Plunging jets are investigated as potential outfalls for the discharge of brine from desalination plants. Compared to offshore submerged outfalls that rely on momentum to induce mixing, plunging jets released above the water surface utilize both momentum and negative buoyancy. Plunging jets also introduce air into the water column which can reduce the possibility of hypoxic zones. For unconfined plunging jets, the entrained air bubbles sink to a penetration depth below the water surface with a modest dependency on the jet density. In contrast, confined plunging jets include a downcomer around the jet which increases the penetration depth of the bubbles and can provide better aeration. However, the presence of this downcomer can hinder mixing with surrounding water. Laboratory measurements of dilution are made with both unconfined and confined plunging jets. In addition, qualitative observations of bubble penetration depth are also used to discuss aeration potential. For designs that increase the bubble penetration depth as compared to unconfined plunging jets, results show that dilution decreases as the depth of the downcomer is increased. However, it is shown that confined plunging jets can be designed with a short downcomer to achieve a higher dilution than unconfined jets. The effect of the downcomer diameter on dilution is also investigated and a non-monotonic effect on dilution is observed.

Use of plunging liquid jets for the dilution reject brine from desalination plants

ACS Fall 2021

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