OCR Text |
Show Refinery Reater Simulation by Rottel Zoning Method Integrating from 0 ~ r ~ ~ , the axial momentum H is related to the total mass flow Wz by H - Wz2 K / 2 ~ Pz z2 Eq. 12. For a nozzle having a uniform velocity profile, its momentum Is H - Wn 2 / ~ Pn rn2 Eq. 13. where P is the flue gas density. The total mass at z to that entering is Eq. 14. 13 A simplified picture of the jet is to treat it as a cone having a half angle Q and to relate a to the Gaussian flow constant K by: K tan2 Q - 2 Eq. 15. Albertson et aIlS summarized their results by [2/Kl~ - 0.16 which is equivalent to Q equals 9.l R and K - 78. For weak swirl, up to S - 0.6, Beer and Chigier16 recommend K - 92 / (1 + 6 S) which is equivalent to a maximum Q equals l7.5 R • The user specifies the jet half angle and the throat diameter for each burner. The total flue gas flow at each XY plane in the finer mesh is computed by momentum balance and the recirculation flow outside the jet by the continuity equation. The transformation from the cone geometry to XYZ mesh is made assuming constant velocities within and outside the cone. 2. Plane of Maximum Recirculation The radius, r c ' of the jet at z to the nearest surface zone, r w , was taken from the IJmuiden hot furnace data 17 : Eq. 16. For a natural draft heater , rc/rw is about 0.6. 3. Dissipation of Momentum 15. Albertson, H. L. et aI, "Diffusion of Submerged Jets", Proc . ASCE, 71, 1571-96 (1948) 16 . Beer, J.H. and N. A. Chigier, "Combustion Aerodynamics" Halstead Press Div., John Wiley (1972), Section 2.1 Jets 17. Beer , J.M. and N . A. Chigier, "Combustion Aerodynamics" Halstead Press Div ., John Wiley (1972), Figure 2.17 |