Compressed Air System Flow Rate
Compressed Air System Flow Rate
(OP)
I'm trying to ascertain the dynamics of a compressed air system. A simplified example would be to consider a 5.5 bar supply on 12mm OD nylon tubing to a spool valve with a 6mm OD outlets supplying an actuator 10 meters away.
So for simplicity I have treated the valve as an orifice reducing from 12mm to 6mm (in reality I realise there will be some pressure drop). Based on this assumption I have used Bernoulli's equation for incompressible fluids.
My concerns are:
A) The version of Bernoulli's equation I have used to my knowledge only applies to incompressible fluids or gases travelling at velocities lower than the speed of sound. So do I need to alter my formula?
B) I haven't allowed for friction or pressure drop in the valve or tubing. I would like to know how to calculate pressure drop and friction but I have no idea how. Any ideas?
I have attached a copy of my calculation from Mathcad as a PDF. Please take a look, if I have made any mistakes (likely) please let me know
Regards
Dan
So for simplicity I have treated the valve as an orifice reducing from 12mm to 6mm (in reality I realise there will be some pressure drop). Based on this assumption I have used Bernoulli's equation for incompressible fluids.
My concerns are:
A) The version of Bernoulli's equation I have used to my knowledge only applies to incompressible fluids or gases travelling at velocities lower than the speed of sound. So do I need to alter my formula?
B) I haven't allowed for friction or pressure drop in the valve or tubing. I would like to know how to calculate pressure drop and friction but I have no idea how. Any ideas?
I have attached a copy of my calculation from Mathcad as a PDF. Please take a look, if I have made any mistakes (likely) please let me know
Regards
Dan





RE: Compressed Air System Flow Rate
Patricia Lougheed
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RE: Compressed Air System Flow Rate
For now though, If you look at my calc you will see that I worked out the flow rate through my 6mm OD section to be 0.03 cubic meters/sec (1800 litres/min).
Really all I need to know for the time being is that will my flow rate change by more than say +/- 200 litres/min if I account for turbulance/pressure drops/friction etc.? just roughly
Regards
Dan
RE: Compressed Air System Flow Rate
RE: Compressed Air System Flow Rate
I cannot accept that just from reducing a 12mm OD air line at 5.5 bar to 6mm OD (a fairly standard procedure i'm sure) will cause such a problem?
RE: Compressed Air System Flow Rate
You reduced the flow area by 75%, that would cause a problem.
Sonic flow is about 343m/s.
Ted
RE: Compressed Air System Flow Rate
Thanks
Dan
RE: Compressed Air System Flow Rate
RE: Compressed Air System Flow Rate
Ted