BOOH III

[Nutcase]

Okay, so I bought a roll of 1/2" Superwool HT. This stuff is 6 pcf density, supposed to be not biologically persistent, so it's less of a health hazard if you inhale the fibers. The HT version is rated to survive 2300˚F. $100 for a 100 sq. ft. roll, picked up at High-Temp Inc.
I made this build by rolling three strips of the 2' wide material twice around an 8" diameter circular core, again concrete reinforcing mesh to hold the chimney together. The burn channel is just sort of propped up in a more or less square configuration. This is just more quick and dirty to get a feel for things with a minimum of time invested in the build.



Here's another shot of the burn chamber, a little easier to see what's going on. It was supposed to be 6"x6", but it got kinda scrunched, particularly where it entered the chimney, closer to 5"x5". I put a piece of the fiberock in as a point of contact for the sticks.



Got to do different things, will get back to this tomorrow.

[Nutcase]

It was pretty easy to get this thing to draw, but it was smoky during most of the run. The top of the barrel peaked at only 430˚F. The stainless steel sheet I was using to support the left side of the burn channel got up to at least 300˚F. My overall impression was that the system isn't sufficiently insulated. Some back of the envelope calculations had led me to expect that 1" of this insulation would be marginal at best. Radiative heat loss through the fuel port and air leakage, particularly around the burn chamber/chimney connection were secondary factors. The fuzzy inner surface may interfere with complete mixing in the burn zone. Looking at the pictures, 5"x5" may be an overestimation of the actual burn chamber cross section.

[Nutcase]

After it burned down, I took it apart to see how the material had held up. The Superwool chimney was somewhat sooty where the barrel covered, but otherwise much the same. The burn chamber showed no visible damage. However, the material feels like it became somewhat more stiff, though it can still be unfolded and reshaped. This stuff won't hold up to a lot of handling, but it is sturdy enough for what I am trying to do here.



The bits of orange fluff are from some Roxul rockwool I was using at the end to throttle the inlet.

[pa_friendly_guy]

Interesting experiments Nutcase. After you have tried several different shapes and designs do you plan of building a permanent unit to use at your place using what you have learned as a guide ?

[Nutcase]

Now it gets ugly. But more functional.

There are several ways of course to increase the insulation around the burn chamber and/or the chimney. The simplest would be to just use more layers of the Superwool, but I'm reluctant to use more of it without testing cheaper and comparably simple alternatives first. So I rebuilt it with an outer layer of the Roxul, using pieces I had already cut, supported with a wire mesh frame I had already made. Here it is without the barrel.



The frame is 14", the Roxul 2x3 1/2", the Superwool 4x1/2", so the width of the burn chamber is 5", and about 7" tall. I used some of the hexagonal chimney to cover the top.
It's not pretty. However, I am confident that insulation of the burn chamber is not the weak link in this system.

Yes, pa_guy, I will eventually replace our conventional wood stove, and probably put another rocket in the sunroom at the other end of the house.

Anyway, chickens! Chickens are curious about what people are doing.

[Nutcase]

The burn with this system (barrel on) started to draw almost immediately with no encouragement. The barrel top eventually got up to 630˚F. It was still intermittently smoky, though less so than the earlier version.

Later today I will take this system apart and see what there is to see about how the Roxul held up. If it didn't reach its melting temp, then it may yet turn out to be useful in a final system. However, I suspect that a larger, higher power system will run too hot for it with only an inch of the Superwool. I've got an old water heater core on hand, and so I can always make a chimney at least with a Superwool inner layer and some loose perlite.

[matt walker]

Sweet. It looks like you have quite a long burn tunnel on this one. I'm guessing that may be affecting your top temps. Did it burn clear, no smoke, after it got going?

Round two looks like it is going to be a hot burn for sure.

[Nutcase]

By the way, Matt, am I overdoing it with the pictures? Flickr is hosting them, so I don't think I'm eating a lot of your bandwidth directly, but I dunno.

[Nutcase]

The burn channel is 2' up to the entry to the chimney, so it is the same as BOOH I but longer than BOOH II. The smoke was intermittent, increasing whenever more wood went into burn, even when it was at max temp. It probably wouldn't take much to get it to stop smoking from here. Might be enough to just insulate the chimney, or smooth the channel with refractory cement, or increase the system size by another inch, or reduce the radiative heat loss from the fuel inlet. I'm sure I'll get there one way or another.

Well, it's supposed to start raining in the next few hours, so I need to deconstruct sooner rather than later.

[matt walker]

No problem with the pictures. The more the better as far as I'm concerned.

I am loving following your experiments. Thanks a ton for sharing here.