An assessment is made of the importance of vortex shedding which occurs from UV lamps on the efficacy of disinfection in UV channels. The focus is on the high Reynolds-number regime where turbulent flow conditions prevail and where there exists a strong interaction between the periodic mean-flow unsteadiness and the random turbulent motions. Simulations are performed of the flow around four circular lamps with axes perpendicular to the flow and which are arranged in a diamond configuration. Turbulence closure is achieved using a modified version of the k − ɛ model which takes into account the modification of the turbulence energy spectrum due to vortex shedding. The disinfection efficiency is estimated using a Lagrangian approach in which the trajectories of massless particles are tracked to estimate their residence time and the dose received. The modified turbulence model shows that the occurrence of vortex shedding produces wide variation in the particles trajectories and, consequently, in the UV dose received. These and other results strongly suggest that the effects of vortex shedding on disinfection are very important and thus must be accounted for if the uncertainties inherent in the use of computational fluid dynamics (CFD) for the design of UV treatment channels are to be reduced.
Keywords: CFD, disinfection, Lagrangian dose estimation, turbulence modeling, UV, vortex shedding