Development of a CFD-based model for the simulation of immobilized photocatalytic reactors for water treatment

• Main Author: Duran, Jose Esteban Duran
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/27443

A computational fluid dynamics (CFD) model for the simulation of immobilized photocatalytic reactors for water treatment was developed and evaluated experimentally. The model integrated hydrodynamics, species mass transport, chemical reaction kinetics, and irradiance distribution within the reactor. For the development of this integrated CFD model, each of the above phenomena was individually evaluated against experimental data and proper models were identified. The experimental evaluation was performed using various configurations of annular reactors and UV lamp sizes, over a wide range of hydrodynamic conditions (350<Re<11,000). The comparison of modeling and experimental data indicated that the developed CFD model was able to successfully predict the photocatalytic degradation rate of model pollutants (benzoic acid and 2,4-D) in the analyzed reactors. In terms of hydrodynamic models, the results demonstrated that the laminar model performed well for systems under laminar flow conditions (error < 8%), whereas the Abe-Kondoh-Nagano (AKN) low Reynolds number (error < 12%) and the Reynolds stress (RSM) (error < 19%) turbulence models gave accurate predictions of the coated photoreactor performances under transitional or turbulent flow regimes. The degradation prediction capability of the CFD model was largely determined by the external mass transfer prediction performance of the hydrodynamic models utilized. The developed radiation field model included the lamp within the computational domain allowing to incorporate important interactions between the UV radiation, the quartz walls, and the Hg vapour inside the lamp. A modification of the extensive source volumetric lamp emission model that incorporates the high photon absorbance/re-emission effect produced by the Hg vapour in the lamp (ESVERA model) showed excellent agreement with near- and far-field experimental data. An effective optimization design approach which combines CFD modeling and the Taguchi design of experiments (DOE) method was presented for annular reactors with repeated ribs as external mass transfer promoters. The statistical analysis showed that the reactor performance was improved using small outer tube diameters, large inner/outer tube diameter ratios, intermediate (rib height)/(hydraulic diameter) ratio, and small (rib pitch)/(rib height) ratios. Moreover, the (rib height)/(hydraulic diameter) ratio was the design parameter having the greatest impact (57%) on photoreactor performance.