nemo
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Post by nemo on Dec 10, 2014 16:21:10 GMT -8
Satamax, thank you for the drawing and the metric conversion. I think I will stick with the half barrels. My system is an 8" not 6 so I'm thinking I could add more bell space or flue. You say that if i keep the tops on the barrels and link them with my 8" tube 8cm from the ground, they would act as a bell? I'm really hoping to use an extension exiting the second half barrel and make a backrest for the bench, just like in this drawing. Do you think this is possible? Is there any way to calculate if that would be a working option or I just have to experiment? Im not going to use the wall bell option because i'm constrained with de measurements of the bricks and how to build them. Don't have the patio pavers and so on.
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Post by satamax on Dec 10, 2014 23:04:54 GMT -8
Nemo, two half barrels as bell are small for an 8 incher. Can't you add a third one where you have drawn the elbow comming out of the barrel? Just a pipe comming in the side of that half barrel instead of an elbow. You don't necessarily need to connect the barrels with a pipe in between. A shallow and wide port cut into the two tops is good too. As long as you respect the CSA Let say 8cm high from the ground and 40cm long would do. And your pipe you want to use for the backrest needs to plunge at 5cm form the ground. A bell, since the hot gases rise is like using a bucket reversed to hold them. So for a bell low entrance, and low exit. if you want to do a triple bell, low entrance and low exit for each of theses. How long is that wall? How to measure the efective ISA of the tube's horizontal part 2/3 of circumference X Lengh to add to the ISA of the barrels. For an eight incher, iirc, don't go over 6M² Hth. www.stove.ru/index.php?lng=1&rs=16Max.
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nemo
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Post by nemo on Dec 10, 2014 23:58:14 GMT -8
Max, I think I can do 3 half barrels there as you said, one instead of that elbow. And I thought of another way to increase the ISA: what if I mix half barrel with bricks and make the half barrels higher. I can add two layers of bricks on each side(dont know how many tall)and put the barrels on top of that. It would look like a wall with half barrel roofing. What do you think? My wall is 2.9m. And you say that the hole linking the barrels has to be of 40cm? I can remove the tops alltogether and weld all three half barrel together.( does that affect the gas movement negatively?)
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Post by satamax on Dec 11, 2014 3:39:26 GMT -8
Nemo, three half barrels used as a single bell is not enough ISA, that's about 2.2m², if you leave the ends, and treat as three separate bells, you will be nearer the right ISA. So leave the ends. What i was saying is a shallow cut of thoses ends, near the floor, of 8cm high, by 40 wide. But if you raise the barrels one brick high 6cm, you don't even have to do this, just don't put bricks under the two partitions between two barrels. Get it? Don't go any higher, otherwise you'll have problems sitting on the bench. Final measurement should be between 45 and 50cm with a layer of cob. So 34 or 36cm without cob should be good. If you don't have enough cob on top, you will have a hot spot in the middle.
Hth.
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gjh42
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Post by gjh42 on Dec 11, 2014 6:29:05 GMT -8
At 2.9 meters of available length, three half barrels would have to be tight together, and their facing ends would be pretty irrelevant for heat exchange. I would suggest raising the barrels on bricks as described, leaving the ends on for strength while cutting a hole near the top of each so the heat can equalize between them and there will not be a hot end and a cool end of the bench. The brick addition to the height should compensate for the loss of barrel end area.
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nemo
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Post by nemo on Dec 11, 2014 15:18:54 GMT -8
So, gjh, you tell me to leave a hole on the top and max tells me about one near the floor. Soo, both ,or which one would be the correct answer? Talking about the hole between the half barrels.
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gjh42
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Post by gjh42 on Dec 11, 2014 17:37:05 GMT -8
One near the bottom will let each barrel function as a separate bell, and each successive one will be cooler. Holes at both top and bottom will let the barrels all act as one bell, with uniform temperature across the top. I think that would be the better plan, unless you want the different temperature bench tops.
