Year

2012

Degree Name

Masters of Engineering - Research

Department

Faculty of Engineering

Abstract

A study of global water supply has been made. Five billion people are predicted to die between 2040 and 2060 if nothing is done. A brief review of the water situation in Sydney, Australia and surrounding areas is also presented. Desalination may present a solution, if effective scale control can be achieved. An extensive study of scaling, calcium carbonate polymorphs, and existing scale control mechanisms and methods has been made. Many methods appear to exploit the same mechanism: changing a portion of calcium carbonate scale in its tenacious calcite form to the more easily removed aragonite. However, the mechanism behind changing forms is not known, and is currently impossible to test. There are many postulates, but no definitive proofs.

Investigations were made into an existing scaling control system known as the Carefree Conditioner to determine its impacts on calcium carbonate scale. The system suits remote areas that have ‘hard water’ problems and little access to expensive treatments. The device relies on turbulence, and does not use magnets or electric currents. Tests have been made on the conditioner’s effects on particle size and scale morphology. The Carefree Conditioner significantly reduces suspended calcium carbonate particle size by up to 50%. X-Ray Diffraction tests prove the Conditioner’s ability to change up to 70.2% of scale from calcite to aragonite, if the calcium carbonate was dissolved during conditioning. It does not change the morphology of suspended solid particles.

Computational Fluid Dynamics models of old and new Conditioner designs have quantified that the new spiral design at a flow rate of 10L/min produces 7.2 times the average turbulent kinetic energy (k) and 131 times the average turbulent energy dissipation (ε) of the old Venturi design at the same flow rate. There is room for further improvement, as the old and new designs have the bulk of their turbulence generated in the front half, with little at the end. Turbulent features of the old and new designs have also been quantified for a range of flow rates.

Turbulence results from CFD modelling have been combined with polymorph ratios calculated from XRD analysis to determine the optimum flow rate for calcite transformation. Results suggest a threshold value close to 2.45 x 10-3 J/kg for average k and 0.272 J/kg.s for average ε. Increasing flow rate and dissipating more energy beyond those values reduces the effect, and increases the amount of calcite. A possible mechanism has been described.

Turbulence results from CFD modelling have also been combined with particle size results to determine the optimum flow rate for particle reduction. The best result of a 50.0% reduction in particle size occurred at a flow rate of 0.193 kg/s. Results suggest that there is a threshold value at a flow rate of 0.11 kg/s (average k of 2.5 x 10-2 J/kg and average ε of 17.2 J/kg.s) for reducing particle size. Increasing the turbulence beyond that value does not significantly change particle size. The new design was shown to reduce particle size 35.3% more than the old design at the same flow rate.

This is the first time such findings have been achieved. These will contribute significantly towards the Care-free Conditioner’s acceptance in the market, and in developing future Care-free Conditioner designs.

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