Micro-segregated two-dimensional fluid and mass transport modelling in unsteady rotating annular photocatalytic reactor

Abstract

Rotating annular photo-reactor (RAPR) is the state-of-the-art solution to the global challenge of wastewater treatment. Its widespread application needs elemental theoretical. In this work, the reactor is segregated into repetitive units of identical squares, each with one photocatalyst particle. First-principle based two-dimensional unsteady fluid and convective-diffusive-adsorptive-reactive mass transport equations are considered. For the solution, finite element method based COMSOL Multiphysics software v5.6 has been used. The numerical solution methods are based on the weak formulation of the PDE system and discretizing the system with the Galerkin method. The simulated results are grid-size independent. Spatial concentration variation in the unit domain and the optimum ratio of inter-particle distance and particle diameter are recognized. The effect of Peclet number, adsorption rate, capacity, convection rate, are analyzed. Sizing of annular space and mass transfer profile evolution with Peclet and Damkohler number is investigated. The model is experimentally validated for varied contaminant concentrations and catalyst dosages. Detailed mass and momentum boundary layer analysis in the micro-domain reveals importance of space variation for comparable rates of adsorption, desorption and reaction. Parametric study denotes that the ratio between adsorption and reaction rate should be minimum 10 for best reactor performance. The optimum system parameter α has been identified as 10. The concentration gradient is much stronger for smaller ratio of inter particle distance and particle diameter. With small values of Da1 and Pe, the mass transfer rate becomes more important as the reaction progresses. This study will contribute immensely towards optimisation, scale-up and customization of RAPRs.