[Divegod]

Oh, and as for shaping the steel, I wasnt envisioning anything other than cutting to size. Same width as the chamber and the trough. Flatten the bottom of the chamber/vessel by hammering down the outer edge that generally is molded into the shape. As long as one has about 50% contact, I think that would be sufficient transfer, but Im just guesstimating.
Anyone know where to get some high temp thermocouples? Id like to run a basic experiment, see what sort of temps would be generated thru the conductance option.
DG

[Michaelangelica]

Are these old designs of interest?
Solar Concentrators & Furnaces: US & Foreign Patents, & Articles

[DougF]

Thanks Michaelangelica,
I found them very interesting,
most of the new stuff is based on this technology and they will tell you about the improvements assuming you already know how they got there.

This fills in some of the blanks for me, Thanks.

[Nitack]

Originally Posted by Divegod

Yes, the metal plate would likely be a bit expensive. The copper coil idea makes sense, but I wonder if it can sustain the temps being discussed/used. If it can, why not just route hot copper tubing into the chamber itself. That way you can heat the mass, but not have to worry about the containment/pyrolysis vessel being able to withstand the heat? Frankly, those are some of my top concerns when working with a concentrated beam of heat like is produced by a Fresnel. You can diffuse the beam a BIT, but you rapidly lose sufficient heat in that manner, and you have to have pretty precise adjustments. I think using some sort of impervious material to conduct the heat to the vessel is going to be part of the solution....Im going to price out some plate steel. Maybe its not as expensive as Im afraid it is.
Another thought: using a concrete block lined pit and heating, thru an opening, to a thermal mass (Again, plate steel?) that lies within the pit. Alternatively, heating a tubing and running that thru the pit. Hmmm, now Im going to have to try some variations.....Gotta get a Fresnel.....Ack! Another experiment!
DG

OK, so this got me thinking really hard

Introducing the copper piping into the material might be a possibility. That would take some of the heat transfer issues out of play. Also, dropping your vessel into earth would help insulate it too. Here is my thought...

Method
Creating a reservoir as your base. In here you would fit either water (safe choice) or oil (no so safe choice but better heat transfer). This reservoir should be large enough for your vessel (dutch oven or eventually trash can) to sit on top. Copper piping could be pumped directly from the reservoir into the vessel. The piping would coil through the vessel and distribute heat at multiple points. The piping would exit the vessel at the top, and connect back to your reservoir at the base. This way if you keep the heat focussed on the reservoir heat will transfer up the piping.

Benefits

• Using a closed loop system will help you to retain heat.
• Having the coils in direct contact with the biomass will allow for more heat to hit the medium.

Possible issues

• If you use water (the safer option), it is possible that the steam produced will never get up to the superheated thresh hold you need.
• If your steam does get up to the thresh hold you need, the huge increase in pressure will very likely blow a hole in your closed loop at a weak point and you start losing heat and water.
• If you use oil, you are creating a very serious fire/safety concern. Superheated oil burns very quickly when exposed to oxygen and an ignition source... like a concentrated sun beam. This option might land you on the radar of local cops and fire departments...
• Copper tubing is extremely expensive.

[Divegod]

Very good summary of my concerns about using using tubing and a liquid conductor. Its just primed for failure when doing that sort of thing on an amateur level. Compressed water vapor can seriously injure, and oil is even more dangerous. Solid state system would be the way to go for a backyard unit. Fewer moving parts is usually best for backyard type units. Murphys law and all that.....
You also touch on my concern about a vessel that holds the items to be carbonized vs. a 'dutch oven' type of arrangement. When concentrating solar, you get a very hot point source. Diffused heat would be much easier to work with and much less likely to rupture the carbonization chamber, which is my primary concern (release of hot gases and contamination with oxygen being the main drawbacks of such a failure). Thus, Im left with a system that relies on the conduction properties of a more robust primary recipient of concentrated solar radiation in close contact with a carbonization chamber. The primary material can withstand the concentrated beam, while diffusing this heat through its mass and conducting this heat to the carbonization chamber. Getting involved with tubing and a liquid conductor is a job for well funded professionals. Static conduction (!?) of the heat is preferrable from a safety, simplicity and probably materials cost standpoint.
DG

[Nitack]

DG, love your insights... Just as an FYI though, about a year ago some of us did some very involved testing trying to use similar systems to what you propose. The results were not promising. Too much heat was lost to simple air flows. partially burying the vessel might work, but I am not sure you will actually be able to get it hot enough. even a slight breeze will sap out heat. That was when we started postulating that copper piping might be the answer. I still think that it might be the best option, if not inside the vessel, surrounding the outside.

[Nitack]

My friends I think i may have our answer if we wanted to use Divegods methodology. Steel plates are not the answer... however what about the Miracle Thaw? Read this, Skeptic Friends Network - Miracle Thaw - The Bogus Miracle. It is not great for it's designed use, but for our purposes it is perfect. Made from metal that easily conducts ambient heat... so we raise the temperature on one part of the plate and the rest of the plate will swiftly get that hot... solar powered cook top!

[freeztar]

I'm not sure about that Nitack. Apparently it is just teflon coated aluminum.

There are pans with heat diffusers built into the bottom of them, but you'd still lose a lot of heat from the sides and you would almost have to use the buried pot/mirror idea that we discussed last year.

[Nitack]

Originally Posted by freeztar

I'm not sure about that Nitack. Apparently it is just teflon coated aluminum.

There are pans with heat diffusers built into the bottom of them, but you'd still lose a lot of heat from the sides and you would almost have to use the buried pot/mirror idea that we discussed last year.

Aluminum is a great heat transferring material, hence we use it for pots and pans. So although we don't need the thawing plate, for $10 at a cooking store, we won't worry about ruining it. Although you can just use an old pan... big thing as always is heat loss... so perhaps burying most of it and let the earth insulate?

[Nitack]

So I have been giving this more thought lately. I do think that aluminum will be the way to go. The way that it conducts ambient heat will achieve the same heat disbursing effect that we were looking for with the coil and oil setups. Our main concern will still be heat loss though. Even a slight breeze is going to kill us, so I have a few thoughts.

Goal:
To get the heat inside a sealed or semi-sealed container to reach 400+ degrees F. The idea of this, at least when we start, is to bring a rather small container to the heat we want

Method:
Our active methods have all centered around heat concentrating setups. My preference is the use of a Fresnel lens because I find the "Solar Death Ray" angle appealing. My design (to be tested in a month or so when I am out of my apartment and back in a house) is to use my fresnel lens focused on an aluminum plate/sheet that our vessel will sit on top of. For a vessel I had been using a cast iron dutch oven. I am going to switch from that to this:
Gibraltar Industries Standard Size Black Premium Aluminum Rural Mailbox - ALM110B0 at The Home Depot. It is an aluminum mail box. direct contact with the aluminum plate should allow it to heat quite nicely. Finally, the issue of wind has come up to us many times. I think what might be a cheap and easy fix (previously suggested by Freeztar, is to build surrounding walls using cinder blocks. And, to complete the insulation and even create a greenhouse effect... a sheet of glass to go over the top. That way the heat should all be trapped inside there, getting us high enough to create charcoal.