smurf
New Member
Posts: 1
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Post by smurf on Mar 16, 2017 9:43:32 GMT -8
hello. I've made a few rocket stoves, the typical j-tube with a bench for thermal mass, they all work perfect. I'm planning now on another stove witch should have a very litle footprint so I was thinking on a bell instead of a bench but with a j-tube feed and a metal barrel outside the masonry bell. (it will be a 8 inch heat riser) The main reason is that it should be a low budget project so the bell can be build with normal fired clay bricks or even with homemade sundried claybricks and the roof of the bell don't have to be made out of expensive refractory material. Another advantage is that the metal bell will give immediately heat after lightning the fire. After investigating on this forum it schould look more or less like this donkey32.proboards.com/thread/803/evaluating-6-dragon-burnerbut with firebrick burnchamber and riser and the 8 inch version so bigger I was looking around the web and this forum but I cannot find how to calculate the bell exactely. So here are some questions.... 1) is it correct that the CSA from the bell can be anything bigger than 4 times heat riser size? for exemple 2700 cm2 ? 2) How big schould be the ISA of the bell for a 8 inch j-tube? I suppose I have to add the ISA from the first metal bell (oil drum) to the ISA of the brick bell. 3) how thick I have to make the walls of the brick bell, about 15cm thick sounds good to me for heat tranfer, is this OK?
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Post by coastalrocketeer on Apr 2, 2017 9:42:46 GMT -8
I can't answer the bell calculation question, but my understanding is that the port going INTO the bell is the one that must be oversized to 4+ times CSA. The exit can be system CSA.
This is to slow down the gasses entering, reduce their ability to "stir" the gasses already inside the bell, and thus maximize stratification.
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Post by DCish on Apr 2, 2017 16:43:16 GMT -8
I can't answer the bell calculation question, but my understanding is that the port going INTO the bell is the one that must be oversized to 4+ times CSA. The exit can be system CSA. This is to slow down the gasses entering, reduce their ability to "stir" the gasses already inside the bell, and thus maximize stratification. Actually, it is primarily to avoid creating a restriction point, as I recall.
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Post by coastalrocketeer on Apr 3, 2017 12:40:55 GMT -8
The sole function of eliminating a restriction point is on the exit from the barrel, which may be functioning as a bell, or more of a downdraft channel, depending on system CSA, overall open space inside the barrel and amount of gasses flowing through.
In an actual pure bell the incoming gasses are also desired to have minimum velocity, and create minimum turbulence in the overall cavity, thus allowing for better stratification, thus better heat extraction, and only the coolest gasses escaping the exhaust...
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Post by coastalrocketeer on Apr 3, 2017 12:43:27 GMT -8
It is definitely also true as you state, that the exit from the barrel (the manifold) normally functions best when it is significantly more than system CSA.
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