Near-field dilution of a vertical dense jet impinging on a solid boundary

Abstract

Experimental measurements of concentrations were performed for vertical dense jets discharged downwards to a horizontal or a sloping bottom, aiming at: (a) determining the dilution at the impingement point on a solid bed and assess the influence of the boundary, and (b) evaluating the additional dilution achieved within the density current, which forms in the vicinity of the impingement point. It is found that the presence of the solid boundary affects the axial dilution of the approaching jet up to a distance of h_D, which is well correlated to the source height and the length scale L_M. The dilution at the impingement point on the boundary is reduced appreciably compared to that of a boundary-free jet at the same location. The additional dilution within the density current on a sloping bottom is well correlated to the dimensionless distance from the impingement point. Dimensionless empirical equations are proposed for the dilution at the impingement point and in the density current near the bed, in terms of geometrical parameters and the densimetric Froude number.

Keywords:

• Desalination
• Dense jets
• Brine disposal
• Marine outfalls
• Dilution

Acknowledgments

Research leading to this paper was partly co-financed by the European Union (European Social Fund—ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF)—Research Funding Program: Heracleitus II. Investing in knowledge society through the European Social Fund.