MIT's Technology Review informs us of the latest advance in scientific understanding.
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?
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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.
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Benilov and co imagine that to start with, the bubbles are distributed evenly throughout the liquid. In a perfect cylinder, they would simply rise together. The bubbles in each volume of liquid are steadily replenished from below.
But imagine a container that is narrower at the bottom and wider at the top so that the walls rise at an angle, as in a pint glass. In this case, the simple act of bubbles rising creates a region of low bubble density next to the angled wall because the bubbles are not being steadily replenished below.
By contrast, the bubble density is higher in the middle of the glass because the bubbles are replenished from below.
That would set up exactly the circulation pattern that is observed, say Benilov and co.
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Of course, the essence of experimental science is repeatability. Many readers will not be content with mere visual evidence from a video but insist on repeating this experiment on their own terms, perhaps in a hostelry of their own choosing. Quite right.
There's more at the link.
Why can I so easily imagine a team of undergraduate students deciding that the formation and pattern of bubbles in beer is a suitable subject for scientific and technological research - particularly 'field experiments'? And why do I suspect that 'peer review' of their experimental results is underway in dozens - nay, hundreds! - of universities, even as we speak?