Cramer
Junior Member
Posts: 129 
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Post by Cramer on Dec 24, 2013 18:51:59 GMT -8
The sketchup file attached details the desired dimensions of the bell. I want to dump and store 90 percent of the heat from the burner and it looks to me like a 6 inch J Tube burner will suffice for the application. How though in a bell this short would one incorporate the burner into the inside of the bell to make this bench work? A small cooking surface and/or white oven would not be necessary but if it simplified things it could be incorporated, it might even come in handy. I am considering the use of dense fire brick for it's heat holding capacity for the bell material.
Does incorporating the burner into the bell mean I should increase the ISA of the bell because there will be minimal immediate heat loss before the gasses fill the bell?
If I make a 6 inch J Tube burner will the height requirement for the riser dictate that I must raise at least one end of the bell to accommodate the gap between riser and ceiling of the bell?
I have laid brick before a great many years ago but have forgotten all of what I once knew. Is there a way to span a two foot gap with brick for the top of the bell or would one use a different type of cap for that purpose?
Getting closer by the week to beginning on this project.
Thoughts or suggestions? I have added some notes on the file about the dimensions, please keep them in mind when commenting. Thanks to you all!
[File removed to make space for later files]
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Post by satamax on Dec 24, 2013 21:52:17 GMT -8
Cramer, i would say a six incher J is too small. An 8 incher should be all right tho.
you need a different material for the top, if you don't arch it. A cooking plate could do the job. A thick steel plate supported by RSJ, and then partialy covered by bricks could also work as cooking plate and mass.
Gap wise, you could angle the riser as Matthewwalker has discovered lately.
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 25, 2013 6:37:19 GMT -8
Angle the riser? I must have missed that thread! That opens up possibilities...
Okay, let's say I cut the length by one brick width by laying one extra course inside the flue side of the bell bringing the ISA down as shown in this iteration (attached) leaving the ISA now at 41.68 ft^2 (3.873 m^2). I know the burn tube will need to be as short as possible to keep the riser length to a manageable height but I am left with around 9 ft^2 of ISA for maybe a "pop up" in the bell to allow for riser height and if the riser can be angled a bit that might leave sufficient clearance to the top of the bell. I have not figured that one out yet but if extra height is needed for the "pop up" for clearance above the riser then a course of brick could be laid length wise instead of width wise cutting the ISA at that end of the bell another 4 1/2 inches.
RSJ?
[FILE REMOVED TO MAKE ROOM FOR LATER FILES]
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Post by satamax on Dec 25, 2013 8:19:58 GMT -8
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 25, 2013 12:56:50 GMT -8
Clean out idea duly noted, I might just want to devise a method where the entire top can be lifted on a hinge along the back side to clean out the entire thing. I will have to ponder on that a while. I know it will be mighty heavy but nothing a bit of hydraulics couldn't handle.
How about this sketch: Any thoughts?
RSJ, oh! Steel I Beam... I would guess it would be a good idea to insulate them with an inch or two of superwool?
[File removed to make room for later files]
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 26, 2013 18:33:16 GMT -8
I have a sketch of the proposed burner here. Working on the theory (proven anecdotally so far as I have read from Peter and Donkey) that the riser can be at least less than vertical. This one is 60 degrees from vertical. Before I build this I want to run it by you all to make sure you think it will work though. Probably will cast the J Tube and use a superwool and rigidizer riser. I am thinking even with rigidizer I will still need to support the riser as it will be so far off of the vertical plane. Thoughts?
Edit: It just occurred to me that I might be able to use an 8 in inside diameter ceramic flue liner cast into the J Tube mold with the rigidized superwool inside of that. I could make the inside of the riser extend beyond the length of the flue liner to keep the heat off of the end of it. Any problems with this thought?
