Design Optimization of UV Reactor for Seawater Purification by Coupled Fluence Rate and Fluid Flow Simulations

Abstract

This paper presents new design of UV system for ballast water treatment in cargo ships and UV dose calculation platform which can be coupled with CFD tool to improve the disinfection efficiency. Numerical model is developed for UV inactivation process in the reactor with the realizable k-ɛ turbulence model, and multiple segment source summation (MSSS) fluence rate model is coupled to the predicted flow field through the reactor to estimate the reduction equivalent dose (RED) distribution. The stochastic tracking approach is used to describe the dispersion of particles based on the discrete random walk (DRW) model and all governing equations are solved utilizing commercial Ansys FLUENT software. Presence of short-circuiting flows near to the reactor wall with small residence time and low UV light exposure makes a negative impact on the reactor performance. In the proposed method, it is possible to capture these flow particles in order to determine the baffle structure dimensions to provide more uniform flow and fluence distribution. The results showed that with the final UV reactor design, short circuiting flows were effectively minimized subsequent to significant increase in RED.