I need to calculate the flow rate of air through a 3/4" orifice from the pressurized side of a 1000 PSI (~250 cu ft at pressure) tank to the open atmosphere and know the time it will take to release 20%  35%  50% of the volume of the pressure tank.
Tank size ~1.5 cu ft at atmospheric pressure, ~250 cu ft at max working pressure. (approx. 2500 PSI)
Basically I need to know how to calculate the the flow rate of a high pressure tank discharging to the atmosphere by knowing the following:
1. Tank Volume at pressure.
2. Tank pressure.
3. Tank orifice size.
4. Assume a discharge nozzle length of 1" the same size as the orifice.
5. Using an explosive burst disk to initiate the flow (time 300 ns)
The flow calculator at pipeflowcalculations.com/airflow are not doing the trick for me due mostly to my inability to completely understand their use.
High pressure tank discharge rate calculation

 Posts: 3
 Joined: Sat Dec 31, 2011 10:18 pm

 Posts: 57
 Joined: Sat Sep 17, 2011 8:50 am
Re: High pressure tank discharge rate calculation
Calculator for gas discharge is under development and will be available soon. But your problem is calling for nonsteady flow calculation which is another kind of problem.
Here are results for 1000 psi 3/4" orifice discharge (chocked flow):
1. pressure in position 1 (p1):
p1 : 1000 psi
2. pressure in position 2 (p2):
p2 : 101325.0 Pa  atmospheric pressure
3. pressure drop (p1p2):
p1p2 : 6793675 Pa
4. tube diameter (D):
D : 0.75 in
5. volume flow rate (q1):
q1 : 204.95366 m3/h
6. weight flow rate (w):
w : 17096.828 kg/h
7. velocity (V1):
V1 : 199.74394 m/s
8. expansion factor (Y):
Y : 0.606
9. temperature (T1):
T1 : 288 K
10. density (ρ1):
ρ1 : 83.41802 kg/m3
11. gas constant (R):
R : 287 J/kgK
12. K factor  minor losses coefficient (K ):
K : 1.5
Please note that q1 is on p1 and T1. To have it on standard conditions that flow should be converted: q=13947 m3/h; p=101325; T=288K
Mass of air in the tank will change over time as air flows out of the reservoir and on 50% of pressure 50% of mass will be in it (volume is the same).
For 1" pipe 3/4" diameter I get 202 m3/h which is almost the same as without it (q1=205 m3/h).
Here are results for 1000 psi 3/4" orifice discharge (chocked flow):
1. pressure in position 1 (p1):
p1 : 1000 psi
2. pressure in position 2 (p2):
p2 : 101325.0 Pa  atmospheric pressure
3. pressure drop (p1p2):
p1p2 : 6793675 Pa
4. tube diameter (D):
D : 0.75 in
5. volume flow rate (q1):
q1 : 204.95366 m3/h
6. weight flow rate (w):
w : 17096.828 kg/h
7. velocity (V1):
V1 : 199.74394 m/s
8. expansion factor (Y):
Y : 0.606
9. temperature (T1):
T1 : 288 K
10. density (ρ1):
ρ1 : 83.41802 kg/m3
11. gas constant (R):
R : 287 J/kgK
12. K factor  minor losses coefficient (K ):
K : 1.5
Please note that q1 is on p1 and T1. To have it on standard conditions that flow should be converted: q=13947 m3/h; p=101325; T=288K
Mass of air in the tank will change over time as air flows out of the reservoir and on 50% of pressure 50% of mass will be in it (volume is the same).
For 1" pipe 3/4" diameter I get 202 m3/h which is almost the same as without it (q1=205 m3/h).
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 Posts: 3
 Joined: Sat Dec 31, 2011 10:18 pm
Re: High pressure tank discharge rate calculation
Thank you very muck for your time and trouble, this information will be very useful.

 Posts: 6
 Joined: Tue Mar 13, 2012 6:21 pm
Re: High pressure tank discharge rate calculation
Hi
My problem is very similar to the previous one. I need to know how internal pressure i need to have in a reservoir of 8 m3, to achieve a discharge mass flow of 45 kg / min instantaneously via an outlet 2.5".
Thanks.
My problem is very similar to the previous one. I need to know how internal pressure i need to have in a reservoir of 8 m3, to achieve a discharge mass flow of 45 kg / min instantaneously via an outlet 2.5".
Thanks.
Re: High pressure tank discharge rate calculation
You can use gas discharge calculator (now it is finished), but it is for steady flow. As reservoir discharge, pressure will decrease and so will flow rate.
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 Posts: 3
 Joined: Sat Dec 31, 2011 10:18 pm
Re: High pressure tank discharge rate calculation
Again thank you for your efforts and continuing to assist me. I now have enough information to scale the tanks I am going to be using.
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