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Efficiency of Heat Transfer Boosted by Jumping Water Vapor Droplets

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mqdefaultWater vapor condensed on metal plates, also known as condensers, is the main driving mechanism in most industrial power plants. Depending on how easy these droplets form and how fast they fall to free space for new droplets, the efficiency of the plant is either higher or lower.

The efficiency of a power plant can be greatly increased when the heat-transfer coefficient of the condensers is increased. According to Nenad Miljkovic, a doctoral student in mechanical engineering at MIT, this coefficient determines the speed of transferring away heat from the surfaces.

The journal of Nano Letters published the study conducted by Miljkovic, Evelyn Wang, an associate professor and five other researchers from the Device Research Lab in MIT. They designed, made and tested a surface, coated with nanostructured patterns, which showed great increase in this heat-transfer coefficient.

As Miljkovic explains, typically water vapor condenses on the surface of a flat metal plate, and until gravity clears it away, it acts as a barrier to heat transfer. This is the reason why the team decided to look for ways to remove the droplets from the surface as quickly as possible.

The surfaces covered with copper oxide features caused droplets to jump away, which increased the efficiency of the process greatly. The team demonstrated that small droplets merged with large ones, making the process not dependent entirely on gravity.

The team reported that the patterns can be made and applied under room temperature, while the growth process can stop by itself. In addition, the shape of droplets can also enhance the heat transfer, which can now be measured.

The use of these surfaces could increase the efficiency of heat transfer by up to 30 percent. Aside from using them in power plants, these surfaces could also be incorporated in heating and cooling systems for buildings or in dehumidifiers.

The big challenge that is left to tackle is related to the so-called “flooding” of surfaces, which also leads to reduced heat-transfer ability. Miljkovic, however, is convinced that they will find the robust solution to this in the very near future.

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