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Freezing water droplets form sharp ice peaks

Date:
October 5, 2012
Source:
American Institute of Physics (AIP)
Summary:
Photos reveal how water droplets placed on a cold surface freeze to a sharp point that sprouts a “forest” of tree-like ice crystals.
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Once the liquid is completely frozen, the sharp tip of the drop attracts water vapor in the air, much like a sharp metal lightning rod attracts electrical charges. The water vapor collects on the tip and a tree of small ice crystals starts to grow, as seen in the image.
Credit: Oscar R. Enríquez, Álvaro G. Marín, Koen G. Winkels, and Jacco H. Snoeijer Physics of Fluids Group, University of Twente, Enschede, The Netherlands

Researchers at the University of Twente, in the Netherlands, placed water droplets on a plate chilled to -20 degrees Celsius and captured images as a freezing front traveled up the droplet.

The approximately 4-millimeter diameter droplets took about 20 seconds to freeze. During the final stage of freezing, the ice drop developed a pointy tip.

The effect, which is not observed for most other liquids, arises because water expands as it freezes. The vertical expansion of the ice, in combination with the confining effect of surface tension on the spherical cap of remaining liquid, leads to the point formation.

Once the liquid is completely frozen, the sharp tip of the drop attracts water vapor in the air, much like a sharp metal lightning rod attracts electrical charges. The water vapor collects on the tip and a tree of small ice crystals starts to grow, as seen in the image.

An opposite effect has been shown to preferentially extract water molecules from the sharp edge of potato wedges in the oven, the researchers note.


Story Source:

The above story is based on materials provided by American Institute of Physics (AIP). Note: Materials may be edited for content and length.


Journal Reference:

  1. Oscar R. Enríquez, Álvaro G. Marín, Koen G. Winkels, Jacco H. Snoeijer. Freezing singularities in water drops. Physics of Fluids, 2012; 24 (9): 091102 DOI: 10.1063/1.4747185

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American Institute of Physics (AIP). "Freezing water droplets form sharp ice peaks." ScienceDaily. ScienceDaily, 5 October 2012. <www.sciencedaily.com/releases/2012/10/121005092911.htm>.
American Institute of Physics (AIP). (2012, October 5). Freezing water droplets form sharp ice peaks. ScienceDaily. Retrieved May 27, 2015 from www.sciencedaily.com/releases/2012/10/121005092911.htm
American Institute of Physics (AIP). "Freezing water droplets form sharp ice peaks." ScienceDaily. www.sciencedaily.com/releases/2012/10/121005092911.htm (accessed May 27, 2015).

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