rst
New Member
Posts: 24
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Post by rst on Jun 10, 2014 17:21:12 GMT -8
Am I about to do something stupid? I prepared this inner form for casting the heater core based upon videos and threads on here, but I'm questioning myself on it. The cross section of the tube is approximately 8 x 8 inches. The second image is blurry, but I attempted to make a place for a tripwire, which is about 3 inches long and tapering toward the front, around 1/4-3/8" at its thickest. I attempted to do a kicktail/backsweep as well, but the transition was kind of sloppy so I might try smoothing it out a bit with taping some cardboard where the curve begins. Also, as I was assembling it, I began to question where it was wise to be making the tube 8 x 8 inches, since I intended to use an 8" round pipe as the interior form for the heat riser, and use 8" ducting in part of the bench. Is that going to create problems? Also, the length of the burn tunnel top (on the form) is about 9 1/4 inches total, so from middle of feed to middle of heat riser would be 17 1/4 inches I figure. This is my first actual build, and even though I find it an interesting subject, I'd rather get it right the first time and not need to build more. Please criticize so I can make any appropriate corrections before actually "setting things in stone", so to speak.
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Post by Donkey on Jun 11, 2014 6:53:54 GMT -8
I've always thought it best to go with 7x7 or slightly larger depending on the bricks.. Yes, square aspect will not move gasses through as fast as round, but it's best to slightly small the feed anyway, less chance of smoke-back that way.
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rst
New Member
Posts: 24
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Post by rst on Jun 11, 2014 7:49:01 GMT -8
So I'll probably need to reduce it to 7x7 square I suppose? What do you mean by "slightly small the feed"? Thanks
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Post by DCish on Jun 11, 2014 12:22:31 GMT -8
If i remember correctly, Peterberg has posted several times regarding heat riser sizing that a good rule of thumb is that flow-wise, an 8" square pipe is equivalent to an 8" diameter round pipe due to the fact that flow through a square pipe is not as efficient as flow through a round pipe.
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rst
New Member
Posts: 24
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Post by rst on Jun 11, 2014 14:40:36 GMT -8
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Post by DCish on Jun 11, 2014 16:26:34 GMT -8
Yup! Nail on head! Sorry for not finding the quotes myself, I download and read this forum offline while commuting, so can't look stuff up in the moment...
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Post by Donkey on Jun 19, 2014 18:40:15 GMT -8
What I mean by "slightly small the feed" is that it is better if the feed as slightly LESS CSA than the rest.. Bigger or equal CSA has a tendency to smoke back, smaller less so. So, I would rather go with 7X7 as it's slightly smaller in CSA and is trouble-free more often than not.
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joseph
Junior Member
Posts: 66
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Post by joseph on Sept 19, 2014 6:03:18 GMT -8
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