# PROBLEM: Scalar mass fraction

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 July 14, 2008, 03:49 PROBLEM: Scalar mass fraction #1 Lorenzo Guest   Posts: n/a Dear all, I've got a problem with some scalars in my model. The numerical domain is represented by a slice of a cylindrical burner, in which I have imposed symmetry boundary condition, pressure condition both for the inlet and outlet. The model uses also the EBU combustion model. The model presents the following setup for the scalars: CH4 (Active, Transport), MIX_1 (Passive, Transport), O2 (Active, Transport), CO (Active, Transport), H2O (Active, Internal), N2 (Active, Internal), MIX_2 (Passive, Transport), CO2 (Active, Internal). N2 is also the background fluid. The Inlet boundary condition presents the following definition: CH4 (85%), N2 (15%) and MIX_1 (100%). The Outlet boundary condition presents the following definition: O2 (23.3%) and N2 (76.7%). The scalars initialization presents the following definition: O2 (23.3%) and N2 (76.7%). By running the simulation with the above setup I got good residual convergence, but if I do some post processing I point out that at the Inlet, the N2 mass fraction is not 0.15 (as imposed by the boundary condition) but is almost 0%. Therefore I have tried to modify the scalar solution method by changing only the N2 solution method from Internal to Transport, such as: CH4 (Active, Transport), MIX_1 (Passive, Transport), O2 (Active, Transport), CO (Active, Transport), H2O (Active, Internal), N2 (Active, TRANSPORT), MIX_2 (Passive, Transport), CO2 (Active, Internal).By running the simulation with the above setup I always got good residual convergence, but if I do some post processing I point out that at the Inlet the N2 mass fraction is now right at 0.15, but the O2 mass fraction all the computational domain is not 0.233 (as imposed by the initialization) but is almost equal to zero. Have you got any idea in order to solve this problem and have the right mass fraction for all the scalars?

 July 14, 2008, 03:50 Re: PROBLEM: Scalar mass fraction *NM* #2 Lorenzo Guest   Posts: n/a