Posted by brian on August 17, 2008, 2:29 pm
I want to to make a compound parbolic concentrator. (ideally like a big bell
upside down). But mylar does not go to bell shapes easily. I was going
instead to make 4 mylar troughs joined together to make a reasonably close
bell shape. I want to test it before making to see that it will still
concentrate fairly well. Is there a program where you can make a shape on
computer, and then shine a line of light on it and see where it bounces to?
No more than 5 bounces are necessary. And it would be nice to be able to
move the first "ray" to simulate the sun moving.
My compound parabolic concentrator is to be good for 3 hours of solar
cooking at the bottom of the upturned bell. (It will be about 6 ft high and
collect about 1m2 of light and concentrate it to about a ft square area. I
think 34 cm by 34 cm to be more exact.
Thanks in advance.
Brian White
Posted by Morris Dovey on August 17, 2008, 10:08 pm
brian wrote:
> I want to to make a compound parbolic concentrator. (ideally like a
> big bell upside down). But mylar does not go to bell shapes easily. I
> was going instead to make 4 mylar troughs joined together to make a
> reasonably close bell shape. I want to test it before making to see
> that it will still concentrate fairly well. Is there a program where
> you can make a shape on computer, and then shine a line of light on
> it and see where it bounces to? No more than 5 bounces are necessary.
> And it would be nice to be able to move the first "ray" to simulate
> the sun moving. My compound parabolic concentrator is to be good for
> 3 hours of solar cooking at the bottom of the upturned bell. (It will
> be about 6 ft high and collect about 1m2 of light and concentrate it
> to about a ft square area. I think 34 cm by 34 cm to be more exact.
I'd like to have that same piece of software, and finally decided that
it was easier to just build the trough (you can see some photos of the
construction method I used at:
http://www.iedu.com/DeSoto/Projects/Stirling/Heat.html
I'd still like to be able to model other reflecting surfaces but while
modeling isn't really difficult, it does get a bit "messy".
I've heard that this might be possible in some CAD programs - and if
anyone in alt.solar.thermal is aware of a package that does this, I'd be
interested, too.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by ohara5.0 on August 18, 2008, 12:16 am
On Aug 17, 11:37 pm, david.willi...@bayman.org (David Williams) wrote:
> -> I want to to make a compound parbolic concentrator. (ideally like a big bell
> -> upside down). But mylar does not go to bell shapes easily. I was going
> -> instead to make 4 mylar troughs joined together to make a reasonably close
> -> bell shape. I want to test it before making to see that it will still
> -> concentrate fairly well. Is there a program where you can make a shape on
> -> computer, and then shine a line of light on it and see where it bounces to?
> -> No more than 5 bounces are necessary. And it would be nice to be able to
> -> move the first "ray" to simulate the sun moving.
> -> My compound parabolic concentrator is to be good for 3 hours of solar
> -> cooking at the bottom of the upturned bell. (It will be about 6 ft high and
> -> collect about 1m2 of light and concentrate it to about a ft square area. I
> -> think 34 cm by 34 cm to be more exact.
> -> Thanks in advance.
> -> Brian White
> It's difficult to use a flexible material such as mylar to form a
> parabolic reflector. It always ends up with wrinkles that scatter light
> in wrong directions.
> You may do better to go to a builders' supply store and look for small
> glass mirrors. They're sometimes used to cover walls, like tiles.
> Sometimes a lot of them are sold glued to a flexible mesh, so the whole
> panel can be put on a wall in one quick operation. Usually, the
> individual mirrors are about 5 cm (2") square. You can glue them to the
> interior of your "bell". There will be spaces, but you should be able
> to cover most of it. The mirrors should be much better reflectors than
> wrinkled mylar.
> dow
google "Ray Tracing". There are some free programs available and some
that cost a lot. The one i am most familiar with "OptiCad" is costly
but easily does CPC type optics and allows you to introduce things
like poor shapes.
Posted by renewable_sources on August 18, 2008, 9:54 am
To bond your tube to the flat plate try a mix of Epoxy resin with
powdered aluminum and carbon for color ( or grind up some graphite or
aquarium filter charcoal) use enough to make a filet on both sides of
the tube. Gel type epoxy resin is best to prevent run off. It should
be a thick paste in consistency. Heat transfer is provided by the
powdered aluminum.
Bob
wrote:
>I want to to make a compound parbolic concentrator. (ideally like a big bell
>upside down). But mylar does not go to bell shapes easily. I was going
>instead to make 4 mylar troughs joined together to make a reasonably close
>bell shape. I want to test it before making to see that it will still
>concentrate fairly well. Is there a program where you can make a shape on
>computer, and then shine a line of light on it and see where it bounces to?
>No more than 5 bounces are necessary. And it would be nice to be able to
>move the first "ray" to simulate the sun moving.
>My compound parabolic concentrator is to be good for 3 hours of solar
>cooking at the bottom of the upturned bell. (It will be about 6 ft high and
>collect about 1m2 of light and concentrate it to about a ft square area. I
>think 34 cm by 34 cm to be more exact.
>Thanks in advance.
>Brian White
Posted by Solar Mike on August 21, 2008, 5:00 am
> To bond your tube to the flat plate try a mix of Epoxy resin with
> powdered aluminum and carbon for color ( or grind up some graphite or
> aquarium filter charcoal) use enough to make a filet on both sides of
> the tube. Gel type epoxy resin is best to prevent run off. It should
> be a thick paste in consistency. Heat transfer is provided by the
> powdered aluminum.
I have already tried this and after a while the bond always breaks, caused
by the different expansion rates of the two metals. The break then becomes a
thermal barrier. Best to use a filler that never sets or sets to a flexible
joint.
Silicon grout is a suitable choice as it contains a ceramic filler that
helps conduct the heat, or use a thermal heatsink compound, or high a temp
grease.
Cheers
Mike (NZ)
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> big bell upside down). But mylar does not go to bell shapes easily. I
> was going instead to make 4 mylar troughs joined together to make a
> reasonably close bell shape. I want to test it before making to see
> that it will still concentrate fairly well. Is there a program where
> you can make a shape on computer, and then shine a line of light on
> it and see where it bounces to? No more than 5 bounces are necessary.
> And it would be nice to be able to move the first "ray" to simulate
> the sun moving. My compound parabolic concentrator is to be good for
> 3 hours of solar cooking at the bottom of the upturned bell. (It will
> be about 6 ft high and collect about 1m2 of light and concentrate it
> to about a ft square area. I think 34 cm by 34 cm to be more exact.