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| Ryzekiel |
 Posted: Fri Jul 04, 2008 9:11 am Post subject: IR mirror |
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Forum Freshman
Joined: 04 Jul 2008
Posts: 6
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I'm working to develop some material for high school students that uses solar energy technologies to communicate various topics in their physics class. I'm trying to show how energy is absorbed in a solar collector and how radiation works in general. I'd like to find some sort of material that would function as an infrared mirror for demonstrative purposes. Any ideas?
Thanks, |
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| Ryzekiel |
| Posted: Fri Jul 04, 2008 9:20 am Post subject: |
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Forum Freshman
Joined: 04 Jul 2008
Posts: 6
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| I just read that gold reflects a lot of IR so I think I might try some gold leaf on a surface. Any better ideas though? I mean, it's gold, so it's a bit pricey. |
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| Harold14370 |
| Posted: Fri Jul 04, 2008 10:31 am Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1578
Location: Pennsylvania
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| Old Fool |
| Posted: Fri Jul 04, 2008 12:13 pm Post subject: |
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Forum Freshman
Joined: 17 Jul 2007
Posts: 67
Location: England
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| Gold is a good reflector for infra-red. Gold mirrors are often used in the carbon dioxide laser which emits in the infra-red. But most metals reflect well in the IR. Aluminium (or aluminum to foreigners) is a good IR reflector. |
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| Dishmaster |
| Posted: Fri Jul 04, 2008 3:17 pm Post subject: |
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Forum Junior
Joined: 30 Apr 2008
Posts: 258
Location: Heidelberg, Germany
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| It depends on the exact range of the IR spectrum. If you are talking about thermal infrared (around 5 to 10 microns wavelength) then a simple metal plate that is non-reflective for visual light is just fine. For more about IR radiation, there is a nice webpage to be found here: http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/ |
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| Ryzekiel |
| Posted: Mon Jul 07, 2008 5:30 am Post subject: |
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Forum Freshman
Joined: 04 Jul 2008
Posts: 6
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| Thanks for the tips, folks. I'll try some aluminum foil over a stove top and see how that fares. |
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| Harold14370 |
| Posted: Mon Jul 07, 2008 9:16 am Post subject: |
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Forum Professor
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Posts: 1578
Location: Pennsylvania
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| How were you planning on detecting the reflected infrared? |
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| Ryzekiel |
| Posted: Tue Jul 08, 2008 8:14 am Post subject: |
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Forum Freshman
Joined: 04 Jul 2008
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| Well, I'm not exactly sure yet. This demonstration was meant to be sort of a side note so if there is a temperature difference which can be physically felt between the two surfaces that should suffice. It really depends on how effective the material is at reflecting heat. Ideally, I'd like to wrap beakers filled with water in two different materials and then record a difference in water temperature. |
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| Harold14370 |
| Posted: Tue Jul 08, 2008 9:09 am Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1578
Location: Pennsylvania
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| That might work but you'd have to make sure the two materials had the same conductive insulation properties. I was thinking of something along the lines of bouncing a signal from a TV remote control (they use IR) off different materials to the receiving device. |
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| Ryzekiel |
| Posted: Tue Jul 08, 2008 9:35 am Post subject: |
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Forum Freshman
Joined: 04 Jul 2008
Posts: 6
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| That is a good idea, but I'm trying to keep it heat-centric. I want to inevitably show that infrared contributes to heating a solar panel and analyze what kind of materials are good for use as a collector and what is good as an insulator. I'm not sure what it is about aluminum that actually reflects IR. I'm assuming that painting it would render it useless as a reflector since many solar panels use matte black aluminum collectors, which need to gather as much heat as they can. So If that holds true then I can have one sheet painted and one not. that way they both have the same thickness and thermal conductivity. |
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| bit4bit |
| Posted: Tue Jul 08, 2008 10:22 am Post subject: |
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Forum Ph.D.
Joined: 14 Jul 2007
Posts: 623
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You could fire an IR led at the foil, and detect the reflected beam using an IR phototransistor, which has a linear relationship between gain and flux, then read off the voltage on a multimeter. Then replace the aluminium foil with a matt balck painted surfaxce, and repeat the experiment. If all goes to plan the reading will be less, and you have demonstrated that aluminium foil is a better reflector for IR than matt black surfaces. You'll probably have to enclose the LED, around the edges, with a small strip of foil, to ensure that the light is directed in a fairly straight path, rather than duispersed, and picked up staright away by the photo transistor. Then you'd have to make sure the angles are right.
Then set up a seperate experiment with a more intense IR source, that demonstrates the heating effect of IR....like a calorimetry experiment with a polystyrene cup, water, and a thermometer.
_________________
Chance favours the prepared mind. |
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| Ryzekiel |
| Posted: Tue Jul 08, 2008 12:34 pm Post subject: |
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Forum Freshman
Joined: 04 Jul 2008
Posts: 6
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| That's a really great idea. This way we will have some solid, numerical data. I'm going to pick up a set of transmitters/receivers asap! |
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