How can you throw flames?

By Simon Jones

Flame-throwers are fascinating devices, which I’m exploring in this week’s engineering blog. From large scale weapons in the First World War to small scale accomplishments in civil engineering, we can use flame-throwers to make heat and transfer thermal energy.

Warfare

Flame-throwers were first conceived at the start of the 20th Century, by a German scientist. These flame-throwers were later refined and deployed during World War I, although they weren’t used extensively, mainly as they weren’t very effective! The Germans pioneered “handheld” flamethrowers which were controlled by a crew of four men, spurting flames approximately 10 metres. These flamethrowers didn’t do much damage or take any lives, but did drive out the enemy from trenches, leading them to be shot. Years later the British artfully borrowed the idea and made limited use of their own style of flamethrower; a large scale, non-portable machine which effectively fired rockets of fuel and exploded them up to 40 metres away!

Westfront, Flammenwerfer

“Anyone got a light?” Image: German Federal Archive (CC-BY-SA)

The heat created by these latter weapons was intense. So much fuel was being converted from stored energy into thermal and light energy, at such a high rate, that the injury to people was noticeable, even if they were quite far away from the flames. The point is, that the fire didn’t have to hit you to hurt you.

 

Invisible light

Air is a poor conductor of heat, but easily allows heat to radiate through it as an electromagnetic wave. It was in fact the light energy in the form of intense infra-red waves which caused the damage.

When infra-red reaches an object, it heats it and is converted to thermal energy, In a similar way to the damage ultra-violet (UV) rays from the sun can do to our skin, these intense infra-red would reach human cells, quickly heat them and damage them. And this is exactly what happened to the few soldiers who were unfortunate enough to be near one of these terrifying machines.

Infra-red is only a dangerous form of radiation when it comes in very high doses. In fact, infra-red is all around us and is being emitted from your body to your surroundings right now. Although we can’t see infra-red with our eyes, we can use thermal imaging camera to convert the infra-red waves into visible light. This can be used for example by firefighters, who can detect survivors beneath rubble, even if they can’t see people. But, it can also be used for a bit of fun. In our Beyond the Rainbow show, we use an infra-red camera to see everyday objects differently. Two guesses as to what object this is…

Beyond the Rainbow

See the heat! Image: NASA/IPAC (Public Domain)

From battlefield to camping field

So that’s the infra-red behind the flame-thrower. The civil engineering advantages of this technology are often less appreciated. Apart from a few snow-covered countries which use similar devices for clearing streets of ice, and a certain closing ceremony at a relatively recent Paralympic games event, we don’t use flame throwers in our day to day business. But again, the same technology is modified for modern camping equipment, where gas stoves have fuel spurted out (albeit with far less pressure) and ignited, to form a steady but reliable flame until the fuel source is depleted. It is reassuring to know that engineers have invented a system which burns a flame without exploding or igniting itself.

Whose crew are you?

The science and engineering behind throwing flames is fascinating. We encourage students we speak to do explore the many avenues of engineering. One of the ways we do this is through our Tomorrow’s Engineers shows, where we recommend the Whose crew are you? app for aspiring engineers to try themselves (and for the record, I was recommended the space crew… awesome!).

 

Curriculum links

Key Stage 3:

Physics-

Energy changes and transfers

Light waves

Design and Technology-

Analyse the work of past and present professionals and others to develop and broaden their understanding

Understand developments in design and technology, its impact on individuals, society and the environment and the responsibilIties of designers, engineers and technologists


 

We have a wide variety of engineering shows for primary, secondary and family audiences.

We also work in partnership with Tomorrow’s Engineers to inspire the next generation of engineers!

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Posted in Engineering, Physics