Confined Plunging Liquid Jets for Dilution of Brine from Desalination Plants

Ishita Shrivastava,Edward Eric Adams,Jongyoon Han,Aaron Chunghin Chow,Bader Al-Anzi

doi:10.3390/pr9050856

Ishita Shrivastava, Edward Eric Adams + Show 3 more

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https://doi.org/10.3390/pr9050856

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Abstract

Confined plunging jets are investigated as potential outfalls for the discharge of desalination brine. 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. In contrast to unconfined plunging jets, confined plunging jets include a confining tube, or 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. Therefore, laboratory measurements of dilution are reported here and compared to the dilution of unconfined 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 provide higher dilution than unconfined jets. The effect of the diameter of downcomer on dilution is also investigated and a non-monotonic effect is observed.

Highlights

Seawater desalination is a major source of freshwater for many parts of the world
Confined plunging jets behave to unconfined plunging jets which are described in detail by Chow et al [10]
The jet entrains air as it falls through the headspace and this entrained air is injected in the water column with the jet

Summary

Introduction

A by-product of seawater desalination is reject brine, which is typically discharged back to the sea. Especially those with shallow water, brine is pre-mixed with seawater or power plant cooling water and discharged using surface canals (Figure 1a), which provide limited mixing with ambient water [2]. To get better mixing, brine can be discharged using high momentum submerged outfalls [6,7,8,9] or buoyancy dominated surface outfalls (shown in Figure 1b,c, respectively). These outfalls result in rapid mixing of brine with ambient water in the near-field

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