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July 7, 2013

I just read an interesting article about this guy in Cuba named Sebastian Bianchi – he’s one of those lucky scientists that observes something a little wacky in his normal life and then gets a publication out of it a few years later. I’m envious to say the least, especially because his initial observation was made while pouring himself a cup of tea. He realized that when he poured with the kettle spout too close to the tea leaves, little bits of leaves would actually travel against gravity and make it back into the kettle.

So naturally Bianchi was like, I gotta figure this out ASAP. Cut to a few years later and he’s publishing his findings in The Proceedings of the Royal Society A. Basically he set up a couple of pools in the lab with a spout between them and measured the flow of either mate tea leaves or chalk dust when liquid was flowing from the top pool to the bottom pool. He tested different waterfall heights as well as flume lengths to see how the upward flow of leaves would change.

Here’s an example video in which you can see tiny bits of chalk dust zooming up the far sides of the spout – in this example many of them drop back into the center of the stream and move back into the starting pool, however some of them make it all the way up the spout.

They also tested whether surface tension had anything to do with this phenomenon by adding sufactant (soap) to either the top or bottom pools in order to “break” the surface tension. They found that adding it to the top pool meant no more upstream contamination – whereas adding it to the bottom pool actually increased the amount of particles that would start up the spout. They concluded also that these particles were capable of climbing up a waterfall of up to 1cm, or up a flume of several meters.

The paper explains all the fluid dynamics behind the movement of these particles, and it’s certainly way over my head. The gist of it, however, is that the “downward” pull of the water in the center of the spout actually causes the reverse flow of water up the edges, and surface tension plays an important role in this process. The tea leaves simply allow these naturally occurring water patterns to be visualized more easily.

The point of all this isn’t just to look at how tea could move out of your cup and into your kettle, obviously. They’re proposing that this type of fluid mechanics could contribute to all kinds of contamination situations – the most prominent example for scientists being contamination during pipeting. If cells or molecules can flow upward against a stream of fluid, the act of pipeting (moving liquid with a long, skinny tube) may inadvertently be introducing unknown contaminants into our samples and stock solutions.

Basically this dude played with kiddie pools and tea leaves and contributed to our scientific knowledge. Luckkkyyyy.


From → Physics

One Comment
  1. Wendy permalink

    Oh man, this would totally explain how we ended up with mouse stem cells when we all thought we were working with human.

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