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  1. LarryC

    Miniature Combustion Chamber Design Problems

    mrwolfe - Thanks for your reply to this very old post! Mr Bruce Tharpe, a model jet designer and flyer here in the US, has described a very similar system [though larger] WITH a lightweight miniature PRV! He makes a pressure tank out of large latex surgical tubing [won't hold up under...
  2. LarryC

    Thrust from a compressed gas cylinder

    The simplest representation of thrust is the Zucrow rocket equation, F = [ M / 32.1 ] x Ue where F is the thrust in pounds, M is the ejected massflow rate in lb/sec and Ue is the ejection velocity. This is not adequate for design, but it helps in understanding a couple of important points. The...
  3. LarryC

    Miniature Combustion Chamber Design Problems

    Graham - Sorry to take so long to respond. Yes, this forum is very good, though for pulsating combustion questions like mine, I think it turns out that the 'Mechanical Engineering other topics' forum might be a more direct path to someone actually involved in this kind of work. On the other...
  4. LarryC

    Cleaning Flux from Stainless Welds

    rysep - Thanks -- I'll check that out. After a while, I wasn't sure anyone would EVER answer that post! Not many out there are gas welding stainless (and I don't do much -- this is basically miniature pulsejet development; small stuff, but slow work). Larry Cottrill
  5. LarryC

    Miniature Combustion Chamber Design Problems

    Bruce, this is Larry Cottrill, the same guy who's showed up a few times on Kenneth Moller's Valveless Pulsejet forum, where I've talked to you, Bruno and others a few times (I usually seem to be pontificating about things I know nothing about, since my reading of the theory is almost nonexistent...
  6. LarryC

    Venturi Vaccum Pump

    SteamJetPE - I've been trying to FAX you at 908-575-1573 (as you mentioned way back on 14 Oct) -- it rings many times but won't answer. Please verify here that this is the correct number and/or send a short FAX to LarryC at 515-557-7132 & hopefully I'll get it and send you what I have (OR email...
  7. LarryC

    Venturi Vaccum Pump

    Dear SteamJetPE - That will be fine. This is in danger of becoming The Thread That Never Dies . LarryC
  8. LarryC

    Venturi Vaccum Pump

    Dear SteamJetPE, As usual, intuition (at least mine) is only so good. At least, the tradeoff between capacity and exit pressure makes perfect sense to me -- with more intake air being accelerated into the stream, more of the original stream energy is consumed (i.e. the total momentum is shared...
  9. LarryC

    Venturi Vaccum Pump

    Dear jdsewell, We've gotten into (almost) more of an aerospace discussion now, although what we're talking about is certainly still a valid and interesting mechanical problem. I'd like to get back to memepe for a moment, since he (or she) asked the original question and I'm not sure has ever...
  10. LarryC

    Venturi Vaccum Pump

    Dear jdsewell, The last post from SteamJetPE leads me to think that the ejector principle must be highly under-utilized. The next question I would ask is whether this is due to a) lots of inherent physical problems (e.g. no matter what you do, it's still too low in overall mechanical efficiency...
  11. LarryC

    Venturi Vaccum Pump

    Dear jdsewell - The thrust augmentor is one application, and technically very similar to what I have in mind. The main difference is that in the thrust augmentor (at the exhaust nozzle of a jet engine) the venturi entrance is only slightly larger than the driving flowstream (i.e. the jet...
  12. LarryC

    Venturi Vaccum Pump

    Thanks, jdsewell - The little Java program is very nice for basic venturi calculation, but won't do the job in this case. Here's a more complete explanation (please bear with me!) of what I need (and memepe as well, if I really understood his original question): Assume a smooth venturi of...
  13. LarryC

    Miniature Combustion Chamber Design Problems

    I am working on a miniature pulsejet design, and have several problems due, in one way or another, to the small size of the combustion chamber (approx .75 in. diam x 2.0 in. long). The exit nozzle (approx .75 in. diam down to .375 in. diam) is rather short (about .5 in.) but as smooth as I can...
  14. LarryC

    Cleaning Flux from Stainless Welds

    I have had good success welding stainless with oxy-acetylene technique using high temperature flux all around the weld site, but the flux around the weld remains as a tight black fluoride "glass" coating that is unsightly and a real bear to remove with such techniques as wire brushing...
  15. LarryC

    Venturi Vaccum Pump

    Dear SteamJetPE - It seems to me that this mechanism is known as an "ejector", basically a "driving" flowstream aimed right through the throat of a venturi to induce flow due to the low static pressure in the throat (as sensed from the "upstream" side). If this is...

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