CFD modelling of an annular reactor, application to the photocatalytic degradation of acetone
Résumé
This study deals with the photocatalytic degradation of acetone, which is a typical pollutant of indoor air, in an annular photoreactor. The TiO2 photocatalyst is deposited on a fiberglass support and irradiated by a commercial fluorescent tube placed at the center of the device. Acetone conversion extents up to 90% are obtained for low initial concentrations. Neither external mass transfer nor internal diffusion limitations are observed, and the annular reactor is first assimilated to a plug flow reactor. The Langmuir Hinshelwood model gives a good description of acetone degradation, and kinetic and adsorption parameters can be analytically deduced of the performed experiments. A Computational Fluid Dynamics description of the reactor is then proposed. The classical Navier-Stokes equations describe the flow in the free zone, whereas the Brinkman equation is used for the description of the flow in the porous zone. From an hydrodynamic point of view, a very good agreement between theoretical and measured Residence Time Distribution or upward velocities is obtained, testifying for the good description of the photocatalytic reactor. For a given illumination, the variations of acetone concentration inside the reactor can then be modelled. Comparison between theoretical and experimental outlet concentrations allows finally a better precision in the determination of the Langmuir Hinshelwood kinetic parameters. A relative difference of about 15% appears between the two sets of kinetic parameters (obtained assuming a plug flow or deduced from the CFD modelling). CFD simulations of photocatalytic reactor can thus address a better design of such air treatment devices.