Here's cheers for that scientific sinking feeling

By Richard Macey

March 20, 2004

If he was a drinking man, Md Nurul Hasan Khan would have popped into his local pub this week to celebrate by downing a cold beer.

But the chemical engineer and devout Muslim, who is now with the CSIRO's minerals division, was simply chuffed to know the world finally accepted he was right. Bubbles in a glass of Guinness do sink, as well as rise.

In 1999 Mr Khan, known as Hasan by his friends, used mathematical computational modelling to explain the falling bubbles, something he had seen many times. "I don't drink, but all my colleagues do, and I hang out with them."

It didn't make sense. Gas bubbles, lighter than beer, should only rise. Mr Khan, who did a PhD thesis on bubble behaviour in liquids, believed computational modelling held the answer.

He published his results, but the scientific world remained sceptical until this week when Scottish and Californian scientists announced slow-motion movies of Guinness confirmed its bubbles do fall.

Richard Zare, a professor at California's Stanford University, said he had been aware of the Australian research: "I first disbelieved this and wondered if people had maybe too much Guinness to drink."

To make his discovery, Mr Khan, then at the University of NSW's school of chemical engineering and industrial chemistry, bought a Guinness glass and called the company for information about its viscosity, density and the typical size of its bubbles. He stirred the data in his computer, producing a mathematical model of the world inside every Guinness glass.

"I calculated all the forces acting on individual bubbles and I found some of the bubbles, near the sides of the glass, were going down."

The model revealed that rising bubbles formed a column in the middle of the glass. "But those bubbles try to drag the liquid up," he said. The rising beer spread out at the top of the glass, forcing beer at the sides to go down. Small bubbles on the sides were swept down with the flow. "It took me about six months of work, part time . . . now they [the Scottish and Californian scientists] have found the same thing. I am very pleased."

The Bangladesh-born Mr Khan believes his discovery has significance for breweries and drinkers, because the longer bubbles circulate, the longer beer maintains its taste and smell. He now intends to find a way to keep the bubbles moving.

"Most people do not know computational modelling has some great value," he said.

This story was found at:

http://www.smh.com.au/articles/2004/03/19/1079199418340.html

Bursting a scientific bubble Md Nurul Hasan Khan discovered that in a glass of Guinness bubbles sink, as well as rise - a theory now accepted by the science world. Photo: Glenn Hunt