Fires burn hottest when they are pyramids, according to a new study which explains why human fires always have roughly the same shape.
Researcher Adrian Bejan at Duke University has found that, all other variables being equal, the best fires are roughly as tall as they are wide.
This is why everyone has built fires that basically look the same since the dawn of time, Bejan said.
"Humans from all eras have been relying on this design. The reason is that this shape is the most efficient for air and heat flow," said Bejan.
Bejan found that the fundamental equations governing fires imply that as they get too shallow they can't get enough oxygen, and as they get too tall in relation to their base their core gets cooler, 'The Times' reported.
"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," he said.
In 1996, Bejan penned the Constructal Law that postulates that movement - or 'flow' - systems such as trees, rivers or air currents evolve into configurations that provide easier and easier access to flows.
"Our bonfires are shaped as cones and pyramids, as tall as they are wide at the base. They look the same in all sizes, from the firewood in the chimney, to the tree logs and wooden benches in the centre of the university campus after the big game," said Bejan.
"They look the same as the pile of charcoal we make to grill meat. And now we know why," he said.
The study is published in the journal Nature Scientific Reports.
