Earlier this week, we covered a company, Xefro, that was applying graphene to a home heating system, producing energy savings over traditional systems.
Now research out of MIT is showing that coating power plant condensers with graphene could make them more energy efficient.
In research published in the journal Nano Letters, the MIT team addressed one of the basic elements of steam-generated electricity: heat transfer in water condensation. In a steam-powered power plant, water is heated up to create steam that turns a turbine. The turning of the turbine produces electricity. In this process, the steam is condensed back into water and the whole process begins again.
The MIT team looked at these condensers and found that by layering their surfaces with graphene they can improve the rate of heat transfer by a factor of four.
The researchers believe that this graphene surface could improve condenser heat transfer so that an overall power plant efficiency could be improved by as much as 2 to 3 percent based on figures from the Electric Power Research Institute.
"That translates into millions of dollars per power plant per year," said Daniel Preston, one of the MIT authors of the paper, in a press release.
The condensers gain efficiency because the the graphene resists the formation of films on the condensers. In typical condenser systems, metal coils, usually copper, are placed within the flow of the steam. In some of these systems, the condensation takes the shape of a thin sheet of water coating the surface of the metal tubing; in others, water droplets are formed. When a thin film is formed the heat transfer of the condensation is compromised.
The MIT researchers exploited the graphene coating’s hydrophobic qualities to ensure that the water formed into droplets. While polymer coatings have been used to achieve more or less this same effect, the polymers degrade rapidly. Even worse, the polymer coatings are sometimes so thick that they actually pose a bigger problem to the heat transfer than the films they are supposed to be combating.
After testing the material in an environment of pure water vapor at 100 degrees Celsius, the researcher found that the graphene-coating offered a four-fold improvement in heat transfer compared to bare metal. The MIT researchers have also calculated that these numbers could be improved to a five to seven times improvement by optimizing temperature differences in the system.
Most importantly, the graphene-coating showed no sign of measurable degradation over the two-week period of the test. Just to put that two weeks into context, a polymer coating solution started to degrade in the environment within three hours and completely failed within 12.
The researchers contend that since production of the graphene coating is based on standard chemical vapor deposition, a product based on this could be available within a year.