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-   -   How to give different flow velocity to air and methane at the same inlet?? (http://www.cfd-online.com/Forums/fluent/84721-how-give-different-flow-velocity-air-methane-same-inlet.html)

 dharanishb February 7, 2011 11:36

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

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~~

 ComputerGuy February 7, 2011 20:13

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

 dharanishb February 16, 2011 09:50

Quote:
 Originally Posted by ComputerGuy (Post 294078) 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.