(Press-News.org) CAMBRIDGE, MA -- Many industrial plants depend on water vapor condensing on metal plates: In power plants, the resulting water is then returned to a boiler to be vaporized again; in desalination plants, it yields a supply of clean water. The efficiency of such plants depends crucially on how easily droplets of water can form on these metal plates, or condensers, and how easily they fall away, leaving room for more droplets to form.
The key to improving the efficiency of such plants is to increase the condensers' heat-transfer coefficient — a measure of how readily heat can be transferred away from those surfaces, explains Nenad Miljkovic, a doctoral student in mechanical engineering at MIT. As part of his thesis research, he and colleagues have done just that: designing, making and testing a coated surface with nanostructured patterns that greatly increase the heat-transfer coefficient.
The results of that work have been published in the journal Nano Letters, in a paper co-authored by Miljkovic, mechanical engineering associate professor Evelyn Wang, and five other researchers from the Device Research Lab (DRL) in MIT's mechanical engineering department.
On a typical, flat-plate condenser, water vapor condenses to form a liquid film on the surface, drastically reducing the condenser's ability to collect more water until gravity drains the film. "It acts as a barrier to heat transfer," Miljkovic says. He and other researchers have focused on ways of encouraging water to bead up into droplets that then fall away from the surface, allowing more rapid water removal.
"The way to remove the thermal barrier is to remove [the droplets] as quickly as possible," he says. Many researchers have studied ways of doing this by creating hydrophobic surfaces, either through chemical treatment or through surface patterning. But Miljkovic and his colleagues have now taken this a step further by making scalable surfaces with nanoscale features that barely touch the droplets.
The result: Droplets don't just fall from the surface, but actually jump away from it, increasing the efficiency of the process. The energy released as tiny droplets merge to form larger ones is enough to propel the droplets upward from the surface, meaning the removal of droplets doesn't depend solely on gravity.
Other researchers have worked on nanopatterned surfaces to induce such jumping, but these have tended to be complex and expensive to manufacture, usually requiring a clean-room environment. Those approaches also require flat surfaces, not the tubing or other shapes often used in condensers. Finally, prior research has not tested the enhanced heat transfer predicted for these types of surfaces.
In a paper published early in 2012, the MIT researchers showed that droplet shape is important to enhanced heat transfer. "Now, we've gone a step further," Miljkovic says, "developing a surface that favors these kinds of droplets, while being highly scalable and easy to manufacture. Furthermore, we've actually been able to experimentally measure the heat-transfer enhancement."
The patterning is done, Miljkovic says, using a simple wet-oxidation process right on the surface that can be applied to the copper tubes and plates commonly used in commercial power plants.
The nanostructured pattern itself is made of copper oxide and actually forms on top of the copper tubing. The process produces a surface that resembles a bed of tiny, pointed leaves sticking up from the surface; these nanoscale points minimize contact between the droplets and the surface, making release easier.
Not only can the nanostructured patterns be made and applied under room-temperature conditions, but the growth process naturally stops itself. "It's a self-limiting reaction," Miljkovic says, "whether you put it in [the treatment solution] for two minutes or two hours."
After the leaflike pattern is created, a hydrophobic coating is applied when a vapor solution bonds itself to the patterned surface without significantly altering its shape. The team's experiments showed that the efficiency of heat transfer using these treated surfaces could be increased by 30 percent, compared to today's best hydrophobic condensing surfaces.
That means, Miljkovic says, that the process lends itself to retrofitting thousands of power plants already in operation around the world. The technology could also be useful for other processes where heat transfer is important, such as in dehumidifiers and for heating and cooling systems for buildings, the authors say.
Challenges for this approach remain, Miljkovic says: If too many droplets form, they can "flood" the surface, reducing its heat-transfer ability. "We are working on delaying this surface flooding and creating more robust solutions that can work well [under] all operating conditions," he says.
The research team also included postdocs Ryan Enright and Youngsuk Nam and undergraduates Ken Lopez, Nicholas Dou and Jean Sack, all of MIT's mechanical engineering department.
The work was supported by MIT's Solid-State Solar Thermal Energy Conversion Center, the U.S. Department of Energy, the National Science Foundation and the Irish Research Council for Science, Engineering and Technology.
Written by David Chandler, MIT News Office
Using brain scans of children and adults watching Sesame Street, cognitive scientists are learning how children's brains change as they develop intellectual abilities like reading and math.
