Although there has been ongoing research on fluidised beds for the past 70 years, the interaction between particles and rising bubbles and the general solids motion in bubbling fluidised beds are still not fully understood. The work presented in this thesis uses the method known as Positron Emission Particle Tracking (PEPT) to track the motion of a single radioactively labelled particle inside a fluidised bed. Recent developments in PEPT include new ways of labelling micron sized tracer particles that can be as small as 60 μm and the new mobile camera system also known as the Modular PEPT camera that can follow particle trajectories in equipment of various sizes and geometries. So far, PEPT has only been used to investigate fluidised beds of Geldart group B and D particles due to the previous limitation in the size of tracer particles. The results outlined in the thesis include group A particles (aluminium oxide) fluidised at atmospheric pressure in an 8 cm internal diameter bed and at elevated pressure in a 15 cm internal diameter bed and group B particles (sand) fluidised at atmospheric pressure in a 15 cm internal diameter column. The three areas that have been investigated are the use of particle trajectories to measure the properties of rising bubbles and the dispersion and general solids motion together with solids circulation as a measure of particle mixing. The protocols required to process the PEPT data used in the thesis were originally set by Stein (1999) but modified and improved versions are proposed and used. The PEPT results are in general agreement with existing models and results published by other researchers. A set of Matlab programs to analyse the results of PEPT experiments and which can be readily used by other users is presented.

The results of the catalytic oxidation in supercritical water of two non-biodegradable and highly toxic nitrogen-containing organic compounds (DBU and quinoline) are presented. The reactions were studied in a tubular xed-bed reactor over three catalysts: Pt/Al\(_2\)O\(_3\), CuO/Al \(_2\)O\(_3\) and MnO\(_2\)/CuO. The effect of operating conditions, namely temperature, pressure, oxygen concentration and initial concentration of the organic compounds were studied to evaluate their influence on its removal. Reaction rates were calculated from the experimental data collected. In addition, the selectivities and stabilities of the catalysts were investigated. Before conducting the experimental study the isothermal and isobaric operation of the reactor was veried together with the complete decomposition of hydrogen peroxide to oxygen and water in the preheating section and the reproducibility of experimental data was verified. Absence of external concentration gradients was determined experimentally for each reaction. The results showed that temperature was the main controlling variable of the catalytic oxidation. On the contrary, the effect of pressure depended on the catalyst used. Increasing the concentration of the organic compound did not aect their oxidation. Meanwhile, oxygen concentration above a stoichiometric ratio of two did not considerably improve the reaction. A power-law kinetic model was proposed to quantify the oxidation reaction. Three Langmuir-Hinshelwood-Hougen-Watson reaction rates were also explored to the experimental data. In the absence of a specic reaction mechanism the kinetic data were best represented by the power-law kinetic model. CO2 was the main carbon product of the reaction with small amounts of inorganic carbon species dissolved in the liquid effluent. Meanwhile, NH\(_4\), NO\(_3\) and NO\(_2\) ions were the only nitrogen species detected in the liquid effluent. Pt/Al\(_2\)O\(_3\) proved to be the most effective catalyst because it promoted faster reactions rates, had higher selectivity towards CO2 and produced lower nitrogen species. Surface analysis of the spent catalysts identied that the loss of activity was due to the 23 reduction of surface area. Leaching of active metals and chemical changes on the surface of the active metals and support of the catalyst were found for CuO/Al \(_2\)O\(_3\) and MnO \(_2\)/CuO. To conclude, it was demonstrated that catalytic supercritical water oxidation is a feasible and effective alternative for the destruction of contaminants in water. The thesis also includes suggestions for further research to continue the development of this technology and consolidate the process at industrial scale.

This work investigates the effect of fat crystal-stabilised interfaces on the transport of solutes between the two aqueous phases in W1/O/W2 emulsions. The aim is to separate solutes (NaCl or KCl) between the two aqueous phases. Fat crystals are used to stabilise the primary emulsion interface. Fat crystals are seeded at the interface during emulsion production using monoglycerides. Subsequently they sinter to form "shells" around the water droplets. It is shown that these "shells" are capable of retaining salt encapsulated within the aqueous phase despite the application of osmotic pressure gradients. The W1/O primary emulsions are incorporated into a double structure. It is shown that primary emulsion droplets retain their structure during the secondary emulsification step, although the shear may cause some damage to their protective "shells". Salt is retained within W1 as long as the primary interface is crystalline. The choice of secondary emulsifier is important to double emulsion stability. The double structure is not stable if small molecule surfactants are used to stabilise the secondary interface. Protruding fat crystals from primary emulsion droplets cause coalescence of double globules and lead to phase separation. The double emulsions are stable if proteins or particles are placed at the secondary interface.

