[pmccourt]

Hi,

I am trying to set the inlet to a specific phase (nitrogen at Inlet) to simulate mixing with air

However the options for volume fractions etc are not showing up.. giving the message "This page is not applicable under current settings"

I have enabled multiphase VOF.. is there any obvious setting I am missing to enable this page?

[Tony.Kang]

I'm assuming you're trying to set the volume fractions in the boundary conditions, correct? If so, when you click your boundary condition for your inlet, you should be able to access a drop down menu under Phase (it should be located directly under the box that lists all your Zones). It's probably set to Mixture, so just go to phase-1 and set your inlet boundary condition (e.g. velocity, mass flow rate, etc), though you wont be able to set the volume fraction for phase-1. Then toggle to phase-2 and set its boundary condition, then you should be able to access the multiphase tab and set the volume fraction for phase-2. Phase-1's volume fraction, I assume, is just 1 minus the sum of your other phases' volume fractions.

Hope this helps; I got stuck on this part for quite a bit myself.

[ComputerGuy]

This isn't really a multi*phase* simulation (unless you're talking liquid nitrogen and vapor "air"). This is a multicomponent simulation. I'd familiarize yourself with the multicomponent tutorials (specifically, look at examples of species transport). These will give you what you want!

ComputerGuy

[pmccourt]

Thanks for your reply,

Although both phases are the same (both gases), there is no chemical reactions between the two fluids. For this type of problem is not suitable to use the multiphase approach instead?

[ComputerGuy]

The lack of chemical reaction doesn't prohibit using the species transport models (what's the difference between a non-reactive system and a system which has an infinitesimal reaction rate?). I would strongly consider using this instead. A quick google search yields the following Fluent tutorial http://www.afs.enea.it/project/neptu...tg/node224.htm which can help you get started. Just take out or ignore the stuff on the reaction side; let the user manuals guide you how to do this.

Although you could probably "fake" similar results with a multiphase simulation, I don't believe it's appropriate to use.

If you're stuck on using a multiphase simulation, recall you will have to handle the mass transfer from one "phase" to another. Fluent has some very basic mass transfer mechanisms already defined. Otherwise, all you'll have is ever-decreasing sizes of pure nitrogen "bubbles" floating in your air. Physically, this isn't correct. You need to diffuse the air into the nitrogen and nitrogen into the air to get a more appropriate representation of the physics.

Try out the species model; let us know if you're stuck.

ComputerGuy

Originally Posted by pmccourt

Thanks for your reply,

Although both phases are the same (both gases), there is no chemical reactions between the two fluids. For this type of problem is not suitable to use the multiphase approach instead?