| OCR Text |
Show The constants b1,2 and Cl,2 are derived from burner geometry and from averaging of the in-flame measurements to best represent the generic furnace, as shown in Fig. 2a, and hence are independent of the burner scale. The resulting proportionality constants are b1,2 = 1.8 and 4, respectively, and Cl,2 = 0.83. Under perfect aerodynamic similarity, the volumes then scale as (10) and the constants d1,2 are 1.27r and 1.57r, respectively, from b1 ,2 and Cl ,2 given above. The size of the near-burner region changes with turndown. Based on the in-flame data, V1,2 are taken to scale with turndown as - Q Vl,2lturndown = Vl,2Ifull-load' Q full-load where Q is the actual thermal input and Q full-load is the design thermal input. 4.1.2 V in Flan1e-Sheet Region (11) The flame-sheet region is an idealized representation of the primary reaction zone, as shown schematically in Fig. 10c. The thickness of the flame-sheet [) f is assumed to be independent of thermal scale and input variations, and based on strained flame calculations is taken as [) f ~ 1 mm. The flame-sheet volume then scales with the flame geometry as (12) Assuming perfect aerodynamic similarity, these geometric parameters scale with burner size Do in Table 1 as (13) \vi th I h corresponding to the visi ble flame length. The constants b3 ,4 are taken as 2.5 and 1, respectively, based on the visible flame length, in-flame measurements, and the burner geometry. Under turbulent conditions, the true flame surface is several times larger than suggested by the visible flame length, and thus additional factor of 3 is used to account for wrinkling of the flame surface. Approximating the shape by a cylindrical shell, the flame-sheet volume then is given by Vflarne-sheet = a3' D~ . [) f (14) where, given the constants for I h,2 above, the constant a3 = 157r. 4.1.3 V in Furnace Region The furnace region accounts for NOx formation in the bulk of the furnace interior, where the temperature and oxygen concentrations are relatively uniform. The dilnensions of this region are determined by the geometry of the furn ace, as shown in the schematic diagram in Fig. 10d. The volume thus scales as (15) 9 |
