Simulation of Light Propagation in Photochemical Fixed-Bed Reactors Using a BRDF-Based Model

Modelling light transport in fixed-bed photochemical reactors can be challenging if the geometry of the packing is the object of investigation. In this manuscript, we present a physically-based model of light transport for the simulation of fixed-bed photochemical reactors to be coupled with explicit consideration of reactor geometry: spatial properties of the fixed bed, such as size, shape, distribution and quality of the surface of packing particles are used as input variables. The existence of a catalytic coating on the packing surface, and its major properties such as spectral coefficient of absorption and surface rugosity can also be easily coupled with the light propagation algorithm. The model was built upon the framework of the bidirectional reflectance distribution function (BRDF), using the microfacets theory (MFT) to evaluate an approximate solution. As an example of application, easily measurable experimental data, such as UV absorption/extinction spectra and surface roughness, and readily available literature data on spectral refractive indices are used as inputs to calculate (i) the fate of the irradiated energy (percentage absorbed, transmitted and scattered-out) and (ii) the spatial distribution of the scattered rays. Taken together, these output data should offer the engineer guidelines for the design of fixed-bed photochemical reactors with optimised light collection and distribution.