# mass fraction of species

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 30, 2011, 06:33 mass fraction of species #1 Senior Member   Join Date: Feb 2011 Posts: 128 Rep Power: 6 Hello everybody, I have got a understanding problem concerning the mass fraction of a species in a mixture at Fluent. I looked up the definition of mass fraction for the case of Fluent: “Mass fraction of species-n (in the Species... category) is the mass of a species per unit mass of the mixture (e.g., kg of species in 1 kg of the mixture).” I have a geometry with one inlet and two outlets. According to the definition of mass fraction I expected the mass fraction at the inlet to be the sum of the mass fraction at the two outlets, but unfortunately my results differ from that expectance: In my case the mass fraction of the inlet and the mass fraction of each outlet are equal (that means the sum of the mass fraction of the outlets is twice as large as the mass fraction at the inlet). I am really confused! Can somebody help me to understand this? Thanks a million in advance! Lilly

 June 30, 2011, 13:16 #2 Member   Micael Boulet Join Date: Mar 2009 Location: Quebec, Canada Posts: 95 Rep Power: 9 You expect that the mass going in is the same as the mass going out. This is correct, but it is wrong to expect the mass fraction at the inlet to be the sum of the mass fraction at the outlets. It could be totally normal that they equal, as you experience. Look further into the concept of mass fraction, you will understand. --- edit: I mean: ...the mass going in... (corrected) Last edited by Micael; July 5, 2011 at 17:31.

 July 4, 2011, 08:14 #3 Member   Byron Smith R J Join Date: Mar 2009 Location: India Posts: 46 Rep Power: 8 hai Mass fraction in a steady, unreacting flow is independent of quantity. for example if you pass air through inlet and the mass flow rate is divided into two at the outlet, the mass fractions of oxygen and nitrogen remain same both at inlet and outlet. mass fractions change only when reactions or additional species inlets are induced in the flow. then mass fractions are calculated using the species transport equations. hope it helps in clearing your doubt

 July 25, 2011, 05:00 #4 Senior Member   Join Date: Feb 2011 Posts: 128 Rep Power: 6 Thank you Micael and byronsmith for your help (and sorry for the late reply)! I thought about what you were writing and I finally found my error in reasoning. Thanks a million!

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Attesz CFX 7 January 5, 2013 04:32 saii CFX 2 September 18, 2009 08:07 paean OpenFOAM Running, Solving & CFD 0 November 14, 2008 22:14 Ahmed FLUENT 0 April 18, 2007 11:57 zhou FLUENT 0 March 3, 2004 23:55

All times are GMT -4. The time now is 22:53.

 Contact Us - CFD Online - Top