The iodide/iodate reaction scheme was used to study the effect of gas sparging and/or solid particles on micromixing in a stirred vessel. A literature review illustrated the need for focused work on this matter and gave valuable ideas for the experiments. For this, the experimental method was first validated for using the added gaseous and solid phases air and glass beads, respectively. The experiments covered a range of conditions for micromixing in single-phase, for validation, in gas-liquid, solid-liquid and gas-solid-liquid systems: power inputs up to 1.94 W/kg, gas sparge rates up to 1.5 vvm and up to 11.63 wt.% solids with diameters from 150 to 1125 μm. For comparison, the power inputs from the impeller were kept constant when affected by the added phase(s). In order to allow better quantification of the experimental data, variations of the Incorporation model were evaluated for taking recent suggestions for the reaction scheme into consideration. The second dissociation of sulphuric acid was included in the model and different kinetic rate laws from the literature on the Dushman reaction were implemented. These variations allowed order-of-magnitude estimates and further comparisons of local specific energy dissipation rates.

Fuel cells are becoming increasingly important in the conversion of our society to clean, and renewable energy sources. However, there are some technical, as well as commercial barriers, which remain to be overcome before the fuel cell industry may be counted a success. One such problem is that of nonlinear current fluctuations, which have been observed under quite general conditions, in solid oxide fuel cells. This thesis attempts to elucidate the mechanisms driving this undesirable be- haviour, by developing a rational mathematical model based on fundamental chemical kinetics, and mass transfer effects, which take place within the porous anode of the fuel cell. A system of nonlinear, coupled ordinary differential equations is derived to describe the reaction and transfer processes associated with this fundamental model. This system is then rationally reduced to a planar dynamical system and the cases of weakly and fully humidified fuel streams are considered. Self-sustained, temporal oscillations are shown to arise through Hopf bifurcations in each case, and key parameter regimes leading to oscillatory behaviour are identified. Experiments have been conducted on commercial fuel cells, with results presented in Chapter 5.

This thesis presents an investigation into the use of four biochars (wood, rapeseed, miscanthus and sewage sludge) to generate a hydrogen-rich syngas that can be utilised in solid oxide fuel cells. Experimental investigations are split into three sections; (i) biochar characterisation, (ii) biochar gasification and (iii) the use of syngas in a single, microtubular solid oxide fuel cell. Characterisation revealed that wood biochar had the highest carbon content at 71.58%, sewage sludge had the lowest at 30% and rapeseed had the highest mineral content. The effects of temperature on gasification were investigated over a temperature range of 650 - 850°C at a steam flow of 172 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar and effects of steam flow at 850°C over a steam flow range of 54 - 277 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar. Results revealed the transient behaviour of the process as well as the effects of temperature and steam flow. Dry gas yield increases with both temperature and steam flow, with wood biochar giving maximum values of 2.58 m\(^3\) kg\(^-\)\(^1\) at 850°C and 277 g min\(^-\)\(^1\) kg\(^-\)\(^1\) biochar. Hydrogen content decreases at high temperatures and peak hydrogen content, 58.7%, was achieved at 750°C from the rapeseed biochar. Syngas from wood and rapeseed biochars was collected and used in a microtubular solid oxide fuel cell. Gas from rapeseed had a negative effect on the fuel cell performance, leading to a 28% decrease in the performance over the 30 minutes of potentiostatic operation of 0.7 V. Gas from wood biochar was more suitable and was used in the solid oxide fuel cell for approximately 500 minutes, giving an initial electrical efficiency of 16.8% at 0.7 V.

