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Power/Alternative Energy??

Graphene-coated condensers boost power plant efficiency

Posted: 02 Jun 2015 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? power plant? graphene? condenser?

It doesn't matter whether electricity-producing power plants are powered by coal, natural gas, or nuclear fission, they essentially make electricity by generating steam that turns a turbine. That steam then is condensed back to water, and the cycle begins again. However, the condensers that collect the steam prove to be inefficient, and improving them could mean the world of a difference in overall power plant efficiency.

Now, a team of researchers at MIT has developed a way of coating these condenser surfaces with a layer of graphene, just one atom thick, and found that this can improve the rate of heat transfer by a factor of four, and potentially even more than that, with further work. And unlike polymer coatings, the graphene coatings have proven to be highly durable in laboratory tests.

Condenser

An uncoated copper condenser tube (top left) is shown next to a similar tube coated with graphene (top right). When exposed to water vapour at 100°C, the uncoated tube produces an inefficient water film (bottom left), while the coated shows the more desirable dropwise condensation (bottom right). Courtesy of the researchers

The findings are reported in the journal Nano Letters by MIT graduate student Daniel Preston, professors Evelyn Wang and Jing Kong, and two others. The improvement in condenser heat transfer, which is just one step in the power-production cycle, could lead to an overall improvement in power plant efficiency of 2-3 per cent based on figures from the Electric Power Research Institute, Preston said, enough to make a significant dent in global carbon emissions, since such plants represent the vast majority of the world's electricity generation. "That translates into millions of dollars per power plant per year," he noted.

There are two basic ways in which the condensers, which may take the form of coiled metal tubes, often made of copper, interact with the flow of steam. In some cases, the steam condenses to form a thin sheet of water that coats the surface; in others it forms water droplets that are pulled from the surface by gravity.

When the steam forms a film, Preston explained, that impedes heat transfer, and thus reduces the efficiency, of condensation. So the goal of much research has been to enhance droplet formation on these surfaces by making them water-repelling.

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