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Post by satamax on Jul 29, 2012 6:27:22 GMT -8
Hi everybody! Well, on, this one Len at permies sugested that i add a bell next to it. Metal one that is. So i have started cutting a new big bottle of gaz, i did a round cut where the tap was, to fit a tube inside which would go prety much to the bottom; leaving the proper gap. My question is, can i make the inlet into the "bell" higher than the exhaust? Or do they need to be at aproximately the same level? There's one thing for sure, i wouldn't go under the feed tube of the rocket level. Thanksa lot and best regards. Max.
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Post by peterberg on Jul 29, 2012 11:33:44 GMT -8
Max, A bell like that has to be exhausted as close to the bottom as possible, and the inlet a little bit higher. The inlet and outlet are best placed more or less opposite of each other, no tube or whatever is required inside. The difference in weight between the hotter and cooler gases will take care of the segregation. The hotter gases will rise and the cooler ones will go down, to be exhausted. Height difference between inlet and outlet need to be there in this situation in order to avoid shortcutting of the hot gases.
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Post by satamax on Jul 29, 2012 12:23:40 GMT -8
Thanks Peter.
Well, i have to have the tube inside, and centered, since it's the only way it'll fit in that space. So, if the inner tube goes lower than the intake tube, segregation of gases will be done properly?
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Post by peterberg on Jul 30, 2012 12:40:23 GMT -8
No Max, Not in the way a bell will do. I do understand you want to fit the thing in the space which is shown in the picture. You would do better to take the bricks out and fit the bell in there. Otherwise, with the exhaust channel inside the bell there won't be enough space above the inlet to act as a bell and the thing will shortcut to the exhaust side.
So, the gas bottle will only work properly as a bell when there's much more space above the inlet than the combined cross sectional area of the inlet and outlet. To give you a rough idea of the dimensions, when the inlet is 15 cm diameter, the bell need to be at least 30 cm diameter. So the c.s.a. of the inlet (or outlet for that matter) is 1/4 of the c.s.a. of the bell. By this way, the velocity of the incoming stream will slow down enough to allow the hotter gases to rise.
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Post by Donkey on Jul 31, 2012 7:25:42 GMT -8
Interesting.. There's that 1/4 ratio again.. We have air intake to system size, intake/outflow to bell size... I wonder where else that ration appears?? Peter?
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Post by Donkey on Jul 31, 2012 7:29:01 GMT -8
And.. Max, Won't the first arrangement stay the same?? You're just adding a second gas bottle next to what you have currently in the image? If so, pipe straight across.. I guess I don't see the issue.
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Post by satamax on Jul 31, 2012 10:52:52 GMT -8
Guys, thanks a lot for your replies.
Ok Peter. Would it shortcut if the exhaust tube went lower than the intake tube?
Donkey, nearly exact same arangement. An horizontal tube between the two botles. I was thinking of enlarging the size of the tube. I have some 18cm thick metal tube that i could put there to shortcut the bootleneck that you usualy get at this spot. And the downwards tube you see at the left would go in the second bottle. Then, i could always put the tube inside, slanted, to get it further away from the intake. Does all this make sense?
Thanks.
Max.
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Post by peterberg on Jul 31, 2012 11:08:16 GMT -8
Interesting.. There's that 1/4 ratio again.. We have air intake to system size, intake/outflow to bell size... I wonder where else that ration appears?? Peter? <grin> ;D Although it do sound like a sort of golden ratio for rocket stove heaters, in reality it isn't. The intake to system ratio is more or less a fact, 90% of rocket stoves will run quite happily using that. This inlet to bell size ratio is an educated guess and moreover, I would say it's a minimum. The chance of proper separation will be greater when using a larger bell. But I'll keep my eyes and ears open, just in case.<grin off>
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Post by satamax on Jul 31, 2012 19:04:59 GMT -8
<grin> But I'll keep my eyes and ears open, just in case.<grin off> I'll have to try it then
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Post by Donkey on Aug 1, 2012 0:59:03 GMT -8
Donkey, nearly exact same arangement. An horizontal tube between the two botles. I was thinking of enlarging the size of the tube. I have some 18cm thick metal tube that i could put there to shortcut the bootleneck that you usualy get at this spot. And the downwards tube you see at the left would go in the second bottle. Then, i could always put the tube inside, slanted, to get it further away from the intake. Does all this make sense? Umm.. I think so, yeah.. Seems to me that if you have no troubles with the stove in it's current configuration, you will not need to increase pipe size. I would think that IF any change in pipe size is needed, it would be to reduce size at the chimney (final exhaust).. That would depend on the temperature of the exhaust of the second bell. If it's very cool, stepping down a little may improve draft. That said, if it's not broke, don't fix it. Peter??
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Post by satamax on Aug 1, 2012 9:44:27 GMT -8
Donkey. The system size is 6 inch or thereabouts. And the exhaust tube 111mm (slightly bigger than four inches. So getting it colder would may be help This thingy, when there's wind, smokes back a fair bit. But i think it's normal.
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Post by Donkey on Aug 1, 2012 16:06:36 GMT -8
Ah.. That makes sense.. In that case, I WOULD use the 18cm pipe between bottles, and maybe use the (existing) 111mm exit-to-chimney. You'll have to forgive me for being slow at metric units.. We Americans insist on still using the Kings system, even though we kicked his butt back to England sometime ago... I don't think in metric, so don't be surprised if when you pop off a measurement, I just stand there with the glassy-eyed, uncomprehending, slack-jawed look..
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Post by satamax on Aug 14, 2012 12:42:21 GMT -8
Well, as sussed by Peter, it bypasses. The tube is plunging deeper than the intake into the bell, but still bypasses. Tho, i'm extracting mo heat Within minutes the bottom of the bell was barely touchable. After an hour, the top half, xept the rounded end was still touchable. What d i do now, remove teh inner tube and rely only on the slowing down of the flow? Or leave it like this? Thanks a lot guys.
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Post by matthewwalker on Aug 14, 2012 13:43:40 GMT -8
I'm speculating that by having the exit tube inside the bell it heats up and creates quite a draw, adding to the bypass situation. Why not plumb it in from the outside down low? I'd also raise the inlet if possible.
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Post by Donkey on Aug 14, 2012 15:15:47 GMT -8
My thought is similar to Mattew's. Also, with the central tube there isn't really enough room for that gas bottle to act like a bell. Why not attach it from the outside (down low)?? I know that your answer is likely gonna be that the space is too tight.. 'Course yer probably right and you'd know about that better than me, but what about it?
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