Modeling Christopher R. Schulz, P.E., DEE CDM Inc. Denver, Colorado Carrie L. Knatz, P.E. and Veronica Ortiz CDM Inc. Carlsbad, California Joseph Yelpo Sunlight Systems, Inc Allendale, New Jersey Introduction Recent research has demonstrated that computational fluid dynamics and irradiance modeling (referred to as CFD-i modeling in this paper) can be used to accurately predict the fluence (or UV dose) in flow-through UV reactors. For example, the Metropolitan Water District of Southern California (Mofidi, 2004) compared predicted CFD-i modeling and measured validation testing results for a 3-mgd Calgon Sentinel reactor with four medium-pressure (MP) lamps. The model predicted validation results within 0.1 log reduction of MS-2 coliphage. Similarly, CFD-i modeling and biodosimetry testing results were compared for a 18-mgd Wedeco K3000 reactor with low-pressure high-output (LPHO) lamps under various lamp power and UVT conditions (Rokjer, 2002). The percent difference between predicted and measured reduction equivalent dose (RED) using B. subtilis as the target organism, ranged from 5 to 20 percent for CFD-i runs at ten different flow and water quality conditions. Due to its demonstrated accuracy, CFD-i modeling is now routinely used by UV equipment suppliers for developing new or optimizing existing UV reactor designs. This paper presents CFD-i modeling results for a new UV reactor design being developed by Sunlight Systems, Inc. of Allendale, New Jersey for drinking water disinfection applications. The results were related to: optimization of the UVBox reactor design; and, a comparison of the dose delivery and hydraulic efficiency of the UVBox reactor with an unbaffled annular reactor. CFD-i modeling was used to optimize the design of the UVBox reactor with respoect to: dose delivery (RED); residence time distribution (RTD); hydrodynamic flow patterns in the reactor; and, pressure drop across the reactor. Three UV reactor configurations were analyzed using CFD-i modeling: UVBox unbaffled reactor with 30-inch inlet/outlet flanges, rectangular vessel dimensions of 30 inches wide by 30 inches high by 30 inches long and four MP lamps positioned perpendicular to flow; UVBox baffled reactor with the same vessel dimensions and lamp configuration as above, plus six angled flow deflector baffles positioned upstream and downstream of the lamps to direct the flow closer to the lamp sleeves and introduce flow recirculation patterns between the upstream and downstream baffles; and, annular unbaffled reactor with 30 inch inlet/outlet flanges and tubular vessel dimensions of 30 inch inlet/outlet flanges and tubular vessel dimensions of 30 inches long by 30 inches in diameter. Includes 7 references, tables, figures.