Browsing by Author "Rautenbach, Christo"

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    Modelling of flow through porous packing elements of a CO2 absorption tower
    (Stellenbosch : University of Stellenbosch, 2009-12) Rautenbach, Christo; Du Plessis, J. P.; University of Stellenbosch. Faculty of Science. Dept. of Mathematical Sciences.
    ENGLISH ABSTRACT: Packed beds are widely used in industry to improve the total contact area between two substances in a multiphase process. The process typically involves forced convection of liquid or gas through either structured or dumped solid packings. Applications of such multiphase processes include mass transfer to catalyst particles forming the packed bed and the adsorption of gases or liquids on the solid packing. An experimental study on the determination of air flow pressure drops over different packingmaterialswas carried out at the Telemark University College in Porsgrunn,Norway. The packed bed consisted of a cylindrical column of diameter 0.072m and height 1.5m, filled with different packingmaterials. Air was pumped vertically upwards through a porous distributor to allow for a uniform inlet pressure. Resulting pressure values were measured at regular height intervals within the bed. Due to the geometric nature of a Raschig ring packing wall effects, namely the combined effects of extra wall shear stress due to the column surface and channelling due to packing adjacent to a solid column surface, were assumed to be negligible. Several mathematical drag models exist for packed beds of granular particles and an important question arises as to whether they can be generalized in a scientific manner to enhance the accuracy of predicting the drag for different kinds of packing materials. Problems with the frequently used Ergun equation, which is based on a tubular model for flow between granules and then being empirically adjusted, will be discussed. Some theoretical models that improve on the Ergun equation and their correlation with experimental work will be discussed. It is shown that a particular pore-scale model, that allows for different geometries and porosities, is superior to the Ergun equation in its predictions. Also important in the advanced models is the fact that it could take into account anomalies such as dead zones where no fluid transport is present and surfaces that do neither contribute to shear stress nor to interstitial form drag. The overall conclusion is that proper modelling of the dynamical situation present in the packing can provide drag models that can be used with confidence in a variety of packed bed applications.
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    Study of the Durban Bight shoreline evolution under schematised climate change and sand‑bypassing scenarios
    (South African Institution of Civil Engineering, 2018-12) Rautenbach, Christo; Theron, Andre K.
    ENGLISH ABSTRACT: The Durban Bight beaches, on the KwaZulu-Natal coast of South Africa, have been the topic of several studies in the past, because of their recreational and economic value. These beaches are mainly nourished via a sand-pumping scheme, which has been the case since the 1980s. The present study investigated the longer-term dynamic stability of the Durban Bight beaches using a one-dimensional numerical shoreline model. The wave conditions that drive the longshore transport of sand were simulated using the numerical spectral wave model Simulation WAves in the Nearshore (SWAN). The shoreline model was calibrated and validated against existing historical data. The calibrated model was then employed to simulate possible future scenarios. These included climate change phenomena and the influence of anthropogenic changes. Each of the simulations predicts a twenty-year period, with results extracted at five-year intervals. The results are presented and discussed, and the emphasis is placed on the importance of maintaining the required sand-bypassing rates and the awareness of the possible effects of climate change on shoreline maintenance and management.
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    A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management
    (2019-08-08) Pfaff, Maya C.; Logston, Renae C.; Raemaekers, Serge J. P. N.; Hermes, Juliet C.; Blamey, Laura K.; Cawthra, Hayley C.; Colenbrander, Darryl R.; Crawford, Robert J. M.; Day, Elizabeth; du Plessis, Nicole; Elwen, Simon H.; Fawcett, Sarah E.; Jury, Mark R.; Karenyi, Natasha; Kerwath, Sven E.; Kock, Alison A.; Krug, Marjolaine; Lamberth, Stephen J.; Omardien, Aaniyah; Pitcher, Grant C.; Rautenbach, Christo; Robinson, Tamara B.; Rouault, Mathieu; Ryan, Peter G.; Shillington, Frank A.; Sowman, Merle; Sparks, Conrad C.; Turpie, Jane K.; van Niekerk, Lara; Waldron, Howard N.; Yeld, Eleanor M.; Kirkman, Stephen P.
    Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems-oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas.