Study of dilution, height, and lateral spread of vertical dense jets in marine shallow water

Abstract

Abstract This study provides information for the design of sea outfalls to dispose of brine from desalination plants into shallow lagoons of the sea. The behavior of vertical dense jets was studied experimentally by discharging cold saline water vertically upward into a tank filled with hot freshwater under stagnant ambient conditions. The minimum return point dilution, μmin, was determined using thermocouples, and the maximum height, Zm, and the lateral spread, Rsp, of the fountains were determined by observing shadowgraph pictures. The flow was turbulent and the densimetric Froude number Fr0 varied from 9 to 18.8. Three mixing regimes were identified: deep, intermediate, and impinging mixing regimes. In the intermediate mixing regime, μmin and Zm were analyzed and compared with the results of deep water studies. The μmin and Zm values of fountains at an intermediate water depth were found to be higher than those of fountains at deep water depths. In the impinging regime, μmin decreases rapidly when a fountain starts to continuously impinge on the water surface, showing a noticeable disturbance in the water surface. Therefore, a good rule of thumb is to reduce the flow through multiport diffusers from desalination plants when the noticeable disturbance is observed from the top water surface.