discharge time from compressed tank

[spvega]

Thank you for receiving me in this forum.
Need help to determine the time required to drain a pressurized tank.
It's a 5 cubic meters tank, with air at 100 psi and need to drain to atmosphere through a 12 mm orifice.
Problem is that the tank pressure will be gradually reduced as it is being drained, so I assume the flow is being reduced, and cannot find the rationale (formula) to determine the time used to fully drain the tank (to 0 psi).
Thank you for the help.
Sergio

[admin]

In order to solve this problem you should use equations for non steady flow which is differential equation. At the moment I do not have the solution but will try to answer it later.

[spvega]

Thank you for your assistance. Hope you can find it. Will try on my side as well.

[pedrosydow]

I have the same problem.. Anyone can help us?