Increasing fuel prices, carbon emissions and energy security are all key drivers in the search for alternative sources of energy. Tidal stream power is a relatively new area of research and development activity, aimed at harnessing the predictable nature of the tides. Multi-element wing profiles provide a competitive edge in mptorsports and are also a proven technology within aerospace, however their use within turbine design appears elusive. This thesis explores the use of multi-element profiles applied to vertical-axis tidal stream energy devices to determine if the additional complexity offers any significant advantage to turbine performance. A panel based method has been used to generate aerofoil performance data of standard profiles and multi-element profiles for a relative comparison of lift and drag coefficients. This data has then been applied to a cross-flow turbine model to assess the potential performance gain. Scale testing of models is used to validate results and the thesis includes the design and build of appropriate apparatus to facilitate this testing. Results demonstrate that the addition of a trailing edge plain flap increases the peak lift to drag ratio by 26% in comparison to a single blade of equivalent chord. The gains predicted for a turbine are in excess of this due to an increase in the tangential force vector, along with an increase in the range of angles which the blade is active for. A true performance comparison is difficult to achieve given the complexity of the downstream turbine behaviour.

Before privatisation of the electrical generation and distribution industries in the United Kingdom, the CEGB, owner and operator of the national grid, distributed electricity from electrical power stations to areas local to those stations. After the privatisation of the electrical industry the National Grid Company was formed and is obliged to supply the consumer with the cheapest supplier of electricity, irrespective of supplier and user, and this has caused an increased demand on the national grid. Due to the difficulty of obtaining the right of way for new overhead electricity transmission lines, the National Grid Company plc has focused its attention on developing an electrical conductor which has higher electrical conductivity than the present conductor alloy but with similar mechanical properties. To develop a new conductor it is important to gain an understanding of the factors that affect the electrical resistivity of aluminium conductors. The aim of the present research has been to investigate the effect of microstructural features on the electrical resistivity of aluminium and to measure the individual contribution of those features. The microstructural features examined in the present work are: intermetallic particles, dislocations, grain and sub-grain boundaries. The research involved manufacturing aluminium-based wires which contained a number of alloying additions that were subjected to varying levels of deformation up to true strains of 4. By using various thermo-mechanical treatments, it was possible to produce sets of aluminium wires of 1.18mm in diameter which contained varying volume fraction of intermetallic particles, varying dislocation densities and varying sub-grain sizes and grain sizes. The electrical resistivity of the wires was measured and related to their microstructure. Microstructural characterisation of the sets of wires was mainly carried out by transmission electron microscopy, scanning electron microscopy and optical metallography. This involved measuring dislocation density, grain/sub-grain size, sub-grain misorientation and volume fraction of intermetallic particles. The electrical resistance of the wires was measured using the four probe method. It was found that all microstructural features described above increased the resistivity of pure aluminium. The relationship between volume fraction of intermetallic particles and resistivity was found to be linear for volume fractions of less than 5%. The resistivity of the alloy could be calculated by considering the intermetallic particles and the aluminium matrix as two resistors in parallel. Cold working aluminium and aluminium alloys caused an increase in the resistivity. For the aluminium-iron alloys the rate of increase in resistivity was dependent on the volume fraction of intermetallic particles. The particles increased the rate of generation of dislocations as the alloy was deformed due to the plastic incompatibility between the matrix and the particles. For the aluminium-magnesium alloys the rate of increase in resistivity was dependent on the concentration of magnesium is solid solution. The rate of increase in resistivity when the wires were cold worked up to true strains of 1 was larger than when the wires were cold worked from true stains of 1 to 4. The microstructure of the wires that were cold worked to true strains of up to 1 was found to be dominated by dislocations. The relationship between dislocation density and resistivity was found to obey a power-law relationship. At low levels of deformation «0.3 true strain) the dislocations were randomly distributed and acted as individual electron scattering centres. As the dislocation density increased the dislocations became tangled and the degree of scattering of conduction electrons for each dislocation decreased. As the samples were deformed in the plastic strain range of 1 to 4, the dislocations formed dislocation cells / sub-grains. The increase in resistivity was found to be inversely proportional with sub-grain size due to scattering of conduction electrons by sub-grain boundaries. The relationship between grain size and resistivity was found to be inversely proportional to the grain size. This was the same relationship as that between sub-grain size and resistivity. The findings reported in this thesis provide an understanding of the way in which particles, dislocations and grain boundaries affect the resistivity of electrical conductors. The results show that, in general, factors which increase conductivity also increase strength. This information is vital when attempting to develop a conductor that combines high conductivity and high strength.

