Numerical modelling of horizontal flow in sand filters

Abstract

This research investigates the option of using horizontal sand filters for water filtration to replace the currently used vertical filters. This project carries out the investigation using computational fluid dynamics (CFD) software to develop an optimal configuration for a horizontal sand filter using baffles in the geometry to disrupt the flow. Saturated sand consolidates to 95% of its unsaturated volume and creates a channel in the top of a horizontally laid sand filter, which the majority of the water flows through due to Darcy’s law. Previous research on the topic has determined that the addition of baffles to disrupt the flow in the channeled area reduces this effect. The development of an optimum configuration was done using CFD software, and the findings were validated using experimental data. The numerical modeling results show that the optimal baffle spacing in the case of a 0.2m diameter pipe, for inlet velocities of between 0.002 and 0.01 m/s is 4.5cm with a baffle depth of 0.05m. More importantly it has been found that a relationship between the velocity profile and the baffle spacing exists which allows for filter designs to be optimised based on targeted filtration effectiveness.