Solar Parabolic Trough Charcoal Oven

[Turtle]

Then what?

Mix finished product in the soil? or Make enough for super-rich Potted Plants soil?

the 'coon

 

Caution! I do not think this size oven is sufficient to make charcoal. It sounds like charcoal briquets crushed up will work. Don't use the self-lighting kind.

:)

[gost]

Argggh- I missed the jump to this new thread when it first started. I'm so stupid sometimes...

 

Hey Turtle, thanks for all your hard work and posting on this. I bet you could cook some serious hot dogs with that thing. I think I will take your advice and try to use aluminum foil as a reflecting surface. Believe it or not, I've actually had some experience using AOL discs as reflectors and found that they become more or less transparent after only a few months of outdoor exposure. My guess is that all the mylar based materials will do the same. While the aluminum may not be quite as reflective, it should certainly last longer. Besides, you don't really need a mirror finish, just need to focus onto a four inch width. I'm going to try to build an 8 foot trough, perhaps wide enough for two stovepipe lengths, over the next few weeks. Will let everyone know what happens and try to post some pics. Hope maybe the group here can come up with a design that really cooks ash! ... Er, charcoal, I mean.

[Turtle]

Argggh- I missed the jump to this new thread when it first started. I'm so stupid sometimes...

 

I'm going to try to build an 8 foot trough, perhaps wide enough for two stovepipe lengths, over the next few weeks. Will let everyone know what happens and try to post some pics. Hope maybe the group here can come up with a design that really cooks ash! ... Er, charcoal, I mean.

 

Excellent gost! Looking forward to your progress.

I emptied the tube & found the material very dry but no evidence of any charcoaling or browning. It may help retain some heat if I enclose the ends with reflective material as well, which is tantamount to using the 'positive' cutout as we discussed earlier in the thread.

 

:thumbs_up :lol: ;) :cup: :cup: :cup: :cup:

[gost]

LOL. Guess you found a novel way to dry firewood.

 

I think the "positive" cutout for the ends makes sense as long as the wrap around material is rigid enough to give it strength. I was thinking about using eighth inch masonite, with half inch plywood ends, then gluing on the foil with spray adhesive. The parabola is cut from two by eight foot plywood using X^2 = 4(24)y. If the masonite is 46 inches wide, a 4 foot stovepipe can be supported at the ends using three metal pins (screws) to keep it from touching the plywood. The biggest problem with the positive ends is that they will cast a shadow if you don't keep the thing aligned to the sun.

[cwes99_03]

Hey I want some physics here (pounds fist like a little child.) Do you have some data or a graph yet of your temperatures plotted throughout the day? Are you even interested in that, or just building and testing it without examinging the data? Just wanted to know, because I myself won't build one, but might be able to make suggestions based off of design and data.

[Turtle]

The biggest problem with the positive ends is that they will cast a shadow if you don't keep the thing aligned to the sun.

 

:shade: Good point. Without an automatic tracking system the open ends make more sense.

Hey I want some physics here (pounds fist like a little child.) Do you have some data or a graph yet of your temperatures plotted throughout the day? Are you even interested in that, or just building and testing it without examinging the data.

I made no graph of temps, & gost isn't that far along yet. While I checked the temp periodically, doing so meant taking an end off the pipe & so letting the built up heat escape. At optimum conditions (no clouds, full Sun, squarely oriented) my oven raised the temp in the tube to 190°F. In looking at a lot of web articles for both commercial & home project ovens I saw no temperature data of any kind. Perhaps if we write one of the commercial plant's engineers & ask?

:doh:

[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]

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 :eek2: ) 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! :eek2: 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]

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.

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?

[Turtle]

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

 

Or possibly a brayer.:)

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?

The thought did occur to me to insulate the top portion of the receiver tube that lay above the plane of the trough. Any thoughts on what material? Fiberglass wool? Asbestos?:eek: Cogitating.:cup: