Transient radiative heat transfer within a suspension of coal particles undergoing steam gasification

Transient radiative heat transfer in chemical reacting media is examined for a non-isothermal, non-gray, absorbing, emitting, and Mie-scattering suspension of coal particles, whose radiative properties vary with time as the particles undergo shrinking by endothermic gasification. A numerical model that incorporates parallel filtered collision-based Monte Carlo ray tracing, finite volume method, and explicit Euler time integration scheme is formulated for solving the unsteady energy equation that couples the radiative heat flux with the chemical kinetics. Variation of radiative properties, attenuation characteristics, temperature profiles, and extent of the chemical reaction are reported as a function of time. It is found that radiation in the visible and near IR spectrum incident on a cloud of coal particles greater than 2.5 mu m is more likely to be forward scattered than absorbed, but the opposite is true as the particles shrink below 1.3 mu m. The medium becomes optically thinner as the particles shrink and this effect is more pronounced for smaller initial coal particles because these offer higher volume fraction to particle diameter ratio and, consequently, attain higher temperatures, reaction rates, and shrinking rates.