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## Simulation CFD

Contributor
Posts: 24
Registered: ‎05-22-2013

# Setting up high pressure flow

111 Views, 4 Replies
05-22-2013 07:48 AM

I have a system operating at 510psi and need to analyze the flow.  I'm not sure how to set this up.  I've looked into 'compressible flow' but I don't think this fits because I'm not compressing the gas with the actual flow. Here are my conditions:

Ambient pressure = 510 PSIG

Flow Rate = 4.7 CFM

Flow gas = 98% He, 2% O2

On systems that are at 1 ATM, I simply create a boundary condition at the inlet for the flow rate and a 0 PSI condition at the exit.  Can I simply create a new flow material that is the corresponding density (of the He/O2 mix at 510 PSI) and set up the analysis the same way?

Product Support
Posts: 971
Registered: ‎08-25-2011

# Re: Setting up high pressure flow

05-23-2013 12:26 AM in reply to: DelNegro

Hi,

I think first we need to clarify Compressible. This is used if we are likely to see high enough mach number to cause the gas density to change. To start with, run incompressible and take a look at the flow speeds and maximum mach number to decide if we need to switch to a compressible model. Post up the results from your first analysis and we can help you decide.

You could create a new material for sure, is it different enough from pure helium to be worth it? Changing the fluid density to suit the higher pressure would be fine, although if we need to switch to compressible, you would need a material where the density is able to change.

You can increase the environmental pressure by right clicking on Materials and increasing the value from ambient up to the desired level.

If you can run incompressible, start with a modified material and let's see what the results direct us towards. Then we can look to change the environmental conditions etc.

Thanks,

Jon

Jon Wilde
Contributor
Posts: 24
Registered: ‎05-22-2013

# Re: Setting up high pressure flow

05-23-2013 05:55 AM in reply to: DelNegro

Thanx Jon.  I don't think the flow will be high enough to be compressible. I didn't realize that there was an ambient pressure setting in the material as well.  That sounds like what I will need. I'll run it and let you know what happens.

Contributor
Posts: 24
Registered: ‎05-22-2013

# Re: Setting up high pressure flow

05-23-2013 11:04 AM in reply to: DelNegro

I ran a test (not my actual device, as I'm still waiting on files) to see if I could see any difference with the changes you suggest.  I ran the first test with the standard He and the second with the ambient pressure set to 510psi.  The results were identical.  Would you expect this?

Product Support
Posts: 307
Registered: ‎08-31-2011

# Re: Setting up high pressure flow

05-29-2013 08:11 AM in reply to: DelNegro
Tony,
The results can be simliar between the two depending on the stup of the model.
For sea level we might have had 0psi at theoutlet and the CFM at the inlet.
For your situation you can run with the same and modify the Material Environment (this will change the reference pressure such that materials that are based on the Eq. of State will compute a new density at that pressure).

The density between 1ATM and 500psi is quite a bit such that for the same Volume flowrate i would expect that you have different mass flowrates through the system.

Your getting identical mass flowrates and pressure drops through the sample model with the modified environment?

As Jon mentioned this would be our approach and then if we see high enough velocities we would consider running compressible.