Disputation2
Linn Karlsson. Photo: Simon Eliasson View original picture , opens in new tab/window

Dissertation about frozen water droplets

Published: 3 March 2020

What really happens inside a droplet of water when it freezes to ice? Linn Karlsson has studied this in her doctoral dissertation, and she hopes it will lead to better opportunities to prevent ice formation.

Wind turbines, aircraft and roads in cold climates are greatly affected by ice formation. This can lead to large costs for removing the ice, and in the worst case, serious accidents or death.

Complex

– There are quite good systems to prevent this today, and a lot of research has been done on it. But ice and water are very complex, and there is a lot of research missing, says Linn Karlsson.
She recently defended her dissertation "The Internal Flow in Freezing Water Droplets", where she studied what happens to the internal flow when water droplets freeze to ice – something that has been overlooked. One reason for that may be the difficulty in actually observing what is happening.
– It is simply very difficult to see into the drip when the water freezes, as both the curved drip surface and the ice make it difficult. We have found a method to study the flow anyway, says Linn Karlsson.

Uneven surface

The study has been carried out so that a drop of water is applied to a surface of alumina and illuminated from below with laser. From the side, the freezing process, which is made visible by particles introduced into the water, is filmed. What happens in the drip during the first quarter of the freezing process is then studied.
– After that it basically stands still in the drop, says Linn Karlsson.
Initially, a number of problems arose, including the drop being subcooled and not frozen even though the temperature of the water was below zero.
– It turned out that we needed a surface that was more uneven than we thought. With too smooth a surface, we simply did not get the drop to freeze, says Linn Karlsson.

Basic research

In the long run, she hopes more studies will be done on the subject.
– What I have done is basic research. Then it is important to look at this in a broader perspective – how the environment affects this process, for example. The air flow around the droplet, humidity, things like that, says Linn Karlsson.
– We have taken the first step now in being able to improve coatings to prevent ice formation. There are no answers yet, but this is definitely a step in that direction, says Linn Karlsson.