Terminator Posted November 4, 2002 Share Posted November 4, 2002 A butterfly mechanism, offers variable restriction in a pipe, but how much Can any one tell me a formula a for calculating the amount of restriction offered by the butterfly at a set angle, 90 degrees being fully open therefore a theoretical nil restriction and 0 degrees being theoretically closed maximum restriction. I would like to relate the data to an equivalent fixed restriction i.e. a ring of smaller diameter than the pipe. I am no good at fluid or aerodynamics just need a formula to stick in a spread sheet. Just an idea brewing. Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted November 4, 2002 Share Posted November 4, 2002 Given the shape of the butterfly restriction and angles involved, I could give you a formula to calculate the restriction area as a percentage of the total unrestricted area, but I suspect this would be of bugger all use when it actually comes to a substance flowing through the pipe. Quote Link to comment Share on other sites More sharing options...
Terminator Posted November 4, 2002 Author Share Posted November 4, 2002 Nice one Graham thats a start. Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted November 4, 2002 Share Posted November 4, 2002 Actually without thinking of this in the slightest I leave myself open to looking a real tit here, but wont the restriction percentage simply be the cosine of the angle? Thats assuming a disc obstruction, fully open at 90 deg, fully closed at 0 deg. I prepare to look silly now. Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted November 4, 2002 Share Posted November 4, 2002 Originally posted by Graham Rudd I prepare to look silly now. Not as silly as I feel. 'Cause I don't understand a word you just said! Quote Link to comment Share on other sites More sharing options...
Alex Posted November 4, 2002 Share Posted November 4, 2002 Originally posted by Matt Harwood Not as silly as I feel. 'Cause I don't understand a word you just said! Glad I'm not the only one!! I really should have paid more attention in school.... Quote Link to comment Share on other sites More sharing options...
Adam W Posted November 4, 2002 Share Posted November 4, 2002 I know that I have this info, and I'm pretty sure I can remember how to use it! Give me a couple of days and I should be able to give you an answer. Do you know the pipe diameter? Quote Link to comment Share on other sites More sharing options...
Mark D Posted November 4, 2002 Share Posted November 4, 2002 I don't know if this is any help, but I remember the formula for laminar fluid flow. Flow rate = pressure * pi * radius to fourth power divided by 8 * viscosity of fluid * length This is known as the Hagen-Poiseuille law It would follow that changing the radius of the pipe or the angle of the restrictor will significantly affect the rate of flow because it is proportional to the fourth power. Hope that is useful. (Also hope you guys aren't going to have a go at me for being a nerd and remembering that from school. My physics teacher would be proud!) Quote Link to comment Share on other sites More sharing options...
Mark Ayling Posted November 5, 2002 Share Posted November 5, 2002 Originally posted by Mark D ...I remember the formula for laminar fluid flow. Flow rate = pressure * pi * radius to fourth power divided by 8 * viscosity of fluid * length This is known as the Hagen-Poiseuille law It would follow that changing the radius of the pipe or the angle of the restrictor will significantly affect the rate of flow because it is proportional to the fourth power. Respect! Quote Link to comment Share on other sites More sharing options...
Adam W Posted November 5, 2002 Share Posted November 5, 2002 Right; I'm assuming this is for gas flow not liquid. I've found the equations you need and they're bloody complicated, I understand them but not well enough to explain them to someone with no experience of fluid dynamics (not wishing to be patronising or Mycroftian here, but I'm guessing that's you!). To get really accurate figures, I'd need lots of information about the pressure difference across the valve, the flow rate through it in metres cubed, and the absolute temperature of the gas going through it. ie things which are pretty difficult to measure without a fair bit of gear. However, if you give me the diameter of the butterfly in mm I can do you a table of opening angle vs percentage of max flow rate, based on lots of assumptions etc which should be accurate to within 15% or so. If you want accurate figures, you're going to have to invest in manometers, temp probes, a hotwire flow meter, all sorts of crap! Quote Link to comment Share on other sites More sharing options...
efc Posted November 5, 2002 Share Posted November 5, 2002 er.........I like Supras:moo: Quote Link to comment Share on other sites More sharing options...
Terminator Posted November 5, 2002 Author Share Posted November 5, 2002 Thanks guys I knew I could rely on you. Adam I don’t have any of the crap to which you refer. I will mail you off list some time with details. You are right we are talking about, a gas flow not liquid. Temp will be variable in the range 600 to 900 centigrade. My experience of fluid dynamic is fairly extensive but in a very specific field associated with the consumption of alcohol, not much use here I fear. I don’t need mega accuracy I just want some rough idea of potential flow rates for a given angle. It is my limited understanding that the change in restriction will be fairly limited as the plane of the butterfly moves from a position parallel to the flow. The most significant flow change per degree of turn will be towards the closed position or approaching 90 degrees to the flow. Quote Link to comment Share on other sites More sharing options...
Adam W Posted November 5, 2002 Share Posted November 5, 2002 OK Phil, I just need a diameter or a range of diameters to give you a table of numbers. Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 6, 2002 Share Posted November 6, 2002 So when you have built your variable-restriction exhaust system, can I have one too? -Ian Quote Link to comment Share on other sites More sharing options...
tDR Posted November 6, 2002 Share Posted November 6, 2002 Originally posted by efc er.........I like Supras:moo: Me too. Eggz are goode! Quote Link to comment Share on other sites More sharing options...
Paul K Posted November 6, 2002 Share Posted November 6, 2002 Originally posted by Adam Wootten Right; I'm assuming this is for gas flow not liquid. I've found the equations you need and they're bloody complicated, I understand them but not well enough to explain them to someone with no experience of fluid dynamics (not wishing to be patronising or Mycroftian here, but I'm guessing that's you!). To get really accurate figures, I'd need lots of information about the pressure difference across the valve, the flow rate through it in metres cubed, and the absolute temperature of the gas going through it. ie things which are pretty difficult to measure without a fair bit of gear. However, if you give me the diameter of the butterfly in mm I can do you a table of opening angle vs percentage of max flow rate, based on lots of assumptions etc which should be accurate to within 15% or so. If you want accurate figures, you're going to have to invest in manometers, temp probes, a hotwire flow meter, all sorts of crap! Brainiac:stupid: Quote Link to comment Share on other sites More sharing options...
Adam W Posted November 6, 2002 Share Posted November 6, 2002 Heh heh, if only that were true! Quote Link to comment Share on other sites More sharing options...
Andrew Dunk Shaw Posted November 6, 2002 Share Posted November 6, 2002 I know why i quit fizzicks now and swapped to kemistree, wasnt much better at that, but had some great fun with all those kemiculls. Regards Andrew(dunk)Shaw Black uk mkiv tt Quote Link to comment Share on other sites More sharing options...
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