Parabolic Trough Mirrors?

[Dan M]

I found a listing on ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=20580&item=4329552680&rd=1

Anyone have any experience with these?

I'm trying to quantify how flexible they are.  It seems they would be perfect for a parabolic trough reflector if the minimum bend radius is small enough?

-Dan M

[Norm]

 Do a Google search for Solar hot dog cookers (parobolic reflectors...Mylar lined plastic might work just as well and cheaper. http://www.eia.doe.gov/kids/classactivities/SolarCookingIntermediateActivity.pdf

http://genesismission.jpl.nasa.gov/educate/scimodule/CollProcess/CollProcess_pdf/HotDogCookerSA.pdf

                     ( :>) Norm

[ghurd]

Hi Dan,

I've used the same or similar stuff. Seems like regular plexiglass.

$5-6, X-mart mirrors, 16"X48", have about the same stuff.

I bent it to a sharp 90' and longer radius with heat.  Heat it very slow or suddenly bubbles appear. A 'heat gun' was easier than a propane torch. Worked fine after the first couple trys. When heating, it suddenly turns very soft.

(I heated some smaller pieces over the toaster, but don't remember how that went)

Drilling 1/2" holes caused cracks 80% of the time, 3/16" holes cracked 50%, because of the grabbing like sheet metal. Plywood on both sides when drilling may have stopped it.

G-

[Dan M]

Are these the cheap mirrors that you might hang on the back of a door?

If so I didn't realize they were that flexible.

Thanks,

Also, for anyone out there, is there a means of quantifying the amount of light reflected, distortion, efficiency, etc of a mirror? (reflection coefficient?).

-Dan M

[ghurd]

Yes- The cheap one for the back of the door. Take one out of the box, hold it at the middle (2'), hold it flat. Wow. Look at that bend!

In the box, push with one finger in the center...

The one on my daughter's door is like a fun house mirror. Gets worse with age.

I think it is held 'almost' straight only by the frame.

Seems like we got it for $3 during a "White" sale 5 years ago from one of the X-mart stores.

G-

[veewee77]

that stuff will bend ok for a parabolic reflector if you use it the 4 foot way, not the 2" way.

You can make a wider curve with ti longways than you can shortways.

Ds

[tecker]

 Hot dogs I like it .They have those cigar lighters too . I made a good reflector this week end out of a Wok lid I got from goodwill and I glue on the mylar from chips bags .

just to make some tests on asmall unit.  

[nothing to lose]

"I've used the same or similar stuff. Seems like regular plexiglass.

$5-6, X-mart mirrors, 16"X48", have about the same stuff."

Beware not all those cheapo mirrors are plexy. My daughter had one in her room leaning against something not yet hung up, she triped and fell into it. She only got a little scratch but the mirror was in slivers on the bottom half. It didn't shatter or break to pieces like a thicker glass window would have, but it certainly did not break like plexy either. It was glass and I figure so thin the frame and cardboard stopped the most of the shattering and only where the impact was really broke bad the rest kinda bent and cracked alot near the bottom, and the top did not bend as much and was fine.

Course I tossed the entire mirror out, I should have saved the top half I guess.

[jacquesm]

Hi I have made some dirt cheap trough mirrors like this:

Trace your parabola on a piece of plywood, twice

Cut the line with a jigsaw

Insert a piece of reflective mylar in the groove

Stand on end: Voila, dirt cheap parabolic trough mirror...

You'll have to connect the two pieces of plywood using 2x4's or some angle or so.

If you want I can dig up a picture of the thing, I used it to heat an oil filled copper tube.

regards,

  Jacques.

[tecker]

 If your just needing a start for test plexi is a really good start .It starts to turn

hazy soon .I think the best reflecting surface I have found is small sections of mirror glued down on a concentrating surface. Easily cleaned or replaced I you use silicon .I use urethane roof sealant I have a glass cutter and work 1" sections and it fills in

like a tile surface put on the urethane with a small serrated thrall an set in the mirror sections. With the silver surface you  get a really large spectrum of light.  

[steveO]

Home Depot carries extender tubes for the Solar Tube skylight packages. These extender tubes are 12" in diameter and can be opened up to form a half circle or trough. The bonus of this material is that it's a perfect mirror and extremely reflective. The draw back is for a 24" x 12" diameter is about $37 per unit. I haven't used this stuff yet, but it seems like it would work really well for a trough heater. Any ideas?