Modeling of a falling-film photocatalytic reactor: Fluid dynamics for turbulent regime

Abstract

The falling-film photocatalytic reactor is a photochemical device used for several environmental applications due to its simple buildup and its high solar radiation usage. As most of photocatalytic reactors, modeling the falling film photoreactor can be a challenging task. The most difficult aspect of modeling is the photon absorption by the solid catalyst. Nonetheless, modeling the fluid dynamics in turbulent regime of a falling film reactor can also be very demanding. In this work, the eddy viscosity approach was applied for estimating the average velocity profile and the film thickness for turbulent regime. Also, a sensitivity analysis was made for determining how different variables like: flow rate, tilting angle and fluid viscosity, affect to the average velocity profile and the film thickness. As remarkable results, it was found that the flow rate was the most significant operating variable and affects both considered parameters. The model was validated with experimental measurements of the film thickness at three different flow rates. The relative errors between the experimental values and the film thickness values estimated with the model can be considered as plausible, since the maximum was 13.06%. However, regarding to the local volumetric rate of photon absorption (LVRPA) estimation from the calculated and experimental values of the film thickness, the errors were negligible. According to previous works, high flow rates ensure the turbulent regime and therefore, the mass-transfer limitations due to catalyst settling can be avoided; but also with larger film thicknesses can reduce the photon absorption because of longer optical paths. So, the optimization of the photon absorption, based on the film thickness and restricted to the turbulent regime, is a necessary study that can be developed in a future work.