Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Raouf E. Baddour

Abstract

Brine is a byproduct of many industrial and mining processes, including desalination. Brine is commonly conveyed in long pipe lines and disposed in the bottom of the sea through multiport diffusers, forming dense jets, also known as fountains. An acceptable level of brine concentration is required to be achieved at the boundary of a regulatory mixing zone surrounding a point of discharge. Such mixing zones are allocated with the objective of limiting environmental deterioration within their boundaries. Mixing zones are, nevertheless, not allowed when discharging brine in sensitive areas and when brine is toxic.

The main contribution of this study is the introduction of the concept of minimum return point dilution, to regulate brine at the point of discharge, as an alternative to the mixing zone approach, which has well recognized limitations.

This study examined experimentally the dilution and development of turbulent negatively-buoyant upward and downward fountains. The study included low and high densimetric Froude number investigations of fountains in stagnant surroundings, and for linear water equation of state conditions. The dilution and spread of fountains were measured with fast responding thermocouples. Downward thermal fountains were found dynamically similar to upward dense fountains. The mean and maximum vertical jet penetrations obtained using temperature data were consistent with previous studies based on visual data. The minimum return point dilution of vertical fountains was found by analyzing the temperature data to be always located just outside the edge of the nozzle. The proposed minimum return dilution equations are providing simple modeling tools to design vertical fountains to comply with any required regulatory dilution at the source. This study also recognized the advantage of using vertical fountains, as opposed to inclined fountains. This is to take advantage of variable sea currents occurring in any direction. Furthermore, the study revealed that relative density difference, on a broader range applicable to the desalination industry, reduces noticeably dilution and height of fountains. Finally, a theoretical two-coefficient entrainment model of fountains was formulated based on mass, momentum, and buoyancy conservation principles, and the sensitivity of model predictions to the calibrated values of entrainment coefficients are discussed.

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