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Show In this paper, an empirical correlation is derived for calculating the particle residence time for an entrained flow reactor with a coaxial jet flow nozzle. The turbulent mixing is characterized by an eddy viscosity determined from a mixing length model. The panicle size change is related to the overall particle burnout. The correlation is verified against the calculated particle residence times using the computer code PCGC-2 (Pulverized Coal Gasification or Combustion, Two-Dimensional; Smith et al., 1985). 2.0 COMPUTER SIf\1ULATIONS OF GAS·PARTICLE FLOW In order to determine the particle residence times, the complete gas-particle flow was simulated fITst using a readily available computer code, PCGC-2 (Smith et al., 1985). The mathematical model and the numerical method are presented in detail in Smith et al., (1985) and Celik and Chattree, (1988). Some of the major features are described briefly below. The gas flow model solves the time averaged conservation equations in an Eulerian frame of reference. The velocity, pressure, temperature and density of the mixture are calculated by solving numerically the conservation of mass, momentum and energy equations along with the equation of state for ideal gases. The turbulent transport terms that appear in the time averaged equations are determined via the standard k -E model; where k is the turbulent kinetic energy and E is the dissipation rate of k. The partial differential equations are discretized by integrating over a finite control volume and then solved in sequence using the SIMPLER algorithm (patankar, 1981). The mixing of the gas streams -- the primary (coal conveying gas), the secondary (oxidant), and the coal-off gas -- is tracked by solving the transport equations for the mixture fraction of the primary stream, f, and the coal off-gas mixture fraction,,,. The reactor is assumed to be adiabatic, hence, the mixture enthalpy can be calculated from h = [f hp + (1 - f) hsl (1-11) + 11 he where, hp , hs and hc are the enthalpies of the primary, secondary and coal off-gases, respectively. Crocco similarity (i.e. equality of turbulent diffusion coefficients) is invoked so that the mixture properties such as the density, temperature and species concentrations are unique functions of f and 11. The time averaged mixture properties are calculated by convolution of these functions with appropriate probability distribution functions for turbulent fluctuations. -3- |