[FILE REMOVED TO MAKE ROOM FOR LATER FILES]
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Dec 27, 2013 1:38:07 GMT -8
Gap wise, you could angle the riser as Matthewwalker has discovered lately. I thought the angled riser Matthew referred to applied to batch box rockets? |
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Post by satamax on Dec 27, 2013 2:10:50 GMT -8
Cramer, i should admit i don't like the look of the slanted to the side riser. Tho, it might work. The best way to go about this, is to do a steel prototype. With cheap flue pipes, hvac piping or whatever scavenged materials. Insulated for sure. And it would be best to test it in a bell, to see if it can cope with the drag. Morticio, true enough. I hadn't thought about this aspect of the problem, a rocket is a rocket in my mind.  |
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 27, 2013 3:52:03 GMT -8
Ah, Morticcio, you throw water on my fire! I had not thought about the batch box vs. J Tube aspect of the slanted riser. Thanks very much for pointing that out! Satamax, thank you also, I don't actually "like" the looks of the slanted riser either but if it works it would solve a host of bell design problems, especially ones where vertical space is at a premium.
Testing of the slanted riser with expendable material is a great idea! I wanted to get this done on the first shot but I also want to have a working unit so if I am to attempt the slanted riser with a J Tube it would be prudent to test one beforehand.
Would a dry stacked bell with a bit of a "leaky" lid suffice for a testing of the hypothesis do you think?
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Post by satamax on Dec 27, 2013 4:43:25 GMT -8
Well, voids creating leaks can be plugged with rockwool.
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Post by matthewwalker on Dec 27, 2013 10:30:06 GMT -8
I've been running a broken riser on a 6" J for a couple weeks now. It runs great, and so far the numbers look pretty good. I think it works well enough for me to use it when I want to keep overall height low, but I'm certainly not suggesting it's superior to a normal configuration. Just another tool in the kit.
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 27, 2013 15:13:08 GMT -8
Thanks for that Matt! Have you looked at the sketchup? In your opinion, would a configuration like the one shown in the file work? Is the "broken" riser you mention in your comment one that has some vertical rise then angles or is it angled straight off of the bottom of the horizontal burn tube? I am hypothesizing that if the riser is angled all the way down to the "floor" of the burn tube that there would be minimal disruption of the gas flow and the burner will act pretty much the same as the vertical version of the same length. The proposed configuration could save a lot of vertical space for a bell.
Can you tell me how much of an angle you are running and if it is vertical from the bottom of the burn tunnel then at the top of the box it angles or is it much like the drawing I presented? Which I present again here for convenience:
[FILE REMOVED TO MAKE ROOM FOR LATER FILES]
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Post by matthewwalker on Dec 27, 2013 17:30:51 GMT -8
Ok, just d/l'd sketchup again so I could look. I haven't built one like that, but I am of the opinion that it would work fine, as long as you get the outlet of the riser above the feed by a bit. The way it's drawn there may or may not work, since they are so close in height. I really don't know the rules here though, I've just run a couple configurations so far. The one I've tested is "broken riser" style, and the angle is honestly not far from horizontal. Not by design, but it ended up that way and is working well. I haven't tested one yet, but I agree "angled riser" is a better plan. Max linked the post above that has my drawings of those terms. I say try one and tell us how it goes, that's the only way to find out.
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Dec 27, 2013 19:52:48 GMT -8
Okay, one more time and I am going to build and test this one. Raised the riser height 10 degrees which puts the end of the riser a bit more than 9 inches above the highest point of the feed tube and 31 inches above the center of the burn tube. The length of the riser is twice the length of the burn tube at 36 inches. Do you think it has a better or worse than 80% shot at operating within rocket parameters? I will see if I can get Peter's opinion on it also. Maybe Donkey will comment since he has operated a "broken riser" also (I think). The 3' 3" measurement will be the top of the bell the burner will go into with an ISA of about 41.69 ft^2 and a chimney at the opposite end of the burner from the riser. Any concern that the feed tube is too tall? Might it be a better idea to have the chimney exit at the burner end of things considering the way the angled riser will be pointing? Burner Rev1.skp (146.39 KB) Bell mock up with dimensions Rev2.skp (204.25 KB) |
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Post by satamax on Dec 27, 2013 23:05:27 GMT -8
Cramer, on your second drawing with the bell, why exhaust soo low below the top surface? I would say the top of the tube can nearly touch the top plate, and no wories about top gap either.
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