Rheological Modelling of Turbid River Water

Sumia Salih Mahmoud, Isam Mohammed Abdel-Magid, Sarra Ahmed Mohamed Saad

Abstract


This study focused on impact of sediment laden water of the Nile - especially during flood season - on viscosity, rheological properties and flow characteristics of water within water network and piping systems. Laboratory experiments, performed at the National Research Centre Laboratories at Khartoum, were conducted on water samples collected from the Blue Nile and for carefully prepared synthetic slurries that resembled turbid flood water during the period 2009 to 2011. Experiments showed that water viscosity increased due to an increase in amount of sediment load and concentration in tested water samples. Moreover, laboratory investigations revealed that viscosity of water laden with sediment increased whenever sediment remained within the water for a period of time. Experimental results on rheological

characteristics of samples showed that slurries and water laden sediments have flow properties of Non-Newtonian fluids with thixotropic characteristics and flow behavior. This may be attributed to the nature of suspended loads, characteristics of colloidal solids and particulate matter constituting the sediments. Such behavior will have its critical impact on pumping of such waters, their transportation and conveyance within networks and piping lines. SPSS program was used for analyzing laboratory data to deduce an equation that would suitably reflect and explain the relationship between water viscosity and sediment concentration. Likewise, the study achieved same results as laboratory investigations and findings. Modeling through COMSOL multiphysics program. enabled developing a relationship between viscosities, pressures and flow velocities within water network systems. Flow pattern, streamlines, changes in velocity, variations in velocity gradients, pressures, currents and pattern of flow under different structural, loading and hydraulic conditions were significant. Results and findings showed the decrease of velocity of flow with an increase in sediment concentration and load. The integrated holistic modelling tested in this research work reflected the influence of rheological aspects of quality factors (such as viscosity), engineering design parameters (such as hydraulic loading conditions), geometry and shape (such as size and area of conduits). Such modelling approach will have its significant impacts on decision making, design concepts and economical costs and benefits relationships when dealing with transportation and conveyance of turbid sediment laden waters.


Keywords


rheological properties; Nile water; modelling

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References


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