Water-shedding surfaces can be made to last

Sep 20, 2013 by David L. Chandler
On typical hydrophobic coatings, seen here, droplets forming from high-temperature steam soon spread out to coat the surface (as is beginning to happen at the bottom), quickly degrading their performance. The new coating maintains its ability to foster droplet formation over long periods. Credit: RESEARCHERS

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.

Now, a team of researchers at MIT says they have found a way to do just that.

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 findings are reported this week in the journal Advanced Materials by MIT professors Karen Gleason and Kripa Varanasi, graduate student Adam Paxson and postdoc Jose Yagüe.

"Over the last several decades," says Varanasi, the Doherty Associate Professor of Mechanical Engineering, "people have always searched for a durable surface treatment" to make condensers hydrophobic. With the discovery of a way to make highly durable on , "the potential impact this can have has now become real."

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

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.

When materials currently used to make surfaces hydrophobic are exposed to 100 degrees Celsius steam, "after one minute, you start to see them degrade," Paxson says: The condensing water becomes "a film that covers the surface. It kills the hydrophobic surface, and degrades heat transfer by a factor of seven." By contrast, the new material shows no change in performance after prolonged endurance tests.

"There was really negligible degradation," says Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering at MIT. According to degradation models, the material might be durable for much longer than these initial tests: "We're thinking tens of years," Gleason says.

Varanasi and Paxson were part of a team that published research earlier this year on a different kind of durable hydrophobic material, a rare-earth ceramic. Varanasi says that the two approaches will likely both find useful applications, but in different situations: The ceramic material can withstand even higher temperatures, while the new coating should be less expensive and appropriate for use in existing power plants, he says. "Before, we had nothing, and we have two possible systems now," he 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."

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NikFromNYC
1.3 / 5 (13) Sep 20, 2013
Phys.org fails to mention both the nature of the new coating (fluorine? silicone? fuzziness? monolayer?) or offer a link to the article. Fluff fluff fluff, Global Fucking Warming and a steady supply of unmoderated death threats define Phys.org. David L. Chandler isn't a Phys.org editor, though, just MIT's media guy and yet another science writer with no lab experience, a dickhead environmental journalist too who writes a greenie blog instead of fills in details for his paid job....

"eXtreme efFiciency
Yes, we really can have all the modern conveniences and clear consciences and a safe planet, too.
We just have to make the right choices"

"...how to get this nation weaned off oil altogether. That's what this blog is supposed to be about...."

GET BACK TO SCIENCE!

WHAT IS THE NATURE OF THE NEW COATING?

Initiated Chemical Vapor Deposition isn't explained with clip art and an uber tacky recruiting video with pink and purple columns floating around.

(cont.)
NikFromNYC
1.5 / 5 (13) Sep 20, 2013
iCVD:
http://www.optics...11/yuan/

They use suspended hot wires to initiate vapor phase polymerization of monomer vapor mixed with a thermally unstable free radical initiator. This seems to allow some covalent cross linking too in the deposited film, I assume by including cross linking monomers to the vapor phase. Any non-polar or silicone polymer is hydrophobic so this is just expensive paint, not a nanotech advance. The article hasn't appeared yet, so I don't know more, and 40 °C "steam" is also confusing, dear Mr. Chandler.

A water phase diagram of 40 °C (313 °K) means this "steam" is condensing under vacuum?
http://www.opensc...edia.png

Yup!
http://en.wikiped...ondenser

"By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased...."
italba
5 / 5 (3) Sep 21, 2013
It's perfectly normal, for power plant steam turbines, to have a lower than atmospheric steam pressure in the condenser. And 40 °C for condensing water sure needs a low pressure, but not vacuum.
alfie_null
5 / 5 (4) Sep 21, 2013
Phys.org fails to mention both the nature of the new coating (fluorine? silicone? fuzziness? monolayer?) or offer a link to the article. Fluff fluff fluff, Global Fucking Warming and a steady supply of unmoderated death threats define Phys.org. David L. Chandler isn't a Phys.org editor, though, just MIT's media guy and yet another science writer with no lab experience, a dickhead environmental journalist too who writes a greenie blog instead of fills in details for his paid job....

All the free time you seem to have, haunting this site, why don't you start your own science blog? You don't like what's written here. You attack the authors, the editors, and the other posters. Judging from responses and ratings, nobody here particularly agrees with you.

Why are you wasting your time here? Considering your winning personality and outstanding writing skills, who knows what you might achieve.
arq
1 / 5 (2) Sep 21, 2013
@nik, Getting agitated over this indicates....you have issues man! Visit a therapist.
EnricM
1.3 / 5 (13) Sep 21, 2013
Why are you wasting your time here? Considering your winning personality and outstanding writing skills, who knows what you might achieve.


He tried, but the IPCC (Iluminaty Poker Club California) send a group of Climate Scientist Ninjas who destroyed the servers where he had his blog hosted. He was able to kill the Ninjas thanks to his Ph4ars0me Skillz, but his blog was gone.

It was a very good blog, there was Science, live streaming of lynching of liberals, strippers and he even contracted a guy to periodically post death threats to give his site more scientific credibility. A great loss for humanity, no doubt.