In an effort to reduce the cost of conventional fin and tube photovoltaic thermal (PV/T) collectors a novel mathematical analysis was developed which determines the optimum absorber plate configuration having the least material content and thus cost, whilst maintaining high collection efficiency. The analysis was based on the "low-flow" concept whose advantages include: improved system performance, smaller pump (less expensive with lower power consumption), smaller diameter tubes requiring lower thickness and thus cost of insulation, less construction power and time for the optimum absorber configuration. In this novel thermoeconomic optimization, the mechanisms of heat transfer from the fin to the tubes of the absorber plate and expressions of absorber plate material content and thus cost were identified and developed to allow for the absorber plate parameters (tube spacing, tube diameter and fin thickness) of the fin and tube PV IT collector to be optimized. In order for the useful collected heat (or thermal efficiency) of the PV/T collector to be held constant, the optimization procedure was based on holding constant the value of the PV IT collector efficiency factor.

This thesis presents the results of work on the optical properties and design optimisation of the luminescent solar concentrator (LSC). The optical properties of a range of uorophores were measured and it was found that the Lumogen F Rot 305 organic dye exhibited properties which make it ideal for use in LSCs, namely a wide absorption range (300-650 nm), 100% quantum yield at concentrations up to 1700 ppm, and the highest photostability of all the Lumogen F dyes, although the overlap of the absorption and emission spectra results in reabsorption (RA) losses. Despite these optimum properties, a detailed analysis showed that LSCs based on Rot 305 cannot compete with conventional glass/glass laminate modules on grounds of either cost or embodied energy. Since Rot 305 represents an optimum dye, this suggests it is unlikely that LSCs based on organic dyes will ever be competitive with conventional technologies. The only solution is the use of a uorophore with greatly reduced RA losses, for example a rare-earth (RE) complex. The RA losses of a europium-containing complex were found to be less than those of the Rot 305 dye, despite the lower quantum yield of the complex (86 %). The solar-to-electric conversion e ciencies of several LSC modules based on Rot 305 were measured. Modules with dimensions of 10 cm x 10 cm and 60 cm x 60 cm had e ciencies of 2.7% and 1.84% respectively, both measured without a back re ector. In addition, the technique of current-matching the edge cells was successfully demonstrated, resulting in a 15% increase in power output from an edge using matched cells relative to an edge using unmatched cells.

It is widely accepted that climate change is a very serious environmental concern facing the world today. Levels of carbon dioxide (CO2) in the global atmosphere have risen by more than a third since the industrial revolution and are now rising faster than ever before. Power generation accounts for a large proportion of GHGs emissions. Many different options are being proposed for CO2 emissions mitigation from the power generation sector. They have been extensively investigated in the scientific literature, but selection of better candidates for future investments is difficult and uncertain. Cont/d.

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No description available.

This thesis is a fundamental study of air-particle flow fields where the experimental parameters are characteristics of coal-fired electricity generating stations. The optical flow field measurement technique Particle Image Velocimetry (PIV) was adapted to study the particle flow fields and, in addition to the velocity vector map, particle concentration information was obtained. On phenomenon under investigation was the formation of ropes (high density ribbons of pulverised coal) in a small scale model of the pneumatically driven pulverised fuel transport lines of coal-fired power staions. The main findings of the study were that ropes form in bends and, when in contact with the bend wall, ropes are slowed by frictional forces. After they leave the bend, ropes fall throught he main airflow, maintaining their coherence. If the length of horizontal pipework is sufficiently long, the ropes will form a deposit. The Froude number is the relevant scaling parameter for the deposit's equilibrium position since the dominant influence on this position is the distance, L(f,s), for the rope to slow to zero when it is travelling along the bottom of the duct. The equilibrium position of the deposit, for a given Froude number is dependant upon the air-to-particle ratio: the higher this ratio then the further downstream the deposit. The factors influencing particle jet dispersal were investigated in view of their relevance to the coherence of the ropes. This study is also of relevance to the behavior of coal burner systems where an air-coal mixture is injected into a complex, usually swirling, airflow. The broad conclusions of the experimental results are as follows: 1. For a given particle loading and background velocity, the behavior trends of air-particle jets issued into a background airflow at velocities comparable to the mainstream values are similar to the theoretical description of singlee-phase jets which was derived by Squire and Troucer (1944). These general trends are as follows: (a)As the issuing velocity of the jet increases, its concentration half-width increases. (b)As the issuing veloccity of the jet increases, the rate of decrease of the centre-line velocity decreases, almost linearly with injection velocity. 2. For a given jet velocity, the higher the air-particle loading of the jet, the less the jet disperses and the less rapid the acceleration of the jet. 3. For a given relative velocity ratio between the jet and the background airflow, the higher the background airflow velocity, the more the jet disperses, the greater the rate odd acceleration of the jet and the more uniform the cross-sectional velocity profile.

No description available.

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