[mumtaz ersan]

Hello Everyone,

I draw some kind of nozzle and then try to obtain pressure-drop in my drawning,

Actually in my system, 1,1 bar inlet pressure at 120lt./min air passes through from this nozzle(At 298 Kelvin),

i test the system in two different way,
My first way, i use the volume-flow;
For my inlet face, i define 0,002 m^3/sn=120lt./dak air ,
For my outlet face, i define environment pressure,
Then i define a goal for my inlet to obtain static-pressure,
And calculate DeltaP = Environment-Static Pressure in the inlet face and i obtain 84,72 Pa....

In my second way , i decide the use mass-flow because of it is compressible fluid,
For my inlet face, i define 0,0026 kg./sn mass-flow ,
For my outlet face, i define environment pressure,
Then i define a goal for my inlet to obtain static-pressure,
And calculate DeltaP = Environment-Static Pressure in the inlet face and i obtain 101,2 Pa....

I am a little bit confused,

I think it is better to trust in my second way calculation because of it is mass-flow, Am i right?????

And which way is better for these kind of examples ,to define volume-flow, mass-flow or Velocity ??????

Can anyone explain this situation?????

[Chris_321]

Measure the density (or temperature) at the inlet and compare the volume flow with the mass flow to find the difference between your simulations.
Whats the "better" simulation depends on what you have measured and what you want to calculate.

[mumtaz ersan]

Hello Chris, First of all , thanks for your answer,

I tried to do your suggestion and i find the density on the inlet surface,The Flow-simulation said me , the density is 1,18....

Actually, in my conditions are like this;Temperature=298 K,R(constant value)=0,287 and my pressure is 1,1 bar(110 kpa),So at this conditions if i calculate density by my manually, i find the value ;density is 1,2862...

In my first way;
If i use density(which i got from Flow-simulation);
Volume-flow*density=mass-flow
0,002(m^3/sn)*1,18=0,00236 but my actual mass-flow must be 0,0026 so it looks like it isn't quite good,

In my second way;
Mass-flow/density=Volume-flow
0,0026/1,18=0,0022(m^3/sn.)=132lt/min, it isn't correct because i know only 120lt/min is pass through the nozzle...

Still, i am confused , i don't define the inlet-pressure to the program, so i don't expect the actual density value from the program but still which way is more trustable, because From both of them , i got uncorrect results....

For example , to calculate Kv value for this nozzle...

I hope, i can explain why i am confused....

[Chris_321]

Do you use air?

I would suggest you define a Fluid named "Air@Simulationparameters" and set a constant density to your specific needs.

I just wonder why EFD takes 1,18 as Density not something around ~1,29

[mumtaz ersan]

Yes, i use air,

I think, you mean to define a new material for my need,
But , when i try to define a new material, i can't define a density,Program let me only define name,specific heat ratio,dynamic viscosity,specific heat capacity and thermal conductivity....

Is it possible to define a constant and specific density to a user-defined gas????

[Chris_321]

Hello,

it is possible. You can specify the density trough the molar mass

[mumtaz ersan]

Hello,

I can't manage to define specific density, But maybe i can define inlet pressure to the inlet boundary in addion to volume-flow,

Is it possible to define inlet-pressure and volume-flow at the same time to the inlet boundary????

If it is yes,Program can calculate the desired density....

You can see circled area in the attach. pic.,In this circled area can i define inlet pressure????

And lastly,

In the results,After calculation finish, Program gives me Total-pressure value in the inlet boundary, Is this value gauge or absolute pressure????

By the way , thanks again for your interest and answers....

[mumtaz ersan]

I hope at this time, i can manage to add a pic....

[Chris_321]

Did you solved your problem?

[mumtaz ersan]

Hello Chris,

Actually, i couldn't solve...

I try to define volume-flow and also inlet pressure for inlet boundary condition to get the desired density.(I am not sure , do i have a option in flow-simulation to define volume-flow and also inlet pressure to the same boundary??? but i tried it)

I define 0,002 m3/sec. (which means 120 lt/min) for inlet volume-flow and also i changed the the default pressure value to 110000 Pa(Which means 1.1 bar)

In attachment pic., i circled the areas which are filled by me, But nothing is changed. i got the same results...

In Flow-simulation i can only define inlet-velocity,inlet-vloume-flow,inlet mass-flow, Do i have a chance to add inlet-pressure?????

[Chris_321]

The flow just depends on the pressure difference in a system. You can have 5 l/min with a delta_p of 100 mb at 1,1 bar inlet and 1,2 bar outlet.

If you have 5 l/min at 5 bar at the inlet the outlet pressure will change to 5,1 but the pressure difference will be the same.


I would still follow my suggestion about creating a specific gas, that has just one temperature independent density.
If you cant define the density then do it with the molar mass.

The molar mass is Density * R * T/p

R: 8,314472 J/K mol
T:Temperature
p : pressure

Good luck.

[mumtaz ersan]

Hello Chris,

I want to thanks for your interest and help,

You are very kind and willing to help,

Thanks again....

[Chris_321]

Hello,

thats what im here for. Everybody need guidiance at the beginning. Just like my post when they help you.

Regards
Chris