# How to give different flow velocity to air and methane at the same inlet??

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 February 7, 2011, 11:36 How to give different flow velocity to air and methane at the same inlet?? #1 New Member   ravi teja Join Date: May 2010 Posts: 7 Rep Power: 8 Hi I am trying to simulate combustion in a multiple slot burner used in an idealized household boiler Inlet velocities of fuel slot of methane and primary air are given as 1.013m3/hr and 11.57m3/hr respectively. I am at a loss as to how to give 2 inlet velocities at the same boundary condn(mass_flow_inlet). Plz Help~~

 February 7, 2011, 20:13 #2 Senior Member   Real Name :) Join Date: Jan 2010 Location: United States Posts: 193 Rep Power: 8 It looks like you're trying to specify the inlet based upon volume fractions. If that's the case, what you want to do is change volume fractions to a mass fraction, specify the inlet velocity such that it gives you the appropriate in situ volumetric flow rate, then voila! If you're unsure how to do this, let us know. Those two gases behave pretty ideally, so this isn't a tough problem to set up by mass. ComputerGuy

February 16, 2011, 09:50
#3
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ravi teja
Join Date: May 2010
Posts: 7
Rep Power: 8
Quote:
 Originally Posted by ComputerGuy It looks like you're trying to specify the inlet based upon volume fractions. If that's the case, what you want to do is change volume fractions to a mass fraction, specify the inlet velocity such that it gives you the appropriate in situ volumetric flow rate, then voila! If you're unsure how to do this, let us know. Those two gases behave pretty ideally, so this isn't a tough problem to set up by mass. ComputerGuy
Thank you very much for taking time out to reply Computer Guy.
The case that i am trying to run is from an article called "Sensitivity of temperature and concentration measurements in hot gases from FTIR emission spectroscopy"
In the article the flow rates of methane, primary air( methane +air), and secondary air are given as 1.013m3/hr, 11.57m3/hr and 1.93m3/hr respectively
I took your advice and found out the mass fractions and specified the corresponding inlet velocity for primary air(7.67m/sec) and secondary air(0.178m/sec) by dividing the volumetric flow rate by the area of cross section.
I am running the simulation in 2D
Unfortunately with the above inlet velocities i am getting an absurd result.

Last edited by dharanishb; February 17, 2011 at 07:41.

 June 13, 2011, 14:52 #4 New Member   Ahmed khamis Join Date: Jun 2011 Posts: 4 Rep Power: 7 now i am trying simulate the same burner but i am failed i need help meca_zag@yahoo.com

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