building a parabolic with mirrors.

[Corona]

You are right on about the price. I just bought a bunch of 12" x 12" mirrors tonight and they were $1.48 each.

You used a focal point of 18" on your system. If you changed the size of the mirrors to 4" x 4" would that change the focal length you would use?

[SolarFreak]

well I got the gallery started on my site
http://heliospheric-labs.com/gallery...ini+parabolic/
I didnt have much time to work on it this weekend but here a few pictures.

[SolarFreak]

Originally Posted by Corona

You are right on about the price. I just bought a bunch of 12" x 12" mirrors tonight and they were $1.48 each.

You used a focal point of 18" on your system. If you changed the size of the mirrors to 4" x 4" would that change the focal length you would use?

yeah I wish I could them that cheap here.

4" X 4" mirrors I would go for a focal point of 36" - 40"
but it really depends on how wide your radius of your mirror array is going to be.

how many rows are you planning on doing?

[Corona]

Thanks for posting all the pics of your project. I will take pics of my attempt when I start in a couple of days.

I was going to do a type of trough design but while in the shower this morning I had an idea I want to try that is more like what you did.

I believe the material needs to be headed up to around 450 F to become charcoalized. Do you know for how long a period we need to keep it at that temp?

[EStein]

Originally Posted by SolarFreak

yeah I wish I could them that cheap here.

4" X 4" mirrors I would go for a focal point of 36" - 40"
but it really depends on how wide your radius of your mirror array is going to be.

how many rows are you planning on doing?

SolarFreak, WONDERFUL PICTURES!!
I think a some of us are trying to understand the concept of a flat mirror's focal point. I think you mean aperature and the associated distortions. The larger the aperature, the less distortion. This is not much concern when focusing heat and light for your purposes. The greatest concerns are finding a material that will take the abuse and not be too reflective. Larger units actually use a coolant in the collector, liquid sodium, for example, which in turn is used as a working fluid. The working fluid could power your Stirling engine(s) but would need to be returned to the collector after the heat was extracted by the engines. Otherwise, you could experiment with using a fan to cool the radiative side of the Stirling engine. The fan would use a relatively small part of the total energy produced.

[Turtle]

Originally Posted by EStein

SolarFreak, WONDERFUL PICTURES!!
I think a some of us are trying to understand the concept of a flat mirror's focal point. I think you mean aperature and the associated distortions.

See post #7 of this thread for an explanation of a flat mirror's focal length.

[arkain101]

I have seen someone build one out of tin or other kinds of shiny sheet metal and it created alot of heat!

You could construct a wooden face and then place any kind of reflective material on that face. The more smoother and equaly curved you make it the more powerful the device will become, obviously by taking a few square feet and condensing it into a square inch.

[EStein]

Originally Posted by Turtle

See post #7 of this thread for an explanation of a flat mirror's focal length.

I looked at the link in post #7. Technically speaking, that is not a focus. Smaller mirrors will create a smaller dot but under magnification any individual smaller dot is no more in "focus" than the larger one. The difference in using smaller mirrors is that the more compact arrangement of smaller mirrors used more closely approximates a true parabolic shape. Then, the combined smaller dots at the focal point produce a sharper image. Then, there is the whole thing about aperture vs wavelength affecting acuity which, for the discussion here, is irrelevant.

[EStein]

Originally Posted by arkain101

I have seen someone build one out of tin or other kinds of shiny sheet metal and it created alot of heat!

You could construct a wooden face and then place any kind of reflective material on that face. The more smoother and equaly curved you make it the more powerful the device will become, obviously by taking a few square feet and condensing it into a square inch.

A friend and I made a beautiful one in the 1960's using cardboard, thick construction paper, tape, and aluminum foil. It was about 5 ft in diameter, had about a 4 ft focal lenght, and roasted a mean hot dog.

[arkain101]

hehehhe,,,

get'er'done.. !