Stagnation Reduction in Drinking Water Storage Tanks through Internal Piping with Implications for Water Quality Improvement

Abstract

Poor mixing in storage tanks can cause stagnant zones that could pose negative public health effects. To eliminate stagnant zones in a cylindrical water storage tank, this study investigated the feasibility of a novel internal piping configuration consisting of a sprinkler-type inlet piping that distributed the incoming flow evenly across the water surface and a corresponding upside-down sprinkler draining configuration at the tank bottom. The experiments were conducted on seven types of inlet and outlet configurations. Experiments were performed using acoustic Doppler velocimeter (ADV) and electrical conductivity (EC) measurements. Various stagnation metrics, like the time for the water to be well mixed, and water particle velocity and direction, were used for each configuration. In addition, a new metric is introduced to evaluate short-circuiting conditions in storage tanks. Inlet or outlet convergence time is defined as a simple indicator in which the lower the value, the higher the risk of short-circuiting. In the next step, experiments were performed with a temperature difference between the tank and the inflow because of density-driven flows. Results indicated that the novel piping resulted in parallel downward streamlines that eliminated most of the stagnation zones in the tank.