## Irish Mathematicians Solve The Guinness Sinking Bubble Problem

• Posted by a hidden member.
And now you know.

http://www.technologyreview.com/blog/arxiv/27880/?p1=blogs

Bubbles sink in Guinness because of the peculiar geometry of pint glasses, say a dedicated group of researchers at the University of Limerick

One of the more intriguing conundrums in fluid dynamics is the puzzling behaviour of bubbles in Guinness, the famous Irish stout.

As many drinkers will attest, the bubbles in Guinness appear to sink as the drink settles and the head forms. How can this be, given that bubbles are less dense than the surrounding fluid and so should rise?

Over the last ten years or so, physicists have begun to pick this problem apart. Most recently they've shown that it is not the bubbles that sink but the liquid, which circulates in a way that is downwards near the glass walls and upwards in the interior. As long as the downward flow of the liquid is faster than the upward motion of the bubbles, they will appear to sink.

But that still leaves a puzzle: why does the liquid circulate in this way?

Today, a dedicated team of Irish mathematicians reveal the answer. Eugene Benilov, Cathal Cummins and William Lee at the University of Limerick say the final piece in this puzzle is the shape of the glass, which has a crucial influence over the circulatory patterns in the liquid.
• Posted by a hidden member.
Now for the big question: Assuming the temperature of the liquid is equal through the pint, what causes the convection-like motion?
• Posted by a hidden member.
it took them 10 years to figure this out?
• Posted by a hidden member.
ChangeofName saidit took them 10 years to figure this out?
Hangovers inhibit research.
• Posted by a hidden member.
LOL
• Posted by a hidden member.
Well, wouldn't the beverage in contact with the glass warm faster? Assuming that it's poured cold and the ambient temperature is warmer. Also, body heat from your hand would be conducted inward whenever you lift it for a drink.

Another interesting thing about Guinness is that co2 is not used with it, as you would with a standard draft beer. Guinness requires that nitrogen be used for their kegs instead. Yes, I once tended bar where we served it. I don't know if that applies to bottles however.
• Posted by a hidden member.
Sungod17 saidWell, wouldn't the beverage in contact with the glass warm faster? Assuming that it's poured cold and the ambient temperature is warmer. Also, body heat from your hand would be conducted inward whenever you lift it for a drink.
According to the laws of fluid dynamics, that would cause the fluid to rise along the edges and sink in the middle...total opposite of what Guinness does. Also, any other beer will have rising bubbles along the edge even when it's poured into a frosted mug.
• Posted by a hidden member.
One pint pls!

Ive just had two pints... forgive me for the random posts
• Posted by a hidden member.
• neosyllogy

Posts: 1714

@PaulF
I haven't read the article and so don't really know, but I'd guess it's the carbonation (or whatever is in beer? I don't know, I don't really drink).
As gas escapes the fluid and forms bubbles they move upward and create motion in the glass. The upward movement has to be balanced resulting in convection of course. The fluid will move more slowly along the edges than the center due to the friction of the glass wall, which I assume is related to the apparent bubbles dropping in pine glasses (with the math involved presumably showing how the velocity of downward flow is high enough to counteract bubbles floating to the top).
No idea if that's true, just a guess.