Fun_People Archive
10 Jan
Why Bubbles Float Down in a Glass of Guinness

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From: Peter Langston <psl>
Date: Mon, 10 Jan 100 16:25:42 -0800
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Subject: Why Bubbles Float Down in a Glass of Guinness

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	WHY BUBBLES FLOAT DOWN IN A GLASS OF GUINNESS

A computer simulation has been used to show that even though bubbles
float up, they also go down in a glass of Guinness. Professor Clive
Fletcher and students at the University of New South Wales, Sydney,
Australia, used FLUENT computational fluid dynamics (CFD) software from
Fluent Inc. to illustrate that bubbles go both up and down in a glass of
Guinness. Fletcher's team used the software to simulate the motion of
the bubbles and discovered that, as expected, most bubbles do move
upwards. The bubbles in the center of the glass, free from the effects
of the glass wall, move upwards most quickly and drag liquid with them.
But the liquid moving up in the center of the glass, having nowhere else
to go, must eventually turn towards the walls and start to move
downward. The liquid moving downward near the walls tries to drag down
bubbles with it. Larger bubbles have sufficient buoyancy to resist but
smaller bubbles are continuously dragged to the bottom of the glass.

© 2000 Peter Langston