How to use math to build the perfect campfire


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  • To make a good bonfire, you need to stack your wooden structure as high as it is wide, like a pyramid.
  • This approach was first described in 2015 paper Posted in Scientific reports.
  • If you don’t have a fireplace, make your fire on the ground or near a fire blanket.

    Although fire is one of the oldest human technologies, building a bonfire and keeping it safe is not always an easy task. After collecting dry wood or twigs around your campsite, you need to decide how to arrange them for optimal combustion. Is arranging them in a pile, like a log cabin, the right decision? Or maybe just throw them in a pile and see what happens?

    In theory, there are countless ways to organize your fuel source, but depending on Adrien Bejan, professor of mechanical engineering at Duke University, there is only one surefire way: your fuel must be stacked as high as it is wide, like a pyramid. It is no coincidence, says Bejan, that a pyre and a pyramid are so linguistically similar.

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    Even though this perfect solution has been hiding in plain sight for millennia, Bejan first laid out the mathematical formula for it in an article from 2015 in the review Scientific reports. “I was able to solve it as a homework problem for my students,” says Bejan. “It took about two hours one evening.”

    Why fire is like Swiss cheese

    The answer, he says, starts with understanding what kind of science dictates how fires burn. It’s an extremely multifaceted question, but it boils down to two big contenders: thermodynamics and fluid dynamics.

    “Thermodynamics is the science of power, [in this case] the power of fire,” says Bejan Popular mechanics. “Which is then used to move things around [like air] … This airflow feeds the combustion reaction, then the heat generated is carried away by the airflow itself.

    You can think of a fire as a piece of Swiss cheese. Between the different pieces of fuel (whether you use coal, wood or another source) there are many holes or spaces through which air can move. If your fire is too dense, air cannot circulate to support combustion; if your fuel is too loose, the air can’t get enough power to move quickly. The scientific term for this type of hole-filled shape is a “porous medium,” Bejan says.

    However, Bejan says cone-shaped lights are not the only effective form. As long as this aspect ratio is maintained, he says there is no real limit to the shape of fire. Too flat or too high, the fire will not be able to maintain its heat for very long, or even ignite properly.

    Advice from a firefighter

    Understanding the mathematical principles behind building a fire is just the start, says Daniel Jimenez, a research engineer at the Missoula Fire Sciences Laboratory. After starting a fire, understanding the math involved in keeping it safe and putting it out efficiently are essential skills not only for firefighters, but also for nature enthusiasts.

    As part of his work, Jimenez helps facilitate an online course teach firefighters the math behind the fires they fight.

    “Most of the math in our course is just basic geometry,” Jimenez said. Popular mechanics. “But it gets a lot more advanced when you start thinking about volumes and pressures and [water] distribution systems.

    While some firefighters enter the career after college and have a basic knowledge of physics and math, it’s also common for others to become firefighters right out of high school, Jimenez says. This online course helps provide a common foundation of scientific and mathematical knowledge to keep firefighters safe and accurate on the job.

    Jimenez also designs mathematical modeling software to help firefighters track the progress of wildfires. These app-based and computer-based software can include landscape and wind modeling and replace what used to be physical pocket guides. This helps firefighters not only contain fires, but also perform safe prescribed burns that can help prevent wildfires later in the season.

    As for how to protect your mathematically perfect campfire, Jimenez says the answer is pretty simple: containment. A great way to make sure your fire won’t accidentally spread beyond its base is to make sure its fuel source is discontinuous, says Jimenez, which means there’s no fuel. lost near the fire.

    A metal fire pit is an easy way to do this or you can build your fire on the ground or near a fire blanket. And before you leave your fire, be sure to extinguish the thermodynamics at work with a good sprinkling of water.

    “If I had one piece of advice for someone who has campfires, it would be to drown them out,” Jimenez says. “You can’t put too much water on a campfire.”


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