Constant mass flow rate, pressure differential through a valve


#1

Hi!

I am simulating an in-compressible steady flow through a Choke valve with the objective of validating the pressure drop through the valve against experimental values. The conditions are as stated:

Inlet mass flow = Outlet mass flow = 2.116 kg/s (through mass conservation)
P_inlet = 17.595 MPa
P_outlet (experimental) = 17.237 MPa
Area_inlet = Area_outlet = 0.00342 m^2
Rho_inlet = Rho_outlet = 994.98 kg/m^3 (constant)

I would like to prescribe the inlet pressure and measure the outlet pressure. For this, I have used P_inlet and Outlet mass flow, No-slip walls and Symmetry as my B.C.'s. The problem I am facing is that as soon as I prescribe the inlet (or exit) pressure, I get velocities in the domain exceeding 10^6 m/s which is of course not the case.

Below is the link to my project:
https://www.simscale.com/workbench/?pid=2450536785748278493#tab_2-0

The only way I get correct values for the pressure drop is if I set P_inlet = 0 Pa (gauge) and Outlet mass flow which gives me the Delta_P caused due to structures in the domain [Simulation run: Incompressible_Steady_State_April_24_Condition_1_A]. I would like to see the effect of changing input pressure keeping the mass flow constant through out the domain.

Looking at the project, do you think I have made a mistake somewhere in creating the simulation? I have tried multiple iterations of the boundary conditions (combinations of different conditions), but nothing seems to be working. Looking forward to your help! Thank you!

Cheers,
Aadit


#2

Hi Aadit!

I think we might have such an example in the project library but I am not 100% sure. @Get_Barried, @vgon_alves & @Anware , can you guide our user please?

Cheers!

Jousef


#3

Hi guys,

My question is, are not you interested in considering the output pressure equal to input? After all in both you are having something about 17MPa. If it serves for you, you can set the variational pressure inlet and set the outlet pressure constant.

I’m jumping in the project now, I’m not an expert on valves but I can already say that you can see the effect of changing your input pressure using a .csv file which contains the time and the P variation like this:
csv

Hope it helps you!
I keep curious about your project. Certainly another PowerUser will give you more tips.

Cheers,

Vinícius


#4

Hi Vinícius,

Thank you for your reply. According to my understanding, I was getting diverging results due to the boundary conditions I had imposed on the domain.

The inlet and exit areas are the same, and the flow is incompressible. Manually calculating velocity at the inlet (continuity equation) and using the Bernoulli equation for velocity at the outlet gives two different values for velocity, hence violates mass conservation.

Instead, only prescribing inlet total pressure (in order to drive the potential difference) and inlet (= outlet) mass flow rate (to enforce continuity satisfaction), I get the pressure drop across the valve body at varying inlet pressures. You could have a look at the new simulation runs (Condition_1…Condition_5) if you are interested. Thank you, @jousefm for your participation in solving my problem!

Cheers,
Aadit

P.S.: If you do end up looking at the runs and possibly find some anomalies, please do get back to me! :slight_smile: