Mathematical modelling of lamella plate settle hydraulics

Abstract

A small-scale physical model of a high-rate, inclined-plate settler was used to gather data for modelling water treatment plant hydraulics. The objective of the experiment was to test the validity of the Rebhun and Argaman (RA) simplified model and the several-reactors-in-series (SRS) model to predict flow pattern characteristics. Sodium chloride and dye were used as tracers to analyse the hydraulic behaviour of the fluid in the settler under several experimental conditions. Test variables included number of plates, inlet manifold and outlet spill configurations. Response variables included water velocity in the cells and the resident time distribution of the fluid within the vessel. Photographic visualisations of flow patterns in the unit were also performed. In all the experiments, the hydraulic behaviour of the unit departed from the ideal plug-flow configuration. Both the RA and SRS models predicted the occurrence of local plug flow and perfectly mixed areas within the vessel with similar accuracies, but failed to predict stagnations and short-circuit areas. Further implications on the use of RA and SRS models are discussed.