1 reply to this topic

[pleckner]

Yes, if the pressure drop is less than 10% of the upstream pressure, then you can use incompressible flow equations for gases/vapors. However, I urge you to look at the the Isothermal flow equation (can be found in any fluids book or Perry's). This is just as easy as using Darcy and you won't have to be concerned about the magnitude of the pressure drop.

Any other guidelines? Just one big one. You must check for choked flow (or critical pressure) first. If you have choked flow or critical pressure, then your pressure drop will be greater than 10% of the upstream pressure and the incompressible equations will no longer apply. This is why I urge you to use the simple Isothermal flow equation. It will apply to choked conditions as well.