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Post by Donkey on Jan 11, 2007 10:28:57 GMT -8
An experiment in forming Rocket Stove heat risers with plastic 5 gallon buckets: I found a spare 5 gal. bucket and a piece of six inch stove pipe. Mixed sawdust with clay (natural earth clay) slip, making a firm but sticky batch. Placed the stovepipe inside the bucket, "eyeballed" to center. Packed in the sawdust/clay mixture. After the bucket was filled with a firmly tamped (not rammed) straw/clay mixture I slid out the stovepipe and let the bucket sit in the sun for things to gel a bit. I made two, using the same bucket and finished drying them on the rocket stove in my house.. The second one came out of the bucket a bit too wet and slumped somewhat in the process. The insides were smashed a bit but still close to the same volume I then Built a stove bottom with firebricks on my test bed.. The dried heat riser parts were then stacked onto this stove bottom. The whole mess was plastered over with straw/clay to seal everything well. I was careful to line the internals up as well as I could. Then I took a cob saw and smoothed the insides of the pipe and corrected for the squished nature of the top piece. Looks a bit like The Cat in The Hat's hat.. Luckily, the thing fits the barrel in the background there just about perfectly. It burns well. My test bed is pretty wet from recent rains but it started and ran quickly. After some time to dry things out it was impressive hot. It looks a bit ungainly.. The riser pieces are tapered on the outside and create a funny volume inside the barrel. I don't know if this will effect performance, worth looking into. I could have let the second piece dry more before taking it out of the bucket. Holes in the bucket bottom would allow for faster drying time, though it would ruin an otherwise useful bucket. I really don't know how long the sawdust/clay will last. So far it appears that the clay is firing a bit and the sawdust is turning to char.. What I like about it is that it's easy. The parts for the form are just laying about. With a row of buckets, one could make several heat risers a day. And now, the fire!
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Post by Donkey on Jan 23, 2007 19:10:13 GMT -8
Huh.. Interesting.. Yesterday, I burned a fire in the test stove above. I drilled A hole in the back of the heat riser twards the bottom and inserted a pyrometer given to me by a friend. After a short warm-up period temperatures hovered around 1300 deg. F.. Today, again stsrted a fire in the stove and temps were much lower. Around 1000 - 1100 deg. F. No amount of fussing with the wood or changing to drier fuel helped. After a few minuets to cool down, I broke the heat riser open and inspected the materials. Sawdust on the insides was carbonised and the works had become quite brittle.. Downright crumbly. I'm guessing that somehow the materials from the heat riser are becoming progressively less insulative, stealing heat from the stove. Just A guess. It seemed to act like my home stove did when the wood ash that was my original insulation compacted and stopped working. I'll post pictures of the broken parts of the heat riser perhaps tomorrow. It shows definate banding of carbonization inside, like tree trings.
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Post by Donkey on Jun 7, 2007 16:26:47 GMT -8
Here's that pic that I promised..
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Post by Rhyddian Knight on Aug 28, 2007 13:11:14 GMT -8
Hmmm... how about encasing the whole lot in a layer of fire cement?
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Post by Donkey on Aug 30, 2007 17:19:21 GMT -8
Well, the point was to avoid using products like castable refractories and such.. It was an attempt to form the working high-temp guts out of free or found, low tech materials. I still have hope in similar methods.. Will be experimenting later.
I have used high temp castables and they perform quite well, though tend to be a bit brittle.
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ernie
New Member
Posts: 32
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Post by ernie on Dec 20, 2007 11:16:59 GMT -8
Donkey how about useing vermiculite and clay or mix sand in with the sawdust Cob. the saw dust should burn out and the sand ought to add stability to the whole structure. I might also add that if you refined the clay a little (thin slip and settle out method "dish soap is your friend") you might get a finer clay better able to handle the heat and stronger.
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Post by Donkey on Dec 20, 2007 12:24:18 GMT -8
Yes man.. Ive considered the sand. Not tried it yet as my brain has temporarily wandered in other directions.. Also, my body a slave to that old reality called income and feeding a family of four. I find I have less time than I would wish to fiddle lately.
The exercise was to avoid mined or refined products - not including (of course) what can be done simply at home. So, pearlite would be out (for this experiment).
Its my feeling that I didnt really give this one its due. Perhaps rising atmospheric humidity could have been part of the problem. I did not consider it at the time, but winter is my safe playtime, after decent rains. My test bed is out in the open... Perhaps the thing just soaked in its environment, and gathering moisture stole heat from the system, showing the result above (lowered temps).
