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Post by peterberg on Mar 29, 2012 2:09:26 GMT -8
One thing though, in a pipe you get a lot of laminar flow which reduces heat transfer. The dynamics in a bell are different.Wouldn't there be better transference to a bell? Do we need to take this into account? Unless the bell is made of steel, the transference per square foot of active surface area would be about the same. Laminar flow in the pipe versus the slower take up of heat by the masonry mass of the bell. The only 8" system that I do know about with a bell-like bench to compare against the theory is the one in Boxtel, Netherlands. This has been built in a curved shape, average length is 11.5 ft. Despite seemingly having a shortcut via the inner curve, the whole bench warmed up, even the outside of the curve. This bench has been built as a bell, in the sense that the intake and outlet were quite close to the floor. So there would be no need to have those openings on opposite ends exactly.
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Post by Deleted on Mar 29, 2012 3:43:28 GMT -8
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Post by Donkey on Mar 29, 2012 6:39:12 GMT -8
Too much drag in the flex piping.. I wouldn't use it.
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Post by canyon on Mar 29, 2012 22:47:38 GMT -8
Despite seemingly having a shortcut via the inner curve, the whole bench warmed up, even the outside of the curve. This bench has been built as a bell, in the sense that the intake and outlet were quite close to the floor. So there would be no need to have those openings on opposite ends exactly. So are you thinking that one could have a bell bench with the input say halfway on the length and the outlet at one end and still have somewhat even heating of the whole bench? This is intriguing and if correct leads me to lots of exciting possiblities!
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Post by peterberg on Mar 30, 2012 1:10:54 GMT -8
So are you thinking that one could have a bell bench with the input say halfway on the length and the outlet at one end and still have somewhat even heating of the whole bench? This is intriguing and if correct leads me to lots of exciting possiblities! Canyon, you make it sound like a cure for all diseases but believe me, it isn't. There's no such thing as a free lunch. ;D In fact there's a sliding scale between working excellent and not at all. The whole bell phenomenon is based on gravity, so it'll work best in vertical direction. In a box that's higher than wide and deep it's OK to have a dead end, it will get the same temperature as everywhere else. A bell of these proportions is a dead end in itself and it will do an excellent job in separating the cooler gases from the hotter ones. When there's no level difference between the inlet and outlet, those can't be right beside each other. Unless... there's a height difference between those two, the inlet just, and only just, higher up compared to the outlet. For example, a 50 gallon barrel with the inlet in the bottom and the outlet in the side close to the bottom. The inlet do need a short piece of pipe that end just above the upper rim of the outlet, this will work fine. In a bench, there won't be much vertical difference between floor and ceiling and less opportunities to create a difference between in and outlet. In order to reach the dead end on one side as you described, the only possibility is to have the outlet in the bottom of the bench. In this way, it will work but it'll create more friction in the smoke path. In case the bench could be built at a height of 2ft. inside you won't have this problem. Having the in and outlet sufficiently separated and right at floor level would be fine. It greatly depends on the space above the in and outlet whether it will do a nice job or not. Conclusion: when carefully designed, a bench containing a dead end in horizontal direction will work. However, the tolerances are small.
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Post by canyon on Mar 30, 2012 10:51:05 GMT -8
Thanks so much for sharing that information Peterberg(and all that you the information that you share for that matter!)! This is opening my eyes to more exciting possibilities but not to worry, I am aware of energy exchange being a trade, no free lunch expectations here but excitement of different ways of putting these together for different needs.
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Post by matthewwalker on Apr 17, 2012 9:20:31 GMT -8
Well, I built a whole bench as a bell this weekend, and it works great. Yesterday my neighbor opened up his bench and got rid of some flue to make a cold section into a bell as well. So far, huge success. Thanks for the inspiration Donkey. My "Boiler/BBQ...." thread in "Experiments, results" has some details of the system.
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Post by rgbarnes on Sept 1, 2012 12:26:00 GMT -8
How are you sealing your "clean out" at the end of the bell? You call this a six inch stove. What portion of the stove is six inches? I am assuming that you refer to the combustion stack interior.
I am studying how to make a similar sized unit using an old crucible. The crucible is a 18 inches tall and 12 inch top opening. The crucible should never deteriorate as will a metal barrel. I have two crucible to experiment with and plan to use your bell bench made with adobe. Any suggestion?
Ron
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Post by Donkey on Sept 1, 2012 16:06:44 GMT -8
The cleanout has a thin earthen plaster seal. Just clay rich soil, chopped straw and water.
All of the internal working parts have a cross sectional area the size of a six inch stove-pipe.
The bench in this thread is NOT a bell design. If you plan to build an adobe bell in the bench, I would say you need a way to hold the adobes on the top (the seat of the bench) without allowing them to crack under weight. I doubt that the adobes themselves will be strong enough to sit directly on without a steel plate or something underneath.. Unless you build up the adobes quite thickly on top, which will either make your bell quite low, or the seat quite high.
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Post by koldenburg on Sept 17, 2012 13:15:26 GMT -8
To me the picture looks like the system has the exhaust exiting after the loop through the bench. Can you please tell me how you define the exit if it's not where the stove is essentially done with the loop or bell? Peter says it should exit a bit lower so would that mean it should have gone out the cob at a level slightly lower than the burn chamber?
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Post by Donkey on Sept 18, 2012 7:11:48 GMT -8
I think you may be confusing a couple things... In bells, the exit (of each bell) needs to be lower than the entrance. The stove in this thread isn't a bell. There is a space within it that acts a bit like a bell, but that was entirely accidental. This stove here is all piping.. It doesn't much matter where the exit goes, it's pumping exhaust straight through from end to end.
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Post by woodburner on Oct 11, 2012 21:36:12 GMT -8
I've been making cob from my soils for over 12 years and know them well. In other places, I would have to do a lot of testing to acquire the same confidence. I know how to go about that. Do you have any links that give a guide to cob testing?
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Post by Donkey on Oct 13, 2012 7:00:25 GMT -8
I thing I did a riff on it in the materials area. Just try different proportions with several test blocks.. Test WELL above and below what you think is "right". You'll know the best mixes.
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