hpmer
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Post by hpmer on Oct 8, 2011 4:00:08 GMT -8
If 8" pipe is used in the bench, can I use an 8" square burn tunnel/heat riser, or do I need to use a 7" since that would match the cross sectional area (CSA) better?
I know it has been suggested that stepping down the pipe size helps maintain flow as the gases cool, but am wondering if the stepdown needs to be further downstream (the book states that the heat riser needs to be the smallest part of the system).
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Post by Donkey on Oct 8, 2011 9:13:24 GMT -8
Yeah, it would be the 7" square. It'll run better if you don't increase size in the heat riser area.
I'm not sure that the book is quite accurate on that score either.. Seems to me that if yer stepping down pipe sizes to maintain proper flow, the smallest part of the system would be down at the end of the run, where the step(s) is.
I've messed with tapered heat risers, thinking that playing with pressures would help.. I still think there may be something there, but my experiments so far have been inconclusive. So far, my best stoves use a tallish, well insulated, heat riser AT system size.
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hpmer
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Posts: 240
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Post by hpmer on Oct 8, 2011 11:10:14 GMT -8
Yeah, that's what I thought. Thanks.
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Post by Donkey on Oct 8, 2011 20:00:58 GMT -8
Oops.. That wasn't super clear.. I think you understand my meaning, but I'll fix it anyway.. Step downs in pipe size should be placed down the run AFTER gasses have cooled and contracted somewhat.
What's needed is a rule-of-thumb about where to place step downs, how big a step, etc. It'll look something like: An eight inch system needs an inch reduction every so many feet of cob or masonry..
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Post by martinm on Oct 10, 2011 1:15:41 GMT -8
Hello I am building a rocket stove which will be fired in one room and the heat storage bench and the vertical riser willbe in the adjacent room . as far as I know the vertical insulated shaft should be taller than the distance betrween the inlet ( feeder) and the bent to the vertical shaft . I at least 8n this case it makes at least 85 cm. so the riser should be taller than that . Is it too far ? Thank you in advance .
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Post by stovol on Oct 10, 2011 7:27:41 GMT -8
hello all, i've built three (very amateur) rocket stoves.. first out of clay sewer pipe (not insulated) just to see if it would work...... second from fire brick with the same clay pipe as burn tunnel and heat riser.. insulated with ash and vermiculite... third with clay sewer pipe buried in ground with coffee can heat riser inside 8 inch stove pipe insulated with perlite and vermiculite covered with a 55 gallon barrel.. my question is... i have found two suppliers, one in chattanooga and one in knoxville for insulating castable refractory... both places i can get a complete roll of ceramic blanket 50 sq ft for around $63 and the insulating castable refractory for right at $40.. I want to cast a J shaped rocket stove. Can you guys give me some advice about the system size ? How has a rectangular chamber and riser performed... thought i might experiment with something like 6x9 .. any suggestions on chamber length? casting tips? was hoping to make it out of cardboard and burn it out.. maybe cast an internal bell if this works? thanks all... great site!
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hpmer
Full Member
Posts: 240
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Post by hpmer on Oct 10, 2011 13:35:41 GMT -8
Donkey's had some success using cardboard forms (there's a thread on that somewhere here) but I have not. My attempt slumped badly and was essentially ruined. I changed over to a thin sheet of floor underlayment which worked very well.
A square system seems to work better for me than the round ones I've built, probably due to better mixing of gases due to the corners. I've only built square systems, not rectangular ones.
The larger systems have worked better than the smaller ones for me (6" worked much better than the prior 4" one for example.)
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