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Post by joselb on Apr 24, 2008 19:27:59 GMT -8
Hi, Don, what about expanded argila as you suggested with clay?
An interesting thing in your last photo: it's more burned at left than at right. This can give a clue on what side the riser is hotter or have more pressure? ANd if you still have that riser, doing sections on it, you could see what are the proportional temperatures along the riser?
Jose
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Post by Donkey on Apr 26, 2008 20:50:56 GMT -8
Yep.. argila should do fine. Answered in the other thread.Funny you should mention it.. I methodically broke it apart, from the top down and inspected the bits. The hottest part was from just above the junction with brick (at the bottom) to about one-third up towards the middle. This is a pattern that I see a lot. Usually about a quarter to a third of the way from the bottom of the heat riser seems to get hottest. I am sure there are ways to move that hot spot up or down the pipe. "Turbulators", flame-holders and volume/shape changes come immediately to mind.
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Post by chronictom on Aug 22, 2008 22:25:02 GMT -8
Why did you use the sawdust in the first place? besides having it around I mean.
I have no clue if this makes any sense or not, but it seems to be, anything combustible, even if made non-combustible by mixing with clay will cause the same problems over and over with carbonization. I suggested this on another thread as well, and perhaps I'll get the same answer to both, but why not just go with a sand/clay (clay brick) mixture?
I don't know why this thread hasnt gotten a lot more attention... Take a plastic bucket and go build a stove?? That just pure genius in its simplicity if a stable natural mixture can be found for it.
Tom
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Post by chronictom on Aug 24, 2008 19:04:41 GMT -8
I did some reading into this...
What you did was make basically a light weight fire brick.
When you make a mixture like you did, and fire it at 1000 degrees, the sawdust burns out of it, leaving an insulating firebrick...
So I think unless you completely fire it, and then start doing your tests, will you know how it performs...
But it did lead me down another path...
If you did the same thing, but made the outer half of the riser from just clay/sand, and the inner half sawdust/clay/sand, once you got the mixture right, you would have both the insulation for the riser tube on the inside, and the thermal mass on the outside, which is what I gathered was wanted for a good riser?
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Post by Donkey on Aug 27, 2008 1:41:33 GMT -8
Uhh... Well, the riser should be insulated to the nines.. The mass comes after. In theory the heat riser should have as little thermal mass as possible throughout. So, yeah.. I was going for high insulation value, low embodied energy, low tech material, low tech (and low skill level) construction technique that anyone, practically anywhere can do. I know that pearlite treated in the same way works fine. It's quite brittle, but placed out of harms way, fine. I've thought that perhaps waterglass could be used as a sealing coat or possibly added to the mix as a binder. But again, Sodium Silicate and Pearlite are industrial materials which is NOT the aim of this exercise.
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Post by chronictom on Aug 28, 2008 15:58:16 GMT -8
I'm not a fan of industiral materials either, just from a cost standpoint, I would much rather a solution that was homemade.
So forget the idea of a double layered riser then and just the highest insulation value we can?
Besides the size of the surrounding chamber, does the thickness of the riser walls really matter? As in is there maximum, or could we just use more of a lower insulating material?
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Post by Donkey on Aug 29, 2008 17:40:25 GMT -8
As far as I know, there is no real maximum thickness for heat riser walls, other than the limits set by the necessities of each situation and the limits of practicality. For instance, building a rocket stove bench with a barrel, Cob Cottage style.. There we find limits set by the size of the barrel and the channel needed to flow heat down and into the bench.. ETC.
As to using more of a lower insulating material.. Lesser insulation values tend to point to corresponding raising of thermal mass. This is a situation we would like to avoid. More mass saps heat from the riser, reducing it's effectiveness. So, adding more would be shooting ones self in the foot, so to speak.
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Post by chronictom on Aug 30, 2008 8:54:42 GMT -8
Okay, got it...
Took me a bit to work through the logic... any mass on the outside of the riser (before the heat battery or radiator), would tend to slow the system down, and worse yet, make it a real pain to light when semi warm. Once the heat starts into the channel of a bench for example, as long as the run has a slight upwards direction, stored heat will add to the circulation.
On the matter of the radiator (barrel), 1/3 of it will be facing the wall, so would it be better to insulate the outside of the barrel there, or add some form of shield on the inside to block the back part from radiating as much heat? Or (crossed my mind as I was typing, would it be better to have a heat reflector on the wall behind it and leave the barrel as is?
Amazing how something that seems so simple at first glance grows to more and more complexity as you go... lol
Tom
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