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nemo
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Post by nemo on Dec 12, 2014 8:36:18 GMT -8
Thank you max and gjh, I made a picture in my mind and i'll soon get to work. One last question gjh, how big has to be the hole at the top of the barrel? Thanx and I'll post some images of my work in progress!
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Post by satamax on Dec 12, 2014 9:45:00 GMT -8
I was telling you the solution for best heat extraction. As you haven't enough isa for extracting all the heat possible in one bell. Peter explains in this post, donkey32.proboards.com/post/12100/threadThe total required ISA goes down by 15% as compared to a single bell, all else being equal. I've tried this with a triple bell as well and that went down by another 15% or thereabout. This is talk about stacked bells, when these are side by side the situation is different. An eight incher J could cope with 6m² ISA i think. You would have 1.86m² for the barrel on top of the heat riser. 1.86m² for the two half barrels at each end +0.80m² for the half barrel in the middle, if used as a single bell. Let's say 6 x 0.85; as we could consider the barrel as a first bell, somewhat. 5.1m². What we have above is 4.52m² If we do triple bell, reduce another 15% So that's 5.1 x 0.85 that's 4,33m². that's bellow the 4.52m² above, plus one partition between two half barrels. Which is 0.13m² 4.52+0.13= 4.65. So neither case is good, if the theory of using 6m² with an 8 incher J is good. Mind you, we shouldn't account for the height of the barrel sides below the exit of the bell. And if the chimney adds a bit of draft, we would gaing a bit of possible ISA. So, it's your decision.
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gjh42
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Post by gjh42 on Dec 13, 2014 9:25:43 GMT -8
"This is talk about stacked bells, when these are side by side the situation is different." What we are talking about here is like side by side, so I think we need "official" clarification on the capacities. I don't know whether separating the barrels into separate bells with the ends touching is any better than a single bell, but I doubt it.
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Post by satamax on Dec 13, 2014 9:37:01 GMT -8
Stacked or side by side, a double or triple bell is still a double or triple bell! Actualy, the side by side version might have a slightly better extraction, as there's no warming of the top one by conduction.
What makes a bell, is stratification, exchange surface and volume. Volume keeps the heat inside for longer time, via the stratification. The more time heat stays in the bell, the more it has to transfer to colder material of the bell. And the more exchange surface, the more heat you can conduct into the mass.
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nemo
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Post by nemo on Dec 19, 2014 16:36:30 GMT -8
Is there a way to calculate the isa needed taking into account that the barrels are higher on bricks. Max, how did you come up with 2.2 for the three half barrels. Can you please tell me the formula used? Shouldn't I calculate in cubic meters since I am using bricks to make more isa under the half barrels? I need a good formula so I can know how many half barrels I need on top of the bricks. The sistem is really a7' eqhuivalent since my heat riser is 18x18cm. Thank you!
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gjh42
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Post by gjh42 on Dec 20, 2014 7:34:21 GMT -8
The ISA of the bell would be increased by the height of the bricks x the perimeter of the bell base. The volume is not relevant to ISA except as a larger volume is likely to have a larger ISA... there is no fixed numerical relationship.
The ISA of a barrel would be its height x diameter x pi (3.14) for the sides. A half barrel is half of this. A barrel end (or two half barrel ends) would be 3.14 x (diameter / 2) squared.
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nemo
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Post by nemo on Dec 20, 2014 10:57:11 GMT -8
Thank you! I am learning so much here thanx to you guys! How big has to be the hole connecting the half barrel to the first bell(barrel). Does it have to be same size as the sistem? 6' or 8' or in my case 7'.? Another question for another case where I have to build a rocket I was wondering if i can make the exit, the manifold, 90degrees angle next to the feed tube? I mean going with the thermal mass to the right or left instead of continuing on a same line with the feed and riser.
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Post by satamax on Dec 20, 2014 12:05:01 GMT -8
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