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(2021)ThesisEmerging membrane technologies such as forward osmosis (FO) and membrane distillation (MD) can provide alternative engineering approaches to current water-treatment membrane technologies, but without the high-pressure requirements. Currently, greater industrial implementation of these technologies is hindered by limitations with low flux, flow polarisation issues, design optimisation and issues with membrane deformation. An experimental and numerical assessment of a plate-and-frame (PF) FO module, revealed significant occlusion of the draw-channel under applied transmembrane-pressure (TMP), at points up to 70% while under an applied TMP of 1.45bar. Subsequently, 3D computational fluid dynamics (CFD) simulations were performed and validated against pressure loss data under TMP, to reveal the impact of flow indicators known to affect concentration polarisation (CP), such as Reynolds number, velocity profiles and shear strain. The pressure-loss method was then applied to a range of commercially available modules, found to occlude a cross-sectional area from 12-16% for the spiral would (SW) types and 49% 1.45bar for the PF module. CP models were then developed in conjunction with flux data to establish the degree of CP occurring in the modules. The CP data was then related to a CFD characterisation to establish detailed relationships on the impact of TMP on CP effects. Finally, a solar vacuum-membrane distillation (solar-VMD) system was developed and assessed experimentally to apply the lessons learned from the FO investigation in another emerging membrane technology. Lab-scale experiments were used to develop and validate a CFD model, using predictive hydrodynamic factors such as Reynolds number and shear strain, to mitigate temperature polarisation (TP) using turbulence promoters. A parametric analysis of the CFD data revealed the flux improvements and TP mitigation available through the addition of a baffle, combined with an economic analysis for real world use (demonstrating a viable decentralised drinking and hot-water supply). Flux performance of the MD system was found at >8LMH in solar conditions of ~800W/m2, with a payback period of 2.06 years. Overall, this thesis provides a detailed assessment of the impacts of applied TMP in FO processes, as well as potential design optimisation pathways by furthering the knowledge of CFD analysis in emerging membrane technologies.
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(2022)ThesisChitosan is a promising material for making edible, active and biodegradable packaging films for foods; however, pure chitosan films have poor mechanical and barrier properties. This Master of Philosophy study was conducted with the aim to improve the physicochemical and biological properties of chitosan films by incorporating epoxy activated agarose (EAA) and three flavonoids, namely catechin, quercetin and luteolin into the film. Chitosan films were prepared with chitosan of three molecular weights (low, medium and high) and by drying at 21 °C, 40 °C and 50 °C. EAA and the flavonoids were incorporated into chitosan, both at 1-10%. With increased MW of chitosan, the film thickness, tensile strength (TS), elongation at break (EAB), and swelling ability increased while the moisture content, solubility, water vapor permeability (WVP) and the melting temperature declined. Higher drying temperatures led to greater TS and higher melting temperature for the films. Incorporation of the EAA significantly improved the moisture related properties and flexibility of the chitosan films. Moreover, with higher amounts of EAA, the film thickness and opacity increased while the TS and thermal stability declined. Incorporation of flavonoids had significant (type and concentration dependent) impact on the physicochemical and biological properties of chitosan films. Addition of flavonoids up to 5% resulted in films with greater TS, EAB and thermal stability, whereas at concentrations of up to 3%, the films produced had improved WVP. All the chitosan-flavonoid composite films exhibited antimicrobial activity against Listeria monocytogenes, Salmonella typhimurium, Escherichia coli and Staphylococcus aureus. Beef samples wrapped with pure chitosan or chitosan-flavonoid composite films had significantly lower microbial counts and a more reddish color after two weeks of storage at 4 °C than those packaged with cling wrap. Storage of the chitosan films at 21 °C and 4 °C for six weeks resulted in significant reductions in the TPC, TFC, antioxidant activity and the flexibility of the films, which occurred at a faster rate at 21 °C. Overall, this study demonstrated that incorporation of EAA and flavonoids at appropriate levels can significantly improve some of the physicochemical and biological properties of chitosan films.
