Discussion
Thank you David. I enjoyed your posts on that site. You explained the flow bench you designed and i had a question you said your flow bench program includes the complete range of flow equations and i was wondering where i could find all these equations, i am interested in building a bench just like you described.
Thank you David
Thank you David
The equations are in British Standard 1042 and no doubt the American equivalent whatever that is. There seems to be a version online here.
http://wenku.baidu.com/view/768612260722192e4536f6...
In addition you need the Isentropic Exponent of air which is 1.4201
Air density at 15c and 101325 Pascals is 1.22505 kg/m3
Density of water at room temp is approx 0.999
Conversion of mm of water from the manometer readings into Pascals is therefore 0.999 x 9.80665 (gravity) = 9.79684
There's also a bunch of constants needed for the Dynamic Viscosity calculation for whatever the measurement fluid is (in this case air) and I can't remember whether those were in the Standard or I had to look them up elsewhere. I do recall having to do quite a bit of ploughing through other books in the local university library.
Most of the calculations are just to get the Discharge Coefficient of the orifice correct. If you're prepared to estimate that from tables instead and not bother about Reynolds Number, Kinematic Viscosity and the full Stolz Equation you can simplify the whole thing enormously but I decided to go the whole hog so it would work with any orifice size, pipe diameter etc and not just the actual setup for one specific bench.
The Reynolds Number calculation has to be an iteration because it both affects, and is affected by, the actual flow rate calculation. So you take an estimated starting point for the RN, feed that into the calculations, generate a new RN, feed that back into the calculations and so on until the RN stops changing.
Most important thing is to get the position of the manometer tappings correct without which the whole bench will fail to work. The one under the cylinder head MUST be right at the top of the downpipe directly under the cylinder head or under the bore adaptor the head sits on. You get pressure recovery further down that pipe and if the tapping is low down it'll read an incorrect pressure drop across the cylinder head or other test piece. That's the single most common error I've found looking at other people's home made flow benches and it leads to a horribly skewed flow profile where the percentage error changes as the mass flow changes so there's no simple way to correct it with a fudge factor.
http://wenku.baidu.com/view/768612260722192e4536f6...
In addition you need the Isentropic Exponent of air which is 1.4201
Air density at 15c and 101325 Pascals is 1.22505 kg/m3
Density of water at room temp is approx 0.999
Conversion of mm of water from the manometer readings into Pascals is therefore 0.999 x 9.80665 (gravity) = 9.79684
There's also a bunch of constants needed for the Dynamic Viscosity calculation for whatever the measurement fluid is (in this case air) and I can't remember whether those were in the Standard or I had to look them up elsewhere. I do recall having to do quite a bit of ploughing through other books in the local university library.
Most of the calculations are just to get the Discharge Coefficient of the orifice correct. If you're prepared to estimate that from tables instead and not bother about Reynolds Number, Kinematic Viscosity and the full Stolz Equation you can simplify the whole thing enormously but I decided to go the whole hog so it would work with any orifice size, pipe diameter etc and not just the actual setup for one specific bench.
The Reynolds Number calculation has to be an iteration because it both affects, and is affected by, the actual flow rate calculation. So you take an estimated starting point for the RN, feed that into the calculations, generate a new RN, feed that back into the calculations and so on until the RN stops changing.
Most important thing is to get the position of the manometer tappings correct without which the whole bench will fail to work. The one under the cylinder head MUST be right at the top of the downpipe directly under the cylinder head or under the bore adaptor the head sits on. You get pressure recovery further down that pipe and if the tapping is low down it'll read an incorrect pressure drop across the cylinder head or other test piece. That's the single most common error I've found looking at other people's home made flow benches and it leads to a horribly skewed flow profile where the percentage error changes as the mass flow changes so there's no simple way to correct it with a fudge factor.
Edited by Pumaracing on Monday 24th November 19:40
horsepowerfreek said:
David, once I doing all the reading and research is the program difficult to write
Depends how hard you find fairly basic high school maths.[quote]and what software would I use to put a program together?
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