A methodology for performing radiative transfer calculations in computational fluid dynamic simulations of gas-liquid multiphase flows is presented. By considering an externally irradiated bubble column photoreactor as our model system, the bubble scattering coefficients were determined through add-on functions by employing as inputs the bubble volume fractions, number densities, and the fractional contribution of each bubble size to the bubble volume from four different multiphase modeling options. The scattering coefficient profiles resulting from the models were significantly different from one another and aligned closely with their predicted gas-phase volume fraction distributions. The impacts of the multiphase modeling option, initial bubble diameter, and gas flow rates on the radiation distribution patterns within the reactor were also examined. An increase in air inlet velocities resulted in an increase in the fraction of larger sized bubbles and their contribution to the scattering coefficient. However, the initial bubble sizes were found to have the strongest impact on the radiation field. 1. Introduction 1.1. Challenges in Modeling Multiphase Radiative Transfer Modeling radiative transfer in multiphase flows is important in several applications such as solid fuel combustors [1, 2], externally irradiated gasifiers [3], photocatalytic reactors [4, 5], and photobioreactors (PBRs) [6, 7]. While the procedure for coupling radiative transfer with the hydrodynamics has been well established in dilute multiphase flows (local dispersed phase volume fractions less than 10%) such as pulverized fuel combustors [8], the effect of radiative transfer is often neglected or grossly simplified in computational fluid dynamic (CFD) simulations where all the phases are present in significant fractions such as bubbling bed and circulating fluidized bed gasifiers [9, 10]. This simplification often takes the form of an “optically thin” radiation exchange between the phases to approximate the radiative source term in the phase energy equations. In the optically thin approximation, a radiation temperature of the phases is computed and is employed in conjunction with the phase thermodynamic temperature, an empirical radiative heat transfer coefficient to compute the radiative source term, and consequently the temperature change in the phases resulting from radiative heat exchange. Since a rigorous solution to the radiative transfer equation (RTE) is not carried out in this approach, the optically thin approximation cannot predict the radiative fluxes at different
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