Motion-driven energy harvesters can replace batteries in low power wireless sensors, however selection of the optimal type of transducer for a given situation is difficult as the performance of the complete system must be taken into account in the optimisation. In this thesis, a complete piezoelectric energy harvester system model including a piezoelectric transducer, a power conditioning circuit, and a battery, is presented allowing for the first time a complete optimisation of such a system to be performed. Combined with previous work on modelling an electrostatic energy harvesting system, a comparison of the two transduction methods was performed. The results at 100 Hz indicate that for small MEMS devices at low accelerations, electrostatic harvesting systems outperform piezoelectric but the opposite is true as the size and acceleration increases. Thus the transducer type which achieves the best power density in an energy harvesting system for a given size, acceleration and operating frequency can be chosen. For resonant vibrational energy harvesting, piezoelectric transducers have received a lot of attention due to their MEMS manufacturing compatibility with research focused on the transduction method but less attention has been paid to the output power electronics. Detailed design considerations for a piezoelectric harvester interface circuit, known as single-supply pre-biasing (SSPB), are developed which experimentally demonstrate the circuit outperforming the next best known interface's theoretical limit. A new mode of operation for the SSPB circuit is developed which improves the power generation performance when the piezoelectric material properties have degraded. A solution for tracking the maximum power point as the excitation changes is also presented.

This work addresses the way in which a viscoelastic granular medium dissipates vibration energy over broad ranges of frequency, amplitude and direction of excitation. The viscoelastic properties (modulus and loss factor) of polymer particles are obtained experimentally both by deriving the master curve of the material and by measuring the stiffness of these spherical particles at different frequencies using a test rig designed for this purpose. Three dimensional Discrete Element Method (DEM) is used to develop a numerical model of the granular medium and is validated by comparison with experimental results. Despite the simplifications the model was found to be in good agreement with experiments under vertical and horizontal vibrations with different numbers of particles over a range of frequencies and amplitudes of excitation. The study is extended to investigate different phases that occur under vibrations of granular materials. The low amplitude vibrations when the particles are permanently in contact without rolling on each other is called solid phase. In this phase, most energy is dissipated internally in the material. A theoretical/numerical approach is considered for this phase and it is validated by experiment. At higher amplitude vibrations when the particles start to move and roll on each other (the convection phase) there is a trade-off between energy dissipation by friction and viscous/viscoelastic effects. Energy dissipation is relatively insensitive to the damping of individual particles. At extremely high amplitude vibrations particles spend more time out of contact with each other (the particles are separated from each other – gas region). It can be seen the particles with lower damping reach the gas region earlier because they are less sticky and more collisions can happen so although the damping for each individual particle it less, the total damping increases. ii The effect of parameters of particles on energy dissipation is also studied using sensitivity analysis. The benefit of doing this is to better understand how each parameter influences the total system damping.

The aim of this project was to benchmark energy utilisation of bread manufacturing and to provide methodologies and results with the aim of improving efficiency in commercial bakeries. The bread industry is an important provider of staple food products across the world. Owing to the large energy use in bread manufacturing, bakeries have come under increased scrutiny to reduce their environmental impact. The proving process exposes dough to heat and humidity in order to encourage yeast activation. Provers (responsible for 5 % of carbon emissions in bakeries) are over-engineered to the extent that energy costs impact upon performance. The industry standard practices that use large volumes of airflow to maintain food safety have not been scientifically justified. Experimentally validated Computational Fluid Dynamics (CFD) simulations showed the residence time distribution profiles for different numbers of air changes. The results have indicated that it is possible to reduce airflow by 33 % and electricity demand by over 70 %. A system-level thermodynamic analysis was developed in order to measure and model heat streams in industrial bread ovens. The model was subjected to a sensitivity analysis to ensure the calculations could be trusted to give suitably accurate results. A number of measurement techniques were employed and the methodology was designed to increase the potential for industry-wide use to assess the efficiency of ovens. The results showed that between 40 and 49 % of heat is wasted in industrial ovens. The model has been successfully distributed to industry. Experimental measurements of heat transfer for a range of regimes used in baking ovens were undertaken. The results were validated by previous correlations published in literature. Investigation focussed on three particular novel research areas. Firstly, comparisons between nozzle types showed that rows of circular jets could be approximated as slot nozzles for mean heat transfer. Secondly, the ratio of convective to radiative heat transfer was investigated. Thirdly, the prevalence of secondary peaks in local heat flux profiles was compared for two nozzle sets. These unique results can be used to help design baking ovens with energy efficient operating conditions.

