CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

N2 flow in air

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 20, 2015, 08:15
Post N2 flow in air
  #1
New Member
 
Simone Spanu
Join Date: Feb 2015
Location: Italy
Posts: 2
Rep Power: 0
simospanu is on a distinguished road
Hello,
I'm new here, so hi to everybody !
I'm writing because i have a problem in fitting my simulation to experimental data.
The simulation is about a tunnel with a conveyor belt at its bottom and three inlets on its top. At the beginning the tunnel is full of air and N2 is flowing inside of it from each inlet. I set it up as a multicomponent simulation, creating a variable composition mixture of air ideal gas and N2 ideal gas. On the inlets i set mass flow rate and N2 mass fraction equal to 1. At the beginning and at the end of the tunnel i set an opening condition (N2 mass fraction equal to 0 and atmospheric pressure). Then i ran it for 4 s with a time step of 0.02 s.
With this configuration I achived N2 mass fraction of about 0.77 in the tunnel and Air mass fraction of 0.23, from which i calculated O2 residual (about 5%).
From the tests i have that O2 residuals at the tunnel center is between 1% and 2% wich means i have a much higher N2 concentration there!
I tried to modify some parameters but the simulation result doesn't get better.
I was thus wodering if my model is correct and if there's a way to improve it.

Many thanks.
simospanu is offline   Reply With Quote

Old   February 20, 2015, 08:38
Default
  #2
Senior Member
 
Join Date: Jun 2009
Posts: 1,880
Rep Power: 33
Opaque will become famous soon enough
If you are interested in O2 mass fraction, or concentration, does it make sense to consider Air as a pure substance with fixed composition? Is the N2 in the Air different than the one being injected that is not allowed to mix ? Similarly, is the Air composition in the test accurately known before N2 is injected ?

I would have setup the case as variable composition made of O2, N2 and Ar (if you think it matters). Setup the initial condition for the domain to the known composition of Air (say 78%N2, 21%O2, 1%Ar +/- tolerance), and perform the calculation.

Then, you can compare your results to the tests. I would check for sensitivity to the initial conditions, is your Air O2 rich, or O2 deficient ? You are looking at differences of 1->2% between tests and simulations w/o stating the deviation on the tests.

Hope the above helps,
Opaque is offline   Reply With Quote

Reply

Tags
air, cfx, gas, multicomponent, nitrogen


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
mass flow in is not equal to mass flow out saii CFX 12 March 19, 2018 06:21
Modeling the mixing of air and kerosene in a flow channel StefanG CFX 3 June 11, 2012 21:21
air bubble is disappear increasing time using vof xujjun CFX 9 June 9, 2009 08:59
Problems modeling subsonic engine air inlet with flow separation TWaung CFX 2 March 29, 2009 19:42
Air flow inside infant incubator housing...help!!! Danny Ditroia Phoenics 0 March 30, 2008 22:24


All times are GMT -4. The time now is 14:55.