Modeling of light scattering in photochemical reactors

Heterogeneous photochemical reactions in fluid (water or air) environments have been pining increasing interest in the past fifteen years, the main application being in pollution abatement by solid semiconductor photocatalyzed systems. One of the unsolved problems is the proper evaluation of the rate of absorbed radiation energy by the participating medium due to the existence of simultaneous absorption and scattering. This is a key property in quantifying kinetic models and designing photoreactors. A model derived from radiative transport fundamentals and chemical reactor engineering concepts is presented. It permits a rigorous quantification of the local volumetric rate of radiant energy absorption (LVREA) inside the reactor. The method was experimentally verified by analyzing the scattering effects (performance changes) produced by addition of transparent, inert particles to a homogeneous photochemical reacting system. With the validated model, and employing radiation absorbing particles (titanium dioxide), the proposed approach was compared with other methods currently in use to evaluate the LVREA. It was shown, in a quantitative way, that the proper application of the radiative transfer equation is a requisite for obtaining accurate results. Finally, the results of changing particle concentration and particle size on the magnitude of the scattered light were explored.