Air Flow through a choke calculation

[daewoo]

What would be the airflow through a 4/1000" choke at 60 psi air pressure?

 

[TD2K]

I get about 0.86 scfh with an assumed air temp of 100F.

 

[quark]

TD2K!

I got 0.786scfh (density at 74.7 psia and 100 deg.F is 0.4322 lb/cu.ft and at std. conditions it is 0.0763 lb/cu.ft). What are your values? I think there may be mathematical errors due to unit conversion and rounding up in my calculation.

Daewoo! Here is a link for you.

http://www.air-dispersion.com/usource.html

Regards,


Believe it or not : Goldbach's conjecture says any even number can be written as a sum of two prime numbers. Postulated in 16th century, nobody could, so far, prove it nor disproove it.

 

[israelkk]

My calculatios using the Lee Company software gives 0.0146 scfm (0.414 Std Liter per Min). The orifice is 0.004" (~0.1mm) meaning 47500 Lohms. At 60 psig the absolute pressure is 74.7 psia at 100F. This is the theoretical flow rate. The actual flow can be 80-90% of this depends on the type of orifice.

 

[TD2K]

Quark, how do you get a density of 0.4322 lb/ft3? For air at 60 psig and 100F (14.7 psia atmospheric base pressure), I get 0.36 lb/ft3.

That still doesn't explain though why you are getting a lower flow rate since that higher fluid density 'should' make your flow rate higher. In any event, I'm pushing my spreadsheet, I should do a manual calc as a check.

Plus, since the Reynold's number is going to be low in the upstream piping (and the OP doesn't give the pipe ID), my estimate of the orifice coefficient is suspect.

 

[quark]

A little interpolation of the values stated here. The Cd I considered was 0.72 and I did the calculation as per the formula given in the above link. Anyhow I will check it as per Crane's Technical Paper this night.

http://www.cleandryair.com/air_density_3.htm

BTW, can you tell me whether the density data given in the above link is correct?

Regards,


Believe it or not : Pythagorus theorem was used 2500 years before Pythagorus was born.

 

[TD2K]

The values in the density link you provided look right. I use the equation density = P*MW/(Z*10.73*T)

density = lb/ft3
MW = lb/lbmole, 28.96 for dry air.
Z, unitless, taken as 1.0 for this example
T = absolute temperature, deg R

 

[israelkk]

I have used the exact formula that we have used/developed for designing high pressure very fast (100hz) ON-OFF electro-pneumatic valves and servo actuators, and received the same flow rate 0.41 Std liter per minute. This agrees with 0.86 scfh from TD2K.

 

[quark]

TD2K!

Would you please detail me your assumptions and method.

Regards,


Believe it or not : Pythagorus theorem was used 2500 years before Pythagorus was born.