# The Naked Scientists Forum

### Author Topic: solar furnace  (Read 4154 times)

#### mroberts

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• Posts: 2
##### solar furnace
« on: 17/07/2006 22:00:02 »
As a demonstration for some classes I teach, I use a car headlamp housing (bulb taken out) to make a "solar furnace" that will easily melt lead. 2  questions:
1. What is the theoretical maximum temperature I could reach inside my "furnace" by pointing it at the sun,
2. What part(s) of the suns spectrum contribute to the heating effect?

Thaks. Bye. Mike.

Mike Roberts
« Last Edit: 17/07/2006 22:20:05 by mroberts »

#### ukmicky

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##### Re: solar furnace
« Reply #1 on: 17/07/2006 22:20:19 »
Dont know but i found this if its of any help.
http://www.sesec.fsu.edu/documents/lectures/ECS2005/SolarThermal.pdf

Michael

#### eric l

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• Posts: 514
##### Re: solar furnace
« Reply #2 on: 07/08/2006 15:16:45 »
You can also try this one, on the French prjoect in the Pyrenees
http://www.imp.cnrs.fr/index_en.html
(This is the English language version; the French version appears more extensive !)
They mention temperatures as high as 3800°C.
There is also this one, on a smaller project
http://www.four-solaire.fr (English language version available)

#### daveshorts

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##### Re: solar furnace
« Reply #3 on: 08/08/2006 01:53:16 »
the absolute theoretical maximum temperature is that of the surface of the sun. It is impossible to focus non-laser light down to be more intense than where it was formed.

#### another_someone

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##### Re: solar furnace
« Reply #4 on: 08/08/2006 04:58:26 »
quote:
Originally posted by daveshorts

the absolute theoretical maximum temperature is that of the surface of the sun. It is impossible to focus non-laser light down to be more intense than where it was formed.

I can understand if the light is emitted from a point source, then this would be true, but if the light is emitted from a surface, I cannot see why it could not be focused onto a smaller surface.

George

#### eric l

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• Posts: 514
##### Re: solar furnace
« Reply #5 on: 08/08/2006 09:50:11 »
There are two imortant parameters to this maximum temperature.  First temperature rise for an oject will be proportional to the ratio between amount of energy received an specific heath.
But the net amount of energy received will be the difference between radiation energy received from the sun via the mirrors, and radiation ennergy emmited by the object.  This energy emmitted is proportional to the 4th power of the absolute temperature of the object.  So there will be some temperature at which the object emmits as much radiation energy as it receives.  I'm not sure wether this maximum temperature will be influenced by the nature and size of the object.

#### lightarrow

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##### Re: solar furnace
« Reply #6 on: 09/08/2006 12:07:17 »
Sun is seen from earth as ~ a blackbody with a temperature of ~ 6000°K. At this temperature, most of the energy emitted is in the visible spectrum (around 550 nm = yellow-green colour).

#### The Naked Scientists Forum

##### Re: solar furnace
« Reply #6 on: 09/08/2006 12:07:17 »