In this work, two intensified catalytic reactor systems applicable for energy conversion have been studied. The first is an intensified membrane reactor combining oxygen separation from air using dense oxygen selective composite perovskite type membranes with a chemical reaction at the permeate side. In this part of the work, a membrane reactor made of stainless steel was designed, constructed and a fabricated planar oxygen ceramic membrane of the L0.6S0.4C0.2F0.8O3-δ (LSCF6428) type tested in it. A challenge in this work was developing a procedure to hermetically seal the ceramic membrane to the stainless steel holder. An inexpensive soft glass composition was used and with some surface treatment of the stainless steel substrate was found to bond well with both the ceramic membrane and the stainless steel casing. Oxygen permeation experiments were conducted using the membrane reactor at a temperature of 650oC, under inert (helium) and reactive (CH4 or CO) conditions. Results obtained have shown that oxygen permeation increased with a chemical reaction by 1-2 orders of magnitude compared to permeation under permeate inert conditions. At operating temperature of 650oC, oxygen flux of about 0.025mLmin-1cm-2 and 0.40mlmin-1cm-2 under air/helium gradient and air/(He+CO) or air/(He+CH4) gradient respectively were obtained. This result shows that from an oxygen permeation point of view, performance is superior in a combined separation and combustion mode than in a separation first to produce oxygen and combustion in a separate chamber. Further studies can explore the possibility of depositing catalytic nanoparticles on the permeate membrane surface to prevent complete oxidation and rather promote partial oxidation of methane to CO and H2. Post operation examination of membrane showed permeate side surface changes which show some chemical stability issues of the membrane material. The second is a DBD plasma activated reforming of methane to hydrogen or syngas. In this study, the effects of different parameters such as applied plasma power, feed gas mixture flowrate, molar composition ratio of CO2 and CH4 and inclusion of catalyst particles in plasma volume on the conversion of reactants and selectivity of products were experimentally investigated. Results obtained have shown the potential of plasma activated reforming of methane with carbon dioxide in one step to produce hydrogen or syngas and Higher Hydrocarbons (HCs) and oxygenates. The results from the experimental investigations in parametric effects can be used to optimise the process for the desired conversions and product selectivity. An important finding of this work was that the main products of this reforming process is not syngas as widely reported in literature, but a mixture of HCs and oxygenates, which may actually be very valuable products. Only about 10-20% of the carbon in the converted methane forms CO while the rest forms HCs, oxygenates, and, depending on conditions, carbon black. Experimental results have shown that carbon black forms in low concentration of CO2 in the feed gas. CO2 in higher quantities inhibits formation of carbon deposits in the plasma volume. The reported energy inefficiency (in literature) of plasma based reforming process may have been concluded from a syngas yield point of view while other products were considered as worthless by-products. An analysis of the “by-products” has shown that this might not be the case.

Today’s power systems are becoming heavily loaded and operating close to their stability limit. This raises issue of voltage security and small signal stability, which may lead to the system being forced to operate way below its rated capacity. The impact of renewable technology such as wind and other technologies are likely to further strain existing power networks and infrastructure, hence, likely to adversely affect voltage stability of the power network. The intermittency associated with these sources could also adversely affect on the damping of the system’s oscillatory modes. The work presented in this thesis develops techniques for identifying which controls are effective to improve voltage security margins. Using distributed series impedance, a device that can either increase or reduce line impedance, and margin sensitivity, it is shown that voltage stability margin can be effectively enhanced. Validation is performed on a 39 bus system following a major line outage contingency. Ways of improving the accuracy of margin sensitivity with respect to various controls are presented. Techniques for designing controllers to improve system mode damping have been developed. Unlike techniques using predominately state-space method, these which utilise polynomial methods, yield robust controller of low order and whose structure can be pre-specified. Three techniques are presented. The first uses Kharitonov’s theorem and results in bilinear matrix inequality (BMI) stability conditions. The second uses the theory of positive polynomials which results in linear matrix inequality (LMI) conditions for stability. The last uses conic programming to the controller design problem as a two part problem, first involving phase compensation design, then gain tuning. The effectiveness of the techniques is validated by designing controller for an 68 bus test system model.

