application is in aviation where it can help avoid the build-up of ice on flying aircraft.

The novel ceramic material is not the only interesting product to have emerged from Varanasi’s lab at MIT. In the recent past, this team developed a colourless, odourless material that could be a dream come true for homemakers who cannot abide even a smidgeon of waste. The food-grade material could persuade that last drop of ketchup or mayonnaise in a bottle to slide out with ease. Called Liqui-Glide, an MIT spin-off firm headed by Varanasi’s student David Smith is bringing it to the market.