MIT research into condenser surfaces may lead to reduction of global emissions of greenhouse gases.
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Water droplets condense on a lubricated surface Image: Phys Org/MIT |
Recently published MIT research has described a new hydrophobic (water-shedding) surface architecture which may boost the performance of condensers, particularly for the power generation industry.
Crucial to both power and desalination plants, condensers are a critical component in nearly 80% of the world’s fossil-fuel power plants which have generators turned by steam-powered turbines. The condensers turn steam back to water after it has passed through the turbine. The discovery of a new surface allows for more efficient heat transfer within the condensing process, which could have a significant impact on global CO2 emissions. "Even if it saves one percent, that's huge," says Kripa Varanasi, Doherty Associate Professor of Ocean Utilization at MIT.
The new surface architecture will also allow desalination plants to improve the production rate of fresh water.
To date, understanding the processes of wetting and water-shedding has been dependent on computer modelling, as the interface between a surface and a liquid (for example, as water condense) has been hidden from view by the droplets themselves. However, a new technique - developed by MIT - provides detailed images as the droplets are rapidly frozen in place on the surface, cut into a cross-section with an ion beam and then imaged with a scanning electron microscope.
Easily manufactured, the improved surfacing uses a combination of microscopic patterning together and a lubricant such as oil. The nanotextured surface is covered with bumps or posts just 10 micrometres across and the minute spaces between the posts use capillary action to hold the oil in place.
The speed at which the droplets of water condense on this surface is an astonishing 10,000 times faster than surfaces with just hydrophobic patterning. In essence, they glide on the surface, allowing new droplets to form much faster.
The surface requires a minimal amount of lubricant which forms a thin coating and is pinned securely in place by the posts. There is a small reservoir at the edge of the surface which allows for any lost lubricant to be easily replaced. It’s even possible to design the lubricant with extremely low vapour pressure to prevent evaporation in a vacuum.
No specific configuration of the surface texture is required; it simply needs approximate dimensions and a very thin coating of lubricant: about a quarter/half teaspoon to coat a square yard of material. An additional benefit of the lubricant is it's corrosion protection for the underlying metal surface.
Meanwhile the MIT observation technique offers new opportunities to study interactions between different liquids or gases and solid surfaces.