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Post by patamos on May 3, 2015 8:57:45 GMT -8
Beautiful heater. Poopy plaster and all. Peter, it could be that the unequal heat distribution in the benches has to do with how a slight difference in direction of gas flow can set up a positive feedback loop. Benoit posted this link a while back in bell theory: heatkit.com/docs/advanced/Pages%20from%20TheFlowOfGasesInFurnaces.pdf
the explanation is better articulated there. It may or may not apply to your situation though. I'm curious also to know if fine particulate matter was measured from the chimney of your MHA heater. I wonder if the high PM levels that Matt received at the Woodburning Decathalon in Washington had more or less to do with the lack of mass in his test model. In other words - we assume that the fine particles from a high turbulent batch burn are ionized and stuck in the gas stream. But that theory might not be entirely correct. Thanks for all the great work folks.
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Post by peterberg on May 3, 2015 11:38:43 GMT -8
Does it exist in other countries? Not that I know of. There has been some events in the Netherlands but there isn't an annual meeting of professionals and amateurs in this field.
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Post by peterberg on May 3, 2015 11:47:41 GMT -8
I'm curious also to know if fine particulate matter was measured from the chimney of your MHA heater. I wonder if the high PM levels that Matt received at the Woodburning Decathalon in Washington had more or less to do with the lack of mass in his test model. In other words - we assume that the fine particles from a high turbulent batch burn are ionized and stuck in the gas stream. But that theory might not be entirely correct. No PM testing has been done on this heater during MHA meeting. The high PM levels at the Decathlon could have something to do with a too narrow bell construction, but this is just guessing. In the Netherlands there has been done a single PM test by a German chimney sweep which came out real good. But there are no similar tests done on a straight batch box so I really don't know what the results would be. Without comparable test results there is no way to know where we are now. As it is, PM testing equipment is beyond my financial options.
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Post by pyrophile on May 3, 2015 12:47:51 GMT -8
Peter, What do you mean as "mirror of ceramic glass"? Thanks Benoit
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Post by pyrophile on May 3, 2015 16:02:02 GMT -8
About the heater made at Wildacres, in what range was the temperature of exhaust gases? And can I suppose that the "main" bell's ISA was roughly about 6 sq meters and each bench's ISA about 2 sq meters?
Benoit
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Post by peterberg on May 4, 2015 1:19:47 GMT -8
Peter, What do you mean as "mirror of ceramic glass"? A piece of ceramic glas will act as a mirror in the dark. And is heat-resistant, very important.
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Post by peterberg on May 4, 2015 1:24:51 GMT -8
About the heater made at Wildacres, in what range was the temperature of exhaust gases? And can I suppose that the "main" bell's ISA was roughly about 6 sq meters and each bench's ISA about 2 sq meters? Exhaust gases, measured during one hour of running nearly full tilt, were 185 degrees Fahrenheit maximum. That would be... 85 degrees Celsius, just enough to drive the chimney stack of bare stovepipe. The ISA of all the parts together was 10.3 m2, just a bit too much for the circumstances. I don't know what exact size the benches were. But you could well be right about that, see the design drawing, which is open source.
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Post by pyrophile on May 4, 2015 1:59:54 GMT -8
Thank you, Peter! And did you make a ceramic glass mirror by painting ceramic glass with high temperature grey painting?!
Benoit
EDIT : Sorry, I didn't see your answer!
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Post by pyrophile on May 4, 2015 2:38:31 GMT -8
I am wondering the role of the benches, if they are important or not in lowering draft as the gases turn on themselves insides the benches to go back to the exit. It would be interesting to be able to close the benches temporarely to check the difference of temperature of exhaust gases.
I won't surprise a lot if I say that I doubt that the rather little rise in ISA had so much consequence in draft. Even if the exhaust temperature is not high(85C°), it is not that low and I suppose that the next morning the inside of the bell was still a bit warm, making the start easier. I can see a few reasons to have a difficult start the following day of a new built stove, above all, outsides. For example, a lot of humidity isides the pipe. But there are other possible reasons. It is never easy to make conclusions with a new stove and very few trials in conditions that are not all controlled.
And maybe, it is right that the rise in ISA was responsible of the problems!
PS : I sometimes disagree with people here (above all about ISA!) but I would not want that it could be taken in a bad way! I am always ready to change my mind!
Benoit
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Post by pyrophile on May 4, 2015 3:05:51 GMT -8
Maybe I should add that it is possible that, in my opinion, those 85°C don't say a lot for two reasons : - in a new wet stove, there is a huge heat exchange (transfer) because the walls of the bell take a lot of heat to dry - in the two skins stove which was planned, one must heat the bell a lot for heat to croo both skins and to store enough heat for one day in both skins. Then, insides'bell's temperature would have been higher and the transfer (delta) would'nt have been so good. Then exhaust gases would have been hotter, in my opinion.
Benoit
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Post by peterberg on May 4, 2015 7:00:37 GMT -8
The MHA heater was fired initially from 16:00 hours up to 3:00 that night, running as hot as it would get. The air inlet was left intentionally open after that, so it could shed more heat and moist to the outside. Around 10:00 that morning the whole thing wasn't warm but dried out for 90%. The added ISA was about 0.55 m2, which probably tipped the balance a bit too far. Starting the thing wasn't difficult by the way, it went off just like that unlike the 6 other workshop heaters on the premises.
On the other hand you could be right. When wet, the delta T couldn't be high because of the evaporating water. When nearly dry the bricks could extract a lot more heat I'd think. Closing one or both of the benches would influence the exhaust temperature, no doubt about that. The benches got warm almost as quick as the bell itself and shutting off would shed more heat through the exhaust. And what about this: in a blind bench this shutting off could act as a way to heat up the stack quicker, much the same effect as a bypass.
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Post by pyrophile on May 4, 2015 11:10:04 GMT -8
That is what I thought also (about closing the benches as a bypass). Excuse me, Peter, I don't understand : " it went off just like that unlike the 6 other workshop heaters on the premises" . Do you mean, it stopped burning wood correctly suddenly?
EDIT : if it so, during the stage when the stove worked well, the wall of the bell had warmed up and then the difference of temperature beetween gases and walls got smaller. Then exhaust gases were hotter and draft improved. Am I wrong somewhere?
Benoit
EDIT 2 (after Peter 's following answer) : OK!
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Post by peterberg on May 4, 2015 11:46:59 GMT -8
Hihihi... No, it's an expression to indicate that it (the heater) was very easy to lit. Unlike the other workshop heaters.
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