Gas flow equation and the utilisation of compressibility factor

[Prag]

Hi there,

Which equation of state (or the gas flow equation) is used in computing the compressible gas flow in the pipes? 

Also since viscosity, specific gas constant, specific heat are the only possible gas properties that can be entered in the pumpsim presets how does it account for the compressibility factor for a gas mixture? using what method? (In my understanding the compressibility factor is a function of reduced pressure and reduced temperature which is again a function of the individual gas properties of the  gases in the gas mixture).

Also can you explain what is free air quantity (someone from pumpsim did explain but I didn't understand fully)

Regards,

Pragathi

[Martin Griffith]

Hi Prag, 

The flow is calculated using the Darcy Weisbach equation, with the density calculated with the Ideal Gas law. The temperature, specific heat and the gas constant need to be set by the user. Pumpsim cant calcualte these for mixtures. The users needs to configure the mixtures themselves and determine the properties themselves. Including gas mixing in the Pumpsim solver is something we are working on for the future. 

The Free Air Quantity is the flow rate, but with the gas at standard density, rather than the local density in the pipe. This is sometimes useful with compressible gas flows where the quantity is changing along the pipe with the change in pressure and density. The Free Air Quantity is similar to a mass flow, it will only change where flows meet at an intersection, so can be more "readable".

[Prag]

Thank you.