OCR Text |
Show qwall = lwall,leaving - 2:= In· O/m 11incident(O/)W'm (31) n·{1'm<O (32) where the leaving intensity is indicated by the situation when n . 0 > 0 The above computational procedures serves as a basis for the CFD /Heat Transfer code, called FERA2, which has been developed in the CAGCT at Queen's University over 5 years. The FERA2 code is the mathematical furnace model to be investigated in this work and compared to the CACGT research furnace. A Ts quadrature set of Thurgood [12] was used in this calculation. Two grids were employed, 45xllx30 and 91x21x61, to model the combustion chamber. The computation was carried on an IBM RS/6000 AIX workstation. 5. Treatment of the Flames and the Burner exit Geometries Employing a high-order combustion model, to model flames in large-scale furnaces with many and complex burners definitely requires a fine grid to capture details of fields near the burner exit. This grid will be too fine for the bulk of the furnace. For example, in the case of the CAGCT furnace, one burner requires at least 15 more additional control volumes in each direction. This leads to the enormous computational demands to solve the problem. For large scale furnaces, active combustion zones typically occupy a minor fraction of the furnace volume. In the present work, focused on furnace heat transfer, we therefore treat gases leaving the burner exit as fully burn adiabatic combustion products. Enthalpy, temperature, heat capacity and compositions of the gas products are computed as in local thermodynamic equilibrium. Dissociation was taken account. The burner exit is modeled by an array of contiguous square ports presenting approximately the same gross area. An example of the transformation of the burner exit geometry is shown in Fig. 5. Constraints to satisfy macro-scale physics, such as mass flux, momentum flux, total enthalpy flux and C/H/N/O element ratios are imposed on the simplified burner exit. These macro-scale physics match the real burner. At given C/H/N/O rations and specific total enthalpy, constraints on mass and momentum flux alone dictate two levels of velocity on the burner exit. Three levels of velocity will require an additional constraint. In this work, two levels of velocity are used. The detail of the calculation the velocity levels on the simplified burner exit is given by Becker [16]. 9 |