The novel use of brain imaging during everyday activities like watching TV, say the scientists, opens the door to studying other thought processes in naturalistic settings and may one day help to diagnose and treat learning disabilities.
Scientists are just beginning to use brain imaging to understand how humans process thought during real-life experiences. For example, researchers ...
Researchers have uncovered a new way that some bacteria survive when under siege by antibiotics.
This survival mechanism is fundamentally different from other, known bacterial strategies. Understanding it may be useful for designing drugs that target hard-to-treat bacterial strains, such as drug-resistant tuberculosis, an increasingly urgent public health problem. The study is based on Mycobacterium smegmatis, a cousin of the microbe that causes TB, and its response to the TB drug isoniazid.
The research, by Yuichi Wakamoto of the University of Tokyo and Neeraj Dhar ...
LA JOLLA, CA – January 3, 2013 – Scientists at The Scripps Research Institute (TSRI) have achieved a feat in synthetic chemistry by inventing a scalable method to make complex natural compounds known as "polyhydroxylated steroids." These compounds, used in heart-failure medications and other drugs, have been notoriously problematic to synthesize in the laboratory.
The researchers demonstrated the new strategy by synthesizing ouabagenin [wa-bah-jenn-in], a close chemical cousin of ouabain, which Somali tribes once used as a potent poison on the tips of their arrows but ...
By studying a set of fossil corals that are as much as 7,000 years old, scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a...
Click here for more information.
By examining a set of fossil corals that are as much as 7,000 years old, scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a Pacific Ocean climate cycle that affects climate worldwide. The ...
It's often difficult to completely eliminate a bacterial infection with antibiotics; part of the population usually manages to survive. We've known about this phenomenon for quite some time, dating back nearly to the discovery of penicillin. For more than 50 years, scientists have believed that the resistant bacteria were individuals that had stopped growing and dividing.
Up to now, in fact, it hasn't been possible to track the growth of cells before and after their exposure to antibiotics, which makes any analysis of the phenomenon quite imprecise. "Using microfluidics, ...
Washington, D.C.—After extensive analyses by a team of scientists led by Carl Agee at the University of New Mexico, researchers have identified a new class of Martian meteorite that likely originated from the Mars's crust. It is also the only meteoritic sample dated to 2.1 billion years ago, the early era of the most recent geologic epoch on Mars, an epoch called the Amazonian. The meteorite was found to contain an order of magnitude more water than any other Martian meteorite. Researchers from the Carnegie Institution (Andrew Steele, Marilyn Fogel, Roxane Bowden, and Mihaela ...
CORVALLIS, Ore. – Marine resource managers often gauge the health of species based on overall biomass, but a new study of predator-prey relationships in the Bering Sea found that it isn't the total number of individuals that predators care about – it's how densely they are aggregated.
It's more than searching for an easy meal, the researchers say. Predators need to balance how much energy they expend in searching for food with the caloric and nutrient value of that which they consume. When prey doesn't aggregate, however, the search for food becomes much more difficult ...
MADISON — A science-inclined audience and wide array of communications tools make the Internet an excellent opportunity for scientists hoping to share their research with the world. But that opportunity is fraught with unintended consequences, according to a pair of University of Wisconsin–Madison life sciences communication professors.
Dominique Brossard and Dietram Scheufele, writing in a Perspectives piece for the journal Science, encourage scientists to join an effort to make sure the public receives full, accurate and unbiased information on science and technology.
JACKSONVILLE, Fla. — Researchers at Mayo Clinic in Florida have identified a new target to improve treatment of pancreatic ductal adenocarcinoma cancer, which accounts for more than 95 percent of pancreatic cancer cases. This fast-growing, often lethal cancer is resistant to conventional chemotherapy. The findings are published in the Jan. 3 online issue of PLOS ONE.
The researchers decoded a molecular pathway that is switched "on" at all times, promoting accelerated growth of pancreatic tumors, and that discovery revealed ways to disable the pathway. They say one strategy ...
CAMBRIDGE, MA -- Researchers at MIT, the Broad Institute and Rockefeller University have developed a new technique for precisely altering the genomes of living cells by adding or deleting genes. The researchers say the technology could offer an easy-to-use, less-expensive way to engineer organisms that produce biofuels; to design animal models to study human disease; and to develop new therapies, among other potential applications.
To create their new genome-editing technique, the researchers modified a set of bacterial proteins that normally defend against viral invaders. ...