CHAPTER 14: Fundamentals of Radiation Transport in Absorbing Scattering Media

In photocatalytic process there is always at least one elementary step initiated by artificial or natural (solar) radiation. This activated step takes place after absorption of photons having the required energy. The rate of photon absorption by the photocatalyst, needed to formulate the reaction rate of the initiation step, can be obtained by means of a radiation balance. The radiative transfer equation (RTE) applied to absorbing and scattering media is derived from radiation energy transfer fundamentals. From the RTE, expressions to calculate the local volumetric or surface rate of photon absorption for polychromatic irradiation are presented. The boundary conditions for integrating the RTE are described considering: emission models of tubular lamps with superficial or voluminal emission, reactions initiated by solar radiation, and reactions performed with chemical actinometers. Finally, the main numerical methods of solving the RTE applied to participating (absorbing and scattering) media are briefly described. This rigorous approach to fundamentals of radiation transport in absorbing and scattering media can then be used for the analysis, design, optimization and scaling-up of photocatalytic reactors.