Tuesday, June 09, 2015

The shape of a perfect fire

http://www.eurekalert.org/pub_releases/2015-06/du-tso060215.php

Public Release: 8-Jun-2015
Duke University

From ancient Egyptians roasting a dripping cut of beef next to the Great Pyramid of Giza to a Boy Scout learning to build a log cabin fire in his backyard, everyone builds fires with the same general shape.

And now we know why.

In a study published in Nature Scientific Reports on June 8, Adrian Bejan, the J.A. Jones professor of mechanical engineering at Duke University, shows that, all other variables being equal, the best fires are roughly as tall as they are wide. This is why, he argues, everyone has built fires that basically look the same since the dawn of time.

'Humans from all eras have been relying on this design,' said Bejan. 'The reason is that this shape is the most efficient for air and heat flow. Our success in building fires in turn made it possible for humans to migrate and spread across the globe heat flow from fire facilitates the movement and spreading of human mass on the globe, which is a direct prediction of the Constructal Law.'

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