UV reactor performance modeling by Eulerian and Lagrangian methods.

A study was performed to investigate the influence of hydrodynamics on the performance of ultraviolet (UV) reactors. Two general UV disinfection models were developed by integrating fluence rate models and inactivation kinetics within a commercial computational fluid dynamics (CFD) software package to predict reactor performances. Both a particle tracking (Lagrangian) random walk model and a volumetric reaction rate based (Eulerian) model were implemented. Simulations were performed for two characteristic annular single-lamp UV reactor configurations, with inlets concentric (L-shape) and normal (U-shape) to the reactor axis. Two fluence rate models, the infinite line source assumption and the finite line or multiple point source summation (MPSS), were used. First-order inactivation kinetics was assumed for disinfection, with rate constants from MS2 bacteriophage assays. The simulation results provided detailed information on the velocity profiles, reaction rates, range of absorbed dose, and areas of short circuiting of the UV reactors. Model predictions based on both the Lagrangian dose distribution and Eulerian concentration distribution were in good agreement with each other at high flow rates but showed some discrepancies at lower flow rates. Experimental verification of the general models was performed by simulating the disinfection performance of an industrial prototype UV reactor. Results from both integration approaches were shown to be in good agreement with the provided biodosimetry data.