Mixing behavior of multiport diffusers with non-uniform port orientation

Abstract

This study addresses the disposal of hypersaline brines from desalination plants through multiport diffusers into seas and oceans. Experiments are reported on multiport diffusers with non-uniform port orientations to limit the negative effect of jet merging on the mixing process, thus augmenting dilution. Laboratory experiments on uniform and non-uniform diffusers, with varying port angles in the range of highest reported dilution rates for dense discharges (40°-70°), are reported. Concentration fields were mapped using the laser-induced fluorescence (LIF) technique, and the major flow properties and merging processes were compared. Investigations revealed that the non-uniform diffusers had 22 % to 25 % higher dilution rates, attributed to different mixing behavior in the interaction zones. Non-uniform port orientation provided more space between the jets to expand before interacting with their neighbors, resulting in higher dilution rates. This study questions the application of formulae obtained from experiments conducted with single jets for multiport diffuser designs and proposes considering source characteristics specific to multiport diffusers, such as angle difference, for the efficient design of desalination outfalls. The new data and analysis can benefit the design of desalination discharge systems with environmental risk reductions and potential cost savings due to shorter diffusers with non-uniform jet orientations.