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September 21, 2013

New hydrophobic material could benefit power plants, cooling systems.

Steam condensation is key to the worldwide production of electricity and clean water: It is part of the power cycle that drives 85 percent of all electricity-generating plants and about half of all desalination plants globally, according to the United Nations and International Energy Agency. So anything that improves the efficiency of this process could have enormous impact on global energy use.

It has been known for years that making steam-condenser surfaces hydrophobic — that is, getting them to repel water — could improve the efficiency of condensation by causing the water to quickly form droplets. But most hydrophobic materials have limited durability, especially in steamy industrial settings. The new approach to coating condenser surfaces should overcome that problem, the MIT researchers say.

The covalent-bonding process the team developed is significantly more stable than previous coatings, he says, even under harsh conditions.

Tests of metal surfaces coated using the team’s process show “a stark difference,” Paxson says. In the tests, the material stood up well even when exposed to steam at 100 degrees Celsius in an accelerated endurance test. Typically, the steam in power-plant condensers would only be about 40 degrees Celsius, Varanasi says.




The new coating can easily be applied to conventional condenser materials — typically titanium, steel, copper or aluminum — in existing facilities, using a process called initiated chemical vapor deposition (iCVD).

Another advantage of the new coating is that it can be extremely thin — just one-thousandth of the thickness of conventional hydrophobic coatings. That means other properties of the underlying surface, such as its electrical or thermal conductivity, are hardly affected. “You can create ultrathin films, with no effect on thermal conductivity,” Varanasi says, “so you’re getting the best of all worlds here.”

Sumanta Acharya, the program director for the National Science Foundation's Thermal Transport Processes Program, who was not involved in this research, says, "In my opinion this work represents a major breakthrough in condenser technology. It offers the potential for significantly higher heat-transfer coefficients, high vapor-condensation rates and rapid removal of the condensate." He adds that condensers are widely used in the power industry and in residential heating and cooling, and says this work "can potentially provide radical improvements."



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