A 2-D transient multicomponent simulation model: Application to pipe wall corrosion

A transient multicomponent water quality (WQ) model of a distribution system is developed and then applied to the problem of predicting the concentration of corrosion-related chemicals released into a bare pipe system. The modeled reactions include dissolved oxygen (DO) which oxidizes iron (Fe) at the pipe wall to produce ferrous and hydroxide ions (Fe2+and OH−). These chemicals can then interact to produce substances like iron hydroxide, which ultimately deposits on the pipe wall. In this study, 1-D and 2-D simulation models are considered and the movement of each chemical is represented by the advection-diffusion-reaction equation (ADRE), which is coupled to the continuity and momentum equations for flow. A five-region turbulence model is used to represent cross-sectional variations and a combination of finite difference and characteristic methods are used to integrate the governing equations. The effects of key parameters (e.g., pH, initial DO concentration, and pipe diameter) are briefly explored and clearly show an increase in dissolved iron with increasing initial DO and pH, and in smaller pipes. The study highlights the influence of velocity profile on the diffusion of oxidants from the bulk flow to the pipe wall and thus underlines the importance of both the turbulence structure and pipe diameter to reactions in general and to corrosion in particular.