Learning Forum

[Ammar Ahmed]

Hello everyone, 
I am trying to simulate a tank filled 90% with fluid (lets say water) and is pressurized by nitrogen gas in the 10% volume availabe in tank. I am confused as to which physical model should i use to simulate this as my main aim is to see pressures achived at outlet. The nitrogen is maintained at 230 bars and water is supposed to be maintained at 60 bars so thatr at outlet i can get 60 bar with 3kg/s flow rate. the inlet and outlet dias are 25.4 mm. I have a pipe attached at outlet as shown below

[Rob]

OK, have a look at the various options in Fluent. Gas can be compressible, so that's not a problem. But.... If you already know the pressure and flowrate, what are you trying to find out from the model? 

[Ammar Ahmed]

The aim is to find out inlet conditions at which i can have a specific mass flowrate and pressure of water at outlet of pipe and what is the expected pressure drop.

[Rob]

So you don't need the free surface? Water isn't compressible (well mostly it isn't) so you can push the desired mass flow though the system and find the pressure loss.

[Ammar Ahmed]

Sorry didnt understand your point can you please elaborate.

[Rob]

Part of the CFD modelling process is working out what you actually need in the model. In your case, if you want to know the tank pressure to get a set mass flow, and given water is incompressible, how much do you really need to include?

[Ammar Ahmed]

Thankyou for your help I just have one more question.

So i performed cfd with different inlet speed and i got my desired inlet and outlet mass flowrate but the static pressure at inlet and outlet is 33 MPa and 10 MPa.  How can I calculate the pressure drop theoratically and from CFD? Is the difference of static pressure at inlet and outlet the pressure drop?

 

[Rob]

Inlet P - Outlet P = dP. It really is that simple for incompressible fluids; just watch you're comparing like for like pressure. 

[Ammar Ahmed]

Great Thanks