Enhancing 'breath figures' using electric fields

June 4, 2018 by Wiebe Van Der Veen, University of Twente
Development of droplet size and distribution in time, without electrowetting (upper images) and with electrowetting (lower images) . Credit: University of Twente

Breath figures are the typical condensation patterns we know from breathing on a cold surface. In physics, this term is used to describe dropwise condensation patterns. The evolution of these patterns and roll-off of droplets can be changed strongly under electric field effects 'electrowetting' - leading to higher heat transfer rates. Researchers of the University of Twente presented these findings in Physical Review Letters.

Dropwise can be seen in many natural phenomena like dew formation; it is also the basis for technologies like , desalination units and water-harvesting systems. Optimizing these industrial applications requires thorough knowledge of the whole process of condensation, including droplet growth dynamics and mobility. It is possible to do this by modifying the characteristics, for example by applying a thin water-repellent coating that improves droplet mobility. The UT scientists now show it is also possible to actively influence the condensate by embedding electrodes in the surface.

Applying electric fields changes the 'wetting state' of the surface. This is called electrowetting. The typical breath figure has randomly distributed drops, but under electrowetting, the evolution of condensation can be controlled. The electric field influences the distribution and the size of the droplets: they merge faster caused by the electric forces and form bigger droplets in shorter time. Furthermore they move to become aligned along each other.

Enhanced heat transfer

In this way, under electrowetting, the breath figure undergoes a major transformation of properties like surface coverage, size distribution and average radius. By rapid merging of droplets, their net surface coverage is reduced compared to typical cases, leaving more 'bare surface' for further condensation. Furthermore the droplets roll off faster on the surface. This increased mobility leads to more efficient , as preliminary measurements show – done in collaboration with a research group of MIT. Apart from practical applications, like improved exchangers, the research gives more fundamental insights into theoretical analysis of dropwise condensation at a wide range of energy levels: it shows what the preferred locations for the alignment of droplets, for example.

The research has been done in the Physics of Complex Fluids group of Prof Frieder Mugele, part of the MESA+ Institute for Nanotechnology of the University of Twente. It was supported by the Netherlands Organisation for Scientific Research (division Applied and Engineering Sciences) and the Vici-programme.

Explore further: New research could make dew droplets so small, they're invisible

More information: Davood Baratian et al. Breath Figures under Electrowetting: Electrically Controlled Evolution of Drop Condensation Patterns, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.214502

Related Stories

Better droplet condensation could boost power efficiency

June 24, 2013

Researchers at MIT have developed an innovative approach to improving heat transfer in power plants and cooling systems. The new system could provide a 100 percent improvement in the efficiency of heat transfer over conventional ...

Electric fields can push droplets from surfaces

December 20, 2013

Researchers at MIT have followed up on their discovery that droplets of water acquire an electric charge when jumping from certain condenser surfaces by finding a way to make use of that effect: They found that by applying ...

An engineered surface unsticks sticky water droplets

August 31, 2015

The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets ...

Recommended for you

How community structure affects the resilience of a network

June 22, 2018

Network theory is a method for analyzing the connections between nodes in a system. One of the most compelling aspects of network theory is that discoveries related to one field, such as cellular biology, can be abstracted ...

The pho­to­elec­tric ef­fect in stereo

June 22, 2018

In the photoelectric effect, a photon ejects an electron from a material. Researchers at ETH have now used attosecond laser pulses to measure the time evolution of this effect in molecules. From their results they can deduce ...

Water can be very dead, electrically speaking

June 21, 2018

In a study published in Science this week, the researchers describe the dielectric properties of water that is only a few molecules thick. Such water was previously predicted to exhibit a reduced electric response but it ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.