OCR Text |
Show equations. In the flux approximation to the integro-differential radiative transfer model, the anisotropic scattering term is modeled by assuming that the radiation is scattered into one of six mutually orthogonal directions--forward, backward and the four sides. This approximation leads to ordinary differential equations for flux sums (sum of the forward and backward flux) Rx' Ry , and Rz • The equations are: ..!!(r dRx ) + S = 0 dx dx x (14) d ( dRy) - r- + S = 0 dy dy y (15) ~ (r dR,) + Sz = 0 dz \ dz ( 16 ) where, 1 r = K (1 - Wf + Wb) t (17) and S x = K t [-(I-Wf-Wb)Rx -2WsRx +2Ws(Rx +R y +R z )+2(I-W)Eb ] (18) S = K [-( l-Wf-Wb)R -2WsR +2WS(R +R +R )+2( l-W)E ] y t y y x y z b (19) S = K [-( l-Wf-Wb)R -2WsR +2Ws(R +R +R ) +2( l-W)E ] z t z z x y z b (20) In Eqns.(17)-(20), Eb is the black-body emissive power, f is the fraction of radiation scattered in the forward direction, b is the scattered component in the backward direction, s is the scattered component in a sideward direction and W, the albedo for scatter, is defined as: K K W = s 5 = (21) K + K K sat 2.6 NO Formation Model In coal combustion, pollutant reactions occur during the entire sequence of particle reactions including: coal devolatilization, gas phase reactions and reactions with char. In the gas phase, NO can be formed by three separate reaction processes: thermal NO, 5 |