1 Copyright © 2014 by ASME MULTI-GROUP TWO-PHASE FLOW MODEL OF DRIFT DROP PLUME Vladimir M. Agranat Applied Computational Fluid Dynamics Analysis Thornhill, Ontario, Canada Sergei V. Zhubrin Applied Computational Fluid Dynamics Analysis Thornhill, Ontario, Canada Igor Pioro University of Ontario Institute of Technology Oshawa, Ontario, Canada ABSTRACT A homogeneous two-phase multi-group model of drift drop plumes emerging from natural draft cooling towers has been developed and validated using the experimental data obtained in the 1977 Chalk Point Dye Tracer Experiment (CPDTE). The conservation equations for mass fractions of water droplets having different sizes are solved in addition to the standard conservation equations for mixture mass, momentum, energy, water vapor mass fraction and turbulent quantities (turbulent kinetic energy and its dissipation rate). Extra terms are provided to the conservation equations for mass fractions of liquid water to account for the drift of water drops due to their gravitational settling. Various formulations for drift velocity and terminal velocity have been tested and compared. The phase change effects (condensation, evaporation, solidification and melting) are assumed to be negligible due to specific conditions of the experiment. The droplet-size distribution available at the cooling tower exit and containing the 25 groups of drops is simplified to 11 groups. Also, the 3-group and 1-group options are considered for comparison. The individual drop deposition fluxes and the total deposition flux are calculated and compared with the experimental data available at the sensors located on the 35° arcs at 500 and 1000 m from the cooling tower centerline. The total deposition flux is calculated as a sum of products of individual group mass concentrations of water drops and corresponding terminal velocities. The model has been incorporated into the commercial general-purpose Computational Fluid Dynamics (CFD) code, PHOENICS. The study has demonstrated a good agreement between the CFD predictions and the experimental data on the water vapor plume rise and the total drift deposition fluxes. In particular, the plume rise predictions agree well with experimental values (the errors are from 4% to 34% at different distances from the tower centerline). The predicted deposition fluxes are in agreement with the experimental values within a factor of 1.5, which is well within the industry acceptable error limits (a factor of 3). The model developed is recommended for analyzing the drift drop plumes under the conditions similar to CPDTE conditions of small Stokes numbers. It is easier to use and not less accurate than the multiphase Eulerian-Lagrangian CFD models used recently by various researchers for modeling CPDTE plume. The model has a potential to supplant or complement the latter in the computational analyses of gravitational phenomena in complex two-phase flows in engineering equipment and its environment. INTRODUCTION Over the past three decades, CFD (see Versteeg and Malalasekera (1995) for more details) has been increasingly used as a predictive tool in the analyses of plumes emerging from industrial settings such as cooling towers, etc. It is becoming a validated and user-friendly computational tool in the environmental assessments of dispersion and deposition of pollutants. The standard practice is to use the commercial general-purpose CFD codes such as PHOENICS, ANSYS FLUENT, ANSYS CFX, etc. for such analyses. In particular, Markatos et al. (1987) used the PHOENICS software for studying the behavior of cooling tower effluent under various environmental and operating conditions. They developed a customized homogeneous two-phase flow model accounting for the water droplet drift via inclusion of additional source terms into the conservation equations for mass concentrations of water vapor and water droplets. The phase change effects were accounted for and the specific formulae Proceedings of the 2014 22nd International Conference on Nuclear Engineering ICONE22 July 7-11, 2014, Prague, Czech Republic ICONE22-30010