Gas-liquid mass transfer, agitator power consumption, rheology, gas-liquid mixing and gas hold-up have been studied in an agitated, sparged vessel of diameter, T = 0.3 m, with a liquid capacity of 0.02 m\(^3\), unaerated liquid height = 0.3 m. The solutions of sodium carboxymethylcellulose used exhibit moderate viscoelasticity and shear thinning behaviour, obeying the power law over the range of shear rates studied. The gas-liquid mass transfer was studied using a steady state technique. This involves monitoring the gas and liquid phase oxygen concentrations when a microorganism (yeast) is cultured in the solutions of interest. Agitator power consumption was measured using strain gauges mounted on the impeller shaft. Various agitator geometries were used. These were: Rushton turbines ( D = T/3 and D = T/2 ), used singly and in pairs; Intermig impellers ( D = 0.58T ), used as a pair; and a 45° pitched blade turbine ( D = T/2 ), used in combination with a Rushton turbine. Gas hold-up and gas-liquid flow patterns were visually observed. In addition, the state of the culture variables, (oxygen uptake rate and carbon dioxide production rate), were used to provide a respiratory quotient, the value of which can be linked to the degree of gas-liquid mixing in the vessel. Measurement of point values of the liquid phase oxygen concentration is also used to indicate the degree of liquid mixing attained. The volumetric mass transfer coefficient, k\(_L\)a, was found to be dependent on the conditions in which the yeast was cultivated, as well as being a function of time. These variations were associated with variations in solution composition seen over the course of each experiment. Steps were taken to ensure that further k\(_L\)a values were measured under identical conditions of the culture variables, in order to determine the effect on k\(_L\)a of varying viscosity, agitator speed and type and air flow rate. Increasing solution viscosity results in poorer gas-liquid mixing and a reduction in k\(_L\)a, as has been found by earlier workers. Thus high agitator speeds and power inputs are required to maintain adequate mass transfer rates. In the more viscous solutions used, large diameter dual impeller systems were required, to mix the gas and liquid phases. Of these a pair of Rushton turbines ( D = T/2 ) gave the highest k\(_L\)a values at a given power input. In these solutions the dependence of k\(_L\)a on the gassing rate, which is seen in intermediate and low viscosity solutions, virtually disappears, with k\(_L\)a highly dependent on the power input and the apparent viscosity. At intermediate viscosities a smaller pair of Rushton turbines showed the most efficient mass transfer characteristics, here k\(_L\)a is dependent on the power input and the gassing rate, but independent of viscosity. This is linked to the flow regime force in the vessel, which at intermediate viscosities lies in the transition region between the laminar and turbulent flow regimes. Variations in gas hold-up, rising then falling with increasing impeller speed, were linked to variations in the gassed power number, falling then rising with increasing impeller speed. These effects are considered to be due to variations in the size of the gas filled cavities behind the impeller blades.

This thesis is a study of the chemical and physical changes which can occur to gas turbine lubricants as a result of exposure to operational conditions. The continual evolution toward more efficient gas turbines is accompanied by increasing thermal and mechanical loading which the lubricant must be able to withstand. In this thesis two major degradation issues are studied; thermal oxidative degradation and lubricant deposition. In the area of thermal oxidative degradation, efforts are made to better understand the key parameters which determine the lubricant breakdown mechanism. Through control of these parameters and comparison to service derived gas turbine oil samples a new laboratory methodology is proposed for the assessment of lubricant oxidative degradation. The study of lubricant deposition in this thesis is concentrated on the regions of highest risk, the bearing chamber feed (single phase) and vent (two phase) oil pipes. Development of existing laboratory scale deposition simulators was conducted to increase how engine representative the methods are of gas turbine conditions. These simulators were used to evaluate the rate of deposition with a range of lubricants, simulated engine cycles and pipe surfaces.

The spray and combustion characteristics of the new bio-fuel candidates, 2,5-dimethylfuran (known as DMF) and 2-methylfuran (known as MF), are examined using optical diagnostic methods. A macroscopic spray characteristics study using high speed imaging has been performed to gain the understanding of the bio-fuels’ spray behavior under various conditions compared to gasoline and isooctane. The droplet sizes of the bio-fuel injections under different operating conditions are also studied using Phase Doppler Particle Analyzer (PDPA). The laminar flame propagation and the turbulent flame propagation for MF and DMF have been benchmarked against isooctane.

From the plethora of possible microbial hosts, Escherichia coli remains the most widely used “microbial factory” for recombinant protein production (RPP). However, despite the numerous advances, RPP in E. coli is still a significant challenge. Strong promoters to achieve high expression and protein production levels are often used, however, the underlying effects on the host physiology are often unseen. This thesis reports the development of “stress-minimisation” approaches for the production of recombinant proteins, either targeting the cytoplasm or the periplasmic space. First, the fermentation conditions for the production of TNFα in the cytoplasm were optimised. The expression vector, culture medium, temperature, inducer concentration and induction point were optimised, yielding 5.35 g ∙ L-1 of rhTNFα, 70% being accumulated as a soluble product. Second, different approaches for the production of recombinant proteins targeting the periplasm were evaluated, using an antibody fragment, scFv163R4, as a model protein. The effect of different growth conditions and signal peptides on the production of the scFv163R4 were evaluated. However, the selection of the optimal signal peptide was proven to be challenging, establishing the requirement of a high-throughput screening assay. This resulted in the development of a screening assay using β-lactamase as a reporter protein, for the evaluation of mutant signal peptide libraries with improved translocation activity. Initial evaluations resulted in the selection of two mutant signal peptides with enhanced translocation of scFv163R4-A, yielding almost 1 g ∙ L-1 of periplasmic scFv163R4-A. The generation of mutant signal peptide libraries in combination with the β-lactamase screening assay represents an important advance for the production of disulphide bonded proteins for the biotechnology industry.