Residence time distribution and dispersion in a contact tank

Historically, contact tanks have been designed by empirical correlation, physical model studies, or tracer studies conducted after the contact tank has been built. Recently, computation fluid dynamics (CFD) models have been applied to investigate flow and solute transport in disinfection tanks. The objective of the paper is to present the preliminary results of a numerical study undertaken to investigate hydrodynamics and turbulent transport and mixing inside a contact tank. Flow field was obtained using standard k-ε model. Tracer transport was analyzed in the cases of a pulse release using the advection-diffusion equation. Transient concentration data were used to derive residence time distribution (RTD) function for the tank in order to evaluate its performance. Finally, dispersion coefficients were computed for the tank and they were finally related to the standard deviation of the cross-sectional profile of longitudinal velocity inside the tank