OCR Text |
Show The Eddy Breakup model The Magnussen eddy breakup model is an intuitively simple model , where the reaction rate is computed as the minimum of the kinetic reaction rate and the mixing rate. Also, for global reaction modeling, it is computationally tractable. The natural gas composition is as shown in Table 3. Associated species included CO2, N2, O2, and H20. Mass balance equations are solved for each species. To account for the effects of dissociation of combustion products, the average specific heats of CO2, H20, and O2 were modified according to Table 4. Specific heats for other species were taken from J ANN AF tables. Inlet Flows Air Fuel Mixture Mass Fraction of "fuel" 0 0.97 Mass Fraction of CO2 0 0.008 Mass Fraction of N2 0.7685 0.022 Mass Fraction of O2 0.2315 0 Table 3: Mass Fractions in the Inlet Flows for the Eddy Breakup Model Species CO2 H2O O2 ao 5.35446e+02 1.9378e+03 8.7632e+02 al 6.39334e-01 -5.90386e-01 6.1414e-02 a2 -1.8225ge-04 1.2145e-03 1.8610e-04 a3 -5.9556e-08 -7.1582e-07 -3.0062e-07 a4 3.78408e-11 1.5191e-10 2.2948e-10 as -8.5396e-14 a6 1.2237e-17 Table 4: Coefficients of the Polynomial Function Defining the Specific Heat Capacities of the Species The source and the sink terms in the chemical species transport equations are computed according to the Magnussen model. Here, the rates and formation and destruction of the chemical species considered are related to eddy dissipation rate. The reaction rate is computed to be the minimum of the kinetic and the mixing rates as described by Magnussen and Hjertager[3]. No modifications were made to the values of the mixing rate coefficients A and B originally suggested, i.e., A = 4 and B = 0.5. The combustion reaction for the single step scheme was described according to: fuel + 2.03302 ---4 1.022C02 + 2.022H20 For the two-step scheme, the reaction was described by: fuel + 1.52202 ---4 1.022CO + 2.022H20 The conserved scalar pdf model (2) (3) (4) The pdf model is extremely useful when time scales of reaction are much smaller than the mixing time scale. Under these conditions, the entire reaction mechanism can be described by a system of species going to equilibrium. Such 3 |