Experimental investigation on optimization of invert trap configuration for sewer solid management

Invert traps have been successfully used to collect sediments at convenient locations within the sewer network, where large volumes of solids can be stored. In the present study, experiments have been performed in 15 cm wide and 5 m long channel for the measurement of retention ratios of five different invert trap configurations (namely, rectangular, trapezoidal with one side vertical, trapezoidal, trapezoidal with rectangular base, rectangular with trapezoidal base) having top width of 32 cm and depth of 28 cm with slots of three different sizes (namely, 5, 9 and 15 cm) for the flow of seven different sediment types (namely, two types of sand, glass beads and four types of plastic beads) at different flow rates for each trap. The flow rates selected in present study cover entire range of flow rate expected in channels during dry weather flow and monsoon. Flow field and retention ratio predictions for each invert trap configuration have been carried out using CFD modeling with the help of FLUENT software using Renormalization Group (RNG) k–ε along with Discrete Phase Model (DPM). The simulation results are capable of showing particle trajectories, the effect of flow rate and trap geometry on the flow patterns, developed within the trap. Based on CFD modeling and experimental measurements, it is concluded that the invert trap having rectangular shape with trapezoidal base is the most efficient trap configuration with highest sediment retention ratio.