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Maximum Bell Volume on Rocket system?  RSS feed

 
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I've been jumping all over the place in the RMH stuff here and on Donkey's site... and I've seen some really cool things done by Matt Walker and others on Donkey, and have read a few things here too. 

But...  I was curious if (like in the flue pipe system through a mass bench) there is a magic volume that it is best not to surpass?  Part of me thinks that the Rocket might not be able to draw or really get ripping as it fills a really large bell, but when I was reading about it, I thought... wait a minute, the same vacuum exists no matter how big the Bell is, and so as long as the cooler outlet is the right size and below the hot inlet and the bell, all should function no matter how big the bell is.  Is that right?
 
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There's an article on bell theory at the batchrocket resource site. And connected to that one, an article on bell sizing. At this moment I am unsure what type of rocket you are planning to build. All this is applicable to batch rockets, there isn't such a spreadsheet for j-tubes.
 
Roberto pokachinni
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At this moment I am unsure what type of rocket you are planning to build. All this is applicable to batch rockets, there isn't such a spreadsheet for j-tubes.

I don't have a set plan yet for any particular style.  Mostly just brain storming, and gathering materials.  I think I have access to good barrels, so the barrel based bell, or double bell (... or triple bell?) might be in my interest.  I will check out those links.  I don't think that I've been to them yet.  Thanks much, gents.
 
Roberto pokachinni
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Since it seems that the driving force (draw) and efficiency (heat extraction verses fuel energy available) is based on the amount of heat absorption/loss in the system, It seems that if the exhaust portal was below your mass bell level but also came up right beside your heat riser/bare barrel, this would increase the exhaust pipe temperature (and thus the exhaust temperature) enough to solve some of the problems associated with Bell size.  No?
 
Peter van den Berg
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The vertical exhaust pipe close to the barrel is a way to warm the exhaust well before the rest of the heat extractor(s). As such, it's a good thing, but that heating of the pipe could also be seen as lost heat during the rest of the burn. I am a firm advocate of good design as opposed to using stop gaps, but when it works it is a solution as good as any other.
 
Roberto pokachinni
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Thanks for that, Peter.  Yeah, I would rather go for better design as well.  But the idea popped into my head, and I thought that it might be a good question to ask while I had your ear.  I will continue to read those links and get back to you, and Satamax if I have any further questions.    ...no doubt I will.     
 
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