Solar Parabolic Trough Charcoal Oven

[cwes99_03]

I'm all for that. Go to radio shack and get a thermal resistor then connect it inside your tube. Just be gentle about stuffing it. Wait a minute didn't someone already suggest this? Anyway, now all you need to do is hook your laptop up to it on a sunny day and let it record away, say every 5 minutes.

[redgreenblue]

Hey Turtle,

This is a really interesting project...
In order to get things hot enough, how about using a sheet of glass to create a sort of greenhouse effect? The solar ovens that others have posted about use this technique to sometimes get up to 300-400F. You'd probably have to let the charcoal tube vent to the outside though to prevent the tars/gasses from the charcoal from condensing on the glass....

let me know what you think... it may save you from building a ginormous reflector.

redgreenblue

[Kayra]

Originally Posted by redgreenblue

Hey Turtle,

This is a really interesting project...
In order to get things hot enough, how about using a sheet of glass to create a sort of greenhouse effect? The solar ovens that others have posted about use this technique to sometimes get up to 300-400F. You'd probably have to let the charcoal tube vent to the outside though to prevent the tars/gasses from the charcoal from condensing on the glass....

let me know what you think... it may save you from building a ginormous reflector.

redgreenblue

Double pane it. Then the inside one can be black as it likes.. only absorbs more heat.

[InfiniteNow]

Wouldn't using double-paned glass increase it's R value and thus limit it's heating potential? Isn't that the whole point of double-paned glass, more visibility/less heat transfer?

[Kayra]

I thnk that was the prupose of coating the glass.
Double pane (at least in Canada ) is used to prevent heat from being conducted out. it used the transparent air trapped between the panes to do this.

[InfiniteNow]

Cool indeed. I really was asking. Thanks Kayra! I think it's filled with a compressed gas of some sort...

[GAHD]

Double or triple Pane glass prevents hot air (molecules) from escaping, but allows radiant heat(photons) to pass through. It ususally has an inert gas at a low pressure trapped inside, not standard 'air'. This could help the oven if the oven was completely boxed in air tight.

[Turtle]

Originally Posted by GAHD

Double or triple Pane glass prevents hot air (molecules) from escaping, but allows radiant heat(photons) to pass through. It ususally has an inert gas at a low pressure trapped inside, not standard 'air'. This could help the oven if the oven was completely boxed in air tight.

I agree. The expense at that point is likely as high as having a glass blower make you a Dewar tube as I mentioned earlier.

Originally Posted by Turtle

A feature of the large solar troughs is the inclusion of Dewar tubes around the receivers to retard heat loss to the atmosphere. I am not getting a Dewar tube. [sic]
http://en.wikipedia.org/wiki/Dewar_tube
http://en.wikipedia.org/wiki/Dewar_flask

I wrote la communique de la electronique to a commercial producer of solar troughs enquiring as to design dimensions etc. & refering them to this thread.

[gost]

The problem with trapping heat inside of the trough is that it would then require the entire contraption to be made from non-combustible materials. The temperature we're trying to reach is around 470F. Part of the idea here, at least to me, is to create a design that's cheap and easy for a home gardener, or a third world farmer, to reproduce. It needs to be made from materials that are readily available and preferably cost under $100US, if possible.

It occurs to me that a layer of some kind of insulation could be put on the top of the pipe to help retain the internal heat. This would reduce the total solar gain, of course, but the overall conservation of heat might be worth it. Any chance you could test this idea on your trough Turtle?

Update on my own trough: I have the design worked out and the parabola plotted. I hope to buy materials this weekend and start building. The design uses one sheet of half inch ply, a half sheet of eighth inch masonite, two lengths of four inch stovepipe, two two by twos for legs, and a roll of aluminum foil, plus assorted glue, paint, nails, and screws. I've played around with a piece of the foil out in the sun and found that it does disperse the reflected light quite a bit, since it's not a mirrored finish, but I'm still optimistic that it can focus well enough onto the four inch pipe using the two foot focal length of the design. We'll see. LOL, In part it will depend on how wrinkle-free I can manage to keep the foil when I glue it on. Hmm...I wonder if beer would help or hinder this process.

[GAHD]

This is where a squeegee could come in handy, eh gost?