No description available.

Energy storage is a crucial condition for both transportation purposes and for the use of electricity. Flywheels can be used as actual energy storage but also as power handling device. Their high power capacity compared to other means of storing electric energy makes them very convenient for smoothing power transients. These occur frequently in vehicles but also in the electric grid. In both these areas there is a lot to gain by reducing the power transients and irregularities. The research conducted at Uppsala university and described in this thesis is focused on an all-electric propulsion system based on an electric flywheel with double stator windings. The flywheel is inserted in between the main energy storage (assumed to be a battery) and the traction motor in an electric vehicle. This system has been evaluated by simulations in a Matlab model, comparing two otherwise identical drivelines, one with and one without a flywheel. The flywheel is shown to have several advantages for an all-electric propulsion system for a vehicle. The maximum power from the battery decreases more than ten times as the flywheel absorbs and supplies all the high power fluxes occuring at acceleration and braking. The battery delivers a low and almost constant power to the flywheel. The amount of batteries needed decreases whereas the battery lifetime and efficiency increases. Another benefit the flywheel configuration brings is a higher energy efficiency and hence less need for cooling. The model has also been used to evaluate the flywheel functionality for an electric grid application. The power from renewable intermittent energy sources such as wave, wind and current power can be smoothened by the flywheel, making these energy sources more efficient and thereby competitive with a remaining high power quality in the electric grid.

Determination of the heat transfer coefficients for natural and mixed convection in horizontal annuli is important for designing double pipe heat exchangers and for energy storage systems. In part one and two of this study, the 2D numerical solution of the laminar natural convection of water in six internally finned horizontal annuli has been obtained. The fins are attached to the external surface of the inner cylinder. Only the symmetrical half of the horizontal annulus with three equally spaced longitudinal divergent solid and porous fins are considered. The parameters of the problem are Rayleigh number, fin height, permeability and porosity of the porous fin, etc. The above parameters are suitably varied to ascertain their effects on fluid flow and heat transfer. The results show that traditional solid fins provide much higher heat transfer rates compared to the porous fins. Part three of this work deals with mixed convective heat transfer (laminar natural and forced convections) of water in a vented annulus. The forced flow conditions are imposed by providing an inlet at the top and an outlet at the bottom. For various parameters of the problem, the average and local Nusselt numbers along the inner cylinder are calculated for water for both aiding and opposing flows. The fourth part of this study deals with numerical modeling of natural convection of nanofluids in a horizontal cylindrical annulus. Simulations are carried out for Cu-water nanofluids. The results, in general, show that nanoparticles systematically decrease the natural convective heat transfer coefficient on the inner cylinder. Practical and useful correlations are provided for calculating average heat transfer rates from the inner cylinder in the form of average equivalent thermal conductivity and average Nusselt number for all of the four cases discussed above. These correlations are new and will be helpful in designing heat exchangers.

This work examines the role of charge redistribution in the self-discharge of electrochemical capacitor electrodes. Electrochemical capacitors are charge storage devices which have high power capability and a long cycle life, but have a low energy density compared to other devices, coupled with a high rate of self-discharge which further diminishes the available energy. The mechanisms of self-discharge in electrochemical capacitors are poorly understood, and it is important to gain a better understanding of the electrode processes which lead to self-discharge, in order to minimize self-discharge and enhance electrochemical capacitor performance. To learn more about charge redistribution and its role in the self-discharge of electrochemical capacitors, multiple self-discharge experiments were performed on carbons with various surface areas/pore structures and in various electrolytes. Charge redistribution was also examined in a model pore (a transmission line circuit based on de Levie?s model of a porous electrode) and results from this model were compared to the self-discharge of a high surface-area carbon. Results demonstrate that charge redistribution is a major component of the self-discharge in high surface-area carbons. Results also indicate that charge redistribution requires a much longer time than previously thought (tens of hours rather than minutes) which further highlights the importance of charge redistribution during self-discharge. Therefore when performing mechanistic studies of self-discharge in electrochemical capacitors, it is important that effects of charge redistribution are not neglected. The self-discharge profiles of various pore shapes were also examined using the model pore, and results emphasize the superiority of cone and cylindrically shaped pores, and the disadvantages of restrictive pore mouths and bottlenecks for high power applications.

