Numerical Computational Fluid Dynamics-Based Models of Ultraviolet Disinfection Channels

Various numerical modeling approaches, all based on computational fluid dynamics (CFD) solutions for the flow field, are studied for an ultraviolet disinfection system in which the lamps are oriented perpendicular to the flow direction. A two-dimensional model assumption is made in all simulations, for which turbulent flow solutions were obtained with commercial CFD software (FIDAP). Two modeling approaches were studied. A continuum Eulerian approach was taken in formulating an appropriate advection-diffusion equation which is solved for the viable micro-organism concentration. Alternatively, a Lagrangian approach, in which particles are numerically introduced into the flow and their trajectories through a spatially varying field of ultraviolet intensities were computed, was also investigated. The effect of modeling unsteady-flow features associated with vortex shedding and motion on the extent of disinfection was examined by comparing time-averaged results based on an unsteady-flow continuum model with the results from an analogous simulation assuming a steady flow. Under the steady-flow assumption, differences between predictions of the Eulerian continuum approach and the Lagrangian particle-trajectory approach were also considered. Both modeling approaches yielded similar predictions over a range of loadings, and tended to underestimate the extent of disinfection when compared to measurements at the pilot scale.