| In this dissertation, a two-dimensional Computational Fluid Dynamics (CFD) method is developed to account for the influence of the vortex shedding which occurs from the UV lamps in Ultraviolet (UV) treatment channels on the efficacy of the disinfection process. The focus is on the high Reynolds-number regime where turbulent flow conditions prevail and where there exists a strong interaction between the organized mean-flow periodicity due to the vortex shedding and the random turbulent motions. The modified k -- epsilon turbulence model which takes into account the modification of the turbulence energy spectrum due to vortex shedding is adopted for most studies in this dissertation. Various flow situtations are validated against experimental data and other researchers' numerical works: (i) single square and circular cylinder, (ii) two circular cylinders in side-by side and tandem arrangemwnt, (iii) single square cylinder and four circular cylinders in a diamond-liked configuration.;There are two approaches, Lagrangian and Eulerian, used in predicting the UV disinfection efficacy. With Point Source Summation (PSS) model to estimate the UV intensity field and first order Chick-Watson equation to model microorganism inactivation kinetics, both approaches are applied to predict the disinfection efficacy in the vertical lamps system. Three kinds of lamp arrangement in terms of the number of lamps are discussed: (i) four UV lamps, (ii) eight UV lamps, and (iii) twenty-five lamps. The disinfection efficacy predicted by the Lagrangian is relatively conservative compared with Eulerian. Besides, Grid Convergence Index is used to estimate numerical prediction error. The last work of this disertation is to discuss the furtreatment plant. It is showed that the lost disinfection efficacy can vary by different positions but the same number of lamp failures. |