In this thesis proposals for different designs of a borehole thermal energy storage (BTES) have been developed for the building DN-huset in Stockholm, Sweden. To build a BTES results in savings in energy costs by approximately 44 %, i.e. 2 million Swedish crowns annually. Furthermore, a BTES would reduce the annual environmental impact with roughly 75-157 tonnes of CO2 equivalents per year, depending on how the electricity consumption’s environmental impact is estimated. The payback period is about 11 years, including the warm-up period that is necessary before commissioning the BTES. The savings in environmental impact and operating costs are a result of energy being reused. During the summer heat is stored in the bedrock beneath the building for retrieval about half a year later in the winter, when there is a heating demand. In addition to developing proposals for different BTES designs the thesis also examines the influence of certain design parameters, conservative choices and operating conditions.

A study has been undertaken of the detailed photoelectrochemistry of a number of III-V and oxide semiconductors. In particular, the work has been aimed at obtaining a material which can act as a stable and efficient photoelectrode for the solar photoelectrolysis of water. However to achieve this aim, it was considered essential to obtain a far deeper understanding of the mechanisms of the electrochemical reactions taking place at the semiconductor/electrolyte interface. The mechanism for Hydrogen evolution from the surfaces of the p-type III-V materials has represented a particular problem. P-type GaP was chosen as the representative member of the III-V materials and a mechanistic study has been made of the material using a.c. and d.c. experiments in addition to a detailed interfacial impedance analysis. A model for the Hydrogen evolution reaction has been proposed invoking surface bound Hydrogen atoms as both intermediates in the desired reaction and also as photogenerated surface states in parasitic recombination reactions. With the experience of the work on p-GaP, the analagous mechanisms to those found on p-GaP have been found to be consistent with results obtained on p-GaAs, p-InP and p-GaSb. However for these latter materials, additional complexities have arisen from their greater instability with respect to cathodic corrosion. A method has been sought for modifying the surface of the III-V materials in order to obtain improved Hydrogen evolution efficiencies. Such a modification has been discovered for p-GaP by the adsorption of a Ruthenium species from solutions of crude RuC1₃.xH₂0. Its mode of operation is discussed at length. For the oxide materials, a semiconducting oxide has been sought that possesses the ideal band energies and bandgap to obtain optimum photoefficiencies for the photoelectrclysis of water. The design constraints for such a material are presented and some results on a number of novel oxide semiconductors are discussed in relation to their use in such photoelectrolysis cells.

This thesis addresses the future of sustainable energy distribution and transportation in the United States. Predictions of future energy and transportation demands promote localized energy as the most likely situation. Existing proposals outlining the benefits of decentralized energy production fail to engage architecture. Cities will require new architectural typologies that can integrate new energy infrastructure in the city. Los Angeles, the archetype of the decentralized American city, is introduced as a case study. The city is examined at multiple scales for the integration of a decentralized electricity network and an efficient transportation infrastructure. Siting the proposed facilities capitalizes on new and existing transportation infrastructures and local energy resources. The new electricity-transportation infrastructure is adapted to a decentralized network functioning on principles of ecosystems and energy economics at an urban scale. Energy storage is paired with multi-modal transportation to develop new architectural and urban typologies. This enables the decentralized urban proposal to function as a network exhibiting mutually beneficial characteristics.

No description available.

A Ground Coupled Heat Pump System (GCHP) is a heat pump with or without any thermal storage which uses soil as a heat source or sink. Soil, due to its large thermal capacity and inertia, can serve as a heat source or sink, thus offering relatively constant operation conditions for a heat pump. The soil temperature at a depth of about 2.0m fluctuates slightly around the yearly average air temperature at any given location. This offers a lower and stable sink temperature in the cooling mode operation and a higher and stable source temperature in the heating mode operation. The major consequence of this fact for a GCHP operation is a lower energy consumption as compared with a standard air-source heat pump.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 49-50).