Multiport Diffusers for Dense Discharge in Flowing Ambient Water

Experiments are reported on multiport diffusers typical of brine disposal from desalination plants discharging into flowing currents. Diffusers discharging from one side into coflowing and counterflowing currents and from both sides were tested. A three-dimensional laser-induced fluorescence system was used to determine bottom impact dilution, impact location, and rise height. The results were plotted in dimensionless form as functions of port spacing and current speed parameters and empirical equations were fitted. As the current speed increased, the impact location was swept farther downstream, rise height decreased, and impact dilution increased. The merging of closely spaced jets prevents intrusion into the space between the ascending and descending regions, which can alter the flow fields. The results did not become independent of port spacing, at least within the parameter ranges studied and the experimental uncertainty. Raising the diffuser above the bed, which allowed the flow to pass beneath it, can affect the flow patterns significantly. Dilutions were not significantly affected, however, possibly because the nozzles were elevated above the pipe with a spacing that allowed passage of entrained flow between them. The dependence of the observed flow patterns on relatively small changes in source conditions should be considered in diffuser designs to avoid constricting the diluting entrainment flow.