| OCR Text |
Show MODEL DESCRIPfION A combustion model documented in (Fiveland and Jessee, 1994) is used to simulate natural gas combustion. The model is modular and is based on a fundamental description of the various interacting processes which occur during combustion: turbulent flow, gas phase chemical reaction, and heat transfer. Gas phase equations are solved using a control volume fonnulation of the Eulerian equations. The combustion model is based on a single block, structured collocated grid for the equations of mass, momentum, energy, and species. Burner geometries are represented as axisymmetric (r-z) or 3-D cylindrical, and local grid refinement is used to minimize grid-dependent solutions. Gas-phase Flow The flow module solves the equations for conservation of mass and momentum. Pressurevelocity coupling of the equations is obtained using the SIMPLE algorithm (Patankar, 1980). The technique of Rhie and Chow (1983) with the modification recommended by Majumdar (1988) is used to interpolate the control volume face velocities on the collocated grid. Turbulence is modeled using a standard two-equation k-£ model (Launder and Spalding, 1974). Radiation The discrete ordinates method (Fiveland, 1988) is used to solve the radiative transport equation (RTE) for an emitting and absorbing gray medium. The absorption coefficients of the gas mixture are found using Edwards' wide band models (Edwards, 1976). Chemistry The gas phase chemistry is modeled in two steps: 1) fuel is oxidized producing a pool of carbon monoxide and other products, and 2) the pool of carbon monoxide is oxidized producing carbon dioxide, using a rate limiting step between the turbulent mixing (Magnussen and Hjertager, 1976) and the kinetics. 3 |