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(2022)ThesisStructural composite supercapacitors have been investigated as a promising weight-saving technology for electrical vehicles (EV), electric aircraft, and mobile robots. The main objective is to maintain excellent (ideally the same as the existing structure of the same weight) mechanical properties while storing adequate electrical energy. This thesis aims to develop structural composite supercapacitors with both outstanding mechanical properties and electrical energy storage performance. The main findings and contributions of my research presented in this thesis are: (1) A novel structural electrolyte made of carbon nanofibers, epoxy, and ionic liquid (IL) that offers ionic conduction properties as well as mechanical stiffness and rigidity. The incorporation of carbon nanofibres (CNFs) into epoxy-ionic liquid-based electrolytes creates pathways for ion migration, resulting in a 40-fold boost in the ionic conductivity for the resulting electrolytes. The tensile strength and Young’s modulus of the resulting electrolytes exhibit only a slight drop. Therefore, the new solid epoxy-based electrolyte offers great potential for use in energy storage structures, for example structural composite supercapacitors and/or batteries; (2) A structural composite supercapacitor consisting of the high-performance electrodes made by grafting manganese dioxide onto carbon fibre fabrics and the epoxy-ionic liquid electrolyte. Mixing 40 wt.% of IL and 60 wt.% of epoxy (denoted as the 40IL electrolyte) yields the best combination of ionic conductivity and tensile properties. A structural composite supercapacitor has been fabricated using a 40IL electrolyte with high-capacity manganese dioxide coated carbon fibre electrodes. The resulting composite supercapacitors demonstrate excellent mechanical and electrochemical performance compared to the literature data. (3) A novel silane treatment method to enhance the ionic conduction between the electrolyte and the electrodes. The results show that the silane treatment enables the composite supercapacitors to achieve a 3-fold increase in areal capacitance without deterioration of the mechanical properties. Finally, potential opportunities for future studies of the structural composite supercapacitors are discussed.
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(2022)ThesisThe Vanadium Flow Battery is a leading technology for medium to large-scale energy storage, however, the efficiency, capacity, and power density can be impeded by mass transport limitations. In this thesis, advanced flow field patterned modified graphite porous electrodes were produced using an embroidery method. The battery performance and electrolyte distribution were analysed for various embroidered designs on 100 mm x 100 mm graphite felt electrodes. Flow visualisation tests demonstrated that embroidered graphite felt electrodes showed better flow distribution and provided lower pressure drops of 35.0 %, 33.0 % and 11.0 % for the parallel, diamond and perpendicular pattern modified graphite electrodes respectively compared to the pristine sample. The modified porous electrodes were then compared to a pristine graphite electrode in battery tests. Polarisation test results indicated that embroidered electrodes can operate at lower flow rates compared to a pristine electrode saving pumping energy without sacrificing battery performance. The parallel and diamond pattern electrodes improved the overall energy efficiency of the battery system by 3.8% and 5.5% respectively. The flow characteristics of different designs are investigated using computational modelling, and the results were found to agree favourably with the experiment work. An advanced flow distributor has been modelled, reducing the flow uniformity parameter by 27.5 % for pristine, 42.7 % for perpendicular, 36.0 % for parallel, and 32.0 % for diamond pattern modified graphite electrode. A 100 mm wide x 300 mm long cell was simulated with an advanced flow distributor. The pressure drop reduction was 2.0 % for the perpendicular pattern, 38.0 % for parallel pattern, and 40.0 % for diamond pattern design compared to the pristine electrode. The pattern optimisation for parallel and diamond pattern designs was further conducted by varying spacing width and channel width. The results showed that the narrower the width of spacing between each channel and the wider the width of channel, the lower the pressure drop with better flow uniformity. The widest channel and the narrowest spacing pattern considered reduced the pressure drop by 71.6 % and 73.5 % for the parallel and diamond pattern modified electrodes compared to the pristine felt electrode.