While global demand for energy is increasing, it is mostly covered by fossil energies, like oil and natural gas. Principally composed of hydrocarbons (methane, ethane, propane ...), reservoir fluids contain also impurities such as carbon dioxide, hydrogen sulphide and nitrogen. To meet the request of energy demand, oil and gas companies are interested in new gas fields, like reservoirs containing high concentrations of acid gases. Natural gas transport is done under high pressure and these fluids are also saturated with water. These conditions are favourable to hydrates formation, leading to pipelines blockage. To avoid these operational problems, thermodynamic inhibitors, like methanol or ethanol, are injected in lines. It is necessary to predict with more accuracy hydrates boundaries in different systems to avoid their formation in pipelines for example, as well as vapour liquid equilibria (VLE) in both sub-critical regions. Phase equilibria predictions are usually based on cubic equations of state and applied to mixtures, mixing rules involving the binary interaction parameter are required. A predictive model based on the group contribution method, called PPR78, combined with the Cubic – Plus – Association (CPA) equation of state has been developed in order to predict phase equilibria of mixtures containing associating compounds, such as water and alcohols. To complete database for multicomponent systems with acid gases, VLE and hydrate dissociation point measurements have been conducted. The developed model, called GC-PR-CPA, has been validated for binary systems and applied for different multicomponent mixtures. Its ability to predict hydrate stability zone and mixing enthalpies has also been tested. It has been found that the model is generally in good agreement with experimental data.

No description available.

No description available.

World and UK energy resources and use are reviewed and the role of energy conservation in energy policy identified. In considering various energy conservation measures, a distinction is made between energy intensive and non-intensive industries and also between direct and indirect uses of energy. Particular attention is given to the non-intensive user of energy. Energy use on one such industrial site has been studied to determine the most effective energy savL~g measures in the short term. Here it is estimated that over 65% of energy is consumed for indirect purposes, mainly for heating and lighting buildings. Emphasis is placed on energy auditing techniques and those energy saving measures requlIlng greater technical, economic and organisational resources to secure their implementation. Energy auditing techniques include the use of aerial thermography and snow formation surveys to detect heat losses. Qualitative and quantitative interpretations are carried out, but restricted mainly to evaluating building roof heat losses. From the energy auditing exercise, it is confirmed that the intermittent heating of buildings is the largest and most cost effective fuel saving measure. This was implemented on the site and a heat monitoring programme established to verify results. Industrial combined heat and power generation is investigated. A proposal for the site demonstrates that there are several obstacles to its successful implementation. By adopting an alternative financial rationale, a way of overcoming these obstacles is suggested. A useful by-product of the study is the classification of industrial sites according to the nature of industrial energy demand patterns. Finally, energy saving measures implemented on the site are quantlfied using comparative verification methods. Overall fuel savings of 13% are indicated. Cumulative savings in heating fuel amount to 26% over four years although heated area increased by approximately 25%.

There has been negligible adoption of combined heat and power (CHP) for district heating (DH) in Britain, despite continued advocacy. This thesis constructs an account of the treatment of the option, and devises a framework for explanation. Analysis of technological development and adoption, it is argued, should be similar to that of other social processes, and be subject to the same requirements and criticisms. They will, however, show features peculiar to the institutions developing and selecting technologies, their relation to different social groups, and the forms of knowledge in and about technology. Conventional approaches - organisation and interorganisation theories, and analyses of policy-making - give useful insights but have common limitations. Elements of an analytical framework situating detailed issues and outcomes in a structured historical context are derived from convergent radical critiques. Thus activity on CHP/DH is essentially shaped by the development and relations of energy sector institutions: central and local government, nationalised industries and particularly the electricity industry. Analysis of them is related to the specific character of the British state. A few CHP and DH installations were tried before 1940. During postwar reconstruction, extensive plans for several cities were abandoned or curtailed. In the 1960s and 70s, many small non-CHP DH schemes were installed on housing estates. From the mid-70s, the national potential of CHP/DH has been reappraised, with widespread support and favourable evaluations, but little practical progress. Significant CHP/DH adoption is shown to have been systematically excluded ultimately by the structure of energy provision; centralised production interests dominate and co-ordination is weak. Marginal economics and political commitment have allowed limited development in exceptional circumstances. Periods of upheaval provided greater opportunity and incentive for CHP/DH but restructuring eventually obstructed it. Explanation of these outcomes is shown to require analysis at several levels, from broad context to detailed action.