This thesis examine the effects of natural convection on the mixing of localised and distributed discharges into the ocean. It comprises two studies. The first study investigates the behaviour of a localised release, such as a discharge of wastewater from a coastal outfall. Wastewater rises as a buoyant jet above the outfall and then spreads out horizontally at the sea surface to form a cloud of pollutants. We are interested in the natural convection that develops at the interface between a colder and less salty cloud and the underlying warmer and saltier sea water. Convection arises here as a result of the different diffusivities of heat and salt and the opposing contributions of heat and salt to the vertical density profile. This type of natural convection is called double-diffusive convection. We carry out new laboratory experiments and develop a theoretical model to couple the motion of the buoyant jet with the double-diffusive transport. Our results show that the pollutant concentration in the cloud near the jet can increase by 100% compared to the magnitude expected in the absence of double-diffusive convection, in the time-scale required for the cloud of pollutants to reach the coast. The second study investigates the behaviour of a distributed discharge, such as the diffuse flow of hot and mineral-rich sea water through porous rocks at hydrothermal sites on the ocean floor. We are interested in the mechanisms of development of natural convection at the interface between this buoyant, hot sea water and the cold sea water above in the presence of both a density difference and a net flow. We carry out laboratory experiments to measure the velocity field and visualize the growing interfacial instability using PIV and LIF. We also develop a linear stability analysis and a full numerical solution for the system.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:597652 |
| Date | January 2003 |
| Creators | Chow, M. M. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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